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Plasma Science: Enabling Technology,
Sustainability, Security, and Exploration

Committee on a Decadal Assessment of Plasma Science
Board on Physics and Astronomy
Division on Engineering and Physical Sciences
A Consensus Study Report of

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

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This activity was supported by Grant No. PHY-1801266 from the National Science Foundation, Grant
No. DE-SC0018435 from the U.S. Department of Energy, and Grant No. FA9550-18-1-0220 from the Air
Force Office of Scientific Research, and by the Office of Naval Research. Any opinions, findings,
conclusions, or recommendations expressed in this publication do not necessarily reflect the views of any
organization or agency that provided support for the project.
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Suggested Citation: National Academies of Sciences, Engineering, and Medicine. 2020. Plasma Science:
Enabling Technology, Sustainability, Security, and Exploration. Washington, DC: The National
Academies Press. https://doi.org/10.17226/25802.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

The National Academy of Sciences was established in 1863 by an Act of Congress, signed byPresident Lincoln, as a private, nongovernmental institution to advise the nation on issues
related to science and technology. Members are elected by their peers for outstanding
contributions to research. Dr. Marcia McNutt is president.
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Members are elected by their peers for extraordinary contributions to engineering. Dr. John
L. Anderson is president.
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

Consensus Study Reports published by the National Academies of Sciences, Engineering, andMedicine document the evidence-based consensus on the study’s statement of task by anauthoring committee of experts. Reports typically include findings, conclusions, andrecommendations based on information gathered by the committee and the committee’s
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COMMITTEE ON A DECADAL ASSESSMENT OF PLASMA SCIENCEMARK J. KUSHNER, NAE,1 University of Michigan, Co-ChairGARY P. ZANK, NAS,2 University of Alabama, Huntsville, Co-Chair
AMITAVA BHATTACHARJEE, Princeton University
PETER BRUGGEMAN, University of Minnesota
TROY CARTER, University of California, Los Angeles
JOHN CARY, University of Colorado
CHRISTINE COVERDALE, Sandia National Laboratories
ARATI DASGUPTA, Naval Research Laboratory
DANIEL DUBIN, University of California, San DiegoCAMERON G.R. GEDDES, Lawrence Berkeley National Laboratory
GAIL GLENDINNING, Lawrence Livermore National Laboratory
DAN M. GOEBEL, NAE, Jet Propulsion Laboratory
DAVID B. GRAVES, University of California, Berkeley
JUDITH T. KARPEN, National Aeronautics and Space Administration
MAXIM Y. LYUTIKOV, Purdue University
JOHN S. SARFF, University of Wisconsin, Madison
ADAM B. SEFKOW, University of Rochester
EDWARD E. THOMAS, JR., Auburn University
Staff
CHRISTOPHER J. JONES, Program Officer, Study Director
JAMES C. LANCASTER, Director
NEERAJ P. GORKHALY, Associate Program Officer
AMISHA JINANDRA, Research Associate
LINDA WALKER, Program Coordinator
BETH DOLAN, Financial Associate

12

NAE, National Academy of Engineering.
NAS, National Academy of Sciences.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

BOARD ON PHYSICS AND ASTRONOMYABRAHAM LOEB, NAS,3 Harvard University, Chair
ANDREW LANKFORD, University of California, Irvine, Vice Chair
MEIGAN ARONSON, University of British Columbia
WILLIAM BAILEK, NAS, Princeton University
JILL DAHLBURG, Naval Research Laboratory
SALLY DAWSON, Brookhaven National Laboratory
LOUIS DIMAURO, The Ohio State University
WENDY FREEDMAN, NAS, University of Chicago
TIM HECKMAN, NAS, Johns Hopkins University
WENDELL T. HILL III, University of Maryland
ALAN J. HURD, Los Alamos National Laboratory
CHUNG-PEI MA, University of California, Berkeley
NERGIS MAVALVALA, NAS, Massachusetts Institute of Technology
SUNIL SINHA, University of California, San Diego
WILLIAM A. ZAJC, Columbia University
Staff
JAMES C. LANCASTER, Director
GREGORY MACK, Senior Program Officer
CHRISTOPHER J. JONES, Program Officer
NEERAJ P. GORKHALY, Associate Program Officer
AMISHA JINANDRA, Research Associate
LINDA WALKER, Program Coordinator
BETH DOLAN, Financial Associate

3NAS, National Academy of Sciences.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

Preface
Plasma science, the investigation of ionized gases and their interactions with materials, is adiscipline absolutely critical to the U.S. economy, national security and protection of our planet from space
weather events, while also being one of the major and fundamental areas of physical science. The
extraordinary reach of plasma science can be gleaned from the range of plasma enabled technologies thatthe past decades have enjoyed. These span microelectronics fabrication (plasma science underpins the $1
trillion information technology industry), health care, lighting and displays, water purification andmaterials synthesis. Moreover, plasma science offers unparalleled opportunities to address outstanding andcritical societal problems. Not the least of these contributions is making a major impact on society’s ability
to address climate change and energy sustainability through the development of fusion generated, carbon
free electricity. In addition, plasma science is the basis of stewardship of our nuclear deterrent. Control ofintense lasers interacting with plasmas is enabling a new generation of particle accelerators that could
revolutionize X-ray imaging from medicine to industry and enable investigation of new quantum
phenomena. Plasma science as a scientific discipline in its own right is remarkable in spanning a huge
range of physics, contributing to and drawing from disciplines as diverse as space physics andastrophysics, materials science and engineering, atomic, molecular and optical physics, chemistry, biology,
medicine and agriculture.
The importance of plasma science to the nation is reflected by its support from a variety of federal
agencies in developing decadal assessments to measure the impact, accomplishments, future research
directions and the role of plasma science to the United States. This report, Plasma Science: Technology,
Sustainability, Security, and Exploration, (hereafter “Plasma 2020”), is the third in the series of decadal
studies providing this assessment. The Plasma 2020 report was requested and funded by the National
Science Foundation, the Department of Energy, the Office of Naval Research, and the Air Force Office of
Scientific Research. The committee’s statement of task authored by these agencies appears in Appendix
B.
By any measure, plasma science and plasma enabled technologies have revolutionized modern
society and enabled our understanding of the fundamental processes that govern stars and galaxies, themagnetic fields of planets, the atmosphere, interaction of intense electromagnetic fields with matter, andhow energy self-organizes in response to its environment. Besides the fundamental and exciting nature ofplasma science in exploring nature, we indeed live our everyday lives surrounded by the extraordinary
fruits of applying plasma science to any number of applied problems. Technologies ranging from cell
phones to solar cells rely on plasmas for their economic fabrication. The lesson to be drawn from theseexamples of plasma science in our lives is that there is enormous potential for plasma science to makeequal and greater contributions to society moving forward. The recognition of this potential led to a partial
focus by the committee to identify in the findings and recommendations of Plasma 2020 the means tomake these potential contributions a reality.
There is, however, a possible impediment to achieving that potential, and that is the manner inwhich federal funding for plasma science is structured in the United States. Unfortunately, plasma science
funding, because of its wide-ranging utility to so many applications and sciences, tends to be distributed
across multiple agencies and there is a lack of cohesive strategic goals. This has a limiting effect on plasma
science as a whole, but of greater concern is that it leaves opportunities untaken and in some cases
threatens the leadership of the nation in multiple areas of plasma science and engineering. Although ourcomments on this topic are specific to plasma science, the committee expects that our recommendations
may apply to other fields of science and technology as well.

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Plasma science and engineering is intrinsically interdisciplinary. The basic science of the field is in
its own right a unique discipline and fundamental plasma science is in large part supported by the federal
agencies that sponsored this report. However, the majority of the applications and technologies enabled byplasma science are within the realm of other federal agencies (or other offices or programs in thesponsoring agencies). These administrative separations of the fundamental science and the society
benefiting applications is an impediment to performing translational research that produces thetechnologies that empower society. Compartmentalization even occurs within and between agencies thatprimarily support fundamental plasma science. There are many reasons for this compartmentalization,
ranging from interpretation of guidelines that discourage duplication to narrow definitions of missions.
This compartmentalization is not in the best interest of furthering the science of plasmas, and in particular,
is not in the best interest of the nation, which would benefit from more coordinated fundamental andtranslational research, while also addressing the science needs of industry. A major theme of Plasma 2020
is partnerships between federal agencies that can mitigate this compartmentalization. In this regard, thefindings and recommendations of Plasma 2020 extend far beyond the agencies that sponsored this report.
During review and final preparation of Plasma 2020, we are in the midst of the Covid-19
pandemic (March to April 2020). The areas of plasma medicine and plasma biotechnology encompass theuse of plasmas for sterilization of materials and living tissue such as skin, and address the need tophysically kill pathogens without risking antimicrobial resistance. Plasma medicine and plasma
biotechnology are examples of interdisciplinary fields that have fallen between the cracks of the perceived
responsibilities of individual funding agencies. Plasma focused agencies are reluctant to sponsor projects
that involve biological systems and biologically focused agencies are reluctant to sponsor projects thathave a focus on plasma physics. As a result, we may have missed an opportunity to have another tool at
our disposal to aid in the current health crisis.
During the development of Plasma 2020, the DOE Office of Fusion Energy Sciences (FES), in
response to a Congressional request, began a strategic planning process. The Fusion Energy Scientific
Advisory Committee (FESAC) will provide FES with a proposed strategic plan after Plasma 2020 isissued. The plan will be based on a community planning process requested by FESAC and initiated by theAmerican Physical Society Division of Plasma Physics through establishment of an oversight committee.
That community planning process was conducted while Plasma 2020 was being developed. Although the
FES strategic planning process applies only to FES and its operational goals moving forward, FES doessponsor a considerable fraction of the plasma science that is conducted in the United States, and so there
will be some overlap between the Plasma 2020 and the FES report in terms of science challenges. The
purview of Plasma 2020 however extends beyond FES to all federal agencies that sponsor fundamental
research in plasma or benefit from plasma technologies. Having said that, synergies between the reports
emphasize the importance of those topics.
During the development of the Plasma 2020 report, the National Academies of Sciences,
Engineering, and Medicine’s Final Report of the Committee on a Strategic Plan for U.S. Burning Plasma
Research was issued. This report discussed a path forward for the United States to perform the researchand develop the technologies needed to produce magnetic fusion generated electrical power. Magnetic
fusion energy is also a topic of the Plasma 2020 report. As with the FES strategic planning process, thesynergies between the recommendations of the burning plasma report and Plasma 2020 are someindication of their importance.
Given the extreme breadth of plasma science and engineering that is the purview of this report, thePlasma 2020 committee did not make specific recommendations on prioritizing, for example, therecommendations of the burning plasma report over those of developing laser-plasma based particle
accelerators or vice-versa. The intent of Plasma 2020 is to present the scientific science challenges,
prioritize within the sub-fields of plasma science and propose structural changes to how plasma science iscoordinated to address those science challenges and the translational research that produces societal
benefit.
Finally, the committee thanks the national and international plasma science and engineeringcommunities for providing input and their perspectives. These communities were engaged through
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

solicitation and their submission of white papers; participation in a series of town hall meetings atuniversities, national laboratories, conferences and workshops; and through presentations made to thecommittee in closed and open sessions. The committee reached out to numerous members of thecommunity for specific contributions and input where we felt additional insight and expertise was needed.
The committee also thanks the reviewers for their candid and helpful comments, the National Academies
staff and, in particular, Dr. Chris Jones and Dr. James Lancaster for guiding the committee through thisprocess.
Mark J. Kushner and Gary Zank, Co-Chairs
Committee on the Decadal Assessment of Plasma Science

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Acknowledgment of Reviewers
This Consensus Study Report was reviewed in draft form by individuals chosen for their diverse
perspectives and technical expertise. The purpose of this independent review is to provide candid andcritical comments that will assist the National Academies of Sciences, Engineering, and Medicine in
making each published report as sound as possible and to ensure that it meets the institutional standards
for quality, objectivity, evidence, and responsiveness to the study charge. The review comments and draft
manuscript remain confidential to protect the integrity of the deliberative process.
We thank the following individuals for their review of this report:
Jill Dahlburg, Naval Research Laboratory
Roger Falcone, NAS, University of California, Berkeley
Truell Hyde, Baylor University
Justin Kasper, University of Michigan
Christopher Keane, Washington State University
Carolyn Kuranz. University of Michigan
Michael Litos, University of Colorado at Boulder
Michael Mauel, Columbia University
Steven J. Shannon, North Carolina State University
Clifford M. Surko, University of California, San Diego
Toshiki Tajima, University of California, Irvine
Although the reviewers listed above provided many constructive comments and suggestions, they
were not asked to endorse the conclusions or recommendations of this report nor did they see the final
draft before its release. The review of this report was overseen by Richard A. Gottscho, NAE, LAM
Research Inc., and T. Kenneth Fowler, NAS, University of California, Berkeley. They were responsible
for making certain that an independent examination of this report was carried out in accordance with thestandards of the National Academies and that all review comments were carefully considered.
Responsibility for the final content rests entirely with the authoring committee and the National
Academies.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

Contents
SUMMARY

S-1

1

PLASMA SCIENCE: ENABLING TECHNOLOGY, SUSTAINABILITY, SECURITY, AND
EXPLORATION
1-1

2

THE FOUNDATION OF PLASMA SCIENCE

2-1

3

LASER-PLASMA INTERACTIONS: COMPACT PARTICLE ACCELERATORS,NEW OPTICS, AND BRILLIANT X-RAY SOURCES

3-1

4EXTREME STATES OF PLASMAS: HIGH ENERGY DENSITY SYSTEMS

4-1

5

LOW-TEMPERATURE PLASMAS: A UNIQUE STATE OF MATTERFOR ADDRESSING SOCIETAL NEEDS

5-1

6

MAGNETIC CONFINEMENT FUSION ENERGY: BRINGING STARS TO EARTH

6-1

7

THE COSMIC PLASMA FRONTIER

7-1

APPENDIXES
A
B
C
D
E

Statement of Task
Summary of Findings and Recommendations
Survey Data Gathering Events
Committee Member Biographical Information
Acronyms

A-1
B-1
C-1
D-1
E-1

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

Summary
PLASMA SCIENCE: ENABLING TECHNOLOGY, SUSTAINABILITY, SECURITY,AND EXPLORATION
Plasma science and engineering (PSE) is a technological and scientific success story. Advances inplasma science have enabled critical technologies and processes that benefit society, from materials
processing and healthcare to forecasting space weather. That record of translating of advances infundamental science to technologies is continuing to address out nation’s most critical needs.
Plasmas, often called the fourth state of matter, are ionized gases and perhaps the most abundant
form of matter, making up nearly 99.9 percent of the observable universe. Today, plasma dynamics
informs our understanding of the most fundamental processes in the Sun and stars, planetary ionospheres
and magnetospheres, interstellar space, and in accretion disks surrounding black holes. Manytechnologies defining modern society rely on the chemical activation of atoms and molecules that plasmas
enable. Plasma-based technologies have enabled efficient lighting, new materials, welding, internal
combustion and jet engines, medical implants, and water purification. Plasmas—which enablemicroelectronics fabrication through the etching and deposition of materials—have been indispensable tothe information technology revolution. Translating basic research in plasma science and engineering has
the potential to produce new society altering technologies, including: clean energy and energy
independence through controlled fusion, a new paradigm for chemical processing, compact particle
accelerators for science, medicine and industry, forecasting of extreme space weather events, agriculturaland medical advances, all while expanding our knowledge of extreme states of matter that govern
astrophysical phenomena. From magnetic fields generated throughout the universe to the earthly creationof states of matter that exist only in the center of stars, to exploring whether life can exist on exoplanets—
all are enabled by plasma science through theory, computations, observations, and experiments.
Plasma research is primarily funded as a science discipline by the Department of Energy (DOE),
National Science Foundation (NSF), Department of Defense (DoD), and National Aeronautics and Space
Administration (NASA). Several other agencies fund activities that are critical to plasma science by
providing essential fundamental data required for plasma studies. However, the science and technologies
enabled by plasmas are critical to almost all U.S. federal agencies and departments. The interdisciplinary
impact of PSE cuts across many current and proposed federal initiatives. For instance, nanoscience,advances in artificial intelligence, machine learning, accelerators, and quantum-based computing are
made possible by plasma materials processing of microelectronics devices. Similarly, exploration of thesolar system is propelled by plasma-fueled electric propulsion. NNSA’s (National Nuclear Security
Administration) stockpile stewardship depends on high energy-density plasmas, and space weather is a
Sun-Earth plasma system.
The National Academies of Science, Engineering, and Medicine was tasked to assess progress
and achievements in plasma science over the past decade and to identify major science challenges andopportunities for the next decade. This assessment evaluates plasma science’s contributions to the nationand how the discipline supports the U.S. economy and national security. This report also makes
recommendations to ensure the health of the plasma science field, covering workforce development, therole of the United States in international collaborations, and the optimum deployment of resources to meetthe science challenges. The report summarizes progress in the field since the Plasma 2010 Decadal Study.
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Of special note is the emergence of Laser Plasma Interactions (LPI) as a frontier field in advancing thefundamentals of plasma science, high field science, quantum physics and translational research towards
applications. This emergence was recognized by the 2018 Nobel Prize in Physics.
GRAND CHALLENGES OF PLASMA SCIENCE AND ENGINEERING
PSE transforms fundamental scientific research into powerful societal applications. Thisoutstanding strength of PSE is captured in the following “PSE Grand Challenges”—high-level goals,presented without ranking, in which mastery of the complexities of plasma science benefits society:












Understanding the behavior of plasmas under extreme conditions will enable predictive andefficient controllable energy conversion by plasmas, addressing the challenges of sustainability,
economic competitiveness, and national security, while expanding our knowledge of the mostfundamental processes in the universe.
Mastering the interactions of the world’s most powerful lasers and particle beams with plasmas
will enable precision x-ray imaging for medical science, advances in national security, compact
particle accelerators, advanced materials and sustainable energy sources, while opening new
regimes for high-energy and quantum physics.
Developing fusion-generated electricity will tap the virtually unlimited fuel in seawater, to bring
the benefits of energy independence and carbon-neutral power to the nation, through economical,
deployable, and sustainable fusion systems enabled by advances in experimental andcomputational plasma physics.
Demonstrating that lasers and pulsed-power devices can produce inertially confined fusion
ignition by producing plasma-based extreme states of matter that will support stockpile
stewardship, further the goal of sustainable energy, energy independence, and expand ourknowledge of high energy density physics.
Electrification of the chemical industry—that is, driving chemical processing by electrical means
facilitated by plasmas, by controlling the flow of power through low-temperature plasmas (LTPs)
to produce predictable chemical transformations in gases, solids, and liquids, on scales capable ofeconomically establishing a future based on renewable and sustainable electricity, and addressing
pandemic threats to our health through plasma sterilization of surfaces and tissue.
Developing timely and actionable space-weather forecasting and nowcasting will enable us tomitigate the potentially damaging effects of extreme solar plasma storms on spacecraft, humans,
power grids, and infrastructure.
REPORT RECOMMENDATIONSThe PSE community in the United States has seen many changes since the publication of the
Plasma 2010 Decadal Report, with landmark contributions to the science of plasmas, national security,
space exploration and economic competitiveness. These advancements confirm the value and need forboth discipline-centric fundamental research and interdisciplinary research that translates science toapplications.
The interdisciplinary reach of PSE is a strength and testament of its value to the nation; however,
the often highly mission-driven support of PSE also leads to fragmentation of the field, lack of an
identifiable home agency, and a reduced ability to exploit interdisciplinary opportunities. Whileacknowledging that there are common scientific challenges that cross the field, this report is structured
around the subfields of PSE to enable federal agencies to best receive the findings and recommendations
most relevant to their missions. Nonetheless, the committee’s recommendations propose actions to
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mitigate fragmentation of the field, encourage a more cohesive discipline that embraces a diverse andinclusive community, enable greater plasma-related collaboration between programs and agencies, andsupport joint initiatives between plasma-focused agencies and those benefiting from plasma science andtechnology.
The following sections include at their end the most high level recommendations for this report.
(These high-level recommendations, as well as more specific recommendations developed in theindividual chapters, are collected in Appendix B.)
Stewardship and Advancement of Interdisciplinary Research
Fundamental research in PSE can and does rapidly translate to societally relevant technologies,
the benefits of which cut across the missions of many federal agencies. The support for fundamental
research in plasma science by several federal agencies, and particularly by the NSF/DOE Partnership in
Basic Plasma Science and Engineering, is critical to addressing the grand challenges described above.
While the underlying science has common intellectual threads, this inherently interdisciplinary
community is organized into sometimes isolated subdisciplines. This isolation results in part from thediversity of applications that motivates the fundamental research and is reinforced by mission-driven
support at the federal level that may not take full advantage of synergies between fundamental research inthe subdisciplines and applications.
In many areas of PSE, such as plasma materials processing, application-focused development is
the primary mission of a program rather than that the funding of fundamental plasma research. As aresult, the interdisciplinary and multidisciplinary strengths of PSE are not being fully utilized, to thedetriment of the fundamental plasma research and to the detriment of the intended applications. For
example, there is enormous potential for PSE to contribute to one of society’s greatest challenges—
sustainability—while also contributing to economic competitiveness. At NSF, this research would best be
performed in the Engineering Directorate (EngD) while other areas of plasma science would find theirhomes in the Directorate for Mathematical and Physical Sciences and the Directorate for Geosciences.
Historical support for PSE in the EngD has been inconsistent, and particularly so since the Plasma 2010
report, in large part due to the changing priorities of individual EngD programs. This has made it difficult
to develop long-term PSE strategies to address critically important challenges such as sustainability.
The challenges towards leveraging public-private partnerships for economic and national security
benefits are large; however, the potential benefits outweigh these challenges. At the small-business end of
the innovation chain, the resources and know-how required to make breakthroughs in translational
research can fit poorly within traditional Small Business Innovation Research / Small BusinessTechnology Transfer (SBIR/STTR) models. At the large-business end of the innovation chain, there are
extreme pressures from international competition, in large part resulting from strong foreign government
support for fundamental and translational research in key industries.
Recommendation: Federal agencies directly supporting plasma science andengineering (PSE) and those federal agencies benefiting (or potentially benefiting)from PSE should better coordinate their activities extending into offices anddirectorates within larger federal agencies
Recommendation: Federal agencies and programs within federal agencies that are
separately focused on fundamental plasma research, and those that are focused on
science and technologies that utilize plasmas, should jointly coordinate and support
initiatives with new funding opportunities.
Recommendation: The Engineering Directorate (EngD) of the National Science
Foundation (NSF) should, as a minimum, consistently list PSE in descriptions of its
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

relevant programs and consistently participate in the NSF/Department of Energy(DOE) Plasma partnership.
Recommendation: More strategically, NSF should establish a plasma-focusedprogram in the EngD. that would advance engineering priorities across the board,
including advance agricultural systems, energy and environment, chemicaltransformation, advanced manufacturing, electronics and quantum systems.
Recommendation: Federal agencies focused on plasma research, and DOE in
particular, should develop new models that support the translation of fundamental
research to industry. Programs that support vital industries depending on plasma
science and engineering (PSE) should be developed through relevant interagency
collaborations.
Education and Workforce Development
There are great opportunities for new university faculty in PSE to address sustainability,
investigate laser-plasma produced quantum effects, make space weather predictions, and explore exotic
states of matter. However, the current trends in PSE demographics and hiring practices are eroding theability of the field to meet these challenges and national priorities. A multidisciplinary approach has beenat the heart of the success of the field of plasma science, while simultaneously working against its longterm vitality in academia. Plasma physics is a minority discipline in nearly every university department
containing plasma-focused faculty while many physics departments contain no plasma physics faculty. As
a result, maintaining faculty expertise is becoming progressively more challenging. Many universities do
not require or offer plasma physics classes for undergraduates in science and engineering. Plasma-specificeducational and research programs that also provide opportunities to diverse and less advantaged
populations are needed to ensure a critically populated PSE workforce. Increased emphasis on PSE
undergraduate research and internships, particularly at principally undergraduate institutions (PUIs), will
also improve awareness of our field among all undergraduates, and women and underrepresented students
in particular, thus enabling a fuller, more diverse pipeline and hence a more diverse discipline.
The demographics of the PSE workforce indicate that the next decade will likely see significant
turnover, making it critical to take deliberate actions to renew the PSE workforce. Diversity, equity, andinclusion (DEI) broadens a discipline to the betterment of that discipline and to the betterment of thesociety the discipline serves. Regrettably, PSE is among the least diverse of the science, technology,
engineering, and mathematics (STEM) fields. Rectifying this requires a diverse student pipeline and acommitment to welcome, support and retain members of under-represented groups. A professional
workforce cannot reflect society if the student pipeline entering PSE is not diverse. The number anddiversity of students entering the pipeline can be increased by increasing the numbers of undergraduate
students exposed to PSE through research experiences. PSE research programs in PUIs could have adisproportionately large influence in both filling and diversifying the PSE pipeline.
Recommendation: Federal agencies—for example, Department of Energy (DOE),
National Science Foundation (NSF), National Aeronautics and Space
Administration (NASA), and Department of Defense (DoD)—should structure
funding programs to provide leadership opportunities to university researchers inplasma science and engineering (PSE) areas and to directly stimulate the hiring ofuniversity faculty.
Recommendation: Funding agencies (e.g., NSF, DOE, NASA, DoD) should structure
funding to support undergraduate and graduate educational, training, and research
opportunities—including faculty—and encourage and enable access to plasmas
physics for diverse populations.
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

The Competitive International Research Enterprise in Plasma Science and Engineering
The research enterprise in PSE has had broad impact over the past decade; however, this progresshas also been made in an environment of tremendous international investments across the spectrum of
PSE that challenge and may potentially usurp U.S. leadership. International investments in large fusion
devices, powerful lasers, and research networks over the past decade have generally exceeded that madeby the United States; just two examples being the EU investment in the Extreme Light Infrastructure andthe Wendelstein 7-X stellerator. Given these strong international investments, incremental progress infacilities in the United States is insufficient to maintain leadership. Computational plasma science andengineering (CPSE) has become essential across PSE for experiment and mission design and diagnosis,
idea exploration, and prediction. For computations to continue to progress in PSE, the next generation ofresearchers needs to be better educated through the development of plasma-focused computational
textbooks and courses, and through participation in funded computational research projects.
Recommendation: Federal agencies (e.g., NSF, DOE, NASA DoD) should support aspectrum of facility scales that reflect the requirements for addressing a wide rangeof problems at the frontiers of PSE.
Recommendation: Federal agencies whose core missions include plasma science andengineering (PSE)—for example, Department of Energy (DOE), National Science
Foundation (NSF), National Aeronautics and Space Administration (NASA), andDepartment of Defense (DoD)—should provide recurring and increased support forthe continued development, upgrading, and operations of experimental facilities,
and for fundamental and translational research in plasma science. A spectrum offacility scales should be supported, reflecting the requirements for addressing
different problems at the frontiers of PSE.
Recommendation: Federal agencies should support research into the developmentof computational algorithms for plasma science and applications for theheterogeneous device computing platforms of today and upcoming platforms (e.g.,quantum computers), while also encouraging mechanisms to make advanced
computational methods, physics-based algorithms, machine learning, and artificial
intelligence broadly available.
Better Serving the Community
Following the recommendations of the Plasma 2010 report, the DOE Office of Fusion Energy
Science (FES) broadened the scope of its programs to better serve the plasma science community. The
title of the FES office does not now accurately reflect its broader mission, and may actually hamper
collaboration within DOE and with other federal agencies on nonfusion research.
Recommendation 4: Consistent with our recommendations to broaden the impact ofplasma science, the Department of Energy (DOE) Office of Fusion Energy Science(FES) should be renamed to more accurately reflect its broader mission, and so
maximize its ability to collaborate with other agencies and to garner nonfusion
plasma support. A possible title is Office of Fusion Energy and Plasma Sciences.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

Organization of the Report
In this report, outstanding contributions to scientific knowledge, economic vitality, and national
security over the last decade in several fields of PSE are discussed. An initial overview chapter discusses
the key findings and recommendations, while introducing a theme of fundamental research supportingtranslational research and the benefit of coordination and collaboration between federal agencies. The
following 6 chapters each address a sub-field of PSE. Each chapter presents exciting future research
directions, the national benefits that will occur with the translation of scientific advances to applications,and develops individual chapter-level findings and recommendations. Although cross cutting themes andchallenges are discussed, particularly in Chapter 2, the committee elected to make vertical cuts throughthe discipline since this better maps onto the current support infrastructure of the federal agencies. If therecommendations of this report are adopted, the next plasma decadal study will be positioned to organize
the report using horizontal disciplinary cuts. Synopses of the Chapters follow.
Chapter 2: Fundamental Plasma Science
A recurrent theme of the report is linking basic plasma science research and translational
research. We cannot over-emphasize the importance of maintaining strong support for research infundamental and basic areas of the discipline—both for the intrinsic value of that research and in
producing the necessary foundational knowledge that underlies all translational and applied research.
Research in basic plasma science is essential to PSE, and there have been major advances inunderstanding the underlying, unifying principles that transcend plasma science: magnetic reconnection,
waves and shocks, turbulence, particle acceleration, and self-organization. With the focus of basic plasma
research being on understanding fundamental principles, the immediate applications are not always clear.
However, this work provides the foundation for the entire field.
Computational Plasma Science and Engineering (CPSE)
Computation and theory are critical for prediction, diagnosis, and experimental design in PSE,
which will only be enhanced by artificial intelligence (AI) and machine learning (ML). Computational
science is essential to PSE, expanding our understanding of fundamental science and helping develop
technologies. Thus, the continued impact of CPSE will depend on making state-of-the-art computations
accessible to researchers who are not computational experts
Chapter 3: High-Intensity Laser-Plasma Interactions
Expanding plasma-based capabilities in high-intensity ultrafast lasers, with increasing energies,
repetition rates, and control, are opening new areas of high field plasma physics, including theinvestigation of quantum processes and the creation of matter from pure photon energy. Laser andparticle-beam control of the most intense sustained electromagnetic fields in plasmas is opening new
disciplines in plasma optics and particle acceleration. Plasma-driven electron and ion accelerators canachieve high particle energies in a smaller spatial region compared to conventional accelerators and are
opening new regimes for high-energy particle physics colliders and high-performance compact x-ray
sources. These new compact accelerators have important application to medicine, industry and national
security.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

Chapter 4: High Energy Density (HED) Plasmas and Inertial Confinement Fusion (ICF)
Understanding the dynamics of plasmas in the HED regime addresses fundamental questions inastrophysics and space physics, material science and quantum materials, nuclear physics and atomic
physics, and is essential to stockpile stewardship. Major new facilities have had a great impact on the
HED field, helping it to flourish over the past decade. HED physics encompasses inertial confinement
fusion (ICF), the pursuit of controlled fusion in the laboratory by compressing matter to densities found at
the center of stars. We stand at the brink of achieving the milestone of fusion ignition, sharing science,
similar challenges, and the potential for societal benefit with magnetic fusion energy. While existing HED
facilities will produce further scientific advances over the next decade, planning for successor ICF and
HED facilities, both laser- and pulsed-power driven, is beginning.
Chapter 5: Low-Temperature Plasmas (LTPs)
The chemically reactive nature of LTPs has enabled society-wide transformations in our qualityof life, ranging from materials synthesis, to water purification, to enabling the IT revolution throughplasma-enabled fabrication of microelectronics. LTPs are partially ionized plasmas that produce
chemically reactive environments in gases, on surfaces, and in liquids. Over the past decade, LTPs havegreatly advanced atomic-layer etching and deposition of materials, control of electromagnetic waves,space propulsion, human healthcare, and agriculture, and protecting the food chain. LTP technologies arepropelling the electrification of the chemical industry—that is, driving chemical processing by electricalmeans facilitated by plasmas.
Chapter 6: Magnetic Confinement Fusion Energy (MFE)
The societal benefit from MFE could be enormous, as fusion energy can provide a carbon-freesource of electrical power from an essentially limitless source of fuel and enabling energy independence.
Nuclear fusion, the process of fusing lighter elements to create heavier elements and release energy,
powers stars. In the laboratory, strong magnetic fields can confine hot plasmas to produce star-likefusion—Magnetic Confinement Fusion Energy (MFE). The past decade has brought MFE to the brink ofcreating the first burning plasma in the ITER project, scheduled to come online by 2026, and to produce aburning plasma in 2036. A 2019 NASEM study endorsed U.S. participation in ITER as an essential step
toward realizing commercial fusion power in the United States, and recommended using that knowledge
to develop an economical compact fusion pilot power plant.
Chapter 7: Space and Astrophysical Plasmas (SAPs)
SAPs possess properties inaccessible to Earth-bound experiments, raising questions as varied as
the origins of the universe and the habitability of exoplanets. Future Earth- and space-based observing
platforms and space missions will address some of the most profound questions about the universe. The
societal benefits of understanding SAPs extend from the practical to the inspirational. Notably, the past
decade has brought us closer to understanding the origins and effects of space weather, enabling
forecasting and nowcasting that will protect spacecraft, instruments, and humans in space, along withelectrical power grids on Earth—all of which is essential to our national security. Startling recent
advances include detection of a possible neutron star merger through the simultaneous excitation ofgravitational waves, gamma ray bursts, x-ray and visible plasma emission, and the first images of a blackhole, both extraordinarily exotic events that represent SAP research.

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Plasma Science: Enabling Technology, Sustainability, Security, andExploration
A SOCIETY WITH PLASMA SCIENCE
How does plasma science impact today’s society?
The internet, computers, cell-phones, jet turbines, medical implants, lighting, solar cells,
nanomaterials, advanced batteries and spacecraft exploring our solar system are all enabled byplasmas.
Stockpile stewardship, hypersonic flight, space weather, indeed our very national security, relies
on our understanding and mastering the complexities of plasmas.
From magnetic fields generated throughout the universe to the earthly creation of states of matterthat exist only in the center of stars, to exploring whether life can exist on exoplanets—all areenabled by plasma science.

Perhaps our greatest present and future challenge is sustainability. How do we sustainably use theplanet’s resources while having ever more prosperous societies? How do we generate the power we need?
How do we produce the essential chemicals and materials society needs? Plasma science can be a largepart of addressing those challenges. We can envision a future in which plasma science, aggressively
stewarded, can use its potential towards achieving a sustainable society by providing

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
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

Nearly unlimited sources of carbon-free electricity;
Compact particle accelerators for imaging and cancer treatment;
New materials, green chemical production, new modalities for medicine and agriculture;
Secure management of our Nation’s most strategic weaponry; andFundamental knowledge about the creation of the solar system and worlds beyond.

Enabling this vision of the future through the support of plasma science is the topic of this report.
Plasma is often called the 4th state of matter - gases, liquids, solids, and plasma. Plasmas are
ionized gases in which electrons have been removed from neutral atoms to make a collection ofnegatively charged electrons, positively charged ions, sometimes including negative ions, and neutral
atoms and molecules. Plasmas are perhaps the most abundant form of matter, accounting for 99.9%, of
the visible universe. Stars are made of plasmas—the Sun is a plasma. Life on Earth may have started fromamino acids formed by lightning, a plasma, in the primordial atmosphere. A huge array of technologies
that define modern society relies on the chemical activation of atoms and molecules enabled by plasmas,
from lighting to the fabrication of microelectronics devices. Plasmas are increasingly being used tobenefit human health and well-being, from plasma-based medical devices for wound healing and cancer
treatment to the use of plasmas to enhance the growth rate and yield of agriculturally important crops.
Plasmas are the source of electromagnetic radiation and, when combined with intense lasers, could act as
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Plasma Science: Enabling Technology, Sustainability, Security, and Explorationcompact particle accelerators for medical and security imaging, and exploration of the frontiers of highenergy physics. Our national security relies on plasmas, from our strategic weapons to the high-energydensity experiments needed to steward our nuclear deterrent. Plasmas are the basis of one of the mostambitious experiments ever attempted: controlled thermonuclear fusion reactions that one day will
provide sustainable electricity. Understanding the most fundamental processes in planetary ionospheres
and magnetospheres, in interstellar space, and in the matter falling into black holes requires that we firstunderstand the dynamics of plasmas. Spacecraft powered by plasma propulsion are now visiting asteroids
and distant planets, and may propel astronauts to Mars. The existence of life and habitability on planetsand moons in the solar system, and the much larger collection of exoplanets, will in large part bedetermined by space weather, a plasma phenomenon.
In many ways, plasmas are the technological and scientific success story of the 20th century, withthe potential to completely redefine the 21st century. During the 20th century, plasma-based technologies
enabled efficient lighting, new materials, welding, internal combustion and jet engines, medical implants,
and water purification. Plasmas, through microelectronics fabrication by etching and deposition ofmaterials, are singularly responsible for the information technology revolution. We came to understandthe plasma processes that power the stars, how the dynamics of the Sun’s surface affect our atmosphere,
and how dusty plasmas in the laboratory can teach us about the atmospheres of comets.
In the 21st century, translating fundamental research in plasma science and engineering (PSE)
into practice will produce controlled fusion, an entirely new paradigm for chemical processing, compact
accelerators for medical and security imaging, warning systems for extreme space weather events,
agricultural and medical advances, propulsion sending spacecraft and astronauts to the planets, an
expansion of our knowledge of extreme states of matter that govern astrophysical phenomena, andexperiments that reproduce those conditions for study on Earth.
The potential of fundamental research in PSE to translate to societal benefit is captured in thevision of a Future Based on Renewable Electricity (FBRE) where societies are powered by non-polluting,renewable, and sustainable electricity. 1 The source of that electricity will be largely plasma-enabled,from plasma fusion reactors to solar cells that are produced by plasma materials processing. Thatelectricity will be stored in batteries made with plasma-synthesized materials. The electrical infrastructure
will be protected by predictions of space weather events resulting from advanced understanding of theplasma processes connecting the Sun to the surface of our planet. Plasma-based processes will use thepotential energy in that electricity to convert waste products to the chemicals upon which society depends,
and to recover resources and protect public health by cleaning polluted water. Agriculture and the foodcycle will become electricity based, through plasma-based production of fertilizer, enhancement of plant
growth, and ensuring food safety. New modalities in healthcare will become electricity based by taking
advantage of plasma-based patient-specific treatments and imaging.
Plasma science and engineering is perhaps the most interdisciplinary of the major fields ofphysics. With rare exceptions, there are no departments of plasma physics or plasma engineering in U.S.
universities. However, some form of plasma science, from fundamental investigations to technologicalapplications, is found in nearly every engineering, life science, and physical science department incolleges and universities. The impact of PSE is due to its interdisciplinary nature since fundamental
advances in plasma science can rapidly transition to societal benefit. That impact is felt across U.S.
federal agencies and departments. “Plasma” formally appears in the titles of research and technology
programs at the DOE, NSF, DoD, and NASA. However, the technologies and science enabled by plasmas
are critical to the NIH, EPA, NIST, USDA, FDA, NSA, DHS, and across the law enforcement agencies.
As a result, the impact of the interdisciplinary nature of PSE can be found in how plasmas enable current
and proposed federal initiatives. Advances in artificial intelligence, machine learning, and quantum-based
computing are made possible by plasma materials processing of microelectronics devices. Exploration of

1“Science Challenges in Low Temperature Plasma Science and Engineering: Enabling a Future Based on
Electricity through Non-Equilibrium Plasma Chemistry”, http://arxiv.org/abs/1911.07076.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

the solar system is propelled by plasma-fueled electric engines. NNSA’s stockpile stewardship issingularly dependent on high energy-density plasmas.
This decadal study, Plasma 2020, reviews the scientific advances and societal benefits brought by
PSE over the past decade; and discusses the scientific challenges that must be addressed to continue andexpand upon those societal benefits.
AN INTELLECTUALLY DIVERSE FIELD UNITED BY SCIENCE CHALLENGES
PSE is perhaps one of the most intellectually diverse of the physical sciences. Plasmas exist overmore than 10 orders of magnitude in pressure (or energy density) and more than 10 orders of magnitudein spatial scale. At one extreme of spatial scale are the micron-sized cathode-spot plasmas that sputter
metals to place thin metal films on materials. At the other extreme are the plasma jets that emanate fromgalaxies and the diffuse plasmas permeating galactic clusters. Plasmas with temperatures rivaling andexceeding that of the center of the Sun are being investigated to sustain fusion in the laboratory, whileplasmas gentle enough to touch human tissue are being investigated for biomedical therapies.
In spite of these vastly different spatial scales, pressures, power levels, and applications, common
themes and scientific challenges do bring cohesiveness to the field. These common challenges may not
apply universally to every subfield and application of PSE, but there is continuity throughout the field.
Common scientific challenges that unite the field include:
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Complexity arising from multiple scales and phenomena.
Controlling synergistic exchanges in plasma-surface interactions.
Understanding and leveraging how complex phenomena can self-organize into coherent
structures.
Controlling the flow of power through plasmas as means of energy and chemical conversion.
Developing ever more capable diagnostics, theories, and computations to characterize thiscomplexity.

Even with these common themes, the intellectual diversity and breadth of applications in PSE isenormous. As a result, the subfields of PSE are supported by several federal agencies whose missionsalign with those subfields. In many ways, this diverse base of relevance and support among federal
agencies is a strength and testament to the value of PSE to the nation. In other ways, this highly missiondriven support of PSE has led to fragmentation of the field, lack of an identifiable home agency, andreduced ability to capitalize on interdisciplinary opportunities. This is particularly the case in those areasof PSE that involve the life sciences and materials.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

While acknowledging that there are common
scientific challenges, this report is structured aroundthe subfields of PSE. This choice was made to enablefederal agencies to optimally receive the findings andrecommendations that are most relevant to their
missions. At the same time, our high-levelrecommendations propose actions to mediate thatfragmentation of the field, to work towards a morecohesive discipline, to enable more plasma-related
collaboration between agencies and between programsin single agencies, and to jointly support initiatives
between plasma-focused agencies and those benefitingfrom plasma science and technology.
This proposed coordination and collaboration
has great potential to advance both PSE as a discipline
and to advance the missions of agencies. For example,
dozens of low-temperature plasma projects at thevarious NASA Centers span many different areas
important to NASA missions, ranging from plasma
technologies for waste gasification, remediation andsterilization to devices such as plasma contactors andelectric thrusters. These projects tend to be led byengineers and research scientists in different mission
areas who are not necessarily plasma specialists,
without significant leveraging of expertise from otherplasma-focused projects within NASA and without the
input of plasma experts in other federal agencies. The
outcomes of these efforts would certainly benefit from
improved coordination of plasma-focused activities
within NASA, and from outreach by NASA to otheragencies to provide plasma expertise to the projects.
The likely outcome is a better end result and reductionin the time to deployment or flight.
PSE ACCOMPLISHMENTS ANDOPPORTUNITIESFIGURE 1.1 Simulations of Reconnection:
Advanced computations are critical to theinvestigation of fundamental plasma
properties. Here, results are shown of a 3dimensional particle-in-cell simulation ofelectron and ion acceleration in a current
sheet formed during magnetic reconnection.
The particles are shown at their spatial
location (x,y,z) with color indicating theparticle velocity parallel to the backgroundmagnetic field. The simulation used state-ofthe-art high performance computational
techniques with nearly 115 billion
computational plasma particles. Theenergetic particles appear to carry significant
current. The rope-like structures are known
as magnetic flux ropes and can confine
energetic particles (red regions).
SOURCE: S. Byna et al., "Parallel I/O, analysis,
and visualization of a trillion particle simulation,"
SC '12: Proceedings of the International
Conference on High Performance Computing,
Networking, Storage and Analysis, Salt Lake
City, UT, 2012, pp. 1-12.
https://ieeexplore.ieee.org/document/6468542.

The advances in PSE during the past decade have been outstanding in their contributions toscientific knowledge, economic vitality, and national security. As discussed below and in the chapters,
impressive progress has been made on several challenges highlighted in the Plasma 2010 report. For
example, Plasma 2010 cited the inability “to place a satellite at the right place and time to study
reconnection.” The 4 satellite Magnetospheric MultiScale mission (MMS), launched in 2015, has enabledjust such measurements. Plasma 2010 cited opportunities to use HED to study astrophysical plasmas.
Outstanding progress has occurred in laboratory astrophysics, an example being measurements of opacityof iron for studies of stellar interiors. Plasma 2010 recognized the importance of understanding

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration“multiscale” processes in magnetized plasmas.
Impressive insights into these processes have comefrom simulations and experiments—such as
interactions between global MHD instabilities andmicroturbulence. The opportunities to control
plasma-chemical processes were highlighted in
Plasma 2010. Major advances have been made in our
understanding and use of ns pulsed power toselectively produce reactive species for combustionand chemical conversion. Plasma 2010 cited the needfor plasma accelerators, then a nascent field, to bescaled to much longer plasmas and achieve higher
energies. This has been realized, with particle
bunches close to 10 GeV and staging of plasma.
Fundamental Plasma Science
Plasma processes occur in nature,laboratories and in industrial settings over a vast
range of space and time scales. Despite this great
diversity of plasmas, there are unifying themes andprocesses, such as magnetic reconnection, waves,turbulence, charged particle acceleration, and selforganized structures. The past decade has seen
tremendous progress in understanding theseunderlying, unifying principles. This progress wasenabled by results produced by controlled andreproducible laboratory experiments; observations ofsolar and astrophysical processes and missions tospace; advanced computer simulations (see Figure1.1); and by the development of theories that accountfor these observations and simulations while
explaining regimes not yet accessible by either
observations or simulations. Research and educationin fundamental plasma science are essential to theentire PSE enterprise. In spite of its great importance,
the link between basic plasma science and its many
applications is not always appreciated. As a result,
support for fundamental plasma research issometimes deemed of secondary importance tosupporting applications. Furthering discovery offundamental plasma processes is in fact at the root ofand essential to applications, and so can betransformational for PSE.
In the following the committee describes anextremely broad range of plasmas, which span anenormous range of plasma densities, temperatures,composition, and magnetic fields, and are vital to our
economic competitiveness and national security. The
opportunity, the challenge, for basic plasma science

FIGURE 1.2 The Most Intense Plasmas on
Earth. High energy density physics isflourishing at the start of the new decade. The
major facilities (the Omega/Omega EP laser at
the Laboratory for Laser Energetics,
University of Rochester; the National Ignition
Facility at Lawrence Livermore National
Laboratory; the Linac Coherent Light Source(LCLS) at the SLAC National Accelerator
Facility; and the Z-Machine at Sandia
National Laboratory) are producing a wealthof exciting new data. These mature facilities
are complemented by new capabilities in
multi-dimensional computation and novel,transformative diagnostics. In this image, (topleft) a proton radiograph of hydrodynamic
instabilities in a plastic foil experiment on the
Omega laser demonstrates progress indiagnostics, (top right) results from 3dimensional calculations of an imploded
capsule on the NIF demonstrate progress insimulations, and (bottom) a shot-time imageof the center of the target chamber on the NIF
demonstrates the state-of-the-art in facilities.
SOURCE: Top left: L. Gao, Dissertation at
LLE, University of Rochester; top right:
Reproduced from D.S. Clark et al., Phys.
Plasmas 23:056302, 2016, with permission of
AIP Publishing,https://aip.scitation.org/doi/figure/10.1063/1.4
943527; bottom: Lawrence Livermore
National Laboratory,
https://lasers.llnl.gov/media/photogallery?id=sgemp_shot.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

is to make new discoveries and breakthroughs that
help unify the field so that advances in one subfield ofplasma science benefits another, and that thosefundamental advances translate quickly to applications
and societal benefit.
High Energy Density (HED) Plasmas and Inertial
Confinement Fusion (ICF)High energy density (HED) plasma physics isthe study of matter whose energy content exceeds any
FIGURE 1.3 Accelerating electrons using anatural phenomenon on earth. HED physics often
Trojan Horse—One of the challenges indescribes the behavior of space and astrophysicalplasma acceleration of electrons is having theplasmas, and the systems on which the United States
seed electrons accelerated at the right placerelies for national security. HED physics is a fieldat the right time. In experiments at thewith broad, cross-cutting applications in plasma
Facility for Advanced Accelerator
physics. Understanding the dynamics of HED plasmas
Experimental Tests (FACET), the seedaddresses many fundamental questions relevant to theelectrons were released by photoionization ofbroader plasma communities, including space science,neutral atoms inside the plasma. This
material science and quantum materials, nuclear
technique is called the Trojan Horse. In thisphysics, atomic physics, and the generation andimage, a laser beam (red, at left) strips
transport of hard radiation. Major new facilities haveelectrons (blue dots) off helium atoms - thehad a great impact on the HED field, helping it
photocathode. Some of the photo-electrons
flourish over the past decade. These facilities include(red dots) are accelerated inside a plasma
the LCLS (Linac Coherent Light Source at the SLAC
bubble (white elliptical shape) created by an
National Accelerator Laboratory), NIF (National
electron beam (green). SOURCE: Courtesy
Ignition Facility at Lawrence Livermore Nationalof Bernhard Hidding.
Laboratory), Z (the Z-pulsed power machine at Sandia
National Laboratories), and Omega/Omega EP (lasers
at the Laboratory for Laser Energetics at the University of Rochester). Experiments on NIF and Z, asdemonstrated in Figure 1.2, have produced essential data for stockpile stewardship and national security.
Experiments on LCLS and Omega, and supported by the fundamental science programs at NIF and Z,
have enabled extraordinary improvements in our understanding of extreme states of matter.
HED physics encompasses inertial confinement fusion (ICF), which is the pursuit of controlled
fusion in the laboratory by the compression of matter to the densities found at the center of stars. The ICF
community is pursuing several options to achieve fusion, including magneto-inertial confinement, directlaser illumination to compress small pellets of deuterium and tritium (DT), and indirect laser drive.
Ignition of a controlled fusion event in the laboratory is only one of the most visible challenges to HED
plasma science. Significant new understanding of the plasma physics required for ignition and data
essential to our national security have been gained on NIF even without ignition. While the existing major
facilities are expected to continue to produce scientific advances for at least the next decade, planning forthe next generation of ICF and HED facilities, both laser- and pulsed-power-driven, is beginning. LCLS II
is under construction, and proposals to upgrade the MEC (Matter in Extreme Conditions) facility at
SLAC are in progress. If the United States is to continue as the international leader in ICF, the next HED
facility, intended for ignition must be designed and built.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

High Intensity Laser-Plasma Interactions and Accelerators
Laser and particle-beam control of intense electromagnetic fields that can be sustained andorganized in plasmas, far beyond the intensities accessible in ordinary matter, has produced new fields
and capabilities in plasma optics and particle acceleration. Combining plasmas with laser and particle
beams enables focusing, guiding, and amplification of those beams to unprecedented high intensities, as
demonstrated in Figure 1.3. Electrons and positrons can be accelerated in plasmas by resonant plasma
wakefields created by these lasers or particle beams with rates of acceleration that can be thousands oftimes those of conventional accelerators. These plasma-driven accelerators are maturing as a technology
and will improve the performance of future high-energy particle physics (HEP) colliders and enable
compact, short pulse and high intensity X-ray sources. The field is on the verge of creating precise lowdose X-ray imaging systems for medical science and national security in the next decade. Ultrafast, highgradient acceleration by HILPI have produced ion beams in excess of 100 MeV, with potential
applications ranging from medical therapy to probes of HED plasmas. These outcomes will be enabled byhigh average power, high repetition rate, shaped-pulse laser systems, and a new understanding of theirinteractions with plasma. The high-intensity electromagnetic fields produced in these systems areenabling, for the first time, experiments in nonlinear high-field Quantum ElectroDynamics (nQED), thefundamental theory of how light and matter interact.
The electric fields being produced in plasmas areapproaching the intensities capable of producing
matter from the pure electro-magnetic energy ofphotons.
HILPI is strongly linked to other areas ofplasma science in the underlying physics, inapplications and enabling capabilities. With advancesin laser technology, the coupling of lasers and plasma
phenomena can be controlled, providing the ability tomanipulate and measure states in plasmas with
FIGURE 1.4 Predicting the path of Coronal
unprecedented accuracy. Understanding and
Mass Ejections. Computer simulations arecontrolling these new processes are pushing theproviding unprecedented insights, andfrontiers of exascale computing while requiring new
predictions, of solar events such as coronalcomputational algorithms. Continued advances inmass ejections - CMEs, where huge amounts
HILPI supported by new facilities with higherof ionized gas are expelled towards the earth.
precision and repetition rate has the potential toHere are results of a 3-dimensional numericalenable revolutionary new capabilities for society andsimulation of a CME traveling from the outer
to support fundamental studies across the field ofcorona of the Sun into the heliosphere—that
plasma science.
region of space surrounding the Sun. This
Space and Astrophysical Plasmas (SAPs)
Space is perhaps the final frontier forplasmas. Space and astrophysical plasmas (SAPs)
reach regimes inaccessible to Earthbound laboratory
experiments, enabling deep insights into fundamental
plasma processes. Some of these fundamental
phenomena can be sampled directly by spacecraft,while others can only be studied by spectroscopy,
imaging, polarimetry, and other remote sensing
techniques. New observations by ground- and spacebased instruments continually challenge theorists andphysics-based first-principles model gave us
the first capability for predicting the plasma
and magnetic-field properties of the spaceenvironment from 20 solar radii to Earth.
Over the past decade, this and other physicsbased codes have become increasingly
powerful and realistic, transforming ourability to comprehend and forecast space
weather effects throughout the heliosphere.
SOURCE: Courtesy of Dusan Odstrcil,
George Mason University;
https://nsf.gov/news/mmg/mmg_disp.jsp?med_id=68959&from=.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

computational scientists to decipher the underlying plasma physical processes, while increasingly
sophisticated numerical simulations guide the requirements and choice of targets for the next generationof observing platforms and space missions (see Figure 1.4).
The societal benefits of understanding SAPs range from the practical to the inspirational. Overthe past decade, research into the origins and effects of space weather—disturbances throughout the solar
system, including Earth, driven by solar eruptions—has brought us ever closer to linking together thecomplex chain of phenomena that connect our Sun to Earth and beyond. However, we are far from being
able to predict space weather events and impacts from start to finish—an ambitious grand challenge for
PSE in the next decade. Deeper investigations into the adverse effects of space weather on spacecraft,
instruments, and humans in space, as well as our electric power grids and other vulnerable infrastructure
on Earth, are essential for both national security and protection of our upcoming robotic and human
explorations of the Moon and Mars.
The pioneering detection of gravity waves from a neutron star merger was accompanied byobservations of radio, X-ray and visible plasma emission that produced unprecedented insights into thenature of and conditions within this cosmic event. The future of gravitational wave astronomy is
inextricably linked to improving our understanding of these exotic events through SAP research. The
explosion of discoveries of planets orbiting distant stars (exoplanets) over the past decade has driven aparallel effort to apply our knowledge of plasma-produced space weather in our own solar system to thosedistant systems, in order to determine whether some exoplanets may be hospitable to life. SAP science
therefore plays a key role in the formidable challenge of searching for extraterrestrial life.
SAPs are also fascinating and exotic—from solar flares to active galactic nuclei and black holeaccretion disks—giving plasma physics high public visibility and recognition. The importance of the
public appeal of SAPs cannot be overstated in motivating the study of science in general and plasma
physics in particular. We are now experiencing the retirement of an entire generation of researchers who
were inspired to pursue careers in science by our first ventures into space—Explorer, Mariner, Apollo.
The images brought to us by the Hubble Space Telescope and the Solar Dynamics Observatory have beenequally motivational. We can only expect that continuing and expanding our intellectual reach in SAPs
will continue to bring new generations of researchers into science and plasma science in particular.
SAP studies rely heavily on other areas of plasma science, from laboratory experiments onmagnetic reconnection and dynamos to atomic and nuclear calculations of opacities, involving HED
physics, basic plasma science, particle acceleration physics, computational plasma physics, and radiativehydrodynamics. In turn, SAPs serve as unique windows into a vast range of plasma conditions that cantest fundamental theories, motivate novel laboratory experiments, and answer critical questions about
particle acceleration, atomic and molecular spectroscopy, and turbulence. Plasma engineering is essential
for the design and construction of state-of-the-art instruments on spacecraft, capitalizing on the latest
techniques and materials to obtain the spatial and spectral resolution and sensitivity needed to probe everdeeper into SAPs throughout the universe.
Magnetic Confinement Fusion Energy (MFE)
Nuclear fusion, the process whereby lighter elements fuse into heavier elements and releaseenergy, is the power source of stars. In stars, self-gravity confines plasmas hot and dense enough to
produce fusion reactions that are the source of their enormous power. In the laboratory, strong magnetic
fields are used in lieu of gravity to confine hot plasmas to produce fusion - magnetic Confinement Fusion
Energy (MFE), as demonstrated in Figure 1.5. The societal benefit of this research is clear andenormous—fusion energy can provide a carbon-free source of power for generating electricity, utilizing
an abundant and essentially limitless source of fuel. The fusion reaction that most MFE research focuses
on uses two isotopes of hydrogen: deuterium and tritium (D-T). Tritium is radioactive but can beproduced from lithium. Both deuterium and lithium are abundant in sea water, ensuring there is a

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

sufficient supply of both to use fusion power toprovide the energy needs of our planet for many
hundreds of thousands of years. (The amount oflithium that might be used in fusion reactors is a tiny
fraction of that currently expended in batteries.)
Newly investigated approaches to fusion power could
directly produce highly energetic charged particles
that can generate electrical current without also
producing unwanted neutrons. However, their energy
FIGURE 1.5 Record pressure in arequirements for break-even (generating more energy
magnetically confined plasma: In 2016, thethan expended in making the reactions) are more
Alcator C-Mod tokamak achieved a world
stringent than for D-T processes.
record plasma pressure for magnetically
Progress in fusion research over the pastconfined plasmas. To achieve the record,
decade has placed MFE on the brink of creating the
MIT scientists employed over 4 megawatts
first burning plasma—a plasma where self-heatingof radio frequency heating, raising thefrom fusion reactions dominates external heating. The
plasma temperature to over 35 million
goal of the international ITER project is todegrees Celsius or approximately twice as
demonstrate a burning plasma. ITER is under
hot as the center of the Sun. The C-Mod
construction and is on schedule to produce firstexperiments reached a plasma pressure nearplasma by 2026.. A recent National Academies study
the target value for future ITER experiments,(“A Strategic Plan for U.S. Burning Plasma
which was enabled by new understanding of
Research”) endorsed U.S. participation in ITER, andthe stability properties of the boundary of themade the case that knowledge gained from the burning
plasma. SOURCE: Courtesy of the MIT
plasma experiments to be conducted on ITER will be
Plasma Science and Fusion Center.
essential in realizing commercial fusion power in the
United States. The study also recognized that while
the ITER design is a low-risk route to a burning plasma, it is also a high-cost route to commercial fusion
power. A fusion-based electrical power network using ITER concepts may be simply too expensive. The
study recommended that U.S. researchers learn from ITER and apply that learning to the development of
a compact fusion pilot power plant that would lead the way to more economical fusion power. To achieve
this goal, the field must address challenges at the forefront of PSE and take advantage of advancements intechnology (e.g., high-temperature superconducting magnets) that are only now beginning to mature.
Low-Temperature Plasmas (LTPs)
Low temperature plasmas are partially ionized plasmas that contain electrons energetic enough tocollisionally break apart molecules to produce chemically reactive species while also keeping the overallgas temperature near ambient—low enough to contact living tissue. The ability of low temperatureplasmas (LTPs) to produce chemically reactive environments in gases, on surfaces, and in liquids has
already made society-wide transformations in our quality of life—from lighting, materials synthesis, andwater purification to enabling the information technology revolution through plasma-enabled fabricationof microelectronics. Plasmas are now being used to remove harmful substances from water, such as
perfluoroalkyl carboxylate, that have defied other economic means of remediation. Plasma methods thatetch a single layer of atoms from semiconductor devices have enabled the microelectronics industry to
make ever smaller and more capable devices. Clinical trials and practice are now using plasmas to treat
human cancer and promote wound healing. There are many opportunities to advance these applications
further, for example in the anticipated future growth of the integrated circuit industry associated withintelligent machines, autonomous vehicles, and other innovative technologies, and protecting the foodchain, and addressing pandemic spread of bacteria and viruses through plasma sterilization of materials
and tissues.
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

A strategic opportunity for LTP science is toassist in the electrification of the chemical industry—that is, to drive chemical processing by electricalmeans facilitated by plasmas. The key enabling
science will be controlling the flow of energy through
LTPs to produce predictable chemical transformations
in gases, on solids, and in liquids (see Figure 1.6). The
electrification of the chemical industry is a grandscience and engineering challenge that will enable aneconomically viable and sustainable future based on
renewable electricity.
To achieve this goal, we first need to deepen
our understanding of how energy flows throughplasmas, in order to produce more selective andefficient chemical transformations. This challenge will
require investigations of kinetic and collisional
processes, plasma self-organization, transport andplasma-surface interactions under highly nonequilibrium conditions. This new understanding will
also augment plasma-aided technologies across theboard, thereby benefiting nearly every sector of oursociety. Examples include controlling plasma-surface
interactions at the atomic level to enable the next
generation of materials for quantum computing,combating anti-microbial resistance, improving
nitrogen fixation and food safety, creating new energy
storage technologies, and developing plasma-based
propulsion capable of taking humankind to Mars andbeyond.
Computational Plasma Science and Engineering(CPSE)FIGURE 1.6 Low temperature plasmas.
LTPs are a unique state of partially ionizedmatter composed of ions, electrons, atoms,
molecules and reactive and excited species.
Energetic electrons colliding with molecules
can produce a non-equilibrium chemicallyreactive environment in gases and on
surfaces at near ambient temperatures.
Research is focused on how electrical energy
is selectively and efficiently converted into
chemical reactivity, and transporting thatreactivity to the interface between plasmas
and complex materials including liquids,
biological and next generation semiconductormaterials. The atmospheric pressure helium
plasma jet in the image is impinging on asubstrate as a method to treat surfaces,
ranging from inorganic to living tissue. LTPs
have had a transformative impact on society,from water purification to plasma-enabledfabrication of microelectronics. Emerging
applications address grand societal
challenges including combating antimicrobial resistance and cancer, enhancing
food safety and nitrogen fixation and creating
new sustainable chemical conversion andenergy storage technologies. SOURCE:
Courtesy of A.M. Lietz, E.V. Barnat, and M.
Kushner.

Computation is one of the four main methodsof scientific investigation—the others being
theoretical, experimental, and observational. However,computation merits special attention due to its growing
number of uses, including prediction, diagnosis, andexperimental design; the rapidly changing nature of
the field, the emergence of artificial intelligence (AI)and machine learning (ML) as computational
disciplines, and the opportunities for PSE to leveragecomputations to address its research challenges. Overthe past decade, computational capabilities haveincreased by many orders of magnitude, in large partby increasing the number of central processing units (CPUs, also called cores) on a single microprocessor
chip and by very efficiently linking together many microprocessors. These advances have taken
computing from Gigascale (109 floating point operations [flops] per second) to Petascale (1015 flops/s),
making use of 10s or 100s of thousands of CPU and Graphics Processing Unit (GPU) cores. In the next
decade, computational capabilities will increase another 3 orders of magnitude to reach the Exascale (1018
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

flops/s) level. The coming advances will impact every scale of computing. High-performance computing(HPC) will become affordable by small research groups, allowing them to tackle computational analyses
several orders of magnitude larger than they could just a few years ago. Breakthroughs in computational
capabilities make it possible not only to speed up large simulations, but also to discover new realms in theunderlying science.
Specialized CPSE software capable of utilizing the emerging highly concurrent andheterogeneous hardware is under development for specific applications related to the research missions offederal agencies. However, these efforts are not affecting nor are they accessible to all areas of PSE.
Indeed, even in areas of agency-supported research, critically accessible software is not available. For
example, PSE does not have the range of software that is available in computational fluid dynamics(CFD) or structural mechanics, which includes both commercial codes and well-supported, more
research-oriented, open-source codes. This situation is exacerbated by the increasing array of potential
computational devices, including quantum based. The multi-scale, multi-physics and multi-applications
nature of PSE makes it difficult to develop broadly applicable and accessible codes, a condition that is
also exacerbated by segmentation of the field. Concerted effort is therefore needed to better unify
computational efforts across the realm of PSE, particularly for implementing new computational
approaches, such as AI and ML. To date, AI/ML has shown encouraging results in prediction throughpattern recognition, but the possibilities for discovery in PSE using AI/ML, particularly in deriving
underlying fundamental parameters, have not yet been fully developed.
Efforts that will enable the development of more broadly applicable, high performance, and easily
implemented software for PSE, with the goal of achieving the robustness of CFD software, clearly
deserve support. Major thrusts include education, to develop the next generation of computational PSE
practitioners in both software development and scientific discovery, and ensuring that algorithm
development continues in both the mathematical and computer sciences. Even within a single
computation, PSE phenomena are often multi-scale and multi-physics, which makes it difficult to develop
efficient algorithms for machines that require extremely high levels of concurrency. Ultimately,
developing efficient computational platforms for PSE may require codes that take advantage ofheterogeneity (computing across multiple devices of different architectures). This goal becomes evenmore challenging when it is also necessary to make these codes accessible to the broader community—
non-computer experts should not need to become expert code developers to utilize computations. As new
devices become available, such as quantum computers, plasma theorists and computer scientists should
jointly develop new algorithms that account for the multi-physics nature of PSE from the start, as opposedto trying to make existing incompatible algorithms fit new architectures.
VALUE OF PSE TO THE NATIONGrand Challenges of Plasma Science and Engineering
Plasma science and engineering holds rich science challenges while being extremely relevant to
the economic vitality and security of the nation. Addressing these challenges is part of the continuum oftranslational research that begins with fundamental scientific understanding and culminates in societal
benefit. In most fields of PSE, it is not possible to investigate plasma science challenges in isolation
without focusing on some aspect of the science that is motivated by, and whose findings will translate to,an application.
Underpinning these challenges is the need to develop a predictive understanding of plasmas overa vast range of accessible parameters: from weakly ionized, low temperature atmospheric pressureplasmas, through high temperature, high density plasmas, to the extreme plasma conditions that can only
be accessed on earth by ultra-intense lasers. Plasmas are complex physical entities that can exist in statesthat range from weakly coupled to strongly coupled and from non-magnetized to magnetized states.
Plasmas also exhibit a wide variety of self-organized behaviors. These rich scientific topics all motivate
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

the study of plasmas as a distinct scientific discipline. Deep, predictive understanding of plasmas will
provide the fundamental knowledge upon which future applications can be built. There should becontinued investments in theoretical, computational, and experimental exploration of the fundamental
processes of plasmas, not only to advance the science of the discipline, but also as a necessary prelude to
applications.
The translational continuum from fundamental science to applications is an outstanding strengthof PSE, and is captured in the following PSE Grand Challenges—high level goals in which mastery of
the complexities of plasma science benefits society.
●

Understanding the behavior of plasmas under extreme conditions will enable energy conversion byplasmas to be predicted and efficiently controlled, to address the challenges of sustainability,
economic competitiveness, and national security, and expand our knowledge of the most fundamental
processes in the universe.
When astrophysical objects undergo disruptive events, such as the violent ejection of material fromthe Sun that influence space weather or the formation of relativistic jets of material from the black
holes at the centers of galaxies, it is the violent reconnection of magnetic fields that produces massive
plasma outflows and energetic particles. Inside plasma processing reactors, oscillating electric fields
heat plasmas that produce new materials. Powerful lasers generate plasmas that compress matter todensities found in the center of stars. Mitigating disruptive events in fusion plasmas will be an
important achievement in helping to realize the economical production of fusion power, satisfying theenergy demands needed for national security. These are all examples of energy conversion from one
form to another that occurs in plasmas. This conversion empowers societies with beneficial
applications and is the basis of nearly all astrophysical and space plasma phenomena. Understanding
the complexities of these plasma-enabled energy conversions will require new theoretical,
computational, and experimental approaches. At one extreme, controlling and predicting thesecomplexities will improve economic competitiveness and national security. At another extreme,
increasing our knowledge of how our universe operates will enable us to answer fundamental
questions about the birth and death of stars while protecting astronauts on their journeys to theplanets.

●

Mastering the interactions of the world’s most powerful lasers and particle beams with plasmas will
enable precision x-ray imaging for medical science, advances in national security, compact particle
accelerators, advanced materials and sustainable energy sources, while opening new regimes forhigh energy and quantum physics.
The coupling of intense, high repetition-rate lasers with plasmas will produce conditions that havenever before existed on Earth, and the resulting physical phenomena will expand our knowledge of
how matter behaves under intense electric fields. Mastery of that knowledge will enable creation ofplasma optics that control light with unprecedented intensities, new compact particle accelerators,
conditions approaching nonlinear Quantum ElectroDynamics (nQED), and opportunities for
precision plasma physics and control of particle-wave interactions. With the development of petawattclass (1015 W), high repetition-rate lasers, new technologies will emerge ranging from compact
particle accelerators and coherent x-ray imaging to remote detectors for national security. These
capabilities will provide transformational improvements in resolution and capability for medicine,
biology, materials science, and the investigation of fundamental meso- and nanoscale physics. These
next-generation lasers will extend the reach of high energy particle physics, and improve ourunderstanding of the fundamental forces that shape the universe.

●

Accelerate the development of fusion generated electricity, tapping the virtually unlimited fuel in seawater, to bring the benefits of carbon-neutral power to society, through economical, deployable, andsustainable fusion systems enabled by advances in experimental and computational plasma physics.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

Perhaps society’s greatest challenge is sustainability—a vision that will in part be enabled by atransition to carbon-free and carbon-neutral sources of electricity. Having such sources provides for a
future based on renewable and sustainable electricity (FBRE). Controlling fusion reactions will
provide nearly limitless clean power by converting hydrogen into helium in star-like plasmas on
Earth, and holds the promise of providing sustainable electricity. To meet that goal, science andtechnology challenges must be addressed using the most advanced computational and experimental
techniques. The significant investments already made in main-line magnetic fusion energy (MFE)
concepts should continue to determine how to create steady state, disruption-free fusion burning
plasmas and how to engineer the plasma-facing materials to withstand the intense heat generated byfusion reactor plasmas. At the same time, alternative MFE concepts and innovative technologies must
be explored and exploited to achieve economical fusion power that will help enable the FBRE.
Pursuit of main-line and alternative concepts will require investments in and leveraging ofcomputational and experimental investigations of the fundamental yet complex plasma transport
occurring in MFE systems, while partnering internationally to develop the technologies anddemonstration systems required to transition fusion power into a practical source of unlimited carbonfree electricity.
●

Demonstrate that lasers and pulsed-power devices can produce inertially confined fusion ignition by
producing plasma-based extreme states of matter to support stockpile stewardship, further the goal ofsustainable energy, and expand our understanding of high energy-density physics.
The compression of matter by lasers and pulsed power will produce inertial confinement fusion (ICF),
one of the most scientifically and technologically complex projects ever attempted. High energydensity physics, the basis of ICF, involves extreme states of matter that occur naturally only inastrophysical objects. Understanding these extreme states is absolutely essential to the stewardship ofour nuclear stockpile and to understanding supernovae, some of the largest releases of energy in theuniverse. Advancing that stewardship and understanding cosmic phenomena require the mostsophisticated computer simulations ever attempted, advanced pulsed-power facilities, ever morerefined diagnostics, and support for new methods to produce and analyze the fundamental
experimental and computational data produced by and required by these efforts. The states of matterproduced by HED plasmas in pursuit of ICF have never before controllably existed on earth, havenever before been directly studied, and have nearly defied being described computationally from firstprinciples.

●

Enable electrification of the chemical industry by controlling the flow of power through low
temperature plasmas to produce predictable chemical transformations in gases, on solids, and inliquids, on scales capable of economically establishing a future based on renewable and sustainable
electricity (FBRE).
The ability of low temperature plasmas (LTPs) to induce desired chemical transformations in gases,on surfaces, and in liquids has already been exploited to improve our quality of life—from lighting,materials synthesis and water purification, to enabling the information technology revolution throughplasma-based fabrication of microelectronics. An improved ability to control chemicaltransformations through electricity-driven LTPs has tremendous potential to meet a wide range ofcurrent and future societal challenges, including the transformation of the chemical industry fromfossil-fuel–driven to electricity-driven. This enhanced capability in LTPs will broadly benefit society
by controlling plasma-surface interactions at the atomic level to create the next generation ofmaterials for quantum computing, combating anti-microbial resistance, helping to prevent pandemic
outbreaks of pathogens through plasma sterilization of materials and tissue, improving agricultural
efficiencies and food safety, enabling new energy-storage technologies, and developing plasma-based
propulsion capable of taking humankind to Mars and beyond.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration●

With life, technology, and space travel at risk from damaging solar plasma activity, develop thecapability for timely and actionable space-weather observations and predictions to mitigate thepotential effects of extreme solar plasma storms on spacecraft, humans, power grids, andinfrastructure.
Living with a star means enjoying its benefits and dealing with its disruptive behavior. The Sun, itself
a plasma, steadily emits the solar wind while intermittently producing coronal mass ejections andflares in which intense electromagnetic radiation and massive clouds of magnetized plasma can bedirected toward Earth. The high-speed plasmas and energetic particles produced by these extreme
eruptions can collide with and potentially damage spacecraft and harm human passengers, andinteract with Earth’s magnetic field and atmosphere, producing electrical transients that affectcommunications, power grids, and infrastructure. Our aspirations to explore the Moon, Mars, and therest of our solar system are also endangered by adverse space-weather. Although humankind cannot
prevent extreme solar plasma eruptions from occurring, being able to predict those events many daysin advance can provide the time to take protective measures. Achieving this predictive capability will
require substantial advances in our theoretical and computational abilities to model solar eruptions,the acceleration of highly energetic particles, and the interaction of these energetic particles andmagnetized plasmas with spacecraft and planetary magnetospheres. Achieving this capability will
require a new generation of space-based constellations and ground-based observatories. The Space
Weather Operations, Research, and Mitigation (SWORM) subcommittee of the National Science andTechnology Council is leading a community-wide conversation on benchmarking of extreme space
weather events based on studies, data acquisition, and research. Global efforts to develop metrics formodel validation are underway under the aegis of the COSPAR (Committee on Space Research)
International Space Weather Action Team program. Continued interagency and international
cooperation will be key to meeting the grand challenge of accurate and timely space-weather
prediction.

In addressing these Grand Challenges, the humanities and social sciences provide an important lensthrough which all scientific advances can be viewed. Because PSE is integral to so many of thetechnological developments of the last several decades, it is important for the field to be introspective
about the impact of those technologies. Furthermore, because of the great potential for areas such as low
temperature plasmas to impact important societal needs such as water purification and waste cleanup, it
will be important to contemplate topics such as social justice in order to ensure that such critical societal
needs can benefit all of society
Critical Support from Other Science Areas
PSE is an intellectually broad and interdisciplinary field that benefits nearly every other field of
science and engineering. For example, the biotechnology and material disciplines have made and continue
to make advances based on the ability of plasmas to synthesize, modify, and functionalize surfaces andmaterials. At the same time, PSE is exceedingly dependent on allied disciplines for the fundamental datautilized in analyzing experiments and needed for model development. As PSE focuses on translational
research that involves plasma surface interactions, there are critical data needs for how plasma produced
activation energy (energy electrons and ions, chemically species, UV/VUV radiation) interact with hardsolids, liquids and soft and organic materials, including living tissue. These data are best produced byexperts in those disciplines, in collaboration with PSE researchers as needed. We often find thatgeneration of fundamental data that is used by other disciplines sometimes falls out of favor with funding
agencies as that work is perceived as being a service. It is the committee’s experience that these dataneeds are often at the leading edge of science challenges in allied disciplines; and so should be strongly
and robustly supported.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

This need for critical and robust support from allied sciences is nowhere more true than in thesynergistic relationship of PSE with atomic, molecular, and optical physics (AMOP) and chemical
physics (CP). The most basic processes in PSE involve electron and ion impact on atoms, molecules, andsurfaces (solid and liquid) to produce excited states and new functionality, to generate electromagnetic
radiation and energetic particles, and to catalyze chemical reactions between multiple phases. Describing
and analyzing these processes require a wide range of fundamental data, including electron impact crosssections for excitation, dissociation, and ionization of atoms and molecules; optical absorption crosssections; oscillator strengths and opacities; charge exchange cross sections; and reaction probabilities ofplasma-produced radicals, ions, and photons with gases, solids and liquids. The importance of thesefundamental data cannot be overstated—they are essential to the health and advancement of PSE. Well
supported programs in AMOP and CP not only advance the science of those disciplines but also enableadvances in other disciplines, and PSE in particular.
Diversity, Equity, and Inclusion and the Plasma Science and Engineering Workforce
The principle of diversity, equity, and inclusion (DEI) broadens a discipline to the betterment ofthat discipline and to the betterment of the society the discipline serves. Regrettably, plasma science andengineering is among the least diverse STEM fields, for historical and current reasons. For example, datafrom the annual Survey of Earned Doctorates in 2013-2017 shows that the percentage of women annuallyearning doctorates in plasma physics averaged 14% (below the approximately 20% average for physics),
while the percentages of PhDs obtained by Hispanic and African-American students fluctuated around
3% (with several years reporting zero). These data are consistent with statistics from the American
Institute of Physics. Additionally, a 2017 assessment from the University Fusion Association has shownthat the fusion community (which represents a large portion of the overall PSE community) is aging, withan average age of 56. At the same time, STEM fields that may utilize plasmas, such as chemicalengineering and bioengineering, are significantly more diverse.
The committee notes that federal agencies funding research in PSE have greatly differing
expectations for grantees to produce broader impacts in their research and conduct outreach activities.
The committee endorses the premise that the primary focus of these agencies should be addressing thescience and technology challenges in PSE that will lead to societal benefit. However, the committee alsofeels that a more consistent set of expectations among these agencies would deliver a stronger message ofthe importance of diversifying PSE.
A professional workforce cannot reflect society if the student pipeline entering PSE is notdiverse. There are many causes for lack of diversity in the pipeline and many remedies being proposed todiversify the pipeline. Early exposure to plasma science (e.g., the APS-DPP Plasma Expo, science
museum exhibits, and university outreach activities) is important for building an appreciation of plasma
science on the part of students and the general public. A more direct method for increasing interest in PSE
and in diversifying the pipeline is to increase the numbers of undergraduate students exposed to PSE
through research experiences. Such research experiences are more readily available at universities with
PhD programs in physics and engineering than at primarily undergraduate institutions (PUIs). Yet, thehighest degree in more than two-thirds of physics departments in the United States is the bachelor’s
degree, and approximately half of all physics bachelor’s degrees are awarded by departments that do notoffer a PhD. Therefore, the majority of U.S. physics students and potential plasma physics graduate
students are likely not exposed to plasma physics as undergraduates. A significant portion of the future
PSE workforce relies on prospective graduate students encountering plasma research only in graduate
school, and only if a plasma program exists at that institution.
PSE research programs in PUIs could have a disproportionately large influence in developing thePSE workforce by exposing undergraduates to plasma physics and engineering, thus increasing thepipeline of students entering graduate school with the goal of studying plasma physics. PUIs tend to beliberal-arts-focused institutions with broader curricula and more diverse student bodies. Their smaller
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student-to-faculty ratios enables closer mentoring of research experiences involving students who would
not otherwise have research opportunities. Smaller colleges and institutions also have a history of serving
underrepresented minorities and first-generation college students, thereby helping to introduce PSE toprecisely the audience needed to diversify the pipeline.
The committee acknowledges and is concerned about the lack of diversity in the core areas of
PSE. The goal of the PSE community should be to improve the diversity of PSE to reflect the society it
serves by increasing the participation of women, ethnic and religious minorities, gender-preference andgender-identity minorities including members of the LGBTQ+ community, and persons with disabilities,
while recognizing that this list may not be fully inclusive of all underrepresented communities in PSE.
Addressing this persistent problem of underrepresentation should be a high priority in the PSE
community. The committee strongly believes in the benefits that will result from improving that diversity,and strongly encourages community leaders throughout the PSE enterprise to carefully consider andassess the DEI practices within their own organizations. Even more critically, individual members of thePSE community should be involved in DEI activities at the most primary levels in their institutions.
The committee acknowledges and supports the DEI activities that have been initiated since thePlasma 2010 report, and the committee encourages continued community-wide discussions and actions
that will produce a more diverse PSE discipline. Professional societies, universities, national academies,
national laboratories, and federal agencies are now actively engaged in addressing DEI issues in STEM,
and in PSE in particular. Given the demographics of the field, the next decade will likely see significant
turnover in the PSE workforce, providing ample opportunities for improving the diversity of the field.
Although the committee is not formally endorsing a particular organization’s DEI activities, thecommittee strongly endorses the importance of and efforts of the field to diversify.
FINDINGS AND RECOMMENDATIONSThe Plasma Science and Engineering (PSE) community in the United States has had an enormous
impact since publication of the Plasma 2010 report. Internationally leading research has been performed
in all fields of PSE, with landmark contributions having been made to the advancement of the science ofplasmas, national security, and economic competitiveness. These advances confirm the value and need fordiscipline-centric research on the basic plasma science challenges, the interdisciplinary research that willtranslate that learning to applications and support for that translational process. To expand upon that
progress in the next decade, the discipline needs greater interdisciplinary coordination of federal agencies(and programs within agencies) in their approach to PSE, an activity that would be in their own benefit aswell as that of the discipline. The committee notes that the NRC Plasma Science Committee (PSC) at one
time helped to heighten awareness of these opportunities and be a spokes-group for the field.
Unfortunately, the PSC has been inactive for several years. Expanding the impact of research in PSE also
needs an ecosystem of facilities, diagnostics, computations, and, importantly, renewal of the PSE
workforce through education and career enhancement programs. The high-level, findings andrecommendations from this study are discussed below. These high-level recommendations, as well as
more specific individual chapter-based recommendations, are collected in Appendix B.
Stewardship and Advancement of Interdisciplinary Research
Finding: Plasma science and engineering (PSE) is inherently an interdisciplinary field of
research. While the underlying science has common intellectual threads, the community
is organized into sometimes isolated sub-disciplines.
At the same time, examples of initiative-driven and long-term collaborations between federal
agencies in PSE are rare. The recently enacted Space Weather Research and Forecasting Act thatmandates joint activities by NASA, NOAA, NSF, DOD, and FAA, and the NSF/DOE Partnership in
Basic Plasma Science and Engineering, are notable exceptions. This isolation is in part driven by the
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

extreme diversity of applications that motivates the fundamental research. It is also occasionallyreinforced by narrow, mission-driven support at the federal level.
Several program managers contacted by the committee were cautious about participating ininterdisciplinary programs in PSE due to the risk of being perceived as duplicating research priorities ofother agencies, a practice which has been historically discouraged. The committee and the PSE field havea different perspective.
During review and final preparation of Plasma 2020, we are in the midst of the Covid-19
pandemic (March to April 2020). The areas of plasma medicine and plasma biotechnology encompass theuse of plasmas for sterilization of materials and living tissue such as skin, and address the need tophysically kill pathogens without risking antimicrobial resistance. Plasma medicine and plasma
biotechnology are examples of interdisciplinary fields that have fallen between the cracks of the perceived
responsibilities of individual funding agencies. Plasma focused agencies are reluctant to sponsor projects
that involve biological systems and biologically focused agencies are reluctant to sponsor projects thathave a focus on plasma physics. As a result, we may have missed an opportunity to have another tool at
our disposal to aid in the current health crisis.
Finding: What may be narrowly perceived as duplication is actually critically necessary
collaboration needed to address the complex science challenges in PSE while rapidlytranslating results to society-benefiting outcomes.
Finding: Institutional barriers between sub-disciplines of PSE make mutuallyadvantageous interactions difficult, yet interactions between sub-disciplines have led toimportant advances that would have been difficult to produce otherwise.
Finding: A more unified voice for the field would create opportunities forinterdisciplinary and translational research, and initiate activities that exploit
synergies among different subdisciplines of PSE.
Recommendation: Federal agencies directly supporting plasma science andengineering (PSE) and those federal agencies benefiting (or potentially benefiting)from PSE should better coordinate their activities extending into offices anddirectorates within larger federal agencies
One mechanism to facilitate this coordination is to establish an Interagency Working Group(IWG) with representatives from agencies that investigate plasmas as part of their mission (e.g., NSF[MPS, GEO, ENG], DOE [SC, NNSA, ARPA-E], NASA [SMD, HEOMD], DOE [FES, NNSA, HEP,
BES, ARPA-E], NOAA, DoD [AFOSR, ONR, ARO, DTRA]) and those agencies that benefit from (orcould benefit from) plasma applications (e.g., EPA, NIH, DHS, FDA, NSA, and USDA). The IWG would
identify feasible areas of collaboration and build upon current programs that contribute to the missions of
the agencies in basic and applied PSE areas. In this regard, those agencies performing research in basic
plasma science (e.g., NSF, DOE, DoD) could reach out to agencies that benefit or could benefit fromplasma applications (e.g., NIH, USDA, EPA), while mutually soliciting community input on possible
areas of collaboration. Given the breadth of the IWG, this effort would best be coordinated by the
National Science Foundation, perhaps in partnership with the National Science and Technology Council(NSTC) and the Office of Science and Technology Policy (OSTP). (NSTC/OSTP have experience inorganizing such working groups, for example, in HED.) Several potential interagency collaborations on
topics across the field of PSE are listed in Table 1.1. The collaborations listed in Table 1.1 are intended to
be examples of potential partnerships that would meet many of the needs and priorities of the field andnation. The committee intends these suggestions as starting points for discussions.
Finding: Fundamental research in PSE can and does rapidly translate to the developmentof societally relevant technologies, the benefits of which cut across the missions of manyfederal agencies.
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In fact, the majority of PSE research is motivated by the final application, from producing electricity using
controlled fusion and protecting information technology assets from errant space weather, to plasma
synthesis of new materials and medical diagnostics using table-top laser-accelerators. In some areas ofPSE, such as MFE and ICF, the motivating application is contained within the same agency or programthat funds the fundamental plasma research. In these situations, the translational research is well leveraged
towards the intended application. In other areas of PSE, such as plasma materials processing, themotivating application is the primary mission of an agency or program other than that funding thefundamental plasma research. For example, plasma-based accelerators benefit broad interests outside theagencies principally responsible for their development. The DOE High Energy Physics Accelerator
Stewardship is an example of such a program.
Finding: The interdisciplinary and multidisciplinary strengths of PSE are not being fully
utilized. This situation is to the detriment of the fundamental plasma research and to thedetriment of the intended applications.
Although inter-agency and intra-agency collaborations that jointly fund PSE activities exist, these
efforts are largely ad-hoc and not in the form of proposal-driven initiatives. Notable exceptions include
the recurring NSF/DOE Partnership in Basic Plasma Science and Engineering, an outcome of the 1995
Plasma Decadal Study, and the recently announced NSF/NASA Next Generation Software for Datadriven Models of Space Weather with Quantified Uncertainties. Another successful example is the 2007
Interagency Task Force on High Energy Density Physics, with membership from the DOE Office of
Science (OS) and NNSA, NASA NIST, NSF and DoD, which had a significant impact on the high energy
density field. A recent RFI (request for information) issued by the DOE OS to support research inadvanced microelectronics, a component of which is plasma materials processing, involves multiple
programs within the OS. Increased collaboration between agencies to support fundamental research,translational research, and applications-focused research in PSE would benefit all partners. The barriers tosuch collaboration should be reduced. Examples of beneficial cross-agency linkages are listed in Table
1.1.
Finding: Interagency (and inter-program) initiatives would fully exploit theinterdisciplinary and multidisciplinary potential of plasma science and engineering (PSE)in both fundamental and translational research if properly stewarded.
Recommendation: Federal agencies and programs within federal agencies that are
separately focused on fundamental plasma research, and those that are focused on
science and technologies that utilize plasmas, should jointly coordinate and support
initiatives with new funding opportunities.
There are extraordinary opportunities for such jointly sponsored initiatives in, for example,
materials, biotechnology, medicine, agriculture, accelerators, energy, environment, propulsion,
manufacturing, space weather, security, and computations. Some of these opportunities and potential
agency partnerships are listed in Table 1.1. These initiatives will significantly advance fundamental
plasma science while accelerating the translational outcomes of those advances. One of the goals of therecommended IWG would be to address the scope, feasibility, and possible implementation of these
initiatives, an activity best organized by NSF. Within federal agencies whose programs are highly
mission-driven, coordination of such initiatives may best come from higher levels—for example, at thelevel of the DOE Office of Science.
Finding: The potential is enormous for PSE to contribute to one of society’s greatest
challenges—sustainability. The contributions that PSE could make extend from fusionbased, carbon-free electrical power generation to electrification of the chemical industry.
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As the needs for sustainability become clearer, the plasma science challenges will become more focusedand more tied to the applications. Although the research will remain fundamental, the research will also
become more translational. At NSF, this research would best be performed in the Engineering Directorate(EngD). However, support for PSE in the EngD has been inconsistent, and particularly so since thePlasma 2010 report. As the priorities of programs in the EngD change, PSE is added and removed fromprogram descriptions. Programs in the EngD also choose to participate or not in the NSF/DOE PlasmaPartnership depending on the changing priorities. With this inconsistent record of support for PSE in theEngineering Directorate, it is difficult to develop long term PSE strategies to address critically important
challenges such as sustainability.
Finding: The translational nature of fundamental research in plasma science andengineering (PSE) needs to be formally recognized at NSF.
Recommendation: The Engineering Directorate (EngD) of the National Science
Foundation (NSF) should, as a minimum, consistently list PSE in descriptions of its
relevant programs and consistently participate in the NSF/Department of Energy(DOE) Plasma partnership.
Recommendation: More strategically, NSF should establish a plasma-focusedprogram in the Engineering Directorate. that would advance engineering priorities
across the board, including advance agricultural systems, energy and environment,chemical transformation, advanced manufacturing, electronics and quantum
systems.
These efforts would complement the more fundamental plasma physics program in the Mathematical andPhysical Sciences Directorate. The PSE program in EngD could follow the recommendations of the NSF
workshop “Science Challenges in Low Temperature Plasma Science and Engineering: Enabling a Future
Based on Electricity through Non-Equilibrium Plasma Chemistry” [arXiv preprint arXiv:1911.07076(2019)].
Finding: Public-private partnerships (PPP) have long been a benefit to PSE, largely inthe form of SBIR (Small Business Innovative Research) and STTR (Small BusinessTechnology Transfer) programs.
SBIR/STTR programs have been highly successful in translating fundamental science towards
commercialization. Although PSE industries have long funded fundamental research focused towards
developing their own products, the emergence of venture-capital-funded fusion research andinternational competition in industries reliant on plasma science have significantly changed thelandscape for PPPs. One recent development acknowledging the new landscape is the DOE Office of
Science Innovation Network for Fusion Energy (INFUSE), whose goal is to accelerate fusion energy
development in the private sector by opening resources at DOE laboratories and reducing barriers tocollaboration. In another example, an increasing number of small companies that specialize in spaceweather plasma data and models tailored primarily to aviation, aerospace, and defense needs have been
responding to SBIR/STTR calls by several federal agencies, broadening the commercial space-weather
sector.
There are challenges in leveraging PPP for economic and national security benefits for both small
and large companies. The requirements to make breakthroughs in translational research andcommercialization in multidisciplinary fields such as PSE may exceed the resources and know-how ofmany small businesses. These requirements then fit poorly within the traditional SBIR/STTR structure.
For large businesses, there are extreme pressures from international competition, in large part resulting
from strong foreign government support for fundamental and translational research in key plasma-basedindustries. For example, South Korea and China have aggressive national programs to address
fundamental research vital to the plasma-based microelectronics industry.
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Finding: With there being few U.S. governmental programs designed to translateindustrially relevant fundamental science to practice, U.S. industries are at a competitive
disadvantage internationally.
Recommendation: Federal agencies focused on plasma research, and DOE in
particular, should develop new models that support the translation of fundamental
research to industry. Programs that support vital industries depending on plasma
science and engineering (PSE) should be developed through relevant interagency
collaborations.
Examples of translational research that would benefit plasma enabled industries include
development of diagnostics that could be used for real-time control of plasma processes, understanding
and optimizing the production of plasma generation precursors used in materials processing anddeveloping industrially relevant modeling platforms. The United States is well known for being a hotbed
for entrepreneurship and it is unclear whether the PSE research infrastructure is well suited to meet
entrepreneurial needs. For example, many biotechnology startups use plasma processes for biocompatible
coatings, yet are more likely to seek support from NIH than FES. Are their needs met?
The committee acknowledges that this is a multifaceted recommendation with many avenues for
implementation. Certainly, the PSE community could take advantage of existing resources to engage withthe private sector, such as the National Academies Government-University-Industry Research Roundtable(GUIRR). One implementation could be encouraging or requiring more collaborative research between
universities and small companies, both for commercialization and to meet the needs of national
laboratories. In parallel, INFUSE-like programs could be extended through partnerships to support thescience needs of industries and companies, large and small, in areas of national importance that depend on
PSE. Another implementation would be to sponsor translational research to bring plasma-based
capabilities to a level where private research and development can continue. A particularly valuable
implementation would be to regularly convene an advisory board of technical leaders from industries that
rely on or could utilize advanced PSE capabilities, to articulate the needs of industry in fundamental
research. Such an advisory board would guide federal agencies in how best to support translational andmultidisciplinary research, including selection of SBIR/STTR topics that have a high probability forindustrial impact. This could be coordinated by the recommended IWG, with a more mission, outcomes
focused agency, such as the DOE, leading the effort.
The Plasma Science and Engineering Community
Plasma science and engineering is a highly multidisciplinary field, a quality that is reflected by the large
number of federal agencies with interests in plasmas, and the diverse array of university departments inwhich plasma faculty and researchers can be found. At any given university, one is likely to find plasmafocused faculty in physics, chemistry, geophysics, space sciences, astronomy and astrophysical sciences,climate sciences, and many engineering fields (e.g., aerospace, electrical, nuclear, chemical, biomedical,
and mechanical).
Finding: The multidisciplinary approach has been at the heart of the success of the field,
while simultaneously working against the long-term viability of the field in academia.
Since plasma physics is a minority discipline in nearly every department containing plasma-focusedfaculty, maintaining faculty expertise is becoming progressively more challenging. Universities provide
thought leadership and drive innovation, while also training the workforce for the field, and thatleadership and training requires a robust faculty in PSE.
Finding: Lack of a critical mass of faculty in PSE inevitably will lead to an erosion of
U.S. capability in PSE. At the same time, the university leadership in PSE is rapidly
aging and will need renewal in the coming decade.
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There are great opportunities for new PSE university faculty to address sustainability, investigate laserplasma produced quantum effects, make space weather predictions, and investigate exotic states of matter.
However, the committee is gravely concerned that poor PSE demographics and current hiring practices
are eroding the ability of the field to meet national priorities, from security to the economy. There aresimply too few early-career faculty to renew the field. Opportunities for scientific leadership are alsoessential for healthy university programs. This is particularly true for those faculty members whose
primary focus is investigating the fundamentals of plasma science as opposed to their applications.
Recommendation: Federal agencies—for example, Department of Energy (DOE),
National Science Foundation (NSF), National Aeronautics and Space
Administration (NASA), and Department of Defense (DoD)—should structure
funding programs to provide leadership opportunities to university researchers inplasma science and engineering (PSE) areas and to directly stimulate the hiring ofuniversity faculty.
These leadership opportunities are critical to all areas of PSE. Examples of implementing thisrecommendation include soliciting major new facilities or missions with leadership teams composed inpart or wholly by university researchers. Major activities in the field could be organized around centersthat are led by university researchers. Specific programs could be implemented to provide funds for thecreation of faculty positions, following the model of the NSF Faculty Development Program in Space
Sciences.
Finding: Plasma-specific educational and research programs that also provide
opportunities to diverse and less advantaged populations are needed to ensure a critically
populated PSE workforce.
As discussed earlier in this chapter, increased emphasis on PSE undergraduate research and internships,
particularly at primarily undergraduate institutions (PUIs), will improve awareness of our field among all
undergraduates, and women and underrepresented students in particular, thus enabling a more heavily
populated and a more diverse discipline. Stronger links between PUIs and research institutions would
also improve the pipeline.
Finding: Plasma-specific intern programs and summer schools are needed forundergraduate and graduate students, as are programs supporting students withincomplete preparation to progress in plasma physics, such as the American PhysicalSociety Bridge Program.
The past DOE National Undergraduate Fellowship program in plasma physics, now a Science
Undergraduate Laboratory Internship (SULI) program at Princeton Plasma Physics Laboratory, and theAmerican Physical Society Division of Plasma Physics outreach events for students, are two successful
examples. Physics curricula are traditionally sequential, with plasma physics typically covered towards
the end of the sequence (if at all).
Finding: Requiring students to know early in their undergraduate years that plasma
physics is a career goal has limited the number of students continuing in plasma physics
in graduate school and has excluded less advantaged populations.
Finding: Support for junior faculty, for course development, and for curricula
enhancement (e.g., inclusion of plasma physics in other courses) are necessary to enable
students from a wide range of institutions to enter the field.

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Federally funded programs to support undergraduate education, graduate fellowships,
postdoctoral fellowships, and early-career awards have been essential in attracting and supporting atalented and diverse population of junior scientists to PSE. However, recent policy changes haveeliminated many of these programs in important areas of PSE within the DOE Office of Science. While
the policy changes were intended to prevent duplication of educational efforts across agencies, theprograms that were eliminated have no equivalents in other agencies. Consequently, their loss has
significantly affected the ability to attract and retain new talent and university faculty in PSE.
Finding: The committee regards multi-agency investment in education, whether throughdirectly supporting undergraduate and graduate students or programs, or through faculty,
and resource development, as being critical. The more “duplication” of effort in theseareas can only further strengthen PSE.
Recommendation: Funding agencies (e.g., NSF, DOE, NASA, DoD) should structure
funding to support undergraduate and graduate educational, training, and research
opportunities—including faculty—and encourage and enable access to plasmas
physics for diverse populations.
To implement this recommendation, federal agencies supporting PSE research could be allowed toestablish domain-specific educational and outreach programs, reversing recent changes that were intended
to reduce duplication in educational programs across the federal enterprise. New opportunities forundergraduate research in PSE at smaller PUIs would increase exposure of diverse populations to plasma
physics and engineering, thus increasing both the population and the diversity of the pipeline into
graduate school and the profession. This activity could be built on the model of the NSF program in
Facilitating Research at Primarily Undergraduate Institutions. Stronger links between PUIs and research
institutions could be established by postdoctoral or graduate fellowships for researchers to work at PUIs
or jointly with larger plasma institutions, and by broadening REUs (Research Experiences for
Undergraduates) beyond NSF.
The Research Enterprise in Plasma Science and Engineering
The research enterprise in PSE has had tremendous impact over the past decade. Plasma science has
opened opportunities across a remarkably diverse range of areas, including semiconductor processing,new accelerators, understanding astrophysical and planetary states of matter, new energy sources, andenhancing national security. Although the progress has been impressive, it has also been made in anenvironment of tremendous competing international investments across the spectrum of PSE. These
investments challenge and may potentially usurp U.S. leadership in PSE. International investments inlarge fusion devices, powerful lasers and research networks over the past decade have generally
exceeded that of the United States.
Finding: Given these strong international investments, incremental progress in facilities
in the United States is insufficient to maintain leadership.
Finding: A spectrum of facility scales is required by the sub-fields of PSE to address
their science challenges and translational research.
Finding: Mid-scale facilities (e.g., in the $1 million to $40 million range, depending on
agency) offer particularly good opportunities for broadening participation within
academia.
Recommendation: Federal agencies (e.g., NSF, DOE, NASA DoD) should support aspectrum of facility scales that reflect the requirements for addressing a wide rangeof problems at the frontiers of PSE.
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In some cases, advancing the state of the art requires significant investments in large facilities
built over many years, while in other areas, better equipping the laboratories of single investigators withadvanced diagnostics as part of a distributed network best serves the field. However, research facilities
cannot function efficiently without the support of experienced scientific staff, and operations cannot
proceed efficiently without the procurement of increasingly costly essential materials, such as liquid
helium.
Finding: Investment in facilities without the concurrent support of research andoperations is not optimum
Recommendation: Federal agencies whose core missions include plasma science andengineering (PSE)—for example, Department of Energy (DOE), National Science
Foundation (NSF), National Aeronautics and Space Administration (NASA), andDepartment of Defense (DoD)—should provide recurring and increased support forthe continued development, upgrading, and operations of experimental facilities,
and for fundamental and translational research in plasma science. A spectrum offacility scales should be supported, reflecting the requirements for addressing
different problems at the frontiers of PSE.
Finding: Computational Plasma Science and Engineering (CPSE) has become essential
across PSE for experiment and mission design and diagnosis, idea exploration, probing offundamental plasma physics processes, and prediction.
For computations to continue to progress in PSE, the next generation of researchers critically needs to bebetter educated through the development of plasma-focused computational textbooks and courses, andthrough participation in funded computational research projects. At the same time, the computationallandscape is rapidly evolving, with increasing heterogeneity in devices, languages, and coding practices.
GPU computing is just now under development, and new devices, such as quantum computers, are on thehorizon. As a result, writing computational plasma software now requires mastery of multiple
technologies, all of which are swiftly changing, leading to crises whereby small developer teams cannot
build performant software. Simultaneously, new methodologies for prediction, including machinelearning and artificial intelligence, are becoming increasingly possible with new, high-throughput
computing devices.
Recommendation: Federal agencies should support research into the developmentof computational algorithms for plasma science and applications for theheterogeneous device computing platforms of today and upcoming platforms (e.g.,quantum computers), while also encouraging mechanisms to make advanced
computational methods, physics-based algorithms, machine learning, and artificial
intelligence broadly available.
Stronger cooperation between programs within NSF, DOE or DoD that support computer science,
applied mathematics, and physical sciences and engineering is encouraged. Several possible partnerships
are listed in Table 1.1. Proposals should be solicited and supported that include at least as a component,
the development of plasma-focused computational educational materials, and in particular graduate-leveltexts.
Table 1.1 provides examples of interagency (and inter-program) collaborative initiatives on twolevels. The first initiatives are between plasma-focused agencies and are designed to leverage theadvances in fundamental plasma science that they support separately. The second initiatives are designed
to maximize opportunities for translating fundamental plasma science advances to applications. These
initiatives are between plasma-focused agencies that support fundamental plasma science, and nonplasma focused agencies supporting applications that benefit from plasma science. The table contains
examples of such initiatives, not recommendations that each of these initiatives be implemented. ThesePREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION
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Plasma Science: Enabling Technology, Sustainability, Security, and Explorationsuggestions could serve as a starting point for the interagency discussions and collaborations. (Acronyms
for these agencies can be found in Appendix C.)
Better Serving the Community
Following the recommendations of the Plasma 2010 report, the DOE Office of Fusion Energy Science(FES) broadened the scope of its programs to better serve the plasma science community. This broadened
mission, contained primarily within the Discovery Plasma Science (DPS) program of FES, has increased
its support of research on low temperature plasmas, basic plasma physics, and high energy-density
plasmas. FES continues to be a vital member of the NSF/DOE Partnership in Basic Plasma Science andEngineering. The committee gratefully acknowledges the response of FES to the Plasma 2010
recommendations to broaden its mission.
Finding: Although the majority of the FES budget is still devoted to supporting fusion
science, the present office title does not now accurately reflect its broader mission. The
present title may, in fact, impede the ability of FES to collaborate with other offices
within DOE and with other federal agencies, including impeding its ability to garnersupport for non-fusion plasma research.
Finding: The national interest as a whole would be better served by renaming the office
to better reflect the broader mission of FES, maximize its ability to collaborate with otheragencies and to garner non-fusion plasma support.
Recommendation: Consistent with our recommendations to broaden the impact ofplasma science, the Department of Energy (DOE) Office of Fusion Energy Science(FES) should be renamed to more accurately reflect its broader mission, and so
maximize its ability to collaborate with other agencies and to garner nonfusion
plasma support. A possible title is Office of Fusion Energy and Plasma Sciences.

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This table lists examples of interagency (and inter-program) collaborative initiatives on two levels. The first initiatives are between plasmafocused agencies and are designed to leverage the advances in fundamental plasma science that they support separately. The second initiatives aredesigned to maximize opportunities for translating fundamental plasma science advances to applications. These initiatives are between plasmafocused agencies that support fundamental plasma science, and non-plasma focused agencies supporting applications that benefit from plasma
science. The table contains examples of such initiatives—it is not specifically recommended that each of these initiatives be implemented. Thesesuggestions are intended to serve as a starting point for interagency discussions and collaborations. (Acronyms for these agencies can be found in
Appendix C.)
Agencies(Alphabetical. Bold issuggested lead(s).)

TopicStrategic Importance

DOD-AFOSR, DOD-ONR,
DOE-FES, DOE-NNSA,
NASA, NSF-ENG, NSFGEO, NSF-MPS,

Education and career enhancement
programs

With a demographic turnover due to senior scientist and faculty retirements,
the health of Plasma Science and Engineering is at a critical juncture.
Deliberate programs to increase and diversify the pipeline into PSE, andcareer development of early-to-mid career professionals (academics inparticular) are needed. The need for renewal of PSE faculty at universities
and researchers at national laboratories is at nearly crisis levels.

DOD-AFOSR, DOD-ONR,
DOE-FES, DOE-NNSA,
NASA, NSF-GEO, NSFMPS

Mid-scale facilities and networks offacilities for basic plasma science andtranslational research.

The development of mid-scale facilities and networks of facilities for plasma
science is sporadic across agencies. Coordination and collaboration fordevelopment of new hardware for basic plasma science experiments andoperational expenses would leverage the efforts of all agencies. Missiondriven agencies whose facilities focus applications partnering with oraccommodating basic plasma experiments would speed translational research.

DOD-AFOSR, DOD-ONR,
DOE-FES, DOE-HEP, DOENNSA, NASA, NSF-ENG,
NSF-GEO, NSF-MPS

Multi-agency plasma science centers

Multi-agency plasma science centers would provide an ideal environment forinterdisciplinary advances in fundamental concepts, while enabling rapidtranslation to technologies required by mission-focused agencies.

DOD-AFOSR, DOE-ASCR,
DOE-FES, DOE-NNSA,
NASA, NSF-CISE, NSFENG, NSF-GEO, NSF-MPS,

Computational plasma science

Support development of open source models and shared libraries foruniversities and federal centers to more effectively contribute to and benefit
from agency specific missions.

DOE-FES, NASA, NSFGEO, NSF-MPS

Fundamental research in space,heliophysics and astrophysicalplasmas for advancing missions

Adding NASA as a partner to the NSF/DOE Partnership would advancefundamental science in space and astrophysical plasmas while also addressing
the needs of heliophysics and astrophysics missions.

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TABLE 1.1 Examples of Interagency and Interoffice Collaborative Initiatives

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Topic

Strategic Importance

DOD-ONR, DOE-FES,
NASA, NSF-GEO, NSFMPSLaboratory-heliophysics/astrophysics

A synergistic program would enable heliophysical and astrophysical plasma
scientists to collaborate closely with laboratory experimental programs, toleverage their different needs and knowledge bases to advance both fields.

DOD-AFOSR, DOD-ONR,
DOE-FES, NASA, NOAA,NSF-GEO

Geospace and ionospheric plasma
science

Multi-agency approaches to investigating the local space environment, criticalto national defense and environmental stewardship, will leverage more
fundamental approaches with mission driven research. Capabilities indevelopment of single and multi-satellite systems would be more efficiently
shared. Multiagency collaboration would work towards establishingstandards for sharing data between agencies that would greatly enhance basic
research.

NASA-HEOMD, NASASMD, NSF-GEO, NSF-MPS

Charged dust phenomena in
microgravity and on airless bodies

Management of spacecraft charging and dust is critical to developing next
generation space systems (e.g., ISS, cubesats, moon/planetary landers). There
are translational opportunities for collaborative investigation of plasma-dust
interactions on the Moon, Mars, comets, and other airless bodies in the solar
system for future human exploration and resource exploitation.

DOD-AFOSR, DOD-AFRL,
DOD-DARPA, DOD-ONR
AFRL, DOE-FES, NASA,
NSF-ENG, NSF-MPS

Basic plasma physics for electric
propulsion and translation totechnologies

There is little coordination of electric propulsion (EP) programs acrossagencies. In some agencies, EP research is sporadic, and so knowledge can belost. Translational opportunities would be greatly enhanced if fundamental
research performed by more plasma focused agencies would be readily
applied by more technology focused agencies.

DOD-AFOSR, DOE-FES,
DOE-NNSA, NASA

Advanced Space Propulsion

Beyond electric propulsion, colonization and exploitation of the moons andplanets will require massive propulsion systems for mass transfer and speed.
Space propulsion based on fusion drives will become viable as ICF efforts
advance.

DOD-AFOSR, DOD-ARO,
DOD-DARPA, DOD-ONR,
DOE-FES, NIH, NSF-BIO,
NSF-ENGNIBIB, NCI: Plasma cancer
treatment and effects on the immune
system; DNA damage; cellularresponse, migration and proliferation

There are tremendous opportunities for plasma focused agencies (e.g., DOEFES, NSF, AFOSR, ONR) and agencies needing urgent battlefield treatment(e.g., DARPA, ARO) to collaborate with NIH many areas. The goal is toleverage the knowledge of how plasmas are produced, controlled, andinteract with materials with the opportunities for plasma to disinfect, treat

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Agencies(Alphabetical. Bold issuggested lead(s).)

Copyright National Academy of Sciences. All rights reserved.

Topic

Strategic Importanceby plasma; effects of plasma
activated liquid on biomolecules andcells; anti-microbial resistance(AMR)

cancers, promote wound healing, affect DNA, produce immunogenic
response and produce biocompatible materials, Atmospheric pressureplasmas have already shown therapeutic effects in immune responses, cancer
treatment, and tissue regeneration through production of RONS (reactive
oxygen and nitrogen species). However, the adoption of plasma-medical
procedures has been slow because the connectivity between the plasmas
sciences and health sciences is weak. Understanding plasma modification of
biomolecules (e.g. amino acids) is key to the building blocks of plasmamedical sciences. Strategic matters of surgical infection and antimicrobial
resistance (AMR) can be addressed directly by plasma treatment. Topicalplasma application has potential for control of the skin microbiome and its
composition, and treatment of inflammatory skin diseases. As plasma
becomes more adopted into medical science, standards are required for what
constitutes a “plasma dose”, and tissue-specific outcomes that can be used toassess effectiveness across a spectrum of plasma devices must be defined.

NBIB: Dose standardization inplasma medicine.
NIBIB, NIGMS, NINDS: Plasma
tissue and nerve regeneration ,wound healing
NCI: Positron and antimatter beams
for cancer treatment.
NIAMS, NIGMS: Plasma treatmentof surgical infections, and antibiotic
resistant infections.
NIAMS: Plasma altering
microbiome of the skin
NIDCR, NIBIB, NIAMS: Plasma
enhanced biomaterials

Plasma enhances the capabilities of current biomaterials used for surgical,
dental, and wound healing application, but these uses are still at an earlystage. Plasma materials processing has great potential for improving
biocompatibility and antimicrobial properties of conventional wounddressings.

DOD-AFOSR, DOE-ARPAE, DOE-FES, NSF-ENG,
USDA-NIFA, EPA

Plasma agriculture and plasmas forfood safety

Plasma-based technologies offer enormous potential for agriculture processes(e.g., liquid fertilizer production, nitrogen fixation, seed treatment,
pesticides/herbicides, antimicrobial plant treatment) and food safety(decontamination, shelf-lifetime enhancement). The field has advanced basedlargely on empirical studies. Plasma-science–based studies will lead totranslational advances for mission-driven agencies.

DOD-AFOSR, DOE-ARPAE, DOE-EERE, DOE-FES,
NSF-ENG, EPA, USDANIFAElectrification of the Chemical
Industry

Future societies will be powered in large part by renewable and sustainable
electricity. Plasmas are the science and technology capable of using thiselectricity to provide for society’s chemical needs by electrifying thechemical industry. Waste products can be converted to chemical feedstocks
and polluted resources recovered. Plasmas can also play a role indecarbonizing chemical industry process heating.

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Agencies(Alphabetical. Bold issuggested lead(s).)

TopicStrategic Importance

Copyright National Academy of Sciences. All rights reserved.

DOD-AFOSR, DOD-ARO,
DOD-DARPA, DOD-ONR,
DOE-DOE-ARPA-E, DOEBES, DOE-FES, FAA,
NASA, NSF-ENG, NSFMPS

Plasma-based materials processing
and additive manufacturing

Plasma materials processing is at the root of nearly all advanced materials,
from microelectronics fabrication, advanced energy storage materials,
lightweight composites, and photonics, to super-plastic and super-hard andenergetic materials for security applications. An interagency initiative andcollaboration would leverage the fundamental processes in controlling
plasmas for producing reactive species as materials precursors andfunctionalizing surfaces for development materials for mission-focusedagencies.

DOD-AFOSR, DODDARPA,DOD-ONR DHS,
DOE-BES, DOE-FES, DOEHEP, DOE-NNSA, NIHNCI, NSF

Accelerator science, development andapplications; and stewardship

Compact plasma systems offer new capabilities across the broad space ofaccelerator applications. These include high energy sources in compact
packages, miniature ‘endoscopic’ accelerators, high dose rates, highperformance X-ray and neutron sources, and future particle colliders toextend the reach of our understanding of the universe. Advances in thefundamental science of laser and beam driven plasmas, coupled withtechnology development, are needed to enable transformational andtranslational capabilities across agencies.

DOD-AFOSR, DODDARPA, DOD-DTRA,
DOD-ONR, DHS, DOE-BES,
DOE-FES, DOE-HEP,
DOE-NNSA, NIH-NCI,
NSF-BIO, NSF-MPS, NSFENG

X-ray sources and radiography

Transformational x-ray sources enabling both higher resolution and lower
dose in compact systems are emerging based on plasma accelerators, lasers
and harmonics. Development is needed to enable application benefits acrossagencies. These range from enhanced screening for homeland security andnonproliferation, to compact coherent Free Electron Lasers for basic science,
to nondestructive evaluation for industry and stockpile stewardship, toimproved medical imaging and therapy.

DOD-AFOSR, DODDARPA, DOD-DTRA,
DOD-ONR, DHS, DOE-BES,
DOE-FES, DOE-HEP,
DOE-NNSA, NSF-ENG,
NSF-MPS, NIH-NCI, NSF

Ion accelerators, neutron sources, andplasma optics

New ion and neutron sources, together with plasma optics, are underdevelopment that could leverage high intensity lasers to generate new sources
with applications including medical therapy, high energy density science, andsecurity. Fundamental research is needed in plasma- based ion acceleration,neutron sources, and plasma optics in concert with mission- driven agencies
that will use these capabilities.

DOD-AFOSR, DODDARPA, DOD-DTRA,
DOD-ONR, DHS, DOE-BES,
DOE-FES, DOE-HEP, DOE-kHz Ultrafast laser development

Development of high average power ultra-fast lasers and their application tolaser-plasma science and technology addresses mission needs across federal
agencies including accelerators, sources and plasma optics. DOE-HEP
currently has an accelerator stewardship program including kHz lasers todrive plasma accelerators. DoD develops high average power long pulse

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Agencies(Alphabetical. Bold issuggested lead(s).)

TopicStrategic Importancelasers. Extension of such programs is needed to meet application needs forplasma based sources, plasma optics, and HED science.

NNSA, NIH-NCI, NSFENG, NSF-MPS

Copyright National Academy of Sciences. All rights reserved.

DOE-ARPA-E, DOE-FES

Fusion energy and the private sector

The private sector is well positioned to investigate high-risk alternate
concepts on more rapid time scales than at federal and university facilities.
Including the private sector in long-range planning and collaboratively
apportioning the fusion risk-portfolio between the public and private sectors
will speed progress.

DOE-ARPA-E, DOE-BES,
DOE-FES, DOE-NNSA,
NSF-DMR

Materials for fusion

Materials are required that can withstand high neutron fluences and high heat
flux in fusion reactor environments, a need that transcends all fusion focusedagencies. Materials informatics and synthesis techniques are more advanced
in non-plasma centric agencies while the context and test of materials is best
done by the plasma-centric agencies.

DOD-ONR, DOE-FES,
DOE-NNSA, NSF-MPS

High Energy Density Physics Beyond
Thermodynamic Equilibrium

DOD-DARPA, DOD-ONR,
DOD-DTRA, DOE-FES,
DOE-NNSA, NSF-MPS

Intermediate pulsed power facilities

Collaborative theoretical and computational research on atomic physics,
radiation transport and magnetohydrodynamics is required to include kinetic
effects. These developments are required to analyze and diagnose HED and
ICF experiments, and extend current modeling capabilities to be truly
predictive.
Midscale pulsed power facilities are critical to support basic science researchin high energy-density experiments and computations. Fundamental researchat mid-to-large scale will support concepts for next-generation pulsed power
facilities (including the “ZNext” 60 MA accelerator), and high power
microwave sources.

DOD-ONR, DOE-NNSA,
NASA, NSF-MPS

Validation of HED, ICF andastrophysical computations

Advances in HED computations for investigating fundamental astrophysicalplasma physics and ICF must be accompanied by coordinated inter-agency
experiments for validation.

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Agencies(Alphabetical. Bold issuggested lead(s).)

Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

2
The Foundations of Plasma Science
PLASMA SCIENCE—THE ENABLING FUNDAMENTALS
Plasma is the most abundant state of visible matter in the Universe. Plasma processes occur innature, laboratories and in industrial settings over a vast range of space and time scales. Many of theseplasmas are permeated by magnetic fields, which add further richness and complexity to the underlying
dynamics. Despite the great diversity of plasmas, there are underlying unifying phenomena. For example,
eruptive dynamics, where a quiescent plasma undergoes a sudden change in its configuration and releases
large amounts of energy, is seen in disruptions of plasmas in fusion reactors (when a growing instability
can destroy the ability to confine a plasma), space storms in planetary magnetospheres, solar and stellar
flares, and in astrophysical explosive events like flares from the Crab Nebula, and Gamma Ray Bursts(GRBs). The time-scales for these phenomena can vary from milliseconds to several hours, and theenergy liberated exhibits an enormous range, from approximately 107 Joules for a fusion plasma
disruption to 1044 Joules for a GRB. (As a point of comparison, the average U.S. household uses about
108 Joules of energy per day.) These eruptive phenomena are at the leading edge of plasma science andunder intense study. It is widely believed that the dynamics of magnetic fields embedded in these plasmas
play a crucial role in their behavior.
The basic processes that underlie a wide range of plasma phenomena, and provide cohesivenessto the field, are the subject of this chapter. This report discusses some of the foundational concepts ofplasma science that cut across the subfields, and where advances in our understanding of theircomplexities can lead to transformational change across multiple applications spanning the entire range ofplasma science and engineering (PSE), from microelectronics to health care. It is this interdisciplinary
aspect of plasma science that has been a powerful attractor of talented scientists and engineers who are
engaged in a rich spectrum of activity in academia, industry, and national laboratories. The quest tounderstand the fundamental aspects of plasma phenomena and to develop applications for societal benefit
based on that understanding is a unifying theme of this diverse community.
In many fields of science, there is a tension between curiosity driven research and applicationinspired research. PSE is not devoid of that tension. Having said that, the extreme intellectual diversity ofPSE has produced a field that embraces addressing the most critical fundamental science challenges, andtranslating that fundamental understanding into technologies that benefit society. The continuum spans
researchers who primarily address fundamental plasma science concepts to researchers who are focusedon plasma-enabled technologies. The committee cannot stress in strong enough terms the importance of
jointly and holistically supporting the continuum of research from the fundamental to the applied. These
are not separate activities—they are part of the continuum that leads to societal benefit.
While the frontiers of fundamental plasma science continue to be strongly driven byexperiments—small, medium, and large, as well as major international facilities and space missions—computer simulations are playing an increasingly important role and form the “third leg” of discovery (inaddition to experiment and theory). These simulations make use of novel algorithms and softwaredeveloped by applied mathematicians and computer scientists in collaboration with physical scientists andengineers using state-of-the-art computing platforms.
Research in basic plasma science is now supported by and spread across multiple federal
agencies—the DoD, DOE, NSF, NASA, and NNSA. This breadth of support reflects the intellectual
breadth and the interdisciplinary nature of the enterprise. However, there is a danger that in the drive to
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

develop new plasma-based applications, the connection to and support of the underlying science will
weaken. The field should keep in mind the Pasteur Quadrant (Stokes, 1997), a guiding principle that
describes the symbiotic relationship between basic and applied research. One of the objectives of thisreport is to identify such issues and make recommendations for collaboration that span multiple funding
agencies. (See Table 1.1 in Chapter 1.)
The committee identifies four cross-cutting strategic challenges in basic plasma science, followedby more detailed discussions of areas within PSE that address these challenges. These are not the only
basic plasma sciences challenges that span the field, but exemplify unifying challenges. Computational
Plasma Physics, which underlies all of PSE, is discussed first and followed by Magnetic Reconnection
and Waves, Turbulence and the Dynamo Effect—plasma processes that are ubiquitous in plasmas in thelaboratory and nature. This is followed by a discussion of fundamental processes in the context of Dusty
Plasmas, Non-Neutral and One-Component Plasmas and fundamental aspects of Low-Temperature
Plasmas. These specific examples illustrate how cross cutting challenges impact diverse areas of PSE.
This is not an exhaustive list of examples. For example, some aspects of the fundamentals of plasma
shock physics are discussed in Chapter 7.
STRATEGIC CHALLENGES IN FOUNDATIONAL PLASMA SCIENCE
Strategic Challenges in fundamental plasma science are cross-cutting themes that apply across thefield of PSE. Although each challenge may not apply to every sub-field of PSE, these challenges unify thefield.
1. Understand and predict plasma behavior under extreme conditions that challenge our present
models.
“Extreme conditions” in plasmas can be realized in many ways. Some of these plasmas are createdwith such high densities and temperatures that their thermodynamic properties cannot be addressed bycurrent theories and computational models. In other plasmas, extreme is measured by the ratio ofelectrostatic energy to thermal energy—referred to as the coupling constant —being much larger thanunity, making them behave more like soft or solid condensed matter than a gas. For these plasmas, thetraditional methods of kinetic theory, valid for values  much smaller than unity, break down. Other
plasmas, such as planetary magnetospheres or the interplanetary medium, have mean-free-paths between
collisions that are comparable to or even much larger than the system size, and are virtually collisionless.
The optimum form of the fluid equations that are needed to predict their large-scale dynamics during
space weather events remains an open question. Finally, in many astrophysical objects the plasma isrelativistic (in realms where Einstein’s theories of special and general relativity are needed), magneticallydominated (so that magnetic field, rather than pressure forces, controls the overall dynamics), andstrongly affected by radiative and quantum effects like electron-positron pair creation.
2. Quantify and, in the laboratory control, how plasma processes direct the conversion of energy fromone form to another, the transfer of energy across a vast range of scales, and the transport ofenergy in the laboratory and nature.
Fundamental plasma processes such as magnetic reconnection, shocks, turbulence, and the dynamo
effect control the conversion of energy from one form of to another—from magnetic energy to kinetic
energy, from flow energy to magnetic energy, or from gravitational energy to kinetic energy andradiation. The nature and structure of turbulence in weakly collisional or collisionless plasmas, systems inwhich energy from large scales is transferred to small kinetic scales where it is then dissipated, is asubject of intense research. These systems are found in nature (e.g., the flow of energy from the Sun
through the solar wind) and the laboratory (e.g., high energy density experiments). These processes areexamples of where investigation of fundamental plasma phenomena will rapidly translate to applications

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Plasma Science: Enabling Technology, Sustainability, Security, and Explorationin the form, for example, of efficient energy conversion in magnetically confined fusion reactors orplasma processing of new materials.
3. Predict self-organization of plasmas and, where needed, control that self-organization.
Plasmas permeated by electric and magnetic fields can spontaneously self-organize in spatial
coordinates (3-dimensions). They can also self-organize in an expanded space, called phase space (6dimensions), defined by three spatial and three momentum coordinates, producing coherent structures inspace and organizing how particles move with respect to them. (See Figure 2.1.) Examples of selforganization in coordinate space (3D) include the dynamo effect, whereby large-scale and slowly varying
magnetic fields emerge from magnetic and velocity turbulent fluctuations on much smaller spatial scales
and much shorter time scales. Examples of self-organization in phase space (6D) include solitaryelectrostatic waves in space or laboratory experiments. Self-organization can also involve extreme statesof matter, where the fundamental research challenge is to understand how the redistribution of energy,
momentum, and angular momentum in physical or phase space gives rise to coherent plasma structures at
all scales. Understanding these self-organized structures is criticalto developing applications in which these phenomena occur, either
beneficially or detrimentally—plasma propulsion, magnetrons
used for plasma production of thin films, plasma-liquidinteractions in health care and agriculture and beam-plasmainteractions.
4. Control and predict interactions between plasmas and solids,
liquids and neutral gases.
Low-temperature plasmas (LTPs), which involve complex
interactions between plasmas and solids, liquids, and gases, have
revolutionized the microelectronics industry and enabled the
production of high-efficiency lighting, low-cost solar cells, andbio-compatible human implants. The beneficial applications of
LTPs continue to grow rapidly, stimulating research into multiphase plasma systems—plasmas which simultaneous interact withmore than one phase. The plasma-material interactions in fusion
plasmas, which can involve either plasma-solid or plasma-liquidinteractions, are another example of multi-phase plasmas, whichhave critical implications for the performance and economic
competitiveness of fusion reactors. Understanding the fundamental
processing of plasmas sustained in or crossing multiple phases
advances fundamental plasma science and is at the heart oftranslational research leading to technologies.
COMPUTATIONAL PLASMA PHYSICSFIGURE 2.1 Seeking Minimum
Energy. This image shows selforganization of a toroidal fusion
plasma which spontaneously
forms a helically deformed
minimum-energy state. Thisoccurs when the device isoperated at high current(exceeding 1 Mega-Amperes).
This particular device is a
Reversed Field Pinch
Experiment (RFX) at Padova,
Italy. The colored nested
surfaces represent magnetic
surfaces reconstructed from
actual laboratory measurements.
The helical deformations aremuch stronger at the plasma corethan at the edge . SOURCE:
Nature Physics 5, 570, 2009).

Computations have become as essential to plasma physics
as experiments. Computations enable researchers to ask, “Whatif?”, and provide quantitative answers. At the heart of computationis theory, which produces the fundamental relationships (theequations) describing the plasma dynamics that are ultimately
implemented in computations, and for suggesting directions ofinvestigation. Our fundamental understanding of plasmas firstemerges in these dynamical equations. However, these equations are typically not analytically solvable(particularly in multiple dimensions). Computation is the method for extending fundamental

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

investigations beyond that which is analytically tractable and to test the predictions of analytic theory,
which must often rely on approximations to the original equations. This extension of theory thenseamlessly feeds the translational research that produces society-benefiting outcomes, through the use of
these same computer models to, for example, optimize magnetic configurations for fusion reactors, chartcoronal mass ejections from the Sun to Earth, or design plasma materials processing reactors.
Experiments are the ultimate test of theory and computer simulations. However, experiments to be
performed today are limited to the facilities that now exist. For example, at the time of this writing, it is
not possible to carry out an experiment using a 100 Petawatt laser for a laser-plasma interaction, as suchlasers do not now exist. However, it is possible to use computations to describe the dynamics of theselaser-plasma interactions. The outcomes of those computations improve our intrinsic understanding ofthese phenomena and, from a very practical perspective, help us design a better laser and better
experiments.
Computation: Impact on Experimental Design and Diagnostics
Computation is a critical step in experimental design. Usually, no large experiment is built
without some prior guidance from computation. At the very least, engineering design involves significant
computation, which must be performed to ensure that the experiment will operate safely. More relevant toplasma physics, the dynamics of the system are computationally investigated within the range of known
models and the wisdom of the experimental design can be evaluated. For example, will a newly designed
plasma thruster achieve the desired impulse given our current understanding of the turbulent transport ofmomentum? Will a laser illuminated pellet achieve a desired fusion gain given our current theories ofpreheating? In the best of cases, computation can be predictive, providing confidence that certain physicaloutcomes will be experimentally observed, and predict a range of outcomes. Computations also provide ayardstick with which experimental results can be compared and enable us to determine whether thephysics underlying the experimental results is understood. If the results of computations do not agree withexperiments, one possible reason is that the underlying physics may not be understood well enough topredict an experimental outcome. The degree and manner of disagreement then guide further
investigations.
Another area of increasing importance is the use of computations for diagnosing experiments.
Plasmas are notoriously difficult to diagnose, given that they are hot, radiating environments, in which
physical probes may not be able to survive and diagnostic lasers may not be able to penetrate. In otherinstances, diagnostics may not be available due to short time scales or small sizes, or because the plasma
is inaccessible—for example, space and astrophysical plasmas. In the study of laser-plasma accelerationof particles, the time scale of the essential interaction, involving laser pulse profile evolution, electron
trapping and electron acceleration, occur over micrometers of space in less than picoseconds of time,
which is extremely challenging for diagnostics. Computations can be the surrogates for diagnostics inthese inaccessible regimes.
Computations are used across all of plasma science, and opportunities to leverage computations
are expanding. Cloud computing, first developed for commercial use, is putting enormous computational
power into the hands of researchers without their having to make the commensurate capital investment.
These resources are enabling development of new state-of-the-art codes, improving the capabilities of theunderlying theoretical models, integrating across physical domains, and enabling models to address large
ranges in space and time.
The Computational Revolution: Where Is It Now?
Consider a full numerical solution of the plasma in a reactor of the type used for etching anddeposition for microelectronics fabrication. The reactor would have a volume of 10,000 cm3 and a particle
density (both positive and neutral) of 1015 cm-3. The simulation would have 1019 particles each with 6
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

coordinates or 48 bytes of computer storage, for a total of 6  1019 degrees of freedom requiring 5  108
Terabytes of memory for its representation. Performing one integration time step on such a system would
require resources three orders of magnitude greater than available in an exascale computer (an exascalecomputer can perform 1018 calculations per second), and that would still be short of a useful simulationthat would require millions of time steps. While the revolution in computing has brought us high fidelity
simulations, it is far from being able to compute any system with exact fidelity. (In fact, the largest
problems being computed today have of order 1011 degrees of freedom, smaller by 8 orders ofmagnitude.) Nevertheless, computations do strongly impact technology development. (See Figure 2.2.)
Although computations at the outset might sound, in principle, straight forward, considerable
complications are present. In practice, computations first require (like analytic calculations) a step in
identifying the appropriate, approximate equations that can be represented with fidelity on existing
computer hardware and that will result in calculations that can be completed in a reasonable time. A
kinetic approach is used when the dynamics involves detailed changes of the particle velocity distributionfunction. (Kinetics refers to theoretical or computational approaches that include the distribution of thevelocities.) When such detailed knowledge is not needed, or the magnitude of the calculation is too large,
fluid approaches are used. In these methods, an average over the velocity distribution produces equations
for mass, momentum, and energy conservation. Certain assumptions must be made to reduce the numberof fluid moments to a manageable (less than infinity) number in order to make the problem tractable.
These assumptions can introduce significant departures from the physical description provided by theoriginal kinetic model. For example, the dampingof certain waves can be very different from one
type of fluid model to another. Nonetheless, thefluid equations, regardless of the simplifying
assumptions, are typically easier to implement onvery large computers and so are often the methodof choice for analyzing plasmas.
Computational approaches are as varied
as experiments. For example, at the kinetic level,
there are particle-in-cell (PIC) and continuum
approaches. In the PIC approach, the plasma is
treated as a statistical ensemble of particles
moving under the influence of external and selfgenerated electromagnetic forces. In the latterapproach, the system is modeled by partial
FIGURE 2.2 Simulation of plasma etchingdifferential equations (PDEs) for particle
reactor near a semiconductor wafer using particle
distribution functions which move under thein cell (PIC) techniques. The wafer is in blue at
influence of exactly the same forces. The PIC
the lower right. The blue rectangle on the bottom
approach may require less computer memory, butleft is the focus ring, which is used to make thethe continuum approach has less numerical noise.
etching more uniform towards the wafer edge.
Noise can be reduced in particle approaches by
The electric field strength is shown by the color
simply using more particles or using “δf” methods
contours, near zero where it is dark blue, thenwhich track the perturbation in the distribution ofincreasing, shown in red, as the plasma sheath isparticles from a known solution. When theentered near the wafer. The ions are shown asmagnetic field in the plasma is strong, one can use
gray particles, with darker gray indicating a
the gyrokinetic approach, which assumes that thegreater speed in the downward verticaltime scale of variations is long compared with the(impacting direction). The ions are pulled out of
cyclotron period for charged particles orbiting
the plasma and gain downward velocity before
around magnetic field lines, and so only the time
hitting the wafer. SOURCE: Courtesy of Daniel
average motion of the particle is tracked. In theMain, Tech-X.
case of strong magnetic fields and low-frequency
dynamics one can use magnetohydrodynamics
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration(MHD) or multi-fluid equations. (In MHD, continuum equations describe the dynamics of a conducting
fluid under the influence of electric and magnetic fields; and the consequences of the resulting
conductivity and currents on those fields.) For fluid dynamics, one can choose an algorithm that canrepresent thin shock waves in supersonic (or near sonic) flows. For solving systems on time scales longcompared with those of the basic oscillations in the system, implicit methods are useful.
Subscale Processes and Infrastructure
Plasma physics computations rely heavily on subscale physics processes. An example of a subscale
process in a magnetized plasma is the gyrokinetics approximation, which allows one to ignore time scales
smaller than the ion cyclotron period and which are not important to turbulence and transport. At anotherlevel, models have been developed that provide the fluxes of particles, momentum, and energy as afunction of local parameters, like density and temperature gradients. Such reduced models have continued
to be developed and refined in the last decade. Significant progress has also been made in developing
subscale infrastructure that involves atomic and molecular ionization. For example, electric field
ionization is important for plasma generation by laser interaction and has become increasingly importantwith the growth of the sub-field of plasma acceleration.
Development of Novel Algorithms—Theory Based
For continuum approaches (both for traditional fluid and continuum phase-space models), there
have been many developments in improving algorithms and formulations such as least-squares Finite
Elements and Discontinuous Galerkin. There have also been advances in multi-fluid higher fidelity
models (5-moment, 10-moment, 13-moment) and shock capturing methods, which are critical tounderstanding collisionless plasmas.
For particle PIC approaches, there have been advances in implicit methods. These methods avoid
numerical instabilities that occur when the physical spacing between grid points, exceeds the Debye
length. (The Debye length is the characteristic distance over which a plasma exhibits charge separation
effects and does not satisfy charge neutrality.) This resolution requirement can be prohibitive forsimulating practical plasmas. There have been many advances in modeling that more faithfully capture
the dispersion of electromagnetic waves, providing a better model of wave-particle interactions. Thisparticular advance is especially important for accurate modeling of plasma processes such as particle
acceleration, reconnection and shocks.
Development of Novel Algorithms—Computing Based
Parallel and now massively parallel computers have become the norm for advanced
computations. Computations on parallel computers simultaneously use hundreds of thousands ofindividual processors (or cores) to increase the size of the problem that can be addressed. Messagepassing based, distributed memory methods to use these many cores became common in the past decade,and algorithms were adapted to the new computing hardware. For example, computations were rewritten
to maximize computational speed while considering the time required for data to be passed between
cores, and algorithms were developed for load balancing to enable efficient use of large numbers of cores.
Most software was written in a fashion of asynchronous, autonomous applications on each processor,
each performing its own computations, passing information to other processors and waiting on data fromother processors before continuing.
In the last decade, the need to structure data and code became even more important, with theadvent of Advanced Vector Instructions and Graphical Process Unit (GPU) computing. With large
processor core counts, the use of threads, which is a way for a computer program to divide itself into two
or more tasks, has become more important. With GPU computing, the role of asynchronous paradigms
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

has attracted great interest. To make proper use of such devices, one must manage thousands of separate
threads of computation. This is an evolving area, and many different computing paradigms are currently
being investigated.
Code Availability
In plasma physics, state-of-the-art computation is available to a relatively small group of
researchers. This is perhaps best illustrated by way of contrast. Those wishing to make use ofComputational Fluid Dynamics (CFD) simulations have any number of ways to engage, such as using oneof the many commercial codes available, using an open-source code, or using an in-house developed
code. This relatively easy accessibility to CFD codes enables a large group of users to make use of highperformance computation. Commercial codes cater to those needing ease of use, extensive
documentation, and robustness. In-house development of codes is usually undertaken only by the mostexpert, as they must develop the most appropriate algorithms for a class of physical problems that maps
well onto the available computing hardware. This must be done in a manner that produces the desiredscientific and engineering results. Well-maintained, open-source codes provide a middle ground. They do
not typically come with the level of documentation or support provided by commercial codes, but they doprovide a resource that a person with the time to invest in learning can make use of without getting into
the intricacies of code development. However, in PSE there are relatively few commercial plasma codesthat provide an easy point of entry to simulations (and these come at a price). Companies are beginning toprovide such software, but none have reached the level of ease of use and broad applicability as found in
CFD or in the areas of stress analysis, or electromagnetics of structures, each of which are provided bylarge companies and have large markets. There are projects underway to provide some broad, open-source
solutions for PSE. However, the breadth and applicability of these offerings varies widely.
Computation: Training the Workforce
Computational plasma education needs to cover the many methods used in plasma physics—fluid(in particular, MHD or multi-fluid) approaches and kinetic approaches (both continuum and PIC). For the
fluid approaches, there are a wide variety of textbooks, largely due to the use of CFD across many fields.
However, for the kinetic approach there are few modern textbooks. For the particle approach there aresome venerable texts, but it is difficult to find textbooks that address continuum approaches to modelingplasma dynamics. This makes it difficult to introduce students to the field, especially as there have been
many discoveries since the older classic texts were originally published. Indeed, the entire fields ofgyrokinetics simulations, distributed memory computing algorithms, and analysis of large data sets are
missing from the existing texts.
There is little motivation for writing advanced graduate textbooks. It is difficult for researchers tofind the time to write textbooks when they face demands to write research papers and obtain grantfunding. These barriers could be addressed by educational funding that is specific to textbook writing.
There is also a need for education about how to use numerical software. As codes become more widelyused and the users are no longer the developers, the users no longer have an intimate understanding of therelevant algorithms and methods. What those users need is only a high-level understanding, but enough toknow what to look for to indicate that a simulation might not being giving the proper results. In particularthey need to learn about the process of code verification and validation—how to determine whether acode is working by testing it.
In part, the problem of computational plasma education reflects the broader problem of nothaving a dedicated plasma reviews journal in the same way that, for example, Annual Reviews of
Astronomy and Astrophysics serves astronomy and astrophysics. A dedicated plasma review journal thatpublishes 15 to 20 major review articles annually, thus collecting the major findings in a consolidated and

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comprehensive format, would serve the community well, from students to seasoned researchers alike. A
useful side benefit is that the authors of these articles often use them as the basis for a monograph.
The Computational Revolution: What Is to Be Done?
Subscale Methods and Data Infrastructure
Subscale methods are needed for computation in nearly every area of PSE. How can kinetic
effects be represented in global simulations of large systems based on extended fluid equations (such as in
the vicinity of black holes, neutron stars and planetary magnetospheres, or in fusion plasmas)? How does
one characterize viscous effects at the boundaries of plasma thrusters? Can one develop models that
account for the change in the velocity distribution functions in low-temperature plasmas? While analyticalclosure models continue to be subjects of interest, there is significant interest in developing new models
based on deep learning methods.
Although significant progress has been made in developing infrastructure for data, much remains
to be done. For example, the development of LxCAT, a web-based, open-access platform for data needed
to model LTPs, has led to greater availability of critically needed data for the LTP community. This
community-driven effort is volunteer supported and, by any measure, has been successful. However, theexperience has also emphasized the need for ease of accessibility to software libraries for interpolationand implementation, standards for assessing the goodness and consistency of the data, and long-term
support that does not depend on the goodwill of volunteers.
Development of Algorithms—Math Based
A continuing challenge in computation is the need to resolve systems not for physics reasons but
for numerical stability and convergence reasons. For example, one must resolve the plasma frequency in
PIC simulations even though the evolution of the system to the steady state occurs on much longer timescales. One must resolve the Debye length in PIC simulations to avoid grid instability even in regions
where the plasma varies on much larger spatial scales. A common remedy is to use implicit methods.
However, implicit methods can be problematic. Implicit methods typically require solving large matrices,which is time consuming and, in general, such solutions over an entire domain are difficult for distributed
memory computation. Research oriented towards improving this situation would be welcomed and would
have substantial impact on fluid as well as kinetic approaches. Are there explicit algorithms that eliminate
these instabilities? More generally, algorithms that work well in the emerging world of heterogeneouscomputing would be an advance.
Development of Algorithms—Computing Based
Device-based computing is the development of algorithms that are specialized or can only be
used on specific architectures of types of devices. For example, computations on GPU simply needdifferent numerical approaches than used for conventional CPUs (central processing units). The challengeof mapping algorithms onto device specific architectures will become even more important as quantum
computers become available. The advent of device-based computing and computing on huge numbers of
distributed cores has led to experimentation with new data structures. How does one deal with very large
datasets, especially when memory is actively managed, as memory allocation and release of large
amounts data remains costly.
The challenge of device-based computing has been the focus of the DOE Exascale Computing
Project (ECP). While the ECP has been very successful and has been strongly endorsed by the recent
National Academies Report on a Strategic Plan for Burning Plasma Research (2018), the coverage of ECP
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does not include the broad reach of PSE disciplines. Optimizing device-based computing requires a much
more specialized approach in matching the details of the algorithm to the computing architecture. This
unfortunately works against broadly applicable codes that may use different algorithms (e.g., fluid at highpressure, kinetic at low pressure). The lack of a broader ECP-like initiative places the PSE community ina challenging situation. Computations supported by the ECP address specific targeted applications whileareas not supported by the ECP may not have the resources to develop state-of-the-art device-basedalgorithms. Work is required at both ends of the spectrum—device-based algorithms that are moregenerally applicable and more resources devoted to fostering the development of device-based algorithms
across the PSE community. The future promises even greater complications. To date, GPU computing has
been largely performed using the CUDA framework, which works for only NVidia hardware.
Standardization of GPU frameworks would lower the barrier of entry for users and suppliers.
Legacy codes refer to well established, often extremely complex, computer models that have
served the community well, but often do not have state-of-the-art algorithms. A major challenge isbringing legacy plasma codes up to the state-of-the-art in computational standards while notcompromising their physics robustness. This will require deliberate and careful selection. One criterion
might be whether the code to be upgraded will be readily available and widely used. Public-private
partnerships could leverage the expertise in the private sector where, for example, in exchange for making
codes widely available, commercial plasma code developers could be funded to make their codes more
performant. With the increasing complexity of computation, it is increasingly difficult for small teams tohave the expertise and personnel needed to write or adapt codes for the wide range of available
architectures. This implies that research codes will remain confined to small teams, which will not havethe resources to port them to multiple devices.
With quantum computing on the horizon, device-based computing becomes a more important
strategic discussion. How can such computing devices be used in computational plasma physics? The
Fusion Energy Sciences Roundtable on Quantum Information Science (QIS) has identified two Priority
Research Opportunities: “using QIS to do plasma science” and “using plasma science to advance QIS.”
Following this report, DOE-FES has solicited proposals and made awards that make a promising
beginning. There is significant enthusiasm and excitement in the plasma science community about
participating in the quantum computing frontier, which will have an impact across all computational
sciences.
Verification and Validation, and Uncertainty Quantification
Verification and Validation (V&V) are a critical part of computation, as they provide confidence
in the computational results. (Verification refers to making certain that the computations solving theequations properly. Validation refers to the computations accurately modeling the physics.) In PSE, as inother fields, standard problems with established results exist against which codes can be compared. In
plasma physics, some successful computational examples are the Geospace Environmental Modeling(GEM) reconnection challenge, and the Cyclone Base Case that is a standard set of tokamak conditions
intended to compare computations of micro-turbulence. Validation studies tend to be more selective since
they depend greatly on the availability of time on experimental facilities and the required coordinationand interaction with teams of modelers. The adoption of computations for complex plasma systems would
be aided greatly by a more extensive set of validation cases with sufficient (and accurate enough)diagnostics data to provide stringent tests of codes. With experimental costs in some areas of PSE
significantly increasing, accurate validation of computational models is especially needed so thatcomputer simulations can be more reliable in their predictive capabilities.
As computations address frontier areas where fundamental data (e.g., opacities, cross sections,materials properties) and validating experimental data may not be available, uncertainty quantification
becomes more important. How do needed assumptions or estimates of fundamental data, or methods
propagate through a full simulation? There is not a vigorous culture of making such uncertainty
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quantification in PSE computations, particularly for large simulations for which a limited number of runs
can be made. Developing strategies for uncertainty quantification in general, and for large codes inparticular, would benefit the field.
MAGNETIC RECONNECTION: TAPPING THE ENERGY OF MAGNETIC FIELDS
Magnetic reconnection is a fundamental process whereby magnetic fields reconfigure
topologically (sometimes viewed as “breaking” and “reconnecting) and in the process release energy.
Magnetic reconnection underlies many explosive and disruptive plasma phenomena over a wide varietyof plasmas in both nature and in the laboratory and plays a pivotal role in electron and ion heating, nonthermal particle acceleration to high energies, and magnetic flux and energy transport.
In heliophysics, magnetic reconnection plays a key role in a wide range of phenomena, including
solar flares, coronal mass ejections, coronal heating, solar wind dissipation, interaction of interplanetary
plasma with Earth and other planetary magnetospheres, dynamics of planetary magnetospheres such as
storms and substorms, and the interaction of the heliospheric boundaries with the interstellar medium.
Magnetic reconnection is critical to solar and planetary dynamo processes. Without magnetic
reconnection, magnetic fields advected by the plasma will become horribly tangled up and no large-scaleorder can emerge. In astrophysics, the importance of magnetic reconnection has been recognized for starformation in molecular clouds, stellar flares, explosive phenomena in magnetars and pulsars, and cosmicray acceleration. Magnetic reconnection is thought to occur in both coronae and interiors of magnetizedaccretion disks in proto-stellar systems and X-ray binaries, as well as in interstellar medium turbulence.
Magnetic reconnection is believed to occur in the centers of Active Galactic Nuclei (AGN), where matteris accreted onto supermassive black holes. On even larger scales, magnetic reconnection may be
important in extragalactic radio jets and lobes as they propagate and relax, and even in galaxy clusters. In
laboratory fusion plasmas, magnetic reconnection occurs during the sawtooth oscillations in thetemperature profile seen in the tokamak core, the growth of nonlinear instabilities that cause disruptions,and self-organization phenomena in reversed-field pinches and compact tori.
While magnetic reconnection is a fundamental process in plasma physics that is worth
understanding in its own right, such understanding has very practical implications and is critical to ourability to control thermonuclear plasmas for producing fusion energy and predicting space weather, toname two examples. In magnetic confinement devices such as tokamaks, major disruptions can occur due
to the nonlinear interaction of reconnecting instabilities, which need to be controlled and mitigated.
Extreme space weather events producing storms and substorms are thought to be powered, at least in part,by magnetic reconnection. These events can disrupt or damage the electrical power grid, can cause majorinterference with communication networks, damage spacecraft and be a danger to astronauts. Space
weather is discussed further in detail in Chapter 7.
Achievements of the Last Decade in Magnetic Reconnection
During the last decade, thanks to space missions, laboratory experiments, analytical theory andsophisticated computer simulations, our understanding of magnetic connection has advanced greatly.
These accomplishments include:

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

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An improved theoretical understanding of theplasmoid instability (an instability of thincurrent sheets) has been achieved, and has led
to the prediction of a new regime of fastreconnection in which the reconnection rate
deviates from the classical Sweet-Parker theory
and becomes independent of the resistivity ofthe plasma when the resistivity is below a
critical threshold. (See Figure 2.3.)
The instruments aboard the multi-satellite
mission MMS (Magnetosphere Multiscale
Mission) have produced data of unprecedented
spatial and temporal resolution of the
FIGURE 2.3 High-resolution MHD simulation
reconnection layer in the magnetosphereof the standard model of a coronal mass ejection
around Earth down to electron micro-scale(CME) from the Sun in which a large mass of(skin depth). These datasets, while confirming
material escapes from the Sun. The figure
several theories of laminar reconnection, arerepresents an intermediate stage in CME
producing new challenges on the interplay
dynamics, exhibiting the formation of
between reconnection and turbulence. The
plasmoids due to the instability of a thin current
Fermi Gamma-ray Space Telescope, which
sheet that spontaneously forms. The plasmoids
observes the entire sky, has provided
are constantly ejected by the reconnection
remarkable data on gamma-ray spectra fromoutflow, and new plasmoids are generated in thesolar flares, which provides insights into thecurrent sheet until the sheet disrupts, releasingenergetics of magnetic reconnection.
the large balloon-like lobe that breaks away as a
The use of sophisticated diagnostic tools (e.g.,
CME. SOURCE: Courtesy of Yi-Min Huang,electron cyclotron emission (ECE)) on
Princeton University.
tokamaks such as KSTAR, have provided
deeper understanding of sawtooth reconnection
events, bringing into question our past understanding, and posing new challenges for theory andsimulation.
High-energy-density plasma experiments at high-power laser facilities such as Omega at theLaboratory for Laser Energetics (LLE) at the University of Rochester and the National Ignition
Facility at the Lawrence Livermore Laboratory (LLNL) have provided new data for testing thepredictions of theory and simulations of magnetic reconnection, often co-existing with shocks andturbulence. These data have been extended to include magnetized plasmas, having self-generated
Biermann magnetic fields as well as externally imposed magnetic fields.
New laboratory experiments at the Facility for Laboratory Reconnection Experiments (FLARE) at the
Princeton Plasma Physics Laboratory (PPPL) and the Terrestrial Reconnection Experiment (TREX) at
the University of Wisconsin-Madison have exceeded the capabilities of earlier experiments such as
the Magnetic Reconnection Experiment (MRX) at PPPL and the Versatile Toroidal Facility (VTF) at
MIT in size and scope. These new facilities provide an excellent complement to space missions byenabling the exploration of new regimes of reconnection through reproducible experiments anddetailed diagnostics.
Current and Future Science Challenges and Opportunities

In spite of significant progress in the science of magnetic reconnection, major scientificchallenges remain to be resolved. These challenges are discussed these challenges in the context of thestrategic challenges posed here.
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Challenge 1: Understand and predict plasma behavior under extreme conditions thatchallenge our present models.
While our theoretical understanding of reconnection in collisional non-relativistic laminarplasmas is reasonably mature, there are significant gaps in our understanding of reconnection in weakly
collisional and collisionless plasmas, both non-relativistic and relativistic. For collisionless plasmas, there
are many numerical simulation results. However, analytical theory for such systems is much lessdeveloped, which has made it difficult to infer scaling laws for a broad range of realistic plasma
parameters and system sizes. This also applies to the role of collisionless reconnection in compact
astrophysical objects where electrons and positrons are formed and constitute a plasma (also called pairplasma). Experiments in high-power laser facilities have the potential to address relativistic, radiative, andpair-plasma regimes.
Extreme-scale computing will be a valuable tool for addressing the high-Lundquist-number (S)regime where plasmas have a very high conductivity. However, the computational cost to resolve the thinlayers (boundary layers) and follow the system evolution on the Alfven time (i.e., the system size divided
by Alfven wave speed) increases as S3/2 for 3-dimensional explicit simulations. For S~106 , theserequirements can quickly surpass the capabilities of a petascale computer. These limitations require astrategic approach to produce reliable scalings in the high-S regime, which can then be used to better
extrapolate to conditions of interest to astrophysics. In weakly collisional or collisionless regimes, thestructure of reconnection layers involves both ion and electron kinetic scales. As summarized in Figure
2.4, the space and time scales associated with both electrons and ions impose a daunting level of scale
separation both in space and time that is difficult to address in computations.
Challenge 2: Quantify and, in the laboratory control, how plasma processes direct theconversion of energy from one form to another, the transfer of energy across a vast rangeof scales, and the transport of energy in the laboratory and nature.
Magnetic reconnection controls the conversion of magnetic energy to the energy of particles in
the form of plasma flows and heating or accelerating particles to very high energies. The rates at whichsuch conversions occur can be large. Reconnection involves coupling between the largest scale size of thesystem down to the orders of magnitude smaller kinetic ion and electron dissipation scales. Recent results
suggest that plasmoid dynamics may couple these multiple scales efficiently. (A plasmoid is a structurethat looks like a cat’s eyes within which magnetic fields lie on nested surfaces, as seen in Figure 2.3.) Key
questions include how the number and size of plasmoids scale with the system-size and plasma
parameters, and how the reconnection process responds to turbulent fluctuations which span an enormous
range of spatial scales. Two-fluid effects and kinetic transport physics are thought to speed reconnection
while the effects of micro-turbulence on reconnection are not well understood. (In the two-fluid model,
one uses separate fluid equations for electrons and ions.) The latter effect is a particularly important area
to investigate as space observations suggest that that reconnection occurs in a bath of turbulence.
Determining the mechanisms for acceleration of particles to high energies and the apportionmentof energy between different species are among the most important challenges in space and astrophysicalplasmas. Magnetic reconnection, shocks, and turbulence are widely discussed as possible mechanisms. In
planetary magnetospheres, energetic particles in the radiation belts (observed, for example, by the Van
Allen Probe mission) have a significant impact on space weather. In our Milky Way galaxy, cosmic rays
represent only one-billionth of the interstellar particles but carry as much energy as the galaxy’s thermal
plasma for reasons that are not fully understood.
Challenge 3: Predict self-organization of plasmas and, where needed, control that selforganization.
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Magnetic reconnection releases energy that was formerly trapped in magnetic field lines,
converting that energy to other forms, such as the flow of a plasma or highly energetic charged particles.
These other forms of energy can be degraded by collisions and turbulence, resulting in states of lower
energy, heating, and increased entropy. In this process, self-organization can occur. The classic Taylor
theory of plasma relaxation is based on a non-ideal plasma containing multiple reconnecting instabilities.
These instabilities relax to a unique final state of minimum energy subject to global constraints that areapproximately preserved by the dynamics. This process is thought to occur in laboratory andastrophysical plasmas, but the Taylor state is not always realized. What are the constraints that prevent
systems from doing so?
Advances in computational plasma physics have enabled understanding of coherent, selforganized structures in both configuration space in fluid simulations as well as structures such as “phasespace holes” predicted by fully kinetic simulations. In the latter case, there is not yet an underlying
theoretical framework that accounts for the simulation results. Observational tests of theories haveproduced interesting results, but much more work is needed to provide a truly predictive capability formagnetic reconnection.
WAVES, TURBULENCE, AND THE DYNAMO EFFECT
The rich variety of waves exhibited by plasmas is fundamental to a wide range of phenomena inlaboratory, space and astrophysical settings. Plasma waves can transport energy and momentum, produce
heating of electrons and ions, and energize and scatter particles. Plasmas are often far from thermal
equilibrium and instabilities can arise as a result, converting plasma energy into waves. Turbulence, often

FIGURE 2.4 Spatial and temporal scales in collisionless reconnection. The shortest timescale isthe inverse of the plasma frequency followed by the inverse of the electron cyclotron frequency.
Electron spatial scales include the Debye length, the electron inertial length, and the electron
Larmor radius. Mass is denoted by m with subscript i (e) representing ion (electron). SOURCE:
Courtesy of William Daughton, Los Alamos National Laboratory.
driven by unstable waves, is ubiquitous in plasmas and is widely cited as the dominant mechanism forheating and transport of particles, energy and momentum in many settings. Instabilities, waves andturbulence also play a role in the plasma dynamo, processes by which magnetic fields are generated and
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amplified both on small and large spatial scales with lifetimes that can vary widely depending on theplasma medium.
Relevance and Benefits
Waves and instabilities are the first type of dynamics that nearly all forms of collisionless or
weakly collisional plasmas experience. Such collective dynamics result from nearly all ways of describing
plasmas—at the 3D macroscopic level by fluid equations (MHD and multi-fluid), and at the 6D
microscopic level by the kinetic equations. Thanks to decades of close collaboration in PSE between
theory and experiment, our understanding of linear (or small-amplitude) waves and wave-particle
interactions is quite mature. As waves and instabilities grow in amplitude and interact with each other andwith particles, nonlinear effects become very important. These non-linear processes can produce
turbulence, dissipation, heating, and particle acceleration, and a variety of coherent structures. Nonlinear
effects in nature are wide-ranging—momentum transport in accretion disks around compact astrophysicalobjects such as black holes and neutron stars; heating of the solar and stellar atmospheres and of thestellar winds (consisting of high-speed particles) that flow out from the Sun and other stars; particle
acceleration that produce the Northern lights during substorms in Earth’s (or other planetary)magnetospheres; energetic cosmic rays that pervade the Universe; and the rich spectrum of waves that
accelerate and expel energetic particles from the Van Allen radiation belts. These nonlinear effects canalso dominate in laboratory plasmas—laser-induced plasma waves that can accelerate particle beams,
expelling energetic particles from fusion plasmas; and wave-driven currents that offer the potential
benefit of enabling a fusion plasma to operate in steady state. The possibilities are nearly endless.
Studies of the dynamo effect address the question of why our Universe is magnetized? There are
two classes of dynamos. “Small-scale” dynamos amplify magnetic energy but produce negligible
magnetic flux because the averaging of fluctuations over space and time leads to near-perfectcancellations. “Large-scale” dynamos produce large-scale magnetic field structures with non-zeromagnetic flux. Beautiful in its regularity, the Sun’s magnetic field and its 11-year cycle is an example oflarge-scale dynamo. (See Figure 2.5.) The spontaneous emergence of large-scale magnetic fields from

FIGURE 2.5 The Butterfly Diagram for the Sun’s magnetic field, spanning the years 1975-2016(horizontal axis). This diagram, based on observations, tells the story of the 11-year cycle of the Sun’smagnetic field. The vertical axis represents latitudes both above and below the equator of the Sun. The
colors in the plot indicate the magnitude of the solar magnetic field. SOURCE: Courtesy: David
Hathaway, NASA Marshall Space Flight Center.

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disordered small-scale velocity and magnetic field fluctuations is counter-intuitive. However,understanding this behavior is likely required to predict the long-term dynamics of magnetic fields thatgovern everything from the space climate to the launching of powerful jets during neutron star merger
events.
Advances in Waves, Turbulence, and Dynamos
During the last decade, there has been tremendous progress in our understanding of waves,turbulence and dynamos in both laboratory plasmas and plasmas in Nature, aided by theory, simulationand experimental observations. A few highlights of that progress include: Plasma in the Universe is often magnetized and turbulent. Plasma fluctuations in space can span ahuge range of scales, from hundreds of parsecs (1 parsec is 3.26 light years) to hundreds ofkilometers. Observations of the solar wind and the interstellar medium (ISM) reveal qualitatively
similar scaling laws for magnetic, velocity, and density fluctuations, which extend down to the ion
gyro-radius. (See Figure 2.6.) At large scales, MHD provides a good description of plasma dynamics.
The plasma beta (the dimensionless ratio of the plasma pressure to the magnetic energy density) inspace and astrophysical plasmas is often close to or greater than unity, which distinguishes theseplasmas from plasmas in the Sun’s atmosphere or laboratory that are confined by magnetic fields andtypically have small beta values (including fusion plasmas). Typically, space and astrophysicalplasmas are large-scale highly supersonic flows, such as solar and stellar winds, which have large
flow Mach numbers, but nonetheless can have small turbulent Mach numbers. At small scales, at or
below the ion gyro-radius, plasma dynamics become much richer, as two-fluid, and kinetic effects
become important. These scales are harder to address analytically. However, two-fluid, gyro-kinetic
and kinetic plasma simulations have produced promising results in addressing these small scales, suchas suggesting scaling laws that bridge different
energy dissipation mechanisms. Thesesimulations have also shed light on the role ofanisotropic pressure-driven instabilities that selfregulate the nature and structure of turbulence
and magnetic reconnection processes.
 Weak MHD turbulence is dominated by Alfven
waves that weakly interact with each other. The
practical application of this finding is limited innature where turbulence is typically strong.
However, weak MHD turbulence can beaddressed analytically and serves as a test bed
for fundamental studies of the theory of MHD
FIGURE 2.6 The magnitude of magnetic field
turbulence and energy cascades. This
fluctuations in the solar wind, measured by inunderstanding sets the stage for the stronger
situ spacecraft. The fluctuations are binned as aturbulence seen in Nature and the laboratory.
function of the ratio of the temperature
Describing strong turbulence using MHD
perpendicular and parallel to the magnetic
assumes that there is a balance between linear
versus the plasma beta parallel to the magnetic
wave propagation and nonlinear interactions.
field. The data seems to lie within the parameter
However, this assumption is not based on a
space constrained by the so-called firehose andrigorous analytical treatment. As a result, good
mirror instabilities, which are driven by pressure
physical models, numerical simulations andanisotropy, and not by a cyclotron instability.
targeted laboratory experiments (such as at the(AIC). SOURCE: Phys. Rev. Lett. 103:211101,
Large Plasma Device (LAPD) at UCLA) are
https://journals.aps.org/prl/abstract/10.1103/Phy
critical to developing better understanding ofsRevLett.103.211101.
turbulence. A fundamental property of strong
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



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MHD turbulence is its inherent local anisotropy. Small-scale fluctuations are progressively moreanisotropic as the scale length decreases. The balance between linear and nonlinear interaction times
is postulated to be preserved independently of scale length in collision-less plasmas, which is called
the critical balance condition. The validity of the critical balance postulate in kinetic turbulence isbeing investigated with interesting results.
Interaction of turbulence with non-uniform plasmas represents a difficult problem. Methods forinvestigating turbulence in spatially non-uniform plasmas has been an active area of research,especially for fusion plasmas and the interplanetary medium. Turbulence in such plasmas does notseem to directly conform to the classical Kolmogorov-like picture of turbulence whereby energy
cascades from driven large scales to small scales until the energy thermalizes. What seems to occur
instead is that turbulence saturates by channeling energy into stable modes that exist at the same
spatial scales as the instability that drives the turbulence. Multiscale analysis of inhomogeneous
turbulence has produced transport equations that need to be tested against experimental observations.
This leads to extremely demanding computational problems, approaching or exceeding the exascale.
For example, multi-scale, multi-physics, whole-device models for fusion plasmas based on
gyrokinetic theory, needed to address inhomogeneous turbulence, need the power of state-of-the-art
computing hardware. Fortunately, both computer simulations and theory are well positioned to makeprogress on these topics, which can have a strong impact on applications as diverse as coronalheating, evolution of the solar wind as it expands from the Sun, space weather, cosmic ray
propagation and galactic turbulence.
Coherent structures are sustained nonlinear perturbations which are localized in space and time. On
the other hand, waves are localized inwavenumber or frequency—meaning that they
typically have a well-defined wavelength or
frequency. Examples are solitons, ion or electron
phase-space holes or double layers (see Figure2.7) which are now widely observed in Nature
through progress in observational techniques. (Aphase space hole is a region of coordinates andvelocities that are devoid of an electron or ion.)
Such coherent structures, observed in space and
FIGURE 2.7 Phase space holes growing in alaboratory experiments, occur over a wide range
cross-field plasma wake. Here theof spatial scales, ranging from Debye to Alfvenic
background magnetic field is in the ylengths. Coherent structures can be electrostatic asdirection. Most holes move out at thewell as electromagnetic, and are thought to be aelectron orbit speed. One hole remains
nonlinear end state of some forms of turbulence.
stationary and grows large enough to perturb
With the advent of high-power lasers and pulsedthe ions. SOURCE: Physics of Plasmas 24,
power devices, some astrophysical environments
055601 (2017);
can now be reproduced in the laboratory. This ishttps://doi.org/10.1063/1.4976854
the realm of high energy density (HED) physics.
This capability has led to the study ofastrophysical processes in scaled laboratory experiments, including magnetic reconnection, collisionless magnetized shocks, Weibel-mediated shocks, the generation of magnetic seeds at shocks by the
Biermann effect, and the small-scale turbulent dynamo. In conjunction with new capabilities in highperformance computing, these developments have set the stage to achieve significant scientificadvances.

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Current and Future Science Challenges and Opportunities
Challenge 1: Understand and be able to predict plasma behavior under extreme
conditions that challenge our present models.
Waves and turbulence in weakly collisional, high-beta plasmas is poorly understood, despite
recent advances in analytical theory and simulation. An intriguing aspect of this state of matter is therelevance of the magnetic field. Although the magnetic field (in the absence of reconnection) is not thedominant source of energy, it does influence the transport properties of the plasma by imparting
directionality and new degrees of freedom, thereby influencing the large-scale dynamics. The magnetic
field-induced anisotropy introduces a fundamental difference between the dynamics of magnetizedplasmas and collisional plasmas or those that have weak magnetic fields. An unique feature of weakly
collisional, magnetized, very high beta plasmas is that kinetic microinstabilities can make them unstable.
(That is, small variations in the velocities can be amplified exponentially to the point of producing
turbulence.) The dynamics of such plasmas are governed by complex, multiscale interactions between
kinetic physics and large-scale bulk plasma motion. Strategic areas for future investigations include: (1)identifying the most important linear kinetic instabilities; (2) determining how kinetic instabilities interact
with other plasma processes, such as reconnection, heat fluxes, and particle acceleration; and (3)determining how fluid transport on large scale lengths interacts with kinetic transport on micro-scales.
Challenge 2: Quantify and, in the laboratory control, how plasma processes direct theconversion of energy from one form to another, the transfer of energy across a vast rangeof scales, and the transport of energy in the laboratory and nature.
In typical occurrences of turbulence, energy is transferred from large scales to small scales
through a cascade process. The range of length scales in MHD turbulence has a “break-point” where thedissipation of energy becomes more rapid as the length scales get smaller. Turbulent fluctuations withscale lengths smaller than that of the break point form the dissipation range. In weakly collisional space
and astrophysical plasmas, the scale lengths where this breakpoint occurs often has a two-fluid or kinetic
origin (e.g., the ion skin depth or ion gyroradius). While there is clear evidence of these breakpoints inobservations of plasma turbulence in the solar wind or ISM, there are no definitive theories that describe
the transition. Theoretical and computational models based on two-fluid (or Hall MHD, where electron
inertia is ignored) equations, gyro-kinetic equations and fully kinetic equations have been developed tocompare with specific observations, with some success. The results suggest that the dissipation range mayitself be multi-scale with wave damping or particle heating occurring at short scale lengths. Determining
the causes of such electron and ion heating is one of the critical unsolved problems in the study of space
and astrophysical turbulence. Observations to be made by the Parker Solar Probe mission will provide
needed insights to the source of this heating.
Even for a plasma that satisfies the MHD approximation, the large-scale dynamo problem
remains unsolved—what are the mechanisms whereby magnetic fields erupt and decay? Until recently, it
was generally accepted that small-scale fluctuations in the plasma can lead to catastrophic quenching of
the growth of large-scale magnetic fields. However, recent theoretical work on systems with flow shear
suggests that small-scale dynamos, after saturation, can drive the growth of large-scale fields. (Saturationof a dynamo occurs when an exponential growth of the magnetic field produces magnetic forces thatbalance those producing the turbulence.) In the kinetic regime, even less is known. Recent studies havestarted to explore kinetic effects on dynamos. However, our understanding of dynamos in weakly
collisional and collisionless plasmas is limited. The topic is complex, simultaneously touching kinetic
turbulence, collisionless reconnection, non-thermal particle acceleration, and diffusion.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

Challenge 3: Predict self-organization of plasmas and, where needed, control that selforganization.
When influenced by waves, instabilities, and turbulence, self-organization in plasmas becomeseven more complex, bringing forth new and unresolved questions. There appears to be no explanation for
dissipating energy in plasmas that is as successful as Taylor’s relaxation theory for MHD plasmas. In thistheory, energy is minimized while magnetic helicity is kept approximately constant in a dissipativeplasma, with the outcome producing a unique, force-free state as a result of self-organization. However,in MHD systems that are not particularly turbulent, there is a tendency to relax into states that have more
free energy than Taylor states (as seems to be true for quasi-steady states in fusion plasmas). A unifying
principle to describe such states remain elusive. The picture is even more incomplete for kinetic plasmas
that self-organize to form coherent structures. Scientific questions that remain unanswered include: Howand under what conditions will plasmas self-organize? What are the natural processes that produce thenonlinear instabilities that may produce self-organization? Once formed, what role does self-organization
play in defining plasma transport coefficients such as electrical or thermal conductivity or diffusivity? Are
the processes responsible for self-organization also responsible for significant electron acceleration, forexample, in Earth’s radiation belts, at reconnection sites, in the solar corona and wind, and inastrophysical objects? To what extent does self-organization generate or scatter traveling plasma waves,such as Alfven waves or whistler waves? How long do self-organized structures last? What are themechanisms that cause them to break up or dissipate?
DUSTY PLASMAS: FROM COMETS TO FUSION REACTORSIn a dusty plasma (sometimes referred to as a “complex plasma”), the typical plasma components
of ions, electrons, and neutral atoms are joined by a fourth component: solid, charged particulate matter or“dust”. These dust grains are often nanometer- to micrometer-sized objects that acquire charge either
through the direct collection of electrons and ions from the surrounding plasma or through other processes
that can lead to charging (such as the photoelectric effect resulting from UV and VUV illumination or
ionizing radiation). In space and astrophysical environments, dust grains can acquire either a net positiveor a net negative charge, depending upon the conditions of the local space environment. In either case, thedust grain charge is the key property that couples the particles to the surrounding plasma and governs theresulting dynamics of the four-component dusty plasma. An equally important property that distinguishes
a dusty plasma is the possible influence of gravity. In most other plasma systems, the gravitational force
effectively plays no role in the dynamics of the plasma because the electrical, magnetic and fluid forces
are all large compared to gravity. However, for dust grains of several microns in size and whose mass canbe millions to billions of times larger than the ions and electrons, gravity can play a dominating role in the
behavior of the dust component.
Relevance and Benefits
Dusty plasmas are ubiquitous and appear in a variety of contexts in science as well as technology.
In the laboratory, a dust particle of the size of a few microns can attract 10,000 electrons or more at room
temperature. Dusty plasmas are often described by the coupling constant Γ, which is the ratio of theaverage electrostatic energy to the average kinetic energy. For plasmas with these large, heavily charged
particles, Γ can be much larger that unity enabling such plasmas to behave as though they were liquids orsolids. The large size of the dust particles enables them to be tracked and illuminated with lasers,
providing novel tools to study and diagnose strongly coupled plasma dynamics. Dusty plasmas have beenused to experimentally and theoretically investigate fundamental properties of soft condensed matter suchas the phase transition from the liquid to the solid state, defect formation, and melting produced by waves
and instabilities.
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

Dusty plasma research is highly interdisciplinary. It is strongly relevant to studies of astrophysicalobjects, particularly star-forming regions and the ISM, as well as cometary tails and planetary rings.
Charged dust is found on numerous airless bodies throughout the solar system - from comets to meteors
to moons, and can pose both a danger (e.g., due to contamination of space systems) and a benefit (e.g., assurfaces where water and other volatile material could be trapped) for human exploration of the Moon andMars. Controlling dust-particle interactions with the plasma and the growth of particles in reactive
plasmas form the basis for understanding and actively manipulating dust particles for industrial
applications in a variety of low temperature LTPs (Chapter 5).
Within the United States, the dusty plasma community is supported by NSF, DOE, and NASA
with researchers distributed across institutions that range from predominantly undergraduate institutions
to PhD granting institutions to national laboratories. Maintaining a healthy and active U.S. researchcommunity remains a challenge.
Progress and Achievements
There has been substantial
progress in understanding thephysical properties of dusty plasmas
over the past decade. Somehighlights include (see Figure 2.8):Anisotropic and non-reciprocalinteractions: These studies
investigate systems in which theaction-reaction symmetry (wellknown from Newton’s secondlaw) can be broken formesoscopic particles when theireffective interactions are
FIGURE 2.8 Dusty plasma analogues: (a) nonlinear waves andmediated by a non-equilibrium(b), (c) shocks (University of Iowa), (d) dust grid pattern inenvironment. Dusty plasmas
external magnetic field (Auburn University), (e) 2D honeycomb
have provided an ideal medium
monolayer (Max Planck Institute), f) electrorheological dusty
in which to explore the role ofplasma (Plasma-kristall-4 experiment, International Spacesymmetry-breaking.
Station), (g) folding of filamentary structures (Baylor
Binary mixtures and nonUniversity). SOURCE: (a-c) Merlino, R.L., Heinrich, J.R.,
equilibrium phase transitions:Hyun, S.-H. and Meyer, J.K., Phys. Plasmas 19, 057301 (2012),
Most laboratory studies of dusty(d) Thomas, E.J. et al., J. Plasma Phys. 81, 345810206 (2015),
plasma focus on particles havehttps://www.cambridge.org/core/journals/journal-of-plasmathe same size, composition andphysics/article/magnetized-dusty-plasma-experimentmass—that is, they are
mdpx/705433918E9D5311A2F68406ACBE1F48; (e) adapted
monodisperse. For the samefrom https://onlinelibrary.wiley.com/doi/abs/10.1002/
plasma conditions, thesectpp.200910022, doi: 10.1002/ctpp.200910022, courtesy of theparticles will acquire the same
Max Planck Institute; (f) http://eea.spaceflight.esa.int
charge enabling a simpler/portal/exp/?id=9452, DLR (CC-BY 3.0); (g) Hyde, T. W.,
description of the plasma.
Kong, J. & Matthews, L. S., Phys. Rev. E 87, 053106 (2013).
Between monodisperse and thefully polydisperse systems (particles that have different shapes, masses and compositions) that arefound in Nature, recent studies have focused on binary dusty plasmas consisting of two different
monodisperse dust particle species. These binary mixtures have enabled investigation of a variety of
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

phenomena including the dynamics of de-mixing and the formation of lanes as a pattern, relevant for
many applications.
 Atomistic modeling of fluids: The physics of undercooled liquids (i.e., liquids having temperature
below their usual freezing point), especially near the glass transition, is a challenging topic in fluid
physics. Since dusty plasmas enablevisualization of kinetic phenomena on aparticle-by-particle basis, it is possible toinvestigate critical phenomena instatistical mechanics such as thedependence of the structural glasstransition on the number of spatial
dimensions.
 Precision monitoring of particle size
evolution: The dust particle mass, surface
potential, and charge all depend criticallyupon the size and shape of the particle.
Although it is generally assumed that inexperiments, the dust grain size generally
remains constant, recent in situ
measurements of particles reveal that thisFIGURE 2.9 The Magnetized Dusty Plasma
is not always the case due to plasmaExperiment (MDPX) device. The MDPX device is asurface interactions. In the next decade,high magnetic field (up to 4-Tesla),diagnostics that can provide real-time,superconducting magnet system with a split, open
independent measurements of the particle
bore at the center to accommodate substantial radial
size and charge are a critical need.
and axial access to the plasma. The overview image
is a top view of the laboratory facility. The three
Current and Future Science Challenges andinsert images represent experiments from
Opportunities
collaborative users: (Left) Image of a plasma
crystal based on Jaiswal et al., (Middle) Image ofDusty plasma research is connected to
growing silica nanoparticles in vertical “plasma
the four strategic challenges previously
filaments” based on Couëdel et al., (Right) Image
discussed.
of a calibration setup for the Wisconsin In-Situ
Penning (WISP) Gauge for the Wendelstein 7-X
stellarator that was tested on the MDPX device.
Challenge 1: Understand and be able
SOURCE: Top: Magnetized Plasma Research
to predict plasma behavior underLaboratory, Auburn University; bottom, left toextreme conditions that challenge ourright: Physics of Plasmas 24:113703, 2017;present models.
https://doi.org/10.1063/1.5003972; courtesy of
Edward E. Thomas, Jr., Auburn University;
Strongly coupled dusty plasmas arecourtesy of Oliver Smitz and Thierry Kremeyer,
inherently an “extreme” plasma state,
University of Wisconsin-Madison.
characterized by values of the coupling
constant greater than unity. The presence ofthe dust particles enables direct visualization of plasma phenomena at the single-particle and collective
scales simultaneously—enabling unprecedented measurements of the time and space evolution of aplasma component through the direct reconstruction of the distribution function. Dusty plasmas therefore
provide an excellent model system upon which to test models of statistical physics, plasma physics, andsoft-condensed matter.
The large mass of the dust particles— compared to that of electrons, ions and neutrals—and theresulting very small charge-to-mass ratio, means that dusty plasmas can be studied in regimes that are
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

beyond those of typical laboratory LTP systems.
With gravity often a dominant force in laboratory
dusty plasmas, moving to microgravity
environments is a method to study the smallerscale, inter-particle forces. In another regime, verylarge magnetic fields (or very small particle sizes)
are required to investigate the properties ofmagnetized dust. In both microgravity andmagnetic field studies of dusty plasmas, the last
decade has seen technological developments thatwill enable new advances.
The leading efforts for microgravity
studies of dusty plasmas is centered on the“Plasmakristall” (PK) series of experiments on theInternational Space Station (ISS). PK-4 is thecurrent ISS experiment with the focus on fluid-likedusty plasma behavior. PK-5 (also known as“Ekoplasma”) is under development. Without adedicated U.S. microgravity facility, partnership in
the PK-4 and PK-5 consortia are essential toaccessing microgravity conditions. The long-term
future of the ISS as a research platform, support of
the national agencies (in the United States andabroad), and developing a distributed, possibly
FIGURE 2.10 Example of a “probe-induced”
multi-agency, support for hardware development
void in a laboratory plasma. A range of voltages
are all critical challenges facing the future ofare applied to a small wire electrode (central
microgravity dusty plasma research in the next
bright spot in each image). A void (dust free
decade.
region) is formed between the electrode and the
The last decade has also seen substantial
surrounding cloud due to a competition between
progress in magnetized dusty plasma experiments,
electric and ion drag forces on the dust particles.
made possible by a reduction in technology costs,
When those forces come into equilibrium, theimprovements in experimental design as well as
void boundary is formed. Image adapted fromknowledge of plasma operations to ensure plasma
Phys. Plasmas. SOURCE: Physics of Plasmas 25,
stability. For some time, high magnetic field
053705 (2018),
facilities have been operated in Japan, Russia, andhttps://doi.org/10.1063/1.5029338.
Europe, but within the last 5 years, a multi-user,
collaborative research facility, the Magnetized
Dusty Plasma Experiment (MDPX) has begun operating at Auburn University in the United States. (SeeFigure 2.9.) For the next decade, understanding the extended study of steady-state, low-temperatureplasma and dusty plasma regimes at high magnetic field is a critical goal.
Challenge 2: Quantify and, in the laboratory control, how plasma processes direct theconversion of energy from one form to another, the transfer of energy across a vast rangeof scales, and the transport of energy in the laboratory and nature.
Dusty plasmas are a thermodynamically open, non-equilibrium system in which energy flows
freely between the electrons and ions (at the microscopic scale) to the dust particles (at the mesoscopic
scale). In spite of the large-scale separation between the dust particles and the surrounding plasma
particles, there is a continuous exchange of energy between the microscopic and mesoscopic scales. An
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

important emerging area of dusty plasma science concerns the deliberate growth of nanoparticles(dimensions of a few to tens of nm) to microparticles (a few to tens of microns) through the chemicalenergy conversion processes in reactive plasmas. By leveraging inter-particles forces and plasma
chemistry, technologically important nanoparticles with unique particles can be produced. (See Chapter 5
for more details.)
Challenge 3: Predict self-organization of plasmas and, where needed, control that selforganization.
Dusty plasmas can be “tuned” via the Coulomb coupling parameter to exhibit self-organizedbehavior ranging from solid-like to gas-like, while the particles remain suspended in the plasma. In thepresence of a magnetic field, this ordering can undergo significant modifications in ways that are not wellunderstood. Dusty plasmas containing nano- to micro-particles exhibit tendencies to form a wide variety
of self-organized and imposed-structures, such as voids. An example of a “probe-induced” void is, shownin Figure 2.10. While progress has been made in providing plausible theoretical models for void
formation, a comprehensive theoretical framework for predicting self-organized structure formation in
dusty plasmas remains elusive.
Challenge 4: Control and predict the interactions between plasmas and solids, liquids
and neutral gases.
Dusty plasmas are the embodiment of a plasma system that defines the challenge of controlling
plasma surface interactions. Dust particles are charged solid matter that are embedded in a plasma
environment. All of the fundamental properties of a dusty plasma are defined by the interaction between
solid particles and plasmas. A key mission for dusty plasma research is to achieve control over theseinteractions. Some future challenges include:

Determining the dust particle charge. The most fundamental parameter for a dusty plasma is the
charge on the particle. While a number of techniques are used to make charge measurements (e.g.,
two-particle collisions and/or resonant oscillations), these measurements give the charge-to-mass
ratio, and an assumed particle mass is then used to determine charge. A future challenge is thedevelopment of non-invasive, non-perturbative techniques that independently determine the particle
mass and charge. This is particularly important for chemically reactive dusty plasmas in which theparticles grow (or erode), meaning that their size, mass and charge can be functions of position andtime.
Tuning of plasma–dust grain interactions for precision control of trajectories and growth of nanoand micro-particles. In the bulk plasma, the dust particle interaction with the plasma is isotropic.
These interactions produce self-organized structures, for example, single or multiple layers ofhexagonal lattices. However, when particles interact with anisotropic ion fluxes, as can occur in andnear sheaths, the self-organization structures take on different forms, such as linear strings. Thisqualitative change in self-organized structures is due to the production of local space charge throughaltered dust-dust and dust-plasma interactions triggered by anisotropic ion fluxes. Correspondingly, instrongly magnetized plasmas, where ion and electron motion is limited by their gyromotion,
experiments show that the magnetic field may also impose a directional order to the dust particles. A
strategic challenge is to actively control dust-plasma and dust-dust interactions. This capability allows
the preparation of the dust particle state in the plasma, and then the use dust particles as microscopic
diagnostics to provide information about the state of the plasmas and to control the properties of theplasma. Achieving this goal requires the development of plasma chambers with variable internal
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Plasma Science: Enabling Technology, Sustainability, Security, and Explorationgeometries and multi-electrodes to manipulate plasma density and the electron temperature, using
controlled mixtures of particle sizes, or using shaped magnetic geometries, and associated sheath andpre-sheath structures, to manipulate the dust particles.
Dusty Plasma Facilities on Earth and in the International Space Station
The development of dusty plasma research has been dominated by “table top” experiments. Thisis likely to be the dominant mode of exploration for the foreseeable future. The greatest need for current
experiments is the development of new diagnostic tools that can provide real-time, spatially resolved
measurements of both the plasma and the dust particles. Key unresolved questions that may be addressedby a next generation of diagnostics would include: (a) non-invasive, real-time measurements the dust
grain charge; (b) confirmation of the ion flow dynamics and the formation of the ion wake field in thevicinity of dust particles; and (c) the development of new image analysis tools—possibly leveraging new
developments in machine learning—to rapidly process and identify the full three-dimensional motion ofparticles, particularly in cases where multiple synchronized cameras are used or using new types of lightwave (e.g., plenoptic) cameras.
Two areas in which larger collaborative teams have advanced dusty plasma research are the studyof dusty plasmas under microgravity conditions and in magnetized plasmas. The next decade will
hopefully see the continued operation of the PK-4 microgravity facility on the ISS followed by asuccessor instrument, PK-5 (Ekoplasma). The U.S. should consider supporting researchers to pursue
microgravity studies as well as supporting the development of experimental hardware for those facilities.
In exploring dusty plasmas in magnetized plasmas and magnetized dusty plasmas, the last decade
has seen the development of several experimental platforms—many involving superconducting magnet
systems. All these laboratories are generally extensions of the “tabletop” scale groups but requiring
substantially more personnel and diagnostic infrastructure than a single PI laboratory. The MDPX device
at Auburn University is the first facility in the United States specifically designed for supporting external
users. Since beginning operations in 2014, researchers from the United States, South Korea, India,
Germany, and France have conducted studies ranging from dust charging effects and particle growth tomaterials processing to calibrations of fusion diagnostics at magnetic fields up to 3 Tesla. For both
microgravity and high magnetic field studies, partnerships are critical—both through leveraging federal
agencies partnerships (see Table 1.1 in Chapter 1) and promoting national and international partnerships
within the community to grow the field.
NON-NEUTRAL AND SINGLE-COMPONENT PLASMAS: CONFINED IN THERMALEQUILIBRIUM FOR DAYS
The classic definition of a plasma is an ionized gas composed of negative and positively charged
particles that, on average, is electrically neutral. The classic plasma can only be non-neutral over very
short times (defined by the plasma frequency), very short lengths (defined by the Debye length) or near
the boundaries of the plasma where large electric and magnetic fields are applied (defined by the sheath
thickness). Most properties of classic plasmas result from being composed of discrete negative andpositive charges, attempting to assume on the average an electrically neutral state.
In non-neutral plasmas, particle species with only a single sign of charge predominate—that is,
the plasma is intentionally out of charge balance. Often, only a single particle species appears in theplasma (a single-component plasma). A few examples of non-neutral plasmas produced in the laboratory
are pure electron plasmas and pure positron plasmas (both of which are single-component plasmas),electron-anti-proton plasmas, and ion plasmas consisting of one or more species of positive ions. Since
the natural response of collections of charge particles with a net charge density is to produce forces that
reduce the charge density, creating non-neutral plasmas requires specialized experimental techniques.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

Non-neutral plasmas have usefulproperties not shared by neutral or quasineutral plasmas. One important advantage isthe existence in non-neutral plasmas of aconfined thermal equilibrium state using only
static electric and magnetic fields (the“Penning-Malmberg trap” configuration). In
contrast, there is no confined thermal
equilibrium for classical neutral plasmas instatic fields, which is the fundamental reason
why neutral plasma confinement is such a
FIGURE 2.11 Schematic of a non-neutral plasmadifficult problem. (See Figure 2.11.) In nonconfined in a simple cylindrical Penning trap by electric
neutral plasmas, the existence of a confinedand magnetic fields. The electric field E is indicated bythermal equilibrium state enables plasma
red lines. The magnetic field B is parallel to the axis ofconfinement for long times (up to hours, days
the cylinder and indicated by the green line. The open
or even weeks), enables experiments with anends of the cylinder allow plasma flow. SOURCE:
exceptionally high level of reproducibility andhttps://commons.wikimedia.org/w/index.php?curid=619
accuracy, and enables precision industrial
34417; Creative Commons Attribution-NonCommercial
plasma applications.
4.0 International.
A second feature of non-neutral
plasmas is the ability to access extreme
strongly coupled and strongly magnetized states of matter. Unlike neutral plasmas, non-neutral plasmas
can be cooled to cryogenic temperatures without electron-ion recombination (whose rates greatly increaseas the temperature decreases), because there is no oppositely signed charge species with which torecombine. This enables the study of novel strongly coupled and strongly magnetized plasma states inthermal equilibrium (such as pure ion liquids and crystals), which is not possible in any other classicalplasma system. The combination of strong magnetic fields (required in Penning-Malmberg trap
confinement) and cryogenic temperatures produces novel strongly magnetized and quantum plasma stateswith non-ideal -factors that can be similar to those in the environment of highly magnetized neutronstars and white dwarfs.
Relevance and Benefits
Non-neutral plasmas were among the first plasmas studied or employed in industrial applications.
Electron beams used in vacuum tubes, and later in high-intensity radiation sources such as magnetrons,
gyrotrons, and travelling wave tubes are a form of non-neutral plasmas. Understanding collective nonneutral plasma dynamics and radiative interactions is essential to the continuing development of theseradiation sources, as well as other vacuum electronics applications in both the nonrelativistic andrelativistic regimes of operation.
The Penning trap configuration used in non-neutral plasma confinement is also used to stably
confine charged particles for fundamental atomic physics studies, such as measurements of the g-factors(a measure of the magnetic moment and angular momentum) of elementary particles, as well as for highresolution cyclotron mass spectrometry. Such Penning mass spectrometers are found in laboratories
world-wide. The last decade has seen the development of new science involving low-energy non-neutral
antimatter plasmas (i.e., positron plasmas or antiproton plasmas) at energies ranging from 100 eV to lessthan 10−3 eV. Much of this progress has been driven by the development of new plasma-based techniques
to accumulate, manipulate, and deliver antiparticles for specific applications.
The ability to precisely control and manipulate cryogenic non-neutral plasma crystals has madethem attractive systems for use in quantum information studies, which have blossomed over the last
decade. Pure ion crystals consisting of up to several hundred trapped ions are now used to form lattices of
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

quantum q-bits whose interactions and entangled states can be controlled and manipulated using lasers
and microwave signals. These non-neutral plasma crystals are among the most promising technologies forquantum computation and quantum simulation.
More generally speaking, the research in this area of fundamental plasma physics has strong
interdisciplinary connections, contributing to and borrowing from the wider world of plasma physics,
atomic physics, fluid dynamics, astrophysics, soft condensed matter physics, and statistical physics. Using
results from non-neutral plasmas, fundamental questions are being addressed in all of these broader areas.
The U.S. non-neutral plasma community collaborates with many groups outside the United States
on a variety of physics projects. Perhaps the largest international collaborative effort is the CERN(European Organization for Nuclear Research) based effort to produce and study trapped cold antimattersuch as antihydrogen (made of a positive positron and a negative anti-positron). Another international
collaboration involves the production and magnetic confinement of a neutral positron-electron plasma.
The U.S. non-neutral plasma community is also active in the world-wide efforts to trap charged particles
for a variety of purposes, including spectroscopy of trapped high atomic number ions, metrology,
quantum information studies, and high-resolution mass spectrometry of trapped radionuclides.
Progress and Achievements
In the past decade, non-neutral plasmas have continued to provide a rich source of fundamental
physics advances across several areas. Below are a few highlights of recent work.
 Laser-cooled cryogenic pure ion plasmas have been a productive testbed for theories of plasmatransport properties over the years. Recently they were employed to experimentally determine, for the
first time, the Salpeter enhancement to nuclear reaction rates in plasmas for 0 < Γ< 20. (The rates ofnuclear reactions are enhanced by a surrounding plasma that leads to the lowering many-body
Coulomb barriers.) This enhancement is predicted to increase the rate of nuclear reactions inastrophysical plasmas by orders of magnitude for Γ >1, but has not until now been observed inexperiments. The experiments supported the Salpeter theory while challenging competing dynamical
screening theories.
 The dynamics of 2-dimensional (2D) inviscid incompressible fluids have been studied in non-neutral
plasma experiments with Reynolds numbers as high as 105. These experiments enabled precise
control and characterization of non-equilibrium and even turbulent 2D flows. Recent studies havefocused on vortices driven by external time-dependent shear flows, characterizing several novel
effects including vortex stripping.
 Neoclassical transport in magnetized plasmas is a form of cross-magnetic field transport of particles,
momentum, and energy that is enhanced by symmetry-breaking magnetic and electric field “errors”.
Such errors are inherent in many plasma experiments. This transport can induce damaging losses ofenergetic particles in fusion devices. Non-neutral plasmas provide an excellent testbed forneoclassical transport studies since these plasmas can be confined without the turbulent fluctuations
that mask the effect in conventional plasmas, and controlled symmetry-breaking fields can be applied.
Recent theory and experimental work have led to breakthroughs in understanding neoclassicaltransport in fusion plasmas.
 Antihydrogen atoms created through the controlled mixing of cryogenic non-neutral antiproton andpositron plasmas, have been trapped and studied. Directly measuring differences, if any, between
matter and antimatter atoms may help us understand why the Universe is made up almost entirely ofmatter when both matter and antimatter should have been produced in equal amounts in the Big Bang.
 Quantum simulation of spin models can provide insight into problems that are difficult to study withclassical computers. Trapped ions have recently been shown to be a practical system for carrying out
such simulations. Experiments have studied the quantum spin dynamics in a 2D ion crystal consistingof several hundred ions in a Penning trap geometry. Good agreement with ab initio theory lays the
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

groundwork for simulations of more complex
interactions (e.g., transverse-field Ising models
with variable-range interactions) that are generally
intractable with classical methods.
Workforce Development
From the point of view of student education
and workforce development, most non-neutral plasma
experiments are table top or few-investigator devices
compatible with university laboratories. As such they
provide excellent training opportunities forexperimental physicists by providing hands-on
experiences. The overlap of non-neutral plasmas withatomic physics, condensed matter physics,
astrophysics, and fluid dynamics makes this area
attractive to both theory and experimental students
with a range of interests and backgrounds.
Undergraduates with minimal background in plasma
physics can gain useful research experience.
Current and Future Science Challenges andOpportunities
Challenge 1: Understand and be able topredict plasma behavior under extreme
conditions that challenge our present models.

FIGURE 2.12 Defects induced in a 16 ion
plasma crystal confined in a linear Paul trap,
imaged using laser fluorescence. (a) linear
phase. (b-c) zig-zag phases. (d-f) withdifferent dislocations. 1 pixel = 1.7 micron.
SOURCE: S. Ulm, J. Roßnagel, G. Jacob, etal., Observation of the Kibble–Zurek scaling
law for defect formation in ion crystals, Nat
Commun 4, 2290 (2013),
https://doi.org/10.1038/ncomms3290.

Non-neutral plasmas can be cooled into the cryogenic regime of strong coupling, having  >> 1.
Strong magnetic fields can be applied, such that the cyclotron radius of all species is smaller than even the
distance of closest approach between particles. (This magnetization regime is difficult to achieve in “hot”
neutral plasmas, requiring ultra-large magnetic fields exceeding 109-1010 Gauss.) Being able to sustain
non-neutral plasmas under these extreme conditions poses science challenges: (a) What are classical andquantum non-equilibrium transport coefficients in strongly coupled and strongly magnetized plasma(particle diffusion, thermal conduction, viscosity, collision rates)? (b) Progress in understanding the
dynamics of defect formation and growth has been achieved in 1D plasma crystals confined in a linear
Paul trap. (See Figure 2.12.) In this area bordering plasma and soft condensed matter physics, how do
defects form and propagate in 2D and 3D plasma crystals?
Challenge 2: Quantify and, in the laboratory, control how plasma processes direct theconversion of energy from one form to another, the transfer of energy across a vast rangeof scales, and the transport of energy in the laboratory and nature.
The most fundamental energy and momentum transfer mechanisms in a magnetized plasma,collisional heat conduction and viscosity, are not fully understood. Recent experimental and theoreticalwork in non-neutral plasmas has shown that classical cross-magnetic field thermal conductivity and shear
viscosity applies only to plasmas for which the plasma frequency is large compared to the cyclotron
frequency. For plasmas where this is not the case (i.e., plasmas in strong magnetic fields), the classical
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration“Braginskii” coefficients (with transportcoefficients to account for the effects ofmagnetic fields) may be incorrect byorders of magnitude. In fact, transportcoefficients (thermal diffusivity andkinematic viscosity) are independent ofmagnetic field in this regime. The classicalcoefficients neglect transport induced byweakly damped waves carrying energy andmomentum across the magnetic field. It
has been predicted that such long-range
wave-induced transport will dominate
thermal conduction and viscosity in any
quiescent plasma of sufficient size.
Investigations of fundamental transportcoefficients in non-neutral plasmas holdthe promise of providing data required todevelop theories of cross-magnetic fieldtransport applicable to several problems in
PSE.
Challenge 3: Predict selforganization of plasmas and,
where needed, control that selforganization.

2.13 Cyclonic Self-organization Vortex crystal states
were first observed to spontaneously form from relaxing
2D turbulent flow in an electron non-neutral plasma,shown in the top image. Similar cyclones have been
observed at the north and south poles of Jupiter forming
apparent vortex crystal states. There are opportunities todevelop scaling laws in laboratory non-neutral plasmas
that may be applicable to planetary scales. SOURCE:(top) Phys. Rev. Lett. 75, 3277, 1995; (bottom)
Magnetized Plasma Research Laboratory, Auburn
University.

One of the phenomena mostdifficult to explain in Nature is theappearance of order out of disorder.
Turbulent hot plasmas are arguably one of the most disordered “high entropy” states of matter that can beachieved; and yet it is possible for ordered states to appear spontaneously in such systems. One way thiscan occur involves a “backwards flow” (inverse cascade) of energy from fine scales in the turbulence tolarger scales, through the merger of nearly 2D vortical structures into ever-larger size scales. One
example is the appearance of “vortex crystals” from decaying 2D plasma turbulence, first documented inpure electron plasma experiments. (See Figure 2.13.) A similar inverse cascade is responsible for Earth’s
jet stream and the H-mode that appears in fusion reactors, both of which are self-organized large-scale
flows arising from a finer-scale incoherent turbulent background. Recently, vortex crystal states havebeen observed in the atmosphere of Jupiter, having formed spontaneously from the driven turbulence ofJupiter’s atmosphere. Advances in our understanding of inverse cascade produced self-organization from
non-neutral plasma experiments and theory will have wide applicability, from fusion plasmas toatmospheric dynamics for earth and planets.
Challenge 4: Control and predict the interactions between plasmas and solids, liquids
and neutral gases.
Non-neutral plasmas are typically confined away from contact with liquids and solids. An
exception to this rule is in the use of low-energy monoenergetic antimatter beams as a probe of solidmaterials, and for use in studies of the interaction of antimatter with individual neutral atoms. Thesestudies rely on ongoing advances in positron plasma control and confinement. Non-neutral plasma–gas
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Plasma Science: Enabling Technology, Sustainability, Security, and Explorationinteractions are also of importance in a number of other contexts. For example, the collisional dragbetween the plasma and background neutral gas can limit the plasma confinement time, heat (or cool) theplasma and cause deleterious effects such as decoherence in quantum information studies. This particular
process is for the most part well-understood. However, the chemical reactions that can occur between
plasma charges and background gases are not well understood. These reactions, such as charge-exchange
collisions and charged molecule formation and break-up, are of interest in a number of contexts, including
the reactions occurring in low temperature molecular clouds in interstellar space. Some of these reactions
are predicted to have timescales of hours or days, depending sensitively on the plasma temperature anddensity, and therefore are very difficult to measure by standard means. However, in a non-neutral plasma
where the charges are confined for days or weeks, such measurements are possible. The appearance of
new charged ion species could be measured in situ using the newly developed method of ion cyclotron
thermal mass spectroscopy, or in some special cases by means of laser fluorescence diagnostics. This is
another example of where fundamental studies of non-neutral plasmas have impact well beyond thelaboratory and, in this case, to interstellar astronomy.
PLASMA INTERACTIONS WITH LIQUIDS, SOLIDS, AND GASES
Fundamental plasma research is often focused on the physics of waves and instabilities, which areproperties of the bulk plasma far from boundaries. In fact, in these studies the edge effects produced byboundaries in laboratory plasmas are undesirable. However, laboratory plasmas are intrinsically bounded
and the bounding interface can have a huge impact on the plasma properties. Although plasma boundaryinteractions may be undesirable in the context of studying bulk properties, plasma-boundary interactions
are the basis of nearly all plasma materials processing, plasma based biomedical applications and plasma
enhanced environmental stewardship. The fabrication processes used in the optics, solid-state lighting andmicroelectronics industries are based on plasma-boundary interactions. The importance of solid interfaces
in plasmas can even be extended to space plasmas where the presence of dust provides a plasma-solidinterface.
The science challenges more closely aligned with technologies using plasmas are discussed in
Chapter 5. From a fundamental perspective, why are plasma-interfacial interactions so important and why
can they have a dominant impact on plasma behavior? Plasma-interfacial interactions can be highly
complex due to the possible strong coupling between plasma properties and the interfacing material
surface properties. This coupling can be due to different mechanisms depending on plasma and interface
properties:







Surfaces can act as electron sources upon ion or energetic species impact, surface heating or highinterfacial electric fields induced by the plasma.
Surface charging of dielectric interfaces can lead to enhanced or decreased electric fields nearsurfaces even leading to the possible extinction or generation of plasmas.
Liquids have generally smaller energy barriers for species transfer at the interface and can therefore
have a much more pronounced influence on the plasma state. Evaporation of the liquid phase inducedby the plasma can dramatically change the gas composition near the plasma-liquid interface and sochange plasma properties.
The surfaces of liquids and soft matter can deform upon plasma exposure. These deformations cancause increasingly inhomogeneous electric fields and plasma self-organization.
In reactive plasmas, the surface properties can be changed during plasma exposure leading to acontinuous change in plasma-surface interactions.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

The complex interaction of plasmas withsolids and liquids leads to many interesting scientificquestions including what happens to the structure andnon-equilibrium properties of the plasma-solid/liquidinterface during plasma exposure, and the transportmechanisms of charged and reactive species acrossthe plasma-solid/liquid interface. The study of theseinterfacial processing involves in addition to plasma
science solid state physics, material science, andchemistry, and is a highly interdisciplinary subfield ofplasma science.
A significant part of the plasma physics
community is concerned with studying collective
phenomena in plasmas generated at very low pressure
and in noble gases to reduce or even eliminate
collisional effects. Nonetheless in many plasmas ofinterest, both atomic and molecular gases are present
at significant densities or intentionally introduced.
This leads to a rich spectrum of collisional processes
and the generation of a multitude of species andchemical reactions. These studies have provided thefoundation of many plasma-based applications andrely heavily on atomic and molecular physics. As
collisional effects strongly impact the distribution ofelectron energies, reactions directly impact theplasma dynamics and electron kinetics leading to new
plasma phenomena. An example is the recently
discovered ultrafast gas heating mechanism in
atmospheric pressure air plasmas due to rapidly
dissociating, electronically excited molecules. Manyof these collisional interactions lead to new plasma
phenomena enabled by the enhanced complexity ofcollisional plasmas.
Variations in gas composition and densities canalso have a strong effect on plasma dynamics andproperties. An example of the use of changes in gas
composition to control plasma generation is the socalled cold atmospheric pressure plasma jet, shown in
Figure 2.14.

FIGURE 2.14 Model of a guided streamer.
In the last decade cold atmospheric pressureplasma jets have been investigated for theiruse in biomedical applications and materials
processing. The plasma is generated in a tube
through which, for example, helium isflowed, leading to the formation of a helium
channel surrounded by air outside the tube.
The figure shows the electron density in adeveloping ionization wave, or streamer, insuch a helium channel. As the ionization
coefficient is much larger in helium
compared to the surrounding air, a guided
streamer is created by the gas channel andthe surrounding air radially confines thedischarge. SOURCE: J-P Boeuf et al 2013 J.
Phys. D: Appl. Phys. 46 015201.

Relevance and Benefits
Magnetic fusion: In fusion reactors, about 20% of the energy produced cannot be captured to
produce electricity and is instead exhausted in the form of heat and plasma particles in the divertor area.
The huge particle and energy flux, due to the high power density in fusion plasmas leads to uniqueplasma-material interactions making it a key challenge on the path to the development of fusion forsustainable electrical power generation. Plasma-material interactions, which include interactions between
plasmas with solids as well as liquid interfaces at boundaries, is a very important area of research, withsignificant implications for the performance of fusion reactors. (See Chapter 6.)

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

Plasma-material synthesis and processing: Many plasma interactions with solid surfaces havebeen exploited for societal benefiting applications ranging from semiconductor processing and synthesisof nanostructured materials with unique properties to arc welding and the development of plasma-based
medical applications. Plasma-material interactions are utilized as a key enabling technology in thesemiconductor industry, a top 10 industry in the United States, serving a roughly $2 trillion electronics
market. (See Chapter 5.)
Dusty (space) plasmas: Dusty plasmas are the embodiment of plasma-surface interactions as thehighly dispersed solid phase leads to an exceptionally large surface-to-volume ratio. A better
understanding of dusty plasmas will contribute to our understanding of star-forming regions as well as
comets and planetary rings. Dust particles are also believed to play a key role in molecule formation in
space as studied in astrochemistry.
Plasma-liquid interaction: In addition to its importance in magnetic fusion reactors where liquidwalls are being investigated, plasma-liquid interactions have a vast array of applications ranging fromwater treatment to wound healing and material and chemical synthesis. In the last decade an extreme typeof multi-phase plasmas has emerged, which can be seen as an equivalent of dusty plasmas, though withthe dust replaced by liquid droplets or aerosols having sizes of a few microns to a mm. The “plasmaaerosol,” a dynamic suspension of liquid droplets dispersed in a gas, encompasses a wide range of
scenarios that can involve single microscopic droplets up to full sprays and jets while the plasmas
themselves vary from non-equilibrium low temperature to thermal plasmas. Plasma aerosols enhance thetransfer of activation energy from plasma to the liquid thanks to the large surface-to-volume ratio and the
production of species in close proximity of the droplet surface. Demonstrated and potential benefits
include on-demand delivery of designed micro/nanomaterials and delivery of short-lived species synthesisof high value chemicals, drugs and nanomaterials. Enhancing transfer of reactivity from plasma toaerosols will enable on-demand, point-of-use and energy efficient production and delivery of chemical
activity, for fertilizer production, sterilization and indoor agriculture.
Progress and Achievements
There has been impressive progress in understanding of the interaction of plasmas with gases,
liquids and solids over the past decade.


Low temperature plasma (LTP) research has increasingly extended plasma-surface interactions
studies from solid materials to liquids and soft matter. While our understanding is still limited, majoradvances in modeling and diagnostics have been made. This led, for example, to improved
understanding of the role of solvated electrons and H radicals in plasma-liquid interactions and therole of plasma-produced species on plasma interactions with living matter. An example is the role ofplasma-produced O2(1), a very long lived electronically excited state of the oxygen molecule, in theoxidation of capsid proteins of virus and the potential role of O2(1) selectivity of plasma-treatment ofcancer.
A detailed understanding of the influence of metal vapor in thermal plasmas, particularly in welding
arcs, has been developed. Three-dimensional time-dependents models and spatially resolved timedependent measurements have clarified the mechanisms driving metal vapor transport, and theinfluence of metal vapor on arc properties.
The last 10 years have seen a move to more advanced control of power delivery and plasma kinetics
leading to control of plasma-surface interactions at length scales of a single atom, an example being
atomic layer etching. This process has been enabled by an increased knowledge of the underpinningplasma processes by a combination of modeling and diagnostics.

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





The implementation of advanced diagnostics has enabled a broader understanding of the interactionof plasmas with polymers, including the role of UV photons and the effect of plasma-produced
radicals on surface modification and etching.
Boronization (or an equivalent, such as lithiumization), is the plasma deposition of a thin boron (orlithium) containing film on the inner walls of the fusion reactor chamber through the injection ofboron into the plasma. Boronization has been used successfully in tokamaks for many years as ameans of controlling impurities, oxygen in particular. However, the boronization process is poorly
understood and undoubtedly less than optimal. Lithium micro-granule injection, often dubbed powder
or aerosol injection, has been successfully investigated in fusion research demonstrating
improvements in terms of wall conditioning and opening access to high performance scenarios.
Multiple existing experiments are studying tungsten for first walls for fusion reactors in preparation
for its use in ITER. However, the occurrence of melting in these experiments has been greater than
expected. The extrapolation of tungsten erosion estimates to DEMO (the follow-on fusion reactor toITER) indicate unacceptably short lifetimes for the plasma facing components. Concerns such asthese have served to increase interest in the use of liquids as plasma facing materials. A flowing
liquid surface would be melted by design and erosion and re-deposition would have no long-term
effects. However, how liquid films survive real fusion machine environments is still unclear and a
subject of much debate.
Current and Future Science Challenges and Opportunities

In view of the huge potential benefits of the interaction of plasmas with liquids and solids
summarized above, research is supported by a broad set of programs and divisions within NSF, DOE and
DOD that support materials or plasma research. While these diverse funding sources are in some respects
a strength of the field, it has unfortunately led to a silo effect between studies focusing on plasma physics
and on synthesis/material processing from a materials perspective. A key challenge in the next decade is
to bring together experts in plasma science, materials research and chemistry to tackle the major sciencechallenges highlighted below. This will require coordinated initiatives between materials-focused andplasma-focused programs in federal agencies enabling advances in the science and technology of bothfields, as recommended in Chapter 5.
Challenge 1: Understand and be able to predict plasma behavior under extreme
conditions that challenge our present models.
Materials for plasma-facing components are often exposed to enormous fluxes of energetic
particles and energy corresponding to extreme conditions that are far from the conditions under whichmaterial properties have been studied. Similarly, extreme non-equilibrium plasma conditions can beachieved at the interface between low temperature plasmas and solids/liquids due to huge fluxes ofenergetic species at near room temperature. Our current understanding of these unique conditions isextremely limited and requires the development of detailed in situ diagnostics complemented withmodeling efforts if our understanding is to improve.
Major efforts have also been devoted to study plasma generation in liquids requiring much higher
electric fields than in their respective gases/vapors due to the significantly higher density of liquids.
Recently, mechanisms have been formulated to explain plasma generation in liquid water without theneed for bubble generation, complemented with experimental work reporting plasma produced pressures
up to 1 GPa. This research is closely tied to many unresolved questions of the change in structure andproperties of liquids under extreme conditions (such as high electric fields, pressure and temperature) and
its ability to create extreme plasma conditions.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

Another example of such a new scientificfrontier are atmospheric pressure microplasmas
that can lead to relatively high power density LTPs
having microscopic dimensions. In some cases,
LTP plasma densities can approach values typicalof fusion plasmas (1014–1017 cm-3). While theelectron temperature is of the order of a few eVs,
the large surface to volume ratio leads tosignificant losses. This combination results inrelatively low neutral gas and ion temperatures ofabout 0.1 eV. The interfacial region between thebulk plasma and the solid surface consists of aplasma sheath with dimensions ranging from a
micron to tens of microns in which an intenseelectric field induces Fermi level shifts near thesolid interface. These conditions can result in fieldemission of electrons and field ionization in somecases. The interaction of relatively dense and cold
plasma with solid-state materials is a largely
unexplored topic. The coupling between plasmas
and surface increases for higher-pressure plasmas,
and challenges remain in resolving the huge spatial
gradients in species densities near interfaces.

FIGURE 2.15 Self Organization in Plasma
Liquid Interactions. The interaction of plasmas
with soft and liquid surfaces produces a
feedback mechanism that leads to selforganization. In this image, an atmosphericpressure plasma jet sustained in helium entersroom air and strikes a salt solution that serves as
the anode. The plasma self-organizes on thesurface of the liquid. These patterns often rotate
or slowly evolve into different shapes.
SOURCE: Y. E. Kovach, IEEE Trans. Plasma
Science v47, p. 3214 (2019).

Challenge 2: Quantify and, in thelaboratory control, how plasma processes
direct the conversion of energy from one
form to another, the transfer of energy
across a vast range of scales, and the transport of energy in the laboratory and nature.

The key distinctive feature of LTPs is that energy coupling mainly proceeds through electrons in
the bulk plasma and possibly ions in the sheath regions adjacent to surfaces. This leads to highly nonequilibrium plasma kinetics. The kinetic energy of electrons is transferred to atoms and molecules bycollisional processes between electrons and neutral gas atoms and molecules. These collisions can lead tothe generation of tens to hundreds of possible species depending on the gas mixture and electron energy
distribution (EED). The control of ion energies striking surfaces is a dominant need in customizing
plasmas for materials processing. The fundamental LTP challenge involves controlling the energy
distribution of electrons to channel the energy deposition into the production of ions, excited, radical andreactive species that drive the desired processes in the gas phase or at interfaces. Similarly, controlling the
distribution of ion fluxes to surfaces enables control of surface processes having energy thresholds.
The ultimate LTP challenge is achieving predictive control of the plasma initiated chemical
processes. This is particularly complex due to the sensitive two-way coupling between the EED, and thegas composition, including the species produced through collision processes. Many plasma kinetics andchemistry models have been developed but a thorough experimental validation of models is the exception
due to the large complexity of the composition of the plasma. Understanding complex molecular plasmas
requires the development of validated predictive capabilities which in turn requires a large team and longterm efforts. This challenge includes developing highly controlled and accurate benchmark experiments.
While recognizing the increased complexity due to the non-equilibrium nature of LTP, the community
could highly benefit from establishing validated reaction sets complemented with benchmark
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FIGURE 2.16 Plasma surface interaction models – Plasmas interacting with surfaces are key to themajority of applications of low temperature plasma leading to societal impact. Key processes as secondary
electron emission are not well understood. Currently most plasma models use often experimentally
determined coefficients to describe surface processes such as secondary electron emission without
considering the underpinning atomic scale processes. Combining plasma models with atomic level modelsof the interface combined with new in situ surface diagnostics would enable us to move beyond an
empirical understanding of plasma-surface interactions and enable us to apply our new understanding to amuch broader class of plasma conditions and materials. These processes play a key role both in solids andliquids. In this image, molecular dynamics techniques are used to simulate argon ions (5-50 eV)interacting with a chlorine passivated Ge lattice for atomic layer etching (ALE). SOURCE: Phys. Chem.
Chem. Phys., 2019,21, 5898-5902,
https://pubs.rsc.org/en/content/articlelanding/2019/cp/c9cp00125e#!divAbstract.
experimental studies similar to GRI-mech used in the combustion community. This effort should becoupled to transport models and plasma-surface interaction models.
Challenge 3: Predict self-organization of plasmas and, where needed, control that selforganization.
As in many physical, chemical, and biological systems, self-organization is a common
phenomenon at the interface between a plasma and a solid or liquid. While some aspects of thephenomena for specific cases are understand, currently the mechanisms responsible for self-organizationin plasmas interacting with surfaces are not well understood. There is a need for the development of an
overarching model explaining the large variety of often very similar self-organizing phenomena occurring
over a broad range of pressures and power densities. Typically, self-organization occurs in the anode orcathode layer at the interface between a plasma and a resistive or dielectric medium, which could be aliquid. (See Figure 2.15.) When ionization fronts impinge on a dielectric surface the discharge tends tobranch and develop surface ionization waves that can have self-organized patterns. There is a need todevelop more comprehensive plasma models with detailed kinetics capable of predicting the occurrenceof and transitions between these patterns. Detailed spatially resolved measurements other than fast
imaging for model validation are also lacking. Similarly, while 3D simulations of ionization waves andstreamers have been performed in the gas phase (see Chapter 5), surface ionization waves have only beenvery recently modeled and the intrinsic 3D phenomena of self-organization phenomena in surface
ionization waves have not been addressed.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

Challenge 4: Control and predict the interactions between plasmas and solids, liquids
and neutral gases.
While in situ diagnostics for surface characterization during plasma exposure are emerging, amajority of material characterization to date is based on ex situ diagnostics where the material is analyzed
after plasma exposure. The lack of in situ diagnostics adds an additional layer of complexity in theanalysis and interpretation of the actual plasma-material processes. There is a strong need for thedevelopment of in situ diagnostics amenable to a harsh and complex plasma environment. This isabsolutely critical as there is a lack of understanding of the basic processes underpinning many plasmamaterial interactions and there remains a need for model validation.
Significant progress has been made in plasma-surface interaction modeling. (See Figure 2.16.)
However, comprehensive models with a two-way coupling of non-equilibrium kinetics in plasmas
intersecting with interfaces address only specialized systems. The physical processes at the interface of aplasma and a solid or liquid are extremely complex, involving a large number of elementary processes in
the plasma and in the solid as well as fluxes of energetic species across the interface. An accurate andunified theoretical treatment of these processes is very difficult due to the vastly different systemproperties on both sides of the interface: quantum versus classical behavior of electrons in the solid andplasma, respectively; as well as dramatically differing electron densities and length and time scales.
Liquids provide additional challenges over solids as they can have a much more pronounced influence on
the plasma state.
In many models of bounded plasmas, the surface processes are either neglected or treated using
phenomenological parameters such as sticking coefficients, or sputtering rates and secondary electron
emission coefficients given by simple theories. These parameters are known from measurements or
fundamental, materials specific theories or computations only in specialized cases and with limited
accuracy. Similarly, surface physics simulations are usually not linked self-consistently to the plasma. As
a result, the collective influence of the plasma and correlations with surface processes are usually notaccounted for. Such an approach does not account for the mutual influences between plasma and solid
surface, and so do not have broadly applicable predictive capabilities. Integrated modeling of the entire
plasma-solid/liquid interface is needed and is a major challenge for the plasma community.
FINDINGS AND RECOMMENDATIONSThe science challenges in basic plasma physics are immense and the opportunities to translateadvances in fundamental plasma science to develop applications are strategic. Addressing thesechallenges and leveraging these opportunities requires the availability of a dynamic theory-based
workforce. As endorsed in this report, computational PSE is critical to the future of the field. As anecessary complement to the effort in computational PSE, there is a need for supporting fundamental
theory and developing a workforce of the future that is schooled and expert in theory.
Finding: The theoretical PSE workforce is not large enough to meet our current needs
and will become even less able to do so in the future without deliberate measures.
Recommendation: In developing their research agenda, federal agencies supporting
plasma science (e.g., NSF, DOE, DoD, NASA) should make deliberate efforts to
support theory.
Finding: Investigations of fundamental plasma science provide the understanding ofthese complex processes that underpin the behavior of plasmas across the entire realm ofplasma science and engineering (PSE). Studies of fundamental processes tie together
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seemingly disparate phenomena across the PSE discipline and provide a unifying
perspective to the vast array of PSE applications.
However, basic plasma science investigations are often perceived as being separate from applicationinspired research and are often funded separately. As a result, it is increasingly difficult for fundamental
studies and applications to leverage each other’s efforts.
Finding: A widening gap between fundamental studies and application-inspired research
impedes progress in both fundamental studies and application-inspired research andslows the rate of translational research that leads to societal benefiting technologies.
Recommendation: Federal agencies that fund PSE should forge partnerships withother plasma-focused agencies as well as agencies focused on applications benefitingfrom plasmas (or programs within agencies) to close the widening gap between
fundamental plasmas science research and translational research leading toapplications.
This recommendation extends to partnerships between programs within a single agency (e.g., FES and
BES within the DOE Office of Science). The committee specifically draws attention to the numerous
examples of such partnerships listed in Table 1.1 in Chapter 1 for possible adoption of some of thesepotentially cutting-edge partnership projects.
Finding: There has been a general loss of broad collaborative activities within the PSE
community over the last decade.
Finding: In both experimental and theoretical/computational areas, the creation of teams
with the critical mass to address important and complex issues in basic plasma science
are needed.
Finding: Center-type activities can provide opportunities that strengthen the overall
health of the PSE community while providing important incubators for the developmentof the PSE workforce.
Recommendation: The DOE should broaden its support of Plasma Science Centersthrough recurring solicitations at critical funding levels to provide both newopportunities to advance important areas of plasma science as well as to improve
the impact of the plasma science community.
Partnerships with other federal agencies are encouraged, and the committee refers to Table 1.1 in Chapter
1.
Finding: While many of the basic plasma science facilities are aging, the last decade has
seen important investments in several new or expanded facilities in the range of $1
million to $4 million.
Finding: Many U.S. plasma science facilities were built during the last decade withfunding provided by the NSF Major Research Instrumentation program, and many ofthese facilities provide opportunities for external researchers to conduct collaborative
experiments with the host institutions. However, the experimental facility needs ofdifferent communities that are pursuing basic plasma science can vary widely.
For example, there are important collaborative, multi-PI research activities that may require significantly
larger facilities. The recent Report of a Workshop on Opportunities, Challenges, and Best Practices for
Basic Plasma Science User Facilities (2019) makes strategic recommendations on the types of facilities
that are considered important enough to a broader science community to justify significant investment of
resources.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

Finding: Today, facilities at a spectrum of scales and reflecting the requirements foraddressing different problems at the frontiers of plasma science (in the range $1 million
to $20 million) are needed.
Recommendation: NSF, DOE, NASA, and other federal agencies with an interest
and programs in plasma physics should provide regular opportunities for thecontinued development, upgrading and operations of experimental facilities forbasic plasma science at a spectrum of scales.
There are several existing and planned laboratory user facilities that are able to address the challenges inbasic plasma science described here. Currently, the primary mechanism for obtaining support for users ofthese facilities is through the NSF/DOE Partnership in Basic Plasma Science and Engineering (PBPSE).
While many users have been successful in obtaining this support (typically 3-year grants), there are someprojects that do not require a full 3 years of funding to be executed (e.g., performing a one-time
experiment to validate a model or theory).
Finding: Many potential users of these experimental facilities would benefit from small
levels of support to gain experience with and obtain initial data for proof-of-concept
demonstrations that are usually expected in a full proposal to PBPSE. A mechanism toprovide one time-short term funding to perform these experiments would address thiscritical need.
Existing funding models that might be used are the National Laser User’s Facility (NLUF) program at theLaboratory for Laser Energetics at the University of Rochester and the Matter at Extreme Conditions(MEC) facility at the SLAC National Accelerator Laboratory. Coordination across existing user facilities
would be beneficial in implementing this funding mechanism; a model that might be followed is that usedby LaserNETUS.
Finding: In addition, to a shared funding resource for user support, a network of basic
plasma science facilities might also coordinate on proposal selection, users groups, andoutreach activities, thereby addressing the STEM pipeline into plasma science.
Finding: A network of basic plasma user facilities that would provide opportunities foraccess to new and upgraded plasma science facilities needs more coordination andsupport than currently exists.
Recommendation: Federal agencies, particularly DOE-FES and NSF-MPS, should
implement a program for one-time, short-term funding for users of basic plasma
science facilities.
Recommendation: A community wide workshop led by a partnership of DOE-FES
and NSF-MPS should define the parameters and participation of such a programand network of user facilities.
For the most part, computation remains the province of experts. Most non-commercial simulation codes
are primarily used by their developers and a small cohort that can be supported by direct access to thedevelopers.
Finding: Plasma simulation is not optimally accessible to the wide range of potential
users, including experimentalists and industrial users.
As more sophisticated hardware becomes available in the exascale era, codes that were developed using
older technologies face an increasing technology gap and need to be ported to new architectures.
Finding: Funding agencies have not traditionally supported code usability to the extent
needed to make research codes user-friendly, support users of codes, or to transition
existing codes to new computing architectures.
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Recommendation: Funding agencies, and in particular DOE and NSF, should
support mechanisms for making computational plasma software more widely
accessible to non-computing experts, and to transition current codes to newcomputing architectures.
For example, these agencies should examine the role for public-private partnerships that could makeeasily used software available on agency computers. In this regard, to make the broadest impact, open
source software being sponsored by NSF and DOE should be accessible to the non-experts and useable on
a broad range of computing architectures,
Finding: At the time of this writing, opportunities for machine learning (ML) andartificial intelligence (AI) that impact computations (and experiments) are only beginningto be realized. This is an extremely rapidly developing field. Leveraging these advances
may require new approaches to computation.
Recommendation: To assure that PSE computations take advantage of advances in
ML and AI, a periodic workshop should be held to share best practices, jointly
sponsored by NSF, DOE and NASA.
Finding: There is a lack of modern educational and review material in computational
PSE that addresses the methods of computation and how to make effective use ofcomputations.
The latter above is becoming an even greater need as more of computational plasma physics transitions toa situation where fewer but more widely accessible codes exist, each with many users who are notnecessarily the developers.
Finding: With the rapid growth of interdisciplinary research in plasma physics, it is time
to consider the establishment of an annual journal that reviews major developments in allareas of plasma physics, much like the Annual Reviews of Astronomy, for example.
Recommendation: Computational PSE, supported by NSF, should include projects
for writing textbooks and developing courses to train the current and next
generation of computational plasma scientists, and to enable non-computer experts
to make optimal use of computations.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration3
Laser-Plasma Interactions:Compact Particle Accelerators, New Optics, and Brilliant X-Ray Sources

LEVERAGING AND CONTROLLING THE MOST INTENSE LIGHT ON EARTH
An ordinary lightbulb produces only a few to tens of watts of optical power. The Watts-per-unit
area is a measure of its intensity, and for an ordinary lightbulb, the intensity even at the bulb’s surface isat best tenths of a W/cm2. The sun is an extremely powerful source of radiation. However, at the surfaceof Earth, 93 million miles from the Sun, the intensity of solar radiation is only 0.1 W/cm2. Lasers (light
amplification by stimulated emission of radiation) are devices that are capable of producing intensities
perhaps beyond any source found in nature. An ordinary laser-pointer has a continuous intensity of about
1 W/cm2. Industrial lasers used for cutting and welding may produce intensities of more than 100 kW/cm2
in the desired spot size (cross sectional area of the laser beam) of only a mm in radius.
The greatest intensities are obtained from pulsed lasers or particle beams. These devices take agiven amount of energy, and from that produce a very large power by putting all that energy into a very
short pulse (power is energy/time). A 10 Joule laser having a pulse length of 50 fs (a fs, or femtosecond,is 10-15 seconds, a millionth of a billionth of a second) produces 200 TW of power (1 TW = 1012 Watts).
Focusing that laser pulse to a small spot, say 50 µm in diameter, produces an intensity of more than 2 1018 W/cm2. Such intensities immediately ionize any material, converting it to a plasma. When,subsequently, lasers with such high intensity are focused inside the plasma, an entirely new realm ofphysics opens up. This realm corresponds to the physics of the largest electric fields ever produced byhumankind. This is the field of laser-plasma-interactions (LPI). In this field, there are many challenges, incontrolling this intense light, in using this intense light (e.g., for acceleration of charged particles), and ingenerating light of even greater brightness (brightness controls the ability to focus the light to a given
intensity).
Since high-intensity laser fields immediately turn anything into a plasma, plasmas are the only
way to control and harness such laser fields. This has led to the new field of plasma optics, in which theplasma is configured to act as an optical element. By controlling the properties of the lasers and plasmas,
the plasma can be used to scatter, absorb, reflect, focus and refract the laser light—much likeconventional mirrors and lenses are used to manipulate ordinary light. Plasma optics also encompasses
waveguiding, creation of atmospheric filaments, plasma compression, laser beam combiners and transfer
of energy between laser beams. It additionally includes forming light with a structure that enhances or
suppresses some particular effect. The plasma can be used to amplify and polarize lasers. Since theplasma can switch the state of light and can control unprecedented intensities, this field is often known as
Plasma Photonics or the Nonlinear Optics of Plasmas (NLOP). (See Figure 3.1.) In the last 10 years, newmethods of controlling sequences of laser pulses and laser bandwidth control, together with a newunderstanding of multi-beam interactions in plasmas, have transformed the field. NLOP offers thepotential to mitigate instabilities that occur in laser driven inertial confinement fusion (ICF, covered inchapter 4), and to shape and control light. The fundamental challenge is: How can plasma optics shape

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

and be shaped to manipulate controllably
ultra-intense radiation, to enable laser
conditions physics regimes, and applications
unobtainable by conventional optics?
Harnessing the extreme fields ofplasmas offers a new generation of compact
particle acceleration methods. In the absenceof a waveguide, an electromagnetic wave
cannot continuously accelerate charged
particles because the electric field istransverse to the direction of wave
propagation, so that the accelerated particles
leave the region of the laser field. However,
the interaction of a laser pulse or particle
beam with a plasma can generate longitudinal
electric fields, so called wakefields, for which
the generated electric field is oriented along
FIGURE 3.1 Transferring energy between laser
the direction of propagation of the particle.
beams. Recent advances in plasma optics have
The accelerated charged particles can movesignificantly improved laser beam performance. As
with the accelerating field for long distances,
shown in the image, multiple laser beams intersecting
and consequently be accelerated to very highin a preheated gas plasma preferentially transfer theirenergies. (See Figure 3.2.) The rate ofenergy to a single red shifted beam. In experiments,
acceleration can be enormous, approaching
more than 3 times the output power was produced
100 GeV/m. (1 eV is the energy gained by anthan was present in any of the pump beams. This
electron falling through 1 volt of electrical
technique can be used to extend the beam power
potential.) For comparison, conventional
available in any single laser beam. More than 20
accelerators like the linear accelerator at theyears of research has demonstrated the potential for
SLAC National Accelerator Laboratory
plasma optics to provide higher performing beams.
accelerated electrons to 50 GeV over 3.2 km,
SOURCE: R. K. Kirkwood et al, Nature Physics, 14,
or 16 MeV/m, i.e., smaller by more than three80, (2018).
orders of magnitude. There is a practical limit
of around 100 MeV/m with conventional
acceleration since for an electric field of that strength, electrons are pulled out of ordinary material. Now
with the ability to control plasmas, wakefield acceleration is under consideration for the development of
future high energy particle physics (HEP) colliders to extend our understanding of the basic laws of theuniverse. (A collider is a pair of accelerators that produce particle beams moving in opposite directions,that then collide head-on. At the current energy frontier, electron and positron colliders will need to belinear to reduce radiation losses from these light particles.) In another method, Direct Laser Acceleration,
the particles interact with the laser fields nonlinearly in order to experience continuous acceleration. The
existence of multiple acceleration mechanisms attests to the richness of this field. A community roadmap,
the DOE Advanced Accelerator Concepts Research Roadmap [DOI: 10.2172/1358081], is guiding thefield towards developing applications in the near term and addressing the challenging requirements offuture colliders. A fundamental question is: How can we control the interactions of ultra-intense(relativistic) lasers and particle beams with plasmas through shaping the laser fields and plasma profiles
to efficiently generate ultra-bright, high energy charged particle beams?

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

FIGURE 3.2 Basics of laser particle acceleration: (left) Compact high energy plasma wakefield
accelerators are created when an intense short pulse laser (or charged particle bunch) driver is focused
into a low density gas or plasma, such as for example into the plume of a gas jet. (center, showing
inset). The driver propagates though the plasma and its radiation pressure (or space charge for aparticle bunch) displaces electrons creating a density wave or ‘wake’. Because the electrons and ions
are separated, electric fields are created, which can be orders of magnitude larger than thoseachievable in conventional structures. The wake travels at the velocity of the laser, close to the speedof light, allowing it to trap and accelerate electrons to high energy. (right) Wakefield acceleration canbe thought of as analogous to the wake of a boat, where the boat displaces water creating a heightoscillation on whose gradient a rider can surf, gaining energy without use of a tow rope. SOURCE:
Left to right: Courtesy of Cameron Geddes, Lawrence Berkeley National Laboratory; Courtesy Remi
Lehe, Lawrence Berkeley National Laboratory;
https://upload.wikimedia.org/wikipedia/commons/5/5c/Fjordn_surface_wave_boat.jpg,
CC BY-SA 3.0.
Ion acceleration by the extreme electric fields produced in plasmas uses a different mechanism,
principally acceleration by the plasma sheath, a region of strong electric field that forms at the edge of aplasma. In this method, the laser ejects electrons beyond the plasma, and the associated sheath accelerates(drags) the ions along to high energies. The goal is to produce compact, ultrafast sources of energeticions. Optimizing this process requires a higher energy density in the plasma than is typical for wakefield
acceleration of electrons. In the last 10 years, high gradient acceleration of ions by the sheath electricfields has been refined and new physics regimes have been developed. Radiation pressure and magnetic
vortices have been investigated to provide high performance compact ion beams, which may be useful inmedical therapy and for electric and magnetic field probes in high energy density (HED) plasmas. A
fundamental question, in analogy with that of electron acceleration, is: How can mechanisms of highdensity laser coupling and ion acceleration be understood and controlled to efficiently produce quasimonoenergetic high energy ion beams?
The electrons accelerated by LPI are a further source of very bright x-ray beams. The electrons
oscillate transversely in the laser-induced plasma fields, and this transverse oscillation (called betatronoscillation) causes the generation of x-rays, just like oscillating current in an antenna produces radio
waves. This light has very high brightness, which means that it can be focused down to greater intensities
using less powerful lenses. (Brightness is a technical concept that is roughly the product of the beam
angular divergence and the length scale of the light source.) Another mechanism to produce x-rays is tocollide the accelerated electrons with yet another laser. In either case, one may generate bright x-ray
beams in a device much smaller than current approaches that utilize large laboratory light sources. The
resulting photons may reduce radiation dose and increase resolution for nuclear security, medicine andindustry, as well as being diagnostics for HED science. The fundamental question is: How can weunderstand, develop and control novel plasma-based radiation x-ray sources to enable new capabilities
in imaging for medicine, biology, national security and physics diagnostics?
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

The combination of high intensity lasers and particle beams in plasmas will open up new physics.
One example is nonlinear high field Quantum ElectroDynamics (nQED) with collective plasmainteractions. nQED describes how light and matter interact while incorporating both quantum mechanics
and special relativity. Under conditions of very strong light intensity, it has been predicted that the lightwill spontaneously convert to matter and antimatter, in keeping with Einstein’s famous equation E=mc2.
Over the past 10 years theoretical frameworks have been developed that predict specific signatures, show
how newly developed laser and beam capabilities can be used for initial tests, and these can advancecapabilities presently on the horizon. Work has been started to develop the required models and tointegrate these into plasma simulations. Note that related opportunities in quantum and exotic states ofmatter are described in Chapter 4. The fundamental question is: How to develop more complete
theoretical models, with the computational capabilities to capture those models, and to design
experiments for current and new laser capabilities to open up new physics frontiers?
High-level science challenges for the field of LPI have been described in reports over the past
decade, over the past decade, including the following: Basic Research Needs for High Energy Density
Laboratory Physics (2009), Frontiers in High Energy Density Physics: The X-Games of Contemporary
Science (2013), and Workshop on Opportunities, Challenges, and Best Practices for Basic Plasma
Science User Facilities (2019), as well as the preceding Plasma 2010 decadal study. These reports, and an
ongoing two-year effort started in 2018 by the Department of Energy Office of Fusion Energy Sciences(DOE-FES) to establish a long-term strategy for the field, have provided key insights to this study. The
areas addressing fundamental science challenges are intimately tied to rapidly developing advanced
capabilities in high-intensity ultrafast laser facilities. These capabilities include increasing pulse energies,
repetition rates and control, all enabling new areas of research. For example, chirped pulse amplification,
the subject of the 2018 Nobel Prize in Physics, is the basic technique used to produce short (<10s fs), highenergy (0.1–10 J) laser pulses, and has had particular impact in enabling higher laser powers. High-level
laser development challenges have been described in recent reports, including Workshop on Laser
Technology for Accelerators (2013), Workshop on Laser Technology for k-BELLA and Beyond (2017),
and Opportunities in Intense Ultrafast Lasers: Reaching for the Brightest Light (2018).
Funding for laser-plasma optics, particle acceleration and laser sources is spread over several
federal agencies. This funding is often mission or result focused rather than oriented towards investigating
the basic science that underlies the applications. For example, DOE-HEP funds development of laserplasma wakefield acceleration (LWFA) and particle beam driven plasma wakefield acceleration (PWFA)
as a path to future lepton colliders and, under its Accelerator Stewardship program, also addresses midterm applications of high-intensity lasers. DOE-FES funds ion acceleration and plasma optics as part ofits stewardship Discovery Plasma Sciences (DPS). DOE-NNSA funds laser-plasma interactions withemphasis on coupling for ICF and HED science experiments. NSF funds broad basic research in all ofthese areas, including as part of the NSF/DOE Partnership in Basic Plasma Science and Engineering. The
Naval Research Laboratory (NRL) has a broad internal program in LPI. The Air Force Office of
Scientific Research (AFOSR) funds internal and university projects on LPI and formation of plasma
filaments. Other offices within DOE, such as Basic Energy Science (BES), have occasionally funded
projects relevant to LPI, such a free electron laser (FEL) development. There are many opportunities forthese agencies to coordinate and collaborate on supporting both the fundamental science and translatingthat science to applications. This coordination and collaboration will be to the betterment of the scienceand the application.
There are strong linkages of LPI across plasma science in the underlying physics, applications,enabling capabilities, and methods (computations, diagnostics). Plasma physics linkages include resonant
excitation processes and control of the particle-wave interactions that underlie accelerators and plasma
optics. LPI can be accomplished with high precision and at high repetition rate at relatively modest costcompared to other HED systems. This provides the ability to flexibly manipulate and precisely measurestates in plasma-wave-radiation interactions, and space-time control of such interactions, that can benefit
other areas of plasma science. Access to high field physics, including nQED, has broad impact acrossscience. Newly developed precision, ultrafast photon and particle sources can serve as high resolution
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

probes and diagnostics for other plasma experiments (HED sciences, ICF), and potentially other areas
such as Fusion Materials and Technology (FM&T), and magnetized experiments. Computational methods
being developed for LPI have strong overlap across other areas of plasma science. These methods include
particle-in-cell (PIC), direct-simulation Monte Carlo (DSMC), fluid and Vlasov methods for simulating
acceleration; and 3D magnetohydrodynamics (MHD), fluid, and PIC-DSMC codes for analysis ofirradiated targets. (See Figure 3.3.) Advances in computations needed to investigate the new LPI regimes
include reduced and integrated models, the ability to capture comprehensive physics including wall andboundary effects. A further important need is to reduce barriers to entry for use of codes by non-experts.
There are many opportunities for collaborations between programs focused on LPI and those scienceareas that would benefit from LPI capabilities. This coordination and collaboration will improve both thescience and the application.
In the following sections, we discuss accomplishments, opportunities and challenges in theapplication areas of plasma optics, LPI acceleration of light particles, LPI acceleration of heavy particles(ions), bright x-ray generation and non-linear QED. The underlying science challenges to theseapplications areas include:What are the fundamental processes that occur during the interaction of ultra-intense (relativistic)laser pulses and beams with plasmas?
How can we use these interactions to generate and control energetic particle beams, and enable newphysics regimes, including addressing frontier HEP and nQED questions?
How can LPI research be translated into compact photon and ion sources that offer revolutionary
performance for medicine, national security and industry?
PLASMA OPTICS

Plasma optical techniques have beendeveloped in the last decade that can control
and improve LPI performance in regimes
beyond those accessible by conventional
means. Plasma-based optical components,
already consisting of ionized gas, havesubstantially higher damage thresholds thansolid state components and can beinexpensively and rapidly replaced, forinstance, at the repetition rate of a gas jet or
capillary. Similar to conventional optics, thetime and spatially dependent phase of a laser
pulse propagating in plasma is determined by
the refractive index—and that refractive index
is dominantly determined by the plasma
density. By controlling the spatial variation,
evolution, or nonlinearity of the plasma
density, the plasma can produce dispersion,refraction, or frequency conversion. In
principle, a plasma can be made to mimic any
solid-state optical component.

FIGURE 3.3 Using simulations to understand LPI.
Simulations showing electrostatic perturbations
driven by two-plasmon decay (TPD), a key laserplasma instability in fusion experiments. The
simulations were performed using the LPSE (Laser
Plasma Simulation Environment). The effects oflaser-bandwidth and pulse structure on TPD andmore generally laser-plasma instabilities (LPI) could
help control LPI and expand the ICF and HED
science design space. SOURCE: Physics of Plasmas
24, 102134 (2017),
https://aip.scitation.org/doi/10.1063/1.4998934.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

Plasma optical components include plasma
gratings; plasma waveguides that combat diffraction,
extending the interaction length in LWFAs; and plasma
mirrors, along with optical pulse shaping to enhance or
suppress specific dynamics. These components canincrease intensity contrast by orders of magnitude,
allowing for impulsive laser-matter interactions nearly
free of premature heating; and redirect laser pulses in
multi-stage LWFAs without degrading electron beamemittance. This advance resulted from improved
understanding of and ability to shape laser-plasmainteractions. As such, control of high intensity laser
pulses is enabled in ways not otherwise possible. Inturn, these new methods allow excitation and control ofplasma states both for investigation of fundamental
physics and applications.
Progress and Achievements

FIGURE 3.4 Focusing on the fly. A
chromatic focusing system coupled to aspectrally chirped laser pulse can be used togenerate a “flying focus”. This is a structurethat enables a laser's peak intensity to
propagate over long distances and at any
velocity—including faster than the speed oflight. A flying focus is produced by creatingplasma lenses that focus colors at different
distances with a chirped laser beam (a laser
with colors that change in time). Combining
such novel optical designs with plasmas is
opening opportunities for laser-plasma
applications including acceleration andamplification. SOURCE: Image courtesy ofDustin H. Froula, University of Rochester.

Inertial confinement fusion (ICF) was one of theearliest applications to harness high-power lasers. The
field has implemented innovative optical techniques that
produced step-changes in performance. These
techniques include efficient optical frequency tripling,spatial coherence control (phase-plates), and induced
temporal incoherence (e.g. Induced Spatial Incoherence,
ISI, and Smoothing by Spectral Dispersion, SSD).
Techniques that take advantage of the bandwidthavailable on current laser systems have been developedthat can inhibit low-frequency laser-plasma instabilities
that are detrimental to ICF. For example, stimulated
Brillouin scattering (SBS) can be avoided by detuning
the interaction between multiple laser beams or to movespeckles before the instability can grow.
ICF experiments must still navigate aroundlaser-plasma instabilities, the consequences of non-uniform laser illumination and damage by scattering
laser light into unwanted directions. Such instabilities can generate super-thermal electrons that preheat
the fusion fuel, reducing its compressibility, and seeding instabilities. Plasma optical manipulation ofplasma states, including use of bandwidth or STUD (spike trains of uneven duration and delay) pulses,
provide solutions to these issues. The emergence of high-power, high-repetition-rate (> kHz) ultrashortpulse lasers enables creation and investigation of nonlinear propagation and material interactions
governed by a combination of non-thermal and thermal modifications to matter.
Shaping of the optical drive of the plasma has been extended to techniques that control theapparent velocity. This opens new regimes in exciting Raman amplification, photon acceleration,
wakefield acceleration, and THz generation. Spatiotemporal shaping can produce laser pulses that appear
to violate special relativity. The peak intensity of a self-accelerating light beam can follow a curved
trajectory in space, while the peak intensity of a “flying focus” pulse can travel at an arbitrary velocity,
surpassing even the vacuum speed of light (see Figure 3.4). These arbitrary velocity intensity peaks result
from the chromatic focusing of a chirped laser pulse. (A chirped laser pulse has a frequency that is afunction of time or space.) The chromatic aberration and chirp determine the location and time at which
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Plasma Science: Enabling Technology, Sustainability, Security, and Explorationeach frequency component within the pulse comes to focus and reaches its peak intensity. By adjusting
the chirp, the velocity of the intensity peak driving the many plasma processes can be tuned to nearly any
value, either co- or counter-propagating along the laser axis.
Propagation of an intense laser pulse in air balances self-focusing and ionization of the air tocreate extended plasma filaments. Plasma filaments are long, narrow strings of plasma whose non-linear
properties (e.g., self-focusing) create more plasma having similar string-like properties. Experiments haveshown that a train of laser pulses can heat air through a combination of thermal and nonthermal effects,
such as thermal blooming, ionization and Raman excitation processes, leaving behind a long-lasting low
neutral density channel that can guide subsequent laser pulses. This delicate multi-physics process has
numerous applications, including enhancing the collection efficiency of photons for remote detection. In
high-repetition rate laser-material interactions, a laser pulse will interact with matter than has beenstrongly modified by the non-thermal heating of previous pulses. This heating can create periodic surface
structures, change the reflectivity and absorption, or alter the molecular composition altogether.
Orbital angular momentum (OAM) laser pulses can impart angular momentum to a plasma. Thistransfer of momentum can modify the topology and dispersion of the plasma waves produced by the laser
and the phase space of the charged particles they accelerate. For example, a laser pulse with a helicalintensity profile, or “light spring,” can nonlinearly excite a wakefield that traps and accelerates a vortex
electron beam—a beam that rotates around the optical axis. OAM can also modify the nonlinear
propagation and interaction of high-power pulses with transparent media, resulting in helical plasma
filaments or high harmonic radiation with vortex phase structure. Special phase plates are used to impartangular momentum to laser pulses.
Plasma laser amplifiers use multi-wavelength interactions to transfer energy from a long laser
pulse seed to amplify a short laser pulse. Progress has been made in the amount of energy transferred andin the gain of the short pulse. The technique could eventually provide a final power-amplification stage
for high energy applications or to operate in novel wavelength regimes.
Current and Future Science Challenges and Opportunities
Plasma-based optical components could provide the disruptive technology needed to usher in thenext frontier of laser-plasma research. Plasma optics also has the potential to enable new capabilities inbroader high-energy and high-average-power laser applications; and to enable guiding/steering andcontrolling x-rays in ways unattainable today. The unexpected features of the combination of structured
light and LPI are relatively unexplored due to the technological challenges of creating such structured
pulses. The further development of ultrafast pulse shaping techniques to manipulate the spatiotemporal
optical properties of plasmas would bring about novel laser-plasma interactions.
Laser, target and diagnostic capabilities, together with simulation, are enabling understanding andcontrol of plasma states that will enable plasma optical components to have increasing impact. Already,plasma waveguides are core parts of advanced particle accelerators. Other plasma optics components,
while still in the early stages of development, have been successfully demonstrated in experiments that
include: lenses, waveplates and polarizers, q-plates, beam-combiners, compressors, and amplifiers.
Advancing these methods will provide access to new laser and plasma parameter regimes. A critical needto achieve these goals is the development of novel diagnostics that measure not only the bulkhydrodynamic properties of the plasmas but also the underlying particle distribution functions. Diagnostic
accomplishments and needs are discussed below.
Concepts have been developed for further control of instabilities using broad bandwidth lasers.
Broad bandwidth lasers for ICF could deliver pulses with the temporal incoherence necessary to suppress
high frequency instabilities like two-plasmon decay and stimulated Raman scattering, while also
providing smoothing to mitigate disruption of the capsule. Generally speaking, the broad-bandwidth
mitigates laser plasma instabilities by detuning the interaction between multiple waves or incoherently
drives many small instabilities instead of a single coherent instability. Bandwidth can also be used to
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

coherently create controlled trains of shorter pulses (in the ps range) within the longer pulse envelope (inthe ns range). If these manipulations can be performed faster than the growth of electron plasma waves,the train of pulses can be used to control the excited plasma state. This STUD concept, introduced above,
opens the possibility of coherent laser control of plasma states and hence of laser coupling and transport.
STUD and other sculpted time dependent wave structures could further be harnessed to drive far more
controlled nonlinear responses in plasmas. Experiments using high repetition laser pulses aided bymachine learning could identify time sequences and profiles of laser pulses that could tame the highly
nonlinear kinetic and chaotic responses exhibited by plasmas driven strongly by laser beams over long
periods of time. Such techniques could mitigate laser plasma instabilities by modulating the intensity toshrink individual hot spots and disperse hot spot patterns. This well controlled laser illumination could
further help steer the flow of energy in plasmas to self-organized and self-sustaining states far fromequilibrium or make and control plasma structures on demand to direct photons as in plasma optics.
Spatiotemporally structured ionizing laser pulses enable control over the velocity of an ionization
front, thereby allowing the tailoring of the target plasma for acceleration. Controlling the plasma rise andfall and its width as a function of longitudinal distance allows improved matching of the pump laser pulsethat creates the accelerating electric field and it controls the transverse focusing of the electron beam in
beam-driven systems. There are numerous opportunities here for finding more optimal systems or new
systems altogether.
Control of plasma optics is likely to advance several other plasma-based applications, including
Raman amplification, photon acceleration, relativistic mirrors, and THz generation. Orbital angularmomentum may offer an additional degree of freedom through which laser-plasma instabilities can be
mitigated or controlled. As in cross-beam energy transfer, multiple interacting beams could drive aspectrum of plasma waves each with a different value of orbital angular momenta instead of a single
coherent plasma wave with no angular momentum. A next-generation high-power laser with plasma
optics could deliver extremely high intensity pulses with unprecedented control of plasma states and laser
propagation. These methods could transform the landscape of laser-plasma interactions, from acceleration
to fusion to applications such as remote sensing and X-ray sources.
PLASMA ACCELERATION OF LIGHT PARTICLESOver the past decade, compact plasma-based accelerators have progressed from first
demonstrations to a well-developed field. (See Figures 3.5-3.7.) These devices utilize the strong
longitudinal electric fields present in laser or particle beam driven plasma waves to provide accelerating
gradients (energy gain per unit length) that are orders of magnitude greater than those sustainable inconventional metallic accelerating structures. Electron bunches that are loaded (or injected) into theplasma wake of the driving pulse can gain energy at rates of 1-100 GeV/m. Milestones that were achievedprior to the previous Plasma 2010 decadal survey included the injection and acceleration of plasma
electrons in a laser-driven plasma wakefield accelerator (LWFA) in 2004. The electrons were accelerated
up to 100 MeV over a distance of millimeters, producing a mono-energetic beam with tens of picoCoulomb’s (pC) of charge. In 2006, particle-driven plasma wakefield accelerators (PWFA) provided up
to 30 GeV gain in energy to the most highly accelerated particles of a wake-driven electron beam over a
distance of one meter. These experimental results were the outcome of decades of work since theinception of the field in the late 1970s, and demonstrated clearly the promised large accelerating
gradients. In the ensuing decade, the field has grown significantly and great progress has been madetoward realizing the first application-ready plasma accelerators. There have been multiple demonstrations
that achieve nearly 10 GeV of energy gain in a single LWFA and PWFA. Several sophisticatedtechniques have been developed to improve the quality of the outgoing electron bunches. Based on thepromise shown by plasma accelerators, the DOE roadmap Advanced Accelerator Development Strategy
Report was developed in 2016 that provides a plan for realizing plasma-based high-intensity X-ray photon

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

FIGURE 3.5 Laser Acceleration of Electrons to 8 GeV. (left) Compact high energy laser-plasma
wakefield electron accelerators are created when an intense short pulse laser is focused plasma, herecreated in a capillary tube. Scaling to higher electron energies requires longer plasmas at lower plasma
densities, which in turn requires new techniques for guiding the laser pulse. (center) Use of a laser tolocally heat a capillary discharge plasma steepens the radial plasma density profile, enabling guiding at
lower density and over longer distances. (right) This improved capability enabled production of 8 GeVelectron beams at Lawrence Berkeley National Laboratory in just 20 cm of plasma, an energy
conventional linear accelerators would require the better part of a kilometer to produce. SOURCE:
Courtesy of Anthony Gonsalves, Lawrence Berkeley National Laboratory; middle image from
Gonsalves et al., Phys Rev Letters 122, 084801 (2019).

FIGURE 3.6 A hollow channel plasma wakefield accelerator. (left) Image of a bunch of positrons(blue), the antimatter siblings of electrons, travels down the center of a tube of plasma (orange), andcreates a wake in the walls (shaded orange) which accelerates a trailing positron bunch. (right) Data
from SLAC FACET experiments shows an energy loss in the driving beam consistent with a high fieldof 230 MV/m excited in the plasma channel. The process will also work using a laser or electron driverand a positron witness bunch. The experiment is being used to engineer the plasma in a way that decouples the accelerating and focusing forces to provide a path for high-gradient stable positron
acceleration. SOURCE: Left: Courtesy of Greg Stewart, SLAC National Accelerator; right: S. Gessner,
E. Adli, J. Allen, et al., Demonstration of a positron beam-driven hollow channel plasma wakefield
accelerator. Nat Commun 7, 11785 (2016), https://doi.org/10.1038/ncomms11785.
sources and ultimately, a plasma-based high energy physics collider. A TeV-class electron-positron
collider based on plasmas would potentially reduce the size of the machine from tens of kilometers tohundreds of meters, and with lower cost.
Progress and Achievements
Plasma-based accelerators are now able to regularly provide multi-GeV energy gain to monoenergetic beams of 100 pC to 1 nC in a single plasma accelerator. (An electron bunch of 1 pC of charge
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

contains 6  106 electrons. A 1 nC bunch contains 6  109 electrons.) LWFAs have utilized high peakpower laser systems (100 TW to 1 PW) fired into plasma sources that are centimeters in length withplasma densities of ~1017 to 1019 cm-3. PWFAs used up to ~20 GeV electron drive beams with ~1 nC of
charge in plasma sources roughly 1 meter in length with plasma densities of ~1016 to 1017 cm-3.
Several laboratories are now able to regularly accelerate 10–100 pC of charge to energies of 10–
100 MeV in multi-millimeter-length, high-density gas jet plasma sources using laser pulses with a moremodest peak power (10–100 TW). These LWFAs often rely on the relativistic self-SPU
focusing of the laser pulse in the high-density gas jet to achieve laser intensities that would beinaccessible by other means. Such gas jet LWFAs, though more modest in terms of energy and beam
charge, have led to vibrant and growing plasma accelerator research at university laboratories the world
over. While national laboratories have continued to carry out most of the research at the energy frontier,much of the fundamental physics research has been conducted at smaller university laboratories. Thissynergistic research has, in turn, rapidly increased the pace at which the field is advancing.
The record for energy gain in a LWFA was set at the BELLA (Berkeley Lab Laser Accelerator)
facility at Lawrence Berkeley National Laboratory (LBNL) in 2019, accelerating about 10 pC of electrons
from rest to 8 GeV in a 20 cm-long capillary discharge plasma source, driven by a ~0.85 PW laser pulse.
This result was achievable thanks in large part to the development of an advanced capillary discharge
plasma source that provided a guiding channel for the wake-driving laser pulse. (See Figure 3.5.) The
plasma waveguide was generated by pre-heating the discharge plasma column with a separate nanosecond
laser pulse ahead of the femtosecond wake-driving pulse, deepening the channel that is formed naturally
through hydrodynamic expansion of the initial plasma filament. This structure enabled guiding of thewake-driving pulse over a longer distance, thereby increasing the total energy gain of the electron beam.
The highest energy gain achieved for a low energy spread PWFA bunch was at the Facility for
Advanced Accelerator Experimental Tests (FACET) at the SLAC National Accelerator Laboratory in
2015. This demonstration provided 9 GeV of energy gain to ~100 pC electron bunch with an initialenergy of 20 GeV in a 130 cm-long lithium heat pipe oven plasma source driven by a 20 GeV, ~1 nC
electron bunch. The energy transfer efficiency from the driver to the accelerated beam was as high as 30%
in the FACET PWFA experiments. This efficiency is a critical parameter in determining the power costfor future high energy, high repetition rate applications. Coupling of two high-energy LWFAs (known as“staging”) was demonstrated for the first time at BELLA in 2018 by refocusing the electron beam
between the two plasma stages with an active plasma lens. (See Box 3.2.) This provided roughly double
the energy gain to the electron beam compared to the acceleration received in a single plasma stage. The
ability to perform efficient staging is also critical to future high energy applications in order to reach thefinal target energy. Overall, great advances have been made in the past decade in providing high energy
gain with low energy spread for a significant level of charge in both laser-driven and particle beam-driven
plasma accelerators.
Significant strides have also been made in improving the quality and stability of the accelerated
beams. (See Figure 3.7.) The quality of the accelerated electron beam in a LWFA or PWFA is determinedby the trapping and focusing dynamics in the plasma wake. There are multiple methods of controlling theelectron beam injection process to produce output electron beams with minimal energy spread andemittance. (Minimizing emittance means containing electrons in the smallest volume in the 6-D phasespace of spatial coordinates and velocity.) In these techniques, background electrons move fromuntrapped orbits that are part of the fluid motion sustaining the plasma wave to trapped orbits comprising
the accelerated electron bunch. Laser-based and density-gradient-based triggering of particle trapping has
been a topic of active research and has enabled a continuous improvement in beam quality. Energy
spreads of less than 1% in the accelerated beams and emittances of less than 1 mm-mrad have been
regularly achieved, comparing favorably with conventional accelerators.
SLAC’s FACET facility was able to provide high energy (20 GeV), high charge (~1 nC) positron
beams in the past decade and used them to explore the acceleration of positrons in beam-driven PWFAs.
Positron bunches were successfully accelerated in a hollow channel PWFA, producing a few hundred
MeV gain in energy. (See Figure 3.6.) To achieve this outcome, custom diffractive optics focused a ~1
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

TW laser pulse into a non-diffracting, high-order Bessel intensity pattern that was sustained over tens ofcentimeters to ionize a tube of neutral gas in a flooded vacuum chamber, thereby forming the hollow
channel plasma source. The transverse wakefield theory was studied and confirmed by inducing
transverse kicks to the beam prior to entering the hollow channel PWFA. In another experiment at
FACET, a single, high energy (20 GeV), high charge (~1 nC), short (~30 µm) positron bunch waslaunched into a 30 cm-long lithium heat pipe oven plasma source. The results surprisingly produced amono-energetic positron beam that gained several GeV of energy, revealing a previously unpredicted
regime of non-linear positron PWFA physics. With the assistance of particle-in-cell (PIC) computer
simulations using the code QuickPIC, the dynamics of this interaction were understood. The mechanism
was shown to rely on a longitudinal and transverse self-loading of the wake by the positron beam.
At CERN (European Organization for
Nuclear Research), the Advanced Proton Driven
Plasma Wakefield Acceleration Experiment(AWAKE) experiment demonstrated the ability
to accelerate electrons in a high-energy proton
beam-driven plasma wakefield accelerator(PDWFA). The motivation for building such amachine is to take advantage of existing
infrastructure to produce high energy, highcharge proton beams and to transfer that energy
to an electron beam over a relatively shortdistance. This approach could produce lepton
collisions at high energy without the need to
FIGURE 3.7 Injecting particles in a Laserbuild a new, 30 km long linear accelerator that
Plasma Accelerator. Plasma accelerators arewould be needed if using conventional
driven by plasma waves at the tens of micron
technologies. Another attractive feature of thescale, creating the need for new methods to inject
PDWFA is that it requires only one (albeit long)the particles that will be accelerated. Injection
plasma stage, avoiding the complications
methods include several techniques using multiple
associated with staging. A challenge of PDWFA
laser pulses and/or density structures to create theis that the drive beam needed is significantly
injector inside the plasma. Here a simulation
longer than the wake period.. The problem isshows injection of particles (yellow) via
mitigated by inducing a laser-triggered beaminteraction between the plasma wakes (blue)
plasma instability that segments the proton beam
driven by two laser pulses (white) modelinginto “bunchlets” that are spaced at the plasma
experiments at the Extreme Light Laboratory,
period, thereby creating a wakefield train that
University of Nebraska, Lincoln. Such methods
can then be loaded with a train of electron
promise unprecedented acceleration phase control,bunches to be accelerated. Another challenge
as well as the injection of electrons into multiple
presented by PDWFA is the efficient coupling ofaccelerator buckets. SOURCE: Courtesy ofan electron beam into the plasma accelerator. In
Grigory Golovin and Donald Umstadter,spite of these challenges, a proof-of-principle
University of Nebraska-Lincoln.
experimental demonstration has beenaccomplished, with the acceleration of ~10 pC of electrons by 2 GeV over a distance of 10 m.
A key to successful plasma accelerator applications is the ability to produce bright (i.e., highcharge, high energy, low emittance, low energy spread, ultra-short) electron beams. The outsized
longitudinal electric fields in plasma accelerators can serve to achieve this goal through the process ofcontrolled electron beam injection. The main principle of injection in a plasma accelerator is to trap a
dense, small cluster of electrons in the plasma wake and to accelerate them to ultra-relativistic speeds as
quickly as possible. Plasma electrons can be directly trapped in the breaking plasma wave at the rear of
the wake bubble, a region where plasma electrons are completely evacuated. However, the stochastic
nature of this process often leads to significant fluctuations in the properties of the beam that is produced.
Researchers have therefore devised and begun experimenting with various forms of controlled injection.
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

One such method is to produce a sharp “density downramp”—that is, a rapid longitudinal decrease inplasma density near the start of the plasma source. This results in a rapid elongation of the plasma wake,permitting local plasma electrons to be preferentially trapped and suppressing the subsequent trapping ofadditional electrons further downstream. Another method utilizes a plasma source generated by a lower
ionization threshold (LIT) gas, such as hydrogen, to form the plasma accelerator in the presence of abackground of neutral high ionization threshold (HIT) gas, such as helium. A wake driver is sent into the
LIT plasma source, and a small volume of the HIT gas is ionized directly inside the blowout wake
following the driver. (The blowout regime refers to plasma electrons being completely exclude frombubble-like region behind the wake driver.) The ionized HIT gas electrons are then trapped and rapidly
accelerated to produce an ultra-high brightness beam. Ionization mechanisms that have been used in such
experiments include a dedicated laser pulse, and the strong electric fields of the wake-driving electron
beam.
There are now many university laser labs capable of carrying out fundamental LWFA research,
and a growing number of national laboratories throughout the world with facilities appropriate for—andin many cases solely dedicated to—energy-frontier plasma accelerator research. Petawatt laser systems to
be used for high-energy LWFA research in the next decade, include BELLA at LBNL, ZEUS/Hercules atUniversity of Michigan, DIOCLES at the University of Nebraska, and the Texas Petawatt Laser System at
the University of Texas at Austin, as well as many facilities in Europe and East Asia. High energy PWFA
research facilities in the next decade will include FACET-II at SLAC, the Advanced Test Facility (ATF)
at Brookhaven National Laboratory, FLASHForward at DESY (German Electron Synchrotron), andAWAKE-II at CERN. There is ongoing research at various 100 TW-class LWFA laboratories and lower
energy accelerator facilities. This increases access for universities, to facilitate a more widely distributed
base of fundamental research on LWFA, PWFA and PWFAs driven by LWFA electron beams.
Sophisticated diagnostics have been developed to more directly probe the plasma accelerator
itself. One of the more commonly used techniques, typically referred to as “shadowgraphy”, analyzes thephase pattern imprinted on a low energy, ultra-short laser pulse by the plasma. This can be used to study
the plasma source profile prior to the arrival of the wake driver, though more advanced co-propagating
schemes have been able to study the structure of plasma wake itself. The latter application currently
represents the most direct method of observing these speed-of-light wakes, and their use will likely
expand in the coming decade.
Due to the great challenge of developing and applying experimental diagnostics for plasma
accelerators, theory and computer simulations have been a cornerstone in the research portfolio over the
past decade. Various PIC and related codes, including OSIRIS, VSim, QuickPIC, WARP, and EPOCH,
have provided deeper understanding into the physical processes than could have been gained otherwise.
These tools have been used both to design experiments and to interpret experimental results. Computer
simulations have also played a major role in studying the limits of the capabilities of plasma accelerators,
helping to shape the research roadmaps and community consensus on where to prioritize research efforts.
As the power of parallel and device-based (GPU) computing has increased over the years, so too has the
speed of the major codes. The concurrent improvements in computing hardware and in advanced
algorithms that are able to take advantage of the new hardware have permitted simulations of exceedinghigh detail and scope. The quality and scale of these simulations would have been difficult to predict in
the prior decade.
Current and Future Science Challenges and Opportunities
The major milestones that are likely to motivate and guide the next decade of plasma accelerator
research include the production of high quality electron beams that can be utilized for X-ray free electron
lasers (X-FELs) and other photon sources. These would be electron beams with sufficient control andreproducibility that they can be used in production-level applications, requiring elimination of instabilities
and kilohertz-level repetition rates. Meeting these goals will require the mastery of controlled injection
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

techniques, improved loading of the plasma wake to minimize beam energy spread, beam emittancepreservation at the plasma-vacuum interface, and the highest possible energy transfer efficiency.
Alongside research motivated by these goals will be continued research into more novel applications,such as positron acceleration and proton-driven plasma accelerators. In addition, improvements in staging
efficiency will need to be studied and perfected. These will drive the continued development of plasmas
accelerators for particle colliders to address the needs of the high energy physics (HEP) community.
A community roadmap has been developed to guide efforts towards enabling photon source
applications in the nearer term and the challenging requirements of future colliders. (See Figure 3.8.) If
the goals of the roadmap are realized, during the next 10 years we will achieve improved control ofparticle injection and laser guiding to enable phase space shaping and efficiency, 10 GeV laser particle
accelerator modules, staging of multi-GeV modules, controlling emittance, and demonstration of positron
acceleration. To facilitate these science advancements, lasers having repetition rates of kHz and average
powers of kW will need to be developed to enable higher precision experiments by leveraging active
feedback control. Several different methods of initiating electron trapping in the pondermotive potentials
have been proposed to improve the beam quality (e.g., beam emittance and brightness) significantly
beyond the current state-of-the-art, and it is likely that others will be discovered. Research is ongoing on
how to efficiently excite large amplitude nonlinear electron plasma waves over long distances. Achieving
this goal requires greater understanding of the nonlinear laser-plasma interaction, including energy
deposition and laser propagation physics. The latter depends on many processes, including relativistic
self-focusing, pondermotive self-channeling, interaction with preformed plasma channels and laserexcited plasma wakefields, and short-pulse laser-plasma instabilities, such as laser self-modulation andhosing (defined below). Plasma source development will be a major topic of research. Multiple

FIGURE 3.8 The LWFA Roadmap. The plasma-based accelerator field benefits from having a
guiding roadmap for advanced accelerator research and development. (Left) Representative
development goals from the roadmap for laser-plasma acceleration which is similar to that forparticle bunch driven systems. SOURCE: Advanced Accelerator Development Strategy Report:
DOE Advanced Accelerator Concepts Research Roadmap Workshop, 2016. (Right) Status of thedevelopment effort.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

FIGURE 3.9 Primary accelerator laser driver parameter ranges of interest for plasma accelerators.
The boxed lines two and three could be part of a single development track. The other two classes
would be separately developed. Note that additional beams are desired for injection and guiding
control but are typically at lower energy and do not hence drive overall laser development. SOURCE:
Courtesy of Cameron Geddes, Lawrence Berkeley National Laboratory.
techniques are being considered for improved plasma sources, including laser ionized guides, discharge
and helicon plasmas, using gas jets, capillary tubes, clustered targets, and alkali heat pipe ovens.
The topic of hosing has garnered much theoretical interest over the past decade but has yet to bethoroughly studied experimentally. Hosing is an instability driven by head-to-tail transverse wakefield
effects acting on the accelerated electron beam that can lead to catastrophic beam break up. As LWFA
and PWFA beam quality continues to improve, the beams will become more sensitive to this instability.
Some theoretical solutions have recently been proposed and are currently under study using PIC
simulations. One such solution utilizes a modest degree of ion motion within the blowout cavity, which
can suppress the resonance in the beam’s transverse motion that leads to hosing. Further work in this area
is needed.
A goal of a future high energy physics lepton collider is to collide counter propagating electron
and positron beams with center of mass energies of and beyond 1 TeV. Plasma accelerators are able toaccelerate positron beams, although it poses significant challenges. In the highly nonlinear blowout
regime used in most high energy plasma accelerators, the plasma electrons are completely evacuated in a
bubble-like region behind the wake driver. This leaves behind a column of positive ions that can provide
transverse focusing to a negative electron beam due to the Coulomb forces. Unfortunately, positively
charged positron beams are defocused by the positive ion column. Nonetheless, significant progress has
been made toward high gradient acceleration of positron beams in the past decade, both in theory andexperiment. One theoretical proposal is to accelerate positrons in the linear wake regime, which, unlike
the blowout regime, responds symmetrically to electrons and positrons. Here challenges include
overcoming scattering in the plasma and the natural tendency for the beam to focus in the plasma until it
drives a nonlinear wake and ruins the beam. Another proposal is to use hollow channel plasma
accelerators, which avoid the production of an ion column altogether. Challenges for this scheme include
the minor transverse asymmetries in the beam profile or position with respect to the plasma channel thatcan lead to the buildup of strong transverse wakefields that induce a beam break up (BBU) instability,
which again ruins the beam.
To address future high energy physics collider applications, staging of multiple plasma
accelerators in series will provide the highest system gradient and is desirable in managing the charge andphasing of the bunches of charge that are accelerated. This challenging process has been demonstrated byaccelerating electrons to the 0.1 GeV level using a 100 TW laser driver. Multi-GeV experiments are inpreparation (See Box 3.2). Simulations indicate that managing the pulse shape of laser drivers can achieve
high efficiency acceleration and high beam quality.
Major efforts are needed to develop more advanced plasma sources over the next decade in orderto achieve most of the aforementioned goals. (See Figure 3.9.) It is likely that there will be no “one size
fits all” solution, but rather there will be specialized plasma sources that serve particular goals. For
example, a laser-ionized gas plasma source may be well suited for electron beam-driven PWFA purposes,
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

whereas a helicon plasma source may be better for a proton beam-driven PDWFA. Continuous evolutionof gas jet plasma sources for LWFA are likely to lead to improved injection control and beam extraction
capability for lower energy beam sources, while advancement in semi-hollow plasma waveguides willlead to greater beam energy and quality for high energy beam sources.
Progress in plasma acceleration and X-ray sources has been driven by parallel and mutually
reinforcing advances in laser (and particle beam) driver technologies and deeper understanding of thelaser-plasma and beam-plasma interaction physics. In this regard, the maintenance and upgrade ofexisting facilities and facility networks is essential. However, the improving the repeatability, reliability,
and repetition rate of plasma accelerators depends on the development of new laser technologies forincreased precision, control and repetition rate. (See Figure 3.9.) There are three areas with distinct needs
for laser development. For colliders and many photon sources, the main stages must operate at highefficiency with charge and laser energy requirements perhaps uniquely set by the interaction point
physics. The properties of these lasers may differ from those of the injector stage that may benefit fromlong wavelength drivers. For HEP applications, stages have tens of GeV acceleration are likely required,while for HED probes, electron bunches having high charge are of interest. Both applications motivate
higher powers but perhaps different architectures. For low energy applications such as medical andultrafast electron diffraction, laser systems have pulse energies of a tens of mJ and pulse derations of a
few-fs systems are needed. Laser technology is discussed in the section on Facilities.It is important fortheoretical models and computer simulations to continue improving in terms of physical accuracy (e.g.,
suppression of artificial numerical instabilities), to reduce computational cost, scalability, and include
more physics to help solve the more challenging problems facing the community in the next decade. One
area that needs to be addressed is in the modeling of plasma sources, which has received less attention
compared with the acceleration process. These improved models will help in the development of plasma
targets with precisely shaped density profiles, using methods that have strong overlap with low
temperature plasmas to, for example, match the laser and particle pulses into the plasma. End-to-end
simulations of plasma accelerator systems that are capable of resolving detailed dynamics within theelectron beam and (where appropriate) laser pulse will be required. In addition, there is a call formodestly simplified simulations that can be run with sufficient speed so as to provide rapid feedback torunning accelerator systems in real-time. All of these modeling goals are extremely challenging and will
require deliberate effort and investment to achieve. Deliberate investments in this area would produce amuch needed improvement in the ability to predict and understand the behavior of actual, physical plasma
accelerator systems.
Particle acceleration using plasmas is rapidly progressing in terms of beam quality, stability, anddiagnostics, and in the important physical understanding that is the basis for improving performance. The
next steps in advancing the field include the transition to kHz repetition rates which will enablestabilization and precision, and application relevant average powers. Taking these steps will require newlaser technologies. Progress is being made towards meeting the challenge of phase space shaped particle
beam generation and manipulation of ultra-bright beams, and the applications these capabilities would
enable. Advanced plasma accelerators and photon sources will enable advances in fundamental science aswell as society benefiting applications, from compact TeV class HEP colliders to medical imaging
technologies.
LPI ACCELERATION OF HEAVY PARTICLES (IONS)
Laser-driven acceleration of ions has a long history, starting with the acceleration scheme
proposed by Veksler in 1957, and has become a very active area of research worldwide. (See Figure
3.10.) In particular, high-intensity ion beams driven by short pulse lasers have emerged as an importantarea of plasma research. Ion acceleration mechanisms are different from those for light particles becauseof the different dynamics. A light particle at 100 MeV is ultra-relativistic, whereas that energy is very

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

sub-relativistic for a heavy particle. One
cannot easily trap sub-relativistic
particles in the near relativistic plasma
waves produced by laser-plasmainteractions, and so a different
mechanism is necessary.
The methods of ion acceleration
include target normal sheathacceleration (TNSA), shock wave
acceleration, and mechanisms that rely
on volumetric laser plasma interaction
due to relativistically induced
transparency and radiation pressure. The
FIGURE 3.10 Advances in Proton Acceleration.
most studied mechanism, TNSA, works
Recentinvestigations into proton acceleration withby using the plasma sheath, which forms
multi-ps, kJ-class lasers have revealed the role ofat a plasma boundary, in this case a
new acceleration mechanisms such as Direct Laser
narrow plasma that comes from hitting a
Acceleration (DLA) and the time-dependence offoil with a laser. The radiation pressure
short-pulse laser-matter interactions to accelerate
pushes the electrons out the far side; theparticles. This plot of maximum proton energy as acharge imbalance creates a plasmafunction of laser intensity shows the 5-10 times
sheath that accelerates the ions. In thehigher proton energies measured on the NIF-ARC
last 10 years, high gradient acceleration
relative to other short-pulse facilities at sub-ps pulse
by the sheath fields created in dense
lengths at comparable intensities. SOURCE: Mariscal
plasma targets has been refined into a
et al., Phys. Plasmas 26, 043110 (2019)
controllable technique. Motivating thishttps://aip.scitation.org/doi/10.1063/1.5085787.
research are numerous potential
applications discussed below.
Laser-driven ion accelerators are projected to have multiple applications. Biomedical applications
include cancer therapy and production of isotopes for Positron Emission Tomography (PET). Laserdriven ion beams can also be a path for producing fusion energy through fast ignition. They could enable
compact neutron sources for security and industry, advanced proton radiography and isochoric heating forhigh energy density science, and ultrafast beams for radiation damage and single event effects. Once theions are accelerated by the laser-irradiated target, the beam has to be transported and delivered based on
the requirements of a specific application. A major goal is to design a system whose ion beams can beused for applications, the challenges for which are similar to those faced in accelerator physics andsignificantly more research is required in this area.
Progress and Achievements
The ion acceleration field recently made major advances due to the availability of ultrahigh power
lasers with focused intensity up to 1022 W/cm2, and laser technologies that allow a temporal intensity
contrast of 14 orders of magnitude. Maximum proton energies approaching 100 MeV have been achieved
experimentally using ultra-thin targets. These experiments have produced proton beams from a variety oftargets, ranging from nanometer to micron scale foils of solid density, to near-critical plasma density

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

FIGURE 3.11 The future of ion acceleration. New regimes of laser-driven ion acceleration and highperformance are becoming accessible. (left) The parameter space of the laser intensity (W/cm2) vssurface density nel0 of the target (ne is the electron density in the target and l0 is the target thickness).
PW-class laser systems enable access to new regimes such as radiation pressure and magnetic vortices.
(right) The maximum proton energy vs normalized laser intensity. Experiments (black, blue, and red)
are shown along with simulations projecting future regimes (purple). SOURCE: Left: Courtesy of PaulMcKenna, University of Strathclyde, Glasgow; S.S. Bulanov, E. Esarey, C.B. Schroeder, S.V.
Bulanov, T.Z. Esirkepov, M. Kando, F. Pegoraro, W.P. Leemans, Radiation Pressure Acceleration: thefactors limiting maximum attainable ion energy, Phys. Plasmas 23, 056703 (2016).
targets (see Figure 3.11). Recent results from large laser facilities (National Ignition Facility-NIF,
Advanced Radiographic Capability-ARC and the Omega EP laser at the University of Rochester) haveshown that a dramatic increase of proton energies can be achieved by increasing the laser pulse duration.
(See Figure 3.10.)
A technology advance that has had a transformational impact on ion acceleration is the use ofplasma mirrors (see section on plasma optics). Plasma mirrors made it possible to dramatically reduce thelaser pre-pulse, which allowed ultra-thin and structured targets to remain intact without losing theirstructural integrity prior to the arrival of the main part of the laser pulse. Plasma mirrors enabled theexperimental demonstration of mechanisms relying on relativistic transparency in ultra-thin targets.
Another breakthrough is the development of novel target designs to better couple laser energy to thetarget. These include nano-structured targets that enable one to reduce the average target density. There
are also targets with a structure whose size is comparable to the laser wavelength. These targets enable
guiding of the laser pulse without defocusing. Such features have been utilized to increase coupling andperformance of ion acceleration regimes. Recently developed liquid crystal thin-film targets, together
with liquid and cryogenic jets, can enable higher repetition rate experiments, which important as PW
lasers have made the transition from shots per day to shots per second. (1 PW = 1015 W.) The same
approach can be used for plasma mirrors.
The results obtained in the last 10 years for ion acceleration demonstrate a high level of synergy
between theory, computer simulations, and experiments, which will be a prerequisite for all futureadvancements in the field. The rapid development of high-performance computing resources that
occurred over the last decade enabled fully 3D kinetic simulations in many regimes of laser-plasmainteractions relevant to ion acceleration. This has had a tremendous impact since 2D simulations wereunable to capture the ion energy gain by a quasi-static plasma electric field. 3D simulations made it
possible to provide quantitative predictions for meaningful comparisons with experimental results. It has
also been shown that kinetic simulations might have to be coupled to hydrodynamic simulations in order

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

to reproduce the physics that takes place at lower intensity prior to the arrival of the main laser pulse. Thisapproach has produced results that can quantitatively reproduce experimental results.
Current and Future Science Challenges and Opportunities
There are many challenges and opportunities in the field of heavy particle acceleration. Multiple
new regimes have been proposed for the next generation of laser systems with higher power and/or
intensity and better contrast. These regimes are expected to enable a significant increase in ion energies.
They are also predicted to deliver mono-energetic beams. Novel and efficient acceleration regimes havebeen proposed. To be useful for applications, energies have to be increased, and the systems have to
become more stable. This leads to technical challenges as well, in the development of targets and otherareas. This is an opportune time to address these challenges, with increased access through LaserNetUS,
new high-power lasers in the European Extreme Light Infrastructure and Asia, and the opportunity for anext generation of domestic facilities.
Application challenges include stable ion acceleration with well-controlled and predictable ion
beam parameters. Two particular challenges are increasing ion energy gains well beyond 100 MeV (this is
the key to many applications since the stopping distance is directly correlated to the energy) and thegeneration of mono-energetic ion bunches with charge in the nC range. Even though multiple theoreticaland computational models predict such parameters, it has not been possible to experimentally demonstratethese values with currently available laser technology. While experimental results exhibit a promising
trend towards higher ion energy, further improvements in technology are necessary to achieve thepredicted ion acceleration performance. This will require a multi-faceted approach that involves further
developments in both laser technology and targets to fully exploit effects such as relativistic transparency,
radiation pressure, and magnetic vortices. At the same time, these topics advance the fundamental plasma
science of laser-plasma coupling, heating, and acceleration.
Technological challenges include progress in targets, in laser contrast and intensity. Advanced
targets, such as those with structure, have shown great promise in terms of improved and well-controlledlaser energy coupling to the target. However, these targets remain expensive and the cost may become
prohibitive for experiments with high-repetition rate laser systems, and certainly for applications. A
challenge is to significantly reduce cost while improving target control. In the absence of reusable targets,
technologies must be developed for replacing the targets at an appropriate rate, which may include
evolution of liquid crystal or liquid jet targets. Another important technological challenge is to increaseon-target laser intensities with very high contrast. Multiple ion acceleration regimes with uniqueproperties have been predicted at intensities that are yet to be reached experimentally. Hence, theupcoming development of multi-PW laser systems in a variety of pulse duration regimes is important, as
are methods for laser contrast and pulse shaping in space and in time.
Theory and simulations predict that a PW-class laser system can generate ion beams with a maximum energy of several hundred MeV. Further scaling to systems at the tens of PW level is of greatinterest and an opportunity for future facilities. A breakthrough in laser-driven ion acceleration is
expected once the high-power high-intensity laser facilities at the European Extreme Light Infrastructure(ELI NP) and ELI Beamlines become available to users, delivering previously inaccessible laserparameters. These laser systems will enable experimental access to new regimes that have been explored
only via numerical simulations and analytical theory. Significant increases in ion energies and charge will
likely open up opportunities in biomedical research fast ICF ignition, compact neutron sources forsecurity and industry, advanced proton radiography and isochoric heating for high energy density science,
hadron cancer therapy, ultrafast beams for radiation damage and study of single event failure effects inelectronics, and drivers and probes for the studies of warm dense matter and HED physics. To enable
these opportunities, major prerequisites are not only high performance but also reliable and reproducible
beam characteristics.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

FIGURE 3.12 Roadmap for ion acceleration. The roadmap for ion accelerations has several stages.
These stages include: the laser system, target development and ion beam delivery across componentsof the integrated laser-driven ion accelerator system, and potential applications. SOURCE: Alexey
Arefiev, UCSD; Adapted by Miriam Holtzman from J. Schreiber, P.R. Bolton, and K. Parrodi, Rev.
Sci. Instrum. 87, 071101 (2016).
The ion acceleration community has identified a path forward to achieve many of these goals. A
road map towards an ion accelerator based on laser-driven plasmas is shown in Figure 3.12.
BRIGHT X-RAY GENERATION
A bright beam is one with a large amount of energy in a small region of phase space—that is,short time, small dimensional, and with small angular spread. Because of phase-space volume
preservation, a brighter beam can be manipulated more easily to place a large amount of energy into asmall physical volume. Said another way, less powerful lenses are needed to focus the energy into aparticular volume. As a result, brighter beams are more effective for diagnostics, because they provide
greater reactivity in a smaller volume. Light generated through laser-plasma interactions is naturally very
bright in part because it is produced in a small volume, so that with some directionality, it then occupies asmall phase space volume.
Compact photon sources with narrow divergence, producing femtosecond bursts, are enabled byplasma acceleration of electrons. Broadband betatron X-ray emission results from the betatron oscillationsof particles in the plasma and/or laser fields and is a diagnostic of the beam properties inside theaccelerator. Nearly monoenergetic Compton, or Thomson, scattering of a laser beam from the particle
beam produces tunable, narrow bandwidth X-rays of higher energy and flux than betatron radiation, and
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

can extract detailed beam evolution
information for studying beaminteractions with plasma waves.
Coherent free-electron lasers are being
developed using conventional magnetic
undulators (or wigglers), with future
concepts for compact plasma undulators.
Coherent X-ray emission can also becreated in plasmas via population
inversion and from harmonics of laser
field generated in plasma interactions. In
these cases, plasma optics is an important
ingredient. Control of these mechanisms
and photon sources requires precision
shaping of the laser pulses. Additionally,
one must have sensitive control of theplasma profile, preparation, and pumping
by the laser pulse.
High performance X-ray lightsources enable precision measurement inmaterials science, industry, security,
nuclear nonproliferation, and medicine.
Plasma-based X-ray and EUV radiation
sources are both important frontiers inplasma physics with broad application,
and an enabling technology to provide
diagnostics (and potentially pumps) for
high energy density plasma (HED)
science, and high resolution and low
radiation dose imaging. (See Figure
3.13.)
Progress and Achievements

a

b

c

d

FIGURE 3.13 Applications of LPI Produced X-Rays.
Plasma acceleration-based sources can enable: (a) precisionhigh performance X-ray and MeV photon sources incompact packages suitable for applications in
nonproliferation, industry, security, medicine and otherareas. These X-ray are produced from Thomson scatteringand Free Electron lasers. (a-b) brilliant probes for highresolution High Energy Density Science, (c) Futurecolliders can extend the reach of our understanding of theuniverse, and (d) multi-modal sources from a single laser tocombine capabilities. SOURCE: (a) Courtesy of Cameron
Geddes, Lawrence Berkeley National Laboratory; (b) S.S.
Bulanov et al., On the design of experiments to study
extreme field limits, AIP Conf. Proc. 1507, 825 (2012), doi:
10.1063/1.4773805; (c) Reproduced from Physics Today
62 (3), 44 (2009) 2009, with the permission of theAmerican Institute of Physics (d) Courtesy of Cameron
Geddes.

Coherent soft X-ray sources
have been demonstrated using solid andgas targets for High Harmonic
Generation (HHG). Thesedemonstrations include sources in theattosecond domain, thereby permitting
attosecond temporal resolution, which isthe scale of atomic processes, hence
allowing one to observe atomic
dynamics. X-ray lasers have been
demonstrated with mJ/pulse energies
down to wavelengths of 46 nm, and fromenergies of J down to 6.8 nm using
multi-pulse ps lasers. Population
inversions can be driven by a variety ofmechanisms including electron impact excitation, collisional recombination, and photoionization. Plasma
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target shaping including nano-wire arrays has greatly improved coupling of laser energy into the X-ray
producing plasma. Seeding (initiating) coherent X-ray amplifiers with HHG has been exhibited andallows full coherence. Power scaling is being explored to produce sources that could meet the needs forlithography in the semiconductor industry and other applications.
Several brilliant, ultrafast, synchronized X-ray sources based on plasma accelerators have been
demonstrated. These sources enable advanced X-ray capabilities in compact laboratory setups with broadreaching impact while also improving our understanding of the plasma accelerators. Experiments haveshown the unique properties and advantages of these sources. Betatron emission (from the transverse
oscillations in the generated plasma wave) produce keV broadband radiation sources with micron
emission spot sizes that have been used to enable sensitive phase contrast imaging and ultrafast
diagnostics of high-energy density experiments. These experiments demonstrate that the beam quality of
x-rays produced by plasma accelerators can be competitive with that obtained in conventional X-ray
sources. Thomson scattering of a laser pulse from the electron beam has been used to produce quasimonoenergetic X-rays at selectable energies from keV to multi-MeV. Experiments have verified thatthese low-energy spread beams could simultaneously reduce radiation dose and increase sensitivity in Xray applications ranging from medicine to security. Several programs are investigating plasma driven
FELs to enable compact, ultrafast coherent sources.
CURRENT AND FUTURE SCIENCE CHALLENGES AND OPPORTUNITIESDevelopments over the past 10 years have established the single shot parameters needed for Xray applications, including keV to MeV mono-energetic sources produced by Thomson Scattering, keV
broadband betatron sources and plasma based soft X-ray lasers. Experiments have begun to demonstrate
the benefits of these sources at the few-Hz repetition rates allowed by current laser systems, primarily for
fundamental physics studies. However, applications require repetition rates at kHz and beyond.
Current photon sources including Thomson and betatron, and the ongoing development of FELs,
are attractive for investigating near-term applications. These sources typically use GeV-class LPAs,
which map to laser pulses of few Joules in tens of fs. The energy spread of the accelerated beams needs to
be in the range of 0.1 to 10%, and emittances from nm to µm. These capabilities, with improvement inbeam transport and beam disposal, will enable experiments now and in the next few years using state of
the art LWFAs. These technology improvements for photon sources will also benefit long term researchon advanced colliders. Repetition rates of kHz are needed for applications and developing such sources
are now realistic at the required few-Joule-per-pulse energies. The first PWFA applications are likely to
be a single-stage afterburner (e.g., the use of plasma acceleration to double the energy of an alreadysubstantially accelerated charged particle beam) for a Free Electron Laser (FEL), or high brightness,broadband betatron X-ray or gamma ray sources. A brightness transformer for FEL operation may also be
within reach.
Plasmas offer the potential for photon sources which are both more compact and more advanced
in performance than conventional systems. For example, LPA based photon sources have demonstrated
the ability to decelerate the electron beam after photon production. (See Box 3.2). For Thomson
scattering, the plasma can also guide the laser to reduce required electron current per photon produced.
Both of these capabilities reduce undesired radiation generation. The Thomson process can also provide
details on electron beam evolution for studying beam interactions with plasma waves. An LPA produced
electron beam could be used in an FEL with appropriate transport and phase-space manipulation (forexample, by de-compressing the ultra-short beam). Such a compact FEL would be an enabling capability
for many scientific disciplines and several projects are in progress.
Particle accelerators and the X-ray photon sources they power are fundamental technologies
supporting basic science, medicine, industry, and national security. Advanced X-ray light sources enableprecision measurements that have revolutionized a broad range of basic and applied sciences at large user
facilities. However, the size of these sources means that they are not accessible to many applications.
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FIGURE 3.14 The classification of collective high intensity processes: Collective, high intensity
processes address special relativity, quantum mechanics and atomic/molecular physics. These fields
and their interactions can be visualized as a cube of theories, with the three axes corresponding to:
relativistic, quantum, and high intensity effects. The vertices of the cube are classical mechanics,
special relativity, quantum mechanics, quantum field theory, classical electrodynamics, atomic,
molecular, and optical physics, and high intensity physics. SOURCE: Central Image: Phys. Rev. A 87,
062110 (2013). 4-wave mixing: Phys. Rev. A 74, 043821. Surrounding images courtesy Stephan S.
Bulanov, Lawrence Berkeley National Laboratory
Compact plasma based sources could enable broadly accessible mono-energetic hard X-rays from keV to
MeV energies with smaller emission spots, and coherent X-ray free-electron lasers at venues outside of
km-scale facilities. Realizing this vision would produce enormous benefits to industry, security, nuclear
nonproliferation, and medicine, or for high energy density science.
NONLINEAR QEDExtremely intense lasers under development and being proposed will give rise to a new field ofstrong-field quantum electrodynamics (SF-QED). This is the study of electron-positron pairs and plasmas
directly produced from the intense laser fields. In essence, with strong laser fields, one can create aplasma from the vacuum.
A large body of mostly theoretical effort has indicated that SF-QED can fundamentally change
the nature of the interaction of charged particles and plasmas with strong electromagnetic fields. These
interactions include significant transfer of beam energy to radiation, prolific production of electronpositron pairs and radiation dominated regimes, where particle motion is mainly determined by theradiative processes. These theoretical efforts have greatly advanced our understanding of charged particle
interactions with intense electromagnetic (EM) fields and their linkage to collective plasma effects. The
next generation high intensity laser and accelerator facilities will access a regime dominated by SF-QED
effects to test these theories and enable new applications. These facilities will provide new sources ofparticle beams for material and nuclear science studies. (See Figure 3.14.)

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Progress and Achievements
In the last 10 years a large body of mostly theoretical effort was devoted to the study ofmultiphoton Compton and Breit-Wheeler (BW) processes and subsequently, the EM cascade, wasidentified as a new phenomenon. (Compton processes are the scattering of photons from high energy
particles that change the wavelength of the photon. Breit-Wheeler processes produce positron-electron
pairs from the collision of two high energy photons.) Workshops and reviews have outlined the principal
schemes, and the methods needed to study these effects experimentally. See, for example, Workshop on
Opportunities, Challenges, and Best Practices for Basic Plasma Science User Facilities (2019 andSummary of strong-field QED Workshop (2019) [arXiv:1905.00059v1].
Electron beam collisions with high intensity laser pulses produce SF-QED effects at the lowest
laser intensities. Two experiments demonstrated the depletion of the beam energy due to photon emission
in multi-photon Compton process and initiated a new era of experimental exploration of SF-QED effects
using current PW-class lasers, advances possible by rapid progress in laser technology and by LWFA ofelectrons.
CURRENT AND FUTURE SCIENCE CHALLENGES AND OPPORTUNITIESIn the course of the study of multiphoton Compton and Breit-Wheeler processes, it wasunderstood that they cannot be treated analytically in either vacuum or plasma. Several numericalapproaches have been developed, from simple reduced order estimates for Compton and Breit-Wheeler
effects, to massive 3-dimensional simulations. QED-PIC codes are extensively used to study theinteractions of high intensity EM fields with energetic beams of charged particles and photons, andplasmas of different composition and density. Computer simulations of multiple shower-like photon
emissions and pair production and relied on the separation of scales. The characteristic scale of the SFQED emission process is much smaller than that of EM Field or plasma phenomena scales. Apart fromeither enhancing or suppressing acceleration, the strong fields were found to modify the trajectories ofcharged particles in the radiation dominated regime. In this regime positrons and electrons are trapped onstable or quasi-stable trajectories inside the EM fields. Development of such models continues to be an
active and important topic.
Current models are not capable of describing new regimes of collective high field interaction.
One example is the Local Constant Field Approximation (LCFA), which is the backbone of almost all
numerical tools now being employed. Recent studies point out the parameter regimes where LCFA
predictions are significantly different from full QED calculations. A number of solutions to this problem
were proposed by modifying the LCFA for plane Waves. However, there are processes that cannot be
described by the plane-wave model and a self-consistent treatment is needed. Furthering ourunderstanding of these phenomena will require well-orchestrated collaborations between development of
new computational capabilities and new facilities and diagnostics. (See Figure 3.15.)

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FIGURE 3.15 Timeline of the QED-plasma studies envisioned as a two-stage process. A near term
facility, potentially an extension of current PW-class lasers combining multi-GeV electron beams andintermediate laser intensities, can enable the study of fundamental strong-field QED processes. A
future multi-beam facility at extreme laser intensities could study the interplay between collective
plasma effects and strong-field quantum processes. SOURCE: NSF Workshop on Opportunities,
Challenges, and Best Practices for Basic Plasma Science User Facilities (arXiv:1910.09084),
Another open question is the consequence of back reactions, either pair production or photon
emission, on the intense electromagnetic field. Usually these processes are considered using an external
field approximation. However, it has been pointed out that the creation of new particles can lead to thedepletion of the electromagnetic field energy, which invalidates the approximation of the external field.
Theoretical and simulation studies of the cascades up to now have relied on the formation length and time
being much smaller than the spatial and time inhomogeneities of the electromagnetic field. However, afull QED treatment of these processes has yet to be achieved. Another example of the scientific andcomputational challenge is the interaction of charged particles with super strong EM fields. For these
conditions, strong field perturbation theory is no longer applicable, since the contribution of the second
order process becomes comparable with the first order ones. Proper treatment of spin and polarization
effects on plasma dynamics is also of interest.
Further theoretical and numerical studies of SF-QED will not only advance our understanding of
the EM field interaction with plasmas at highest intensities but will also provide critical insights into
allied scientific fields, such as accelerator research and high energy physics. Advancing ourunderstanding of SF-QED also requires a concentrated experimental effort, which requires a collaboration
between these allied scientific fields, to validate the findings, test theoretical and numerical models,paving the way for future applications and exploring new phenomena. The study of SF-QED effects
requires high power laser facilities and sources of high energy (multi-GeV) electron beams, either from
LWFA or conventional accelerators. In this sense SF-QED has strong connection with laser andaccelerator technologies. Moreover, different regimes of charged particles interacting with high intensity
EM pulses might lead to the development of high brightness sources of X-rays and gamma-rays.

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As laser intensities continue toincrease SF-QED effects will become
increasingly important, entering the regime of
QED-plasma, where the number of produced
particles is so large that they begin todemonstrate collective behavior, otherplasma-based processes start to be affected bythem. These processes include laser driven ion
and electron acceleration and high harmonics
generation. A series of experimental regimes
will become accessible with laser
technologies that will result from following
the roadmap. These new regimes start withadvanced experiments in collisions of beams
with lasers accessible on near-term PW laser
facility extensions. Over the longer term, tensof PW multi-beam laser facilities could enable
FIGURE 3.16 Measuring Plasma Waves. The
new regimes strongly affected or evenstructure of a plasma wave accelerator has been
dominated by SF-QED-plasma interactions.
directly measured using optical holography with a(See Figure 3.15.)
separate probe laser pulse. This is an example of
The study of SF-QED phenomena
advanced diagnostics that are enabling tuning andopens new physics across many fields. With
control. The image is the phase oscillation profile of
SF QED effects entering the regime of QEDthe wake (colored surface) that a 30 TW pump pulse
plasma, where the number of produced
generated in He2+ plasma with density 2.2  1018 cm3,
particles is so large that they begin tosuitable for GeV-class acceleration. The grey-scaledemonstrate collective behavior, otherimage is a projection onto a plane. Original citation:
plasma-based processes start to be affected.
P. Dong et al., New J. Phys. 12, 045016 (2010).
These processes include, for example, laser
Meta-citation: M. C. Downer et al., Rev. Mod. Phys.
driven ion and electron acceleration, and high90, 035002 (2018). SOURCE: P Dong et al 2010
harmonics generation. The field shares a
New J. Phys. 12 045016.
common analytical basis, as well as common
plasma accelerator technology needs, withhigh energy physics. SF-QED plasma studies can potentially relate to studies of high-energy hadroninteractions and the creation of quark-gluon plasmas as well as the interaction point of future lepton
colliders Future light sources built on the SF-QED effects will provide photon beams that could be usedin nuclear and material science as drivers and as probes. The construction of second beamlines, targets,and diagnostics at high-repetition-rate (1 Hz) PW facilities as well as support for theory and simulation
programs should be a near term priority in order to achieve rapid progress in SF-QED studies in the
United States. In the longer term a many-PW facility will be needed to fully exploit this regime.
DIAGNOSTICS
Diagnostic and computational advances have enabled deeper understanding of the plasma state.
For example, collective Thomson scattering has proven to be a valuable tool for diagnosing the hot
plasmas typical of inertial confinement fusion, providing either spatially or temporally resolved
measurements of the plasma density, electron and ion temperatures, ionization state, and flow velocity.
Recent experiments have even exploited the Faraday rotation of the Thomson scattering probe laser tomeasure the dynamo amplification of magnetic fields in a turbulent plasma. In the past decade, opticalinterferometry has provided insight into the spatiotemporal dynamics of plasmas from the spatial structureof laser driven wakefields to the ultrafast transition of matter from a gaseous to plasma state.
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Development of new diagnostics to measure the plasma distribution function, wave amplitudes anddistributions, and particle phase space, continue to be required. (See Figure 3.16.)
A critical component is the development of novel diagnostics that can measure not only the bulkhydrodynamic properties of the plasma, but also the underlying electron velocity distribution functions(eVDFs). Experiments have begun using Thomson scattering to measure the shape of the eVDF. Theseexperiments have demonstrated that processes such as cross-beam energy transfer (an interaction in ICF
and many plasma optics) and Raman amplification cannot be predicted without considering the shape ofthe eVDF. Fundamental processes such as inverse Bremsstrahlung absorption, collisional ionization andatomic processes, and heat transport can all modify the eVDF in ways that effect laser plasmainteractions. For example, the flattening of the eVDF at low velocities due to collisional absorption can
reduce the energy transfer between crossing laser beams—an effect that could be misinterpreted as anonlinear saturation process. A similar effect could arise in Raman amplification due to electron heat flux.
The heat flux can alter the Landau damping of the plasma waves leading to erroneous predictions for thelength of the amplifier required to reach saturated gain (i.e. pump depletion).
Virtually all of the needed technological advances described above and science advances that will
be enabled by those technologies require diagnostics to characterize the state of the plasma. This is true inall sub-fields of plasma science and particularly challenging in LPI due to the small volumes and shortdurations of the laser- or particle beam-plasma beam interactions. The HED community has been quite
successful in leveraging diagnostics in a synergistic way to improve laser and pulsed power technologies
while advancing our fundamental understanding of the underlying plasma physics. The LPI field would
greatly benefit from a similar collaborative development of diagnostics.
COMPUTATION
Computation (or numerical modeling) of plasma acceleration, radiation generation, and theassociated laser-plasma interactions has been essential to the development of the field of LPI.
Computations are synergistically supported by advances in theory, which new enable improve
fundamental understanding required to develop the numerical algorithms. Computation enables one toinvestigate laser or beam interaction with plasmas that are otherwise unobservable with current
diagnostics due to the fact that they occur in very short times in small regions of space. Computation
enables the exploration of scenarios, such as electron injection by ionization in mixed gases, prior toincurring the expense of experimental development of such systems, and enables one to consider regimes(such as much higher laser powers) that are not currently available. These computational investigations
are essential to defining the experimental path forward. Once that path has been determined, computation
enables improved design of experiments by, for example, optimizing the shape and materials of plasma
targets.
Computation is intensive and challenging in this field due to the presence of multiple time scales
and the need to resolve the long distance of propagation of lasers and beams. The longest time scale is theplasma channel formation time, ~ns, and this physics is typically modeled by magneto-hydrodynamic(MHD) codes. In the low plasma density regime, as needed for high-gain, single-stages, Direct Simulation
Monte Carlo, Particle In Cell (DSMC-PIC) codes are now being used. This work is in its early stages. The
next longest time scale is that of laser propagation through the channel, tens of ps, followed by the pulse
duration, which is approximately the plasma period, ~10-100 fs. The shortest scale is typically the laser
period, ~0.3 fs. The laser pulse propagation and plasma wave excitation are typically modeled using
particle-in-cell (PIC) codes. However, this is sufficiently challenging that many physics problems can beaddressed only with reduced models. Major progress has been made in both computational performanceand in reduced models that take advantage of special properties of the interaction, for example byrelativistically boosting to a frame that moves with the laser pulse or by averaging over its period. Thesemethods have enabled modeling of meter-scale, multi-GeV experiments. Simulations are now routinely
performed in coordination with experiments and theory to design concepts and interpret results. ThesePREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION
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modeling-experimental interactions improve confidence in our understanding of the physics and improve
confidence in computations for designing more advances systems.
In spite of progress in the United States in computations in LPI, we have seen a movement of thecenter of such computations to non-U.S. venues. At the beginning of the decade, computation in LPI at
U.S. institutions was dominant. For example, in 2004 all of the experiments for the Dream Beam issue of
Nature (Volume 431, Issue 7008, September 2004) showing narrow electron beam spreads withaccelerations to near GeV were accompanied by simulations performed with U.S.-developed codes.
However, that dominance has steadily eroded. In at least one case, the center of development of codes
originating in the United States has moved to non-U.S. institutions. In other cases, codes that wereoriginally open source moved to a closed-source model to obtain sufficient resources for development.
One outcome is that a large number of researchers have moved to using codes developed internationally.
The resource sharing aspect of these internationally developed codes is good. However, it also means that
U.S. researchers will have less influence over the development of features for those codes. The end result
is that implementing features in these cases that are specific to U.S. research needs will have lower
priority, if implemented at all.
Another result is that in the United States, with all resources concentrated in one code, one will
not have the innovation that comes from healthy competition in algorithms and approaches. With
university efforts in code development for this field having largely disappeared there is a reduced
production of new computational researchers in the United States capable of code development. Althoughdifficult to quantify, it appears that hiring at national laboratories in computations is shifting towards
foreign nationals who have this skill set. The lack of intellectual diversity in code development in the
United States is in stark contrast to the situation in facilities, where there is a large range of facilities atnational laboratories and universities investigating different drivers (beams versus lasers), plasma targets,diagnostics, and scales. Finally, we mention that there is little development in the modeling of plasma
sources.
ENABLING TECHNOLOGY AND FACILITIESProgress in LPI, plasma optics, and plasma acceleration will continue to be driven by advances inlaser technology. A healthy ecosystem of facilities, programs and capabilities, having diverse andcomplementary capabilities and instrument size, is required to enable advances in accelerator, photon
source, nonlinear optics, high field, and ion sources. The current ecosystem has supported the impressive
progress in the field, and includes laser and beam drivers at multiple scales and LaserNetUS, a newly
emerging network for coordination and user experiments. Rapidly advancing laser technology creates
opportunities to advance the field, in several forms. Existing laser facilities should be upgraded by adding
beams to support injection, shock drive and other capabilities. They should be equipped with advanced
beam shaping technologies (spatial and temporal) to enable control of the interaction processes. New
facilities will be needed to drive the field forward.
Collaborations have been and continue to be important to the development of the LPI field.
Discussions on access between LaserNetUS and similar networks and facilities in Europe have started.
International collaborations broaden access to unique facilities and techniques, the combination of whichis stronger than any one effort. Roadmap exercises are also an important connection, recent examples
being U.S., European and UK accelerator strategies. There are excellent opportunities for student training
in LPI due to the growth of this exciting and relatively new field, which attracts students, internationaland domestic collaborators, users and new researchers. International collaborations will take on increasing
importance to exploit state-of-the-art facilities being commissioned in Europe (in particular the Extreme
Light Infrastructure -ELI) and Asia, which will in the near term will lead the multi-PW frontier. (SeeFigure 3.17) The U.S. community is large but fragmented across programs sponsored by the DOE, NSF,
and the defense agencies. Little cross-agency coordination exists.

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Much of the progress in PWFA research over the past decade has been driven by increasingly
precise drivers at national facilities, coupled with a research community at both universities and thelaboratories. Major Facilities include the Advanced Accelerator Experimental Tests (FACET) at SLAC
National Accelerator Laboratory, the Advanced Test Facility (ATF) at Brookhaven National Laboratory,
and the Advanced WAKEfield Experiment (AWAKE) at CERN.
Over the past 10 years compact sources of high-power (up to PW) ultrashort (sub-100 fs) lasers
have become available at a few Hz repetition rates. These laser capabilities have enabled broad progressin LPI and LWFA. The availability of laser capability has enabled studies with sufficient statistics to scale
resonantly driven plasma acceleration up to the 10 GeV. This is the energy scale that is viable for stages
in HEP colliders and X-ray FELs (XFEL). (Other applications such as Thomson sources, medical
accelerators, and ultrafast diffraction can use lower electron energies and laser powers.) These low-andhigh energy examples emphasize that progress in LPA and photon sources has been enabled by a broadarray of facilities at varying scales, from small single investigator university systems to large national
laboratories. These many scales have enabled access to the field, training and the ability to take risks inaddressing science challenges. In this regard, in 2018, the LaserNetUS facility network (Sidebar 1) wasestablished to provide broad access to mid-scale laser facilities.
To address the science challenges discussed in this chapter will require a range of new facilities in
the next decade. In this regard, there are several research and technology frontiers with opportunities to
produce new capabilities and science, and provide opportunities for U.S. leadership. Stable, highrepetition-rate lasers accompanied by precise control and diagnosis of target properties are required topush the boundaries of experimental precision. In the near term, modification of existing facilities will be
required to develop plasma optics and secondary particle sources, provided that cascade efficiencies of

FIGURE 3.17 Location and Capability of High Power Lasers. High power laser facilities havedeveloped rapidly over the last decade and continued growth is anticipated. Activity has recently
shifted from the United States and is now centered in Europe and Asia. SOURCE: C. Danson et al,High Power Laser Science and Engineering, 7, E54 (2019), doi:10.1017/hpl.2019.36.
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

the acceleration process, the low emittance of conventional accelerators, and the need to stage
acceleration stages are overcome or addressed. In the longer term, co-location of multiple beams will bean enabling strategy, for example, by combining high energy drivers and short-pulse probes. Temporalcontrol at multi-THz bandwidths (for high-energy and high-peak-power facilities) and high-order spatial
phase control are necessary innovations. Specifically, the system requirements include: a) multi-kJ ns
laser pulses with shaped or stochastic pulse trains co-located with other short pulse beams such as 100
J/100 fs and 30 J/30 fs; b) laser intensities exceeding 1021 W/cm2 for high field physics and new
wavelength regimes; and c) kHz-class repetition rates for precision control and machine learning to drive
performance, and for accelerator and photon source applications. These needs have been detailed in acommunity report, (Brightest Light Initiative, Workshop Report, Roger Falcone chair, 2020).
Two technology frontiers define the path beyond current facilities: repetition rate and intensity.
High repetition rate, efficiency and control define the core electron/positron accelerator and X-ray source
laser requirements. Lasers with repetitions rates of kHz and higher with greater efficiency and control are
required for LWFA. These lasers will enable stability and reproducibility of the accelerated electron
beams with repetition rates of kHz through feedback control systems. Beam properties are strongly
affected by fluctuations in facility properties—ground motion and air motion. The impact of thesefluctuations falls off above hundreds of Hz. Operating at higher repetition rate enables more beam fluencein a given time, but also enables active laser feedback control where the pulse frequency (>kHz)significantly exceeds the fluctuation frequency (<kHz) of the facility. Feedback control has been
demonstrated on low energy laser systems (mJ-class) and needs to be extended to systems that drive
LPAs. This need defines a core accelerator development track—a few-joule-per-pulse, kHz system (withstabilization and shaping) enabling precision. The range of needs motivates a range of facilities
addressing different capabilities and approaches. A near term priority is a few-Joule per pulse kHz systemthat will enable light sources and precision LPA through real-time-control stabilization. In addition to
enabling science advances, this system will provide the learning required to develop a 10 J/50 kHz
collider stage driver. In the near term many of the control techniques required for high repetition ratelasers can be prototyped on existing lasers or extensions of them. Additional beams for injection andguiding control that are at lower energy do not drive overall laser development, but they do drive facility
configurations.
Other lasers are also of interest for accelerators. In particular, these include long wavelength
drivers for injectors and large bubble generation. (A bubble is a cavity free of cold plasma electrons.)
High energy and high intensity systems are the path to next generation HED science probes, ion
acceleration, and high field drivers. These include multi-PW facilities reaching to kilojoules and beyond
at tens of femtoseconds to hundreds of femtoseconds depending on application. Correspondingly,
repetition rates will be lower than Joule class systems, with rates of one to a few shots/hour being
accessible now, and tens of shots/hour in the near future. Such lasers are of particular interest whencoupled to high energy ns drivers or additional high intensity beams for heating and target shaping (HED)or particle beam generation (high field science), and for advanced probe capabilities. It is important tohave a balance between user facilities where new ideas can be tried at moderate cost, and dedicatedengineered beamlines where high performance and control can be advanced.
Plasma acceleration, X-ray sources, and optics have connections to industry both through laser
development and through potential applications. A recent DOE-HEP Basic Research Needs Workshop(Compact Accelerators in Security and Medicine, 2020) with participation from multiple agencies andindustry, discusses the importance that compact accelerators, and electrons and ions, and X-ray sources
will have for applications in industry, medicine and security. These applications include nondestructive
characterization (security and industrial) and medical imaging with improved resolution and lower
radiation dose, new medical therapies via FLASH (high-fluence, short duration) rapid irradiation or
endoscopic techniques, and improved security screening. The potential for orders of magnitudeimprovement in resolution and reduction in dose potentially enabled by laser-plasma sources would havediscipline changing impacts. Correspondingly, progress in plasma acceleration has been driven in largepart by laser development, and this investment has been reinforcing. Lasers which enable greater
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

capability in LPI produce scientific results that define the need for more capable lasers. The recent heavy
investment in Europe and Asia in laser facilities and science advances has shifted the center of highpower laser development to those areas, with follow-on industrial benefits to areas such as shock peening
for metallic surface hardening and laser machining. Future investment should combine opportunities inlaser development, applications and plasma science, areas that synergistically feed on each other and thatdrive progress. The improved accelerators resulting from this synergy will similarly advance scientificand technical disciplines that rely on accelerators as scientific tools.
An example of the synergy between technology development and science advances is thedevelopment of short-pulse, high-intensity lasers based on chirped-pulse amplification (CPA) by
Strickland and Mourou for which the 2018 Nobel Prize in physics was awarded. CPA has made compact
sources of high-power (up to PW) ultrashort (sub-100-fs) lasers readily available at Hz-class repetition
rates. Although higher laser power and intensities are needed for some investigations (e.g., ion
acceleration and SF-QED), many of the fundamental physics challenges described here do not necessarily
require higher intensities. Instead, they require laser technology advancements in precision, control,
repetition rate, efficiency, and access to flexible regimes of operation (e.g. multiple beams, various
wavelengths, coupled external accelerators). Presently, high-peak power, short-pulse systems are basedon Ti-sapphire laser technology and operate at 1-10 Hz. This low repetition rate limits feedback control
and machine learning that, with higher repetition rates, would enable sub-microradian pointing stability
needed for combining stages of LPA. With higher repetition rate enabled control, laser shaping would not
be limited by facility fluctuations. This would in turn enable precision control of injection andacceleration. Such control has been demonstrated on kHz lasers with small pulse energies, and achieving
the energies needed for LWFA at such repetition rates is a key technical need.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

BOX 3.1
The LaserNetUS Facility Network Provides Broad Access and Collaboration Opportunities
across a Range of Mid-Scale Laser Facilities
The LaserNetUS network was established in 2018 by the DOE FES to provide U.S. scientists
increased access to unique high intensity laser facilities. The LaserNetUS facilities are located atuniversities and national laboratories distributed geographically throughout the US with one in Canada:
University of Texas at Austin, Ohio State University, Colorado State University, Université du Québec,University of Michigan, University of Nebraska- Lincoln, University of Rochester, SLAC National
Accelerator Laboratory, Lawrence Berkeley National Laboratory, and Lawrence Livermore National
Laboratory. These facilities are listed in the context of others in the community in Chapter 4, Table 4.1.
The range of parameters accessible in LaserNetUS facilities will enable U.S. scientists to perform
experiments at conditions not available at their home institution. LaserNetUS is designed as a step
towards addressing strong international competition and loss of U.S. dominance in high-intensity laser
research and related applications. LaserNetUS benefits the entire field of plasma science by providing
broad access to state-of-the-art mid-scale laser facilities. The network also provides a platform fortraining the next generation workforce on short pulse, high intensity laser science and applications.
LaserNetUS provides smaller institutions and single investigators access to PW-class laser systems.
This type of network can strengthen relationships between national laboratories and universities,
provide more cross-collaboration opportunities, and engage a broader community including industrial
users. Likewise, improving diversity requires casting a wide net so that all have access to state-of-theart facilities. Part of the LaserNetUS mission is to provide access to high intensity lasers to the large
number of university groups. It will also facilitate interchange with international laser facility networks,
which is in progress. Programs to facilitate added capabilities and upgrades for the laser facilities arebeing discussed.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

BOX 3.2
Staging of Plasma Accelerators Sets the Stage for Future Colliders and for More Compact Light
SourcesSequentially combining plasma wakefield accelerators (PWAs) to reach successively higher
energies is an attractive path to future high energy physics particle colliders. On the other hand,sequential staging of PWAs to decelerate electrons (after production of photons) may be an enabling
technology for broad applications of advanced light sources to reduce radiation shielding that could
otherwise dominate size. An experiment recently demonstrated both concepts, and illustrates bothprogress and challenges in the field. The experiment required a series of laser-plasma accelerator
techniques to operate reliably in combination. To produce a stable injector stage, one laser pulse was
focused onto a supersonic gas jet, yielding a plasma accelerator with stability but modest beam
quality. Stable electron beams with mean energy of 120 ± 5 MeV, a 60% energy spread, charge of
33 ± 5 pC, divergence of 4 ± 0.3 mrad and pointing stability of 0.3 mrad were achieved over hours of
run time, thousands of laser shots and over more than 10 days. To couple this electron beam to thedecelerating stage, a short focal length electron lens was developed based on the discharge current in aplasma capillary enabling a compact setup and preventing degradation of the electron beam over longpropagation distances. The second stage plasma accelerator was powered by a second laser pulse.
Plasma mirrors were used to turn the laser at 90 degrees in a few cm before the second stage. The
short coupling distance is important both to compactness and to limit ballistic lengthening of theelectron bunch as it propagates, which could spoil efficiency. Acceleration and deceleration wereobserved at alternating timings as expected. Precision experiments to realize high performance, stableaccelerators and couple them efficiently and while maintaining beam quality are now in progress for
future applications.

Recent experiments combined multiple laser driven plasma accelerator stages, demonstratinga critical capability. (left) A schematic of the apparatus. The inset shows the evolution of the electron
beam waist simulated along the beam path. Part of the broad energy spectrum from the firstaccelerator is focused at the entrance of the stage 2 plasma. (right) Spectra of electron beams from thetwo coupled laser-plasma stages show the effect of the second structure (a) 100-shot averageunperturbed reference before arrival of the second laser pulse. (c)-(f) 2D charge map for the first two
maxima and minima of the energy oscillation. SOURCE: S. Steinke, et al. Steinke, S., van Tilborg, J.,
Benedetti, C. et al. Multistage coupling of independent laser-plasma accelerators, Nature 530, 190–
193 (2016). https://doi.org/10.1038/nature16525.

Findings and Recommendations
The study of plasmas driven by intense lasers and particle beams is opening new fields in plasma
optics, high field physics, particle acceleration, and radiation sources and enabling new applications
across science and society. These include
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




Transforming our understanding of the fundamental mechanisms of laser-plasma coupling andparticle acceleration, and developing predictive models across experimentally available parameter
spaces;
Implementing plasma optics in laser systems to both support current experiments and access new
plasma regimes;
Advancing control of particle and radiation sources with good reproducibility, detailed on-shot
characterization, and high fidelity predictions by simulations/models;
Developing secondary beams for probes and pumps in HED physics and for applications in security,
industry and medicine.

Laser and Beam Plasma Wakefield Acceleration: Many important firsts have been demonstrated in
wakefield and underdense acceleration, and brilliant X-ray sources. These accomplishments haveestablished a path to meeting needs in applications ranging from extending the reach of high energy
physics to transforming the performance and dose for X-ray imaging. The rich physics of resonant control
needs to be explored and exploited to achieve advances in accelerator performance. Next steps intechnology development include kHz repetition rates enabling stabilization and active feedback for
precision shaping of the plasma state, and new regimes in driver intensity and wavelength.
Ion acceleration: New mechanisms for ion acceleration are now accessible, including via radiationpressure and magnetic vortices. New laser, diagnostic and target capabilities are now emerging to enablehigher repetition rate and control. Although existing facilities are being used to demonstrate importantfundament concepts, new facilities with increased intensity and contrast are needed to achieve theenergies predicted by theory and computations. These compact ultrafast ion and neutron sources could
enable more effective cancer therapies, advanced HED science pump and probe sources, and neutron
sources for industry and security. (Additional important opportunities in lasers co-located with coherent
X-ray light sources are discussed in Chapter 4.)
Strong field science: Laser-plasma interaction studies have opened a new regime whereby the physics of a
relativistic plasma is strongly affected by strong-field quantum electrodynamics (SF-QED). These
opportunities include laboratory analogies of Hawking radiation in electric fields and Unruh radiation,
processes important to cosmology and astrophysics. Advances in strong-field science open the possibilityof investigating the basics of astrophysical objects, including black holes, pulsars, and magnetars, in thelaboratory; and uncovering the dynamic interaction of inner shell electrons with highly ionized, heavy
nuclei. Extensions of existing facilities will enable early experiments of laser-electron beam interactions.
Future facilities at and beyond the 10 PW power level are important to fully exploit these opportunities.
Plasma optics: Beyond adjusting parameters like intensity and frequency, the spatiotemporal structure oflight offers additional degrees of freedom for controlling the interaction of intense laser pulses withplasma. Broad-bandwidth lasers could revolutionize ICF by providing unprecedented spatiotemporalcontrol over laser-plasma interactions. Magnetization has recently emerged as a new capability to modify
collective behavior and manipulate plasma optics.
Across the LPI area, the Chapter 1 findings and recommendations on workforce, demographics
and academic representation apply. Importantly, the state of the academic and national laboratory
workforce is nearing a critical point and addressing these concerns is crucial to ensure continued progressin LPI. The U.S. workforce issues are particularly critical to LPI. There is unprecedented international
growth and competition. The U.S. LPI field is strongly reliant on international graduate students and postdoctoral researchers. As international facilities take the lead over U.S. facilities, the international
workforce will be attracted away from the United States, which could place the LPI field in the UnitedStates at risk.
Compact plasma accelerators, plasma X-ray sources, and plasma optical methods were in largepart invented in the United States, and the United States has held a leadership position in most of the fieldin past decades. However, as reported in the National Academies study Opportunities in Intense Ultrafast
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Lasers: Reaching for the Brightest Light (2017) (RBL) the United States has recently lost dominance inhigh-intensity laser research, which is impeding progress in the essential areas of plasma science outlinedin this chapter. The loss of leadership in large part is due to large investments in new laser facilities andcorresponding research programs made and being made in Europe and Asia. (See Figure 3.16.) These
international investments have in particular emphasized development of multi-PW systems, and thesefacilities are driving forward capabilities in all the research areas discussed here. RBL concluded that the
research performed on non-U.S. facilities does have great value for the nation. However, without
additional U.S. investments in laser facilities, leadership in LPI will drift away from the United States.
Findings and Recommendations
Finding: Compact plasma accelerators, X-ray sources, and optics were invented in the
United States. However, as reported in the NAS Opportunities in Intense Ultrafast
Lasers: Reaching for the Brightest Light, the United States has lost dominance in highintensity laser research and related research that is essential to plasma science,accelerators, and their applications.
Finding: There are strategic opportunities in the next 10 years to build scientific facilities
that can leap-frog international competition and enable the United States to maintain aleadership position in laser-plasma interactions.
Recommendation: To restore U.S. leadership, DOE and other agencies should
formulate a national strategy to develop and build new classes of high-intensity
lasers that enable now inaccessible parameter regimes.
Facilities constructed through the strategy above would produce the technologically highest intensities toopen up new regimes in high field physics and ion acceleration, having repetition rates at and beyond 1
kHz, with shaped pulses enabling precision control, and with active feedback and machine learning foracceleration and plasma optics.
Finding: Plasma acceleration and controlled laser-plasma optics are rapidly advancing,driven by newly available capabilities in short pulse/broad bandwidth lasers.
On the horizon are kHz lasers with active feedback together with pulse shaping and bandwidth control
capabilities that together will drive progress. This will enable new capabilities ranging from X-ray
characterization (medicine, industry, and nuclear nonproliferation as well as transformative HED
diagnostics) and inertial fusion to medical therapy and future particle colliders. Long term translational
and applied laser source development and high repetition laser driver development are required to realize
applications. However, there are currently few efforts to achieve these goals.
Finding: Applications require robust, compact drivers. A long-term plan and resources
for developing technologies that can leverage science advances into society benefiting
applications are needed.
Recommendation: DOE and NSF should lead a collaborative effort with otheragencies to develop an extended stewardship program for long-term, applicationoriented research to enable the development of revolutionary laser sources thattranslate to applications.
Very high repetition rate, precision-controlled lasers and plasma methods will need to be included as partof the stewardship program.
Finding: Collaboration between agencies focused on source development (DOE, NSF)
and potential user agencies (e.g., NIH, DoD) is needed to ensure that advanced laser
capabilities are developed.
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

Examples of such potential collaborations are given in Chapter 1, Table 1.
Rapid research progress relies on access to the latest laser and related technology, and it is important thataccess be available beyond the few institutions with large programs. LaserNetUS provides important
access opportunities to mid-scale facilities.
Finding: There is need for multiple programs and approaches in experiment, theory andcomputation, ranging in scale from single investigator experiments to user facilities anddedicated mission focused facilities or centers.
Recommendation: Agencies focused on the fundamentals of LPI (NSF-MPS, DOEFES, DOE-NNSA) should collaboratively augment and create programs in plasma
acceleration and optics that support a range of scales and multiple efforts and thatcoordinate research, user access, and educational support.
Table 1.1 in Chapter 1 lists opportunities for cross-agency collaborations.
Finding: A blend of science innovation (e.g., development of new physics regimes inhigh field science) and long-term engineering efforts to develop new facilities has been
essential to progress in laser-plasma interactions.
Finding: Together with support from other agencies and DOE support concentrated at
the National Laboratories, NSF support devoted to LPI at universities is essential to thefield.
Recommendation: NSF-MPS, DOE-SC, and DOE-NNSA should strongly support
research in the fundamental physics of plasma optics, high field acceleration andlaser sources in collaboration with other agencies. This includes research, centers,
and mid-scale infrastructure.
Finding: Computation and theory has been essential to the development of the field ofLaser-Plasma Interaction (LPI), providing insights and crucial input into experiment
design. U.S. computation, once dominant, has lost that advantage.
Leadership in computations has transitioned to non-U.S. institutions, particularly in Europe wheremultiple code development efforts are being supported. In contrast, funding in the United States no longer
provides significant support for multiple, competing code efforts.
Finding: A range of needed computational tools, both fluid-based and DSMC-PIC, isalso needed for modeling plasma sources.
Finding: The innovation that comes from healthy competition would help restore U.S.
leadership in computations for LPI.
Recommendation: NSF-MPS, NSF-CISE, and DOE-SC should support a diversityof computational and theoretical efforts to help restore U.S. leadership incomputations for LPI.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

4
Extreme States of Plasmas: High Energy Density Systems
HIGH ENERGY DENSITY PLASMAS, INERTIAL CONFINEMENT FUSION, AND WARM
DENSE MATTEROn the surface of Earth, we live at a pressure of 1 atm. In terms of energy, 1 atm corresponds toabout 105 J/m3 or about 0.03 eV per molecule of air. In the types of atmospheric pressure plasmas that areused for sterilizing surfaces for biomedical applications, the electrons can have high energies (3-4 eV)compared to the gas, but the fractional ionization is small, and so the energy density of the systemremains small. In arcs, this energy density may rise to 0.5 or 1 eV per molecule, but even these energies
are relatively low—low enough that atoms and molecules in plasmas having these energies still interact
by forces determined by the electrons orbiting in the outer shells around nucleus. At these low energies,
matter predominantly interacts chemically through the breaking and making of bonds facilitated by orbital
electrons. Plasma chemistry uses the more energetic electrons to create excited states and radicals to
selectively speed chemistry. However only a small fraction of the ordinary matter in the universe exists at
the low energy densities that are experienced on Earth.
Most of ordinary matter in galaxies is in a high energy density (HED) state. Stellar interiors,
planetary interiors, and supernovae can all be classified as HED matter, where the material energy density
is > 1011 J/m3, (or, equivalently, at a pressure of > 1 million atmospheres (1 Mbar)). At these high energy
densities, all matter has been ionized and all molecules dissociated. The interactions in HED matter are
between highly ionized ions, the deep inner shell electrons that may remain bound to the atoms, the freeelectrons that have been liberated, and the photons the plasma produces. This definition of HED is not
fixed. High energy density physics, HEDP, begin to appear in materials at about that pressure. The plasma
regime now known as “warm dense matter” (WDM) approximately covers the range of matter havingenergy densities well above those of typically industrial plasmas and reaching the lower bounds of HED
plasmas. As more is learned about the dynamics of HED systems, new ways of describing that behavior
have been proposed - organized complexity, systems far from equilibrium, self-organized structures, andmaterial controlled and manipulated via intense fields—however, these are all systems at HED, as shownin Figure 4.1.
Inertial Confinement Fusion (ICF) is that field in which matter is compressed to high energy
densities in an effort to controllably initiate fusion reactions in the laboratory. Many methods have been
proposed to accomplish ICF in the laboratory. The two primary methods are compressing pellets of frozen
deuterium and tritium (DT) targets (or capsules) using ns pulsed lasers, and compressing targets using theplasma forces enabled by pulsed power. ICF is considered to be part of HEDP because for most of theduration of an ICF implosion, the ablators and the DT core are in the HED regime. Indeed, most HED
studies began as support for (and were supported by) ICF needs. While the three fields have historically,
and will remain, closely linked, HED, WDM, and ICF are now three independent and flourishingbranches of plasma physics.
High energy density plasma physics is also closely linked to other branches of plasma physics. At
HED pressures, researchers can study laboratory fusion, create intense x-ray sources, and measure theintrinsic properties of materials at extreme conditions (such as density, strength, opacity, and equation-ofstate—the relation between pressure, density and temperature) that are critical to astrophysical systems(such as the Sun and stars, supernovae, giant planets, and exoplanets) and necessary for stewardship of
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

our nuclear deterrent. For example, the plasma property of opacity (the transmission and absorption ofradiation) is important across all plasma regimes, but is particularly important in the HED regime asradiation is a dominant form of power transfer. Precise knowledge of opacity is critical to astrophysics,
ICF and stockpile stewardship. Fundamental AMO (atomic, molecular and optical) physics data formolecules, atoms, and ions, such as energy levels, collisional-radiative rates, spectral line shapes,
equations-of-state, and transport coefficients, are essential for understanding and analysis of all fields ofplasma physics; and particularly important tounderstanding of radiation transport andionization kinetics in HED physics. The needfor this data, which is difficult toexperimentally measure, has led to thedevelopment of sophisticated computational
tools. Continued development of thesecomputational tools is essential to furthering
HED physics.
Plasma physics in the HED regime isalso important to the field of quantum
materials—systems in which interactions
between atoms are dominated by quantum
effects. New experimental and computational
capabilities developed at HED science
FIGURE 4.1 The Regimes of HED Plasmas.
facilities can tune conditions to produce new
Plasmas can exist over an incredible range ofphases of materials and preserve metastableconditions – here characterized by their temperaturestates with enhanced properties, both near and(10 orders of magnitude and density (18 orders of
far from equilibrium. The realm of quantum
magnitude). High energy density (HED) plasmas
materials had previously been limited to low
occupy the area above and to the right of the black
temperatures, limiting the breadth of quantum
line, having pressures greater than about 1 million
phenomena that can be investigated andatmospheres. This is the regime of astrophysicalexploited. In the past few years, however, aobjects and is now being routinely explored by
new generation of HED capabilities haslaboratory experiments. In the case of plasma
enabled the controlled manipulation ofaccelerators, temperature is related to the plasmapressure, temperature, composition, andmomentum spread rather than a thermal distribution.
magnetic fields (P-T-X-H) as well as time,
SOURCE: Courtesy of Adam Sefkow, University ofenabling development of revolutionary
Rochester, and Gail Glendinning, Lawrence
quantum materials. Controlled Mbar (100 GPa
Livermore National Laboratory.
or 1 million atmospheres) to Gbar (1 billion
atmospheres) pressures enable up to a 1000fold compression of materials, providing precision control of interatomic distances and thus overlap ofquantum orbitals. Dynamic compression can now control the thermodynamic path, states, and processes
to still higher (e.g., atomic scale) pressures. These capabilities have crossed into a new frontier ofquantum HED matter, one that can leverage quantum properties of materials at high temperature.
The status of ICF and HED was summarized in the Plasma 2010 Decadal report. In this report,
there was great optimism for achieving ICF ignition through laser-driven indirect drive (LID) on the
National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL). It was recognizedthat shock timing and symmetry would be challenging, and it was anticipated that laser-plasma

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

instabilities (LPI) would add substantial
uncertainties to predicted ignition scenarios.
However, it was believed that gas-filledhohlraums would mitigate LPI and allow forcontrolled symmetry, and that implosions
could be performed with the available laser
energy. The option of laser-driven direct drive(LDD) for ICF, primarily investigated at theLaboratory for Laser Energetics (LLE) using
the Omega laser facility, and Naval ResearchLaboratory (NRL), was not specificallyaddressed. LPI was expected to be asignificant problem for only laser beams
FIGURE 4.2 Imaging Collisionless Shocks in HED
interacting with hohlraums. The ignition
Plasmas. These proton radiographs from anchallenges for laser-driven direct drive wereexperiment on the Omega laser at the Laboratory forseen as symmetry, laser-seeded hydrodynamic
Laser Energetics show the creation of magnetic
instabilities, and shock timing (very similar to
fields, in two counterpropagating plasma flows, due
LID). The idea of direct magnetic drive,to the Weibel instability. Such magnetic fields are
currently under investigation at Sandia
believed to be responsible for the creation of shocks
National Laboratories (SNL), was not yet
in a plasma where the mean free paths of the particles
developed at the time of the Plasma 2010
are large (collisionless plasmas). The protons in thereport. In spite of its more recent
radiographs are deflected by the strong magnetic
development, indirect magnetic drive at SNL
fields created in the originally unmagnetized
had achieved high neutron yields in Z-pinch
plasmas. Experimental results are shown on the top
13
driven wire-array hohlraums (10 neutronsand synthetic radiographs from a 3D particle-in-cellfrom DD filled targets, which would give
simulation are shown on the bottom.
15~10 neutrons for a DT filled target). Direct
SOURCE: C. Huntington et al., Fiuza, F., Ross, J. et
magnetic drive was seen as a possible
al. Observation of magnetic field generation via thealternative to LID, especially as a neutron
Weibel instability in interpenetrating plasma flows.
source.
Nature Physics 11, 215 (2015),
Shortly before the Plasma 2010https://doi.org/10.1038/nphys3178.
decadal survey, HED science had been the
topic of a consensus study report (“Frontiersin High Energy Density Science,” 2003) with emphasis on the requirements for stockpile stewardship. In
order to fulfill those stockpile stewardship goals, the Plasma 2010 Decadal survey listed the following
requirements and benefits: Accurate understanding of material properties in a wide range of pressure and densities;
 Well-diagnosed experiments for validating codes covering solid-to-WDM-to-weapon-relevant
conditions; Large-scale 3-dimensional simulations; Validating codes through simulations of igniting ICF capsules, and Potential to engage new workforce participants for stockpile stewardship due to the scientificchallenge of ICF.
Stockpile stewardship falls within the mission of the National Nuclear Security Agency (NNSA)
which supports much of the HED investigations performed at national laboratories. While basic science is
not the mission of the agency, NNSA in 1998 had established the Stewardship Sciences Academic
Alliances (SSAA) and Stewardship Sciences Graduate Fellowship (SSGF) programs. It was predicted in
the Plasma 2010 survey that use and applicability of advanced computer simulations of HED plasmas
would need to expand to meet both ICF and stockpile stewardship goals. The expanded capabilities were
expected to include, for example, density functional theory calculations of equations of state, and
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

extending particle-in-cell (PIC) codes to larger
volumes and longer time to study laser-plasmainteractions and interpenetrating plasmas.
Investigations of coupled radiation andhydrodynamics in HED regimes were seen as
relevant to astrophysical systems, particularly
radiation driven shocks, radiating shocks, jets,
and ablation by radiation. Atomic physics inthe HED regime was expected to significantly
affect the understanding of opacity, andspectroscopy from igniting cores was
anticipated to enable the exploration of new
regimes.
The commissioning of the Linac
Coherent Light Source (LCLS) was expected
to be especially productive and exciting to the
WDM field, with a short pulse, monoenergetic
x-ray probe coupled to a laser driver. Plasma2010 particularly emphasized the importanceof encouraging strong outside users’
programs, such as that at LLE, at othernational facilities, as shown in Figure 4. 2. It
was anticipated that ion beam drivers would
be very useful for creating WDM conditions.
The WDM field was poised to begin relevant
work on radiative properties in intense
magnetic fields, particularly relevant to whitedwarf conditions.
HED PHYSICS —DYNAMIC WITH
BROAD IMPACT

FIGURE 4.3 Compressing matter to the Extreme.
When even common materials are under extremely
high pressures, they take on unique structures. For
example, as the pressure is increased in an Al sample,
AIRSS (Ab Initio Random Structure Searching)calculations predict that the ion cores of the metal
will occupy a larger fraction of the volume. For
pressures over 32 Mbar, the valence electrons will beforced into pockets, forming a structure known as an“electride,” in which the electrons act as a masslessnegative ions. Pressures up to 1 Gbar have beenachieved on NIF experiments, but the X-ray
characteristics required to measure the structures by
x-ray diffraction are currently only available from thebrightest monochromatic sources (e.g., LCLS).
SOURCE: Courtesy: Chris J. Pickard, University ofCambridge, and Gilbert Collins, University ofRochester.

The applications of HED science span a tremendous range. In the NNSA 2018 Stockpile
Stewardship and Management Plan, the challenges and strategy for the Science Program for 2018-2025
includes HED science and the importance of understanding materials and conditions in the HED regime
for stockpile stewardship. For example, the Z-machine at SNL has been used to evaluate plutonium aging
in weapons by comparing properties of fresh plutonium with those of more than 50-year-old plutonium
extracted from the Nation’s weapons stockpile. These are exceedingly important and necessary studies
that can only be accomplished using HED national facilities. At the other extreme, understanding plasma
opacity through HED experiments can contribute to improved industrial designs for extreme ultra-violet(EUV) plasma sources for lithography required for the development of microprocessors having eversmaller features.
The study of plasma physics in the HED regime is closely connected to other branches of physics
and can help address many fundamental questions relevant to the broader community. These related fields
and questions include
1. Astrophysics: How are hydrodynamic shocks and instabilities affected by radiation? What nonlinear
process occur when plasmas collide? HED facilities with either high-energy laser or pulsed power
drivers can create conditions similar to those in astrophysical systems, and where relevanthydrodynamic problems can be studied in a controlled environment from known initial conditions.
Type-II supernova explosions are Rayleigh-Taylor unstable and stellar wind flowing around a
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

planetary magnetosphere is subject to the Kelvin Helmholtz instability, both of which can be studied
in HED facilities to advance astrophysics when applying appropriate scaling parameters. There is an
opportunity for astrophysically relevant experiments to investigate the interplay of magnetic fields onhydrodynamics flows, such as the amplification of galactic magnetic fields, and how radiation affects
the growth of structures in core-collapse red supergiant supernova explosions. The data produced by
HED experiments can aid in validating and guiding astrophysical modeling and theory. An example
of such HED data is shown in Figure 4.2. In this experiment on the Omega laser, a collisionlessplasma is generated by laser ablation. Where the plasmas interact, the Weibel hydrodynamic
instability seeds the creation of magnetic fields, which are detected by the deflection of protons
generated by an imploding ICF capsule. The plasma and proton deflections were simulated in three
dimensions using a particle-in-cell code.
2. Material science: What are material properties at the pressures and densities present in the interiors ofplanets, or white dwarfs? These are critical issues to understanding the formation and evolution ofthese astrophysical objects, yet their properties cannot be directly observed. In this pressure regime,
which combines classical solid state and plasma physics, first-principles material properties
calculations are required. These calculations typically use density functional theory with molecular
dynamics that should be benchmarked with experiments. The technique of ramp-compression, in
which pressure is gradually increased to minimize heating of the material, has been used on NIF and
Z to study samples in the solid state at pressures greater than 10 Mbar, comparable to the interior andformative conditions of terrestrial planets. Dense plasma states are being experimentally generated ateven higher pressures, which are difficult to achieve in solids, matching the interior conditions of gas
giant planets, non-terrestrial-like exoplanets, and the outer regions of brown dwarfs. The insulatormetal transition in dense fluid deuterium at pressures up to 3-6 Mbar has been experimentallymeasured, providing benchmarks for theoretical calculations used to construct planetary models.
3. Nuclear physics: How are nuclear reactions affected by dense plasmas? Nuclear physics has
traditionally been studied in the laboratory using accelerator-beam techniques. In spite of their greatvalue, such techniques may not address issues relevant to astrophysics and ICF, where all nuclear
reactions occur in a plasma environment. This class of plasma physics relevant nuclear reactions canbe explored using modern HED experimental capabilities. Light-ion fusion reactions are an important
topic to both basic nuclear physics and astrophysics. For example, recent studies of T+T fusion
reactions, revealed an unexpected dependence of the neutron spectrum on plasma temperature eventhough the plasma temperature is orders of magnitude less than the nuclear energies involved. This
discovery is potentially important for the many nuclear reactions that occur in in plasmas such as
those in stellar interiors and supernovae. Similar studies are now being performed on 3He+3He, thelast step of the main proton-proton chain. In a plasma, the charged particle fusion reaction rate isenhanced by electron screening of the Coulomb barrier. In stellar cores, the screening effect canenhance some reaction rates by tens of percent. In a high-temperature plasma environment, plasmanuclear interactions can populate excited nuclear states through processes including nuclear excitation
by electron capture and by electronic transitions. Understanding the coupling of nuclear states to theplasma is therefore important for understanding nucleosynthesis, particularly of the heavy elements,
in astrophysical environments.
4. Atomic physics: Atomic physics and HEDP have a strong synergistic relationship. The product of
atomic physics investigations is absolutely essential to the analysis of HED experiments and thedevelopment of HED computational models. The validation of atomic physics in these regimes is best
performed by the controllable conditions possible in HED experiments. At the heart of this synergistic
relation is - what atomic physics in HED regimes is not treated properly or is missing? The ionization
potential of ions in a dense, strongly coupled plasma is lowered, due to the interaction with thesurrounding plasma (continuum lowering). This continuum lowering is intimately connected to theequation of state and, thus, an accurate treatment is crucial for most HED and ICF applications. Thisis particularly the case for plasma mixtures and conditions having severe gradients in plasma
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

properties. The standard plasma densitydependent analytical models forcontinuum lowering are inadequate todescribe solid-density plasmas at HED
temperatures. For example, measurementsof continuum lowering for both singlespecies and mixture plasmas—the sameion but in different materials at different
densities—performed in free electron laser
isochoric-heating experiments havehighlighted the critical need for new
methods and theories to computeequations of states in strongly coupled hot
dense plasmas. X-ray spectroscopy is
FIGURE 4.4 Astrophysical HED. Many of the mostanother synergistic atomic physics-HED
energetic phenomena in the university originate fromphysics topic. There has been a recent
HED plasmas. To explain the energetic events
surge of experimental techniques toassociated with to Gamma Ray Bursts, Active
diagnose HED and ICF plasmas using xGalactic Nuclei, and Black Holes, one needs torays, which has already advanced our
invoke relativistic electron-positron pair plasmas andunderstanding of both hohlraum andjets which were major components of the earlycapsule physics.
universe. The image shows the electron-positron pair
5. Opacities in solar and space physics anddensity as a function of plasma temperature.
the semiconductor industry: What new
Although no experimental platforms are yet available
experimental techniques and new atomic
that can simulate the relativistic pair plasma
and radiation physics modeling are needed
processes that replicate astrophysical conditions,for solar opacity measurements in thelaser-generated HED plasmas can produce electronlaboratory? Just as opacities are critical topositron plasmas, shown as the yellow region in the
HED physics, opacities are critical to theplot. Increasing the pair plasma density over about
investigation of any plasma dominated by1015 will require lasers with intensities > 1024 W/cm2.
radiation transport. That is particularly
SOURCE: Courtesy of Hui Chen (LLNL), Frederico
true for solar physics where radiation
Fiuza (SLAC) and Bruce Remington (LLNL).
transport is the dominant form of powertransfer from the interior to the surface. Opacity experiments are challenging to perform because theyrequire precise understanding of the laboratory drive and equation of state in addition to highprecision spectroscopy and control over experimental conditions. As such, techniques developed andmeasurements made of opacities in HED physics are critical to a wide range of fields, including solar
physics, astrophysics and stockpile stewardship. This also includes the high intensity EUV sources
used in the semiconductor industry for lithography.
6. Quantum materials: What new materials might be achievable in the HED regime? The new science
frontier of novel quantum HED structures combines quantitative cutting-edge experiments, theory,
and ab initio simulations. These capabilities enable exploration of this extreme quantum regime withthe prospect of a new types of synthesis and recovery of novel quantum materials. In the HED
regime, theory now predicts new and exotic quantum states. There is a growing list of predictions forsuch behavior in everyday materials (e.g., Al; see Figure 4.3) with potential energy applications. New
HED laboratory capabilities now provide the first platforms on which controlled and calibrated,laboratory-based experiments can be performed into the atomic pressure range, where the quantum
shell structure of atoms is destroyed. In addition, novel hydrogen-rich superconductors have been
discovered at high (few megabar) pressures with critical temperatures at or above room temperature.
The combination of high pressure and hydrogen is predicted to produce a broad range of suchsuperconductors.
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

IGNITION, INERTIAL FUSION ENERGY, AND STOCKPILE STEWARDSHIP
Inertial fusion energy (IFE), the commercial production of electricity from inertial confinement
fusion, offers the prospect of a nearly carbon-free energy source with a virtually unlimited supply of fuel,as with magnetic fusion energy. IFE has been a long-term goal of ICF programs for decades, and several
conceptual studies have been performed based on anticipated laser requirements and fuel management
schemes. However, the unexpected challenges in achieving ICF ignition has tempered and delayed
discussion of IFE systems until that critical demonstration of ignition occurs.
a

b

c

d

e

f

FIGURE 4.5 Strategies for Ignition. There are currently three top contenders for achieving ignitionand high energy yields with inertial confinement fusion (ICF). (a) Indirectly driven ICF target, withlaser beams striking the inside of a gold cylinder (hohlraum) and bathing the capsule in an X-ray
drive. (c) 3D computer simulation of complicated density perturbations in the imploded core of thecapsule, seeded by asymmetry in the X-rays, fill tube (used to fill the capsule with DT), and “tent”(capsule mount). (b) Direct drive geometry, where lasers uniformly illuminate a capsule. (c) The drive
process for the MagLIF concept of magneto-inertial fusion. First the cylinder of DT inside the high-Z
liner is immersed in a static magnetic field; then a laser is fired along the axis to increase the adiabat
and stabilize instability growth; finally, the DT is compressed by imploding the liner with the Z-pinch
drive. SOURCE: (a-c) Campbell et al., Matter and Radiation at Extremes 2, 37 (2017);
https://doi.org/10.1016/j.mre.2017.03.001; (d) Phys. Plasmas 22, 022704 (2015),
https://doi.org/10.1063/1.4907179; (e) Reproduced from D.S. Clark et al., Phys. Plasmas 23, 056302(2016) with permission of AIP Publishing, https://aip.scitation.org/doi/figure/10.1063/1.4943527; (f)https://lasers.llnl.gov/science/icf.
The prospects for IFE were examined in detail in the 2013 NRC report, “An Assessment of theProspects for Inertial Fusion Energy”. The report recommended a series of milestones to be used in aroadmap to assist in planning the recommended national IFE program, leading to a demonstration plantfor producing net usable energy. The first milestone is ignition. Achieving ignition is a prerequisite before
serious plans for a demonstration plant can be considered. Ignition will provide data and insights that will
be required for future decisions on whether to pursue IFE. For example, achieving this milestone will
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

clearly establish the energy requirements for ignition and possible capsule architectures that can be used.
The report concluded that various target designs and driver approaches had both potential advantages anduncertainty, and that the best driver approach was not yet established. IFE will require target designs anddrivers that can operate at high repetition rates (5–20 Hz) while delivering a net energy gain of ~10 per
pulse. (Gain is the ratio of energy produced by fusion reactions compared to the energy used to initiate thefusion reactions. In this context, energy gain is fusion energy compared to the total facility energy.) These
capabilities are well beyond the capabilities of existing ICF drivers which have pulse repetition rates from
1 per hour to 1 per day. Recently LLNL delivered a sub-scale version of an IFE laser concept, for theworld’s first 10-Hz PW laser system. This laser is supporting HED and discovery science experiments atthe ELI-Beamline Facility in the Czech Republic. This investment ($53 million) by the European Union
in laser technology developed in the United States illustrates how investments in ICF and IFE laser
technology enabled advances in other areas.
There are still clearly challenges in achieving ignition and challenges in developing drivertechnologies that would be required for an IFE power plant. Even with those challenges, a modest IFE
program in the United States would strategically leverage the significant investments made, and to be
made, in the mainline HED program. The United States still leads the world in ICF research, highrepetition-rate lasers, and pulsed power drivers, all of which are prerequisites for an IFE program.
Maintaining a modest IFE program would open the way for partnering with the private sector as is now
occurring in magnetic fusion energy (MFE). Industrial engagement has been very helpful for MFE. Suchengagement for IFE would help build the knowledge base for IFE and, more broadly enhance the HED
infrastructure. Pursuing ICF ignition is an extremely important goal, even without the current prospect ofcommercial energy. The pursuit of ICF ignition enables plasma studies at conditions relevant for nuclear
weapons stockpile stewardship and other HED science applications.
The importance of HED science for the stewardship of the nation’s nuclear stockpile was clearlystated in the NNSA 2018 Stockpile Stewardship and Management Plan. In order to fulfill its stewardshipmission, NNSA listed strategic objectives of the Science Program. Specific objectives relevant to HED
science for stockpile stewardship include: Enhanced capabilities will need to be developed to recreate more weapon-like conditions inexperimental facilities;
 Focused experiments such as material characterization at HED conditions will be needed to support
annual assessments;
 HED conditions will be needed to understand the impacts on performance of aging and of newmaterials and processes, and Promote academic alliances to recruit and train new generations of scientists.
Evaluating the HED plasma environment requires innovative, sophisticated diagnostics.
ICF ignition and gain, important for the future of inertial fusion energy, are also important for
stockpile stewardship. The degree of relevance to stockpile stewardship is to some degree correlated withthe fusion energy yield. With higher energy yield from an ICF capsule, one can gain access to more
weapons-relevant physics. For example, the following physics follows from achieving a given fusion
yield.
 Yield = 0.01: Interplay of thermonuclear fusion burn and mix, nuclear physics data (reaction-in-flight,
fission, and radiochemistry). This yield is currently available on the NIF which can provide amaximum yield of ~0.05 MJ.
 Yield = 0.1 MJ: Transport of charged particles in plasmas, threshold for fusion-fission physics.
 Yield  a few MJ: Threshold for enabling complex mix physics studies, robust radiation and charged
particle transport, robust fusion-fission experiments.
 Yield = 20-30 MJ: Higher fidelity versions of the above experiments are possible, neutron sources formaterials and environmental studies

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Plasma Science: Enabling Technology, Sustainability, Security, and ExplorationYield = 500 MJ: Use of fusion targets to drive complex experiments, use of fusion targets for material
properties (EOS, opacity) research, combined neutron and x-ray environments for outputs and effects
studies.

The training of scientists through the study of HED physics is an excellent contribution to the
STEM workforce. These individuals gain fundamental, interdisciplinary knowledge of extreme states ofmatter using the most advanced technical systems that exist. For that reason alone, research at universities
in HED should be strongly supported. However, the investigation of HED physics at universities also
serves a strategic and critical role for national security. Science-based stockpile stewardship requires auniquely trained and mentored workforce, which is best produced by actually researching HED physics,
computationally and experimentally. It is difficult to imagine maintaining the technical expertise required
for science-based stockpile stewardship in the absence of university programs in HED physics. To help
advance education in the field of HED, and to increase access to HED resources for scientists in the field,
the NNSA Stewardship Science Academic Alliances (SSAA) Centers of Excellence were started in thelate 1990s. The first was the Institute of Shock Physics at Washington State University, founded in 1997.
The funding of these Centers increased after the launch of the NNSA-DOE Office of Science Joint
Program in HED Laboratory Plasmas in 2007. Subsequent studies have commended these Centers andrecommended increased funding for them. Currently, nine Centers are funded with five focused on HED
physics. Center funding has recently been flat with funding per Center decreasing from (typically) $2.5
million per year to $1 million per year, to enable more Centers to be funded. However, a stagnant funding
environment has the potential to reduce the number of new facilities, given that operating existing centers
is likely to be less expensive than creating a new center, and the overall number of students trained. The
viability of stockpile stewardship rests on its scientific workforce, and the Centers are critical to providingthat workforce.
Individual investigator support is also extremely important in supporting university research in
HED and advancing the training of scientists in HED physics. This need is supported in part by the DOE
Office of Science (SC) Fusion Energy Sciences (FES) and the DOE/NNSA/DP Joint Program in HighEnergy-Density laboratory plasmas (HEDLP). This program, started in FY2007, remains a major sourceof funding for individual investigator work in HED. Individual awards range from $50,000 to $250,000
per year for grants from 1 to 3 years. In 2018, the program awarded 26 grants, totaling $13.8 million.
However, this funding has been at risk in recent years. The program should be strongly supported as asignificant complement to the larger HEDP Centers.
In addition to HEDLP, federal agencies have supported university research in HED science andclosely related disciplines, including DOE-NNSA, DOE-SC, NSF, AFOSR, ONR, and DTRA. The major
facilities in the NNSA ICF program (NIF, Omega, Z) have university use programs, while LaserNetUS
network (launched in 2018 with DOE-SC support) is dedicated to providing “mid-scale” facility access to
the HED science community. These efforts have enabled strong university collaborations and significant
fundamental scientific discoveries, including helping in developing the future technical workforce.
However, there remain significant concerns regarding workforce development. Universities are notprovided a sufficient level of resources and attention in several technical areas relevant to ICF and HED
physics, making it difficult to provide for future workforce needs, particularly where there are citizenshiprequirements. One such area is pulsed power-driven HED science and technology.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

FIGURE 4.6 Getting Laser Energy Into an ICF Plasma. Laser driven ICF is challenged by uniformly
depositing energy from the laser into the plasma. In many ways, the plasma fights against being
uniformly heated by the laser due to a variety of instabilities that occur. Each instability has a thresholdenergy or power at which it is launched. In this image, the plasma density is shown by the black line,
and increases towards the right. At the lowest density the laser may drive ion-acoustic waves in theplasma, reflecting light backwards, creating filamentation in the plasma, or transferring energy fromone laser beam to another. Any of these will affect how the laser couples to the plasma. At higher
densities, the laser may couple to the electrons and drive electron plasma waves, creating high energy
electrons. These energetic electrons can penetrate into the unablated, dense target and raise its
temperature and entropy. Laser plasma instabilities present challenges for the ICF community, but may
represent opportunities as a way to create plasma optics. SOURCE: D.H. Froula, et al., Plasma Phys.
Control. Fusion 54, 124016 (2012).
HED AND ICF ACHIEVEMENTS
In the past decade, the fields of HED physics and ICF have flourished. The following sections
summarize some of these accomplishments.
Laser Driven ICFs
ICF ignition designs, whether driven by x-rays, magnetized liners, or directly by lasers, attempt tocompress DT fuel to high enough densities to ignite fusion reactions. The DT fuel is initially heated by
the work done in compressing the fuel. This, in principle, is accomplished by assembling DT fuel in asmall, dense, hot region at the center of the target (“hot spot”), which is surrounded by dense, cold, DT
fuel. After ignition of the hot spot, a burn wave of fusion reactions propagates into the cold fuel, greatly
increasing the yield. During fusion reactions, energetic helium nuclei (-particles) are produced. Two
threshold definitions are common in ICF: (1) A burning plasma is achieved when the energy depositionby the fusion-produced -particles contributes more than 50% of the heating of the fuel in a capsule; and(2) Ignition occurs when the -energy deposited in the hot spot is equal to the energy losses due toemitted x-rays and electron heat conduction.
The laser energy delivered by NIF to the target is at its maximum achievable level with thepresent design. This new capability brought research for laser indirect drive ICF to scales and conditions
for ignition. (In laser indirect drive, LID, laser illumination of a small cavity holding the target, thehohlraum, produces short wavelength radiation that heats the target.) However, currently laser plasma
instabilities and hydrodynamic instabilities are limiting indirect drive target performance. LPI occur when
the lasers interact with the plasma inside the hohlraum, consisting of a combination of low atomic weight
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration(low-Z) atoms ablated from the hydrocarbon
capsule containing the DT fuel and high atomic
weight atoms ablated from the hohlraum,
typically coated with gold. LPI of various kinds
can change the direction of laser beams (affecting
symmetry of illumination of the target), transfer
energy into electrons rather than ions (making theenergy transfer less efficient and preheating thelow-Z capsule), and reflect the laser energy backup the laser amplification chain (possibly
damaging optics).
The laser direct drive (LDD) approach to
ICF also has the potential to provide the highfusion yield required both for stockpile
stewardship and for IFE. In LDD approaches
laser beams are focused onto the surface of thetarget, possibly seeding hydrodynamic
instabilities. LDD thus requires particularly
FIGURE 4.7 Very High Intensity Laser Interactions
uniform illumination to prevent instabilities. Bothwith Materials. The Matter at Extreme Conditionshydrodynamic and laser-plasma instabilities(MEC) end station at the Linac Coherent Light Source(LPI) similar to those occurring with indirectly(LCLS) at SLAC uses the LCLS x-ray source to probe
driven capsules are expected as laser direct drivematerial in HED states. Here a sample of singletargets approach ignition. For example, complex
crystal silicon is shocked by the MEC short pulse
hydrodynamic flows similar to those simulated
laser, and the shock is imaged at high resolution by afor the indirectly driven capsule are predicted tophase contrast imager. An elastic wave and a plastic
occur for directly driven capsules. Although
deformation wave can be seen, with clear increases inwithin directly driven targets the plasma consists
density and phase transition to polycrystalline Si. The
of only low-Z atoms, LPI can still distort the
x-ray beam is also diffracted (b) This image shows theincoming laser beams and produce high energy
diffraction patter from the entire image. By narrowing
electrons which preheat the target. The main
the field of view of the optics, the diffraction patterns
advantage of LDD is the higher coupling
can be sampled at different locations: (c) in theefficiency of laser energy into the kinetic energy
unshocked single crystal, (d) behind the elastic wave,of the shell (by a factor of 3 to 5 compared toand € behind the plastic wave). SOURCE: Review of
LID). This higher efficiency results in less
Scientific Instruments 87, 103701 (2016),
stringent ignition requirements for the maximum
https://doi.org/10.1063/1.4963906.
pressure at the hot-spot in the center of the target
and by how much the shell of the target must be compressed. (This compression is measured by theconvergence ratio, CR, the ratio of the hot spot radius to the initial capsule radius.) At LLE. where mostdirect-drive ICF implosions are performed, progress in diagnostics and modeling over the last decade
have resulted in significant improvements in predicting the properties of a compressed target usinghydrodynamic codes, enabling significant improvements in capsule performance.
Magnetically Driven ICF
In magnetically driven ICF, the inwardly pointing J  B forces that occur in, for example, highcurrent discharges such as a z-pinch are used to compress a plasma to fusion densities. Some of theearliest concepts for laboratory fusion, dating from the 1940s, were magnetically driven. Unfortunately,
due to challenges in overcoming instabilities, magnetically driven ICF fell out of favor. In fact, the field
was not reviewed in the Plasma 2010 study, as there was little relevant research at the time. However, in
the intervening years, a class of magnetized ICF known as magneto-inertial fusion has attracted more
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Plasma Science: Enabling Technology, Sustainability, Security, and Explorationinterest. At SNL’s Z-machine, integrated experiments using magnetized targets preheated by a kilojoulelaser source (“MagLIF”) have demonstrated significant neutron yields. The strong magnetic fields
decrease the plasma density required to stop -particles so that they heat the fuel more efficiently,
reducing the convergence ratio required to produce fusion from a DT target. Thus, the mix of cold ablator
material into the fuel introduced in high-convergence, high velocity implosions (such as those in laser
direct or indirect drive) may be mitigated. In addition to reducing the range of -particles, the magnetic
field reduces the thermal conductivity and keeps the fuel hot. The high efficiency of pulsed-powermachines such as z-pinches makes them an attractive candidate for IFE drivers.
MagLIF and its targets, unlike the spherical targets in LDD, operate in a cylindrical geometry.
The target DT fuel is first magnetized by an external magnetic field and then preheated to about 500 eVby an external laser. Finally, the target liner is imploded by the high MA currents produced by the Zmachine, compressing the DT fuel. Successful MagLIF experiments on the Z-machine showed significant
thermonuclear yield in 2014 and helped invigorate research efforts in magnetized target fusion. In
addition to SNL, the Alpha program in DoE’s ARPA-E has provided funding to universities to performfundamental research applicable to MagLIF fusion as an alternative energy concept.
User Access to HED Facilities
Since the Plasma 2010 report, LLNL and SNL have established external user programs whereby
scientists outside the NNSA laboratories are granted access to the NIF and Z-machine HED facilities. The
programs offer opportunities for a broad range of users to perform experiments in HED science, including
laboratory astrophysics, planetary science, high pressure materials science, unique regimes of plasma
physics, nuclear science, and particle acceleration. These regimes are found in planets, stars, galaxies,
supernova dynamics, astrophysical shocks, and accreting massive black holes. Since the inception of the
Z Fundamental Science Programs (ZFSP), major discoveries have been made in the areas of matter at
extreme conditions and laboratory astrophysics. As one example, researchers have been able to achieve
very high pressure, high density conditions that are relevant to planetary interiors. Solid state samples arebeing studied at pressures matching the interior and formative conditions of terrestrial planets, and at evenhigher pressures to match the interior conditions of gas giant planets, exoplanets, and the outer regions ofbrown dwarfs. Other experiments have measured opacity at stellar interior conditions in the laboratory(e.g., the opacity of iron). These experiments, performed on the Z-machine, produced opacities higher
than theoretically expected, showing that the standard opacity models used by astrophysicists may need tobe revisited. Although these programs provide excellent opportunities for external users, the community
would benefit from there being a lower barrier for entry and support for the LLNL and SNL scientists
who help external users navigate the system to gain access.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

High Brightness Sources
The brightest free electron laser x-ray source, Linac Coherent Light Source (LCLS) at the SLAC
National Accelerator Laboratory is enabling new investigations of HED plasmas. Studies using the Matterin Extreme Conditions (MEC) facility at LCLS have explored HED plasmas generated by long and shortpulse lasers, using the femtosecond x-ray pulse from the LCLS. This has allowed, for example,
investigations of warm dense matter structures and properties, nanometer-scale plasma features, dynamic
phase transitions and lattice dislocations, andshock waves in materials. Diagnostics at the
MEC allow direct measurements of material
properties on each shot. The MEC is a major
DOE/OFES investment in HED science anda major facility completely devoted to HED
basic science.
Diagnostics and Simulations
A wealth of new results has emerged
from ICF experiments over the past decade,
FIGURE 4.8 An Experimental Setup. While the strong
enabled by diagnostics improvements, andelectric and magnetic fields created in hohlraums
have led to significant improvements in our(typically ~108 V/cm and ~100 T) have long beenscientific understanding. After the first set of
expected, calculating the formation and effects of such
ignition experiments on NIF (known as thefields is an ongoing area of research for indirectly
National Ignition Campaign, NIC), it was
driven ICF. High energy protons are now being used torecognized that hydrodynamic instabilities
diagnose these very strong fields, but multiple ion
were degrading the quality of the implosions.
species and energies are probably required to constrain
Reducing instability growth (at the expense
the analysis. Two experimental radiographs show theof hydrodynamic efficiency) improved target
deflection of 15-MeV protons (left) and 3-MeV protons
yield by an order of magnitude. The ability(right) passing through a gold hohlraum driven by theto model targets at high resolution in three
Omega laser at the Laboratory for Laser Energetics.
dimensions has led to a better understanding
The protons are deflected by the strong electric fieldsof the impact of capsule “engineering
generated by the hohlraum (the 3-MeV protons morefeatures” such as fill tubes and mounts. Bythan the 15-MeV protons). The five-fold symmetry is
improving these features, target performancedue to the laser irradiation symmetry, as the strong
has also improved. Understanding the impact
fields are produced at the collisions of expanding gold
and control of the x-ray drive on the capsules
bubbles from the capsule. SOURCE:
has also improved. For example, the
Science 2010: 1185747 doi: 10.1126/science.1185747.
emerging field of plasma optics plays a roleby using laser-plasma instabilities to create
plasma gratings, in order to steer the laser beams in NIF hohlraum and improve capsule implosion
symmetry. Implementation of many lines of sight for neutron detectors has given a clearer picture of thesymmetry of neutron production in the hot spot, with asymmetry in drive linked to motion in the hot spot.
These new diagnostic-enabled results have motivated a complementary improvement in ourability to analyze, simulate, and deal with unprecedented volumes of data. Increases in computer power
combined with improved algorithms have considerably improved the ability of simulations to model
plasma experiments. Higher fidelity simulations with more fundamental physics and better resolution
have improved our understanding of the physics controlling the performance of these experiments. For
example, ICF simulations of indirect drive ignition targets and capsules can now include a broad range of
perturbation sources such as surface imperfections, engineering features and drive asymmetries in a fully
3D geometry. These new capabilities have significantly improved the ability of simulations to match a
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

suite of experimental observations across a range of targets. Simulations of direct drive targets andmagnetically driven targets have also increased in fidelity and realism. The United States leads the fieldof ICF plasma simulations. This leadership has important implications for national security as well as
future energy security and economic competitiveness.
Diagnostics on the major ICF facilities are proposed, prioritized, and scheduled (depending on
funding) by the ICF National Diagnostic Leadership Group, based on input from the ICF National
Diagnostics Working Group. As described in the “Energy and Water Development Appropriations for2011 Hearings”, the mission of the working group was to support the development of radiation hardened
diagnostics for use on NIF after ignition was achieved. Its mission now encompasses diagnostics for thethree major U.S. ICF facilities: NIF, LLE, and Z. NNSA sponsors workshops that are open to alltechnically qualified participants (the most recent was held in 2017, with 105 participants). Based on theoutstanding results from diagnostics fielded in those three facilities over the last decade, this model works
well. The National Diagnostic Working Group could be expanded to officially encompass diagnostic
specific to HED, technology transfer to and from mid-scale facilities, and data analysis and data mining
techniques.
Plasma Optics
Since the Plasma 2010 report, plasma optics has emerged fully as a field of research. Interactionsof beams in plasmas have the potential to produce plasma-based optics that are capable of supporting
much higher intensities and fluences than is possible in solids. Plasma mirrors, starting in the early 1990s,
have been used to improve the contrast of short pulses and as a final focusing mirror for short pulse
systems. In the past decade, several other plasma components, while still in the nascent stages ofdevelopment, have been successfully demonstrated in experiments: lenses, waveplates, q-plates (whichtransfer angular momentum of photons between spin and orbital angular momentum), beam-combiners,
compressors, and amplifiers.
SCIENCE CHALLENGES IN HED AND ICF PHYSICS
There are many science challenges unique to HED and ICF physics. In particular, it is clear that
fusion ignition remains a grand challenge. Initial indirectly driven ICF experiments on NIF were strongly
affected by implosion asymmetries and perturbations. Significant improvements in target engineering
reduced perturbations seeded by capsule roughness, bettered hohlraum design to reduce asymmetries
driven by LPI, and refined capsule design to reduce geometrically seeded asymmetries. The end result isthat experiments on NIF achieved as much as a factor of three higher yield than that calculated without particle heating, near the threshold of a burning plasma. However, even with these successes, the cold fuelaround the hot spot is not measured to be as dense nor as uniform as simulated, and laser-plasma
instabilities remain a challenge that limits the maximum usable laser intensity. NNSA has a milestone for2020 to identify and quantify the improvements needed to obtain ignition on the NIF, if it has not beenachieved, and to determine the scaling to multi-megajoule yields.
Ignition may represent the most visible challenge, but it is far from the only one. As the HED
field evolves to address the fundamental questions listed above, other challenges will arise to address theneeds for the next generation of facilities, requirements for diagnostics in completely new regimes, andadvances in computational techniques. These challenges include:
1. Further investigations into the astrophysical, opacity, and material science questions described above
will require a new generation of drivers—lasers or pulsed power. Higher energy densities are needed
to reach more relevant plasma regimes. These plasmas will need to be larger in spatial scale and more
uniform to improve the quality of measurements.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

2. Investigating those same fundamental questions will also require the brightest possible x-ray sources
coupled to high-resolution diagnostics capable of interrogating higher energy densities. The paradox
is that in creating larger, more uniform plasmas at higher energy density with more energetic drivers,
the currently available x-ray sources (such as the SNL Beamlet backlighter and NIF’s ARC petawatt
laser) will be insufficient to diagnose density, temperature, ionization, and other required plasma
parameters. Brighter sources, more like that currently available at LCLS, will be required for
diagnostics. The requirements for better diagnostic resolution also increase requirements for source
brightness.
3. Diagnosing exotic quantum materials likely means investigating the plasma conditions created by thehighest intensity lasers at ever shorter time scales. Higher repetition rates (on the order of MHz
proposed for LCLS II and a proposed upgrade to MEC) will achieve unprecedented precision andproduced unprecedented amounts of data. Advances in computational capabilities for data mining andmachine learning will be needed to deal with the large volumes of data produced.
4. While the existing major facilities are expected to continue to produce scientific return for at least thenext decade, planning for successor facilities (both laser driven and pulsed power driven, for both ICF
and HED) has started. The construction of LCLS II is underway, and proposals to upgrade the MEC
facility are in progress. To continue the United States lead in ICF will eventually require the next
facility intended for high gain ICF to be designed and built. Given recent discoveries, whether pulsed
power or laser driven, the current HED facilities and technologies are likely be inadequate to achieve
high gain ICF. Developing the driver technology to meet this goal will require early investment indesign and proof of principle prototyping. The lead time is long and postponing such fundamental
science and technology investigations until a funding decision is made to construct the next facility
would result in significant delays. A Next Generation Pulsed Power Facility (NGPPF) based on linear
transformer driver technology is a leading candidate to replace today’s Z-machine. Understanding the
low-density plasmas in the anode-cathode gaps of large pulsed power machines is important not only
for electrical power transmission in such a high gain facility, but also for target implosion dynamics
and overall target performance. These investigations can be done now to prepare for the next
generation of machine.
5. Computations and fundamental Data: Computational advances will certainly be necessary to design,
diagnose, and understand HED and experiments. Precise, ab initio simulations of materials in theplasma state are required to predict material properties such as opacity and equations of state. Thesesimulations will need to be validated by focused and perhaps dedicated experiments designed forvalidation. Kinetic effects, magnetic and electric fields, and other detailed physics models must be
improved from the current approximations. These will require significant improvements in current
computational capability. Given these validated codes, simulations of the response of an integrated
system such as an imploding ICF capsule, a supernova, or the interior of a giant planet will bepossible.
These first-principles simulations will need fundamental data such as cross sections forelectronic and nuclear interactions, opacities, transport coefficients and oscillator strengths. Althoughgeneration of this data is generally thought to be the realm of AMOP (atomic molecular and opticalphysics) and NP (nuclear physics), it is nearly impossible to separate these disciplines from HEDP.
The ability to simulate HEDP systems and interpret HEDP diagnostics critically depends on theavailability of fundamental data. The HED/ICF computational and diagnostic goals can only be met
by a synergistic relationship with a well funded AMOP/NP community in which fundamental data is
produced and tested.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

6. Uncertainty quantification, artificial intelligence, and machine learning: The large datasets beginningto be produced in HED/ICF facilities will need the same computational techniques for data analysis,
uncertainty quantification, artificial intelligence (AI) and machine learning (ML) currently being
implemented in other fields of science and engineering, though likely modified to the specialized
types of data produced by these experiments. There is certainly a role for conventional methods of AI
and ML which are in large part based on pattern recognition and optimization. However, there arealso great opportunities to develop physics-based machine learning algorithms so that fundamental
parameters can be derived, which can then be used as input to advance simulations. For example,
currently the MEC operates at a maximum of about 5 Hz. A proposed upgrade will increase the data
rate to 120 Hz. Future upgrades are planned for a 1 MHz repetition rate. This increases by orders ofmagnitude the volume of data produced, and this will need far more sophisticated data analysis tools.
Modeling NIF cryogenic implosions requires ensembles of 104 to 105 simulations to cover theappropriate range of uncertainty in inputs. Storing, processing, and mining these ensembles requires
ever improving data analysis techniques.
The need for improved, moresophisticated data analysis anduncertainty quantification is being
recognized by the community. In
2014, there were only two talks at
the APS Division of Plasma
Physics Annual Meeting that dealt
with either uncertainty
quantification or data mining for
HEDP. That number increased to~10 in 2018 and 2019 (with amini-conference in 2018).
However, HEDP generally lags
behind other branches of plasma
physics in these areas. Of themini-conference talks in 2018,
FIGURE 4.9 The Future of Pulsed Power for HED.
less than a third were from an
Concepts for future high fusion yield pulsed power machines
HEDP/ICF perspective (6 of 22
are based on the Linear Transformer Driver architecture. This
talks), although contributed oralarchitecture, conceived of in Russia at the High Current
talks from HEDP/ICF made up
Electrons Institute in the 1990s, has been developed into fast
more than half of the conference
single cavities which are shown here implemented in a
(22 of 42 sessions).
modular design for future facilities. Another possible
In addition to laser and pulsetechnology is based on the Marx generator (used by thepower technologies, advances inexisting Z facility at Sandia). However, for either type of
diagnostics and computations will be
device, the multiscale plasma physics required to understandbroadly applicable to other areas ofand design the power coupling in a next generation machine
plasma physics and even beyond
remains a challenge to the HED physics community. Midplasma physics. For example,
scale (> 1 MA) pulsed power facilities are almost nonexistentdiagnostics necessary to understandand there is a need for such a facility to support progress in(and advance) ICF/HED science will
the pulsed power field. SOURCE: W.A. Stygar et al., Phys.
find application in nuclear physics,
Rev. ST Accel. Beams 18, 110401 (2015), Creative
space physics, optical science andCommons Attribution 3.0 License.
pulsed power development.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

FUTURE OPPORTUNITIES FOR
HED AND ICF PLASMAPHYSICS
Addressing the sciencechallenges above represents anopportunity to increase the relevanceand impact of HEDP and ICF, and toempower other disciplines. Plasma
physics is intrinsicallyinterdisciplinary, and HEDP/ICF is no
exception. Addressing fundamental
plasma physics challenges requires
discipline-centric investigations of theunique conditions of HEDP, yet thosesame investigations rely on advancesin fundamental AMO/NP data,
diagnostics, optics, electronics,
computations (e.g., AI/ML). At thesame time, the science andtechnologies produced by investments
in HEDP/ICF have huge impact onother disciplines and national
priorities, from studying supernovae
to stewarding our nuclear stockpile.
Ultra-Broadband Laser
Technologies

FIGURE 4.10 Looking into the “Unseeable.” Improved
diagnostics for HED and ICF plasmas represent opportunities
for greatly increased understanding. It is a problem of looking
into the “unseeable.” The internal dynamics of an imploding
capsule are unseeable using conventional optics – other
innovative diagnostics are needed. In this example from an
implosion on the NIF, the imploded core near peak neutron
production time (BT) is imaged with the AdvanceRadiographic Capability. Four 1 kJ, 30 ps laser beams are
incident on two 25 m gold wires, providing two 25 m xray sources separated by ~150 ps. The dense fuel scatters the
x-rays, providing a density map of the fuel. During this timeinterval, fuel in the imploded core clearly flows from the topof the image to the bottom, showing the direction of residual
kinetic energy in the core. SOURCE: Courtesy of Ricardo
Tommasini, Lawrence Livermore National Laboratory.

One such example is thedevelopment of ultra-broadband laser
technology. ICF designs are limited tointensities below the threshold ofcommon laser-plasma instabilities.
LPIs inhibit the deposition of energy in the ablator and risk damaging the laser by scattering light back up
the optical chain. These instabilities can also generate super-thermal electrons that preheat the fusion fuelwhich reduces its compressibility. For LDD schemes, any non-uniformity in the illumination of thetarget—the so-called laser imprint—can produce instabilities. When using nearly monochromatic lasers,
speckle can appear on the surface of the capsule, seeding a Rayleigh-Taylor instability which can cause
the capsule to break up during compression.
Ultra-broadband lasers are a technology that may significantly mitigate the energy lost to laserplasma instabilities in ICF, enabling more efficient use of laser energy with better coupling to the targets,
whether directly or indirectly driven. (Ultra-broadband lasers would be an order of magnitude larger
bandwidth than that produced by chirping techniques to generate femto-picosecond pulses.) This
capability could dramatically expand the design space available for HED and ICF experiments.
Techniques have been proposed for both gas (ArF and KrF) and solid state lasers. Optical parametricamplifiers create high power, broad bandwidth light that can be seeded with a variety of temporal formats.
Preliminary experiments have demonstrated that another technique, using stimulated rotational Raman
scattering, can broaden the spectrum of solid state and KrF laser pulses to multi-terahertz bandwidths.

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Time compressing an ultra-broadband
laser pulse (amplified to ~ kJ levels)
could result in pulses in the range oftens to hundreds of petawatts. Suchhigh-power lasers would provide
access to completely new physics
regimes such as ultrahigh field
physics and relativistic astrophysics.
In this field too, the United States is
uniquely poised to make significant
advances in laser technology, with
impact well beyond ICF and HED
physics.
Laser Plasma Optics for ICF
Ultimately, advances in laserFIGURE 4.11 Publications in HED and ICF. International
plasma interactions will require laser
collaborations are crucial to the current vibrant state of HED
pulse repetition rates or intensities
plasma science. More than half the HED publications in highthat exceed the damage limits ofimpact journals are multi-national collaborations. The Unitedsolid-state optical components. Even
States remains the leader in HED and ICF research, aswith improvements in optical coatings
measured by publications. The chart shows the fraction ofthat are less damage prone to highpublications relevant to HED science that have an author
intensities, the size the opticalfrom the country shown. Over half of these publications hadcomponents would likely need toscientists from U.S. institutions among the authors during
increase to keep energy fluences
2009-2014 and 2015-2019. However, if publications on ICF
below tolerable levels. Aside from theare not included, there appears to be a downward trend for theincreasing cost of such large optics,
United States. Over the last 5 years, U.S. participation has
this approach will eventually become
dropped from 62% to 50%. The trend is consistent with thecounterproductive. Larger optics canrecent flourishing of high intensity laser facilities outside thetransmit higher total laser power, but
United States. (This is a major topic of the 2018 NAS reporttheir fabrication introduces surface
Opportunities in Intense Ultra-Fast Lasers: Reaching for theaberrations that reduce the ability toBrightest Light.) Collaborations at large U.S. facilities arefocus the laser beam and, as a result,frequently multinational; for example, about 20-30% of basic
reduces the peak intensity.
science efforts at the National Ignition Facility and the
Although mediating laserLaboratory for Laser Energetics include non-U.S.
plasma instabilities is one of theresearchers. SOURCE: Courtesy of Gail Glendinning,
greatest challenges in achieving
Lawrence Livermore National Laboratory.
ignition in ICF, leveraging these
instabilities also represents anopportunity to address the limitations of solid state optics. With a deep understanding of the physics of
LPI, one could establish and control efficient interactions between electromagnetic fields and charged
particle motion. This capability would enable researchers to harness the LPI to create plasma optics for arange of light manipulation applications. For example, energy transfer from one laser beam propagating
through a plasma to another (cross-beam energy transfer or CBET) has been controlled on the NIF by
adjusting the difference in laser frequency between the two beams. In principle, with a robust andaccurate predictive capability for LPI, a plasma could be designed to provide optical dispersion,refraction, or frequency conversion to mimic any solid-state optical components. In recent NIF
experiments, multiple laser pump beams were shown to interact in a preformed plasma with a seed beam,
which was amplified by a factor of about 5.7, an energy higher than the energy of any of the individual
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

beams. The fluence of the amplified beam was about 4 kJ/mm2, or about 300 times the damage thresholdof Nd:glass in a laser amplifier.
Computational HEDP and ICF
The United States is a leader in the field of computational plasma physics, however the majorityof that capability lies in the computational tools that are not broadly available. Unlike many other areas ofplasma physics, advances in HEDP and ICF have national security implications, and that is nowhere moretrue than with computations. Having said that, there are opportunities to create shared, open source codesin the HED/ICF fields that are focused on the fundamental physics of HED/ICF. As discussed in the 2018
JASON report Prospects for Low Cost Fusion Development, on the ARPA-E Alpha initiative onmagneto-inertial fusion, “The National Laboratories should contribute their unclassified state-of-the-art
simulation codes to collaborations with academic and commercial efforts, and support training of
qualified users.” The committee adds that this recommendation should include unclassified codes for data
analysis, uncertainty quantification, and data mining (machine learning).
X-Ray Sources and Diagnostics
The new capabilities in x-ray sources arising in the laser-accelerator field hold great potential foradvancing HEDP. Perhaps the greatest potential is in the use of these x-ray sources as imaging
diagnostics. However, these sources first need to be coupled to the systems where they are most needed—
the largest-scale drivers for HED/ICF experiments. Recently, 30 ps duration radiographic snapshots were
produced on the NIF from ~100 keV radiation generated by a 4 kJ, laser. These images tracked the time
evolution of density in the imploded core of a NIF implosion. With multiple bright, small, short pulse,
high repetition rate x-ray sources, a fully three-dimensional evolution of the hot spot can be imaged.
Another need for advanced x-ray imaging is the study of hydrodynamic instabilities in HED
plasmas. For example, a uniform, large spatial scale and long temporal scale drive is needed to pushhydrodynamic instabilities from the linear regime to fully turbulent mix. (Such drives are now only
available at NIF and on the Z-machine.) To better understand such hydrodynamic instabilities, imaging of
the evolution of materials in the mixing region is required. This imaging could be accomplished with thehigh-repetition-rate, bright X-ray sources currently only available at the LCLS. A proposed upgrade at the
Matter at Extreme Conditions (MEC) end station at LCLS would add high repetition rate petawatt classand long pulse drive lasers. This would complement the ongoing upgrade of LCLS to a 25 keV X-ray freeelectron laser (FEL) beam. If the proposed upgrade is implemented, the improved facility would enable asignificant step forward in understanding hydrodynamic instabilities in HED plasmas, and in fundamental
processes of HEDP and ICF such as new superconducting and quantum materials and dynamic phasetransitions. Co-location of coherent and/or brilliant mono-energetic X-ray sources, produced using
conventional or new plasma based methods, with mid-scale or NIF or Z-machine scale facilities would
enable significant advances in imaging these fundamental processes.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

Matter-Electromagnetic Coupling
While the plasma physics
relevant to breakdown of a plasma in
an intense electric field does not occur
in the HED regime, the process iscentral to understanding, predicting,and designing the next generation ofpulsed power machines. A higher
priority must be placed onelectromagnetic field-matter couplingthroughout the HED community inorder to better understand the lowdensity plasmas and plasma
breakdown in pulsed power machines.
These processes include the study ofintense electric and magnetic fields invacuum interacting with dense metaland dielectric surfaces as well as bulk
materials. Such a fundamentals
focused program would include thedevelopment of new models andcomputational algorithms that arecapable of handling the multi-scale
FIGURE 4.12 The Impact of Discovery Science on thephysics encountered as electric andNational Ignition Facility. The Discovery Science program atmagnetic fields terminate abruptly
NIF
has resulted in U.S. and international researchers having
across very steep density gradients
access to the NIF laser. Their experiments span a wide(such as across a vacuum-metal orbreadth of topics in HED science. Many have direct relevancevacuum-plasma interface).
to fundamental astrophysical and material science questions.
A need that transcends plasma
About eight percent of the experimental time on NIF is
physics in general, and not limited to
devoted to Discovery Science projects. SOURCE: Top:HED regime, is an improved
Courtesy of Lawrence Livermore National Laboratory.
understanding of plasma emissions.
Bottom: Nature Communications 9:1564 (2018).
All plasmas produce and absorb
radiation in some manner, and those
processes can dominate power transfer. This is another example of where advances in understanding
fundamental processes in HEDP are closely linked to AMOP to provide the needed data for modeling andinterpreting diagnostics. In the HED and WDM regimes, methods developed in the condensed matter
community are able to predict spectral structure appropriate to high plasma densities and low
temperatures. However, these methods are not likely to be applicable to the WDM regime now being
produced using X-ray free-electron lasers (XFELs). The critical need for consistency between thefundamental data and the resulting plasma transport is highlighted by model discrepancies withexperiments in the quasi-continuum of the L-shell iron opacity. This inconsistency may be the result of a
weakness in the theory (e.g., continuum resonances in partially bound states) or another as yet notunderstood atomic processes acting within a plasma environment. A multi-laboratory effort was launchedto reproduce the results on the NIF to address the discrepancy. Resolving this opacity inconsistency byrefining our understanding of this fundamental matter-field coupling will impact not just HED plasmas
but also the astrophysical problem of stellar structure.
Opportunities to leverage the many linkages between HED plasma physics and other branches ofphysics will continue. For example, high-energy-density plasmas can produce, via nuclear fusion
reactions, significant yields of MeV neutrons, protons, and other ions, and facilitate the ponderomotive
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acceleration of protons and light ionsin laser-irradiated foils, as well as
electron wakefield acceleration. These
accelerated particles can be used toinitiate reactions in a range of nuclear
physics experiments.
The conditions found instellar interiors and stagnated ICF
targets share unique conditions
perhaps not found elsewhere. Nuclei
in stellar interiors are immersed in a
degenerate electron continuum
whereas nuclei in conventional matterare surrounded by bound electrons.
These differences can significantly
affect the screening of nuclear
interactions triggered by charged
particles. HED plasmas can populate
low-lying excited nuclear states,
which, in turn, would affect theneutron-induced reaction rates. The
physical similarity between the stellarinterior conditions and the laboratory
HED plasma environments opens newopportunities for experiments relevant
both for nuclear physics andastrophysics.
THE U.S. ROLE IN THE
INTERNATIONAL HED
PHYSICS AND ICF FIELDSFIGURE 4.13 Radiation Transport in HED. Radiation
absorption by stellar material helps determine the internal
temperatures of stars. This absorption is determined by theradiation mean free path, or opacity  density, of the material
near the radiation/convection boundary (much of which isiron). When this measurement of iron opacity was publishedin 2015, it was the first measurement of opacity under starlike conditions in the laboratory. The difference between
measured and calculated opacity, shown as a ratio in thebottom plot as a function of radiation wavelength, is as large
as a factor of four at some energies. Replication of thismeasurement (from the Z Fundamental Science Program on
the Z machine) is the subject of a significant effort using the
NIF laser to achieve similar star-like conditions.
SOURCE: Bailey, J., Nagayama, T., Loisel, G. et al. A
higher-than-predicted measurement of iron opacity at solar
interior temperatures. Nature 517, 56–59 (2015).
https://doi.org/10.1038/nature14048.

The United States is theinternational leader in HED researchby many metrics, including thenumber of publications. Over the last
5 years, 50% of publications in HED
are attributed to the United States. The
next largest contribution is from the People’s Republic of China with about 15% of the publications.
However, there are interesting trends in the publication statistics for HED research.
1. High impact journal publications in the HED field are more likely to be international collaborations.
About 60% of the publications during 2018-2019 were multi-national collaborations. Although this isa from a fairly small sample size, it is clear that international collaborations are vital to producing
high-impact work in HED physics.
2. Over the last 5 years the number of non-U.S. publications in HED has risen faster than the number ofU.S. publications. In 2009-2014, the number of publications with U.S. authors was about 62% of thetotal, compared with the 50% during 2014-2019. The largest increase has been by authors from
European countries, with France rising from 10 to 15% of the total, Germany rising from 9 to 13%,and Russia increasing from 7 to 10%. The number of publications in this time increased from 167 to
316 in the Web of Science analysis. Many of the new publications are tied to high-intensity, short
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pulse lasers, where the UnitedStates has not maintained its
original lead in facilities (asdescribed in the Brightest Light
report).
Many international
collaborations are in progress at thelarge U.S. facilities. For example, in
the National Laser User Facility(NLUF) program to use the Omega
laser at LLE, all proposals must have a
U.S. principal investigator (PI). Of
those investigators, ~50% haveinternational collaborators and ~25%
have multiple international
collaborators. In NIF’s Discovery
Science program, 2 of the 10 proposals
approved in 2019 have a non-U.S. PI
and three others are multinational
collaborations. Although the UnitedStates is an international leader incertain aspects of HED facilities (e.g.,
NIF, Z-machine), that is not the caseacross the spectrum of HED and WDM
physics. Experiments that require
single or multiple beams of ultrafast
multi-PW (10 PW-scale) lasers foradvanced laser plasma-based particle
acceleration or study of collective
plasma effects with extreme fields
must be performed outside the UnitedStates. As noted in the Brightest Light
Study, the United States is fallingbehind both Europe and Asia in PW
laser capabilities.

FIGURE 4.14 The Expanding Field of HED. The number ofpublications on HED and ICF appearing in high impact(impact factor > 10) journals has greatly increased since theearly 2000s. This significant change is correlated with thecommissioning and operation of several major new facilities
since 2007 (Omega EP, NIF, and Z Refurbishment.) In
addition, there were recommendations in the Plasma 2000
(1995), Plasma 2010 (2007), and Frontiers in High Energy
Density Science (2007) reports that basic research besupported in HED at the major facilities. In the Plasma 2010
report, one conclusion was that “User programs on the major
NNSA facilities at the national laboratories that provide asignificant amount of facility time for investigator-driven
research are lacking.” All of the major facilities now devote
some fraction of the facility time to basic research, accessible
to outside users through proposal processes. SOURCE:
Courtesy of Rulon Linford of Lawrence Livermore National
Laboratory.

HED FACILITIES AND MAJOR
PROGRAMS
The largest HED/ICF facility is the National Ignition Facility (NIF), which came online in 2009.
The 192 beams of NIF routinely deliver 1.8 MJ of laser energy at a peak power of 500 TW at awavelength of 0.351 m. In 2018, in support of a milestone to reach 2.1 MJ, NIF delivered 2.15 MJ.
Currently there are about 60 diagnostic instruments. Depending on the complexity of the shot, one shot isfired about every eight hours. NIF currently produces 400 shots/year (although some of these are facility
shots rather than for physics experiments).
The Discovery Science program at NIF allocates about 8% of the shots to investigators to conduct
fundamental HED experiments that are not necessarily closely aligned with the NNSA mission. Theseshots are awarded through a competitive proposal process. In the last call, there were 25 proposals, ofwhich 10 were selected. Typically, a Discovery Science proposal is awarded 1-3 days of shot time.
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The Laboratory for Laser
Energetics (LLE) at the University ofRochester is home to both the Omega
laser and the Omega EP laser. Omega
is a 60-beam Nd:glass laser, operating
since 1995, routinely delivering 30 kJ
at a peak power of 100 TW at awavelength of 0.351 m. Omega EP,
completed in 2008, has four NIF-likebeams. These deliver, as on NIF,
about 10 kJ at 0.351 m, or, after
compression and expansion, in a shortpulse mode with a peak power ~1 PW
at a wavelength of 1.05 m. The two
FIGURE 4.15 Breakdown in Pulsed Power Devices andlasers beams may be propagated to
Midscale Facilities. Breakdown is the process of creating
the same target chamber forplasma from a non-plasmas state. Breakdown is a necessary
experiments requiring both highand desired process if you want plasma. However, when you
energy, uniform illumination andwant gaps to be free of plasma, as in the circuitry of pulse
short pulse, high intensity
power devices, breakdown is something to avoid. These
illumination. About 35-40% of the
optical images show emission from breakdown and plasma
shot time is allocated to ignition, 30formation in a 200 µm gap between two Al cylinders (shown
35% to HED studies, and 25-30% toby the red circles) in the COBRA pulsed power device at
fundamental science. The
Cornell University. The bright spots show non-uniformity infundamental science allocation isthe azimuthal distribution of breakdown. COBRA one of adivided between the Laboratory Basicgroup of university pulsed power machines used for basic
Science program (for LANL, LLNL,
research and training students in HED physics. Several such
NRL, SNL, and LLE scientists) andfacilities are described in Table 4.2. However, there are
the NLUF program for scientists fromessentially no mid-scale (current >1 MA) facilities available
academia or industry. Manyfor researchers in the United States. The lack of suchdiagnostics designed for the NIF are
facilities is a disadvantage, as is the lack of a coordinatedfirst fielded and demonstrated on
network to support science, applications, and technology of
Omega.
pulsed power machines, similar to LaserNetUS. SOURCE:
The Z-machine at Sandia
Physics of Plasmas 23 092711 (2016).
National Laboratory can deliver over
2 MJ of radiation with a spectrum thatis comparable to that of the interior of the Sun. The Z-machine produces currents exceeding 26 MA in
100 ns to 1 s long pulses and voltages exceeding 5 MV. High currents also allow the Z-machine togenerate up to 8 Mbar (million atmospheres) pressure from magnetic fields, and flyer plate velocities
exceeding 40 km/s. Work on Z-machine is funded by NNSA for defense and related applications. These
include producing intense UV and x-ray radiation for a variety of applications, intense magnetic fields
and pressures for dynamic materials properties measurements, ICF research, stockpile stewardship, andthe creation of extreme environments for astronomy experiments. Like LLNL and LLE, SNLA supports
use of the Z-machine by the broader science community for fundamental basic science experiments. This
program is the Z Fundamental Science Program (ZFSP). The first call for proposals under the ZFSP wasin 2010. A second call for proposals was issued in 2017, and 10 teams from 9 institutions were awarded
time. A third call was issued 17 June 2019. The ZFSP has executed 107 shots on the Z-machine since2010. The scientific impact of the program has been notable with many publications in high impact
journals.
The Linear Coherent Light Source (LCLS) at SLAC National Accelerator Laboratory began
operation in 2009. Since coming online in 2010, the Matter in Extreme Conditions (MEC) end-station at
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LCLS has been a state-of-the-art user facility for studying laser-plasma interactions, warm dense matter,and dense material physics. Its ability to diagnose wide-angle x-ray scattering of the LCLS source enables
the entire angular distribution of scattering vectors to be captured in a single shot. This capability has
produced new insights into the atomic structure of materials in compressed or heated states while thematerial is dynamically evolving.
In addition to these major, world class HED facilities there are many mid-scale facilities in the
United States. One of the recommendations for HED science from the Plasma 2010 report was that midscale facilities needed to be maintained, expanded, and utilized as effectively as possible. Table 4.1
describes the high intensity laser facilities, many of which are linked through LaserNetUS.
LaserNetUS is an advance in support for users of mid-scale, high-intensity laser facilities.
LaserNetUS was established in August 2018 to help restore U.S. dominance in high-intensity laser
research, and to specifically address some of the recommendations of the NAS Brightest Light report. The
report recommended that the DOE create a broad network of lasers to support the science, applications
and technology of intense, ultrafast lasers. LaserNetUS is intended to provide institutions and single
scientists access to PW-class laser systems. Most facilities enable active participation by the users and so
provide an ideal training ground for students and early career scientists in state-of-the-art laser
technology. Given its short operating record at the time of this report, its long-term effectiveness cannot
yet be assessed. However, in 2019 LaserNetUS provided experimental access to 200 researchers fromdozens of institutions in the U.S. and abroad. An important role fulfilled by LaserNetUS is the training ofstudents and postdoctoral researchers. Well over 100 students and postdoctoral researchers have alreadyparticipated in LaserNetUS experiments.
TABLE 4.1 U.S. Mid-Scale Laser Facilities
Location

Laser

Properties

Colorado State University*

Advanced Beam
Laboratory

Petawatt class, femtosecond pulses, intensities
0.6–1022 W/cm2

Lawrence Berkeley
National Laboratory(LBNL)*

Berkeley Lab Laser
Accelerator (BELLA)

Dual beam(1) PW class, 30 fs, 40 J, 1 Hz;(2) 10–50 TW, 40 fs

Lawrence Livermore
National Laboratory(LLNL), Jupiter Laser
Facility*

Janus

Dual beam, 1–15 ns, ~1 kJ

Titan

Dual beam, one Janus beam and one short pulse(0.7–40 fs), 1019–1020 W/cm2

Comet

0.5 ps to 2 ns, 10 J

Nike

248 nm, 4–5 kJ, 4 ns

Electra193 nm, 700 J, 1–5 Hz, 50 ns

Scarlet30 fs, 10 J, 5  1021 W/cm2

Naval Research Laboratory

Ohio State University*

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

SLAC National Accelerator
Laboratory, Linac Coherent
Light Source (LCLS)*

Matter at Extreme
Conditions (MEC)(laser only)

10 ns, 60 J
50 fs, 5 J

University of Michigan,
Center for Ultrafast Optical
Science (CUOS)*

Hercules

30 fs, 300 TW, 1e22 W/cm2

T-cubed Laser (TTT)*

400 fs, 8J, 3e19 W/cm2

University of Nebraska,
Extreme Light Laboratory*

Diocles

0.2–0.7 PW, 0.1 Hz

Diocles HRR

100 TW at 10 Hz

Archimedes

10 TW at 10 Hz

University of Rochester,Laboratory for Laser
Energetics (LLE)*

Omega EP

Short pulse—2 beams 0.7–100 ps, 0.5–2.3 kJ
Long pulse—2 beams, 5 kJ/beam, ns pulses

University of Texas atAustin, Center for HighEnergy Density Science*

Texas Petawatt Laser

140 J at 140 fs, 2  1022 W/cm2* = Member of LasernetUS.
There are several small scale (1–3 MA) pulsed power facilities at U.S. universities. However,these generally do not meet the requirement of mid-scale facilities accessible to users, (with capability
between 1 MA and 20 MA). These facilities are summarized in Table 4.2. Several of the university pulsed
power systems are used for technology development and not HED/ICF experiments. There is noequivalent to LaserNetUS for pulsed-power facilities. However, the first “ZNetUS” workshop, hosted by
The Center for Energy Research at UC San Diego, is planned for January, 2020. The organizers intend to
discuss recent developments in Z-pinches, focusing on several specific topics. Among these is the needfor a mid-scale user facility.
The availability of mid-scale pulsed power facilities is clearly less than that for mid-scale laser
facilities. As described above, a Next Generation Pulsed Power Facility (NGPPF) based on improved
linear transformer driver (LTD) technology is a leading candidate to replace today’s Z-machine, whichuses the older, more mature but less efficient Marx generator/water pulse-forming lines technology. The
LTD technology offers an opportunity to address the dearth of mid-scale facilities, providing a lower cost
path to achieving significantly higher pulsed power performance. Mid-scale facilities (5-15 MA) could bebuilt with LTDs to provide facilities for investigating HEDP and technology concepts in the gap between
the majority of university facilities and national laboratory facilities. The LaserNetUS concept has been
embraced by the pulsed power community. At community forums held for this report, a similar network
for access to mid-scale pulsed power facilities was proposed on several occasions.

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TABLE 4.2 Small-Scale Pulsed Power Facilities
Location

Facility

Properties

Cornell University

COBRA

1 MA Marx-pulse forming line

Naval ResearchLaboratory*

Hawk

800 kA Marx

Mercury

300 kA Insulated Voltage Adder (IVA)

Sandia National
Laboratory*

Mykonos

1-MA, 5-cavity LTD

University of California,
San Diego

GenASIS250-kA LTD

University of California,
San Diego

LTD-III~1-MA LTD

University of Michigan

MAIZE

100 ns, 1-MA single cavity LTDBLUE

150 kA, 4 cavity LTD

University of Nevada, Reno

Zebra

1-MA Marx-pulse forming line

University of New Mexico

LOBO

200 kA LTD

University of Rochester

HADES~1 MA, 6-cavity LTD

University of Washington

ZaP-HD450 kA, 1-2 Tesla, 30-70 s

FuZE

200 kA, 1-9 Tesla, 20-40 s*While the NRL Hawk and Mercury, and the SNL Mykonos machines, are not user facilities, scientists
from outside NRL and SNL collaborate in many of the research projects on these machines.
NOTE: LTD = linear transformer drive, Marx = Marx Bank.

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FIGURE 4.16 The PETAL, LMJ and Jets.
The Laser MegaJoule (LMJ) in France has
been operational since 2014, beginning with
8 of its eventual 176 beams, and performing
experiments with 40 beams (150 kJ) since2017. The petawatt laser PETAL was added
to the LMJ facility in 2017. Currently about
20-30% of the operating time is accessible toacademic researchers. The images shown arefrom one of the first of a series ofhydrodynamic instabililty experiments,
showing the evolution of a hydrodynamic jet.
Initially the jet is a small surface perturbationon the target shown at left. When a shock
launched by an x-ray drive incident from thebottom crosses the interface between highdensity (red) and low density (gray) material,
the perturbation introduced by the surface
shape forms a rapidly growing jet, as seen in
the x-ray radiographs. Simulations accurately
capture the size of the jet as a function oftime, as seen in the plot on the right.
SOURCE: Jean-Luc Miquel and Emmanuelle
Prene 2019 Nucl. Fusion 59 032005.

FIGURE 4.17 A Different Approach to
Hohlraums. The ShenGuang III laser is currently
operational in China. It has 48 beams, operates (asdo NIF and Laser Magajoule LMJ) at 351 nm, andhas a designed maxim um energy of 180 kJ.
Optimized for a hohlraum geometry, experiments
at the facility are exploring novel hohlraum
geometries such as spherical hohlraums, and,shown here, a novel shape called “TACH”. This
design uses six small hohlraums open at one end todrive a central cavity. In this way, all the laser
beams are incident at the optimum 50° angle, andthe symmetry is inherently spherical, thus greatly
reducing the effects of the cross-beam energy
transfer laser instability and improving drive
uniformity. SOURCE: Kuang, L., Li, H., Jing, L. et
al. A novel three-axis cylindrical hohlraum
designed for inertial confinement fusion ignition.
Sci Rep 6, 34636 (2016).
https://doi.org/10.1038/srep34636.

The next generation of large-scale
facilities should be able to achieve high gain inorder to further both IFE and stockpile
stewardship goals. It is now premature to selectone type of driver over another. What is clear isthat fundamental research on the science andtechnology of new pulsed power and laser drives
must be sustained so that wise choices can bemade in defining the next generation large facilities. The current low level of support for mid-scale pulsed
power facilities with access to university researchers works against having a robust community
developing a diversity of options for the next ICF facility.
There are three existing or planned NIF-class laser facilities outside the United States. The Laser
Megajoule (LMJ) in France currently has 40 NIF-like beams, eventually to be 176. It is intended toprovide about 1.4 MJ at 351 nm wavelength. Like NIF, it has a petawatt-class laser (PETAL, currently 1
kJ at 570 fs, eventually reaching 3.5 kJ at 10 ps) that is integrated with the longer pulse drive beams andcan be used for high-energy backlighting and HED experiments. It is configured much like NIF, withbeams oriented for indirect laser drive (in a cylindrical geometry rather than uniformly distributed arounda sphere). The current hohlraum design is a rounded cylindrical (“rugby”) shape, rather than the rightcircular cylinder used on NIF. LMJ and PETAL are available for national and international collaborations
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through the Institute Lasers and Plasmas.
Four experiments were selected from the
16 applications in the first call (2014).
Two experiments selected from thesecond call are to be fielded in 2019,using PETAL, 56 LMJ beams, and 16
diagnostics.
A second currently operating
major facility is the Shenguang III laser
in China. With 48 beams, it is designed
to have a maximum energy of 180 kJ at
351 nm wavelength. It too uses ahohlraum to drive a capsule for ICF
studies, but there are multiple hohlraum
designs being explored. These include
FIGURE 4.18 Pulsed Power in China. The 8 MA, 8 MJ
spherical hohlraums and a novel
pulsed power facility Primary Test Stand (PTS) in China“TACH” shape, shown in Figure 4.18.
is currently the largest operational pulsed power machineThis design uses only laser beams
outside the United States. PTS has been used since 2016
incident at large (~50 degrees) angles.
to study (among other important high energy density
This larger angle of incidence isphenomena) imploding liners (both wire arrays and solid),
predicted to reduce backscatter, crossedshock compressed materials, and behavior of a conductor
beam energy transfer, and symmetry
under pulsed megagauss magnetic fields. PTS is about 1/3
degradations due to expanding hohlraum
the energy and current of Sandia’s Z machine.
walls, all of which result in implosion
SOURCE: Matter and Radiation at Extremes, Volume 1,
degradations seen on NIF experiments.
Issue 1, January 2016, Pages 48-58.
The third international NIF-classlaser is under construction—the UFL-2M laser in Russia. It is designed to have 192 beams (the same as
NIF) but will irradiate the target at 531 nm instead of the 351 nm used by NIF and LMJ. Due to the more
efficient frequency conversion of the Nd:glass produced 1053 nm to 531 nm. and higher damage
threshold for optics at the longer wavelength, its energy is designed to reach 2.8 MJ. The irradiationgeometry is spherically rather than cylindrically symmetric, in order to optimize the symmetry for laser
direct drive.
In 2018 the NAS report “Opportunities in Intense Ultra-Fast Lasers: Reaching for the Brightest
Light” (referred to here as the “Brightest Light report”) was published. As described in the report, most of
the high intensity lasers in the world have been (or are being) built outside the United States. It is now thecase that U.S. scientists studying HED at very high electric field strengths (for example, nonperturbative
quantum electrodynamics effects) are not able to perform research in the United States.
Major pulsed power facilities outside the United States are beginning to compete with U.S.
capabilities. The Primary Test Stand in China (PTS), currently operating, is an 8 MA, 8 MJ Z-pinch
facility (about 1/3 the power and energy of Sandia’s Z-machine). Similar to the Z-machine, the PTS has a
1 kJ laser for backlighting experiments. It is an important part of the Chinese Academy of Engineering
Physics roadmap for Z-pinch fusion. The proposed Baikal facility in Russia is intended to be a 50 MA,
100 MJ Z-pinch machine, or nearly 4 times the energy of the current Sandia Z-machine. Baikal has astated goal of 25 MJ Z-pinch fusion energy. Approximately 5 years ago, however, this project was
postponed due to funding issues.
RELATIONS TO AND PERSPECTIVES OF INDUSTRY
In the 2018 Brightest Light report, possible industrial applications of ultrafast lasers were
described, with a focus on medical applications. In order to understand, predict, and improve these
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possible applications, the HED physics of the interactions of the high-intensity lasers with their targets
must be better understood. While materials processing with ultra-intense lasers is already employed in
manufacturing processes, the plasmas produced are typically not in the HED regime. The goal of theprocess is usually to affect a small volume of a solid material (without, for example, creating shocks andcracks). However, in many other applications the goal is to produce a brightly radiating plasma, or toaccelerate particles to high energy. In this case the plasmas would likely be in the HED regime.
Summarized here are some of the possible industrial and medical applications of intense lasers, describedin more detail in the Brightest Light study, where HED plasma physics understanding plays a role.
1. Ultrafast X-ray radiography in medicine and industry. Ultra-intense (typically petawatt-class lasers)
are used to produce bright x-ray backlighters as described in Chapter 3 and have great utility for
performing radiography of imploding ICF capsules. These bright sources have been demonstrated to
produce high resolution and high contrast images, with the potential to allow 3D reconstruction ofimages. The sources are sufficiently coherent to create enhanced signals around density
discontinuities (phase contrast imaging), allowing discrimination of various tissues (or othersamples). This is not a feature of radiation from conventional medical x-ray sources from x-ray tubes.
Simulation capabilities to quantitatively predict the x-ray characteristics of such sources would aid in
optimizing and designing these sources.
2. Electron beams for cancer therapy. As described in Chapter 3, intense lasers may be used toaccelerate particles. High-energy electrons, whether from cyclotrons, linear accelerators, or lasers,
may be a better choice for tumor therapy than x-rays, as they are more easily focused and targeted on
the tumor. High energy ions also have advantages over x-ray therapy, particularly the ability tominimize damage to surrounding tissue. Laser-based accelerators may offer cheaper, smaller electron
sources than other options.
3. Laser-produced isotopes for positron emission tomography. PET requires positron-emitting
radioactive sources. Production of the positron-emitting isotope 11C was estimated to be 4200 kBq (onPREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION
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the LLNL Titan laser) via the 10B(d, n)11C
reaction, with an illumination intensity of
9  1019 W/cm2. However, this is stillmuch less than the required 800 MBq for
PET. Higher repetition rate lasers such as
ELI at 10 Hz will clearly be a large step
towards feasible production of PET
isotopes.
These possible applications all havedocumented proof-of-principle experiments,
as described in many references in the
Brightest Light report and may be ready for
implementation over the next decade.
The field of high energy density
physics is not limited to national laboratories
and large companies. The High Energy
Density Science Association (HEDSA) was
founded in 2005 to enable academic and small
business high energy density researchers to
advocate for HED physics research. HEDSA
facilitates increased communication andcollaboration between smaller research
programs and businesses and larger ones.
Most of the small business members of
HEDSA focus on software activities,
including experimental design, plasma
simulation, and computational physics.
In addition, large companies areclosely involved in supporting HED/ICF
experiments. General Atomics, for example,
conducts research and development in
ICF/HED targets, and supplies a significant
fraction of targets at the major ICF/HED
facilities in the United States.
FINDINGS AND RECOMMENDATIONSFIGURE 4.19 3-dimensional X-ray Imaging.
Imaging small details in biological tissue is a major
challenge for medical applications, requiring bright,
coherent, and small x-ray sources. These sources canbe produced by irradiating a solid with a highintensity laser. The level of detail obtained in theradiographs shown above and produced by such an xray source is due to the phenomenon of phase
contrast imaging. In this technique, a density gradientcreates interference fringes in a coherent x-ray source
which can then be use to perform 3-dimensional
reconstruction of the target. Quantitative
understanding of the HED physics involved in the
production of x-ray sources would improve thedesign and optimization of such biological andmedical imaging systems. SOURCE: Relations toand Perspectives of Industry, Nature
Communications volume 6, Article number: 7568
(2015).

HED is a field with broad, crosscutting applications in plasma physics. The
field has flourished for the past 10 years.
There are numerous results from many
institutions and facilities that have had a large
impact. The emergence of new major facilities
has greatly expanded HED capabilities andhas resulted in significant data for stockpile stewardship and national security. The ICF community is(and should continue to be) pursuing multiple options for inertial confinement fusion, including direct
magnetic drive, direct laser drive, and indirect laser drive. In the last decade, major facilities have madeimportant contributions to all approaches. There is now greatly improved understanding of the physics
required for ignition due to experiments performed on the NIF, even without ignition.

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Finding: Innovative diagnostics and diagnostic techniques have enabled developing adetailed picture of ICF plasmas and imploded target cores with unprecedented precision,and enabled the investigation of HED matter at previously unattainable conditions.
Finding: Diagnostic innovation is an ongoing need.
Finding: While significant progress in HED science has been made in the last decade,more advances are needed to improve predictive capability.
Recommendation: The DOE-NNSA, DOE-FES, and NSF-MPS should increase
resources for development of new diagnostics and analysis methodologies to addressneeds for ongoing innovation in HED physics.
Recommendation: The current NNSA ICF National Diagnostics Working Group
charter and workshops should be expanded to explicitly include HED diagnostics,
interaction with mid-scale facilities, and data analysis and data mining techniques.
There exist opportunities to improve the fundamental science basis in plasma simulation codes, as well as
to incorporate uncertainty quantification and machine learning techniques. The understanding of laserplasma instabilities (LPIs) and their mitigation, and incorporation of the physics of LPIs into simulations,will benefit HEDP and all approaches to ICF.
Finding: Improving our understanding of LPI is essential for continued progress toward
validated predictive capabilities, which are necessary for ignition and gain.
Recommendation: To achieve the goal of ignition and improve the quality of HED
science, DOE-NNSA, DOE-FES, and NSF-MPS should expand and strengthen
numerical simulation capability, focusing in particular on improved atomic andkinetic modeling (including equation of state), improved radiation transfer(including opacity), improved LPI (laser-plasma-instability) understanding,uncertainty quantification and machine learning.
Recommendation: Where possible the National Laboratories should contribute theirunclassified state-of-the-art simulations codes to collaborations with academic andcommercial efforts, and support training of qualified users.
Finding: Federal support of HED sciences at universities is essential to the health of
HED science.
The university centers established by federal funding have seeded growth in HEDP at universities, havebeen instrumental in achieving the current vibrant state of the field and in providing the needed workforce
for federal priorities.
Finding: The current paucity of mid-scale pulsed power facilities is a potential danger
for the field.
Recommendation: Federal support of HED at universities and mid-scale laser
facilities should continue to expand, not only to benefit HED physics but also tomaintain the critically needed HED workforce.
Recommendation: Mid-scale pulsed-power facilities accessible to universities shouldbe established, with leadership of these new facilities drawn from university
researchers and the national laboratories.
Finding: The basic science programs at NIF, Omega, and Z-machine have resulted insignificant scientific results despite having a small fraction of the available facility time.

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Finding: The high visibility of these basic science HED experiments increases the ability
to recruit new talent while improving the understanding of the universe and the science
underpinnings of other HED/ICF research.
Finding: Guidance is required for how best to leverage and expand the basic science
programs. This guidance could come from a new HEDP Basic Research Needs report.
Recommendation: DOE-NNSA, DOE-FES, and NSF-MPS should continue andincrease support for basic HED science programs at large facilities in collaboration
with universities.
Recommendation: The science program direction and the appropriate level offunding and facility support should be guided by the DOE-NNSA, DOE-FES and
NSF-MPS collaboratively commissioning a new HEDP Basic Research Needs reportfor the HEDP community.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

5
Low-Temperature Plasmas: A Unique State of Matter for Addressing Societal
Needs
LOW-TEMPERATURE PLASMAS—SCIENCE ENABLING SOCIETAL BENEFIT
The ability of low temperature plasmas (LTPs) to produce desired chemically reactive
environments in gases, on surfaces and in liquids has already made society-wide transformations in our
quality of life—from lighting, materials synthesis and water purification, to enabling the information
technology revolution through plasma-enabled fabrication of microelectronics devices. Those plasmaenabled societal transformations will continue into the future. A strategic and new opportunity for LTP
science and technology is to help enable the electrification of the chemical industry—that is, to drive
chemical processing by electrical means facilitated by plasmas. The critical enabling science iscontrolling the flow of energy through LTPs to produce predictable chemical transformations in gases, on
solids, and in liquids. The electrification of the chemical industry is a grand science and engineering
challenge that will enable an economically viable and sustainable future based on renewable electricity.
This chapter presents the case that improving our understanding of the fundamental processes in
LTPs will lead to translational research benefiting nearly every sector of society.
Unique Features of Low-Temperature Plasma Physics
Low temperature plasmas are a unique state of matter composed of neutral atoms, molecules,
radicals, excited states, ions and electrons. LTPs represents a distinct and, in many ways, unique form ofplasma. Most of the plasmas in the universe, including other areas of plasmas discussed in this report, arefully ionized, often magnetized and have average temperatures much higher than ambient. In most LTPs,
only a small fraction of the gas is ionized while the mean energy of electrons (a few to 10 eV) is muchlarger than the temperature of heavy particles (ions and neutrals) that can be as low as room temperature.
So even with energetic electrons, the average temperature of an LTP is low enough that these plasmas canbe in contact with heat sensitive surfaces, including living tissue, an ability that has enabled the field ofplasma agriculture and medicine. Maintaining this non-equilibrium state is possible because energy
transfer from electric fields to the electrons is generally much faster and more efficient than thesubsequent collisional energy transfer between electrons and heavy particles. A large fraction of theelectron energy can then be channeled into the production of electronically excited states, and, in
molecular gases, vibrationally excited species and short-lived radicals. The generation of chemicallyreactive environments at low gas temperature is a defining property of LTPs that enables their use in somany beneficial technologies.
In spite of the unique nature of LTPs, there are common features with other ionized gases. For
example, dust in LTPs can behave similarly to dusty plasmas in space. When high energy density plasma
comes into contact with cold walls—for example, in fusion devices—the plasma in the boundary layercools and shares many characteristics with LTPs. The interaction of electromagnetic radiation with LTPs
is similar to phenomena in other types of plasma. Some of the instabilities and waves found in higher
energy density plasmas also occur in LTPs.
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One feature of LTPs, shared with plasmas in fusion devices, is that nearly all LTPs interact withsurfaces that bound the plasma, either by the need to confine the plasma or intentionally to change thecharacteristics of those surfaces. In LTPs, the neutral gas temperature is near ambient while the electron
temperature is elevated, resulting in the ability to produce controllable fluxes of reactive species onto
surfaces without excessively heating the surface. The relatively high electron temperature and low
electron mass leads to the formation of thin space charge regions—sheaths—at boundaries. The electricfields in the sheaths accelerate positive ions to surfaces which then provide activation energy for materialchanging reactions on surfaces. Low temperature radical generation coupled with normal incidence
positive ion bombardment at surfaces has enabled a tremendous range of industrial applications based on
LTP processing of material surfaces and thin films; and in particular has enabled industrial scale
fabrication of microelectronics.
PROGRESS IN LTPS SINCE PLASMA 2010
The field of LTPs is exceedingly broad and so the review of progress since the Plasma 2010
report is grouped into four representative application areas: aerospace, life sciences, materials
interactions, and environment and sustainability.

Aerospace
During the past decade there have been significant advances in the science and technology of Hall
thrusters. The Hall thruster (HT) is one of the mainline architectures for plasma propulsion, devices used
to accelerate and control the trajectories of spacecraft in earth orbit, geosynchronous orbit and in missions
to the planets. In a HT, ions are accelerated to high energies, and emitted as plume of exhaust that pushes
the spacecraft in the opposite direction—akin to the exhaust of chemical rockets. This acceleration of
spacecraft is very efficient but produces low thrust, thereby requiring long periods of operation for the
spacecraft to reach the desired speed. The development of magnetic shielding has greatly reduced the ioninduced sputtering of the HT chamber walls. This has extended the life of HTs from nominally about 1
year to as long as 5 to 10 years, enabling their use in long duration deep space missions. NASA isdeveloping the Power and Propulsion Element (PPE) for the Lunar Gateway human exploration program,which will use 12.5 kW magnetically shielded HTs to move cargo from Earth to lunar orbits (andeventually Mars). HTs (3–4.5 kW) have been flown on commercial communications satellites in the past
decade, significantly reducing the propellant needed for orbit raising and station keeping, and similarthrusters are planned for upcoming deep space missions. In the past 5 years low power HTs, compatible
with CubeSat architectures have achieved >50% efficiencies (conversion of input power to thrust) andlong lifetimes both enabled by magnetic shielding.
Other advances have been made in the past decade include nested HTs, devices having multiple
annular channels to accelerate ions, which have been demonstrated in powers up to 100 kW with >50%
efficiency. However, erosion of electrodes and plasma-facing surfaces is increasingly problematic and the
topic of continuing research. Investigations of the physics of the cathodes used in HTs have revealed low
frequency plasma oscillations and turbulent ion acoustic waves that contribute to transport and energetic
ion generation. Electrodeless thruster concepts such as magnetic nozzles and Field Reversed
Configuration (FRC) thrusters have been proposed and investigated, concepts that may reduce erosion tothat required for multi-year operation at high powers. However, the efficiencies of these concepts are not
now competitive with state-of-the-art ion and Hall thrusters.

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Life Science Applications
There has been impressive progressin applying LTPs to biology and life sciencesin the last decade. For example, there havebeen many demonstrations of LTPs in
selectively destroying microbes in diverse
environments, ranging from inanimate
surfaces to living tissue, from plants tobiofilms. Advances have been made in direct
therapeutic applications of LTP in bothanimal models as well as human subjects.
There have been investigations in using LTPs
in treating cancer (see Figure 5.1); in healing
and disinfecting wounds; for dermatologicaltreatments; and in dentistry, among others.
The use of LTP to reduce anti-bacteriallyresistant bacteria strains in wounds has
FIGURE 5.1 LTP for cancer treatment – A major
shown promise in many studies.
challenge of plasma-based medical treatment is
A major advance came when the first
selectivity – eliminate the bad cells while notthree LTP sources were approved for humanharming healthy cells. Here is shown a possible
testing in the European Union in 2013.
mechanism of selective LTP treatment of cancer cells
Extensive studies on possible dangers tothereby enabling its application for a novel cancer
patients were conducted on these devices andtherapies. Plasmas produce reactive oxygen species
treatment protocols were developed before(ROS). As cancer cells have larger concentrations of
the approvals for human testing were granted.
ROS than normal cells, a well-dosed plasma
The available clinical studies generally
treatment is able to increase the ROS level in cancer
concluded that LTP treatment causes few orcells above the threshold for cell death while healthy
no significant side effects or complications.
cells remain below the threshold. This dose
There has been considerable progress inrequirement corresponds to a narrow treatment
identifying some of the mechanisms throughwindow requiring a detailed understanding of thewhich LTP acts therapeutically. LTP has
plasma-bio interaction process. SOURCE: Physics ofbeen shown to stimulate sub-cutaneous blood
Plasmas 25, 083504 (2018);
flow and blood O2 content; cell-cell
https://doi.org/10.1063/1.5034355.
communication; and elements of both innate
and adaptive immunity. Another important
LTP-associated mechanism is the biological effects of pulsed electric fields.
Since most biological systems of interest involve aqueous solutions, studies of LTP interactingwith biological targets and liquids have been closely linked. Many studies in the field have addressed therole of reactive chemical species produced by plasma in contact with air adjacent to aqueous solutions.
These synergistic studies have led to a broader understanding of the effects of different types of LTP
sources on biological targets and how LTPs can chemically activate liquids. For example, LTP treatmentof aqueous solutions (including water) produces a liquid that can remain anti-microbial for many days.
In addition to biomedical effects, progress has been made in agricultural and food-related
applications of LTPs. LTP have been shown to promote seed germination and disinfect seeds, and toenhance the growth of plants. Agricultural water treatment for both biocidal and nutrition production has
been demonstrated. Food and food container disinfection by use of LTP is being investigated and indemonstration trials. Finally, nitrogen fixation (e.g., production of fertilizer) have advanced over the past
decade.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

Plasma-Materials Interactions
Major developments in plasma materials processing have included the continuing progress inapplying LTPs to manufacturing of integrated circuits. During the last decade, microelectronics devices
have shrunk to the point that atomic layer control of plasma etching and deposition is required—arequirement that will extend to new quantum devices. Since it is extremely challenging to control plasma
to interact with only a single layer of atoms, self-limited processes and ultra-high materials selectivity areneeded for both deposition and etching reactions. Plasma-enhanced atomic layer deposition (ALD) andatomic layer etching (ALE) processes have been developed to meet these needs (see Figure 5.2). These
goals were met by enhanced control of the interaction of electrons, ions, radicals, excited neutrals andphotons with surfaces in LTP environments. When conventional continuous (steady state) plasmamaterials processes proved not to be adequate, techniques using pulsing were developed—pulsing of theplasma source power, substrate bias, input gases, substrate temperature, and other process parameters.
The development of plasma-materials processes consisting of sequences of individual, self-limited surface
reaction steps, where the total deposition thickness or etched depth is controlled by the number of process
cycles, has been a successful approach to meet the technological requirements. Device structures continue
to get taller (larger aspect ratio), more complex (3-dimensional memory) and with new materials. Plasma
technology has, to date, met these multiple challenges.
During the last decade there has been
wide penetration of plasma surface
engineering (PSE) into other industries
including etching, smoothing, precision freeforming, patterning, hardening, and coating of
surfaces. There has been increasing use of
atmospheric pressure plasmas for materials
treatment, with extension from inorganic toorganic surfaces (such as polymers) andbiological tissue (skin, wound treatment).
These advances have utilized new methods of
excitation. Although historically PSE has been
FIGURE 5.2 Atomic layer etching – Example ofquite empirical, the science of PSE has greatly
thickness evolution during eight cycles of an SiO2
advanced, through use of modern plasma
atomic layer etching (ALE) process. Self-limited
diagnostics techniques. These diagnostics
etching of SiO2 is realized by a number of individual
have led to the discovery plasma instabilities,
reaction steps in the plasma environment, including
turbulence and chaos, in what had been
surface modification followed by low energy ion
considered quiescent devices. Selfbombardment for removal of reacted products fromorganization in process plasmas has also been
the modified surface. The overall etch depth is
discovered, most vividly illustrated bycontrolled by the number of ALE cycles.
instabilities in sputtering magnetrons. The
SOURCE: Journal of Vacuum Science & Technology
development and application of simulation
A 32, 020603 (2014);
tools have greatly improved our
https://avs.scitation.org/doi/10.1116/1.4843575
understanding of PSE systems. Plasmas havealso been extensively investigated forsynthesis of new materials and structures. Major advancements have been made in the plasma synthesis of
nanoparticles and nanostructured materials including 1D and 2D materials.
Thermal plasmas are also intensively used for material processing including welding, cutting anddeposition of thermal barrier coatings. In the last decade, a detailed understanding of the influence of
metal vapor, particularly in welding arcs, has been developed. 3-dimensional time-dependents models andspatially resolved time-dependent measurements have clarified the mechanisms driving metal vapor
transport, and the influence of metal vapor on arc properties, droplet detachment and weld pool depth.
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

This societal benefit of this scientific advance will come with improved welding processes and wire-arc
additive manufacturing.

Sustainability and Environmental Applications
In the last decade, impressive progress has been made in understanding plasma assisted ignitionand combustion (PAIC). The motivation of PAIC is to improve conventional combustion processes byenabling lean combustion and ignition under conditions that improve efficiency and reduce theenvironmental impact of combustion processes. Localized heating and radicals produced by nanosecond
pulsed plasmas were found to be effective for triggering combustion processes. Nanosecond pulsed
plasmas that produce high electric fields efficiently channel energy deposition into electronically excitedstates of the molecules in air-fuel mixtures, resulting in rapid oxygen dissociation by electron impact andin excitation transfer from other electronically excited atoms and molecules. The majority of these studies
have been performed at or below 1 atmosphere, whereas in many engines, the gas is compressed to highpressures. At high pressures, discharge instabilities and self-organization might affect power deposition,induce hydrodynamic effects and alter dominant plasma kinetics—processes that require further
investigation.
The treatment of water contaminated with toxic matter by plasmas has been a strong focus of the
LTP community and the effectiveness of plasma in mitigating different pollutants has been investigated.
Recently plasma has emerged as a unique technology that is able to decompose carcinogenic species likeperfluoroalkyl acids (PFAAs) with energy
efficiencies better than competing
technologies, as shown in Figure 5.3.
The combination of plasma withcatalysts has been extensively studied in thecontext of environmental remediation during
the past decades. Catalysts combined withplasma have shown increased selectivity toremove pollutants from exhaust gases and also
increase catalyst lifetime due to in situ
plasma-based regeneration of the catalyst. In
FIGURE 5.3 Plasma-based water treatment – There
recent years there has been an increased
is a growing concern about perfluoroalkyl acids
interest in using the combination of plasmas(PFAAs) in water due to their toxicity for humans
and catalysts to increase selectivity and yield
and wildlife. Conventional water treatment is notof chemical conversions, with the main
effective for the removal of PFAAs. Recently
motivation being energy conversion. That is,efficient transformation of perfluoroalkyl substances
use plasmas to convert low value materials tocontaminated groundwater by plasma has beenhigh values materials as a form of energy
demonstrated. Interestingly, the research showed thatstorage. Examples include partial oxidation ofhydroxyl, often considered the key reactive species inmethane to make alcohols and ammonia
water treatment, plays no significant role and thesynthesis. The fundamental processes of
efficiency is ascribed to plasma-induced reactions
plasma-catalysis are not well understood. The
with electrons and ions. SOURCE: Environ. Sci.
majority of research has involved performing
Technol. 2017, 51, 3, 1643-1648,
optimization studies assessing thehttps://pubs.acs.org/doi/pdf/10.1021/acs.est.6b04215
consequences of varying input parameters(e.g., voltage, flowrate) on the output while
not necessarily addressing fundamental
processes.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

Societal Benefits of Advances in the Science of LTPs
An improved ability to control chemical transformations through electricity-driven LTP has
tremendous potential in a wide range of current and future societal challenges, including enabling thetransformation of the chemical industry from being fossil-fuel driven to being electricity-driven (seeFigure 5.4). This enhanced capability in LTP will benefit multiple sectors of society. Controlling plasmasurface interactions at the atomic level will enable the next generation of materials for quantum
computing, combating anti-microbial resistance, improving agriculture efficiencies and food safety,
enabling new energy storage technologies and developing plasma-based propulsion capable of taking
mankind to Mars and beyond.
THE ECOSYSTEM OF LTP SCIENCE AND TECHNOLOGY
Funding sources for LTP research in the United States are as diverse as its scope. Currently,
fundamental research in LTP is focused on plasma generation, non-equilibrium kinetics and plasma
chemistry; plasma interaction with solid and liquid surfaces, and near surface (sheath) properties; selforganization, magnetized plasmas and plasma-wave interactions. Funding for fundamental research in
LTP science is mainly by U.S. government agencies, including NSF, DOE-FES, AFOSR, ONR, DARPA
and NASA. As an example, the NSF-DOE Partnership in Basic Plasma Science and Engineering(PBPSE) LTP-focused research (including topics such as dusty plasmas) on the order of $3 million per
year. The DOE FES supported the Center for Predictive Control of Plasma Kinetics for 10 years (20092019) with an annual budget of approximately $1.8 million per year and additionally supported DOE
laboratory efforts in LTPs at a level of $0.6 million to $1 million per year. In 2019, this programtransitioned into support of smaller centersand distributed user facilities for LTP at thelevel of approximately $4 million per year.
The Air Force Office of Scientific
Research (AFOSR) has been a major sponsor
for electric propulsion. In addition, manyagencies including ARO, DARPA, DOE-BES,
NSF (Engineering, Materials), USDA, andNIH support LTP projects that are mainly
focused on the utilization of plasmas for
specific applications of interest for theseagencies. For example, ARO and AFOSR
have sponsored several MURI(Multidisciplinary University Research
Initiatives) that have funding of about $1
FIGURE 5.4 Enabling a future based on electricity
million per year, focused on specific LTP
through non-equilibrium plasma chemistry – Anenabled applications such as nanoparticle
exciting new vision for LTPs is its use as a processer
synthesis and control of electromagnetic
to use renewable resources and waste, convert themradiation. The funding landscape is therefore
into valuable products. This vision leads tohighly dispersed and with a primary focus onelectrification of the chemical industry as plasmas areapplications and translational research. There
ideally suited to be driven by electricity produced byis relatively little inter-agency coordination ofrenewable energy sources (including fusion in the
LTP research with the exception of the
future) and can be used for point of use technologies.
NSF/DOE Partnership in Basic Plasma
SOURCE: Courtesy Mark Kushner, University of
Science and Engineering.
Michigan, https://arxiv.org/abs/1911.07076.
Funding for applied research in LTP
in the United States includes both government
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Plasma Science: Enabling Technology, Sustainability, Security, and Explorationand industrial support. The Small Business Innovation Research (SBIR) and the Small BusinessTechnology Transfer (STTR) programs fund a wide variety of projects that use LTPs for a specialized andapplied outcome, but typically do not emphasize fundamental research. That is particularly the case for
SBIR. STTR requires the small business to collaborate with a research institution, typically a university,and so those programs tend to have a more fundamental component. Each year, federal agencies withextramural research and development (R&D) budgets that exceed $100 million are required to allocate
3.2% (e.g. for FY 2017) of their R&D budget to SBIR and 0.45% to STTR awards. To estimate theamount of funding that involves LTPs in some manner, even if approximate, the SBIR/STTR grants
database over the past 5 years was searched for the term “plasma”, which would include projects that, forexample, simply used a plasma tool to coat a surface but was exclusively focused on other topics, to more
plasma focused work. Projects referring to biological plasma were excluded. The results were $20 million
to $40 million per year. The majority of these projects involving LTP are likely using the plasma as a tooland not investigating plasma properties.
Industry funding is focused nearly exclusively on applications. Obtaining precise numbers for thiseffort is difficult since companies are not required to publish these data and LTP applications in industry
are invariably coupled with other sub-fields of science and technology. One sector that utilizes LTP
extensively is the semiconductor equipment industry. For example, one leading U.S.-based semiconductor
equipment company (Lam Research, Fremont, California) that uses plasma extensively in their equipment
reports an R&D expenditure of about $1.2 billion in fiscal year 2018. Other U.S. semiconductor
equipment companies such as Applied Materials (Sunnyvale, California) probably spend a comparable
amount on their LTP-based equipment development. The chip manufacturing companies also support
internal R&D in their plasma-related activities but no data are publicly available. Given the range andscope of using LTPs in industry (i.e., semiconductor, defense, aerospace, automotive, biotechnology,
materials, environmental), there are no doubt many other companies that support LTP R&D.
In summary, U.S. funding for fundamental LTP science is no more than about $10 million per
year. By contrast, corporate R&D funding for the development of LTP industrial applications probably
exceeds many $1 billion per year. Industrial estimates of total federal funding investments in LTP related
to semiconductor manufacturing, a part of all LTP research, is only 0.01% of the plasma processing
market—a small fraction for such a strategically important technology. The proper ratio is certainly
debatable. However, given that fundamental LTP research underpins several industries that are criticallyto our national economy and national security, the applied-to-fundamental research ratio appears to be asignificantly out of imbalance.
The central role of LTP is often hidden from public view, creating hidden value to the UnitedStates and world economy. The hidden value of plasma technology and the unquestionable value of theunderlying basic science have led to inconsistent research funding for the field. In the absence ofconsistent and reliable funding, it is impossible to sustain a sufficient number of world-class researchgroups in in the United States in LTP science to maintain long term leadership in the LTP field. LTP
research is carried out at universities and research institutes in multiple departments. The field is truly
cross disciplinary. However, this interdisciplinary strength has, to date, been a liability rather than an
asset in securing research funding for the field. Most funding agencies and funding mechanisms continue
to be strongly compartmentalized and discipline specific. Agency statements in support of crossdisciplinary research do not often translate into actual funding programs for cross disciplinary research,which is a severe problem for LTP in the United States. The impact of the already small amount ofgovernment funding for LTP fundamental science is further reduced by being highly dispersed with very
little coordination between funding agencies.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

Level of Effort
An estimate of the number of faculty and senior researchers active in low temperature plasmas in
U.S. academic institutions can be made from a community-generated white paper submitted to the APS
Community Planning Process in 2019. The white paper had 157 co-signers from 74 institutions(universities, national laboratories, companies). Of these co-signers, 136 had academic appointments from58 universities and colleges. Many of these colleagues are also involved in other research areas and many
focus on applications. This count is known to be an undercount, and so to be optimistic, the committee
estimated 175 academic researchers. This is significantly fewer than corresponding numbers in countries
such as France. Colleagues in France estimate that between 240 and 350 researchers are involved in LTP
within CNRS (the French National Center for Scientific Research) and in French academic institutions.
Using the low-high estimates for both countries, on a per capita basis France (population 67 million) has
3.6-5.2 LTP academic researchers/million population. The United States (population 329 million) has
0.41-0.53 LTP academic researchers/million population. On a per capita basis, France has 9-10 more LTP
academic researchers than the United States. The committee concedes that these figures are estimates. As
the LTP field is exceedingly broad and many researchers use plasmas as part of their research, it isdifficult to provide exact figures.
Another estimate of the size of the U.S. LTP community can be made from the number of PhD
and MSc theses published, available from the Proquest database for dissertations and thesis. This
database lists most, but not all, theses from U.S. educational institutions. Searches in this database overthe last 10 years, using the key words “low temperature plasma”, yield an average of about 75 theses/year.
However, typically fewer than 10% of these theses involve fundamental plasma studies. It is important tonote that whereas LTP research involving applications continues to grow, fundamental research in LTP
appears to be declining. There is concern that if this trend continues, within the next 10 years,
fundamental research in LTP that has historically been the basis of the development of LTP applications
will, with a few exceptions, no longer be practiced in the United States.
The demographics in the LTP field will result in a leadership class retiring within the next
decade. Plasma research is a multidisciplinary field and recent university faculty hiring has not produced
early career faculty with a focus on the fundamentals of LTP science. There are simply too few early
career LTP-oriented faculty for the United States to continue to be an international leader when thecurrent leadership class retires.
The establishment of the Low Temperature Plasma Science Center program at DOE since the2010 Decadal study has benefited fundamental LTP research. LTP research at U.S. universities remains
highly dispersed and it is not uncommon that only one faculty member to be involved in LTP research atan entire university. This underlines the need for a coordinated funding model for LTP and the need tostimulate and support inter-university collaborative efforts. The DOE Plasma Science Center Program has
served this role.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

RELEVANCE AND BENEFITS OF LTP
In most LTP applications, control of the plasma to achieve the desired effects is the ultimate goal.
Designing the plasma device entails making
decisions on particulars of the power supply(e.g., radio frequency, pulsed), method of
excitation (inductively coupled, dielectricbarrier-discharge, capacitively coupled)geometry, pressure and composition andrates of gas flow. Proper choices depend on
the details of the application. In addition to
design variables, the process parametersmust be selected and optimized for eachapplication. The challenge of this task is, inmany cases, difficult to exaggerate. For
example, in modern plasma etching
applications in the semiconductor industry,it has been estimated that there can be as
many as 15 different control parameters,
leading to an astonishing 1015 different
process recipes that could be used. Thishuge number results from the multiple film
materials are typically etched, with many
FIGURE 5.5 Plasma contactors. The environment
different gas compositions, coupled withsurrounding the International Space Station (ISS) is
many different possible operatinghazardous to astronauts for many reasons. One major
parameters such as gas flows, pressure,issue is electrons from the sun and local space plasma
multiple power supplies and control ofcharging up the structure. The ISS stores charge likewafer temperatures. Each of thesea capacitor, which can then discharge as electricalparameters can and often are altered as aarcs hazardous to space-walking astronauts. Thisfunction of time, with time variations thathazard can occur in all human exploration missions
range from slow ramps to abrupt pulsing.
and can occur in robotic missions where docking toControlling such a process is a majorother spacecraft is used. The charge buildup ischallenge. In spite of this huge set ofneutralized (and astronauts protected) by “plasma
possible parameters, industry is very good at
contactors,” which spray electrons into thefinding a solution that satisfy their needs.
surrounding ionosphere using hollow cathodeThat solution is not necessarily the best
discharges to maintain the electrical ground of thesolution—it is the solution that time andspace at the same electrical potential as thebudget allowed.
surrounding ionosphere. SOURCE: NASA/JPL.
Other applications may not havequite as large a parameter space, but similar
challenges do exist. How does one designand control the plasma to achieve a desired outcome? LTP is a highly non-linear and complex physicalsystem, including its interactions with its environment, and having more degrees of freedom than any
other plasma discussed in this report. The fundamental research questions in LTP are often oriented
towards this complex optimization and control problem. To deal with this complexity, an understandingof the dominant physical and chemical processes are necessary to build models that are by necessity lesscomplex but represent system well enough to enable predictive capabilities.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

TECHNOLOGY AND SOCIETAL BENEFITS FROM ADVANCES IN LTP SCIENCE
Plasma-Assisted Propulsion in Space Science and Exploration
Propulsion systems based on plasma, typically called electric propulsion thrusters or electricrockets, are an established technology used to keep communications satellites in their desired orbits
against gravitational and solar-flux disturbances that perturb their trajectories. Electric propulsion is also
emerging as the system of choice for deep space science missions. Gridded ion thrusters were used byNASA on the Deep Space 1 and Dawn missions to visit asteroids and were used by the Japanese Space
Agency JAXA to return samples from a near-Earth asteroid. The European Space Agency (ESA) mission
BepiColombo is now using ion thrusters to propel the spacecraft to planet Mercury. The Hall thruster wasused by the ESA to propel the SMART mission to the moon. Hall thrusters are also planned for theupcoming NASA science mission to the asteroid Psyche.
LTP Enabling Long-Mission Human Space Science and Exploration
One of the unsolved challenges for long mission human space flight is life-support-systems. This
challenge extends to long-term habitation on the moon and planets. Life-support requires energy efficient
sources of food, water and oxygen, and recycling of waste products. Plasma-liquid interactions andplasma chemical conversion represent a potential solution for all of these areas. Beyond water treatment,
plasma-technologies can address a wide range of space habitat challenges. Space agriculture would
benefit from the plasma treatment of seeds to reduce microbial load and improve water uptake to enhanceyield and the direct application of nutrients to plants via plasma-activated water.
Plasma-based subsystems are potentially components of life support systems. Unlike
conventional systems, which require high temperatures for chemical conversion, in LTPs chemical
conversion occurs largely at room temperature. LTPs can support atmosphere control through thedecomposition of carbon dioxide into by-products such as CO and oxygen. The potential for a plasmabased life support system has yet to be explored, and would be paradigm shift, enabling for essentiallycomplete recycling of waste-water and gases in the spacecraft. LTP is also key to the safety of spacecraft
and astronauts enabling the alleviation of charging. (See Figure 5.5.)
LTP in Advanced Microelectronic Devices Enables Many Other Areas of Science
The recent detection of colliding black holes by LIGO and the imaging of a black hole by the
Event Horizon telescope simply would not have occurred in the absence of modern microelectronics
devices. Gene sequencing, simulations of weapons, remote sensing, satellite communications, 3D
manufacturing, the display with which the reader is likely viewing this report, are all enabled by
microelectronics devices. The essential role played by LTPs in this enormous advance in humancapability enabled by microelectronics is in the manufacture of those microelectronics devices.
A recent report (April 2019) from the U.S. Semiconductor Industry Association entitled Winning
the Future. A Blueprint for Sustained U.S. Leadership in Semiconductor Technology addresses
semiconductor-related research support in the United States. This report notes the importance ofsemiconductors in emerging areas of advanced scientific exploration such as artificial intelligence,quantum computing, and advanced wireless networks. The fact that LTP is enabling the modern
semiconductor industry illustrates that LTP enables most of modern scientific discovery and technologicaladvances that create a major impact.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

Atmospheric Electricity
Physics of lightning has long been considered as prohibitively difficult to understand from firstprinciples, and so lightning research focused either on observations of the macroscopic phenomena(lightning occurrence and properties) or on lightning protection based on engineering models. Lightning
protection remains a topic of growing importance, particularly given the trend toward composites in theaerospace industry. However, the discovery of transient luminous events (TLEs) between clouds andionosphere in 1989, and the discovery of terrestrial gamma-ray flashes (TGFs) and other high energy
phenomena from active thunderstorms in 1994 have stimulated new plasma physics research on
atmospheric electricity. A new community has developed that is making new observations, undertaking
microphysics-based modeling and simulations and analogous lab experiments.
LTP research will play a crucial role in some of the key science challenges in this area including:Lightning inception: It is now roughly understood how a lightning discharge can start near one
graupel particle (soft hail or snow pellets) due to the local enhancement of the rather low backgroundelectric field in the cloud. The manner how lightning grows to tens of meters and more is not known.
Polarity dependent lightning propagation and stepping: Our understanding of how space charge
dominated streamer discharges propagate is improving, and this understanding also applies to theirlarger relatives, sprite discharges in the thin upper atmosphere. However, when additional effects like
plasma heating and plasma chemistry start to play important roles on larger scales of space and time,
our understanding is still quite limited. This increased understanding is necessary to explain polarity
dependent lightning propagation and stepping.
Lightning attachment: Where and how does a lightning leader attach to a structure (on land or anaircraft) leading to lightning damage? Recent optical observations show how counter-leaders emerge
from tall objects (like apartment buildings) and approach lightning leaders growing downwards fromthe cloud. A better understanding of this process would lead to new lightning protection schemes.

Plasmas in Hypersonics
Hypersonics is the field of fluid dynamics for speeds greater than Mach 5 (five times the speed ofsound). Bodies moving at hypersonic speed through gas will produce an enveloping plasma due toheating by the shock waves at the leading edge of the body. Understanding these plasma dynamics is
critical for the design of efficient, reliable and safe hypersonic platforms—for space access and return,planetary entry, defense applications, and high-speed civil transport. Understanding these LTP dynamics
is also of importance in predicting meteor penetration through the atmosphere and the associated risks
that a meteor impact might have to civilization. The plasma surrounding a body entering into theatmosphere at high velocity produces tremendous heat loads and a communication blackout. These
particular phenomena have been long known, but poorly characterized. However, for vehicles that havemore lift, the leading edges are sharper and heating is much more severe, exceeding many kW/cm2.
Methods to reduce the heating and accurately predict the heat loads are needed to improve the safety of
the crew and reduce the weight of thermal protection system. As the plasma passes around the hypersonic
body, expansion and recombination processes become important. Research on plasma produced radiation
and recombination mechanisms is needed to predict heat loading and to develop methods to minimize it.
The conductivity of the plasma is also of interest for the development of advanced control and power
extraction methods. For example, a magnetic field may be used to force the leading edge away from thesurface, controlling the drag and reducing the heat load. Magnetic fields may also enable MHD typepower extraction methods. Injection or ablation of easily ionized species may be used to enhance theconductivity for some applications.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

High-Power Microwave Generation
Advances in high power microwave (HPM) generation over frequencies of ~0.1–1,000 GHz areneeded for applications such as accelerators, fusion plasma heating, new materials development,
advanced radar, remote threat detection, and the transmission of massive volumes of data over long
distances. Producing high microwave-energy-density systems requires addressing issues of intense beam
generation, dense charged-particle confinement, extreme-environment-compatible materials, intenseradiation and particle diagnostic development, and the development of compact pulsed power. HPM
research and development requires advances in plasma physics theory, computation, experimental
diagnostics, and the integration of advanced electronics (sensors, system control, pulsed power) andsignal processing.
Extending conventional magnetron oscillators to GW power and kJ pulse levels requires better
understanding of beam-plasma interactions, plasma-induced pulse shortening, plasma-enhanced mode
competition, and scalability. Future opportunities include development of time-domain sources, where
HPM radiation is emitted from single-shot (ultrawideband pulses) or periodic-pulse-trains of plasmas
generated by ultra-short-pulsed lasers. There is both a need and opportunity for research of higher power,
compact (portable) sources of mm-wave and THz-regime radiation.
New materials are both the enabler and a research frontier for advances in HPM science.
Advances in predictive computational algorithms, computational materials by design, hardware, andphysical models are leading to new electromagnetic materials (especially plasmonic and metamaterials),
new extreme-energy-tolerant refractory materials (for low-outgassing anodes) and new cathode materials
for thermionic, photo- and field emission. Frontiers in cathode physics include understanding how
interfaces, morphology, microstructural heterogeneity, bipolar flows and space charge effects, including
nanoscale charge transport, determine emittance, brightness, and cathode lifetime, especially in cold (fieldemission) cathodes.
Understanding and controlling interactions between localized, dense plasmas and strong EM
fields is critically important to HPM sources. Multipactor avalanche (where electrons are scattered andmultiply along a microwave window) on conducting and dielectric surfaces by HPM fields can lead to a
localized plasma discharge. Controlling surface breakdown of both distributed and spatially periodic
discharges would enable longer HPM pulses.
Plasmas for Optics and Wave Manipulation
The field of “plasma metamaterials and plasma photonic crystals” involves LTP science in whichplasma elements (individual plasmas, plasma gratings or plasma arrays) serve as, or are integrated into,
electromagnetically active artificial materials to produce desired response to electromagnetic (EM) waves.
“Plasma metamaterials” act as a filter that will pass or reflect only certain wavelengths due to there being
resonances of the EM wave with the plasma array. “Plasma photonic crystals” and gratings relay on EM
wave interactions with repeating plasma structures comparable, leading to Bragg interferences, that willreflect only selected wavelengths.
Plasma integration into Metamaterials (MMs) and photonic crystals (PCs) have already proven
important in a wide range of applications in microwave, mm-wave, and optical-wave photonics—
applications important to communications systems. These devices are typically “static” systems. The
potential of plasma-based MMs and PCs is the ability to rapidly reconfigure these structures by changing
the properties of the plasma. Plasmas can be used to more effectively focus and shape the radiation fieldof antennas or reflectors, be used as invisibility cloaks, provide improved impedance matching, and they
can spectrally filter, guide, and confine EM waves with high quality factors. The plasma introduces adegree of reconfigurability at potentially high bandwidths. In communications applications, several ofthese features relate to the improvement or enhancement of speed and bandwidth (the amount of

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

information that can be communicated). An
example of a plasma photonic crystal is illustrated
in Figure 5.6.
LTP Benefits to the Environmental andSustainability
Water purification: LTP processes help mitigate
environmental hazards and processes that
contribute to man-made climate change. For
example, LTPs as ozone generators have longserved as the basis of water purification inmunicipal water systems. Water is commonly
FIGURE 5.6 Plasma wave interactions – A photonic
polluted by pharmaceutical wastes, organic
crystal is a structure that enables the manipulation ofcompounds, odor, NOx, SOx , viruses, agriculturallight and can for example be used as an opticalrunoff and other waste products, including
modulator. Plasma devices can be used to actively
fracking effluent and industrial waste water withtune the properties of the photonic crystal by
persistent pollutants. Cleaning water in anchanging the electron density as their operation
efficient and scalable manner challenges
frequencies are controlled by the plasma frequency.
traditional means of water purification. A
A key advantage is that the tunability can be
relatively new approach utilizes advanced
achieved at relatively high rates as it is only limitedoxidation processes (AOP). These methods useby the ionization or recombination times of thethe oxidizing potential of the hydroxyl radical
plasma which can be significantly faster than(•OH) which is more reactive than ozone (O3) andtypically mechanical, thermal, or fluidic time scales
hydrogen peroxide (H2O2). LTPs are emerging as
used in conventional devices. The image shows an
a strategic technology that can provide theexample of a plasma photonic crystal setup that isreactants in AOP treatment of water. LTPs arecompletely formed by plasma elements that are
being investigated as in-water sources ofindividually controllable.
oxidizing species such •OH, O• and H•, and for
SOURCE: https://doi.org/10.1063/1.4946805
the emission of UV light for disinfection. Plasma
based water treatment is especially attractive
since there is no input required other than electricity. The radicals required to remove contamination,
pollutants and organic matter are derived from the water itself (or air in contact with the water), requiringno additional chemicals.
Closed carbon and sustainable energy cycles: Of all the environmental and sustainability issues that must
be addressed, CO2 engineering is perhaps the most pressing. There is currently no technology available toeconomically and permanently remove CO2 from the environment, or to capture and recirculate thecarbon in a carbon neutral manner. LTPs represent a science able to address many of these needs. Current
research is addressing plasma conversion of CO2 to CO for syngas (a mixture of CO and H2) to recirculate
the carbon for carbon-neutral combustion. Similar LTP processes are being investigated for plasma
conversion of CH4 to hydrogen (the second component of syngas) and to higher value hydrocarbons. The
ultimate closed carbon cycle may involve bio-based carbon raw materials to replace currently
manufactured petro-chemicals. Recent research indicates LTPs may play a key role in this effort.
Utilizing plasmas in energy applications already has a record of success. Thin film solar cells are
economically viable due to the efficiency and selectivity of plasma-assisted deposition and thin-film
etching in industrial scale fabrication processes. LTPs for pollutant mitigation and waste treatment havepotential applications across the industrial and municipal landscape. Pilot plants use plasma torches forconverting municipal solid waste to syngas and minimizing the need to dispose of solids. The syngas canthen be used to sustainably produce electricity. Plasma based systems are used to treat contaminants inindustrial gases, to treat SOx/NOx emission from power plants and to remediate medical waste.
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

Fossil fuel combustion will likely play a significant role in modern society for the next several
decades. Using those precious resources more efficiently positively impacts every measure ofenvironmental stewardship. As discussed above, plasma-aided ignition and combustion (PAIC) is ahighly promising technology to address some of those needs.
SF6 replacement gases in high-voltage switchgear in electricity distribution systems: SF6 has
several favorable properties that have led to its use in high-voltage circuit breakers—it is non-toxic,
stable, is gaseous even under pressures of the several atmospheres that are typically used, it has excellent
insulating properties and, since it has lower energy than any of its decomposition products and is thus
reformed after an arcing event. However, because of its high global warming potential, it is scheduled tobe replaced. CO2 is now being used in some installations but has poorer insulating properties and is also a
global warming gas. New gases, in particular C4F7N and C3F8O, show strong promise; however, they
have relatively high boiling points and therefore have to be mixed with CO2 or other gases. They are also
gradually decomposed after arcing events. Research into the decomposition pathways of these gases
under typical operating conditions, their reactions with metals and vapors ablated by the arc, andcomputational modelling of the arcing process are all required to optimize the design of circuit breakers
that use such gases.
LTP in Education and Workforce Development
LTP is intrinsically multidisciplinary, with investigations extending to other research fields frommaterial science to medicine. As a result, students pursuing LTP topics in their graduate studies receive aninterdisciplinary education. The research in these allied fields similarly has far-reaching educational
impact, helping to train the next-generation of investigators in both the application area and in plasma
physics. Graduates from LTP programs begin their careers in a wide range of science and engineering
disciplines in industry, national laboratories, and academia.
LTP IN ECONOMIC DEVELOPMENT
LTP science and technology have long addressed critical societal problems and have createdsignificant economic impact through the interplay between basic science, applied science, andtechnological challenges. Since plasma technologies are primarily enabling technologies, theircontribution to a specific product or method often remains hidden or even unknown and their direct
impact, especially their economic impact, is often difficult to assess. Success of LTP in advanced
applications has been the result of a significant and sustained investment in basic and applied plasma
research in North America, Asia and Europe over many years. This critical support enabled the plasma
community to (1) leverage basic plasma science breakthroughs for the development of strategic
applications (e.g., integrated circuits in microelectronics) and to (2) use the success of plasma applications
to challenge basic plasma science to thoroughly investigate these new phenomena and provide a scientificunderpinning.

Materials Processing: Semiconductor and Related Industries
As one of the top 10 industries in the United States, the semiconductor industry is a strategic asset to the
U.S. economy and national security. Semiconductor chips are the fundamental technology that enables
computers of all types (laptops, mobile phones, data centers, and supercomputers) and their applications,from medicine to national defense. Microelectronic chips enable the rapidly expanding world of artificial
intelligence (AI), where state-of-the-art chips are increasingly embedded into products such as

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autonomous vehicles, web commerce sites, industrial manufacturing plants, and ultimately supporting thegrowing sophistication of our national security infrastructure.
The chemically reacting environment capable of delivering highly controlled activation energy towafers enabled by LTPs is absolutely essential to the manufacture of these devices. Of the 400-950
processing steps required to manufacture leading integrated circuit (IC) chips, 40-45% are plasma based.
It is no exaggeration to say that virtually every chip in circulation today has been touched by plasma. If
there was a better, cheaper, more reliable method for microelectronics manufacturing than use of LTPs,
the committee believes the industry would have gone in that direction. The reality is, that after decades of
exponential semiconductor scaling, advances in new technologies depend more than ever on plasmabased processing. Plasma etching, alone(“trimming”), or in conjunction with atomic
layer deposition (ALD) has recently been used tocreate mask features with widths of tens of nm to< 10 nm. This “disruptive” technology may
obviate the need for extreme UV lithography inmany applications.
The economic impact of LTPs isenormous and can be quantified in the
microelectronics industry. Currently, the UnitedStates leads that industry with close to half of the
global IC market worth nearly $500 billion,
which serves a roughly $2,000 billion electronics
market. Estimates of future growth in the IC
industry based on current trends suggest that a 5year doubling in revenues is likely. To
manufacture the microchips that enable thismarket, the global IC industry purchases $50
billion (2018) of wafer fabrication equipment per
year, of which approximately $15 billion to $20
billion is plasma based.
FIGURE 5.7 Plasma additive manufacturing –Two robotic welding machines are fabricatingsteel-aluminum aircraft wing ribs using a wire +Materials Processing: Polymers
arc additive manufacturing process (WAAM)
which deposits layers of metal from a wire in a
The use of LTPs in materials processing
technique derived from welding. WAAM
beyond microelectronics fabrication has andfabrication of pieces from metals, alloys andcontinues to have a huge impact. LTPs forcomposite materials is significantly shorter thanfunctionalization of polymers for wettability andusing conventional methods, with considerable
adhesion is the basis of large industries as well as
cost savings. The concept has long been pursued,
emerging applications. Commodity polymers
but recent developments in LTP arc technologies
such as polypropylene, polyethylene andand robotic control are increasing WAAMs
polystyrene are treated with plasmas to produce
importance in the manufacture of, for instance,hydrophilic surfaces that will wet and adhere toaircraft parts which are conventionally machined
other materials. These techniques are now beingfrom solid blocks of metal. SOURCE:
applied to high value materials such as metals,
https://www.alamy.com/stock-photo-wire-arccarbon fiber laminates, 3D-manufactured parts toadditive-manufacturing-at-cranfield-universityremove contaminants and to improve adhesion.
147641206.html.
The development of plasma processing
techniques for biotechnology is also an
established industry with emerging applications. LTPs are used for biocompatibility (e.g., cell adhesion,
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

specificity) and sterilization, and is now finding new markets in treating medical polymers to enable more
precise and reproducible medical studies.
In 2018, the worldwide production value of polymer films and sheets was $120 billion, growing
at 5 to 6% annually, of which 70% involves forms of polyethylene and polypropylene films, virtually allof which require some form of surface modification. The products using these films and sheets have amarket value of over $330 billion. The majority of all products utilizing polymer films require LTP(corona) treatment to enable acceptable final product performance.
Materials Processing: Coatings
LTP sputtering processes are extensively used in industry for coatings and functional films. The
cathodic arc deposition has remained a base technology for high-rate coatings on tools and automotive
parts and gained new importance in deposition of thick thermal barrier and erosion protection coatings
such as on turbine parts. At the same time alternative technologies such as HiPIMS (high power impulse
magnetron sputtering) are becoming established in segments of the industry, especially the high-end
tooling industry. Another major application includes plasma deposition on glass substrates for reflection
and antireflection coatings.
Additive Manufacturing
Metallic additive manufacturing is an increasingly important process, enabling prototyping,production of custom-designed parts and production of complex structures not possible using traditional
methods. Many metallic additive manufacturing processes use metal powder as the precursor (e.g.,
powder-bed approaches such as selective laser melting and selective electron-beam melting, blownpowder approaches). Thermal plasma processes, including spheroidization using inductively coupled
thermal plasma and wire-to-powder using thermal plasma jets, have proven ideal for production of suchpowders.
Wire-arc additive manufacturing (WAAM) is an emerging additive manufacturing approach. In
this process, a wire is fed into a high intensity plasma arc, which rapidly melts the wire to redeposit on an
adjacent surface. WAAM is well suited to the production of large components, since it is fast andrelatively inexpensive (metal wire is much cheaper than powder). There are several challenges that haveto be overcome. These include improved resolution and control, which requires control of the arc andideally a spatially confined arc, separate control over the wire feed rate and the arc current, methods toreduce residual stress and distortion (which occurs due to the repeated heating and cooling cycles), andmethods to control the microstructure of the deposited metal, which determines the mechanical propertiesof the component. An example is shown in Figure 5.7.
LTP Applied to Lighting
Plasma lighting sources have dominated commercial, industrial and public lighting needs for 150
years. In spite of this longevity, plasma-based lighting has made progress in the development of compact
fluorescent lamps and back-lighting for flat panel displays, both of which have extensive commercial,industrial and residential use. In the 2010 Decadal Survey, it was reported that plasma light sources—
fluorescent bulbs and high-intensity-discharge lamps—produced 80% of all the light used in generallighting. While consumers were switching to more efficient plasma (fluorescent) lighting at that time due
to improvements in the quality of the light and the life expectancy of the lamp compared to incandescentbulbs, lighting still accounted for 22 percent of all electricity produced in the United States. Plasma-

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display panels and televisions, also
controlled a significant amount of the display
market in family households at that time.
That dominance of plasma lighting is
beginning to erode with the development ofsolid-state lighting sources (e.g., lightemitting-diodes and laser-diodes) and flat
panel displays. However, the essential role of
LTPs in lighting has actually increased in thetransition to solid state light sources. The
high-volume manufacturing of these devices
requires the controllable chemical reactivity
produced by LTPs in the same manner as
FIGURE 5.8 From fundamental micro-plasma
microelectronics fabrication. Essentially all
research to ozone production for rural point-of-use
solid-state lighting and flat panel displays use
water purification – Fundamental research into theplasma deposition, etching, cleaning andgeneration of plasmas in micrometer sized channels
implantation steps in their manufacturing.
has led to the development of stackable modules of
While plasma may no longer be the main
microplasma channels for efficient low energy ozone
source of the light, it is the source of the
production for rural water purification. The sources canhigher efficiency and lower cost electronic
be powered by solar cells and have proven their value
devices that make and control the light today.
in developing countries and for disaster areas.
The U.S. Energy Information Administration
SOURCE: Photo courtesy of J.G. Eden.
(EIA) estimated that in 2018, only about 8%of the total electricity consumed by the
combined residential and commercial sectors was used for lighting. Advances in plasma processing in thelast decade directly resulted in significant reductions in the amount of electricity required for lighting in
the U.S.
LTP Applied to Flow Control
Plasma-based flow control actuators have seen major advancements that improve the operation of
aircraft. For example, if efficient arrays of LTP can be applied for on-demand vortex generation during
takeoff and landing of aircraft, and be deactivated during the cruise phase, there is the possibility ofsignificant fuel savings during the overall flight. This technology would eliminate the drag penalties
associated with conventional vortex generation in the cruise phase. Alternative opportunities may also
exist for drag reduction by generating plasma at other positions on the aircraft to reduce drag, reducenoise, or eliminate instabilities.
Ozone Generation
LTPs, as ozone generators, have for many decades served as the basis of water purification inmunicipal water systems. The global ozone generation market was valued at $880 million in 2016 and is
expected to reach $1.5 billion by 2023. To be economical, ozone generation systems typically need to beon the scale suitable for municipal water treatment. This discourages their use for rural point-of-use water
treatment far from municipal systems. A recent development is using microplasmas for rural point-of-use
water treatment (see Figure 5.8). (A microplasma is a plasma confined to less than 1 mm dimension.)
Using modular arrays of microplasmas powered by solar cells, ozone-based water treatment has been
made available to “off grid” villages. While ozone generation processes are well known, technologicaladvances continue to be made in the field and are often highly focused on engineering. At the same time,science challenges do remain. For example, the ozone zero phenomenon (where ozone production ceases)
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Plasma Science: Enabling Technology, Sustainability, Security, and Explorationin pure O2 is not well-understood. This is of significant relevance for applications requiring pure ozone asin some semiconductor processing applications.
CURRENT AND FUTURE SCIENCE CHALLENGES OF LTP
Kinetics and Collisional Processes in a Highly Nonequilibrium Regime
The key distinctive feature of LTPs is that power transfer to gases, solids and liquids occurs
through energizing electrons (and ions in sheath regions) followed by collisions of those particles withgases, solids and liquids. This leads to highly non-equilibrium plasma kinetics. The LTP field is often
driven by applications with plasmas in complex molecular gas mixtures and operating over a wide rangeof gas pressures. The fundamentals of plasma kinetics have been studied in atomic low-pressure plasmas.
The investigation of plasma kinetics in complex molecular plasmas and at higher pressures (often
atmospheric pressure and above) and even in liquids has received far less attention, yet applications ofthese systems are where future opportunities lie. The analysis of molecular plasmas often suffers from alack of fundamental data, ranging from electron impact cross sections to ion mobilities. At the interface
between plasma and liquids, such as water, electron and ion solvation play a dominant role, a topic that is
only beginning to be understood.
The driving focus for LTP science is: Controlling the non-equilibrium energy deposition anddissipation in collisional LTPs to enable plasma-produced selectivity. This is an extremely challenging
topic that has a common science base—that being plasma kinetics and collision physics. However, evenfundamental plasma science investigations will have system and application specific solutions. (See
Chapter 2.) This specificity is due to the large number of reactions and species, and the wide range ofplasma conditions, for example, nearly 9 orders of magnitude difference in pressure between
microelectronics processing and plasma-in-water treatment. Bridging this large gap and exploring
selectivity for a broad range of applications places great emphasis addressing fundamentals that will scale
and the development of predictive modeling.
Plasmas generate infrared, optical, UV and VUV radiation—this is the basis of plasma lighting
sources. The consequences of the production and transport of radiation, and particularly UV/VUV
radiation, is perhaps one of the greater unknowns in generation and propagation of LTPs and in plasma
material processing.
Scaling, Instabilities, and High-Pressure Regimes
The high rate of electron- and ion-neutral collisions at atmospheric pressure not only leads toincreased gas heating but also enhances the tendency to develop spatio-temporal instabilities, and selforganization. This increased sensitivity stems from fundamental scaling laws and plasma kinetics. To firstorder, maintaining constant E/N (electric field divided by gas number density) in many LTPs typically
produces similar electron temperatures. At constant E/N, an important scaling law is pd ≈ constant, where
p is the gas pressure and d the plasma scale length. The higher the pressure p, the smaller the plasma scale
length d. In a typical glow-discharge plasma, pd ≈ 1 Torr-cm. Spatially dependent plasma phenomena that
occur over many cm in a 10 mTorr plasma occur over a few microns at atmospheric pressure. This scaling
has enabled an entirely new field of microplasmas, which tends to produce filamentary behavior and selforganization. In addition, the larger range of length scales down to the micrometer level provides uniquechallenges for diagnostics and modeling.
Plasma sustained at high neutral gas density experiences correspondingly higher collision
frequencies of electrons and ions with neutral species compared to lower pressure plasmas. At constant
E/N, another important scaling law is p ≈ constant. The higher the pressure, the shorter the time  overwhich a collective plasma process (e.g., ionization wave) occurs. Plasma phenomena that occur over s to
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

ms in a 10 mTorr plasma tend to occur over ps to ns timescales at atmospheric pressure. These shortertime scales significantly increase the complexity of controlling plasma kinetics at atmospheric pressure.
Under these conditions, plasma phenomena that need to be time-resolved create unprecedented challenges
for both diagnostics and modeling. Several strategies have been developed to minimize gas heating andthe associated development of plasma instabilities. These include nanosecond pulsed plasma excitation to
produce the plasma on time scales shorter than the time for an instability to grow. Such fast excitation
approaches with large amplitude voltages have enabled the production of novel, highly energetic neutral
species as well as run-away electrons. Similar phenomena are thought to occur in poorly understood
upper atmospheric plasma phenomena such as sprites and elves.
An example of a new plasma regime is transient plasmas in atmospheric pressure plasmas andliquids with high ionization degrees (more than 10%) generated by nanosecond voltage pulses. These
unique conditions, particularly at such short time scales, enable the gas temperature to remain relatively
low. Phenomena associated with strongly coupled plasmas start to become important under these
conditions, offering many opportunities to explore novel low temperature plasma with analogs to warm
dense matter as well as non-neutral and dusty plasmas.
Crossed Electric and Magnetic Fields Transport
Anomalously high transport of plasma across magnetic field lines is pervasive, spanning manybranches of plasma physics from fusion to astrophysical plasmas. In LTPs, crossed electric and magnetic
fields, EB, transport is most commonly associated with magnetrons used to sputter in materials
fabrication and in electric propulsion (EP) devices. In these EB systems, instabilities and waves often
occur. The lack of understanding of transport in crossed electric and magnetic fields has precluded thedevelopment of the types of predictive, numerical models that are highly desirable for both analysis anddesign. An emerging consensus is that these instabilities can be attributed to non-classical effects such as
self-organized oscillations and micro-scale turbulence.
There are a number of remaining knowledge gaps about transport process in EP systems such as
Hall effect thrusters (HTs) which are EB devices. For example, there are discrepancies between
modeling results and experimental measurements related to the shape, dominant energy modes, directionof propagation, and influence of micro-turbulence on plasma transport. Recent particle-in-cell simulations
have shown that fast moving electron waves drive coherent, large amplitude, ion acoustic waves. Whencoupled with local ionization, these waves can produce the cross-field transport and acceleration potential
profiles observed in HTs. (Another form of EP the magnetic nozzle, have similar unresolved issues.)
In magnetrons, an array of magnets and a high voltage applied to a cathode produces a closed
loop of electron motion adjacent to the cathode. The plasma in the closed loop can be highly ionized,
producing a large flux back to the cathode to sputter atoms. Magnetrons are geometrically similar to HTs
in having an EB structure that is prone to instabilities and waves, which can lead to reproducibility
problems in industry.
In an effort to address open questions in EB transport, on-going modeling efforts are focusing
both on building direct numerical simulations enabled by increased computational capabilities as well as
physics-based fluid/hybrid models that can approximate non-classical transport. Expanded experimental
efforts combined with new diagnostics will need to be able to measure energy coupling across several
scale lengths, the phase relation between microscale electric field and density, and particle distributions.
Plasma Surface Interactions
In most cases, LTPs are bounded and the bounding interface dominates plasma properties.
Interactions of plasma with interfaces are also recognized as a major challenge in other plasma
disciplines. Examples include the interaction of fusion plasmas with the diverter wall and interactions ofinterplanetary dust with space plasmas.
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

Plasma-interfacial interactions canbe highly complex due to strong coupling
between the plasma properties and theinterfacing material surface properties. This
interaction can be due to surface charging,electron generation, local field enhancement,
sputtering or evaporation of surface material
into the plasma, surface deformation, plasmainduced surface property changes and surface
reactions in reactive plasmas. Many of theseimportant interfacial processes are not wellunderstood particularly for complex surfaces
like volatile liquids and surfaces withcomplex nanometer to micrometer scalesurface morphology such as catalysts.
Understanding plasma interactions withcomplex surfaces will ultimately requiredeveloping a broader range of in situ surface
diagnostics and multiphase modelingleveraging knowledge from different
communities. For example, understanding andcapitalizing on the synergism between
catalysts and plasma remains a major
challenge and topic for future intensive
fundamental and highly interdisciplinary
research. (See also Chapter 2.)
As noted above, low pressure LTPs
are used to alter surfaces and thin films forsemiconductor device fabrication. For
example, progress in maintaining accurate
control of ion energies and angles at surfaces
in plasma etching is an enabling technology inthe semiconductor industry (see Figure 5.9).
The materials challenges in the semiconductor
industry have been and will continue to besignificant. A new group of materials are
becoming more important in this industry,including graphene and other 2D materials,
III-V compound semiconductors, ultra-highdielectric constant materials, complex oxides
and nanoparticles, among others. Control ofplasma-surface interactions will become evermore important, and new experimental andtheoretical approaches will be needed.

FIGURE 5.9 Tailored voltage waveforms – A major
goal in low-pressure capacitively coupled plasmas(CPP) of the type used for microelectronic processing,is independent control of the flux and the energy ofions impinging on a substrate. This implies a
requirement of direct control of the spatial distributionof plasma properties and ionization. Several
techniques have been explored including exploiting
dual-frequency plasma generation, nonlinear plasma
dynamics by tailored voltage waveform engineeringand the electrical asymmetry effect. The figure showsthe effect of the spatiotemporal excitation rates as
obtained by phase resolved optical emission
spectroscopy (PROES) and particle in cell (PIC)
simulations while changing from a sinusoidal driven
CPP (n=1) to a sawtooth waveform (n=5).
SOURCE: B. Bruneau, T. Gans, D. O’Connell, A.
Greb, E.V. Johnson, and J.-P. Booth, Phys. Rev. Lett.
114, 125002, doi:10.1103/PhysRevLett.114.125002.

Self-Organization
Self-organization is an often-observed phenomenon in LTPs. Self-organization can occur in thebulk plasma or in the anode or cathode layer at the interface between a plasma and a resistive or dielectric
medium. For example, a resistive or dielectric medium can stabilize the plasma into an array of spots. In
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

glow-discharges interacting with liquids, andtypically when the water is the anode, selforganization occurs on the surface with visible
patterns ranging from circular to star-like shapes.
When ionization fronts propagating through theplasma impinge on a dielectric surface the discharge
tends to spread as a surface ionization wave that candisplay self-organization. The self-organization isthought to result from 'memory' effects associatedwith surface charge patterns or through non-linear
streamer-streamer interactions. Three dimensional
simulations of ionization waves and streamers havebeen performed in the gas phase whereas surface
ionization waves have only been recently modeled
and intrinsic 3D phenomena have not yet been
FIGURE 5.10 Self-organization in high power
addressed. We currently do not have a generalmagnetron sputtering –Magnetron sputtering is used
understanding of the mechanisms responsible forextensively for the deposition of coatings. The
self-organization in atmospheric pressure plasmas
plasma dynamics, including self-organizing
interacting with surfaces. (See also Chapter 2.)
phenomena such as spokes, can have a significant
Self-organization can also occur in the bulk
impact on the properties of the coatings. In thisplasma. These patterns can arise from non-linear
figure, spoke patterns in a Radio Frequency
electron kinetics, memory effects and plasma-wave
Magnetron Sputtering regime for different dischargeinteractions in magnetized plasmas. Examples
powers and working gas pressures are shown. The
including striations in non-magnetized glow
light intensity is displayed in a color scale.
discharges for a wide range of pressures, filament
SOURCE: Journal of Applied Physics 125, 203303
patterns in dielectric barrier discharges, spokes in(2019),
magnetron EB discharges (see Figure 5.10) and in
https://aip.scitation.org/doi/10.1063/1.5094240.
Hall effect thrusters. While specific models havebeen able to reproduce some observations, a generalscientific understanding is still emerging for many of these self-organized processes. To gain a better
understanding of self-organization the community needs to answer questions related to the role ofgradients, electron kinetics, and the coupling between large- and small-scale plasma structures (energy
cascade).
FROM SCIENCE TO IMPLEMENTATION
Due to the close coupling of fundamental science and motivating applications in LTP, theresearch is nearly always in a state of translation. (Translational research refers to a smooth continuum
that begins with fundamental studies and leads to applications.) The translational nature of LTP science isa tremendous strength, but it also places an implied obligation on LTP science to perform that science inregimes that will produce results that quickly convert to applications. An ever-present theme andchallenge to LTP science is how to bridge the gap between science discoveries and technologies
developed in the laboratory and products that benefit society. Laboratory developed technologies
typically require a combination of advanced testing and predictive modeling to understand how they may
perform beyond controlled laboratory environments. Two representative examples that highlight thecritical challenges faced in implementing LTP technologies for electric propulsion and energy, material,
life and agricultural science are highlighted below.
LTP for electric propulsion (EP):PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION
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

Challenges arise in the ground testing of thrusters—“facility effects.” Thrusters in space emit plasma
into nearly perfect vacuum, conditions that are difficult to replicate on Earth in large enough volumes
and for long enough to conduct life testing.
 High-power, special purpose facilities can address some of the “facility effects.” However improved
understanding of EP physics would also enable alternative, cost-effective tests based on numericalmodels or accelerated wear tests. High fidelity, experimentally validated models are need tounderstand EP physics and mitigate life-limiting mechanisms.
LTP for energy, material, life and agricultural
applications: While there are many different surfaces
and structures that are treated with diverse
goals and objectives, there is a common
challenge. Little is understood about how
to couple plasma source design andoperation to specific applications forchemical, biological and material systems.
Translating fundamental studies ofparticle distributions to activating adesired surface modality is at the forefrontof LTP science.
 There remain significant theoretical and
FIGURE 5.11 Plasma diagnostics developments –experimental challenges to understanding
Diagnostics, critical to advancing LTP science, arethe correlation between a plasma
particularly challenging in multi-species, chemicallytreatment “dose” (the sum of all reactant
reacting environments. New diagnostics are being
species incident on the target) and theenabled by advancements in laser and detector
subsequent biological effect forcapabilities. A recently implemented diagnostic,
biomedical applications.
electric field induced second harmonic generation
 There are extreme challenges due to(EFISH), enables electric field measurements withcoupling of phenomena at vastly different
sub-nanosecond resolution, and unlike previous
time scales. For example, plasma-tissue or
methods, is nearly independent of the species in theplasma-cell culture exposures usually lastplasma. The only requirement is that the gas has afrom seconds to minutes whereas thereasonable polarizability and can be used in most
biological responses occur over minutes
high-pressure plasmas. The example shows 1-D
to days, or even longer in some cases.
measurements of an ionization front in a highSimilarly, plasma produced radicals in thepressure LTPs. SOURCE: Reprinted with permission
gas phase evolve over much shorter times
from Goldberg et al., 1D time evolving electric field(microseconds to milliseconds) compared
profile measurements with sub-ns resolution using
to surface catalytic reaction time scales inthe E-FISH method, Opt. Lett. 44:3853-3856 (2019),
plasma catalysis (seconds to minutes).
© The Optical Society.
Plasma can induce liquid phaseconvection over similar long time scales, all of which impact plasma-liquid treatment.
 The central challenge in many of the proposed applications of LTP activated processes to energy,
water, food and agriculture is in scaling. Even if plasma can be shown to be effective on smalllaboratory scales, the process must be scaled sufficiently to make it useful in an industrial setting,whether in the factory or the corporate farm. One exception might be plasma medicine applications
since the focus is on safety rather than scale-up.
 It is highly likely that scale-up will take a modular approach—arrays of highly efficient plasma
modules that are combined for higher throughput. The modular nature of the technology then enables
off-grid point-of-use applications. These would be, for example, small farms or shops using locallygenerated solar or wind power.
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Plasma Science: Enabling Technology, Sustainability, Security, and ExplorationFor many anticipated applications in medicine, and agriculture, the intended users (e.g. physicians
and farmers) are unlikely to be trained in the complex field of LTP science and technology. This isparticularly the case of off-grid point of use, but also true for medical professionals. There may be aneed for LTP source autonomy where the plasma source is intelligent enough to adapt to changes inthe surface being treated (every patient and plant is different), perhaps borrowing technologies frommachine learning and artificial intelligence driven autonomous vehicles. The concept is ‘one doctor,
one button' or ‘one farmer, one button.’
Diagnostic Development

Recent developments in LTP diagnostics have leveraged laser-based techniques to produce highspatial and temporally resolved measurements. Laser induced fluorescence (LIF) is a widely useddiagnostic that can probe species-specific density and velocity distribution functions (VDFs). Since laser
diagnostics typically involve the absorption and emission of photons, the collisional nature of most LTPs
requires new insights into the consequences of collisions on the measurement. Close collaboration withthe atomic, molecular and optics (AMO) community is needed to fully exploit these new laser
diagnostics. New diagnostics have been developed based on femtosecond and picosecond pulsed lasers.
These short timescale probes, only recently applied to atmospheric pressure collisionally dominatedplasmas, can make measurements between collisions. These techniques hold great promise for future
investigations. The implementation of Electric Field Induced Second Harmonic (EFISH) diagnostics has
enabled, for the first time, measurement of electric fields in a plasma with sub-nanosecond time resolution(see Figure 5.11).
While traditionally reserved for higher temperature and density plasmas, recent advances in laserThomson scattering (LTS) have opened the door to more extensive use of this diagnostic in low plasma
density (e.g., plasma materials processing systems, EP) and atmospheric pressure LTP research. For morecompact LTS setups, the use of volume Bragg gratings (in place of triple grating spectrometers) has been
demonstrated. Development of laser-based techniques with improved spatial resolution that can be usednear surfaces, remains a major challenge.
While the sophistication of experimental techniques continues to progress, there are several
critical aspects of low pressure LTPs that to date have not been experimentally accessible. These include
non-invasive measurements of high frequency (> 1 MHz), mid-wavelength plasma oscillations (e.g. therelationship between density and potential fluctuations). Direct, non-intrusive measurements of the mostfundamental plasma properties (electron densities and temperatures, and electric fields) also continues tobe challenging at atmospheric pressure. Extending diagnostics originally developed for low pressure (e.g.,laser collisional induced fluorescence and microwave scattering) to higher pressures continue to holdgreat promise. At the same time, diagnostics that take advantage of high pressure should also be pursued.
The complexity of reactions and range of species in non-equilibrium molecular plasmas provide
major challenges for diagnostics. A large variety of diagnostics are available including molecular beammass spectrometry, LIF, laser scattering techniques, and a range of absorption techniques including
broadband absorption, cavity ring down spectroscopy, tunable diode laser absorption. However, each ofthese diagnostics, powerful in their own right, have limitations on pressure, species, spatial resolution andtimescale. Further developments to increase the capabilities of these techniques, and to broaden the typesof species that can be measured, should be a key priority, together with exploring new approaches such as
the recent development of frequency comb spectroscopy.
Diagnostics tools are available for material surface characterization and measuring active species
in liquids. However, the majority of such diagnostics are focused on ex situ characterization. An increased
understanding of the coupled physico-chemical processes at plasma-solid and plasma-liquid interfaces
requires further development of in situ diagnostics amenable to a harsh and complex plasma environment.
The development and implementation of new in situ diagnostics to probe changes in surface properties(solid, liquid and soft organic surfaces) and structure during plasma exposure is a critical priority for the
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

LTP field. This could be accomplished by developing new surface diagnostics or adapting, where
possible, surface science techniques.
Modeling and Simulation
Predictive computational modeling capabilities are critically important in advancing LTP scienceand technologies. There are three main physics-based approaches employed to model LTP devices: fluid,particle kinetic and grid-based direct kinetic methods. Hybrid models, where fluid and kinetic methods
are combined for different species and conditions, are also widely used. Despite significant advances in
the field in the past decade, modeling LTP remains challenging due to the multi-physics and multi-scale
nature of the discharge phenomena.
While fluid models are inherently computationally less expensive, they have limited capability inrepresenting the detailed aspects of kinetic-based processes. Examples include instabilities found in E×B
devices, turbulence in low pressure systems, the dynamics of double-layers and in high electric fieldregions as in sheaths and near ionization fronts of atmospheric pressure streamers. The challenge for thesemodels is to develop time-dependent, physics-based equations and closures that account for these kinetic
effects. For kinetic models, which in principle have the highest fidelity, computational time is a major
limitation. For example, current simulations are limited at best to two-dimensional phenomena up to a
few tens of microseconds using explicit particle methods. This is too short with insufficient dimensional
fidelity to resolve or understand, for example,
interplay between collisionless phenomena(beam-bulk instabilities) and three-dimensional
collisional phenomena (e.g. plasma wallinteractions and intermolecular collisions).
Three-dimensional models have been
increasingly exploited in the last few years totackle the intrinsic 3D phenomena of selforganization and inhomogeneous nature of
atmospheric pressure plasmas (see example in
Figure 5.12).
The ultimate LTP challenge isachieving predictive control of the plasma
activated chemical processes. This is
FIGURE 5.12 Three-Dimensional LTP Simulations.
particularly complex due to the sensitive twoSimulationof LTPs is typically highly computational
way coupling between the electron energy
expensive and the majority of simulations to date
distribution (EED) and the gas composition,
have been performed by 0, 1 or 2D models. In the
including the species produced throughlast decade, 3D simulations have been developed tocollision processes. Given the translational
address many important intrinsicallynature of LTP research, models are required
multidimensional phenomena in LTPs. The figurethat are fully fundamentally physics based, butshows an example of a 3D particle-in-cell Montealso have the robustness to be used for design
Carlo collision model with adaptive mesh refinement
and optimization of devices. For example,of the inception of a nanosecond pulsed atmosphericcomplex plasma chemistries may include adischarge near an electrode. This approach is able tohundred individual gas phase species (ions andaddress the highly irregular and inhomogeneous
neutrals), a thousand reactions, and similar
discharge inception – often called branching.
complexity in plasma-surface interactions
SOURCE: Jannis Teunissen and Ute Ebert 2016
needing resolution from microns to tens of cm.
Plasma Sources Sci. Technol. 25 044005.
High-performance computing is required for

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

models that contain the needed physics andreaction complexity while also representing
the geometries of interest for LTPs ontimescales of interest.
Significant progress has been made inplasma-surface interaction modeling for both
non-thermal and thermal plasmas. Nonethelesscomprehensive models with a two-way
coupling of non-equilibrium plasma kinetics
in plasmas intersecting with complex
interfaces such as liquids, including
evaporation, charging, deformation, liquidinterface dynamics and liquid phaseconvection, continue to be a challenge. Whilemodels of thermal plasmas have made major
progress in the last few years, such as thatgained in the detailed understanding of theinfluence of metal vapor in welding arcs, forexample, no self-consistent physically based
FIGURE 5.13 Machine learning in LTP – Big data
models of arc-electrode interaction exist forand machine learning are now emerging in LTP
many situations of practical interest. Similarly,
science. Supervised learning might provide uniquemodels that resolve nano-scale features at
capabilities for LTPs in process control. The image
plasma interfaces and evaluate their impact onshows an example of machine learning enabling thethe plasma properties have yet to be fully
construction of computationally efficient surrogate
developed. In large part, these challenges aremodels for thin film deposition produced by ion
due to the enormous range of coupled length
sputtering of a surface. The algorithms predict
scales and timescales that must be included in
sputtered particle distributions (yield Al/Ti andsuch comprehensive models.
reflection coefficients Ar) for unknown, arbitrary
Developing standards for verification,
shaped ion energy distributions in multi-scalevalidation, and benchmarking of new andmodeling of plasma-surface interactions acrossexisting models will continue to be extremely
multiple length- and time-scales. SOURCE: Plasma
important. Validation of models and reaction
Sources Sci. Technol. 28 (2019),
sets is increasingly important as a
https://doi.org/10.1088/1361-6595/ab0246.
comprehensive understanding of LTP
phenomena requires coupling diagnostics withvalidated models. The development of validated predictive capabilities requires a large team and longterm efforts that are currently not in place for the U.S. LTP community. Such efforts to date have focused
mainly on gas phase kinetics. Model validation including interaction of LTPs with interfaces has yet to besystematically addressed. Chemical reaction sets are, in some cases, available for both gas and liquid
phase plasma models. However, plasma-surface interaction models generally do not match the rigor
associated with models of multiphase phenomena characteristic in fields such as atmospheric aerosol
models. Descriptions of plasma-surface interactions developed for low-pressure etching and deposition
plasmas will need to be extended and adapted to include important processes relevant for a broader classof material properties and plasma conditions.
The purpose of modeling is to better understand the current state of experiments and to predictwell beyond the current state of the art—new systems, new excitations schemes, new configurations, newapplications, new physic for which experimental data for validation might not exist. The required
precision for computationally analyzing well characterized benchmarking experiments is greater than the
precision required for exploratory, first of their kind simulations beyond the current state of the art.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

Data Science, Machine Learning, and Artificial Intelligence
Machine learning (ML) is a branch of artificial intelligence (AI) that seeks to find patterns fromstatistical or probabilistic analysis of large amounts of data. ML is attractive for multiple applications in
not LTP but in all systems involving plasma. ML involves training a computer algorithm to predict the
behavior of a complex system by collecting many examples of input-output behavior. ML methods can besignificantly simpler than using exclusively physics-based models. Fundamentals of ML were developed
over the last several decades, but only recently has it become practical to obtain and analyze the enormous
quantities of data needed for the schemes to work. Learning-based control approaches can potentiallytransform LTP control, enhancing plasma reliability, flexibility, and effectiveness. ML has already had alarge impact for HVM (high volume manufacturing) using plasma processing in the semiconductor
industry where very large datasets are available. However, in laboratory scale experimental LTP, in mostcases, ML will not have true “big data” to work with. The data sets will be relatively small andincomplete. For big data approach to be useful in LTP, it should be well coupled with our priorknowledge of underlying physics and chemistry—that is, physics or algorithmically based ML. This is a
new unique challenge for the LTP field.
Even with its challenges, ML holds the promise to transform LTP modeling, diagnostics, andcontrol. ML and AI could lead to the development of self-aware and self-correcting LTP systems, as will
likely be needed in LTP applications where the target varies from case to case (e.g., medicine,
biotechnology, agriculture). ML is rapidly expanding into many novel applications, typically driven bypractical applications. It is expected that LTP will be not be an exception in the next decade. However,
LTP applications are unique challenges to ML methods due in part to the intrinsically strong non-linear
coupling of multiple parameters for most LTP systems and processes.
FUTURE OPPORTUNITIES IN LTP SCIENCE—STRATEGIC CHALLENGES
Given the great diversity of science areas and applications in LTPs, future opportunities that crossthe area may best be expressed in terms of high-level Strategic Challenges. Here are four strategic
challenges that, while not exhaustive, encompass the breadth of the field.
Developing Plasma-Based Tools for Future Health Care and Food Cycle Needs
LTP is a unique state of matter with characteristics that have, until recently, been exploited
mainly for non-living materials processing and chemical applications. Recent advances have shown that
LTP can be used to decontaminate both inanimate and living material surfaces through a range ofphysico-chemical mechanisms. LTP has demonstrated human therapeutic benefits for applications that
include promoting wound healing and cancer treatment. The fact that LTP can influence biologicalsystems through multiple pathways and mechanisms suggests LTP can be used for many different
biological applications as well.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

For example, over the last several decades, antimicrobial resistance (AR) has reached nearlycrisis proportions. (AR is where microbes, bacteria and viruses, become immune to drugs, rendering thosedrugs ineffective or useless for treating infections.) All reports indicate that AR will continue to become
more severe for the foreseeable future. It is well known that the development of systemic antimicrobial
drugs has slowed down and some knowledgeable observers predict a post-antimicrobial world where
drugs are no longer effective against major
infections. Plasma disinfection andsterilization tools would certainly not solve
all problems associated with AR, but they
could be powerful tools in localized,
resistance-free, selective disinfection
devices. Many bacterial infections in humans
and on medical devices occur in the form of
biofilms. The highlight in Figure 5.14
illustrates one field of active research inapplying LTP to biofilms.
There are many other potential LTP
applications in healthcare. LTP has beenshown to stimulate immune systems inanimal models, promising for many medical
conditions. A relatively unexplored area is
use of LTP devices for cosmetics
applications and skin treatment. The field of
LTP therapeutics is just beginning to indicate
its potential.
Promising LTP applications inagriculture could greatly impact the foodcycle, from plant growth to food safety.
FIGURE 5.14 Plasma-biofilm interaction – A
Food, food system, and water disinfection
biofilm is a community of microorganisms attached
are possible applications of LTP, although
to a living or inanimate substrate and are thecosts and scaling issues represent additional
dominant mode of growth of bacteria. The majority
challenges. Other potential applicationsof chronic human bacterial infections are caused bywould use LTP to reduce or minimize thebacterial biofilms. The methicillin-resistant S. aureus
use of pesticides or herbicides.
(MRSA) bacteria forms biofilms and is one of the
The field of 'bioprocessing' in whichmost common source of biofilm-associatedbiological processes are conducted on a large
infections. Plasma has been shown to effectively
scale to create or alter some chemical
inactivate biofilms including MRSA. The figure
species, could benefit from LTP treatment or
illustrates the active plasma components possibly
enhancement. Recent advances include using
involved in the inactivation and the complex
LTP to treat organic waste to improve its
structure of the biofilm. The interface between thefertilizer characteristics. This technique uses
multi-component plasma and the biological interface
the plume from air plasma interacting withwhich has an order of magnitude higher complexity
biologically decomposing waste inthan traditional plasma-solid interactions provide
bioreactors. This concept could be extended
profound intellectual challenges for the field.
to other bioprocesses.
SOURCE: B.F. Gilmore et al., Cold plasmas for
In each of the potential applications
biofilm control: Opportunities and challenges, Trends
listed above, there is are corresponding
in Biotechnology, 36(6):627 – 638,
challenges, opportunities and need to expand
https://www.cell.com/trends/biotechnology/fulltext/Sand extend LTP science.
0167-7799(18)30091-X.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

Challenge 1: Controlling plasma-surface interactions at the atomic level to enable thenext generation of materials for quantum computing, new communication, sensor, energy
storage and harvesting technologies.
Advances in plasma-materials processing are challenged by the need to choose operating
conditions and plasma devices from and enormous parameter space. There is a serious need for a moredetailed understanding of the fundamental processes underpinning plasma-surface interactions to enable
us to develop predictive modeling capabilities. A huge victory would be predictive modeling that can apriori specify the optimum operating conditions and plasma device architectures. From practicalperspective, having modeling reduces the enormous parameter space would enable more productive
experiments. The implementation of advanced plasma materials processing may require advanced control
schemes, which in turn require better control-oriented mathematical models as well as better in-situ, realtime plasma diagnostics that are compatible with ultra-clean processing. This offers also opportunities for
ML techniques. Major opportunities in plasma materials processing include controlling surface texture at
the nanometer scale and controlling interfaces between atomically defined material layers.
Many novel opportunities will no doubt present themselves as the semiconductor integrated
circuit device industry continues to grow. Advances in device architectures are now exploiting the 3rd
dimension, increasing capability with layers of layers of devices. Memory devices now underdevelopment use 256–512 layers each of which need to be deposited followed by etching with aspectratios (height to width ratio) of on the order of 200. These are major plasma processing challenges.
One example in this area of forward-looking research needs involves post-silicon materials.
Many post-silicon materials will consist only of a single atomic layer (e.g., 2D materials) or require
atomic level precision in their processing. It is clear that plasma etching and deposition of post-siliconmaterials presents challenges much different than those encountered for silicon. These challenges in turnpose new plasma science questions, including unprecedented control of ion energies (<10 eV) near thechemical sputtering threshold. Precursor gases for post-silicon materials processing are much more
complex than in silicon processing. Properties of atomically thin post-silicon materials will be cruciallyaffected by defects created by the interactions of plasma ions, radicals, and photons. Plasma-surface
interaction control will be paramount for defect-free plasma processing of post-silicon materials.
Achieving atomic-scale control over surfaces and structures for multiple new materials and devices
requires a significant increase in understanding of plasma-surface interaction mechanisms and thedevelopment of advanced diagnostics and predictive modeling.
Challenge 2: Electrification of the chemical industry based on renewable electricity toenable a sustainable society.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

LTP science could be crucially important to enable the vision of a future basedon renewable electricity. In this vision, electrification of the chemical industry utilizing
plasma will convert electricity into chemical transformation in an environmentallyfriendly way. The key enabling science will be controlling the flow of energy through
LTPs to produce predictable chemical transformations in gases, on solids, and in liquids.
Liquid phase electrochemistry and photochemistry - both utilizing catalysis - aregenerally thought to be the only
ways to directly convert electricity
into chemical transformation.
However, plasma acts as gas-phaseelectrochemistry, a capability thathas been greatly underutilized.
Renewable energy sources such as
solar, wind, water and hopefully
fusion energy will continue to leadto a more abundant availability ofcheap electricity that will graduallylead to the electrification of thechemical industry.
In addition to energy costs, theother major challenge with using plasma forlarge scale chemical conversion is lack of
selectivity. Plasma tends to create a wide
range of different products with a limited
ability to control which are created. One
obvious strategy to improve plasma
chemical selectivity is to combine plasma
with catalysis, a topic addressed in theexample in Figure 5.15.
The trend towards chemical
FIGURE 5.15 Plasma catalysis – Plasma catalysis
industry electrification will coincide with aprovides possible new exciting opportunities forgradual replacement of chemical feedstocks
selective and enhanced chemical transformations,that originate from fossil fuels to feedstocks
however, the underlying mechanisms are not clear.
produced from renewably sourced raw
The figure illustrates the anticipated effect ofmaterials such as biomaterials. The
vibrational excitation as one of the possible sources
challenge to developing this potentialof catalytic enhancement by plasmas. The upper
application of LTP is to better understandfigure shows a reduction of the energy barrier byand control the flow of energy from thevibrational excitation. The lower figures shows theelectrical power supply to the catalyticenhancement of catalytic site-specific rates by several
surface through key intermediate chemicalorders of magnitude over thermal rates as obtained by
species. This challenge will require detailed
calculations. The development of an in depth
studies to enhance our current
understanding of all possible plasma-induced
understanding of kinetic and collisional
enhancement mechanisms and their relative
processes, plasma self-organization,
importance is of key importance for further progresstransport and plasma-surface interactionsin this field. SOURCE: Mehta, P., Barboun, P.,
under highly non-equilibrium conditions.
Herrera, F.A. et al. Overcoming ammonia synthesis
Only an improved fundamental
scaling relations with plasma-enabled catalysis. Nat
understanding of plasma-chemical speciesCatal 1, 269–275 (2018),
surface dynamics will make this possible.
https://doi.org/10.1038/s41929-018-0045-1.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

FIGURE 5.16 Plasma Physics Enabling
Space Missions – Electric thrusters greatly
expand our ability to propel spacecraft
through the solar system. Missions areplanned for probes and manned missions
using high power Hall thrusters (HT) to
deliver more mass in a shorter period of timethan conventional systems. HT use a crossfield EB plasma to ionize and accelerate
gaseous propellant. When spacecraft re-enter
the atmosphere at hypersonic speeds, anenveloping plasma produces a complex
chemically reacting LTP. Detailed modelingand experiments are needed to better
understand HTs and to provide guidance forscaling to high powers and lifetimes, and tobetter understand the interaction of
hypersonic vehicles and plasmas. SOURCE:
NASA/JPL.

Challenge 3: Enabling space exploration andsafeguarding communication infrastructure
Low temperature plasma physics research is
crucially important to the future of propulsion used forelectric rockets, for in-space propulsion oncommunications satellites, for NASA science missions,and for the development of advanced electric
propulsion (EP) systems that are emerging as a
critically needed component of human space flight tothe moon and Mars. Industry projections suggest that
half of all commercial spacecraft in the next 10 years
will have EP onboard. Plasma-based thrusters arehighly efficient and can reduce propellant fuelrequirements by one to two orders of magnitude overchemical propulsion. This is critically important forcommercial applications, and will likely be enabling forhuman exploration missions that require the transport oflarge amounts of cargo and even people through space.
Fundamental plasma physics investigations on electric
thrusters are essential to improve the thruster
performance and increase the lifetime. An example ofkey plasma science challenges linked to Hall thrusters
is illustrated in Figure 5.16.
LTP SCIENCE FROM AN INTERNATIONALPERSPECTIVE
Due to the breadth of applications enabled by
low temperature plasmas, there is a diverse
international community of researchers. To assess thestate of international research, this committee reached
out to research leaders in LTP science around the world
to solicit their input on their own programs and toprovide their opinions on the state of the U.S. LTP
program. Since this is not a fully comprehensive
survey, the committee has limited the reporting ofspecific numerical data. Nonetheless, the committee
believe that there is a level of consistency among the
responses that allows us to make reasonably informed
statements about the state of international LTP research.

Distribution of Worldwide Effort in LowTemperature Plasmas
Much of worldwide research and technology development in LTP is concentrated in Europe andAsia. From Europe, the committee received input on the status of LTP research in Germany, Belgium,
France and the Netherlands. From Asia, the committee received input from South Korea, Japan, andChina. Among the white papers submitted to this study, the authorship included researchers from France,
Germany, India, Italy, Mexico, Slovakia, Spain, United Kingdom, and Ukraine. Research topics
mentioned by these researchers match many of the topics that are being pursued in the United States. In
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

those nations with reasonably mature LTP research activities, governments generally provide support for
both translational research activities and to support new initiatives, for example, the recent expansion into
plasma agriculture. A key difference between the United States and several other countries is that LTP
research in U.S. institutions is often based on single-PI activities. By contrast, countries such as Germany,
the Netherlands, France and China have clusters of faculty or tenured researchers forming research teams
and group.
Self-Assessment of International Research Activities
In Europe, the LTP community is very active, but the level of activity varies among the different
countries. Across Europe, the total number of researchers involved in LTP research activities seems tohave remained relatively constant in the last 10 years with fluctuations across the different countries:
Germany reports relatively stable numbers, while the Netherlands is experiencing a slight increase, but
France and Belgium are possibly experiencing a slight decrease. According to our data sources, funding is
generally provided via two mechanisms—by national governments and the European Union—but the
majority of the funding generally is at the national level. Because of differences in how funding isprovided, it is difficult to assess precisely how much research funding is devoted to LTP research.
Estimates from European colleagues suggest tens of millions of Euros per year are being provided tosupport research in LTP active countries. On a per-capita basis, this would appear to be substantiallylarger than the funding provided by U.S. funding agencies to support LTP research. It should be notedthat some countries—notably Germany, France, and the Netherlands—have active programs fromgovernment-based Ministries that promote “translational” activities to bring technologies fromuniversities to industry. Many of these are in the form of center-like activities that include European
training and networking grants with multi-year programs that advance a particular topic and stimulate
multi-institutional collaborations. Regardless of the mechanism, in Europe, it is reported that there has
been a substantial conversion of LTP research into new companies.
In Asia, the state of LTP research is more complex. The major programs in this area are based inSouth Korea and Japan, but China is emerging rapidly as a significant competitor, as are developing
programs in Singapore and Taiwan. State support of LTP research varies widely among these locations.
In South Korea and in Japan, where the application of LTP technologies is a large and significant
industrial driver, both nations provide active support for LTP research, reportedly ~$10 million per year.
In both of these countries, state-sponsored funding is available to support translational activities that bring
university and national laboratory ideas to the marketplace. Although much more difficult to quantify,
China heavily invests in translational LTP research.
In comparison to overseas investments, U.S. industrial leaders specifically cite the Chinese
National Guideline for the Development and Promotion of the IC Industry. The goal of this program is todevelop Chinese capabilities in wafer equipment processing to support China's burgeoning IC device
manufacturing industry, and large component of which is plasma equipment. There is nothing analogous
in the United States. China is not alone in support of this critical industry. In South Korea, thegovernment funds major university research partnerships with large companies such as Samsung and SK
Hynix, both major IC manufacturers. Other governments around the world have clearly recognized theneed to fund enabling and breakthrough technology for plasma-based wafer equipment processing.
However, the United States significantly lags in this regard.
U.S. Research Activities in LTP in the Context of the World Program
Data shows that over the last decade, the U.S. publication rate (as a percentage of first authorship)
has generally remained stable around 25% in a selection of journals publishing LTP research, including
the Journal of Applied Physics, Plasma Sources Science and Technology, and Journal of Physics D:
Applied Physics. Nonetheless, the submission of papers from Asia and particularly China is growing and
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

although no exact data is made available, Chinese contributions dominate the LTP section of Physics ofPlasmas.
Europe, Japan, and South Korea are already making significant investments at the national levelto advance their LTP industries. China and India are poised to advance their own LTP research andindustries. In areas, such as plasma medicine, the United States has fallen behind its competitors in bothbasic and applied studies due to a lack of substantial and stable funding. This situation is in stark contrast
to Germany, The Netherlands, France, Belgium, Italy, Japan, and South Korea, who have had andcontinue to have major initiatives in these areas. In newly emergent areas, such as plasma agriculture,
there are already substantial international investments and the United States is in danger of falling behindin this area as well.
Importance of the United States to Current International Collaborations
Many informal collaborations between U.S.-based researchers and their European and Asiancolleagues exist. This is reflected in the significant number of co-authored peer reviewed articles of U.S.
researchers with European or Asian colleagues. However, these are often one-on-one collaborations and,in many cases, no structural (i.e. agency-related) funding is available. This is in contrast to the highlycollaborative international research facilitated by the EU, as well as several formal 1-on-1 international
collaborations (e.g., Russia-France, Japan-Australia). Many leading research groups in the United Statesoften host international scholars from both Asia and Europe as visiting researchers however even thosevisits are now being limited by visa restrictions and universities imposing fees to cover federally
mandated security investigations. The U.S. LTP community has benefited considerably from the existing,limited, degree of international collaboration. However, the U.S. LTP community could greatly benefit
from increased interactions with their European and Asian counterparts.
Given that LTP science is closely linked to applications, many potential international
collaborations are restricted by ITAR (International Traffic in Arms Regulations) considerations. This isparticularly the case in electric propulsion. The committee respects the need for national security
oversight of international collaborations. However, a review and update of ITAR classifications would
benefit international collaborations and also benefit U.S. science.
FACILITIES, MAJOR INSTRUMENTATION, MAJOR PROGRAMS
The last decade of research in low temperature plasmas has seen significant technologicaladvances in the various ways in which LTP is produced. At the start of the decade, the majority of theresearch and applications were performed in low-pressure vacuum systems in highly controlledenvironments and most applications at atmospheric pressure involved high temperatures (e.g., arcs). This
has rapidly evolved over the last decade with the development of non-equilibrium atmospheric pressureplasma sources that aim to produce large volumes of plasma without a vacuum chamber. A further
development has seen the shift of research in LTP processing from semiconductor materials to “soft”
materials such as liquids, biomaterials, and even agricultural products. This evolution in the operating
conditions has necessitated the development of a new generation of complex diagnostics that require
unprecedented time and spatial resolution to resolve exceptionally large gradients and changes in plasma
properties.
The vast majority of laboratory facilities for the study of low pressure to atmospheric pressure
LTPs are in the tabletop scale of devices—often surrounded by a suite of advanced diagnostic tools. The
major investments for a typical LTP laboratory are often complex power supplies including nanosecond
pulsed power capabilities and modulated multi-frequency RF plasma sources, coupled with various probe,
optical, surface and mass spectrometry-based diagnostics. Within the United States, each laboratory iseffectively an independent facility that is generally responsible for its own development of plasma sources
and plasma diagnostic tools. While the last decade has seen some sharing of resources among researchers,
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the operation of individual laboratory facilities remains the dominant research model. This model
provides an excellent training ground for students and seamlessly integrates with the LTP practices inindustry.
While LTP facilities are focused on small-scale experiments, the facilities needed for LTPs
applied to space systems can be very different. LTPs for in-space propulsion requires facilities on the
ground that simulate the space environment in with the electric propulsion (EP) device will actuallyoperate in. These facilities have vacuum vessels capable of reaching low enough pressures to relevant tospace research and large enough to contain the EP device and its plasma plume, while also having theappropriate diagnostics. These facilities are scattered throughout the United States at NASA and Air
Force facilities, universities, and commercial companies, and internationally at locations in Europe, Asia
and Russia. Unfortunately, these large facilities are barrier to entry to the EP due to the high capital andoperating costs. This has driven many companies and universities to investigate smaller thrusters withsmaller facility needs. Investments over many years to install and upgrade test facilities for higher
pumping speeds and higher power levels are typically made to achieve the desired capabilities. As EP
power levels increase, especially to support human exploration missions, large pumping and power
upgrades, and new larger facilities, will need to be brought online.
Needs and Opportunities
Most of the U.S. LTP research community does not utilize the kind of centralized facilities thatare more common in other areas of plasma physics—facilities that are few in number, high in cost, andtake years to plan and build. LTP facilities are much more commonly associated with individual PIs,
typically in universities, but also at a few National Laboratories (e.g. Sandia National Laboratory in
Albuquerque (SNLA) and Princeton Plasma Physics Laboratory (PPPL)). There has been some discussion
within the U.S. LTP community of establishing a federally funded user facility with plasma-, surface- andmaterials-related instrumentation. By coupling plasma and plasma-surface interaction investigations, anopportunity for new fundamental knowledge would be created. One challenge is that the widely different
applications of LTP require significant differences in facilities, instruments, and associated expertise inpersonnel. For example, low pressure plasma studies suitable for semiconductor-related studies would bequite different from atmospheric pressure plasma interactions with biological cells in liquid medium.
Nevertheless, this potentially attractive option should receive further examination and discussion. At thetime of writing this report, the DOE Office of Fusion Energy Sciences established two modest LTP user
facilities at SNLA and PPPL to pilot the concept and gauge use response. The results of these pilot
operations will be used in future facility funding decisions.
International collaborations
There appear to be no significant, federally funded international collaborations at present
involving U.S. LTP researchers.
RELATION OF LTP TO INDUSTRY
LTP science and technology has been of significant industrial importance for more than 150
years. In the section, the committee focus on the role of LTPS in the manufacture of integrated circuits(ICs) and semiconductor devices. This focus is an example to highlight the LTP relation to industry, withthe lessons and outcomes being relevant to other industries as well.
The IC industry plays a key role in the U.S. economy and national security as described above.
Advanced ICs are essential for defense systems, computers and phones. Cloud computing is growing.
Applications in artificial intelligence (AI) are growing rapidly, especially for autonomous vehicles, webcommerce sites and numerous commercial and industrial applications. These future technologies will
depend on ICs and the technology to manufacture them. U.S. plasma technology industry leaders express
concern regarding federal U.S. research funding relevant plasma processes for semiconductors. Many
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federal initiatives include DoD’s quantum computing, DARPA’s electronics resurgence, and DOE’s
Exascale computing project, with a budget of $4 billion spread over 5 years, critically depend on ICs
without there being commensurate investments in the plasma processing required to produce those ICs.
Future IC device technologies will depend more than ever on plasma-based processing. The IC
industry needs advances in LTP science to meet their diverse and extreme challenges, demanding a
deeper understanding of the physics, chemistry and materials-modifying characteristics of LTP used in IC
manufacturing as described above.
The opportunities and benefits of closer connection between the LTP research community andindustry are clear. By investigating in the complex underlying plasma science and establishing basic
scientific principles, these insights and associated experimental and modeling tools can be translated into
industrial practice.
In LTP applications to IC manufacture, one possible suggested strategy is to establish technology
incubators to fund collaborative ventures comprising academia, start-ups, and an established company toenable translational research and eventual commercialization of innovations. Such a program would focus
on applications of LTP to semiconductors with a goal of developing breakthroughs on a 5-10 year
timescale. The federal funding would focus on fundamental research and disruptive breakthroughs thatcan be transferred quickly to industry. The established companies would support the more translational
and applied areas of research. In this vision, research in commercial applications of LTP will encourage
U.S. leadership in this crucially important LTP enabled technology. Strengthening university-based
research in this area by sponsoring graduate students will simultaneously contribute to the development of
the highly skilled workforce needed for that industry as well.
FINDINGS AND RECOMMENDATIONSThe science of chemically reactive environments in gases, on surfaces and in liquids has alreadymade society-wide transformations in our quality of life—from lighting, materials synthesis and water
purification, to enabling the information technology revolution through plasma-enabled fabrication. The
strong track record of low temperature plasma research impacting a broad range of applications
demonstrates exceptional interdisciplinary and translational success. The research performed in the LTP
field overlaps with physics, chemistry, propulsion, energy and materials, with recent extension to biology,
agriculture and medicine. U.S. funding agencies have not embraced this trend, which has led to a loss of
U.S. leadership in some specific areas of LTP. For example, U.S. researchers led the field of plasma
medicine at its birth more than a decade ago. However, in the last few years, the U.S. leading position has
been overtaken by researchers in Europe and Asia. A similar situation is now occurring in plasma
chemical conversion and plasma catalysis.
The extremely successful Low Temperature Plasma Science Center program supported by the DOE
Office of Fusion Energy Science has had a tremendous impact.
Finding: The success of the DOE Low Temperature Plasma Science Center program
underlines that there is a need to sustain LTP research directions for a sufficient period oftime (5 to 10 years) and size with support on the level of ~$2 million per year to enable
scientific impact and translation of research into society benefiting applications.
Finding: The increasing scope of the LTP field into new materials and biotechnology
requires full participation of researchers that are traditionally funded by different
agencies not focused on plasma science. This is particularly the case for electrification of
the chemical industry.
Finding: U.S. funding agencies are often ill prepared to support initiatives that overlap
multiple agencies and should actively pursue synergistic opportunities between agencies
to maintain U.S. leadership in LTP in line with the recommendation in Chapter 1.
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Recommendation: DOE-FES should establish and coordinate a multi-agency Low
Temperature Plasma Science Center Program to support multidisciplinary researchteams and to establish the scientific basis of emerging application areas of low
temperature plasma science.
Finding: Based on the funding level for the LTP science center program, a possible
minimum level of support of $20 million over 5 to 10 years for each topical initiative
would be appropriate.
An example of a first initiative could be LTPs aimed at the electrification of the chemical industry andassociated sustainability initiatives overlapping with research priorities of ONR, ARPA-E, DOE and NSF.
Finding: Advances in plasma-materials processing are challenged by the need to choose
operating and plasma device designs from the enormous set of possible operating anddesign conditions.
Finding: There is a serious need for a more detailed understanding of the fundamental
processes underpinning plasma-surface interactions that will enable us to develop
predictive capabilities.
Finding: Advances in our understanding of LTP interactions with materials will enable
the control of plasma-surface interactions at the atomic level which in turn will enable thenext generation of materials for quantum computing, new communication and sensor
technologies, and energy storage and harvesting.
Recommendation: DOE-FES and DOE-BES should develop a synergisticcollaborative program to focus on the intersection of plasma and materials.
In addition to FES and BES, initiatives could be coordinated and funded between plasma-focused andmaterials-focused programs in federal agencies that would lead to advances in the science and technology
of both fields.
Industry support could also be leveraged to stimulate fundamental research through public - private
partnerships e.g. with the semiconductor industry. This public-private partnership could take the form of
the federal government supporting more fundamental interdisciplinary research and industry co-funding
more translational research.
Finding: The fundamental research performed in LTP is intrinsically interdisciplinary
with societal benefits occurring most rapidly when that fundamental research is guided byapplications.
Finding: Although the NSF/DOE Partnership in Basic Plasma Science and Engineering
is a strong supporter of LTP research, the translational and convergent nature of LTP
research often transcends the scope of the NSF/DOE partnership.
Finding: Support for translational and convergent research in LTP by the NSF
Engineering directorate has not been consistent, has not been long term and has not kept
pace with the opportunities described in this report. Deliberate actions are needed toempower these interdisciplinary opportunities.
An additional level of support of $3 million per year for fundamental research in LTP, similar to thecurrent support from the NSF/DOE partnership, coupled with a similar budget from the application areas,
would enable collaborations between, for example, biologists and plasma physicist. These collaborations
would produce convergent research and translational research opportunities.
Recommendation: NSF-MPS and NSF-ENG and funded at a level of $6 million peryear, should establish interdisciplinary and inter-directorate support for emerging
LTP science topics that lead to translational research.
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The rationale for this funding level is to enable a critical number of projects focusing on a breadth ofapplication areas, while including researchers from the allied sciences who are critical to translational
success.
The establishment of the Low Temperature Plasma Science Center program at DOE since the 2010
Decadal study has benefited fundamental LTP research.
Finding: Continuing initiatives like the DOE Low Temperature Plasma Science Centerprogram will help sustain an internationally competitive LTP community in the UnitedStates.
Finding: LTP research at U.S. universities remains highly dispersed and it is notuncommon to find only one faculty member involved in LTP research in an entire
university. This situation underlines the need for research networks and student training
opportunities.
One model is provided by the European Union. The EU has invested heavily in research networks (e.g.,
COST Action programs) and collaborative research training programs (e.g., Marie-Skłodowska-Curie
Innovative Training Network). Enhanced support to enable mobility of promising early-career researchers
between different laboratories in the United States and abroad would be extremely valuable for the field.
These initiatives initiate and encourage large-scale collaborative efforts and develop and strengthen
emerging research areas.
Finding: There are no multi-institutional, networking programs in the United States
focused on LTPs. Training of a new generation of scientists in fundamental LTP science,
including diagnostics and modeling, is a critical need for the coming 10 years, and would
benefit from such programs.
Finding: Many U.S. PhD students working in the LTP field are trained with an
exclusively application perspective. To sustain the field, more fundamental LTP science
training opportunities for early career researchers are needed.
Taking the EU again as an example, the annual International Low Temperature Plasma Physics school has
provided effective training for the next generation of PhD students in LTP science. There is no long-term
support for such an initiative in the United States.
Recommendation: NSF should support LTP research networks in the United Statesby providing funding for graduate students and postdoctoral researchers toparticipate in exchanges between U.S. universities, and for international researchexperiences for junior scientists.
Finding: Fundamental research in LTP has declined in the United States over the last decade.
There is a concern that if this trend continues foundational research in LTP will, with a few exceptions,disappear from the United States.
Finding: The demographics in the LTP field show that the leadership class will retire
within the next decade with an insufficient number of early career faculty available toassume leadership positions.
LTP research is multidisciplinary and the model for hiring university faculty in multidisciplinary fields
has produced too few early career faculty with a focus on the fundamentals of LTP science.
Finding: There are currently too few early career LTP-oriented faculty in the UnitedStates. The hiring of faculty within universities in the 21st century needs to be viewed
from an interdisciplinary perspective that recognizes the intellectual diversity of a fieldthat spans multiple colleges and departments and would benefit from investment byfederal agencies.
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Recommendation: To strengthen LTP research at universities, NSF and DOE
should establish specific programs that fund the creation of faculty positions similar
to the NSF Faculty Development in Space Sciences program to address the urgencyof losing key expertise and leadership in low temperature plasma science over the
next decade.
Finding: The vast majority of laboratories for the study of low temperature plasmas
consist of tabletop scale devices—often surrounded by a suite of diagnostic tools.
While the last decade has seen some sharing of resources among researchers and use of national facilities(e.g., synchrotron sources for VUV diagnostics), the operation of individual laboratory facilities remains
the dominant research model. Because of the cost and technical expertise associated with advanced LTP
diagnostic development, there have been discussions about the need for a centralized set of diagnostic
tools for the LTP community. That discussion is ongoing and is being put to the test with the recent
establishment of two LTP user facilities.
Finding: Based on its established track record, it is clear that the LTP community does
not generally require nor is there demand for large, single purpose centralized user
facilities having a single plasma source to make societal impact.
Finding: Leveraging the flexibility and interdisciplinarity of individual laboratories
should be considered a valuable asset of LTP community, rather than comparing thatstyle of research to large facilities in other areas of plasma science and declaring thatmode of operation a weakness.
Finding: There is a need to support the flexibility and interdisciplinarity of individual
LTP laboratories perhaps through a mix of user facilities concentrating on diagnostics
and improving diagnostic and source capabilities in individual laboratories that could
form a distributed user facility.
Recommendation: NSF and DOE should expand opportunities to develop andacquire diagnostics, plasma sources, numerical models and reaction mechanisms insupport of low temperature plasmas science, perhaps through the NSF/DOE
Partnership in Basic Plasma Science.
This effort could be configured similarly to LasernetUS, with support for both equipment and use of thediagnostics, sources, numerical codes and reaction mechanisms.

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6
Magnetic Confinement Fusion Energy: Bringing Stars to Earth
A MAGNETIC BOTTLE TO CONFINE A BURNING PLASMA
The driving force behind research in magnetic confinement fusion energy (MFE) is harnessing
nuclear fusion reactions to produce carbon-free energy for large scale societal benefit, from generating
electricity to providing process heat for industry. In fusion, positively charged nuclei of lighter atoms are
fused together to make heavier nuclei. The fusion reaction that is easiest to achieve in the laboratory(having the largest “cross-section” or probability of occurrence) is between two isotopes of hydrogen:deuterium (hydrogen with an extra neutron, abundant in water) and tritium (hydrogen with two extra
neutrons, radioactive but can be made from lithium). (See Figure 6.1.) During this D-T reaction,
deuterium and tritium fuse to produce a helium nuclei (alpha particle), a neutron and a release of energy
in the form of the kinetic energy of the alpha particle and neutron. Since the deuterium and tritium nuclei
are both positively charged, these initial particles must be given enough energy to overcome their mutual
electrostatic repulsion and get close enough forfusion to occur (releasing more than 100 times theenergy given to the initial particles). While fusion
reactions can be generated by firing beams ofenergetic deuterium and tritium at each other, theprobability for the particles to scatter off eachother is far higher than the probability for a fusion
reaction to occur. Only a small fraction of thecolliding beam particles will undergo fusion
reactions. As a result, it is nearly impossible toproduce net energy by this approach (although
FIGURE 6.1 Fusion Basics. The deuteriumsimilar schemes can be useful in using fusion totritium (D-T) fusion reaction will be the basis ofproduce neutrons for other applications, including
future fusion reactors. The fuel for the D-T
the generation of medically relevant isotopes).
reaction is deuterium (plentiful in seawater) andTo produce net energy through fusion, thelithium (which can be converted to tritium fuelD-T particles must be confined in a region ofthrough capturing the neutron produced by the
space long enough to undergo many, many
D-T reaction). SOURCE: Courtesy Nickscattering interactions before finally fusing andHalloway, Culham Centre for Fusion Energy.
releasing energy. The goal is then to efficiently
confine a hot soup of charged particles, a plasma,with a temperature around 100 million K to enable the average particle to have enough energy toovercome the electrostatic repulsion between nuclei and produce fusion reactions. The fusion reactions
can be self-sustaining if some of the energy released can be captured by the plasma and used to heat
additional deuterium and tritium nuclei to fusion temperatures. Energy production above that required tosustain the fusion reactions, can be utilized for other purposes including generation of electricity.
Stars, including the Sun, are powered by fusion. By virtue of its large mass, the Sun confines hot
plasma very efficiently by gravitation. Stars are usually powered by fusion of normal hydrogen nuclei(protons). This is a very low probability (small cross-section) reaction and a typical proton survives in the
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Plasma Science: Enabling Technology, Sustainability, Security, and Explorationcore of the Sun for billions of years before fusing. Fortunately, gravitational confinement is exceptionally
good. The excess energy of these fusion reactions creates the sunlight that enables life on earth.
Gravitational confinement of plasmas for fusion energy production unfortunately cannot be accomplishedon Earth. To produce steady state fusion reactions on earth, another means of confinement must be
devised.
In MFE, magnetic fields are used to confine a sufficiently hot and dense plasma so that fusion
reactions can occur. Magnetic forces can limit the motion of and confine charged particles in directions
perpendicular to the magnetic field. Charged particles move along magnetic field lines much like beads
a

c

b

d

FIGURE 6.2 Magnetic confinement. (a) Charged particles execute helical orbits in the presence of amagnetic field - free to move along the field line, but constrained in the directions perpendicular to thefield. (b) Natural magnetic confinement occurs where hot plasma is trapped on magnetic fields
emerging from the surface of the Sun. . (c) Toroidal confinement uses magnetic field lines that windaround in a torus or doughnut shaped region. Pure toroidal (circular) field lines do not confine
particles due to slow vertical drifts, but helical field lines that wind around the torus will confine
charged particles. (d) A tokamak produces helical magnetic field lines using external coils to generate
circular (toroidal) magnetic field and produces poloidal magnetic field (wrapping the short way aroundthe doughnut) by driving current in the plasma itself. SOURCE: (a) Courtesy Troy Carter, Universityof California Los Angeles; (b) NASA TRACE Satellite; (c-d) EFD-R(07)01 Focus on: JET, The
European Centre for Fusion Research (2007).
on a wire. (See Figure 6.2.) While a range of magnetic confinement schemes have been studied, the mostsuccessful so far is toroidal confinement. Using this scheme, confinement in the third direction (along themagnetic field) is provided by producing magnetic field lines that wind around in a toroidal (doughnutshaped) region. The simplest example of such a magnetic field is produced by a toroidal solenoid. In thiscase magnetic field lines are circular and close on themselves. However, due to gradients in the strengthof the magnetic field, charged particles are not confined by a purely toroidal field. The particles will
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slowly drift out (upward or downward, depending on the sign of the charge) and be lost to the walls of theconfinement chamber. The magnetic field must be made helical to achieve confinement of a charged
particle. In a helical magnetic field, the charged particle is still always slowly drifting, for example,
upward. However, since the particle follows the helical magnetic field line and spends some time on theunderside of the torus, for part of the time drifting upward means drifting back up into the magnetic field
trap. In a tokamak, the additional magnetic field (called the poloidal field) necessary to produce thehelical field structure is generated by running a current through the plasma itself. In a stellarator, external
magnetic coils are utilized to produce the twisted field structure and it is not necessary to drive current in
the plasma. Tokamaks have, to date, achieved the best fusion performance, including the generation ofseveral megawatts of fusion power in the Tokamak Fusion Test Reactor (TFTR, 10 MW) at Princeton
Plasma Physics Laboratory (PPPL) in the United States, and the Joint European Torus (JET, 16 MW) at
Culham Laboratory in the UK.
The international fusion community is working toward the creation of the first magneticallyconfined burning plasma in the laboratory. A plasma is said to be burning when energy released by fusion
reactions is the dominant source of heating in the plasma. In a magnetically confined fusion plasma, thegoal is to magnetically trap the energetic alpha particles produced by fusion reactions. These alphaparticles then slow down and release their energy to the plasma, heating it to reach and maintain atemperature sufficient for fusion to occur. The neutron released by the D-T reaction is not confined by themagnetic field and does not contribute to heating the plasma. Instead, the goal is to capture this neutron
and its energy in a material structure surrounding the plasma where it can be used to generate tritium fromabsorption by lithium atoms and its energy can be captured for generation of electricity. ITER, based on
the tokamak concept, is under construction in Cadarache, France with the goals of producing a burning
plasma in the laboratory and producing more energy from fusion reactions than is required to heat theplasma to fusion temperatures. The ITER project has the goal of producing ~500 MW of power fromfusion while utilizing 50 MW of power to heat the plasma, a fusion gain or ‘Q’ of 10. ITER construction
is more than 60% complete at the time of the writing of this report and first plasma is scheduled for 2026.
A recent National Academies study, A Strategic Plan for U.S. Burning Plasma Research (BPR)
endorsed U.S. participation in the ITER project, citing it as the best path currently available to achieving aburning plasma, a critical step in commercializing fusion energy. That study made an important second
recommendation about the U.S. program beyond ITER. Recognizing that while ITER is a sound and lowrisk path toward achieving the important milestone of a burning plasma and together with the knowledge
gained about burning plasmas, the design is very conservative. Projections using that design extrapolate
to an extremely large and costly fusion electrical power plant. Instead of only following that path, theBPR recommended that the U.S. program also focus on investigating more economic solutions for fusionenergy and pursue the development of a compact fusion pilot plant. These compact fusion concepts will
use technologies that were not available at the time that ITER was designed and carry additional risk.
Following the path of compact fusion reactors would uniquely position the United States in theinternational pursuit of fusion power, leveraging recent advances in our understanding of fusion plasmas
and new developments in technology. The BPR recommendations set the stage for a focused plasma
science and engineering research program needed to enable a compact fusion pilot plant.
This proposed path forward for the U.S. MFE program is enabled by recent technologicalbreakthroughs. In 2017, the DOE Fusion Energy Sciences Advisory Committee (FESAC) was charged“to identify the most promising transformative enabling capabilities (TEC) for the United States to pursuethat could promote efficient advance toward fusion energy, building on burning plasma science andtechnology.” The resulting report outlined a number of recent technological developments that could leadto more rapid progress or enable new promising directions in the quest for fusion energy. Highlighted
were: (1) Advanced algorithms for computation and control, including machine learning and artificial
intelligence; (2) new superconductor magnet technology, in particular high-temperature superconductors(HTS) using rare-earth barium copper oxide (REBCO) materials; (3) advanced manufacturing techniques
including additive manufacturing; and (4) novel new technologies for production, extraction and control
of tritium fuel. Magnets based on REBCO HTS in particular could enable more compact fusion reactors.
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

REBCO conductors can carry an order of magnitude more current density than low-temperature
superconductors currently in use such as niobium-tin. This higher current density allows much higher
field strengths to be reached (REBCO-based solenoids have produced 40 T magnetic fields) and also
allows magnets to reach the same field strength as current low temperature superconductor solutions
while having smaller physical size.
MFE research has and will continue to be at the frontier of plasma science and engineering. MFE
requires understanding and controlling very hot, collisionless magnetized plasmas far from thermal
equilibrium with their surroundings. This endeavor includes plasma physics that spans a tremendous
range of phenomena that must be understood (and controlled) to achieve a burning plasma. Global plasma
instabilities can ultimately limit the pressure and fusion power that can generated while microinstabilities
can lead to turbulence and transport of heat, limiting the efficiency of magnetic confinement. Waveparticle interactions underlie interaction of energetic particles with the plasma and schemes for heating
and driving current. The interaction of hot plasmas with the material surroundings must be controlled toprevent damaging those materials. Engineering is as important, if not more so, than the plasma physics forfusion to be ultimately successful. Solutions are needed for confining materials that can withstand thehigh fluxes of heat and neutrons and maintain their integrity, for efficiently breeding tritium fuel fromfusion neutrons, and for robust, capable and cost-effective magnet technologies. This report will focus on
issues centered on plasma science and engineering while recognizing the importance of materials science,mechanical engineering and nuclear engineering in achieving the goal of commercial fusion power.
At the time this report was being written, the Department of Energy was executing a strategicplanning process for MFE activities within DOE Fusion Energy Sciences (FES) to identify and prioritize
the research required to advance both the scientific foundation needed to develop a fusion energy source,
as well as the broader FES mission in plasma science. The process included a community-driven
discussion, led by the American Physical Society Division of Plasma Physics (DPP) call the Community
Planning Process (CPP). The CPP provided input to FESAC whose task was to produce a strategic planfor fusion research for FES that will include both fusion plasma science and fusion engineering andtechnology. With this study and the CPP being performed at the same time, much of the data andcommunity input from both studies was shared. At CPP workshops, consensus was found in having theoutput of the CPP be broadly consistent with the first two recommendations of the BPR—continue tosupport ITER and to start on a path towards a compact fusion pilot plant. In particular, the CPP will
utilize the second recommendation, the goal of a compact fusion pilot plant, as the basis of its strategicplan.
THE PROMISE OF MFE: CARBON-FREE, SUSTAINABLE ELECTRICITY AND THE
SCIENCE AND TECHNOLOGY OF HOT PLASMAS
The societal benefit of MFE research is clear and enormous—fusion energy can provide a carbonfree source of power for generating electricity or process heat, utilizing an abundant and essentiallylimitless source of fuel. The fusion process that most MFE research focuses on is the D-T reaction.
Tritium is radioactive with a short (13.6 year) half-life and so is not naturally available in sufficientquantities for commercial power production. However, tritium can be produced from lithium byabsorption of a neutron. (See Figure 6.1.) Both deuterium and lithium are abundant in seawater (andlithium can also be mined), suggesting that there is a sufficient supply of both to use fusion power toprovide the energy needs of our planet for many hundreds of thousands of years. (See Figure 6.3.) Besides
providing energy and process heat, fusion reactions can be used to provide a source of neutrons for thegeneration of radioisotopes (e.g., for medical applications) and for transmuting waste produced by fission
reactors into safer by-products.

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MFE research has many links to other areas ofplasma science and technology, advancing other areas ofplasma science and vice versa. The collisionless,magnetized plasmas studied in fusion research exhibit
phenomena that are also important in near-earth andinterplanetary space plasmas and in astrophysical plasmas.
Examples of synergies include wave-particle interactions,magnetic reconnection, and turbulence driven by spatial
inhomogeneities. Energetic particles are often present infusion experiments, either generated by heating (e.g.,
direct injection of energetic particles by neutral beams or
FIGURE 6.3 The fusion fuel needed towith radiofrequency power), as a result of fusion reactions
provide energy for one family for one(helium nuclei, called alpha particles, from D-T fusion) or
year is about 0.08g of deuterium andby disruption of the plasma current in a tokamak
0.02g of lithium. This amount of(producing runaway electrons). These energetic particles
deuterium can be mined from only 2.5
can excite waves that in turn scatter, de-energize and ejectliters of seawater, which contains 1 atom
particles from the magnetic trap. The same processes occurof deuterium for every 6240 atoms ofin Earth’s radiation belts and magnetosphere, wherehydrogen. SOURCE: By Jyi1693, CCenergetic protons and relativistic electrons are trapped andBY 2.5,
similar types of waves (Alfvén and whistler) can both
https://commons.wikimedia.org/w/index
energize and scatter these particles. Magnetic reconnection.php?curid=10443013.
(where magnetic field lines are broken and, reconnect,
producing large releases of energy—see Chapter 2) isubiquitous in space and astrophysical plasmas, leading tostellar flares and perhaps gamma ray bursts (seeChapter 7). This same process occurs in fusion
plasmas in fast nonlinear tearing modes that limit
their performance. Turbulence in fusion plasmas isoften driven by strong spatial inhomogeneities inplasma current or pressure, as is turbulence inEarth’s ionosphere and planetary magnetospheres.
Interactions between fusion, and the basic andspace and astrophysical plasma communities havesteadily grown in ways that have benefitted allparticipants. For example, the gyrokinetic
computer codes created to understand and predict
turbulence and transport in fusion plasmas are used
to investigate turbulence in the solar wind and instellar accretion disks, contributing to our
FIGURE 6.4 Edge Localized Modes or ELMs
understanding of how electron and ion heating
are plasma filaments that erupt from the edge ofworks in these settings.
the tokamak as a result of the growth of the
There are also links of fusion to the low
peeling-ballooning instability. This image
temperature plasma community. All fusion plasmas
shows filaments during an ELM event in theultimately involve interactions with material
MAST spherical torus. SOURCE: © ITER
surfaces. These plasma material interactions (PMI)
Organization, http://www.iter.org/,
can erode plasma facing components and introduce
https://www.iter.org/newsline/229/1229
impurities into the core fusion plasma, potentiallydegrading confinement by processes including
radiation. Similar plasma material interactions occur in plasma processing equipment used to create
semiconductors and in plasma-based thrusters.
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

PROGRESS IN MFE RESEARCH SINCE PLASMA 2010
Since the Plasma 2010 Decadal Survey was published, significant progress has been made on theunderlying science of magnetically confined plasmas for fusion energy research. A number of highlights
are provided below.
Understanding and Controlling the H-Mode Edge
The advances in MFE science in heating and confinement achieved using tokamaks is in largepart linked to the discovery of the high-confinement mode or “H-Mode.” This operational mode can beaccessed through exceeding an empirical threshold in heating power and leads to an edge transport barrier
where strongly sheared radial electric fields suppress turbulent transport. This edge transport barrier isknown as the “pedestal,” which has a very large gradient in plasma pressure, much larger than thepressure gradient in the core region of the plasma inside the pedestal. The pedestal’s formation, height,
and stability are therefore key drivers of overall fusion performance, since fusion power scales with thesquare of the plasma pressure. Numerous mechanisms, including collisional “neoclassical” transport andelectron scale turbulence, can drive heat and particle transport across the pedestal. However, due to verystrong sheared plasma flow, electromagnetic effects, and the presence of large heat and particle sources,
the pedestal is often limited by electromagnetic instabilities driven by pressure and current gradients.
These instability producing processes are known as kinetic ballooning modes (KBM) and peelingballooning (P-B) modes. (See Figure 6.4.) A simple model, EPED, has had significant success in
predicting the pedestal pressure and width, the outcomes of which are particularly important to both KBM
and P-B. (See Figure 6.5.) The model predicts that when the plasma has a highly triangular plasma shapeand a particular range of densities, the pedestal can bifurcate into the usual “H-Mode” and a higher
pressure “Super H-Mode”.
Motivated by theoretical predictions, recent experiments have explored the Super H-Moderegime. A record pedestal pressure of 80 kPa was obtained in the Alcator C-Mod Tokamak at theMassachusetts Institute of Technology. A record fusion gain for a medium scale (major radius R < 2 m)
tokamak was obtained in pure deuterium experiments on the DIII-D National Fusion Facility tokamak atGeneral Atomics. Deuterium-deuterium fusion reactions have a lower cross-section than D-T reactions. If

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FIGURE 6.5 Collaborative computations and experiments (right) EPED code predictions for the HMode (black line), Near Super H-Mode (blue line) and Super H-Mode (red lines) regime are compared
to measurements from an experiment on the DIII-D tokamak (green squares) which accessed very
high pedestal pressure, and high fusion performance. (left) EPED predicted pedestal pressurecompared to observations on 6 devices across a wide range of size, shape, magnetic field and plasma
current find good agreement. The highest pressure cases shown (green circles) were obtained in Super
H mode experiments on the Alcator C-Mod tokamak, reaching pedestal pressure (~80 kPa) near thevalue predicted for ITER (black diamond). SOURCE: Snyder et al, Nuclear Fusion 59, 086017 (2019).
D-T had been used in these experiments a fusion gain (ratio of fusion power produced to heating power
input) of ~0.5 would have resulted.
Operation in H-mode produces significant increases in confinement time and performance over
L-mode (or “low-confinement” mode, without an edge transport barrier). It is expected that ITER willaccess H-mode to achieve the goal of producing a burning plasma. There is a risk, however, since the Hmode pedestal can suffer instabilities that leads to edge localized modes (ELMs). These instabilities causea fraction of the core plasma pressure to be abruptly lost, producing significant heat and particle loads on
the plasma-material interface, especially at the divertor plates where the plasma is exhausted from thesystem. (See Figure 6.3.) Although ELM-induced particle transport has a beneficial effect in allowing
density and impurity control within the core plasma, the pulsed heat load can cause rapid erosion of thesedivertor plates. This instability is a major risk to the ITER device and its operation. Either ELM
mitigation or, preferably, operation without ELMs, is necessary while still maintaining H-mode levels ofenergy confinement combined with adequate particle transport for helium ash removal and impurity
control.
A significant breakthrough over the last 10 years is the use of small, non-axisymmetric, threedimensional (3D) magnetic fields called Resonant Magnetic Perturbations (RMP) to mitigate or eliminate
ELMs. Experiments on the DIII-D tokamak1 were the first to demonstrate that ELMs can be completely
eliminated through application of RMP while maintaining high-performance H-mode transport barriers.
Based on the initial success of 3D magnetic field control research in DIII-D, many of the majorinternational tokamaks, including MAST, ASDEX-U, KSTAR, EAST, HL-2A, J-TEXT and COMPASS
have installed similar capabilities, and have contributed to our physics understanding of the interaction ofthese small non-axisymmetric magnetic fields with the nominally axisymmetric tokamak magnetic
equilibrium. Improved theoretical and computational capabilities have accompanied experimental
progress using a variety of MHD (magneto-hydrodynamic) codes (e.g., M3D-C1, NIMROD, MARS,JOREK, VMEC, TM-1, IPEC/GPEC). These codes have been generalized to include the plasma response
1

A table of fusion facilities appears later in the chapter, providing more information on the devices
cited here.
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to imposed non-axisymmetric magnetic fields. They have been able to explain many, but not yet all, ofthe experimental observations. For example, explanations of observed multimode responses, ELMsuppression bifurcations, rotation thresholds for suppression and density pump-out, have given increased
confidence in use of such techniques on ITER. (Density pump-out is a local reduction in plasma density
due to increased transport associated with the imposed RMP.) Nevertheless, a number of phenomena are
still not yet fully understood, including the exact mechanism of ELM suppression and the robustness ofthe temperature pedestal despite density pump-out. Based on the success of RMP ELM suppression, a set
of 3D magnetic field coils has been incorporated into the ITER design. (See Figure 6.6.)
While progress in ELM mitigation has
been impressive, the effectiveness of thesemitigation strategies is often limited toparticular operational regimes. Identifying ageneral path to ELM-free, high performance
operation is a major goal. Over the last 10
years, two possible operational regimes havebeen identified and their operational space
expanded, these being the intermediate-modeor “I-mode” and the quiescent-H-Mode or“QH-Mode”.
The I-mode is a stationary operating
regime with improved thermal confinement
but unaltered (and favorable) particle
confinement which occurs at input powers
below those required for the L- to H-mode
transition. The I-mode has the following
FIGURE 6.6 3D stabilization of Tokamaks. Coil setscharacteristics: 1) formation of ion andfor the ITER experiment will enable introduction ofelectron temperature pedestals, 2) increase in
3D magnetic perturbations and allow for resonant
stored energy relative to L-mode, 3) little ormagnetic perturbation (RMP) edge localized modeno change in density relative to L-mode, 4)(ELM) control. SOURCE: Lazerson Plasma Physics
flow shear in the edge pedestal region which is
and Controlled Fusion 56, 095006 (2014).
intermediate between that found in L-modeand H-mode, 5) usually no ELMs and 6)
changes in the edge turbulence with decreases
in some frequency ranges and increases in others. Operation with increased energy confinement but
unchanged particle confinement is particularly relevant for future reactors, since fusion power would beenhanced while impurity and ash removal would be facilitated. (Ash refers to the fusion alpha-particles
that have given up their energy to the plasma and must be removed from the plasma.) What is now
recognized as the I-mode was first seen in Alcator C-MOD and ASDEX-U in the late 1990s but its
significance was not apparent at that time and work on this regime was dormant for about 10 years. Imode experiments resumed in C-MOD prior to its decommissioning and the significance of I-mode as astationary regime was recognized. Since the mid-2000s, considerable work on the I-mode has been doneon Alcator C-MOD, ASDEX-U, and DIII-D and EAST.
The QH-mode, a stationary H-mode without ELMs, was first discovered in DIII-D and was
subsequently investigated on ASDEX-U, JET and JT60-U. The initial discovery resulted from operatingin lower density plasmas and forcing the plasma to rotate in a direction opposite to the direction of theplasma current. This was accomplished by driving plasma rotation using neutral beam injection (called
counter-NBI). Experiments over the last 10 years have broadened the range of QH-mode operation to
include plasma rotation in the current direction (co-NBI) and to operate with balanced (no torque) NBI
but using magnetic perturbations from external coils to drive flows. This result makes QH-mode
operation on ITER possible as NBI torque will be limited due to the large size of the ITER plasma andlimited penetration of neutral beams. The key to standard QH-mode operation is the excitation of the edge
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harmonic oscillation (EHO), which is acoherent edge electromagnetic mode. The
EHO provides extra edge transport andprevents the edge pressure gradient fromreaching the stability boundary for ELMs.
The standard QH-mode operates atedge conditions, matching those in future
devices such as ITER. However, to achieve
the predictive understanding needed for use in
future fusion reactors, we need a detailed,validated theory of the EHO. Although resultsfrom linear stability analysis have provided asignificant understanding of the mode, weneed a complete theory of the saturated,
nonlinear state and how the EHO drives crossmagnetic field transport. Some promising
initial modeling of the EHO has been
performed but much remains to be done.
Multiscale Processes in MFE Plasmas
Processes in magnetized plasmas
span a huge range of spatial and temporalscales. For example, the timescales in a
FIGURE 6.7 Fluctuations in electrostatic potential intokamak plasma range from rapid Langmuira tokamak plasma from a multiscale simulation
plasma oscillations, ~0.1 ns, to slow global
demonstrating the coexistence of (and interaction
current diffusion, ~10 s. The Plasma 2010
among) large scale (ion scale) and small scale
report recognized the importance of and(electron scale) structures. SOURCE: Howard et al.,scientific opportunity to study “multiscale”
Nuclear Fusion 56, 014004 (2015).
processes in magnetized plasmas. These
include dynamics with strong coupling between, for example, large and small spatial scales. Gaining
insight into such processes is demanding. Substantial resources in massively parallel simulations are
required to simultaneously resolve both the small and large spatial or temporal scales. Important progressin this regard has been made over the last 10 years. Two examples are in the multiscale interaction
between ion and electron scale turbulence and in the interaction between global MHD instabilities andmicroturbulence.
Decades of experimental and theoretical plasma physics research has shown that turbulence isdriven by unstable gradients in plasma properties (electron density and temperature, ne, Te; and ion
temperature Ti). This turbulence is likely to be responsible for the ‘anomalous’ transport observed in thecore of many fusion devices. (Anomalous transport refers to movement of plasma that proceeds fasterthan classical, linear scaling laws would predict.) Long wavelength turbulence, present at the ion-scale, isdefined as turbulence with a poloidal wavenumber less than the ion Larmor radius (kθρi < 1.0). (Thepoloidal wavenumber, kθ, is the inverse of the typical scale size of the turbulent structures.) At this scale
the ion temperature gradient (ITG) and trapped electron mode (TEM) turbulence are thought to beimportant in explaining experimentally observed transport. The analog of ITG turbulence is known toexist at the shorter electron scale. Electron temperature gradient (ETG) turbulence is found at shortwavelengths, with poloidal wavenumbers less than the electron Larmor radius (kθρe < 1.0). Historically,
the role of ETG turbulence has generally been thought to be limited due to their presumed small eddy
size. However, early numerical simulations indicated that ETG turbulence could form radially elongated“streamers” that increase the transport associated with ETG and could lead to experimentally relevant
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heat flux levels in conditions without longwavelength turbulence. Despite this finding, it
was believed that in the presence of longwavelength turbulence, streamers would likely
be sheared apart by the long wavelength
turbulence leading to a reduced impact of the
ETG.
The evolution of modern
supercomputing platforms has enabled a new
type of gyrokinetic simulation that is able tocapture the spatial and temporal scales of ionand electron-scale turbulence simultaneously.
(See Figure 6.7.) (Gyrokinetic models averageover the rapid charged particle motion in orbits
around the magnetic field to focus on slower,
lower frequency processes including slow
particle drifts and low-frequency turbulence.)
Early attempts at these multi-scale simulations
used artificially heavy electrons to slow their
FIGURE 6.8 (top) Measured temperature profile
motion to better match that of the ions, andaround a small (left) and large (right) Neoclassicalsimplified plasma geometry and profiles toTearing Mode (NTM) island. (bottom) Measured
reduce the range of scales and lessen thefluctuation amplitude change in the presence of small
computational demands. As a result, theseand large islands. With a large enough island,studies generally concluded that electron
turbulence in reduced substantially inside the island
temperature gradients (ETG) would likely playand increased outside. SOURCE: Physics of Plasmas
a minor role in heat transport. However,
24, 056106 (2017);
comparisons of model results showed notable
https://doi.org/10.1063/1.4977533.
disagreements with experimentally measured
levels of electron heat flux. The origin of thesedisagreements was not clear.
Steady advances in computing have enabled the first multi-scale simulation of experiments to be
performed with actual electron mass and all experimental inputs. Motivated by the disagreement inelectron heat flux between ion-scale gyrokinetic simulation and experiment, realistic multi-scale
simulations in the core of the Alcator C-Mod tokamak were performed. These simulations pushed thelimits of supercomputing, requiring ~20 million CPU hours per case. Their outcomes showed that ITG
turbulence could, in fact, coexist with ETG streamers. Complicated cross-scale interactions wereobserved in these simulations. Through modification of the zonal flows and cross-scale energy transfer it
was found that short wavelength turbulence actually increased the heat flux driven at long wavelengths.
An extensive validation of multi-scale simulations with comparisons to experiments demonstrated that
only multi-scale simulations capable of capturing cross-scale interactions could reproduce the observed
heat fluxes found in experiment. These efforts produced a likely explanation for the origin of electron
heat flux in the core of tokamaks. Further simulation studies showed that cross-scale coupling is likely
important in the core of high performance conditions, like those projected for the operation of ITER andfuture fusion devices. The importance of multi-scale turbulence remains an active area of investigation
with important implications for the model fidelity needed for prediction and interpretation of fusion
devices.
Progress has also been made in understanding the multi-scale interaction between global modes
and microturbulence in confinement devices. Neoclassical Tearing Modes (NTMs) are a major
impediment to the development of operational scenarios for tokamaks as they can limit plasma pressure
and can lead to plasma termination—called a disruption. NTMs produce magnetic islands that lead toflattening of the pressure profile within the island. (See Figure 6.8.) This is caused by rapid transport
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FIGURE 6.9 (left) The heat and particles fluxes from a gyrokinetic simulation of a discharge in the
Madison Symmetric Torus (MST) Reversed Field Pinch (RFP). The equilibrium is unstable to trappedelectron mode turbulence. However, if the magnetic fluctuations of global tearing modes are notincluded in the simulation the fluxes are nearly zero after an initial transient (dashed lines). Whentearing mode fluctuations match the experimental tearing-mode level, the fluxes become finite andtheir level matches the fluxes inferred in experiment (solid lines). (right) Without the external
magnetic field perturbation there are strong zonal flows (a) that quench the turbulence; with themagnetic perturbation the zonal flows are markedly reduced (b) in accordance with theoreticalpredictions, and fluxes rise to experimental levels. SOURCE: Left: Physics of Plasmas 22, 012504(2015); https://doi.org/10.1063/1.4905709; right: Williams et al. Physics of Plasmas 24,122309(2017). https://doi.org/10.1063/1.5000252.
(parallel to the magnetic field) within the island. In toroidal plasmas with large enough pressure a selfgenerated ‘bootstrap’ current arises that is proportional to the gradient of the pressure associated withtrapped particles. (Bootstrap current is a toroidal current produced in the presence of a pressure gradient.)
The pressure flattening in an NTM acts to reduce the pressure gradient at the island and hence removes
bootstrap current from that region. This reinforces the island and causes it to grow in size. Turbulent
transport around the island can prevent or reduce this pressure flattening and affect the dynamics of the
NTM island. At the same time, pressure flattening by the NTM also removes the source of turbulence,leading to a complex nonlinear and multiscale interaction between microturbulence and the NTM. The
first direct measurements of this interaction were made on the DIII-D tokamak
In the reversed field pinch (RFP) unstable global tearing modes drive a cascade spanning multiple
scales which has been compared to the magnetic turbulence spectrum of the interstellar medium.
Measurements show that the cascade acquires features at small scale associated with disparate microscale
physics. Gyrokinetic simulations demonstrate that the global and microscales couple through zonal flows.
(Zonal flow refers to plasma flowing within a magnetic surface primarily in the poloidal direction.) These
regulate small-scale turbulence while being regulated themselves by large-scale magnetic fluctuations.
The role played by zonal flows makes this phenomenon potentially relevant to the most important typesof instabilities in magnetic confinement fusion. Recent experimental measurements and modeling showthat this physics also arises in DIII-D tokamak plasmas, where resonant magnetic perturbations (RMPs)
raise fluctuation levels and reduce zonal flows. This has been tested in DIII-D using an RMP whose
magnitude is varied to test the response of turbulent fluctuations. The frequency spectrum of density
fluctuations from beam emission spectroscopy for four different values of the RMP coil current is shownin Figure 6.9. Increasing coil current uniformly increases the fluctuation level over the frequency range of
microturbulent fluctuations (40–120 kHz).

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Energetic Particle Driven Modes
Energetic particles (EP) such as the 3.5 MeV alphaparticles generated by D-T fusion reactions, fast beam ions fromneutral beam injection and high energy tail ions generated byradio frequency (RF) heating play critical roles in heating,current drive, and momentum input. The confinement of these
EP is essential in future fusion reactors. Confinement of theseparticles, however, faces several challenges. The mostsignificant is that these particles can excite a variety of
instabilities, which in turn lead to EP transport or loss. This
interplay between EPs and instabilities is a fundamental waveparticle interaction problem that spans all areas of plasma
physics from the interstellar medium to tokamaks. Since thePlasma 2010 report, research on EP interactions withinstabilities has progressed rapidly due in large part to advancesin diagnostics for both fast ions and the instabilities themselves(see Figure 6.10). For example, measurements of the confined
FIGURE 6.10 Physics Today Cover,fast ion profile are available (using Fast Ion D-Alpha (FIDA)
October 2015.
spectroscopy) and structures are routinely measured using
electron cyclotron emission. A decade ago, measurements of ion transport in the presence of Alfven
eigenmodes (a type of EP driven instability) was an unresolved issue. Research in the last decade has
resolved this issue and revealed the key underlying physics of the measured fast ion transport. This effort
utilized detailed experimental data coupled with theory and simulation. This was accomplished first bytracking energetic particle orbits through magnetic perturbations consistent with measurements andsecond by using massively parallel computation toself-consistently evaluate the interaction between
energetic particles and MHD modes. The primaryfactor causing the transport was found to be theoverlap of many wave-particle resonances.
Comprehensive simulations are now able to identify
not only the basic properties of EP driven but the
feedback that impacts the EP profile.
Optimized Stellarators and Wendelstein 7-X
As discussed earlier, plasmas cannot be
confined with purely toroidal (circular) magnetic
FIGURE 6.11 A stellarator uses purely external
fields due to drifts caused by gradients in thecoils to produce a helical field line (green inmagnetic field. Instead the magnetic field must havefigure) and does not require plasma current tosome “rotational transform,” meaning the magnetic
be driven, a significant advantage over thefield line must be helical rather than circular. In
tokamak. SOURCE: Max-Planck Institut für
tokamaks, external current coils produce a purely
Plasmaphysik.
toroidal field. In a stellarator, the helical magnetic
field is produced entirely by specially designed
external coils, and no plasma current is required. (See Figure 6.11.) To generate the helical field, the coils
cannot be axisymmetric and the resulting magnetic field pattern is three-dimensional and not rotationallysymmetric as in a tokamak. In the past decade, a significant advance in 3D plasma confinement has been
the Wendelstein 7-X (W7-X) stellarator at the Max Planck Institute for Plasma Physics in Greifswald
which began plasma operations in 2015. W7-X, the largest stellarator in the world, is an optimized
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stellarator, designed with a magnetic geometry
intended to reduce neoclassical transport(losses of heat and particles due to collisions
between particles that are in a special class oforbits called trapped orbits). W7-X, achieved
the record fusion triple product (nT - density
× temperature × confinement time) for
stellarators.
The United States supplied a “trim”
coil system for WX-7 that was utilized inconjunction with the flux surface measurement
diagnostics to confirm the accuracy withwhich the 70 superconducting magnetic fieldcoils were placed, an accuracy necessary to
produce the complex array of magnetic fields.
FIGURE 6.12 Image of light emitted as an electron(See Figure 6.12.) Initial operation also
beam follows the magnetic field lines through aenabled the very first assessment of
neutral gas in Wendelstein 7-X, demonstrating good
neoclassical transport behavior including
magnetic surfaces in the device. SOURCE:
bootstrap current. In a tokamak, bootstrap"Confirmation of the topology of the Wendelstein 7currents are beneficial as they reduce theX magnetic field to better than 1:100,000". Nature
amount of plasma current that must be driven
Communications 7: 13493. Figure 2.
by external means. However, in a stellarator,
bootstrap currents can potentially modify themagnetic field structure being imposed externally which can lead to degraded performance. Hence, instellerators, one seeks to minimize bootstrap currents. W7-X experiments further validated theories forthe radial electric field and bootstrap current in stellarators, showing that the device’s optimization forminimal plasma current was successful. Operation of WX-7 with pulse lengths in excess of 30 s (muchlonger than the “energy confinement time” defined as the stored thermal energy in the plasma divided by
the heating power) confirmed neoclassical bootstrap currents in line with optimization criterion.
Toroidal confinement devices utilize a magnetic geometry that directs heat and particles
exhausted from the core plasma to a material surface designed to handle this power exhaust. Thismagnetic geometry and material surface is called a divertor. Installation of uncooled divertor elements
during a second commissioning campaign in W7-X enabled experiments demonstrating the island diverter
concept (a special magnetic geometry for a stellarator divertor), assessing diverter protection elements,
and achieving current pulse lengths of up to 100 s. A set of U.S. supplied diverter overload protection
elements (“scraper elements”) were installed and successfully assessed. Edge spectroscopic
measurements enabled assessment of impurities in W7-X and the ability of the island divertor to prevent
impurities from the edge region from propagating into the core plasma. A desirable mode of divertor
operation, demonstrated on W7-X, is called a “detached” divertor, where power exhausted from the coreplasma is absorbed and re-radiated by a buffer gas before hitting material surfaces. In addition, operationof electron cyclotron resonance heating (ECRH) and frozen hydrogen pellet injection for fueling led tohigh performance discharges. Experiments using edge gas puffing confirmed that not only was diverted
operation possible in steady-state scenarios, but that it resulted in no significant impact on confinement or
impurity screening
At the time of this report, W7-X is finishing installation of water cooled in-vessel componentsthat will enable it to run for 1800 s with 10 MW of injected ECRH power. In 2021, the device will resume
operation with a fully cooled divertor which has been qualified for up to 10 MW/m2 steady-state operation(20 MW/m2 transient). The completed device will enable scientists to address plasma physics related toenergetic particles, turbulence, plasma stability, magnetic island physics, and plasma materialinteractions. A 7 MW neutral beam system and 1 MW ion cyclotron resonance heating system will enable
investigations of energetic particles in three dimensional magnetic fields. Fluctuation diagnostics will be
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TABLE 6.1 Advantages of non-tokamak, non-stellarator magnetic fusion configurations. The lastcolumn identifies inherently pulsed (P) or a steady-state sustainment scenario that is identified (S).
used to investigate how both magnetic fields and plasma gradients influence turbulence. Stability limits
and the physics of magnetic islands can be studied through the device’s flexible magnetic configurations.
For the first time, scientists will have access to heat fluxes up to 10 MW/m2 for up to 1800 s, facilitatingworld leading plasma material science.
Alternative Magnetic Configurations
While the tokamak and stellarator magnetic configurations have demonstrated performanceclosest to those needed for a fusion reactor, these concepts have appreciable engineering complexity.
Tokamaks require plasma current to be sustained, and stellarators, while inherently steady state, requirecomplex non-planar magnetic coils. Other magnetic configurations, often called “alternate concepts”,
offer the potential for significant reduction in engineering complexity while also being challenged inconfinement and stability. The main alternate concepts include: Open magnetic field topologies, for example, the centrifugally confined mirror, the gas dynamic trap
(axisymmetric mirror), and the flow-stabilized Z-pinch; Closed magnetic fields topologies. Those concepts having a moderate toroidal field include thereversed field pinch and spheromak. Those with no toroidal field include field reversed configurationand levitated dipole; Pulsed concepts that rely on magnetic insulation or imploding liners such as magneto-inertial fusion(a.k.a. magnetized target fusion).
Key potential advantages for non-tokamak, non-stellarator configurations are listed in Table 6.1.
There has been progress in developing each of these configurations, but DOE-FES support for alternate
concepts has been greatly curtailed in the last decade.
Much of the recent progress on alternate concepts has been supported by private industry and
DOE ARPA-E. As one example, the Z pinch provides a simple magnetic confinement configuration for
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plasma and has many advantages as acompact fusion reactor, such as an orderunity plasma beta and no magnetic fieldcoils. (The plasma beta is the ratio ofplasma pressure to magnetic pressure.)
Equilibrium in Z-pinches is ideally
produced by the radial force resulting fromthe azimuthal magnetic field that is
generated by the directly driven axial
current. MHD plasma instabilities, wellknown theoretically and experimentally,
have largely precluded achieving long-lived
FIGURE 6.13 Experimental data from the FuZE SFS
high-performance Z-pinch plasmas.
Z-pinch experimental device showing a sustained
Sheared axial flows, where flows along thefusion neutron production (green) when operated
magnetic field are different at different
with deuterium. Neutron production is coincident
radii, were theorized to stabilize thesewith high pinch current (blue) and with the plasma
troublesome MHD modes. Unlike thequiescent period indicated by low magnetic
addition of axial magnetic fields,
fluctuations (red, with gray shading indicating
equilibrium axial flows do not alter thevariation along the axis [5, 15, 25] cm). Total plasma
radial force balance, thereby preserving thecurrent (dashed black) is included for reference.
Z-pinch scaling relations. Separating the
Measurements of neutron yield indicate a steadyplasma properties that determine stability
emission to within statistical expectations. SOURCE:
from those that specify the equilibrium
Courtesy Uri Shumlak, University of Washington.
makes the shear flow stabilized (SFS) Zpinch appealing as a thermonuclear fusion
device and as a research platform for high performance plasmas.
Experimental measurements coupled with numerical simulations confirmed a correlation between
flow shear and plasma stability. These shear flows produced stable plasmas with ion temperatures over 1
keV in a 0.3 cm radius 50 cm long Z-pinch. A collaboration between the University of Washington and
Lawrence Livermore National Laboratory has been exploring the possibility of using the SFS Z-pinch as
a compact fusion device. With a more robust experimental configuration and improved pulsed power andgas injection, the SFS Z-pinch, FuZE (Fusion Z-pinch Experiment), has demonstrated sustained steadyfusion from a quiescent plasma when the pinch current is high. Experimental data are presented in Figure
6.13 that demonstrate sustained fusion neutron production when a H2–D2 mixture was used in the FuZE
device. Neutrons are observed to be produced at a constant rate when magnetic fluctuations are low andpinch current is high.
Scintillator detectors used to image the neutron emission volume on FuZe show that the neutrons
emitted uniformly along a 34 cm long section of the 50 cm Z-pinch can be attributed to a thermonuclear
process. Numerical fluid and kinetic simulations have been tightly coupled with the experimental
investigation and have been instrumental in developing physical insight into the SFS Z-pinch operation.
High-fidelity kinetic simulations demonstrate the effectiveness of sheared flow stabilization and find aflow shear required for stability that is approximately equal to the value from linear theory.
Progress Toward a Burning Plasma: ITER
Successful fusion concepts require a core plasma that is “burning” i.e., the absorption of energy
released by fusion reactions is the dominant source of heating within the plasma. In particular, thisheating is dominated by energetic alpha particles born in fusion reactions. These energetic particles slow
down by collisions with bulk electrons and ions, and in the process transfer energy to them, resulting inplasma heating. However, a significant population of energetic alpha particles can lead to instabilities—
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plasma waves can be resonantly excitedthrough interaction with the alpha particles. Inturn, these plasma waves can cause scatteringand loss of the alpha particles from themagnetic trap and can also cause unwanted
transport and loss of the bulk D-T plasma. In
current tokamak experiments, plasma heating
can be controlled and localized in space inorder to achieve desired plasma profiles andimprove plasma performance. In a burning
plasma, there is a strong feedback mechanism
between the plasma profiles and fusion
heating—more fusion will occur in the hottest
and densest region of the plasma, which
provides positive feedback by providing moreheating locally. The burning plasma cantherefore “self-organize” and the ability to use
FIGURE 6.14 ITER site in Cadarache, France inexternal heating to control plasma profiles is
February 2020. Construction required for first plasma wasdiminished. Studying this self-organized state
69% complete as of March 31, 2020. SOURCE: ©
with dominant alpha-particle heating is
ITER Organization, http://www.iter.org .
critically important to successfully designingand operating a fusion power plant. The studyof burning plasmas was raised as a key scientific challenge for MFE research in Plasma 2010 and willcontinue to be a focus of the field for the next decade.
To perform critical studies of a burning plasma in the laboratory, the United States has been apartner in the international ITER project since 2003. ITER is being built in Cadarache, France by acollaboration of 35 nations. The United States is a 9% partner in the ITER construction project. The ITER
project is one of the most complicated and largest scientific experiments ever constructed. The project has
unfortunately suffered from significant delays over the last decade. The original plan for first plasma was2018 but that has now slipped to 2026. In part because of these delays, some concerns were raised by
Congress and DOE leadership over whether remaining a partner in ITER is the right strategy for the U.S.
program. As a result, the NAS Burning Plasma Committee was charged to evaluate U.S. participation in
ITER in 2015. Around the same time, a change in management occurred within the ITER Organization
with Dr. Bernard Bigot taking over as director. Dr. Bigot’s new management produced a more realistic
timeline and costing for the project; and has kept to the project cost and schedule. At the time of thiswriting (end of 2019), the ITER construction project is over 65% complete (Figure 6.14).
SCIENTIFIC OPPORTUNITIES FOR MFE RESEARCH
Future science challenges and opportunities in MFE are being strongly driven by the NAS
Burning Plasma study recommendations. The first recommendation from that report, that the UnitedStates remain a partner in the ITER project, represents the lowest risk route to studying the physics of aburning plasma. The NAS Burning Plasma Committee released an interim report which states: “burning
plasma research is essential to the development of magnetic fusion energy and contributes toadvancements in plasma science, materials science, and the nation’s industrial capacity to deliver hightechnology components.” Further, the report states that “any strategy to develop magnetic fusion energy
requires study of a burning plasma.” Active participation in the ITER project is necessary for the UnitedStates to derive full benefit from the ITER project in its quest for a domestic fusion power plant. Effective
participation in ITER requires that the United States continue to invest in domestic tokamak facilities andresearch to address operational issues for ITER and prepare the physics and fusion technology needed to
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

enable next step devices. Such an active domestic
experimental program would ensure that the United States
gains maximum benefit from a successful ITER project
along with a strong research and development programthat:

FIGURE 6.15 Dependence of the widthof the region carrying heat flux from thescrape-off-layer to the divertor region as
a function of poloidal magnetic fieldstrength in several tokamaks SOURCE:
Eich et al., Nuclear Fusion 53 09301(2013).

 Provides solutions and technical support for successful
preparation and operation of the ITER facility. In someareas the United States is world-leading and is providing
contributions essential to ITER.
 Prepares and provides a team of talented andexperienced researchers to participate in the ITER
program and bring its results back to the domestic
program.
 Develops the physics basis and tools to take ITER’s
results and make use of them to take the next steps on thepath to developing cost-effective fusion reactors.

By supporting strong U.S. participation in ITER,
including continued strength in these three areas, theUnited States will be positioned to build on ITER’s
accomplishments to move toward the ultimate goal of
fusion powered electricity generation.
The second recommendation of the Burning Plasma Report is that the U.S. program pursue
science and engineering activities leading to the development of a compact fusion pilot plant, representing
a more economical approach to fusion power. More compact reactors require improved performance ofthe core plasma, likely enabled by the increased magnetic field, but also exacerbate the challenge ofhandling the power exhaust from the device by shrinking the surface area over which heat can be
exhausted. Tokamaks must show a route toward high performance, sustained discharges with a solution
for maintaining the plasma current required for confinement. In addition, unplanned plasma terminations
or disruptions and ELMs must be avoided or mitigated to prevent damage to the plasma facing
components and structural components.
Stellarators provide an attractive alternative route to a fusion pilot plant that does not need plasma
current sustainment, so the recirculating power fraction can be reduced and reactor economics improved
absent the requirement for current drive. They are also inherently steady state and do not suffer fromcurrent disruptions. Stellarator research must address core thermal and energetic particle confinement,
which are deficiencies relative to the tokamak, and identify a divertor solution for power handling.
Reactor concepts based on alternate concepts could also reduce cost and complexity by mitigating otherfundamental challenges, like auxiliary heating. Collaboration between private industry, DOE ARPA-E,
and DOE-FES offers the most expedient path forward for the development of these alternatives.
Developing validated predictive capability for core plasma behavior and for plasma material interactions
remains an essential challenge to achieving fusion energy. Multi-configuration research (exploringalternates to the tokamak and stellarator) has been and can continue to be part of the strategy to test
fundamental plasma models and inject innovation.
Taming the Plasma Edge: Solving the Power Exhaust Problem
The MFE research program must establish the scientific and technological basis for ensuring
adequate power handling in a compact fusion pilot plant (CFPP). The region surrounding the core plasma
from which heat flows to the divertor is called the scrape-off layer or SOL. Designing a power exhaust
solution (divertor geometry and materials) for a fusion reactor requires confident projections of the
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expected heat flux in the SOL and the conditions that will result in its mitigation to stay below material
limits. Recent empirical and model-based projections of the heat flux in next-step devices indicate a verystrong scaling with the magnet field. (See Figure 6.15.) For tokamak concepts that rely on increasing themagnetic field, this scaling implies extremely large fluxes that could exceed material limits. This heat flux
can be mitigated by injecting higher mass impurities into the divertor region, with the goal of absorbing
and re-radiating the exhausted power (which will be spread over a much larger surface area). This scheme
can lead to a so-called “detached” divertor, where the majority of the heat flux is radiated away before
reaching the material surface. Investigations of the impurity fraction required for radiative flux to disperse
the exhaust heat in high-field devices suggest that the impurity fractions are manageable for next-step
devices. These scalings require validation and more comprehensive models. Current projections andmodels rely on assumptions for impurity transport that require more theoretical and experimental
corroboration. Confirmation of the predictions for the impurity requirements are essential. There is anupper limit to the impurity content that can be tolerated in tokamaks related to the ability to screen these
impurities from the core plasma and induce further compression in the boundary plasma.
Solutions for the power exhaust problem should not sacrifice high-performance in the coreplasma. The high neutral density needed to enhance radiation in the divertor region and reduce heat fluxes
to material surfaces can have a negative impact in the region of the H-mode pedestal and core plasma.
Research is needed to explore how the divertor geometry can be optimized, leveraging advanced
magnetic configurations or physical design, to limit the negative impacts on the edge/pedestal often seen
during detachment. There is a key capability gap that the United States could fill through a new facility
focused on testing power exhaust solutions
together with a high performance coreplasma.
In the plasma core, well-defined
dimensionless parameters are expected togovern the plasma physics. Extending thisanalysis to the divertor is complicated dueto the importance of atomic physics, nonstandard geometries, and the need tomaintain absolute limits on density andtemperature to prevent damage of thedivertor. Ultimately this analysis, fromdimensionless parameters to full scalecomputations, must address reactor-scale
relevant conditions. Validation of theseanalyses needs data from reactor-scale
devices. Fortunately, the operation of suchnear-reactor tokamaks lies in theforeseeable future, with ITER to begin
operations within the decade, and the newly
formed private company Commonwealth
FIGURE 6.16 Example of a “long-legged” divertor
Fusion Systems aiming for operations ofdesign, an “X-point target” divertor for the ARC
their SPARC D-T device in the mid-2020s.
tokamak being designed by Commonwealth Fusion
Although ITER and SPARC will
Systems (CFS). SOURCE: © 2018. This manuscript
enable essential studies of core-edge
version is made available under the CC-BYNC-ND 4.0
integration, the requirements on the divertor
license http://creativecommons.org/licenses/byof these machines are not the same as those
ncnd/4.0 ,for a CFPP. It is possible, and evenhttps://arxiv.org/ftp/arxiv/papers/1809/1809.10555.pdf.
expected, that these experiments will showthat their baseline divertor scenarios are
inadequate for follow-on facilities. For thisPREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

reason, the world program is actively developing advanced divertor scenarios to reduce risk and to ensurethat a solution is in hand for the post-ITER era. These efforts include the construction of new facilities
dedicated to this task. However, the worldwide power exhaust research program lacks the capability toproperly study the unique physics of a long-legged divertor—divertors that utilize a magnetic geometry
with a long path from the edge of the plasma to the divertor surface to allow magnetic expansion of
exhaust plasmas lowering the heat flux at the target. (See Figure 6.16.) Long-legged divertors must be
studied at high exhaust parameters as part of this risk mitigation strategy. Predictions for this class ofadvanced divertors, in particular the United States developed Super-X and X-point Target concepts,
indicate that they will both mitigate heat flux and potentially increase the isolation of the divertor fromthe core plasma. Recent predictions have also highlighted enhanced cross-field transport driven by
turbulence in the long-legged divertors. There are clearly challenges with utilizing this concept in areactor, which further emphasizes the need to better understand the physics and to gain experience inlong-legged divertor engineering in a more forgiving environment. Establishing the capability to explore
these concepts is essential to fully exploring options for power handling in CFPP.
A key technical and engineering challenge for the development of a working fusion energy
system is developing plasma-facing materials that can survive the intense thermonuclear environment
inside the plasma. Indeed, a detailed discussion of these issues was presented in the 2019 NAS report on aStrategic Plan for U.S. Burning Plasma Research. Some of the key findings are noted here. The essential
properties of the plasma-facing “first wall” materials are that their structural properties should remain
stable under thermal loads that may exceed 1 MW/m2 and subject to neutron fluxes that lead todisplacement events (atoms moved from their natural positions in the material) that can be 50 to 100
times higher than in fission reactors. These materials must be able to survive continuous operation offusion systems in order to satisfy the requirements of tritium retention, safety, structural integrity,
lifetime, and plasma compatibility. Because of these unique operational conditions, the development ofplasma simulators that can operate under steady-state conditions that approximate fusion level particle
and energy fluxes are critically needed. In the United States, devices such as the PISCES facility at
University of California, San Diego, the Tritium Plasma Experiment at Idaho National Laboratory (INL),
and the Material Plasma Exposure Experiment being developed at Oak Ridge National Laboratory(ONRL) are providing the testbed infrastructure for evaluating the performance of materials. The
development of resilient, next-generation materials for the fusion environment is a critical need regardlessof the architecture of the final fusion device. Investing in this materials development before the decision
is made on the architecture of the next generation fusion device would be a highly strategic move. Doingso requires close collaborations between plasma physics, nuclear engineering, and materials science
research, and should involve more collaborative activities that link the Department of Energy’s Basic
Energy Sciences and Fusion Energy Sciences programs. The 2019 NAS Decadal Survey on Materials
Science Frontiers of Materials Research called out “Materials for Extreme Environments,” including forfusion energy systems, as a frontier opportunity for the field.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

Achieving Steady-State, High-Performance, Disruption-Free Core Tokamak Plasmas
The development of a plasma that self-organizes its state to not only heat itself, but also sustain
its own current and thus confinement, represents a fascinating and fundamental challenge in plasma
physics. Previous experiment and theory work havedemonstrated that toroidal plasmas self-generate a‘bootstrap’ current due to collisional spreading of net
currents arising from ion orbit trajectories. Theory
suggests that such currents lead to plasma
configurations that can reach the very high pressuresrequired for fusion and suppress turbulent fluctuations
that would otherwise diffuse fusion heat. However,understanding how to realize this vision rests on anumber of foundational physics mechanisms for which
fundamental understanding must be developed.
Achieving high performance tokamak plasmas
means optimizing the configuration (current, flow,pressure profile) to limit transport losses due toturbulence. This turbulence can be substantiallystabilized by plasma flow and through the radial
variation in the magnetic field line pitch that isestablished by the plasma current profile. Variation inflow and magnetic field line pitch can “tear apart” theturbulent eddies and twist them magnetically.
Significant progress has been made over the last decadein understanding and exploiting this stabilization
process. However, the high pressures and densities in afusion reactor will lead to the increasing importance ofelectromagnetic effects in edge turbulence, and ourunderstanding needs to be extended to this regime toproject advanced tokamak scenarios to reactor relevant
conditions.
FIGURE 6.17 (top) Runaway electrons
Operating at high performance and high plasma
produced by a disruption stimulated bypressure also means operating near global instability
massive injection of Argon in DIII-D create
limits. Instabilities such as NTMs and otherhard x-rays and excite and interact withmagnetohydrodynamic (MHD) modes can arise at highkinetic instabilities (observed on externalpressure and lead to enhanced transport or plasma
pick-up loops). (bottom) Melted plasma
termination (disruption). Much has been learned aboutfacing tiles due to runaway electron damage
these global modes, but work remains including
in JET. SOURCE: Top: Lvovskiy et al 2018
studying electromagnetic effects and wave-particle
Plasma Phys. Control. Fusion 60 124003; ©
resonances that can modify stability limits and mode
ITER Organization, http://www.iter.org.
behavior. Projection to a reactor rests on understanding
these mechanisms and developing quantitative predictive simulation tools.
Understanding global instabilities is important, in particular where that understanding enables one
to avoid those instabilities. However, learning to control these instabilities when they do arise is also
extremely important. ELMs occur in the steep pressure gradients associated with the H-mode edge in atokamak. During ELM events, large filaments can form that reconnect as they are ejected, carrying withthem a substantial fraction of the plasma energy in the edge region. In current devices ELMs are tolerable.
However, in ITER and future reactors, one ELM could lead to significant damage to materials
surrounding the plasma. Several techniques have been developed to suppress or minimize the size of
ELM events including use of 3D magnetic coils to enhance transport and prevent the pressure from rising
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

to the stability limit (RMP suppression). However, RMP is not effective under all plasma conditions.
More work needs to be done to develop full confidence in techniques for controlling ELMs. This will
necessitate both theoretical and experimental efforts. The experimental work would be best done indevices with reactor relevant edge conditions (e.g. relevant absolute pressure so that effects like neutral
penetration are properly addressed). The theoretical work requires extension of the MHD and turbulence
formalisms to new regimes where conventional models break down.
Global instabilities can lead to unplanned plasma termination or “disruption.” Finding ways to
avoid or mitigate disruptions is a major challenge for the tokamak concept. Disruptions result in sudden
loss of plasma thermal energy to the first wall, which can cause substantial damage to plasma facing
components. In addition, there is significant magnetic stored energy associated with the plasma current in
a tokamak. Sudden disruption of this current causes very large inductive electric fields that can induce
currents in conducting structures around the tokamak and accelerate plasma electrons to very highenergies. Induced currents in the tokamak structure (e.g. vacuum vessel) can lead to strong magnetic
forces. In existing tokamaks these forces have been strong enough to move the entire tokamak structure
vertically. (These are impressive forces. The JET tokamak weighs more than 2000 tons and disruptions
have created forces up to 5 MegaNewtons. This is equivalent to the peak thrust of the main engines of thespace shuttle). The large inductive electric fields can also accelerate electrons to very high energies within
the tokamak. These electrons, called “runaway electrons,” can reach energies of 10’s of MeV and cancarry currents equivalent to the original plasma current (which could be several MegaAmperes ofcurrent). The impact of such an electron beam on material components can cause substantial damage.
(See Figure 6.17.) In current experiments, stored energies are in the range of 10’s of MegaJoules. ITER
will have roughly 1 GigaJoule of stored energy, split roughly equally between thermal and magnetic
energy associated with the plasma current.
The primary strategy to maintainstability and prevent disruptions is todesign and sustain an intrinsically stableconfiguration. This will be achieved by
exploiting fundamental understanding of
the source of instabilities, combined withreal time diagnostics, calculations, or
machine learning prediction. If an onsetof a disruption can be detected or
predicted, preventive measures can, in
FIGURE 6.18 Antenna structure installed in the DIII-D
principle. be rapidly implemented.
tokamak to excite “helicon” fast waves to drive plasma
However, it is always possible that acurrent non-inductively. SOURCE: J.F. Tooker, A. Nagy,
fault such as a power supply failure or aJ. deGrassie, C. Moeller, M. Hansink, B. Fishler, C.
structure failure that may inject solid
Murphy, J. Anderson, H. Torreblanca,material into the plasma leading to large
Development of a high power Helicon system for DIII-D,
scale distortion, loss of confinement andFusion Engineering and Design, 123, 2017, 228-231,
a rapid disruption. Safe means of
https://doi.org/10.1016/j.fusengdes.2017.03.055.
quenching such a fault are needed, which
requires solving the triple challenge ofhigh heat (energy) flux, induced device
forces (as current rapidly quenches magnetic forces arise) and induced runaway electron beams. Proposed
strategies to deal with disruptions include avoidance (staying away from instability) and mitigation(intentional plasma termination ahead of disruption). Both approaches require developing understandingof global instabilities including their non-linear evolution. Mitigation schemes include the injection oflarge amounts of neutral gas (massive gas injection) or frozen pellets (single pellets or “shattered” pellet
injection) with the goal of controlled plasma termination ahead of an anticipated disruption. The
dynamics of runaway electrons are particularly challenging, as they create their own confined plasma,
which can undergo dissipative interaction with waves, or become unstable directly.
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

A key challenge in achieving a
steady-state tokamak plasma is to find a way
to sustain the plasma current that is needed. In
shorter pulse experiments, inductive
techniques can be used. A solenoid is threaded
through the “hole” in the tokamak and rising
currents in this solenoid induces a toroidal
electric field inside the tokamak plasma,
driving a current. In this arrangement thetokamak is like a transformer with the plasma
FIGURE 6.19 Magnetic surface rendering (withacting as the secondary. Such inductive drive
magnetic field strength in color in Tesla) of acannot continue indefinitely as there are limits
stellarator magnetic geometry designed byon how long the current in the solenoid can be
optimization to minimize turbulence and turbulent
steadily increased. ITER will use a solenoid totransport. SOURCE: Xanthopoulos, et al., Phys. Rev.
inductively drive current for 400 s. To achieve
Lett. 113, 155001 (2014).
a steady state burning plasma, auxiliary means
to drive current are needed to operate forlonger times in order to maintain the desired,self-stained configuration of current and magnetic fields. Radiofrequency waves can be injected into theplasma to directly drive currents, either by injecting momentum and “pushing” particles in a particular
direction or by introducing collisional asymmetries, making it easier to push particles in one particular
direction. Promising techniques include electron cyclotron resonance, ultra-high harmonic ‘helicon’ fast
wave (see Figure 6.18) and lower hybrid resonances. These techniques need to be demonstrated withappropriate efficiency in reactor conditions.
Using Three-Dimensional Magnetic Fields to Resolve Major Challenges
For optimal plasma confinement, many critical obstacles can be addressed using magnetic fields
that are non-axisymmetric, that is, without continuous rotational symmetry as is the case in the standard
tokamak. As described above in our discussion of the W7-X, stellarators naturally provide stable, steadystate confinement with no disruptions, no runaway electrons, no Greenwald density limit (an operational
limit for the density in magnetic confinement devices), and no need for current drive. Since stellarators
can confine plasma with negligible internal current, they can be used to confine low-density non-neutral
plasmas and pair plasmas (made of electrons and positrons) for basic physics studies, in addition to hightemperature plasmas relevant to fusion. Nonaxisymmetric or ‘3D’ effects are also important in nominally
axisymmetric confinement concepts such as the tokamak, which have small unavoidable departures fromsymmetry. Symmetry in tokamaks is sometimes also intentionally broken by nonaxisymmetric magnetic
fields to control edge instabilities. Nonaxisymmetric plasma states can also arise spontaneously inreversed field pinches, and differences between 2D and 3D geometries are significant in other plasma
phenomena such as reconnection. However, challenges remain to fully realize the potential of 3D shapingof magnetic fields to optimize plasma confinement. Creating the “perfect magnetic bottle” using 3D
magnetic fields is one of the outstanding challenges in plasma physics. The major scientific questions thatmust be addressed to achieve the perfect magnetic bottle by customizing the 3D magnetic field—also
known as 3D shaping—include: Optimizing 3D shaping to separately reduce collisional and turbulent transport (see Figure 6.19),
improve confinement of fast-particle orbits, and stabilize MHD modes. Can 3D shaping be used
to simultaneously optimize all of these processes?
 Is it possible to control turbulence by 3D shaping?
 The confinement of alpha particle orbits in a stellarator fusion reactor—can alpha confinement be
optimized 3D shaping?
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration










What combination of electromagnet topologies, permanent magnets, and diamagnets is best for3D shaping?
How can we design stellarators to make the magnets simple, with generous tolerances?
How can 3D shaping be leveraged to maximize control of the basic properties of the plasma?
What is the best geometry for a stellarator divertor?
In tokamaks, what is the mechanism by which ELMs are suppressed or triggered by 3D fields?
Can ELM control by 3D fields be made reliable and an “every-day” practice?
How do 3D perturbations in otherwise symmetric magnetic fields affect particle and energy
transport?
How can theory and computations be improved and leveraged to optimize and understand 3D
shaping, and investigate configurations that are now beyond current experimental capabilities?

As discussed above, the W7-X stellarator has proven many concepts in using 3D shaping toachieve record confinement and plasma times. The LHD (Large Helical Device), a large stellarator inJapan, achieved several milestones such as a 10 keV ion temperature. The CTH (Compact Toroidal
Hybrid) stellarator at Auburn University has collected more evidence that moderate nonaxisymmetricshaping can be applied to a tokamak to eliminate disruptions. Significant theoretical advances were madeand new codes have been developed for both collisional and turbulent transport, and have demonstrated
that 3D shaping can be optimized to reduce turbulent transport. New algorithms and codes have beendeveloped to design stellarator magnets, and new plasma configurations were demonstrated withexceptional alpha confinement. In tokamaks, 3D magnetic perturbations have been explored,
demonstrating that 3D field perturbations can suppress ELMs, modify edge profiles, and control manyother properties. Theory and simulation of 3D effects in tokamaks have advanced significantly, withmultiple codes now available that include the plasma response to external perturbations.
In the next 10 years, significant developments in 3D shaping are on the horizon. W7-X is being
upgraded with a cooled divertor to enable 30 minute discharges, and a steady-state pellet injector will
enable continuous peaked density profiles. The CFQS (Chinese First Quasi-axisymmetric Stellarator) will
begin plasma operations early in the decade, providing the first experimental realization of a quasiaxisymmetric field. The EPOS experiment (Electrons and Positrons in an Optimized Stellarator) has been
funded to explore pair plasmas. Other stellarator design activities are underway at the University of
Wisconsin, Princeton Plasma Physics Laboratory, and the National Institute for Fusion Science (NIFS) in
Japan. The Simons Foundation recently began an interdisciplinary project to improve understanding of
3D MHD equilibria and bring state-of-the-art applied mathematics to bear on stellarator optimization.
Adjoint analytical methods are now becoming available to obtain the plasma properties (e.g. confinement
quality) with respect to variation in plasma or coil shape. These new techniques could transformstellarator optimization.
Related areas of science, technology, and mathematics are making breakthrough contributions
that will advance development of 3D plasma confinement schemes. First, high-temperature
superconductors enable new options for electromagnetic coils. While it may be difficult to increase themagnetic field strength in stellarators due to the need to support complicated distributions ofelectromagnetic forces, reducing conductor thickness and cooling demands would still provide additional
flexibility in the design. For example, demountable joints in such superconductors would make different
coil topologies feasible. Second, advanced additive manufacturing processes will likely enable here-tofore unachievable 3D configurations. Third, there is enormous expertise in optimizing complex systemdesign available in other fields that can be leveraged for stellarator designs, for example, learning fromthe design of advanced aircraft.
The United States plays a leading role in some areas of 3D plasma physics and has a more modest
standing in others. The use of 3D perturbations for tokamak control was led by the United States, withrelated efforts now on many tokamaks abroad. Though the stellarator was invented in the United States,
the largest such devices today (W7-X and LHD) are located abroad. The United States has made valuable
hardware contributions to W7-X, on which scientists from several U.S. institutions collaborate. There are
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several small stellarators in the United States, all at universities: the Helically Symmetric Experiment(HSX, University of Wisconsin), CTH (Auburn University), and Columbia Non-Neutral Torus (CNT,
Columbia University). In the past decade, many significant theoretical and computational advances in 3D
plasmas have come from the United States. Having said that, the U.S. investment in stellarator research issmall, only ~1.5% of the DOE FES budget in 2019. With a modest increase in this investment, an
opportunity exists to leverage the existing expertise in 3D physics to position the United States as a leader
in this area.
Developing Predictive Capability to Enable Design and Control of Fusion Reactors
Experiments have been absolutely essential to progress in MFE research, leading to key
discoveries such as the H-mode and edge-localized mode (ELM) suppression using 3D magnetic fields.
Experiments are key to developing scientific understanding and validating theory and computation.
Moving forward, there will be a greater and more necessary need for theory and computations to leadexperiments. The cost of state-of-the-art fusion reactors and the time required to approve, construct andcommission systems places a very high premium on having robust, designs from both a physics andengineering perspective. Increasing confidence in the design and construction of new fusion systems will
largely come from fundamental theory and computations. Computations that are based on fundamental
theories and validated using data from existing systems will be necessary for predictive design that has
the confidence of the community. For example, extending the confinement performance from H-mode to
the Super H-Mode regime in tokamaks was only possible due to guidance from the EPED model,
developed and validated through experimental observation. The design of optimized stellarator
experiments was enabled by improved theoretical understanding—the success of W7-X in reducing
neoclassical transport was a result of this understanding. As the U.S. MFE program plans for future
experimental facilities to lead the international community, there is a need for improved first-principles,
validated understanding and predictive capability to help design and then fully exploit these facilities.
Advances in multi-scale, multi-physics theory and modeling capabilities across the MFE
discipline are necessary to predict not only the plasma physics of 3D configurations, but also theinteraction of plasmas and surrounding materials. Perhaps the highest requirement is validating codes onpresent experiments to build confidence in predictions of fundamentally new physics regimes typical of afusion power plant. These physics models must ultimately be integrated into the engineering focusedcodes to develop designs for future fusion experiments, and in particular a fusion pilot plant. There is ahierarchy of approaches spanning whole-plasma modeling (core to first wall), whole-device modeling(adding the divertor, wall and blankets), and whole-facility (including balance of plant and economics tothe site boundary). There is also a hierarchy of types of models needed, from first-principles simulations
to reduced models that enable more rapid computation for use in scoping/design and potentially real-time
control and feedback of experiments.
To meet these computational goals, the MFE program needs to support (ideally collaboratively
with other agencies and offices within DOE) experimental and computational studies on fundamental
fusion-relevant plasma and material physics. Continued development of validated predictive models withtight coupling to experiments is necessary to the future of the field. To increase collaboration between
theory, computation, and experiment, specific programs aimed at this goal are necessary. The DOE FES
and Advanced Scientific Computing Research (ASCR) partnership program Scientific Discovery throughAdvanced Computing (SciDAC) is one such model that can be expanded, bringing in other partners suchas DOE Basic Energy Sciences (BES). These activities would build, refine, and validate predictivemodels of fusion-relevant plasma and material processes over a range of complexities (first principles toreduced models) and computational cost to meet the need. Validation must be performed with rigorous
uncertainty quantification to develop the required confidence in predictive models. Validation should
focus on regimes that are relevant to burning plasmas where possible.

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Innovations in data analysis andmachine learning should be used tocomplement more conventional model
development where appropriate. Investments
should be made in computational
infrastructure and software engineering to
optimally employ current and future highperformance computing platforms; and toenable advanced data management andanalysis, with the goal of improving theinterface between experiments andcomputation. These advances would be
aided by the adoption of data standards andcommon formats to support benchmarking
and accessibility. The MFE program should
FIGURE 6.20 Interior of the DIII-D Tokamak
invest in the processes and infrastructure
vacuum vessel. SOURCE: Rswilcox,
needed to make the outcomes of large-scale
https://commons.wikimedia.org/wiki/File:2017_TOC
simulations available to the broad
AMAC_Fusion_Chamber_N0689.jpg.
community in a way analogous to the
distribution of experimental data by major
fusion experimental facilities. (For example, MDSplus is a set of data acquisition and software tools
widely used by the international fusion community.) Investments should also be made to support software
engineers converting legacy production codes to new architectures, and to develop standardized libraries
to minimize the overhead of new code development.
It is important to have a balanced approach to investing in both developing computing capability(e.g., producing codes that efficiently use the largest supercomputers) and leveraging computing (e.g.,
performing computations needed to advance physics and engineering). For example, first principles
kinetic plasma simulations are essential to investigate the fundamental physics of fusion plasmas, and its
related large computational resource needs are a driver in the plasma community for exascale computing.
In the past, funding priorities have driven the community more toward capability computing (use as many
processors as possible in the largest machines) rather than providing resources to actually use thiscapability to evaluate experimental results, design new experiments and drive the science of MFE
forward. Investing in computations enables both continued use of production codes as well as advancing
high-fidelity modeling capabilities.
MFE FACILITIES IN THE UNITED STATES
Here the committee briefly discuss the MFE facilities in the United States that have contributed to
our understanding of fusion physics and advanced fusion technologies over the past decade. (See Table
6.2.)
DIII-D
DIII-D is currently the largest magnetic fusion research experiment in the United States, locatedat the DIII-D National Fusion Facility in San Diego and operated by General Atomics for the DOE. (SeeFigure 6.20.) DIII-D is a multi-institutional user facility whose primary research goals are to: Provide solutions to physics and operational issues critical to the success of ITER;
 Develop the physics basis for steady-state tokamak operation as required for efficient power
production;
 Contribute to the technical basis for a fusion nuclear science facility, and
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Plasma Science: Enabling Technology, Sustainability, Security, and ExplorationAdvance the fundamental understanding and predictive capability of fusion science.
The DIII-D project began in 1986, and its technical capabilities have continually improved,
making it a flexible device that can study confinement, stability and divertor physics with a variety ofheating and current drive techniques. This capability, in turn, enables development of high-performance,
advanced tokamak concepts having simultaneous control plasma profiles both in the core and at the edgeof the tokamak. Near-term research on DIII-D addresses plasma configuration scalable to the high gain
fusion that is the goal of ITER. Longer-term research focuses on developing techniques to produce stable,
high-performance, steady-state (i.e., non-inductive) operation in ITER and beyond.
DIII-D has a major radius of R = 1.67 m and a minor radius of a = 0.67 with a nominal aspectratio of R/a = 2.5. (R is the radius of the entire tokamak torus; a is the radius of the tube of the torus). It
can operate with a 2.2 T toroidal magnetic field and 3 MA plasma current, although it generally operates
at lower currents, ≤ 2 MA. Eighteen magnetic field-shaping coils operated by a plasma control systemprovide great flexibility in the shape of the plasma, discharge evolution, and divertor configuration.
Divertor cryopumps control the plasma density. DIII-D has 26 MW of external heating capability, split
between 20 MW of neutral beam injection (NBI) heating and 6 MW of electron cyclotron heating (ECH)and current drive. The neutral beams are configured on- and off-axis, and in the co- and counter-current
direction to provide a range of torque and neutral beam driven non-inductive current profiles. A key
feature of DIII-D is sets of internal and external coils that provide a wide range of 3D magnetic
perturbations for edge-localized mode (ELM) suppression and other edge profile control studies.
Shattered pellet injection and argon pellet systems are used to mitigate disruption and runaway electrons.
(This is a technique by which frozen pellets of gas, either whole or shattered, are injected into the plasma
and then evaporate to increase the local gas density.) A lithium and boron “dropper” (a system that
dispenses particles smaller than a few hundred microns) is used for wall-conditioning, and a laser blowoff instrument (where a laser pulse ablates a puff of material into the plasma) is available for impurity
transport studies. DIII-D has an outstanding, comprehensive set of core, edge, and divertor diagnostics. A
close collaboration between theory, computations and experiment enables the data to be readily used tovalidate first-principles physics simulations for the development of high-confidence predictive tools.
Organizationally, DIII-D is managed by a private company, General Atomics (GA). Multiple
national-laboratory and university, as well as GA employees, constitute the scientific staff. Generally, GA
employees operate the major systems. Several major subsystems are the responsibility of national
laboratory teams while diagnostic systems are the responsibility of university, national laboratory, andGA personnel. Experiments are selected from proposals submitted to Research Opportunities Forum thatis open to all and reviewed by a Research Council with experienced team members from GA,
laboratories, and universities. Final allocations for experimental time on DIII-D are made by GA
management. Experiments are conducted by multi-institutional teams that often include international
visitors. The research program is influential. As a measure of impact, consider the papers selected for oralpresentations at the most recent IAEA Fusion Energy Conference (the highest visibility conference in thefield). Of 42 experimental magnetic fusion papers, 15 utilized DIII-D data, the most of any facility in theworld.
NSTX-UThe National Spherical Torus Experiment-Upgrade (NSTX-U) is one of 17 tokamaks worldwide
designed to operate in the low aspect ratio regime. (See Figure 6.21.) It is a high-powered, medium-sized
device that is one of the two largest and most capable low aspect ratio tokamaks in the world, the otherbeing MAST-U in the U.K. The mission of NSTX-U is to: Advance the spherical tokamak (ST) as a candidate for a Fusion Nuclear Science Facility (FNSF);
 Develop solutions for the plasma-material interface, including the snowflake divertor andlithium/liquid metal plasma facing components (PFCs);
 Advance toroidal confinement physics predictive capabilities for ITER and beyond; and
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

Develop the ST for fusion energy
production, for example as an ST Pilot
Plant.
Many of ST physics challenges
were investigated in NSTX, thepredecessor to NSTX-U. NSTX had an
aspect ratio of R/a=0.85/0.68~1.25,
operated with plasma currents up to 1.5
MA and with toroidal magnetic fields of up
to 0.55 T. NSTX had pulse lengths of up to
1.5 s, and operated with either D+ or He++.
NSTX was equipped with a three-source
neutral beam capable of injecting 6 MW ofpower at 90 keV, and up to 6 MW of High
Harmonic Fast Wave RF power for heating
and current drive. Co-axial Helicity
FIGURE 6.21 The NSTX-U Spherical Torus
Injection (CHI) was used for non-inductive
Experiment. SOURCE: Princeton Plasma Physics
plasma startup. Close-fitting passive
Laboratory.
conductors, coupled with application ofactive control algorithms using applied 3D
magnetic fields as actuators, were used to stabilize MHD instabilities and maintain high-performance
operations.
NSTX-U will continue to explore physics issues critical to low aspect ratio tokamaks, but withenhanced capabilities. The toroidal magnetic field will be increased from 0.55–1 T, the plasma current
from 1.5–2 MA, and the pulse length from 1–5 s. A second, more tangentially injecting neutral beam wasadded, doubling the total available power up to 12 MW under normal operating conditions. These
additions make NSTX-U the most powerful ST in the world, with the highest toroidal field and highest
accessible pressure and plasma . This will enable NSTX-U to achieve up to 10 times higher fusion triple
produce (nT𝞽) and four times higher divertor heat fluxes, reaching levels expected in ITER.
The increased current, field and power will enable NSTX-U to operate at higher temperature andup to five times lower collisionality than in NSTX. Operation at reduced collisionality is critical toresolving how confinement varies with this parameter. If this favorable confinement trend with reduced
collisionality is confirmed, that is, exhibiting a stronger trend than observed in tokamaks withconventional aspect ratios, this would be critical information for optimizing designs of compact tokamak
reactors having small aspect ratio, high-.
While there is significant overlap between the two major ST devices—NSTX-U will focus oncore physics, and in a complementary fashion MAST-U will focus on boundary physics. MAST-U isequipped with poloidal field coils that will enable more flexible divertor configurations than those thatcan be produced in NSTX-U. However, NSTX-U can contribute and, in some instances, lead in power
exhaust studies. NSTX-U will be using solid lithium coatings to protect PFCs from high heat fluxes, toimprove confinement and to suppress ELMs, as was done in NSTX. Solid lithium injectors on the top andbottom of the vessel will double the lithium deposition over that in NSTX. Long-term plans include thedevelopment of liquid metal divertors as a possible transformative wall solution.
NSTX-U operated a 10 weeks productive scientific campaign in 2016. However, by the end ofthat period, it was discovered that one of the poloidal magnetic field coils failed, necessitating NSTX-U toshut down for an extended repair. The NSTX-U Recovery is ongoing, with numerous design
improvements, including modification of the vacuum chamber, in order to support flexible operations andincrease reliability to achieve key mission goals. New requirements for the divertor heat fluxes have been
defined, based on recent models for the SOL heat flux. New error analysis has been conducted, with thegoal of optimizing both the global MHD stability and minimizing PFC heat flux asymmetries. New
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

designs of graphite plasma facing components utilize crafted surfaces to reduce the mechanical stresses,
allowing tiles to reach temperature of ~1600 C. Improved divertor coil designs simplify fabrication andfacilitate turn-to-turn testing. The NSTX-U Recovery project is on track to enhance reliability and safety
and provide the highest performance ST device as a robust user facility. NSTX-U is expected to resume
operations during 2021.
Alcator C-Mod
Alcator C-Mod is a compact, high-magnetic field, diverted tokamak that was operated at the MIT
Plasma Science and Fusion Center (PSFC) from 1993 until 2016. (See Figure 6.22.) C-Mod has a 0.68 m
major radius and 0.22 m minor radius and can operate with up to 8 T magnetic field using liquid nitrogencooled copper magnets. The high magnetic field enables the small device to create the dense, hot plasmas(> 100 million degrees) of the type expected in a fusion reactor. C-Mod holds the record for the highest
volume average plasma pressure in a magnetic confinement device, which is an important metric forfusion performance. The plasma is heated to very high power densities using radio-frequency heatingfrom novel antennae and sustained with microwave current drive. The third in a series of high-magnetic
field tokamaks at MIT, C-Mod leveraged PSFC expertise in high-field magnets, high power radio-waves,plasma physics, fusion materials, theory and simulation, and cutting-edge engineering. This experimental
device enabled a wealth of new and important results.
C-Mod has contributed data extending physics understanding into new parameter spaces todevelop new tokamak operating regimes while demonstrating important technical solutions to fusion
problems. The relatively large power in a small device allows for tests of heat exhaust at reactor-relevant
heat and particle fluxes in reactor-relevant divertor geometries. To handle these conditions, C-Mod
pioneered the use of the vertical target-plate divertor with refractory metals, a design that has been
incorporated into other devices including ITER. Studies on C-Mod have clarified the roles of rotation andshear on transport and stability across the plasma and have demonstrated stable operating regimes at highmagnetic field that may eliminate explosive instabilities.
Until 2016, C-Mod was one of three domestic tokamaks and a DOE user-facility. C-Mod engaged
collaborators from all over the world to plan and execute experiments. The team of over 100 professors,scientists, students, engineers, and technicians made C-Mod the largest experiment at MIT withparticipation from many MIT academic
departments. Following completion ofoperations, the facility was placed into safe
shutdown, with no additional experiments
planned at this time. There is a wealth of dataarchived from the more than 20 years ofoperations, and the experimental andtheoretical teams continue to analyze theresults and publish them in the scientific
literature.
Smaller MFE Research Facilities in the
United States
Pegasus is an ultra-low aspect ratio
tokamak at the University of Wisconsin that
operates with a major radius of R~0.35 m, R/a~1.13–1.3 and a toroidal magnetic fieldstrength of 0.17 T. Its mission is to explore
very high- confinement and stability, and to

FIGURE 6.22 Interior of the Alcator C-Mod vacuum
vessel. SOURCE: Courtesy of Mike Garrett.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

develop non-inductive discharge start-up techniques. Pegasus has achieved H-mode plasmas, withthreshold powers for accessing the H-mode well above (~15x) that predicted for the Pegasus operating
parameters with plasma currents up to 100 kA.
Lithium Tokamak Experiment upgrade (LTX-b) is also a low aspect ratio tokamak at Princeton
Plasma Physics Laboratory having R=40 cm, R/a~1.55, a toroidal magnetic field of 0.17 T and plasma
currents up to 100 kA. The purpose of LTX-b is to develop use of liquid lithium walls to protect plasma
facing surfaces, and to study their effect on plasma performance. Its predecessor LTX, used lithium
coatings on a high-atomic weight wall, and it exhibited flat electron temperature profiles and enhanced
confinement without having the lithium dilute the core plasma or radiate power. LTX-b will extend thecapabilities of LTX with 700 kW of NIB heating and fueling, 100 kW of ECH/EBW (electron Bernsteinwave) coupling for electron heating, higher magnetic field and current, longer pulse length, and upgradeddiagnostics.
The Madison Symmetric Torus (MST) at the University of Wisconsin is a reversed-field pinch(RFP) physics experiment, which relies on a transient burst of current to create the plasma and theconfining magnetic fields. In the RFP, the toroidal magnetic field is weaker than the poloidal magnetic
field, and it actually reverses direction in the plasma near the edge. The mission of MST, part of the
Wisconsin Plasma Physics Laboratory user facility, is to study fusion and astrophysical implications ofreconnection, turbulence and dynamo formation. A 1 MW NIB will be used to heat the plasma and enablestudies of fast particles and their role in the reconnection process. A wide range of diagnostics is available
for characterizing the plasma.
HSX, the Helically Symmetric Experiment Stellarator, also at the University of Wisconsin, is aquasi-helically symmetric (QHS) stellarator with R=1.2 m, a=0.15 m and toroidal magnetic field up to
1.25 T. It has up to 200 kW of electron cyclotron heating, which can energize the electrons up to 2–2.5
keV in the core. By the nature of its QHS design, neoclassical electron thermal transport was reduced.
HSX has demonstrated conditions important for reducing turbulence-driven transport, maintaining plasma
stability, and for good particle confinement of trapped high-energy electrons. HSX also serves as aflexible divertor test platform, able to produce either an island or non-resonant divertor.
HIDRA (Hybrid Illinois Device for Research and Applications) at the University of Illinois is aclassical stellarator with R=0.72 m and a=0.19 m, with magnetic fields up to 0.5 T. The main focus of
HIDRA is to study plasma-material interactions, including liquid lithium science and technology. The
Compact Toroidal Hybrid (CTH) device at Auburn University is designed to study how MHD stability ina stellarator depends on 3D shaping of the plasma. It has R=0.75 m, a=0.29 m, magnetic field of 0.7 T,
and it has independently controlled magnet coils that can produce a wide variety of configurations,enabling conditions appropriate to investigating disruptions.
The mission of the HBT-EP device at Columbia University is to utilize an adjustable close-fitting
conducting wall for passive stabilization and applied external magnetic perturbations for active control of
MHD modes. It has R=0.92 m, a=0.15 m and toroidal magnetic field of 0.35 T. The Helimac at the
University of Texas at Austin (R=1 m, 0.1 T) is a toroidal device that is used to study plasma turbulence
at high collisionality. With magnetic field lines having a low pitch, its configuration approximates that ofan infinite cylinder. Flow shear is externally applied and can be controlled. The plasma is colder, with Te~10 eV and number densities of 1011 cm-3.
THE U.S. MFE EFFORT AND ITS INTERNATIONAL CONTEXTU.S. Leadership in the International Fusion Research Effort
Historically, the United States has been at the forefront of the MFE international researchcommunity in virtually all major areas. In large part, this is due to major investments made during 1980–
2000, developing a diverse set of research facilities (TFTR, DIII-D, NSTX, Alcator C-Mod), coupled to astrong base program of experiment and theory. A measure of U.S. scientific leadership is reflected in the
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

recipients of significant international research prizes, such as the Nuclear Fusion Award and the Alfven
Prize. U.S. scientists constitute a disproportionately large number of winners. Eight out of twelve Nuclear
Fusion Awards to-date have recognized work led by U.S. scientists from across the U.S. fusion program.
The Alfven Prize of the European Physical Society was established in 2000, and U.S. scientists have been
recipients in 8 of the 19 years. Although the prize is for all areas of plasma physics, the U.S. winners havebeen mostly from the fusion research community.
This recognition of the excellence of U.S. research acknowledges past accomplishments, and isunlikely to continue into the future unless current trends are reversed. Simply stated, U.S. leadership islagging. The United States is poised to lose research leadership of the world’s MFE programs for two
coupled reasons. First, there is, and has been for several decades, a lack of major investment in new U.S.
facilities and experimental capabilities. Second, there is currently an absence of a U.S. strategic plan forfusion energy. This latter issue is being addressed at the time of this writing by the ongoing CPP(community planning process) for the DOE Fusion Energy Sciences. The committee is hopeful that theresulting plan will be well received, implementable and regularly updated.
While the United States had made significant investment in the international ITER experiment,
the lack of major investment in domestic experimental capabilities is startling when compared toinvestments being made internationally. With a twenty year gap in major investment in new domestic
facilities, along with the closure of TFTR and Alcator C-Mod, the United States is left with only two
major medium-scale facilities—DIII-D (started in 1986) and NSTX-U (NSTX started in 1999 and was
upgraded to NSTX-U in 2012). The contrast internationally is striking, with major investments by ourpartner nations in new facilities in the European Union (the WEST tokamak and the W7-X stellarator
started in 2016), Japan (the JT-60SA tokamak will begin operations in 2021), China (the EAST tokamak
started in 2006), and S. Korea (the KSTAR tokamak started in 2008). Substantial upgrades have occurredor are planned for the JET tokamak (UK), the ASDEX-U tokamak (Germany), and the LHD stellarator(Japan). The 2012 Fusion Energy Scientific Advisory Committee (FESAC) report on “Opportunities andModes of International Collaboration During the ITER Era” states that “the capabilities of new
experimental facilities (most with superconducting coils and very long pulse capabilities) in the EU,
China, Japan, and Korea would soon rival and in several important areas exceed those of major U.S.
fusion facilities.”
U.S. Participation in International Facilities
U.S. fusion research strategy has an increasing focus on participation in newer international longpulse experiments with superconducting magnets including EAST (China), KSTAR (S. Korea), and W7X (Germany). EAST began operation in 2006 and KSTAR began in 2009. Non-U.S. proposals for new
facilities include the superconducting Divertor Tokamak Test facility that would be built by the Italian
National Agency for New Technologies, Energy, and Sustainable Economic Development’s fusion
laboratory in Frascati, Italy, and the China Fusion Engineering Test Reactor (CFETR) is underconsideration as a new fusion facility to demonstrate self-sufficient tritium breeding. While researchers in
the U.S. fusion community welcome these international opportunities, it is not clear how international
cooperation by itself will enable U.S. fusion researchers to maintain a world leadership position without
new facility starts in the United States.
The United States has made and continues to make important contributions to the world’s largest
currently operating fusion device, the Joint European Tours (JET). This includes involvement in testing
important auxiliary systems relevant to ITER (e.g., the ITER-like Shattered Pellet Injector), plasma
diagnostics, and experimental operating scenarios (e.g., deuterium-tritium scenarios). Additionally,
simulation codes (e.g., TRANSP) developed by U.S. scientists have been adopted by international
partners and are now routinely used for scenario modeling in the JET program and across EUROfusion
ITER-related activities.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

For intermediate-sized tokamaks (ASDEX Upgrade, Germany; TCV, Switzerland; MAST
Upgrade, UK), many bilateral collaborations exist between the U.S. and EU partners. Prominent recent
examples of U.S. contributions include temporarily moving diagnostic devices from U.S. facilities to EU
machines, and joint experiments on multiple machines to develop understanding and robust
demonstration of control schemes and new plasma scenarios.
An U.S. contribution to fusion research in the EU is participation in the W7-X stellarator project.
This includes the construction and operation of five large auxiliary coils and an X-ray spectrometer, as
well as the development of fluctuation diagnostics and a pellet injector. This work is carried out at three
U.S. national laboratories (Princeton Plasma Physics Laboratory, Oak Ridge National Laboratory, and
Los Alamos National Laboratory) and three U.S. universities (Auburn University, University of
Wisconsin, Madison, and Massachusetts Institute of Technology), supporting W7-X with equipment thathas been funded, designed, and produced in the United States and with related magnetic field and plasma
diagnosis and modeling.
The United States is playing a significant role in developing new fusion programs in Asia. Major
contributions have been made to new Asian devices, notably in EAST (China), KSTAR (S. Korea), HL2A (China), and J-TEXT (Japan). A strong relationship continues with smaller spherical tokamaks(QUEST at Kyushu University, Japan; VEST at Seoul National University, S. Korea; SUNIST at
Tsinghua University, China). A major focus of an international partnership on QUEST has been in the useof long-pulse superconducting devices to develop steady-state plasma scenarios. Collaborations on EAST
have made advances in plasma control and wall conditioning techniques developed collaboratively withand initially demonstrated on DIII-D. Novel computer science hardware and software infrastructure has
improved data movement, visualization, and communication and enabled scientists in the United States toremotely conduct experiments using the EAST facility. In July 2017, Chinese researchers using EAST
achieved a stable 101 second steady-state high confinement plasma, setting a world record in long-pulse
H-mode operation. Similarly, physicists at Princeton Plasma Physics Laboratory have connected remotely
to run experiments on KSTAR. U.S.-Asia cooperation aided development of HL-2M under constructionin China and in the physics design of the CFETR burning plasma facility under consideration in China,
where the United States provides design expertise and simulation codes.
MFE AND THE PRIVATE SECTOR
Since the Plasma 2010 report, the fusion energy landscape has changed significantly with therapid growth of privately funded fusion companies. The recently formed Fusion Industry Association
includes 21 member companies who are working toward commercial fusion energy within the UnitedStates and abroad. Around $1 billion of private capital has been invested in these 21 companies over thelast 10 years. Prominent examples include: TAE Technologies (Foothill Ranch, CA) has raised the largest amount of venture capital of any
privately funded fusion company to date. (See Figure 6.23.) TAE fusion efforts have focused on abeam-driven field-reversed configuration (FRC) concept. TAE has built a series of devices and iscurrently operating the C-2W device, 30 m long with a diameter of 0.8 m in the confinement region.
Up to 21 MW of neutral beam power is available and has been used to produce FRCs lasting 30 ms
with total temperature up to 2 keV (maximum electron temperature of 400 eV). The company has
expressed interest in utilizing fusion fuel that does not produce neutrons, in particular the p-B11
reaction.
 Commonwealth Fusion Systems (Cambridge, MA), one of the newest fusion companies focused on
innovating the tokamak concept using high-temperature superconducting magnets capable ofproviding very high magnetic field. CFS has attracted major funding from the Italian energy company
ENI and subsequent investment from Breakthrough Energy. Near term focus for the company is thedevelopment of tokamak magnets based on rare-earth barium copper oxide (REBCO). A first test of
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Plasma Science: Enabling Technology, Sustainability, Security, and Explorationthese magnets for CFS would be the
SPARC tokamak, which the company
plans to use D-T to reach the burning
plasma regime. CFS is targeting
construction and operation of SPARC in
the 2020’s.
 General Fusion (Burnaby, British
Columbia, Canada) has raised substantial
capital to develop a fusion reactor basedon a magneto-inertial concept. General
Fusion’s concept is based on utilizing
shock waves driven in liquid metal tocompress a magnetized plasma target tofusion conditions.
FIGURE 6.23 Neutral beam injector on TAE
Technology’s C-2W. SOURCE: Tri Alpha Energy.
 Tokamak Energy (Oxfordshire, UK) is
focused on the Spherical Tokamak
concept as a route to commercial fusionenergy. Tokamak Energy is planning to utilize high temperature superconductors to enable high-field,
compact spherical tokamak fusion reactors. The company is currently operating the ST40 device
which uses a 3T magnetic field and has a major radius of 0.4 m.
Government investment has both indirectly and directly enabled the growing private fusion
industry. The indirect support stems from decades of investment in the federally funded fusion research
effort, which has built a knowledge base that underlies all the current privately funded fusion ventures.
Direct support for the fusion industry is a recent phenomenon and includes investment in a fusion energy
program by the ARPA-E agency within DOE as well as new programs within DOE Fusion Energy
Sciences. ARPA-E had a three-year program focused on fusion energy called ALPHA that wasannounced in 2015. The program was focused on “intermediate density” routes to fusion energy; concepts
that fell between lower density MFE approaches and high-density inertial confinement fusion. This
program primarily involved researchers interested in magnetized target fusion, an approach that blends
MFE and inertial confinement fusion (ICF) approaches. ALPHA program participants included several
fusion companies as well as university-based efforts that eventually lead to the formation of new fusioncompanies, in part due to ARPA-E support. ARPA-E has recently announced a second program in fusionenergy research, the BETHE program, which targets lower-cost fusion energy concepts and innovative
research that can help lower the cost of mainline fusion devices, including tokamaks and stellarators.
DOE Fusion Energy Sciences recently created the INFUSE program as a route to public-private
partnership in fusion energy research. INFUSE is modeled after the DOE Office of Nuclear Energy GAIN
program and gives companies working on fusion energy access to resources at DOE national laboratories(funds go to the laboratories to support work for the fusion company). A limitation in the current INFUSE
program is that it does not allow fusion companies to work with university researchers in the MFE area.
There are public-private programs that go beyond the INFUSE model that could be utilized by DOE FES.
In particular, NASA’s Consumer Orbital Transportation Services (COTS) program was successful instimulating the development of private solutions to reaching near-Earth orbit. A COTS-like program
could also work in the fusion energy space, using milestone reimbursement to incentivize privatecompanies to perform innovative research and development relevant to commercializing fusion energy.
In addition to industry focused on developing fusion reactors, the U.S. MFE program engages
other industry partners, in particular as part of the ITER project. As of June 2019, $616 million incontracts has been awarded to U.S. industry to develop components for the ITER project. These
components have ranged from superconducting magnet components, to cooling water systems to steadystate electrical network components.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

TABLE 6.2 MFE Facilities Cited in This Report
Facility

Description

Alcator CMOD*
ASDEX-U
CFETR**

Facility

Description

Tokamak, MIT Plasma Science andFusion Center.

JET

Joint European Torus, Culham
Center for Fusion Research, UK.

Tokamak, Axially Symmetric
Divertor Experiment Upgrade, Max
Planck IPP, Garching
China Fusion Engineering Test
Reactor, Hefei, China

J-TEXT

Tokamak, Wuhan, China

JT60-U
JT60-SA**Japan Torus 60-Upgrade, Naka
Fusion Institute, Ibaraki, Japan

CFQS***

Chinese First Quasi-Axisymmetric
Stellarator, Southwest Jiaotong
University in China.

KSTAR

Korea Superconducting
Tokamak Advanced Research,
Daejeon, South Korea

CNT

Columbia Non-Neutral Torus
stellarator, Columbia University

LHD

Large Helical Device Stellarator,
Toki, Gifu, JapanCOMPASS

Compact Assembly Tokamak,
Institute of Physics, Czech Republic

LTX-b

Lithium Tokamak Experimentupgrade, Princeton Plasma
Physics Lab

CTH

Compact Toroidal Hybrid stellarator,
Auburn University

MAST*
MAST-U**

Mega Ampere Spherical
Tokamak, Culham Center for
Fusion Energy

C-2W(Norman)

TAE Technologies Field Reversed
Configuration, Foothill Ranch, CA

MST

Reversed Field Pinch, Madison
Symmetric Torus, University of
Wisconsin

DIII-D

National Fusion Facility Tokamak,
General Atomics, San DiegoNSTX*,
NSTX-U**

National Spherical Torus
Experiment and NSTX Upgrade,
Princeton Plasma Physics
Laboratory.

EAST

Experimental Advanced
Superconducting Tokamak, Hefei,
China.

Pegasus

Pegasus Toroidal ExperimentTokamak, University of
Wisconsin

EPOS***

Electrons and Positrons in an
Optimized Stellarator, Max Planck
IPP, Garching, Germany
Fusion Z-pinch Experiment,
University of Washington

QUEST

Tokamak, Kyushu University,
Japan

SPARC***

Commonwealth Fusion Systems
tokamak, Cambridge, MA

HBT-EP

Tokamak, Columbia University

ST-40

Spherical Tokamak, Tokamak
Energy, Oxfordshire, UK

Helimakc

Toroidal experiment for studying
turbulence, University of Texas

SUNIST

Sino-UNIted Spherical
Tokamak, Tsinghua University,
China

FuZE

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HIDRA

Hybrid Illinois Device for Researchand Application, University of
Illinois

TCVTokamak à Configuration
Variable (Variable
Configuration Tokamak), École
Polytechnique Fédérale deLausanne, Switzerland

HL-2A

Tokamak, Chengdu, China

TFTR*

Tokamak Fusion Test Reactor,
Princeton Plasma Physics
Laboratory

HSX

Helically Symmetric Experiment
Stellarator, University of Wisconsin

VEST

Versatile Experiment Spherical
Torus, Seoul National
University, S. Korea

ITER**

International burning plasma
experiment, Cadarache, France

W7-X

Wendelstein 7-X Stellarator,
Max Planck IPP, Greifswald,
Germany

JET

Joint European Torus, Culham
Center for Fusion Research, UK.

WEST

W(Tungsten) Environment in
Steady-state Tokamak,
Cadarache, France*
Not now operational or decommissioned.
** Under construction, renovation or upgrade.
*** Design phase.

THE MFE WORKFORCE
The workforce for the U.S. MFE research program has been evaluated recently through two
processes: (1) a 2014 DOE FESAC subcommittee on MFE Workforce development, and (2) a survey
conducted by the University Fusion Association (UFA) that produced a white paper on the “Status ofuniversity-based fusion science research” in 2017. Both of these evaluations expressed concerns over the
status of university research groups in the MFE area. Survey data indicated an aging faculty anduncertainty on the prospect for future faculty hiring in MFE areas. The reports, and in particular the UFA
report, raised concerns over declining University participation in DOE FES research programs. Over thelast decade, there has been a major shift in the types of FES programs that engage University researchers.
A major university experimental facility, Alcator C-Mod, ceased operations during this period (first slated
for shutdown in 2012 but continued operating until 2016). In addition, a program that had supported anumber of on-campus experimental facilities, the “Innovative Confinement Concepts” (ICC) program,was discontinued. At the time of these transitions, there were limited funding opportunities, and more
importantly, access to intellectual leadership opportunities, for affected university researchers to reengage with FES-funded MFE research. While funding is certainly important to maintaining healthy
university programs, it is intellectual leadership that is often the most important currency in driving
decisions for faculty hiring. University administrators and department faculty want to see that new hires
have the opportunity to work on the most important research that has the most impact in the field inquestion and that there is a path to grow into national and international leadership. If it is perceived thatsuch opportunities are not available, it is likely that hiring decisions will favor other fields of science orengineering. The demise of visible on-campus programs and the lack of equivalent opportunities foruniversity researchers contributed directly to the uncertainty in future hiring prospects in MFE.
FES has recently implemented regular funding opportunities for research using the DIII-D
tokamak, NSTX-U, and international experiments at facilities including W7-X, MAST-U, KSTAR and
EAST. These programs are very welcome and have provided new opportunities to engage university
researchers in the program. However, they do represent a shift to a new paradigm of off-campus research
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and a potentially more difficult path to intellectual leadership in the field. For major user facilities in otherareas of science (and plasma science), such as light sources operated by DOE BES and laser facilities
utilized in HEDP research, the user is the clear intellectual leader in the science being performed. The
operator of the facility is focused on, e.g., providing photons and the high-impact science is tied to thetarget or sample that the user designs. This clear separation of roles is not present in MFE national
facilities. The facility is designed with a particular goal or set of goals in mind and the team operating it isfocused on achieving these scientific goals; as such the scientific leadership is generally controlled by thatteam. For current and past U.S. MFE facilities, the leadership team is a single institution (in contrast withmajor facilities and missions in other fields, such as major space missions where the team generally has
PIs from multiple institutions). This structure does not make it easy for university faculty to see a path tointellectual leadership and to engage in the research program. Credit is due, however, to the institutions
that currently operate U.S. MFE national facilities who have attempted to work within the current
structure and engage collaborators/users in the scientific leadership. For example, while ultimate authority
in setting scientific focus and runtime allocation for the DIII-D tokamak rests with General Atomics(working with DOE FES), the DIII-D program engages collaborators, including university researchers, inleading scientific thrusts and in deciding which proposals get runtime. This structure has led to university
researchers growing into intellectual leadership roles and leading visible research programs on DIII-D.
This is also true on international facilities, in particular the W7-X stellarator which has adopted a “oneteam” approach that engages collaborators in W7-X program leadership. U.S. researchers have been able
to grow visible programs with leadership on W-7X for this reason, including recently hired faculty at U.S.
universities. While it is difficult to change leadership structures of existing facilities, adopting policies
like the “one team” approach, coupled with appropriate funding opportunities, could stimulate moreengagement of universities in existing MFE programs. New major facilities should consider broader
engagement from all stakeholders in the program and might be developed with teams drawn frommultiple institutions including labs, universities and industry. The science of MFE can be addressed at
facilities at a range of scales; there have been very few opportunities over the last decade for new
intermediate scale and small-scale facilities. There are a range of frontier scientific opportunities that
could be addressed at both scales. For example, quasi-symmetric stellarator at intermediate scale and arange of MFE technology and engineering issues could be addressed at small-scale. Opportunities to sitethese kinds of facilities at universities would offer a clear path to scientific leadership and enhanced
visibility of MFE research.
These demographic changes and shifts in the types of funding opportunities for universities comeat the same time as strong growth in privately funded fusion ventures and also a recent growth in federal
funding for fusion research from DOE FES and DOE ARPA-E. There is strong demand for researchscientists in the MFE area and in particular a need for a workforce skilled in fusion engineering issues
including materials and nuclear technology such as tritium breeding. University programs are a criticalsource of skilled researchers for the MFE workforce and these programs must be renewed andstrengthened to meet these needs.
FINDINGS AND RECOMMENDATIONS
U.S. magnetic fusion energy (MFE) research has long defined the forefront of fusion energy
research for the international community.
Finding: While the United States is still a major contributor to international MFE efforts andbenefits from these collaborations, the U.S. program has lost ground and is at risk of losing
leadership in several areas of MFE research.
Funding for MFE through DOE FES has seen unprecedented growth over the last few years,
driven in part by growth in funding for ITER in response to significant progress in and new managementof the project. Private investment in fusion energy research has grown substantially and helped boost
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federal programs through the development of private-public partnerships. At the same time, DOE
leadership and Congress have made it clear to the community that continued strong support for the MFE
program is contingent on the development of a community-driven, consensus strategic plan for MFE. ..
Finding: The absence of a consensus strategic plan for fusion research in the United States is an
important factor in our falling behind on international developments, a situation compounded by
the lack of vetted designs for new experimental facilities.
Such a strategic plan for the fusion program will allow DOE and Congress to make informed
decisions about the specifics of fusion program funding, will position the community to respond to newopportunities (for example, new major facilities) and be able to prioritize in the event of downward
funding pressure. The NAS Burning Plasma report called for regular strategic planning in the U.S. MFE
community and called out the need for new experimental facilities, in particular at large scale. At the timeof this writing, an FES community planning process is being conducted with the goal of developing astrategic plan. There also are opportunities for U.S. leadership to be re-established through investment insmaller intermediate scale facilities.
Finding: A roadmap is needed that is enabled by new experimental MFE facilities in the
United States with opportunities across a range of scales when appropriate,
Finding: To enable proper planning and to enable creation of a roadmap, ongoingfeasibility and facility design activities are essential.
Recommendation: DOE FES should undertake regular strategic planning, led by the U.S.
MFE community, as recommended in the NAS Burning Plasma Report.
Recommendation: Aligning with the NAS Burning Plasma Report, DOE FES should
develop a roadmap for the development of commercial fusion power in the UnitedStates.
Over the last decade, the landscape of MFE research at universities has changed substantially. Programs
that had funded large university experimental efforts were terminated and new equivalent opportunities toparticipate in forefront MFE research were not made available to universities. At the same time, theaverage age of university faculty and researchers is increasing and new hiring in MFE areas has declined.
At some institutions this is reaching a critical point where longstanding MFE programs may cease toexist.
Finding: Declining participation by universities in the MFE program reduces the level ofinnovation in the program and is a direct threat to the health of the field. It is essential that theMFE program respond to this crisis.
Finding: Renewing and growing new efforts at universities could be enabled by providing
university researchers opportunities to participate in and, more importantly, lead the mostimportant research programs in the field.
This opportunity for intellectual leadership is essential to convince university faculty and administratorsthat hiring in MFE should be prioritized over hiring in other areas of research in science and engineering
departments. Creating such opportunities represents an important but indirect way to promote faculty
hiring. Other fields of plasma science have used more direct approaches to re-invigorate their fields, forexample the NSF Faculty Development Program in Space Sciences provides, along with other resources,
funding to pay the salary of a newly hired faculty member until tenure is granted. This has been andcontinues to be effective in creating new faculty positions at several institutions. The program signals theimportance of this area of work to the funding agencies and lowers the cost to the university of bringing
in a new faculty member.

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Finding: There is a need to grow efforts in fusion engineering and an opportunity exists tostimulate university programs in this area using both the indirect and direct mechanisms
discussed above.
Recommendation: DOE FES should structure funding opportunities in MFE to provide
leadership opportunities to university researchers and to directly stimulate the hiring ofuniversity faculty.
Examples of the above include major new facilities or missions that could be organized with leadershipteams that involve university researchers; major activities in the field could be organized around centersthat are led by teams including university researchers; and specific programs could be implemented toprovide funds or other incentives for the creation of faculty positions (example: NSF Faculty
Development Program in Space Sciences).
Finding: A recent Office of Management and Budget decision targeted at limiting duplication in
education and outreach programs in funding agencies caused the loss of discipline specificgraduate fellowships and outreach programs in DOE Office of Science (SC).
In DOE FES, this resulted in the loss of the Fusion Energy Sciences Graduate Fellowship Program andthe National Undergraduate Fellowship (NUF) Program in Fusion. Working within the new rules, SC has
attempted to replace these programs. A new Internship program for graduate students has been
established that provides short-term funding (< 1 year) for students to spend time at national laboratories
working on their thesis project. The NUF program has been merged with the DOE Science Undergraduate
Laboratory Internships (SULI) program that provides research opportunities for undergraduates atnational laboratories, but the possibility of working on MFE research at universities was eliminated.
Finding: These programs are important but lack the effectiveness of the former graduate
fellowship and NUF program in attracting new talent into the MFE field.
The lab internship program is useful for students who have already made the decision to work in MFE but
is not as effective as a 3 year graduate fellowship in attracting students to the field.
Finding: The NUF program and the graduate fellowship could be used as a tool to enhancediversity within the MFE research community.
It should further be noted that the removal of student support for university based MFE research further
disincentives universities from hiring or retaining faculty engaged in MFE science.
Recommendation: The DOE Office of Science should restore discipline-specific graduate
fellowships and undergraduate research programs that support MFE research at U.S.
universities as a vehicle for attracting new and diverse talent into mission-specific areas
such as MFE, and for maintaining a presence in university science and engineering
programs.
Finding: There has been significant growth in non-traditional support of MFE research, i.e.,
support other than that provided by DOE FES, including privately funded fusion companies,
philanthropic organizations, and DOE-ARPA-E.
Most of these efforts are based on non-mainline approaches to magnetic fusion, significantly broadening
the range of risk-reward tradeoff with a goal to develop lower cost paths for fusion. The emergence of
these efforts has occurred while the DOE FES program has become more concentrated on mainline
approaches and ITER. The breadth of the collective MFE portfolio is therefore similar to that when DOE
FES funded a wider range of approaches, like the Innovative Confinement Concepts program. However,the structure is complicated in having private investments and federal support in different offices.
Finding: There is a danger that the knowledge base, including that generated by former DOE
FES supported research, could become increasingly fragmented. Some challenges, for example
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the development of key technologies and materials, are similar even if the fusion configurations
are distinct. Solving these challenges through separate efforts increases overall cost andtimescales.
Recommendation: Federal agencies funding the development of MFE science andtechnology (DOE-FES and DOE-ARPA-E) should leverage privately and philanthropicallysupported fusion research and vice versa.
Collaborative programs that bridge the public-private sectors can advance fusion development
more effectively if they are adequately coordinated. The new INFUSE program is a step in this direction,
however the opportunity to be involved should not be limited to DOE national labs. Many of the privately
funded efforts and those being proposed by ARPA-E are closely related to projects that were formerly
supported at universities. There are also private entities whose business models are focused on supporting
capabilities like computation or technology and not the development of a fusion power source per se. In
particular, DOE FES can facilitate a coordinated effort of the combined public-private sectors throughleveraged investments that support high-risk, high-reward elements of a balanced portfolio of different
approaches and by supporting facilities and capabilities for the development of technologies, materials
and computing capabilities that are largely generic to fusion systems.

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7
The Cosmic Plasma Frontier
OVERVIEW
Plasma heliophysics and astrophysics have been at the vanguard of extraordinary discoveries in
the past decade, exciting worldwide interest from the public and scientists alike. Humanity left our solar
system and took the first physical step into the interstellar medium (ISM) plasma with the venerable
Voyager 1 and 2 spacecraft, the farthest human-made objects from the Sun. The pioneering Parker Solar
Probe (PSP) is plunging repeatedly into the plasma of the solar corona, becoming the closest human-madeobject to the Sun. The first views of plasma orbiting the innermost neighborhood of a black hole, and of
the plasma surrounding two merging neutron stars accompanied by detection of gravitational waves, haveshed “light” on the most exotic events and objects in the plasma universe. The plasma environment’s rolein shaping the habitability of the exploding number of detected exoplanetary systems, ranging from thechemistry of the atmosphere to the development of life forms, is now being explored on many fronts.
These discoveries and the promise of breakthroughs to come are fascinating scientists and the generalpublic alike. All this occurred a mere 60 years after the start of the space age. (See Figure 7.1.)
The vast majority of baryonic (non-dark) matter in the Universe is in the form of plasma,
spanning a stunning range of physical conditions, spatial scales, and dynamics. Space and astrophysicalplasmas (SAPs) reach regimes inaccessible to earthbound laboratory experiments, enabling deep insights
into fundamental plasma processes that impact observations and understanding of the formation andevolution of the universe. Some can be sampled directly by spacecraft, while others only reveal theirsecrets through spectroscopy, imaging, polarimetry, and other remote-sensing techniques. SAPs are alsofascinating and exotic—from solar flares to active galactic nuclei to black-hole accretion disks—giving
plasma physics high visibility and importance in the quest to understand heliophysics and astrophysics.
To understand and predict how the plasma universe around us operates, the fundamental physicalprocesses responsible for phenomena ranging from electron-scale interactions to galaxy clusters need to
be explored. Magnetic fields are paramount in governing the behavior of cosmic plasmas and play a keyrole in determining the habitability of our planet. Progress has been made, but more is needed, in
determining how magnetic fields are generated in planets, stars, and galaxies, and how this magnetic
energy is stored and released impulsively in the form of eruptions, geomagnetic storms, and otherexplosive events. Magnetic reconnection—the breaking and reconfiguring of magnetic fields—is theprimary candidate to explain impulsive energy release, yet it is barely understood why it occurs at certain
locations and times and how the liberated energy is partitioned among mass motions, particle
acceleration, and heating. This ubiquitous mechanism is thought to explain the onset of stellar andaccretion-disk flares and mass eruptions, magnetospheric storms on Earth and other planets, and 𝛾-ray
flares from the Crab Nebula. New observations and computational methods have revealed much about

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

reconnection in cosmic settings,
particularly in collisionless plasmas, but
the fundamental processes governing thisimportant phenomenon are still not wellunderstood.
Eruptive events often drive shocks,
which alter plasma properties substantially,
generate waves and turbulence, and canaccelerate ions and electrons to highenergies. Within our heliosphere (thevolume occupied by the magnetic field
produced by and enveloping the Sun),
shock-accelerated particles can endanger
astronauts and spacecraft; higher-energy
cosmic rays generated by supernova
shocks and other sources can cause evenmore damage and can penetrate far into ouratmosphere, perhaps affecting weather andmutating genes. Reconnection, shocks, andwaves both generate and are generated byturbulence, which redistributes energy
from large to small scales while increasing
the complexity of the ambient plasma.
Turbulence also accelerates and disperses
charged particles, and may heat stellar
coronae. Not all plasmas in the universe
are fully ionized; the solar chromosphere,
FIGURE 7.1 Space and astrophysical plasmas span anplanetary ionospheres, the outerenormous range of scales. (top) The heliosphereastrosphere, the ISM, and protoplanetary
encompassing our solar system contains plasmas
accretion disks all contain neutral atoms
surrounding current sheets in the Sun’s corona (~10-5 km),and molecules, which are not tied to theplanetary plasmaspheres (thousands to millions of km),magnetic field as charged particles are.
and the interplanetary medium (1010 km across). (middle)
Partial ionization substantially alters the
The Voyager spacecraft have already penetrated the limits
dynamics and energetics of the entireof our solar system – the heliopause that separates theplasma system, through interactions
influence of the Sun from interstellar space – on their way
between the charged and neutral particles,
to the Oort cloud (the birthplace of comets) and nearby
different responses to radiative input, andastrospheres. (bottom) Beyond lies the exotic plasma
modifying conductivity and dependent
physics of galaxies (1018 km across) and vast clusters ofprocesses (e.g., reconnection andthousands of galaxies. SOURCE: Top: Charles Carter /turbulence).
Keck Institute for Space Studies; middle: NASA/JPLThe full range of phenomena
Caltech; bottom: NRAO.
found in SAPs has counterparts in otherareas of plasma physics. This overlap isparticularly valuable for advancing our understanding of the underlying fundamental mechanisms.
Magnetic reconnection, particle acceleration, turbulence, shocks, and instabilities govern energy releaseand transport in laboratory devices such as toroidal plasmas and inertial confinement fusion experiments,
as well as in stellar eruptions, planetary and pulsar magnetospheres, and galactic winds. The complex
dynamics and energetics of partially ionized plasmas and ion-neutral coupling dominate stellar
chromospheres, planetary ionospheres, comets, and the ISM, and are the processes in applications of low
temperature plasmas for chemical conversion and materials processing (Chapter 5). Fundamental
dimensionless parameters such as the ratio of the particle mean free path to the system size, the ratio of
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

thermal to magnetic pressure, the fluid and magnetic Reynolds numbers, and the ratio of the gyroradius to
the system size enable advances in apparently unrelated environments to apply elsewhere. For example,
collisionless plasmas are found in Earth’s magnetosphere, stellar winds, and the diffuse medium
permeating galaxy clusters. Fusion devices contain high energy-density plasmas (Chapter 4), as do stellarinteriors, black hole inflows, and the cores of super-Earths and hot Jupiters.
The plasma  (ratio of thermal to magnetic pressure) in SAPs varies widely depending on theenvironment. For example,  is less than 1 in the very local interstellar medium, the solar corona, and theouter regions of molecular clouds, whereas  1 in the solar wind, stellar convective zones, planetary
magnetosheaths, and the intracluster medium. Fusion plasmas (Chapter 6) are necessarily low , and thus
have some commonalities with and substantial differences from high- SAPs. Because of thesedifferences and similarities, we can develop deep insights into different plasma behaviors by studying andcomparing both fields.
Advances in observational capabilities, and extensions to new diagnostic regimes, invariably
uncover new phenomena, challenge existing theories and spark new ones, and motivate cross-disciplinary
collaborations. In the past decade a wealth of new
heliophysics missions populated geospace and ourheliosphere, complementing continuing missions toform the Heliophysics System Observatory.
Breakthrough advances in plasma astrophysics werebrought about by data generated by space-based highenergy observatories. The advent of smallsats andcubesats has begun a new era of in-situ multipoint
observations, which are essential for understanding theconnections between kinetic and global-scale
behaviors, and has driven innovative developments inminiaturization of instruments. In parallel, newground-based facilities have opened new windows on
nearby and remote cosmic plasmas.
The high-resolution, high-cadence images of
FIGURE 7.2 The first direct image of plasma
the solar corona obtained by the Interface Region
orbiting a black hole, taken by the Event
Imaging Spectrograph (IRIS), Hinode, and the Solar
Horizon Telescope. The radio image shows
Dynamics Observatory (SDO) have revealed distinct
hot relativistic plasma surrounding theprerequisites and signatures of magnetic reconnection
supermassive black hole at the heart of thein explosive jets, flares, and coronal mass ejections
galaxy M87, orbiting at nearly the speed of(CMEs): plasma sheets surrounding current sheets,
light. In the center, the shadow of the black
inflows, Alfvénic outflows, and plasmoids. The
hole is silhouetted against the heated materialtransition from the magnetically structured solar
spinning around it. The appearance of the disk
corona to the more isotropic, turbulent solar wind wasis strongly distorted by the general relativistic
seen for the first time in images from the Solar
effects of light bending. From Event Horizon
TErrestrial RElations Observatory (STEREO)
Telescope Collaboration et al. 2019.
Heliographic Imager. Quasiperiodic plasma density
SOURCE: The Astrophysical Journal
structures were tracked from the inner heliosphere to
Letters,875:L5, 2019,
their impact on Earth’s magnetosphere, by combining
https://doi.org/10.3847/2041-8213/ab0f43,
data from multiple spacecraft and modeling. These©2019.
periodic plasma bursts were speculated to be “fossil”
markers of structure generated near the Sun. Suchstructures in the solar wind have long been known todrive compressional oscillations in Earth’s magnetosphere, thus affecting particle energization and losses
in the radiation belts. Recent investigations by PSP have identified other signatures of this solar winddriving and, most important, established that these pulses originate at the Sun. The mysteries of
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

collisionless reconnection are being unraveled by the Magnetospheric Multiscale (MMS) mission, a 4spacecraft cluster. By measuring electron distribution functions in a reconnection site in the magnetotail,MMS found strong support for a leading explanation for magnetic field-line breaking. Van Allen Probes
discovered a third radiation belt and identified waves in the belts that accelerate particles and those that
contribute to particle precipitation. The twin Voyager spacecraft, launched in 1977, have journeyed wellpast their nominal 5-year missions and are headed into the ISM, revolutionizing our understanding of theinteraction of the solar wind with the local interstellar medium (LISM).
An impressive example of exotic plasma physics is the recently imaged supermassive black hole(BH) in the galaxy M87 by the Event Horizon Telescope (Figure 7.2). This image shows the radiation of
the hot, dense plasma orbiting the black hole, which emits no radiation. In conjunction with thegroundbreaking detection of gravitational waves from cosmic events, electromagnetic emissions from theturbulent plasmas surrounding the BH gave vital clues about the nature and characteristics of thesystem—information that could not be derived from gravitational radiation alone. The detection of
exoplanets (planets orbiting stars other than the Sun) in an extraordinary range of plasma environments
has exploded over the past decade. These discoveries challenge our previous understanding of planetary
formation and evolution, while illustrating the power, and success, of applying theories and numericalmodels developed to understand our solar system to investigate exoplanets in the very different
environments of distant stars. These observations and insights are being leveraged to answer some of themost fundamental questions about how Earth evolved, and how the radiative output and eruptive activity
earlier in our Sun’s history affected Earth’s atmosphere, oceans, and development of life. Lessons learned
from these studies will enable us to look for the markers that may indicate that life is possible on otherplanets.
New computational techniques and computer architectures (Chapter 2) have emerged to rapidly
advance our investigations of SAPs. These advances
have enabled massive particle-in-cell (PIC) andgyrokinetic simulations of kinetic-scale instabilities
and waves over larger system sizes than ever before.
Highly detailed magnetohydrodynamic (MHD),
multi-fluid, and hybrid simulations model the
initiation and propagation of solar eruptions fromthe Sun to Earth and beyond, reveal the dynamic
evolution of planetary magnetospheres in stellar
systems, and capture the relativistic chaossurrounding black holes. (See Figure 7.3.)
Substantial progress has been made toward
FIGURE 7.3 General relativistic MHD
overcoming the challenges of assimilating andleveraging huge amounts of data and using that data simulation of the evolution of merging neutronstars leading to the formation of a black hole,to guide complex simulations. Automated featureaccretion torus and hot ejecta, and generation
recognition, machine learning (ML), and artificialof collimated magnetized outflow. The jet
intelligence (AI) methods are being introduced fordata mining and analysis, to cope with the growth of produces a short g-ray burst. The color-code
map shows the density, with selected magnetic
large datasets that cannot be adequately processed
field lines (white) superposed. SOURCE:
by existing techniques for reducing, calibrating,Rezzolla et al. 2011, ApJL 732 L6,
cleaning, and visualizing these data.
https://iopscience.iop.org/article/10.1088/2041
Perhaps the most striking growth area in-8205/732/1/L6/meta.
SAP having direct, on-the-ground societal benefit
has been the science of space weather—the causes
and consequences of activity generated at the Sunthat propagates through the heliosphere toward planetary surfaces, and Earth in particular. Both livingorganisms and technology can be adversely affected by these solar disturbances that interact with ourmagnetosphere and ionosphere. Our worldwide dependence on reliable electricity, global-positioning
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

satellites (GPS), and telecommunications relies on stable and quiescent plasmas surrounding Earth and in
its ionosphere. Consequently, the disruption of these plasmas by energetic particles and hard radiationfrom solar eruptions can lead to widespread power and communications outages, and infrastructuredamage that could take years to repair. Energetic particles and radiation pose even greater threats tomanned space travel and bases on the moon and planets that lack the natural protection that magnetic
fields provide. To understand and ultimately predict space weather events, we must develop deep physicalinsight into all plasma mechanisms that initiate, transport, and transform these energetic storms. Space
weather is now recognized by the U.S. government as a natural threat, motivating disaster preparedness aswell as investments in basic and applied research. The understanding developed from our knowledge ofspace weather on Earth also is more broadly applicable to planetary space weather and to the issue of
habitability on planets and exoplanets. Water may be necessary for all known instances of life, but it is
not sufficient to ensure its survival if extreme space weather events can damage the planet’s atmosphere.
Space and astrophysical plasma research in the United States is funded predominantly by NASA,
NSF, DoD, and DoE. NASA’s Science Mission Directorate funds space missions and instruments, data
analysis, theory and numerical simulations, as well as a small amount of funding for ground-based
observations and laboratory experiments in support of its missions. The research side of NASA’s Human
Exploration Mission Directorate supports applied research on solar energetic particles (SEPs), with theaim of protecting astronauts from harmful exposure. NASA’s Space Technology Mission Directorate
primarily supports development of the crosscutting, pioneering, new technologies and capabilities needed
for current and future missions, using high-performance computing and technology demonstrations to test
emerging instrument concepts. NSF funds existing and new ground-based facilities, a wide range of
research in space, solar physics, astronomy and astrophysics, aeronomy and the plasma physics of theupper atmosphere, the National Center for Atmospheric Research (NCAR) and its subsidiary High
Altitude Observatory (HAO), and some cross-disciplinary programs that bring together basic plasma andspace/astrophysics research. DoD supports university and commercial SAP research through ONR,
DARPA, and AFOSR, and internal (at DoD facilities) research and facilities at the Naval ResearchLaboratory (NRL) and the Air Force Research Laboratory (AFRL). A modest program of space andastrophysical plasma research by the external community is supported by DoE, along with projects within
the agency relevant to DoE needs (e.g., updated atomic physics and opacity tables). Several DoE
international (e.g., PPPL-Max Planck) and domestic (e.g., with NSF) collaborative programs touch on
SAPs. The highly successful but perpetually underfunded NSF/DOE Partnership in Basic Plasma Scienceand Engineering has been extensively utilized by members of the space plasma physics and plasma
astrophysics communities since 1997, often in collaboration with plasma physicists in different
subdisciplines. A significant improvement in interagency collaboration between NASA and NSF wasannounced as this report was being completed. The new program, Next Generation Software for Datadriven Models of Space Weather with Quantified Uncertainties (SWQU), will support teams ofresearchers to develop comprehensive space-weather models from Sun to ionosphere). This exemplarycollaboration will address both fundamental science and translational research.
RELEVANCE AND BENEFITS
Science Advances
Astrophysical Plasmas
The last decade brought us discipline changing discoveries in the field of plasma astrophysics.
For the first time, in August 2017 the Laser Interferometer Gravitational-Wave Observatory(LIGO)/Virgo collaboration detected the merger of two neutron stars in the galaxy NGC 4993 by theirgravitational wave signatures. Just a few seconds later, the Fermi Gamma-ray Observatory (Fermi)
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

observed a 𝛾-ray burst at the same location. Within hours, intense optical emission was detected from thesame region. Ultimately, more than 60 telescopes monitored the electromagnetic counterpart for weeks
until its optical and infrared emission decayed. This long-awaited detection ushered in a new era in multimessenger astronomy (i.e., coordinated observations using different “messenger” signals: electromagnetic
radiation, gravitational waves, neutrinos, and cosmic rays.) The observations were consistent with akilonova—the radioactive-decay–powered ejecta of neutron-rich material—as predicted by state-of-theart MHD models. Emission during a kilonova can come from multiple plasma sources, and eachcomponent can reveal different information about the original neutron stars and their merger.
Much of the excitement surrounding this first detection of merging neutron stars was centered on
their role in producing heavy elements. Low-mass elements are produced in low-mass stars and expelled
into the ISM late in stars’ lives, while heavier elements are produced in supernova ejecta. For heavier, socalled r-process (rapid neutron capture) elements, it was postulated as early as 1957 that neutron starmergers would result in neutron-rich ejected plasma that could produce these heavy elements. The
detection of a neutron star merger, combined with the first spectroscopic detection of elements heavier
than Xe, open up the possibility of probing the formation site of these heavy r-process elements.
However, interpretation, analysis, and modelling of the observed spectra are severely hindered by thesparsity of atomic opacity data and model predictions for these r-process elements under kilonova
conditions.
In many astrophysical settings the magnetic field controls the overall dynamics of the plasma,
while the dissipation of magnetic energy may power the observed high-energy emission. In the past two
decades, magnetars (strongly magnetized neutron stars possessing super-strong magnetic fields), pulsars
and pulsar wind nebulae, jets of active galactic nuclei, -Ray Bursters, and coronae of accreting black
holes have been the subjects of intensive observational studies by X- and -ray instruments on several
satellites. These objects share one important property: relativistic plasmas that are magneticallydominated—the energy density is mostly contributed by the magnetic field rather than by the rest mass.
This exotic, astrophysically relevant plasma regime differs dramatically from laboratory plasmas,
planetary magnetospheres, and the interplanetary medium, and hence requires targeted, systematic study.
Other major discoveries in plasma astrophysics since 2010 include: very short and intense fast
radio bursts; rapid 𝛾-ray flares at GeV photon energies in the Crab pulsar wind nebula; ultra-rapid (~10min) TeV flares in blazar jets emanating from active galactic nuclei; giant BHs swallowing stars in tidal
disruption events; and the IceCube neutrino observatory detection of a very energetic neutrino coincident
with a flaring blazar. The plasma parameters in these events differ substantially from those of traditional
laboratory plasmas, planetary magnetospheres, and the IPM, as they include several “exotic” physicalprocesses. The plasma is often relativistic in terms of particle speeds, bulk motions, and characteristic
wave speeds. Radiation-reaction effects (e.g., synchrotron or inverse-Compton radiative cooling),
electron-positron pair creation, ultra-strong magnetic fields, quantum electrodynamics (QED), andgeneral-relativistic effects are all important.
In the last two decades, exoplanet science has moved rapidly beyond its initial discovery phase.
With thousands of exoplanets already confirmed, researchers are now investigating key issues such asplanet formation, evolution, structure, and habitability. Understanding the properties of the plasmas deepin planetary interiors and their enveloping atmospheres is essential to all these studies. Understanding theinteriors of gas giants and super-Earths requires understanding matter under extreme pressures,
introducing new domains of plasma physics. Fortunately, exoplanet observations and interpretations thatneed knowledge of plasmas under Megabar pressures now can turn to direct laboratory studies of these
extreme conditions (see Chapter 4).
The large number of exoplanets already discovered invites questions about whether those planets
ever had (or will have) conditions that can support life. Cross-disciplinary studies are applying spaceweather theories and models developed for our solar system to answer these questions. With knowledgeof the evolution of our own solar system, the models are being used to investigate conditions on hot
Jupiters, super Earths, and other previously unexplored exoplanet environments. For example,
observations of over 1500 stars by the Kepler space telescope designed to discover exoplanets showed
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Plasma Science: Enabling Technology, Sustainability, Security, and Explorationthat young, fast-rotating, solar-type stars produce
superflares. Simulations of extreme eruptions in suchfast-rotator systems, however, found that the tightly
wound interplanetary magnetic field complicates andextends the routes taken by the resulting accelerated
particles to the exoplanets. Simulations of the possible
effect of superflare produced energetic particles on lifeenabling conditions on orbiting planets suggest that theconditions that could foster Earth-like living organisms
FIGURE 7.4 Two snapshots from a 3D
are quite narrow in terms of radiation dose, atmosphericsimulation of the impact of a large CME fromproperties and chemical composition and presence ofthe young Sun on the magnetosphere andliquid water. Therefore, habitability studies have focused ionosphere surrounding the early Earth. The
on establishing factors besides simple distance from thewhite lines are magnetic field lines, and thestar that can push a planet into or out of the “Goldilocks” color shading shows plasma pressure. Axes
zone amenable to life. Many factors have been clarified
represent distance from the Earth’s center inby adapting heliophysical models for exoplanetary andunits of Earth radius. (left) Initial conditions at
young-Sun conditions: the presence and cyclic nature of
t=0. (right) Two hours after CME launch,a magnetic dynamo, the ability of stellar winds to strip
when the CME hit the early Earth’s
away a planet’s atmosphere, the existence of stellar
magnetosphere. This study assumed a steadyeruptions that are orders of magnitude more energetic
state paleo-solar wind at 0.7 Gyr with a mass
than those of our Sun, and the capability of stellar
loss rate of 1.7 × 10−12 Msun yr−1. SOURCE:
eruptions to change the atmospheric chemistry andhttps://iopscience.iop.org/article/10.3847/2041
irradiate the surface. While our Sun was still “young”,-8205/817/2/L24/meta
for example, solar eruptions (CMEs and eruptive flares)
were substantially stronger and more frequent than today, and Earth’s atmosphere was more nitrogendominated. Recent simulations have shown that energetic particles from those solar eruptions could havechanged Earth’s atmospheric chemistry sufficiently to warm the early Earth through a greenhouse effect(Figure 7.4). The possibility of life elsewhere in the universe excites both scientists and the public, andplasma science plays a key role in this quest.

Heliophysical Plasmas
All solar phenomena include plasma physics. High-resolution, high-cadence imaging of the Sun,by space missions such as the Ramaty High Energy Solar Spectroscopic Imager (RHESSI), SDO, andIRIS, and by ground-based facilities such as the Goode Solar Telescope and the Extended Owens Valley
Solar Array (EOVSA), has revealed key small-scale features and transient events. Distinct signatures ofmagnetic reconnection in eruptive events, from tiny jets to huge coronal mass ejections, and the formationof plasmoids in flare current sheets (Figure 7.5), were detected for the first time, testing long-standing
theories and firmly establishing the role of reconnection in impulsive energy release.
An outstanding unsolved problem in solar physics is how the corona is heated—this outermost
layer of the Sun is nearly 3 orders of magnitude hotter than the surface. The corona is believed to beheated by nanoflares (small reconnection events), ion cyclotron waves, and/or magnetic turbulence.
Observations by IRIS and the rocket-borne EUNIS spectrometer find some evidence for nanoflareheating, including nonthermal electron beams generated by these tiny events, but little agreement yet
exists. The committee anticipates that Parker Solar Probe might provide a definitive answer.
The MHD dynamo that generates and recycles the Sun’s magnetic field is sustained by the energy
of internal plasma motions such as differential rotation, turbulent convection, and meridional circulation.
The toroidal magnetic field is generated through the stretching of the poloidal component of the magnetic
field by differential rotation (different rotational speeds at different latitudes), and is widely believed to be
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

FIGURE 7.5 High-resolution observations
and MHD simulations agree that plasmoids
form in flare current sheets. (top) Time–distance plots of running-difference K-Cor
white-light images along the direction of theflare current sheet behind a CME. The whitecurved tracks, traced by dashed lines, denotethe trajectories of eight anti-sunward moving
blobs (from Cheng et al. 2018). (b) Timedistance plots of sunward and anti-sunward Otype nulls (plasmoids) tracked in a highresolution, adaptively refined, 2.5D MHD
simulation of a CME (from Guidoni et al.
2016). Note that the times and heights in thetwo plots differ, because the simulation has notbeen scaled to the size and characteristic
speeds of the observed CME. SOURCE: Top:
X. Cheng et al 2018 ApJ 866 64; bottom: S. E.
Guidoni et al 2016 ApJ 820 60.

FIGURE 7.6 Schematic of a CME-driven
shock (dotted line) in interplanetary space,illustrating the variation in shock obliquity
along the front and corresponding regions ofhigh injection-energy thresholds (hatchedregions). Curved black lines are magnetic fieldlines originating at the Sun. Here ‘parallel’ and‘perpendicular’ refer to the angle between theshock normal and the upstream direction of the
IMF. SOURCE: G.P. Zank, G. Li, V.
Florinski, Q. Hu, D. Lario, and C.W. Smith,
2006, JGR, 111,
https://doi.org/10.1029/2005JA011524.

stored and amplified at the tachocline, the thin, highly
sheared layer between the Sun’s rigidly rotatingradiative core and its differentially rotating convective
zone. Strong toroidal flux tubes are unstable tomagnetic buoyancy and erupt through the surface,
producing sunspots that are strongly magnetized andgive birth to most fast solar eruptions. The poloidal
field is thought to be regenerated through a
combination of convection-zone turbulence and theredistribution of the magnetic flux from tilted bipolarsunspot pairs. The dynamo-mediated evolution of solar
magnetic fields governs solar irradiance variations anderuption frequency, which affect planetaryatmospheres and magnetospheres. A recent breakthrough in dynamo simulations has produced cyclic,
solar-like polarity reversals of the large-scale magnetic field. Although advances have been made since
Plasma 2010 in understanding the complex, nonlinear dynamo system of our Sun, we are still unable todefinitively predict whether the downward trend in the solar magnetic output during the last few sunspot
cycles will be a long-term decline, as in the Maunder minimum (1645-1715).
Solar eruptions are the most energetic phenomena in the solar system. Large eruptions releaseabout 1024–1025 J and can accelerate particles to energies of several GeV per nucleon. RHESSI has raised
new questions about particle acceleration in solar flares: how can electron-associated hard X-rays (HXRs)
and ion-associated 𝛾-rays be separated by large distances, and how can relativistic flare electrons persist
and produce intense radiation in the corona? Two astrophysics missions also contributed to ourunderstanding of impulsive electron and ion acceleration on the Sun. Fermi observed 𝛾-rays from ions
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

accelerated to at least several GeV, as well as pion decay from accelerated ions in many large eruptions.
More puzzling, Fermi detected 𝛾-ray emission coming from various regions of the solar atmosphere,
prompting heated debates about how particles gain access to and remain in these regions. At the otherextreme, the Nuclear Spectroscopic Telescope Array (NuStar) made great strides in understanding
electron acceleration in active-region microflares—the faintest solar flares ever observed in HXRs.
An understanding of energetic particles in SAPs, as well as laboratory plasmas, is closely related
to our understanding of collisionless shock waves and turbulence. Shocks are ubiquitous in the
heliosphere, ranging from those generated by CMEs (Figure 7.6) to forward and reverse shocks createdby interacting solar-wind streams (co-rotating interaction regions (CIRs)), shocks in the distantheliosphere, and the heliospheric termination shock. Collisionless shocks are observed in the heliosphereas interplanetary (IP) shocks, inferred in supernovae and accretion disks, and are often associated withenergetic particles, With the increase in computational power, theory and simulation of collisionlessshocks have progressed rapidly. Numerous satellites with increasingly resolved plasma and fieldmeasurements provide in-situ observations of shocks. NASA’s growing Heliophysics System
Observatory (Cluster, Time History of Events and Macroscale Interactions during Substorms (THEMIS),
the Advanced Composition Explorer, Wind, and STEREO, in particular) provides multipoint shockmeasurements, yielding global insights into shock dynamics and structure on scales of hundreds tothousands of kilometers. Laser-driven supersonic plasma flows in the laboratory have been used toinvestigate collisionless shocks in a controlled setting using the Omega laser at the Laboratory for Laser
Energetics and the National Ignition Facility (NIF; see Chapter 4). Recent experiments on Omega and
NIF indicate that, in astrophysical environments, strong shocks generate and amplify magnetic fields andaccelerate cosmic rays.
The Magnetospheric MultiScale (MMS) mission, launched in 2015, is a constellation of four
closely spaced satellites that can fly as close together as 5 km. The mission was designed to measureelectric currents and particle properties over a range of scales. Besides investigating Earth’s bow shock,
MMS has enabled new studies of IP shocks near Earth at scales that had previously been the preserve
only of bow shock research. However, IP shocks are dynamically and structurally quite different frombow shocks, especially regarding energetic particles and their back reaction on shock structure. Missions
such as MMS and PSP will provide unparalleled insights into IP shocks from kinetic to MHD and global
scales.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

Solar flares and CME-driven shocks areprimary sites for accelerating electrons and ions as
solar energetic particle (SEP) events, which
propagate into the heliosphere along theinterplanetary magnetic field (IMF). Predicting
SEP impacts at multiple vantage points is of greatpractical importance in the development of reliable
space-weather models capable, for example, of
guiding astronaut safety decisions in the new“Moon to Mars” programs. In-situ measurementsof charged-particle properties show that impulsive
SEP events are primarily associated with solar
flares, whereas gradual events correspond to CMEdriven shock-accelerated particles. Since Plasma
2010, studies of SEP events have benefited frommulti-point observations, revealing that energetic
charged particles can diffuse considerable
distances longitudinally and latitudinally, contrary
to expectations. These investigations have revealed
the complexity of energetic charged-particle
transport, but many open questions remain: inparticular, how particles diffuse transverse to themagnetic field, the precise acceleration mechanism
for impulsive events, and. the properties of the“seed” particles before acceleration required to
explain the observed fluence and energy.
The most likely acceleration process forgradual SEPs is diffusive shock acceleration(DSA), first proposed to explain the acceleration ofgalactic cosmic rays at supernova shocks. Gradual
SEP and CIR-related events typically present an
extended front of particles propagating away from
(CME-driven shock) or towards (CIR shock) theSun. For particles to be efficiently energized at acollisionless quasi-parallel shock (see Figure 7.6),
they must be confined so that they diffuse acrossthe shock multiple times. Ahead of the shock,Alfvén waves excited by a streaming instability
can scatter some of the accelerated particles backtoward the shock. Similarly, downstream
turbulence generated and amplified at the shocktraps particles in its vicinity. The transport of theseenergetic particles through the corona andheliosphere with their many shocks remains adifficult problem. Two competing effects influence
their propagation: focusing along the IMF due tothe decreasing magnetic field strength and pitchangle scattering by IMF turbulence. Strong
scattering allows SEPs to diffuse across the IMF,
whereas weak scattering leads to particles
streaming freely. Numerical modeling of CME

FIGURE 7.7 Ulysses observations of an energeticparticle event downstream of a shock near 5 AU
showing evidence for accelerating charged particles
in a “sea” of small-scale interacting magnetic flux
ropes in the supersonic solar wind. The event
characteristics are inconsistent with the predictionsof diffusive shock acceleration (DSA), but may be
explained by local acceleration in contracting flux
ropes. The panels show Ulysses in situ observations
from 2004 February 13 to March 3. From top tobottom, the panels are the energetic ion counts, themagnetic field strength (|B|), the elevation andazimuthal angles of the magnetic field direction in
the RTN coordinate system, the pitch angle
distribution of 116 eV electrons, proton beta, protondensity, proton temperature, solar wind speed, andthe total plasma pressure. The vertical maroon line
shows the observation time of the forward shock(FS). The dashed vertical lines behind the shock
identify the location of the heliospheric current sheet(HCS), the stream interface (SI), the first reverse
wave (RW), the forward wave (FW), and the second
reverse wave (RW), respectively. Shaded areas
identify Grad-Shrafnov reconstructed magnetic flux
ropes. SOURCE: L.-L. Zhao et al 2019 ApJ 872 4.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

shocks and SEP events reached an impressive level ofsophistication in the past decade, enabling detailed
predictions that compare favorably to observed
spectral, energetic, and temporal characteristics oflarge events.
However, some interplanetary SEP events
have been observed that do not fit the DSA model. For
example, in-situ particle and field observations bymultiple spacecraft near the heliospheric current sheet
and in Earth’s magnetosphere indicate that SEPs may
be associated with dynamically interacting flux ropes(helical magnetic structures that consist of a twist
component and an axial field; also see Chapter 2).
Theory and simulations demonstrate that flux rope
merging and contraction can energize particles locallyin the IPM (Figure 7.7) and in solar eruptive flares.
Flux-rope contraction and coalescence in reconnecting FIGURE 7.8 Data from Van Allen Probes
current sheets therefore appears to be an alternative
revealed the mechanism that accelerates
mechanism for accelerating particles in different
electrons to relativistic speeds in the Earth’s
SAPs, offering a promising avenue for further
radiation belts—local energy transfer from
exploration in the next decade.
intense chorus waves excited by a
MMS has probed the inner core of magnetic
geomagnetic storm. This resolves a longreconnection sites, where both ions and electrons are
standing problem in understanding the origin
decoupled from the magnetic field. This is the actualand evolution of the radiation belts, andregion where the magnetic field breaks andillustrates the importance of simultaneous inreconnects. The magnetosphere and many othersitu measurements of plasma waves andcosmic plasmas are sufficiently rarefied that collisions particles in geospace. SOURCE: Science 30
between particles are infrequent. In such collisionless
2013: 341, 6149, 991-994, doi:
plasmas, identifying the mechanism for magnetic flux
10.1126/science.1237743.
breaking during reconnection has been a long-standing
challenge. For the first time, MMS observations
verified a recent theoretical prediction of the underlying process by examining the shape of electron
velocity distributions within a reconnection region in the magnetotail. This fundamental discovery
illustrates the profound value of combining theory, computation, and state-of-the-art observations.
The recently decommissioned Van Allen Probes (VAP) brought new insights into the source,transport, and loss of charged particles within Earth's radiation belts (Figure 7.8), and the local-global
coupling of the magnetosphere and solar wind. The VAP discovered a transient third radiation belt filledwith ultra-relativistic electrons, which briefly appeared in September-October 2012 after a geomagnetic
storm. Analysis of VAP data identified the long-sought location and source of electron acceleration in theradiation belts. Geomagnetic substorms inject electrons deep into the nightside magnetosphere where they
produce chorus waves (a type of whistler wave), which in turn accelerate high-energy radiation-belt
electrons to even greater energies. The causes of particle loss from the belts remain a topic of debate, but
the likely explanations have been narrowed down by theoretical studies and VAP observations tomagnetopause outflow, charge exchange, and precipitation into the ionosphere. In parallel with theseobservational breakthroughs, laboratory experiments on the Large Area Plasma Device at the Universityof California at Los Angeles, as discussed in Chapter 7, have contributed to understanding radiation-belt
physics by using controlled energetic-electron beams to study the generation of and interaction withwhistler waves.
Ionosphere, thermosphere, and mesosphere (ITM) plasma physics has made substantial progress
on several fronts. Greater appreciation for lower atmospheric forcing of the ionosphere and thermosphere
has emphasized how critical gravity-wave propagation and dissipation are to the thermosphere. MultiPREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

instrument studies by the DoD-NASA C/NOFS (Communications/Navigation Outage Forecasting
System) mission, sounding rockets, and ground-based radar facilities, accompanied by numericalmodeling, have revealed the complex physics of plasma bubbles and depletions in the ionosphere. These
investigations have shown the importance of primary instabilities (e.g., Kelvin Helmholtz) and neutral
wind shears in seeding the more slowly growing Rayleigh-Taylor instability. DARPA’s new Space
Environment Exploitation program aims to accurately predict near-Earth space environment disturbancesand perturbations (on scales as small as 100 km) in 1-hour increments extending out 72 hours, throughadvances in modeling and data collection. Computer simulations that leverage the power of graphics
processing units (GPUs) are providing higher-resolution physics-based perspectives than in the recent
past (Chapter 2). New sensors and missions are being sought to increase the number of measurements in
the greatly undersampled near-Earth space environment, to provide learning sets for advance ML
analysis.
The Global-scale Observations of the Limb and Disk (GOLD) mission, launched in January 2018,
is now a key tool for ionospheric observations, providing the first day-to-day measurements of the region
and its response to forcing by the Sun, the magnetosphere, and the lower atmosphere. GOLD measures
the temperature and composition of neutral gases in Earth’s thermosphere through full-disk UV imaging
spectroscopy of Earth from its geostationary vantage
point above the Western Hemisphere. Because theionized plasma and neutral gases interact in thethermosphere, understanding of plasma processes
and computer modeling play critical roles ininterpreting GOLD data.
Even lower in Earth’s atmosphere, electrical
processes produce lightning flashes that lead toplasma phenomena with measurable effects
throughout the atmosphere and beyond. Sensitive
photometric and high-speed video records obtained
during the last decade indicate that these varied
FIGURE 7.9 Illustration of transient luminous phenomena are dynamically complex. The related
plasma processes exhibit a large variety of visual
events (including elves, sprites, and jets) that
forms, which collectively span the full range ofoccur at stratospheric and mesospheric/lowerionospheric altitudes and are directly related to altitudes between the tropopause and the ionosphere.
electrical activity in underlying thunderstorms. The luminous optical manifestations of theseobserved events roughly distinguish among theEffects on the upper atmosphere andvarious distinctive classes: sprites, elves, and blue
ionosphere of quasi-static electric fields,
jets (Figure 7.9).
electromagnetic waves, and plasmas produced
Powerful lightning discharges can directlyby these events need to be understood, as well
disturb
thelower ionosphere, disrupting very lowas their potential for harming humans andfrequency
radio
waves used commonly fortechnology exposed to the resulting gamma
communications.
Over the last decade, lightning has
rays and accelerated particles. SOURCE:
been found to induce plasma perturbations in the
Pasko, Nature, 423, 927, 2003.
ionosphere that can last tens of minutes. Lightning
processes can accelerate electrons to relativisticenergies. Terrestrial 𝛾-ray flashes observed from space and from the ground are thought to bebremsstrahlung emission from the deceleration of very energetic (tens of MeV) electrons by collisions
with atmospheric molecules. Up to 1017 high-energy electrons and fewer positrons are present in a typicalevent, which can last for fractions of milliseconds and occurs about 50 times per day globally. In addition,lightning can launch strong electromagnetic pulses and create strong quasi-static electric fields, inducing
gas discharges in the upper atmosphere (Chapter 5).
NASA’s Parker Solar Probe (PSP) is a revolutionary spacecraft designed to approach within 10
Rsun (solar radii) of the Sun. PSP is producing unprecedented data on the plasma and energetic-particle
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

properties in the solar wind. For example, PSP magnetic-field and plasma measurements during the firstsolar encounter at 35.7 Rsun identified a slow Alfvénic solar wind emerging from a small equatorial
coronal hole, apparently escaping from above low-lying, complex magnetic structures, which exhibited ahighly dynamic magnetic field with polarity reversals on timescales from seconds to hours. These varying
field structures were associated with clustered radial plasma jets with enhanced energy flux andturbulence. During periods between groups of jets, the sampled solar wind was essentially steady. The
combination of PSP with other solar-heliosphericmissions and observatories will help answer
fundamental questions about the origin of the solar
wind, including how the solar corona is heated, andhow and where the different types of solar wind are
generated.
Observations by Voyagers 1 and 2, energetic
neutral atom (ENA) observations by the Interstellar
Boundary Explorer (IBEX), and sophisticated theory
and modeling have revolutionized our understandingof the interaction of the solar wind with the partiallyionized LISM. The neutral hydrogen component of
the ISM profoundly affects the supersonic wind
through the creation of pickup ions (PUIs), a
suprathermal (~1 keV) plasma component thatremoves energy and momentum from the solar wind
and introduces low-frequency turbulence in the wind
beyond ~10 AU (1 astronautical unit (AU) is the
distance from the Sun to Earth). Remarkably, thedissipation of this interstellar-driven turbulence
gradually heats the distant solar wind, rather than the
expected gradual cooling. The PUI population affects
the dynamics of all ambient shocks, including the
FIGURE 7.10 (Top) 3D MHD simulation oftermination shock (where the solar wind transitions
the global heliospheric magnetic fieldfrom a supersonic to a subsonic flow). Althoughembedded in the interstellar field (white lines),
anomalous cosmic rays (ACRs) were observed toshowing signatures of instabilities in theaffect the termination shock structure, the Voyagers
heliotail. The plasma density in the midplane
did not identify the termination shock as the site at
is represented by color shading. The
which ACRs originate, leaving the debate
heliopause is at the left, heliotail is extended
unresolved. Surprisingly, the inner heliosheath (thetoward the right. (Bottom) Kelvin-Helmholtz
region between the termination shock and theinstability of the heliopause increases withheliopause) is far narrower than expected, and is aincreasing interstellar magnetic field strength
highly turbulent mix of compressible andfrom 3 microG (yellow color) to 4 microG
incompressible plasma. The heliosheath thermal(blue color). SOURCE: N.V. Pogorelov, S.N.
plasma remains relatively cool because PUIs andBorovikov, J. Heerikhuisen, M. Zhang,
ACRs carry much of the thermal energy. The
Astrophys. J. Lett. 812, L6 (2015).
heliopause structure is largely unexplained.
doi:10.1088/2041-8205/812/1/L6.
Both Voyager spacecraft have now begun
humanity’s first in-situ exploration of galactic space,and continue to transform our understanding of cosmic rays. Voyager 1 revealed that the very local
interstellar medium (VLISM) is very much influenced by the solar wind. Even at 145 AU, Voyager 1 isstill observing interplanetary shocks that have propagated well beyond the heliopause, introducing
variations in cosmic ray anisotropies Voyager 1 is measuring the interstellar magnetic field (ISMF)
direction and strength, which determines the global shape and nature of the boundary between the solar
system and the ISM. Preliminary results from the Voyager 2 crossing of the heliopause suggest that the
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

ISMF strength exceeds the corresponding measurement made by Voyager 1 at a much higher latitude.
These observations have guided 3D MHD simulations of the dynamic magnetic field and plasma structureof the heliosphere, revealing its cometary-like shape embedded in the LISM (Figure 7.10).
IBEX discovered an unexpected “ribbon” of energetic neutral atom (ENA) emission originatingfrom the VLISM. This emission is apparently associated with the orientation of the ISMF (Figure 7.11).
The ribbon is thought to be due to the ionization of fast and/or hot solar-wind neutral atoms that propagate
from the supersonic solar wind and inner heliosheath into the VLISM, where they are re-ionized to
become PUIs gyrating about the ISMF. Re-neutralization of these PUIs by charge-exchange withinterstellar hydrogen atoms yields ENAs that can be detected at 1 AU. The ribbon observations of ENAs
by IBEX suggests an ISMF strength that is roughly consistent with current Voyager 1 data. Langmuirwave measurements by Voyager 1 suggest that the heliopause might possess a depletion layer similar tothat observed at Earth’s magnetopause.
Voyager 1 discovered that shock waves propagating in the low 𝛽 (dominated by magnetic rather
than thermal gas pressure) interstellar space are weak, quasi-perpendicular, unusually smooth and very
wide (~104 times broader than similar shocks at Earth). The VLISM shocks are IP shocks that propagate
through the supersonic solar wind, are transmitted across the heliospheric termination shock, propagate
through the heliosheath, and are then partially transmitted into the VLISM at the heliopause. Unlike theheliosphere, the thermal VLISM plasma is collisional with respect to proton–proton collisions thatdissipate energy through heat conduction and viscosity. Because the VLISM shocks are weak, thisdissipation determines their structure.
Although kinetic approaches are now being used in studies of magnetized plasmas, many suchinvestigations assume that the plasmas are in equilibrium with their magnetic fields. In contrast, mostheliophysical plasmas observed since 2010 reveal complex configurations that are not in equilibrium,with signatures of turbulence, strong nonlinearity, and cascade-type processes. High-resolution images(Goode Solar Telescope and SDO), and spectroscopic measurements (Hinode, IRIS, and rocket-borne
instruments) show that the entire solar atmosphere exhibits extraordinarily complex, nonlinear magnetic
activity. The solar wind contains magnetic andkinetic energy density fluctuations fit by a power law
over decades of scale, in addition to persistent,intermittent, and quasi-periodic structures. The
magnetosheath and plasma sheet also exhibit noisy,
bursty, random structures. Ambient turbulence andits transport and coupling to large-scale flows govern
the scattering and transport of energetic charged
particles, while coherent structures such as flux ropes
can scatter, trap and accelerate particles. Our current
inability to predict magnetic fields and particle
distributions at specific locations in the heliosphere,
as well as uncertainties in space weather prediction,
largely stem from our inability to accurately measure FIGURE 7.11 An illustration of theheliopause ribbon seen in IBEX ENA maps
or model local turbulent properties. Understanding(color shading), showing its relation to thethe basic plasma physics of turbulence and its role ininterstellar magnetic field outside thedictating the state of SAPs remains an outstanding
heliosphere (black lines) and the locations ofproblem for the next decade and beyond.
the Voyagers in October 2009. The IMAP
mission is expected to answer many questions
BENEFITS TO SCIENCE, SOCIETY,
about the origin of this mysterious feature.
INDUSTRY, TECHNOLOGYSOURCE: Science 13 2009:326, 5955, 959962, doi: 10.1126/science.1180906.
Advances in understanding SAPs provide
multiple benefits to society and science. The most
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

tangible advantages come from our growing understanding of the causes and consequences of space
weather. The most extreme space weather comes from solar eruptions, in particular the fast CMEs thatdrive shocks, produce SEPs, and smash into our magnetosphere, triggering geomagnetic storms, aurorae,
and geomagnetically induced currents that can affect pipelines and the electric power grid. SEPs candirectly disrupt onboard computers and other instruments on spacecraft, disable GPS and communication
satellites, and induce radiation damage to unshielded humans in space. Geomagnetic storms also cause
energetic particles to be ejected from the radiation belts surrounding Earth, potentially damaging
spacecraft in low Earth and geostationary orbits. The entire causal chain, from solar eruptions to theimpact on the magnetosphere to the space weather effects on our technology, corresponds to a chain of
intimately coupled plasma processes. Understanding the entire chain from the Sun to Earth and beyond
calls for a systems approach and represents a paradigm shift that has emerged in the past decade. With our
critical dependence on technology, PSE is essential for understanding and ultimately predicting space
weather, as well as mitigating its effects.
An associated societal and technological benefit of space and astrophysical plasma research is thedevelopment of experimental equipment and associated detectors, probes, imaging techniques, and data
analysis software. Many techniques initially developed to visualize cosmic phenomena have crossed overto other fields, such as medical imaging, defense, and industrial applications. Large-area astronomical
surveys and their catalogued data over the whole electromagnetic spectrum play important roles indeveloping big data techniques for new discoveries. Numerous important spectroscopic discoveries andmethods with practical utility originated in astrophysical investigations, from the discovery of helium toother species in interstellar clouds. The extreme environments of, for example, planetary and stellarinteriors, pulsar magnetospheres, and intergalactic filaments offer unparalleled opportunities to explore
plasma conditions that cannot be duplicated in laboratories, testing the limits of our theories and models
and perhaps leading to new techniques that can be applied to high energy-density investigations andfusion reactors (Chapter 4). The need to understand extreme plasma conditions also drives thedevelopment of innovative computational techniques and hardware (see Chapter 2).
Finally, space excites people of all ages, motivating the public to learn more about science andattracting the next generation of space and astrophysical plasma scientists and engineers, and scientists
and engineers in nearly all STEM disciplines. Undergraduate research in SAP would expose a morediverse student population to plasma physics, comprising a valuable mechanism to diversify the broader
PSE community. Space science and astrophysics can be taught to non-scientists and physics graduate
students alike. Space missions and ground-based observatories employ scientists, engineers, andtechnicians from the earliest design phase through construction to operations, requiring a vast range ofskills across the STEM domain. Facilities dedicated to SAP research and technology are found inuniversity departments, private industry, aerospace companies, federal laboratories, and international
institutes, all employing the diverse workforce required to keep such organizations thriving. Therefore,
the effects of a healthy SAP program extend well beyond the confines of those engaged in research alone.
CONOMIC DEVELOPMENT/PROGRESS AND ACHIEVEMENTS DURING THE PAST
DECADEThe growing awareness of space weather and its consequences has motivated international efforts
to create or enhance space-weather forecasting facilities and build physics-based and empirical models to
elucidate the underlying processes. These models are enabling increasingly accurate predictions, while theestablishment of new facilities and academic programs in this field is actively increasing sciencecapabilities in both developed and developing countries. Summer schools and other educational programs
are training the next generation of space-weather researchers. In the United States, agencies such as
Department of Homeland Security and the Federal Energy Regulatory Commission began to consider thesocietal and technological impacts of space weather events, and to include them in disaster planning.
Electric power companies, space plasma scientists, and government representatives collectively
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

developed and adopted new reliability standards to mitigate the impacts of geomagnetic disturbances.
Several commercial enterprises that supply space weather products, instrumentation, simulations, andpredictions were founded in the past decade, creating jobs and serving a diverse base of scientific andoperational customers.
The need for high-throughput, high-cadence imaging with ever-increasing spatial and spectral
resolution has driven significant advances in instrumentation and image processing that also benefit thebroader science community, military, and diverse industries such as commercial earth imaging. For
example, recent efforts have focused on developing space-borne photon sieves, hard X-ray spectroscopic
imagers, miniaturized plasma instruments and magnetometers, ion-neutral mass spectrometers, andsodium lidar detectors, as well as ground-based adaptive optics telescopes and interferometers withextremely long baselines. Space applications of PSE range from aerospace vehicle construction andspacecraft propulsion to sensors and detectors (see Chapter 5).
Technology Advances
Since the Plasma 2010 report, technological advances in SAPs have improved the plasma
instruments and diagnostics used to detect, measure, and record the complex multiscale and multimessenger phenomena that permeate our universe. Smallsats and cubesats have become favored platforms
for obtaining multiple samples and views of localized, transient events in geospace and beyond, driving
the development of miniaturized instruments capable of fitting into the highly restrictive size and mass
limits of these small spacecraft. Although this rapidly developing technology is still in its infancy, itoffers enormous potential for answering many scientific questions about the origins and evolution of
space weather effects, from ionospheric disturbances and magnetotail substorms to SEP events. The needfor greater sensitivity and higher spatial and temporal resolution motivates a new generation of detectors,
materials, and manufacturing techniques.
Several laboratory experiments performed in the past decade were designed to better reproduce
important solar and astrophysical conditions and enable comparisons between laboratory experiments and
SAP observations (and models). The Line Tied Reconnection Experiment, a basic plasma physics
experimental facility at the University of Wisconsin-Madison, was constructed to study ideal and resistive
MHD instabilities under variable boundary conditions and equilibria. In particular the line-tied conditions
characteristic of the solar atmosphere and the magnetic launching of astrophysical jets were emphasized.
The Facility for Laboratory Reconnection Experiments (FLARE) at the Princeton Plasma Physics
Laboratory (PPPL) is a new intermediate collaborative user facility constructed by a consortium of five
universities (Princeton University, University of California-Berkeley, University of California-Los
Angeles, University of Maryland, University of Wisconsin-Madison) and two DoE national laboratories(PPPL and Los Alamos National Laboratory). The goal of FLARE is to provide experimental access to
new regimes of the magnetic reconnection process and related phenomena directly relevant toheliophysics, astrophysics, and fusion plasmas. NIF (Chapter 4) also provides new paths to investigate
nuclear processes and structural effects in the time, mass and energy density domains relevant toastrophysical plasma phenomena in a controlled terrestrial environment.
The Basic Plasma Science Facility (BAPSF) at UCLA is a national user facility for fundamental
plasma science sponsored by DOE and NSF. BaPSF, and its primary experimental device, the Large
Plasma Device (LAPD), provides a platform for studying processes relevant to SAP parameter regimes ina reproducible, large volume, magnetized plasma. Examples include the linear and nonlinear physics ofplasma waves (e.g., Alfvén waves), collisionless shocks, magnetic reconnection, interaction between
energetic particles and waves, and turbulence and transport, over a wide plasma 𝛽 range.
The Naval Research Laboratory’s ground-based Space Physics Simulation Chamber (SPSC), an
ONR-sponsored facility, complements theory, modeling, and in-situ measurements with laboratory
experiments. SPSC provides a platform to collaboratively investigate the underlying physics of spaceplasmas under controlled, reproducible, scaled laboratory conditions, particularly those representative of
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

the near-Earth space plasma environment, and a realistic testbed for the development and pre-flighttesting of space diagnostics and hardware. The device is used for the study of ionospheric,magnetospheric, and solar wind plasma phenomena; testing/calibration of space-qualified diagnostic
instruments for missions; spacecraft charging; large-volume plasma generation; and other investigations
requiring a low-pressure environment.
NSF’s National Solar Observatory (NSO) operates cutting-edge facilities, develops advanced
instrumentation both in-house and through partnerships, conducts solar research, and creates educational
and public outreach programs. The NSO Integrated Synoptic Program (NISP), established in 2011,
operates two facilities dedicated to long-term full-disk coverage of the Sun: the Global Oscillation
Network Group (GONG) and the Synoptic Optical Long-term Investigations of the Sun. Data from theworldwide GONG network has advanced our understanding of the Sun through helioseismology (thestudy of the Sun’s interior using observed oscillations, which explores the internal structure in
unprecedented detail) and prominence seismology. NSO’s Community Science Program develops
analysis and modeling tools that will enhance the value of data taken with NSO’s state-of-the-art
observing facilities—the Daniel K. Inouye Solar Telescope (DKIST) and NISP—and to train the next
generation of solar physicists in the use and development of these tools. Until 2018, NSO also operated
telescopes at Kitt Peak and Sacramento Peak Observatories that have been critical to the advancement of
the field. NSF’s National Center for Atmospheric Research/High Altitude Observatory operates andupdates the Mauna Loa Solar Observatory and its two primary instruments, the K-COR Coronagraph andthe COronal Multi-channel Polarimeter.
The Center for Solar-Terrestrial Research at New Jersey Institute of Technology operates the Big
Bear Solar Observatory (BBSO) and Extended Owens Valley Solar Array (see below), the AutomatedGeophysical Observatories and other instruments in Antarctica, and geospace observing facilities acrossSouth America and the United States, with funding through grants from NSF, NASA, the U.S. Air Force,the Korean National Science Foundation, and other government and private sources. BBSO presently
hosts the highest resolution optical solar telescope in the world, the 1.6-m Goode Solar Telescope (GST).
Operating since 2009, with adaptive optics installed in 2017, the GST determines the magnetic field andplasma dynamics in the solar chromosphere and photosphere on scales as small as 70 km. This facility
also served as a valuable testbed for the adaptive optics and instruments being installed at DKIST.
The Extended Owens Valley Solar Array (EOVSA) is a world-class NSF-funded facility for
scientific research at microwave radio frequencies (1-18 GHz) aimed at understanding the Sun and its
influence on Earth and near-Earth space environment. EOVSA focuses on studying the magnetic structureof the solar corona, transient phenomena resulting from magnetic interactions (e.g., solar flares andassociated particle acceleration and heating), and space weather phenomena. The project has provided
solar-dedicated observations since its completion in 2017. EOVSA has yielded groundbreaking
observations of some of the most powerful solar eruptions ever measured and provides unique insights
into the heating and acceleration of high-energy coronal electrons.
Progress in understanding Earth’s ionosphere, thermosphere, and mesosphere (ITM) has long
relied on ground-based observations from multiple international facilities. In the ITM, neutral gas motions
drive ionospheric density and dynamics, affecting currents, plasma instabilities, and vertical coupling of
atmospheric regions. A new class of Incoherent Scatter Radars, including Poker Flat Incoherent Scatter
Radar (built during the past decade), RISR-N, and RISR-C, is enabling leaps forward in our
understanding of ITM phenomena. T-REX, a network of multispectral all-sky imagers in Canada, is a
new capability for comprehensively characterizing the high-latitude thermospheric and ionospheric stateand energy inputs. Next-generation scanning Doppler imagers, such as the new facility built by the
University of Alaska, are starting to collect detailed ground-based measurements of thermospheric winds.
At low latitudes, upgrades and new observational techniques applied in the past decade to the 50-year old
Jicamarca Radio Observatory have produced unprecedented images of the electrodynamics of theequatorial ionosphere. Ground-based lidars, which primarily measure temperature, wind speed, andmetallicity in the low nightside ITM, have been greatly improved since 2010. These lidars have become
more robust and sensitive, covering more species and greater ranges in altitude than ever before. The
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Plasma Science: Enabling Technology, Sustainability, Security, and Explorationinternational proliferation of ground-based GPS receivers, which can measure the total electron content
above them, is providing new insights into the temporal and spatial structure of ionospheric variations,traveling disturbances, and other transient phenomena in the upper atmosphere.
Computations, Diagnostics
SAP research has long capitalized on computational advances in hardware, algorithm
development, and access to new systems to design new instruments, assimilate data, validate predictivemodels, probe extreme conditions in cosmic phenomena, and reach for closure between theories andobservations. Increasing access to graphical processing units (GPUs) enabled substantial speed-up of
select codes, but the need for machine-specific rewriting of programs now limits the potential for
widespread GPU usage. Some MHD codes incorporated more relevant physical processes, such asradiative transfer, ionospheric chemistry, and the effects of partial ionization. The use of adaptive meshrefinement to place the highest spatial resolution where it is most needed, such as current sheets, steep
density gradients, and boundary layers, became more common for modeling phenomena covering large
dynamic ranges.
Because the most interesting physical processes are complex and nonlinear in traditional plasmas,
and even more so in extreme plasmas, our ability to understand them greatly benefits from numericalsimulations. Computational SAP studies are increasingly important, revolutionizing our understanding of
extreme plasmas in exotic astrophysical objects. Particle-in-cell (PIC) codes offer opportunities tounderstand how exotic/relativistic pair plasma is produced, and how coherent radio and high-energy
emissions are generated. These developments are enabling, for the first time, truly ab-initio studies ofimportant phenomena such as Crab Nebula 𝛾-ray flares,
pulsed high-energy emission from pulsar magnetospheres,the coronae of accreting BHs, and pair-production cascades
in pulsar and BH magnetospheres, as well as basic processes
such as magnetic reconnection and particle acceleration inastrophysical plasmas (Figure 7.12). Modeling of extreme
plasma physics has been enabled recently by thedevelopment of radiative 3D general-relativistic MHD codes
and their application to global simulations of accreting BHs
and their jets. These pioneering studies clearly demonstratethat rigorous numerical investigation of extreme plasma
processes is now feasible and realistic, opening up broad
avenues for future exploration.
Developing time-dependent simulations withevolving boundary conditions derived from observations is
FIGURE 7.12 Evolution of the particle
essential to improving the predictive capability of spaceenergy spectrum (as a function of
weather modeling. For example, AFRL’s ADAPT code
Lorentz factor gamma) from a PIC
prepares a time series of magnetograms of the solar
simulation of stressed X-point collapse
photosphere to drive the bottom boundary of coronal andin a magnetically dominated, relativistic
solar wind models. A serious obstacle to this approach is the plasma. The results demonstrate thatlack of information about the changeable photosphericelectrons are quickly accelerated tomagnetic field on the far side of the Sun, which would behighly relativistic velocities by thebest rectified with multiple satellites distributed around thereconnection-induced electric field.
Sun.
SOURCE: Lyutikov et al. (2017).
New, cutting-edge global modeling techniques are
Explosive X-point collapse inbeing developed, such as the multiscale plasma Wave-inrelativistic magnetically dominated
Cell (WIC) simulation method that self-consistently tracks
plasma. Journal of Plasma Physics,
wave dynamics. These capabilities can clarify and predict
83(6), 635830601.
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

the global magnetospheric impact of microscopic kinetic plasma processes, including wave-particle
interactions. Such frontier computational techniques may answer key questions, such as the source ofplasmaspheric hiss, the factors determining whether a geomagnetic storm enhances or depletes electrons,
the global conditions required to form magnetospheric resonators, and the effectiveness of different
radiation-belt remediation techniques.
Novel approaches such as Bayesian analysis, automated feature recognition, and machinelearning are extracting valuable science from large data sets. For example, SDO yields 1.5 TB of data
daily, necessitating innovative techniques for finding key phenomena or features and interpreting theirproperties efficiently. Similar approaches are being introduced to interrogate the massive data output from
3D numerical simulations, particularly for ensembles of physics-based space weather simulations. Recent
application of machine-learning techniques to IRIS observations has increased the computational
efficiency of chromospheric diagnostics one million-fold, compared with physics-based numericalsimulations and inversion codes. This approach quickly provides chromospheric researchers with thetemperature, velocity, density, and unresolved motions or turbulence as a function of height in the solar
atmosphere for every IRIS observation. This new machine-learning based tool, combined with the morethan 25,000 IRIS observations of the solar chromosphere since its launch in 2013, will deepen ourphysical insight into the transfer of energy from the Sun’s interior to the corona.
FUTURE CHALLENGES AND OPPORTUNITIES: SCIENCE
The next decade brings exciting opportunities and daunting challenges for space andastrophysical plasma science. Cross-disciplinary collaborations, international cooperation, novel
observing platforms, new instruments and diagnostic methods, and targeted combinations of theory,computation, experiments, and data analysis will be crucial for answering the most fundamental questions
about the plasma universe.
Astrophysics
Observational advances over the past decade have revolutionized many aspects of astrophysicalplasmas, through innovative and exciting ground-based and space-based missions. Ongoing missions suchas LIGO (The Laser Interferometer Gravitational-Wave Observatory) and planned or under construction
new observational facilities such as ATHENA (Advanced Telescope for High-ENergy Astrophysics,
expected to launch in 2028), ETH (Event Horizon Telescope), XRISM (X-Ray Imaging and Spectroscopy
Mission), LYNX (Lynx X-ray Observatory), LISA (Laser Interferometer Space Antenna), SKA (Square
Kilometre Array), and CTA (Cherenkov Telescope Array) will address major challenges in several subareas of plasma astrophysics:Extreme plasma physics of multi-messenger cosmic plasmas
Physics of extremely rarefied/weakly collisional plasmas
Plasma physics of the early solar system evolution, exoplanets, and the origin of life
Plasma physics of the interstellar medium

Multi-messenger astrophysics combines information from multiple extrasolar electromagnetic
radiation, gravitational waves, neutrinos, and cosmic ray observations. Exploiting these four
“messengers” is transforming plasma astrophysics by opening new windows on the universe. The
challenges in understanding the extreme plasma physics of multi-messenger cosmic plasmas lies in thefact that energetic plasmas around neutron stars and BHs are under extreme, high-energy-density (HED)
physical conditions and are governed by rich physics. These plasmas are often relativistically hot, move at
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

relativistic speeds, and engage strongly with ambient and self-produced radiation fields. The QEDinteraction of photons with each other and with strong magnetic fields may lead to prolific pair creation(e.g., electrons and positrons). These “exotic” relativistic, radiative, and QED aspects of the basic
collective plasma phenomena are novel and do not have analogs in traditional solar, space, and mostlaboratory plasmas, although recent advances in laser technology are now enabling us to access and study
these extreme plasma regimes in the lab. Our understanding of extreme astrophysical and laser-plasma
processes (Chapter 3) is incomplete, as classical plasma theory becomes inapplicable. There is a need fora targeted study of kinetic-level collective plasma phenomena that includes laser-plasma andastrophysically relevant physical conditions, relativistic motions, strong interaction of particles withradiation, and QED effects. This requires developing new physical insights and building a rigorous,
systematic knowledge base for these extreme plasmas, then applying this new knowledge to uncover the
inner workings of the most fascinating and challenging astrophysical objects, including accreting BHs andtheir jets, pulsars, magnetars, and multi-messenger phenomena such as neutron-star mergers.
The global modeling of astrophysical multi-messenger sources is further complicated by themulti-scale nature of the extreme plasma processes. In many systems of interest, the micro- and macroscales affect each other in complex ways, so a simple parameterization of a microscopic process may beinsufficient, and a true multi-scale problem must be solved. For example, in the context of particle
acceleration, the feedback of energetic particles on large scales affects the injection process at small
scales, which requires special techniques for modeling. New approaches to multi-scale simulations ofastrophysical objects need to be developed, including “hybrid” schemes that combine kinetic particles
representing the accelerated component with MHD schemes that can efficiently evolve the backgroundstate. In fact, how to connect small and large scales in meaningful ways is a pressing issue for the entire
PSE community.
The challenges in understanding extremely rarefied/weakly collisional plasmas around BHs andin clusters of galaxies (inter-cluster medium, ICM) involve a complex mix of rarefied plasma andaccelerated particles (and dark matter in the case of ICM). In addition, these plasmas exhibit extreme
separation of micro- and macro-scales. Although these plasmas are dominated by thermal rather thanmagnetic pressure, even weak magnetic fields change the overall dynamics as well as dissipative andtransport properties. The dynamics of such plasmas are governed by large-scale bulk motions andcomplex, multiscale interactions between kinetic phenomena under conditions not in local
thermodynamic equilibrium. Key questions include, where is the seed population of charged particles thatare accelerated to produce the observed radio emissions, what are the properties of magnetized turbulencein this plasma regime, and what is the source of the additional heating needed to account for the observed
X-ray intensity of the deep core of the clusters?
Understanding these interactions presents a challenge for plasma theory, computational studies
and experiments. Numerical investigations of weakly collisional SAP plasmas require fully kinetic (PIC)
studies to explore microscale physics but will benefit from hybrid-kinetic approaches (with fluid
electrons) that address the dynamic range problem. Key areas for study include elucidating the mostimportant kinetic instabilities, particularly in the presence of strong heat fluxes; understanding how
kinetic instabilities interact with other plasma processes, such as magnetic reconnection, thermal
conduction, and particle acceleration; and understanding the interplay between widely separated fluid
macroscales and kinetic microscales.
Partially ionized interstellar plasmas, especially low-ionization plasmas in protostellar cores andprotoplanetary disks, present formidable plasma-physics challenges, with important implications for theorigin of life in the Universe. Effects of dust formation (and the resulting presence of nearly macroscopic
charged particles; see Chapter 2), non-ideal MHD (e.g., resistivity, Hall effect, and ambipolar diffusion),and multi-species plasma components (neutrals, electrons, cosmic rays, molecular and atomic ions, andcharged dust grains) collectively comprise a highly complex plasma environment. The interactions among
the partially ionized gas component, the charged dust grains, the microscale dynamics of dust coagulationand planetesimal formation, the mesoscale dynamics of the magnetorotational instability in protoplanetarydisks, and the macroscale dynamics of outflows and long-term disk evolution are difficult plasmaPREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

physical problems. The low temperature plasma community (LTP) has long addressed partially ionized,
chemically reactive, and multi-phase plasmas, offering possible strategic opportunities for the SAP and
LTP communities to collaborate on low-ionization astrophysical plasmas.
Heliophysics
Space weather is recognized nationally and internationally as a potential threat to our technologydependent society and to our space programs, including human-flight to the Moon, Mars, and beyond.
The complex chain of energy release, transformation, and transport from the Sun to Earth and other sites
in the heliosphere encompasses a vast range of interlinked phenomena, all requiring plasma science toachieve understanding, prediction, and mitigation when relevant. One underexplored area of practicalinterest is extreme events—eruptions at the most energetic end of the scale, on par with or surpassing theso-called Carrington event of 1859. Extreme events challenge our strategic planning, our physical models,and our ability to respond appropriately to loss of communications, electric power, and GPS. Although
the basic physical processes associated with geomagnetic storms on our planet’s magnetosphere and ITM
are understood, our comprehension and ability to model extreme Carrington-scale storms are in theirinfancy. The “average” solar eruptions cannot be predicted with great accuracy, much less the rare but
highly destructive events. By pushing robust first-principles models to their limits and adding key
physical processes that are currently missing, however, the impact of weak to extreme eruptions on thenear-Earth environment can be assessed to identify the most vulnerable areas and the most likely
damaging effects. This will require closer coupling between models of adjacent geospace regions,
including the neutral atmosphere beneath the ionosphere. A sufficiently broad dynamic range of scales isneeded to capture important local-global interactions, such as large-scale magnetic connectivity changes
associated with reconnection, key atmospheric chemistry processes such as nitric oxide enhancements ingeomagnetic storms, and kinetic- (e.g., wave-particle interactions) and MHD-scale processes. This area
would greatly benefit from joint programs with the LTP community, which possesses expertise inatmospheric plasma chemistry.
Several aspects of space-weather ITM modeling are ripe for improvement. Currently, many
global-scale geospace models treat the ionosphere simply as an input boundary condition. This problem isoften exacerbated by actual physical gaps between the computational domains being coupled,complicating realistic simulation of the transfer of plasma, electromagnetic energy, and energetic particles
between domains. Global models today at best rely on parameterizations of local-scale, kinetic, and/or
non-MHD processes such as kinetic instabilities and particle precipitation from the ring current andradiation belts, or neglect these effects entirely. Finally, the high-latitude (open field) and low-latitude(closed field) ionospheres usually are modeled separately, ignoring processes that affect the evolving
open-closed boundary. A critical goal is to obtain a global electric-field model that couples these tworegions and addresses the impact of large geomagnetic storms on the low- to mid-latitude ionosphere.
Efforts to fill in these missing pieces are currently underway. Different combinations of linked models forthe ring current, upper ionosphere, and mesosphere are being tested, and key physical processes within
this complex system are being added. For example, metal ions that affect conductivity, irregularities, andinstabilities are not included in ionospheric models currently, but their effects are being implemented in
NRL’s SAMI3 ionospheric model. By the next Decadal Survey, the committee anticipate having robust,first-principles models of geospace from the ground to the upper reaches of the exosphere andmagnetosphere.
Solar opacity calculations and measurements, especially for iron (Fe), one of the most abundant
minor elements by mass, have received renewed interest due to the “solar abundance” conundrum.
Analyses of the photospheric composition in the early 2000s found smaller abundances than earlier
estimates for many elements. Previously accepted solar abundances were in excellent agreement withhelioseismology data. With the new abundances, however, the structure predicted by solar models nolonger agrees with that inferred from helioseismic studies. Increased opacities for the key elements under
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solar conditions would lessen the discrepancies, but there is little justification at present for such an
adjustment. The opacities of Fe, Cr, and other elements at the typical electron temperature (Te ∼182 eV)
and density (ne ∼ 1022 cm−3) near the solar convective and radiative zone boundary (CZB) were recently
measured and systematically studied on the Z-machine at Sandia National Laboratories, and compared to
the latest theoretical calculations. The calculated and measured Fe opacities agreed reasonably well at thelowest Te and ne, but the models underestimate the opacity as Te and ne approach CZB conditions. Thisfinding awaits resolution. Are the opacity theories missing physics, or is there something unique in theexperimental iron measurement at Te > 180 eV? To confirm laboratory findings, independent experiments
using different platforms, such as NIF, are currently being pursued.
The most fundamental questions concerning particle acceleration on the Sun are: under whatcircumstances do the relevant acceleration mechanisms trigger and operate, and how do accelerated
particles propagate and interact with their environment? Imaging spectroscopy from radio to HXR (hard
X-rays with energies > 10 keV) and 𝛾-ray wavelengths have shed some light on these questions in thepast decade, but such observations need to be continued and improved over the next decade in order toobtain definitive answers. New radio interferometers such as EOVSA and the proposed Frequency Agile
Solar Radiotelescope (FASR) offer new insights into the timing and locations of electron energization andpropagation into the corona and heliosphere, and the solar environment in which the eruption energy wasstored and released. When the RHESSI mission was retired in 2018, the only source of solar-dedicatedhigh-energy imaging spectroscopy was lost. Astrophysical missions such as Fermi and NuSTAR currently
remain the only instruments measuring HXRs from solar flare-accelerated electrons. By ~2025, the STIX
instrument on Solar Orbiter will again provide solar-dedicated HXR imaging and will for the first time
obtain regular data from non-Earth-view locations, though available observation time will be limited by
spacecraft and telemetry constraints. The next generation of instruments designed to study the physics offlare particle acceleration, with sufficient sensitivity and dynamic range to observe faint particle
acceleration sites at the same time as bright flare footpoints, urgently seeks launch opportunities in time
for the next solar maximum. Instruments such as a 𝛾-ray imager/polarimeter could explain the puzzling
separation between electron- and ion-emission source regions, and the existence of long-duration coronal
𝛾-ray sources.
To date, all in-situ observations of solar wind plasmas have been single point measurements orhave focused on a narrow range of scales through the use of carefully controlled formations of a few
spacecraft. Unfortunately, the dynamics of turbulence depends critically on the orientation of themagnetic and plasma fluctuations relative to the mean magnetic field—a 3D quantity that no single
spacecraft can measure. Cluster and MMS, which both consist of four spacecraft in a tetrahedral
formation, employ a limited set of spacecraft separations to sample the multi-directional structure of theplasma. Therefore, these missions cannot simultaneously resolve fluctuations on the range of scales
needed to understand the nonlinear dynamics of plasma turbulence. The largest and smallest scales
sampled by these missions only differ by a factor of 10, which is nowhere near the many orders ofmagnitude necessary for simultaneously measuring turbulent fluctuations through the inertial anddissipation ranges. Future constellation missions with many spacecraft and variable spacing are needed to
unlock the mysteries of solar wind and geospace turbulence.
Two unsolved issues in SEP propagation and acceleration are particularly urgent targets forresolution in the next decade. The recognition that the longitudinal extent of SEP events can varysignificantly came with multi-spacecraft observations (e.g., STEREO) of impulsive and gradual SEP
events. The surprising longitudinal spread of charged particles during gradual SEP events has been
ascribed to cross-field transport in the IPM. Other explanations, such as diverging field lines andlongitudinal particle transport in the corona, have not been thoroughly explored yet. Current SEP models
typically describe cross-field transport via an ad hoc perpendicular diffusion coefficient, and therefore
remains poorly understood. Shock obliquity (the angle between the shock front and the upstream
magnetic field; see Figure 7.6) can affect the injection energy and efficiency for shock-accelerated
particles, the excited wave intensity at the shock, and the associated parallel diffusion. Consequently,
predicting the evolving spectrum of SEPs generated at a particular shock requires detailed knowledge of
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

the shock connectivity to the heliospheric point of interest and a complete description of the competing
physical processes affecting their transport. Although progress has been made in the last decade, thecurrent state of observations and modeling falls short of meeting these requirements. In particular,
temporal and spatial variations in obliquity along a CME-driven shock, from the flanks to the leadingedge, have yet to be incorporated in models of particle acceleration and propagation. The societal quest
for accurate prediction of impacts from individual SEP events on spacecraft and humans at specificlocations throughout the solar system depends critically on answering these questions.
The 42-year old Voyager Interstellar Mission, migrated from the Grand Tour mission exploring
the outer planets, does not have a science payload tailored to exploration of the outer heliosphere and the
VLISM. In a few years, this pioneering mission will end as power supplies fall below critical levels andthe heaters are turned off. Voyagers 1 and 2 have transformed our knowledge of the outer heliosphere andthe LISM plasmas, yet many questions remain unanswered. ACRs do not appear to be accelerated at the
heliospheric termination shock, the heliospheric shock is dissipated by reflected PUIs rather than thethermal solar wind, and most of the pressure in the heliosheath apparently resides in heated PUIs. Because
the Voyager instrument suite was not designed to measure PUIs, a critical component of this highly nonequilibrated collisionless plasma has been inferred rather than measured directly in situ. Voyager and
IBEX observations have challenged and transformed our earlier concepts about the global structure andenergetics of the heliosphere, and of the plasma processes acting at its boundary. IMAP, and eventuallyan Interstellar Probe, will be critical to unraveling the multiple challenges listed above in understanding
the interaction of the solar wind with the LISM.
Energetic particles not only are accelerated by shocks, but also play a fundamental role indissipating shock waves and in determining their structure. Understanding the dynamical effects ofenergetic and suprathermal particles on heliospheric shocks is receiving increased interest. Numerous
observations of shock waves, including some IP shocks within 1 AU, have revealed that the pressure of
the energetic-particle component considerably exceeds both the thermal gas pressure and the magnetic
field pressure. Because most of the thermal heliospheric and VLISM plasma is not equilibrated with theubiquitous energetic particles, understanding the structure and dissipation of heliospheric shocks must
extend well beyond simple MHD models. Instead, multi-fluid models with appropriate closures areneeded, informed by kinetic models of the energetic-particle component and sophisticated PIC and hybrid
codes.
The unprecedented detail of measurements by MMS heralds an opportunity over the coming
decade to considerably deepen our understanding of Earth’s bow shock and nearby IP shocks. The
committee anticipate that future MMS studies will analyze electromagnetic waves upstream of andat/within the shock front; examine the evolution of ion and electron distributions from upstream throughthe shock ramp and into the downstream region; discover PI signatures at the shock; and investigate
periodic nonlinear structures, such as double layers and electron holes downstream of collisionlessshocks.
Whistler waves are very low frequency electromagnetic waves that can be generated in geospaceand other planetary magnetospheres during particle injection events associated with lightning andgeomagnetic storms and substorms. Their interactions with both ambient and injected (energetic)
electrons have been invoked recently to explain particle acceleration in, and precipitation from, theradiation belts. The resulting “killer” electrons are major threats to spacecraft transiting themagnetosphere. Our ability to predict such space weather effects depends on our understanding ofwhistler initiation, propagation, and complex interactions with the electron population. Currently, several
petabytes of data on whistler waves in the near-Earth environment exists in independent databases acrossthe scientific community. By leveraging modern data mining techniques, trends and features of whistler
signals could be extracted on an unprecedented scale. Such techniques will have a tremendous impact on
global space-weather prediction and elucidate basic physics of magnetized plasmas.
Future understanding of plasma processes in Earth’s ITM layers requires spaceborne and groundbased instrumentation capable collectively of full planet coverage. Ionospheric plasmas vary on wide
temporal and spatial scales, so deconvolving the intrinsic evolution requires multipoint spacecraft
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

observations, such as constellations that can observe planetary waves without averaging over a month or
more. Multiple smallsats with instrumentation similar to that onboard GOLD could determine the largescale structure, while widely dispersed ground-based GPS receivers could map the overlying atmosphericproperties on finer scales than presently achievable. To
probe systematically the bottom of the ITM is particularly
challenging with in-situ instruments, because orbits
transiting this zone are short-lived unless onboard
propulsion is included. As a result, the critical“Atmosphere-Space Transition Region” is largely
unexplored, and an important objective for the coming
decade.
The atmospheric region where terrestrial
lightning generates sprites, elves, and blue jets is acomplex interface between the lower atmosphere and thespace environment. This region has considerable practicalas well as intellectual interest, because most UV-blocking
ozone resides there and because local disturbances candisrupt technological systems through their effects on
satellite drag, communications, and electrical power
distribution systems. Fundamental questions remain about
FIGURE 7.13 Illustration of the dynamo
the underlying physics of these events. The close spatial
process operating in the solar interior
and temporal association observed between lightning andclose to solar minimum. Meridional flow
waveguide perturbations implies that the perturbations
patterns (black lines with arrows) in aemanate from plasmas induced by high-altitude
longitudinal plane, magnetic field lines
discharges, but the mechanisms of these perturbations(thin gold lines), the radiative core (innerremain unknown. The seed electrons for these events
yellow), toroidal magnetic-field strength
might be secondary electrons produced by cosmic rays or(red-blue color shading at right), andfrom compact regions around tips of lightning leaders.
radial magnetic-field strength (blueThe radiation dose to people inside aircraft near ayellow shading at left) in longitudinalterrestrial 𝛾-ray source could be significant and should beplanes are displayed. SOURCE: NASA
investigated and quantified. While some upper
Goddard Space Flight Center Scientificatmospheric effects of lightning have direct societal
Visualization Studio.
impact, research on other effects aids in understanding
fundamental properties of gas discharges by exploring
regimes in which experimental studies are not feasible. Research in the next decade will focus onunderstanding the initiation of sprites, elves, blue jets, and terrestrial -ray flashes, their observablesignatures and chemical effects at different altitudes in the atmosphere, the observed gas-discharge
features, and their scaling relationships to other discharge forms.
SAP Crosscutting
Understanding plasma conditions common to both astrophysical and heliophysical phenomena
poses special challenges to PSE. Although the observational techniques and system dimensions candiverge substantially, the similarities in the underlying physical processes in the examples below call forcollaborative efforts to promote advances in understanding.
The origin and evolution of cosmic magnetism remain among the most important outstanding
questions of SAP science. We still cannot explain the origin of the first magnetic fields in the universe(magnetogenesis), or how magnetic fields are amplified and sustained by plasma motions (dynamo;
Figure 7.13). Observations of radiation from very distant galaxies with the upcoming SKA radiotelescope
will shed some light on cosmic magnetism, but a major emphasis should be to further theory,
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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

computation, and experiment. Most astrophysical dynamo studies use an MHD model, often further
assuming that fields grow without back-reacting on the plasma motions (the “kinematic” approximation),while dynamos affected by kinetic physics are only beginning to be explored. Similarly, although plasma
processes and instabilities that can create magnetic fields have been identified, most saturate with weak,tangled fields, and it is unclear whether such fields seeded those observed today. This major gap in basic
plasma physics theory simultaneously involves processes such as kinetic turbulence, reconnection,
particle acceleration and diffusion, anomalous viscosity and resistivity. In the next decade, progress on
cosmic magnetogenesis and dynamos will require the following:






Formulate MHD-like models that are simple enough to solve in complex, astrophysically relevantgeometries, yet detailed enough to capture the multiscale interplay between, for example, kinetic
instabilities, bulk fluid motions, reconnection, cosmic-ray diffusion, magnetic-field amplification, andself-organization.
Develop stable and accurate methods that reduce particle noise and/or computational expense in highplasma  systems, and resolve important electron kinetics without being limited by the speed of light(e.g., implicit PIC).
Increase availability of mid-range supercomputing options (10–50 M CPU-hour) for routine
computational studies involving kinetic methods.
Develop experimental studies of high- plasmas while prioritizing a program for funding new
university-level plasma experiments and dedicated timeon existing devices, accompanied by training of plasma
students. Although the high Reynolds number, high-regime is difficult to produce in the laboratory, there isa large payoff for success.

Understanding how stars cyclically generate andreverse their magnetic fields will not only shed light on ourown Sun but is profoundly important for studies ofheliospheric structure and evolution, exoplanets andhabitability in other stellar systems, and the generation ofmagnetic fields in more extreme environments. Not
understanding the origins of the solar cycle greatly reduces
our ability to predict and mitigate adverse space weather.
The outstanding questions that confront the community
include: are long-term solar cycle predictions at all possible
in such systems; if short-term predictions are viable, what is
the window of predictability; and how best to transition ourphysical insights to predictive models? Successful
resolution of these fundamental questions requires a
combination of new observations, breakthrough theoreticalconcepts, and state-of-the-art numerical simulations.
Analysis of model output can capitalize on machinelearning techniques. For example, observations over a wide
range of spatial scales of the magnetic flux balance at thesolar poles throughout an entire activity cycle, thoughtechnologically challenging, would provide much-needed
information on how much flux is carried from lower
latitudes, emerges in situ, submerges, and is produced by
local, small-scale dynamo action. Key problems that await
solutions in the next decade include:

FIGURE 7.14 Tsunamis in the solar
interior? Six snapshots of simulated
deformations of the top surface of theSun’s tachocline shown at approximately
4-day intervals, illustrating the triggeringand development of tsunami-like waves.
After reaching the mid-latitudes, thesesteep waves lift the weak (nonbuoyant)bands of toroidal magnetic flux (whitetubes) and help them erupt weeks later assunspots at the solar surface. SOURCE:
Dikpati et al. 2019, Nature Scientific
Reports.

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration








Some evidence points to the tachocline (see Figure 7.14) as an important agent in achieving magnetic
self-organization on large spatial scales, while other research indicates that stars without tachoclines
can have strong magnetic fields. What is the role of the tachocline in the dynamo process, and in
determining its cyclic nature?
Simple (e.g., kinematic) phenomenological mean-field-like dynamo models nicely reproduce theobserved evolution of surface magnetic fields over decadal timescales without turbulent induction.
Global MHD models can produce reasonably solar-like large-scale magnetic cycles with decadalpolarity reversals, powered by turbulent induction and differential rotation, but do not reproduce thewell-observed tilted bipolar pairs on the surface. How can these starkly different modelingframeworks be reconciled?
Can dynamically consistent MHD simulations of large-scale magnetic cycles produce grand minima(multiple cycles of suppressed magnetic activity)?
Which aspects of dynamo models are critically dependent on computational details such as subgrid
models?

Collisionless shocks can now be generated in the laboratory, positioning us to answer a multitudeof basic questions about these important phenomena in the next decade.






What are the dominant plasma instabilities that mediate the stagnation of the flow in collisionlessshocks, and how is the magnetic field amplified?
What is the effective ion mean free path associated with shock formation?
How is magnetic turbulence generated at the shock front and how does it decay?
What is the difference between electron and ion thermalization at the shock?
What is the injection process for particle acceleration at the shock front, and what is the efficiency?

For SAP applications, experiments capable of exploring both magnetized and relativistic shocks
must be developed. To study magnetized shocks requires large volume, high magnetic-field generators,
and large phase plates on laser facilities are needed to produce large-scale plasma flows. High-intensity
laser systems (>1022 W cm-2) are needed to create relativistic flows, and low-energy high-resolution
particle spectrometers (<500 keV electrons; <10 MeV ions) to measure the nonthermal component of theaccelerated particle spectrum. Shot opportunities in large laser facilities such as NIF are essential for
meeting these objectives. Massive multidimensional simulations of the laser-target interaction, employing
both radiation hydrodynamics and collisionless PIC approaches, are essential for generating andinterpreting collisionless shocks in SAP-relevant laboratory environments. This project would drive
fundamental understanding of collisionless shock formation and evolution, shock-associated turbulence,and charged particle acceleration.
Galactic cosmic rays, anomalous cosmic rays, and solar energetic particles are thought to beaccelerated by either diffusive shock acceleration (DSA) or some form of stochastic acceleration. Bothmechanisms depend fundamentally on turbulence, either by energetic particles generating their own
waves/fluctuations or through waves from other sources. However, heliospheric particle observations thatare inconsistent with simple DSA indicate that other physical effects must be taken into account, inparticular coherent structures (such as magnetic islands) and turbulent electric fields. A key goal for the
coming decade is to develop models of these alternative acceleration mechanisms while incorporating
numerical representations that capture new understanding of plasma turbulence under relevant conditions.
Turbulence in SAPs can be investigated observationally using ground-based observational
platforms, remote sensing spectroscopy, and in situ satellites. Radio observations provide unique insights
into the nature of the solar wind and ISM plasmas and their turbulent properties. Radio waves scatter as
they propagate through a plasma, allowing a number of plasma properties to be deduced. Observed radio
wave scattering, such as interplanetary scintillations, requires suitable background sources such as quasars
and pulsars to probe the foreground medium of interest. The number and sensitivity of available radio
telescopes (e.g., The Jansky Very Large Array (VLA), Very Long Baseline Array (VLBA), Ooty Radio
Telescope) are limited. Hence, the number and angular density of such sources that are effective probes of
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the solar wind and ISM is not optimal, nor is the distribution of interferometric baselines needed tomeasure turbulent properties of the medium or its velocity. Recommended observational solutions are
discussed in chapter 7.
The exciting new frontier of exoplanetary discovery and the quest for life elsewhere in theuniverse will continue to advance through observations by new missions and ground-based observatories
and innovative computational studies. Broader observational scope and deeper physical understanding areprimary goals for the next decade. Because transit observations preferentially select those planets that areclose to their stars, the focus to date has largely been on exoplanets whose “Goldilocks” zones are very
close to M stars. Late-type M stars are magnetically active, with starspots 10 times larger than sunspots.
That and the close proximity of exoplanets to M stars suggests they experience severe space weather as
they orbit the outer stellar corona. Energy and radiative input to their atmospheres can be immense,
particularly in EUV and X-ray wavelengths, and frequent stellar eruptions can produce a lethal mix ofenergetic particles, high-energy photons, and magnetic interactions with the planet’s magnetic field (if it
has one). Moreover, it remains unclear whether planetary magnetic fields mainly shield planets fromradiation and direct stripping of the atmosphere or function more like sails, enlarging the planetary crosssection to collect and funnel more stellar-wind energy into the atmosphere. Cross-disciplinary studies
have proved highly successful, and should be continued in the next decade. Future studies of stellar
eruptions will estimate the plasma and radiation environments of other Earth-like planets orbiting solarlike stars by using data-based MHD models of evolving solar-like stars and their plasma astrospheres,
based on observations by missions such as NASA’s Transiting Exoplanets Survey Satellite, the Hubble
Space Telescope, XMM-Newton, and the upcoming James Webb Space Telescope (JWST). Data-mining
and ML techniques will enable efficient extraction of the key structures and properties from the resulting
simulation-generated datasets.
PSE and SAP Crosscutting
Multiscale coupling is common to SAPs as well as laboratory plasmas. Bridging the gap between
kinetic- and global-scale phenomena has been a long-standing obstacle to advancing our understanding of
the energetics and dynamics of activity on the Sun, in planetary magnetospheres and ionospheres, theinterplanetary medium, in active galactic nuclei, within accretion disks, and other cosmic plasmas. A
primary approach for addressing this problem is numerical simulation, which requires taking fulladvantage of innovative developments in hardware, algorithms, visualization, and data analysis tools fromacross the PSE community as well as computational physics.
To capitalize on the great progress and ongoing momentum in understanding reconnection in
SAPs, a coordinated program of observations, theory, numerical simulations, and laboratory experiments
need to be employed. Many key topics are ripe for breakthroughs—multiscale coupling, 3D geometries,
energy conversion and partitioning, onset, partial ionization effects, interplay with ideal instabilities,
reconnection in relativistic extreme environments, and connections with turbulence and shocks. DedicatedDOE, NASA, and NSF programs are needed that support the development of next-generation analyticaland numerical models and the application of new numerical technology and theoretical understanding tothese reconnection challenges. Computational advances require fluid, kinetic, and hybrid models, andmulti-fluid models that include kinetic effects through physics-based closure equations. Exascalecomputing will enable us to finally address these questions in fully 3D systems with increasingly realistic
plasma parameters. Over the next decade, unprecedented remote-sensing observations from missions suchas SDO, IRIS, and Fermi, as well as exquisite in-situ data from missions such as MMS, PSP, Solar
Orbiter, and BepiColombo, will deliver a wealth of critical new insights on magnetic reconnection. An
encouraging development is the new NSF/NASA collaborative program, Next Generation Software for
Data-driven Models of Space Weather with Quantified Uncertainties (SWQU).
Turbulent cascades culminate at the dissipation scale through kinetic processes that are poorly
understood. The physics of dissipation is a fundamental PSE problem, since it involves the irreversible
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conversion of collective fluid or kinetic-scale motions into internal energy, or “heating.” Complicating
matters further, intermittency in turbulence can connect dynamically coherent structures (e.g., current
sheets), patchy dissipation, and the entire inertial range of turbulence. Because the dissipation scale isgenerally well below the resolution limit of both observations and numerical simulations, one can onlyinfer its properties in heliophysical and astrophysical objects. For example, the solar corona and windclearly are heated well above the photospheric temperature, but the manner in which the Sun’s magnetic
energy is transformed into heat is an open question. Similarly, the cores of galaxy clusters exhibit far lessstar formation than expected, indicating the presence of an additional heating source that remains amystery. This major problem in SAPs and laboratory plasmas encompasses turbulence scales that range
from fluid to kinetic. Understanding and relating such disparate scales is a challenge for the next decade.
Finite computing resources usually make it difficult to capture the turbulent cascade all the way
down to the dissipation scale when simulating high Reynolds number, multiscale turbulent plasmas.
Subgrid models bypass this difficulty by parametrizing dissipation at the smallest scales that can be stably
resolved on the computational grid, which introduces artificially enhanced dissipation of small-scale
structures. When modeling solar/stellar MHD convection, the challenge is to ensure that larger scales
remain unaffected by the subgrid model. Therefore, the choice of a subgrid model can strongly influence
global characteristics of large-scale dynamo solutions. MHD dynamo simulations with the same code butwith different subgrid models have indeed demonstrated that the resulting magnetic self-organizationdiffers substantially. Choosing the appropriate subgrid model is a difficult decision for simulating otherturbulent plasmas in their large-scale environments, including the solar wind, astrophysical jets, and theICM. Consequently, progress in this area will benefit a wide range of SAP investigations.
New facilities investigating the “warm Universe”, such as the Stratospheric Observatory for
Infrared Astronomy, Atacama Large Millimeter Array, and the upcoming JWST, will study specificplasma environments with low ionization fractions, complicated chemistry, and complex molecularradicals. These observations probe important plasma-physical and chemical processes that lead to theformation of dust and organic molecules. Observations of kilonova emission after neutron-star mergers
indicates the presence of plasma dominated by the low ionization stages of heavy elements (lanthanides
and actinides). Studies of thermodynamic and radiative properties of such plasmas requires highresolution spectral information that comes from atomic, molecular, and optical (AMO) theoretical andexperimental methods. Collaboration with AMO and low temperature plasma researchers is vital for
future progress in this area of SAP physics.
Atomic and molecular opacities are critical for understanding many cosmic phenomena, including
the internal structure and evolution of stars, stellar and planetary atmospheres, pulsating stars, and thelight curves arising from supernovae. Although the complexity of the problem makes accurate
calculations daunting, the advancement of high-performance computing of atomic and molecular data hasgenerated a large amount of more accurate and complete opacity data. Extensive international efforts havecalculated massive databases of opacities for plasmas in LTE, but non-LTE opacity data are still sparse.
Theoretical opacities can only be validated by comparison with estimates derived from observations of
the solar interior, stellar pulsations, and atmospheric spectra of stars and planets, with experimental
neutrino-flux measurements, and with predictions from 3D hydrodynamics simulations. Achieving stellarinterior conditions in the laboratory is very difficult. Only very recently have laboratory experiments beenable to reproduce plasma conditions in the solar convective envelope and approaching the radiative zone.
Dedicated DOE and NSF programs are urgently sought to support the next-generation
experimental facilities and diagnostic instrumentation in concert with SAP observations. Spectroscopic
diagnostics remain a critical element for determining the physical conditions in SAPs. Models of opticallythin radiation (e.g., CHIANTI for calculating spectra from astrophysical plasmas) rely heavily on atomic
cross-sections, ionization/recombination rates, electron excitation rates, and radiative decay rates
calculated theoretically and validated against laboratory data. Besides CHIANTI, the Atomic Data andAnalysis Structure (ADAS) is an interconnected set of computer codes and data collections for modelling
the radiative properties of ions and atoms in SAPs, laboratory fusion devices, and technological plasmas.
CHIANTI and ADAS are currently the only major resources that are used for space and astrophysical
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applications. Although many current SAP investigations involve atomic and spectral data for very heavy
elements, available databases lack essential data on these elements. Moreover, existing codes are unable
to calculate these data, and there has been insufficient funding for new or updated code development. The
benchmarking of atomic data models requires new, high-resolution laboratory spectrometers in the UV
and X-ray wavelength regions. Furthermore, adequate funding for maintaining and updating production
codes and databases, and the workforce for atomic physics calculations, is critically needed.
INFRASTRUCTURE
Research into space and astrophysical plasmas is supported by multiple funding sources, withdifferent requirements, constituents, and goals. Although this situation provides many opportunities andfosters cross-disciplinary studies, it also leaves some crucial areas of SAP science without reliablesupport. One prominent example is laboratory experiments that approach or reproduce scaled-down
versions of plasma conditions in cosmic phenomena. Most facilities capable of performing theseexperiments are supported by agencies whose missions are not SAPs, while the agencies supporting spaceresearch are unlikely or unable to invest the substantial resources that would enable such experiments.
Similarly, theory and computation are not well supported in proportion to their importance in designingand utilizing instruments, missions, and observatories. Large disparities exist in this regard between the
different parts of PSE, and advances in one sector are not always available to others. Targeted costsharing interagency programs would benefit both SAP and basic plasma research (e.g., the recent
NSF/NASA SWQU), potentially revealing new paths toward the goals of national security, energy
independence, and comprehending the universe.
The range of important plasma processes and physical regimes encompassed by the Sun (andother stars) makes it an ideal laboratory for plasma investigations. Similarly, the deep understanding andpowerful numerical techniques developed by the basic plasma research community need to be absorbed
and applied by SAP researchers. Solar and plasma science have a long history of beneficial exchanges,
yet the current level of interaction is not optimal. Focused research programs that target solar phenomena
from a plasma-science perspective would enhance cross-fertilization, with joint funding from all
stakeholders including NASA. A successful model to emulate is NASA’s Living with a Star (LWS)
Focused Science Team program, which attacks community-proposed heliophysics problems byassembling teams of small groups that each address some aspect of the problems. Teams that include
members from both plasma and solar research communities would ensure effective cross-disciplinary andproductive joint research and communication.
Space weather research extends from basic science to operational forecasting. Because different
sponsors focus on different aspects of space weather, it is difficult to apply the systems approach needed
to make progress on key questions. Recently, a national space weather plan has been formulated thatinvolves all agencies whose purview includes space weather. New opportunities for basic and applied
space weather research are being created in partnership with the scientific and end-user communities.
This encouraging development should continue with substantial buy-in from all sponsors, with particularemphasis on establishing long-term, stable funding to tackle the most complex problems and to validate
and transition the most robust, accurate models to operational use. The NSF/NASA SWQU is an
important first step in this direction.
CONNECTION WITH TECHNOLOGY
Better understanding of space weather effects will drive technology development in several
directions. Improving the electric power grid to protect against space weather extremes is alreadyunderway, and further improvements should be made to prevent massive shut-downs, reduce damage totransformers and other vulnerable equipment, and ensure that repairs or replacements are timely. To
predict the impact of space weather events on specific satellites throughout their orbits, models of
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spacecraft charging and other adverse effects on our assets in space should be linked to models of thespace environment. The exploding population of spacecraft and debris in Earth orbit makes it imperative
to characterize atmospheric drag as accurately as possible, to better predict satellite lifetimes, avoid
collisions, and estimate fuel requirements. Current models are inadequate for calculating changes in dragdue to external forcing by solar-wind CIRs, CMEs, and flare radiation, and generally predict timeaveraged conditions in specific orbits rather than instantaneous local conditions throughout geospace.
The sustainability and viability of Earth-based SAP observations are threatened by theunprecedented launch of massive constellations of hundreds to thousands of commercial communicationand internet-providing satellites. The electromagnetic emissions of these satellites are encroaching on
frequencies that are essential to SAP observations. The ubiquitous presence of the satellites is alreadyinterfering with optical observations. To date, there has been little discussion of how SAP research andmassive satellite-based commercial ventures can co-exist. The penalty for not engaging in discussions andestablishing boundaries and processes will be severe limitations on our ability to observe SAPs in future.
FUTURE CHALLENGES AND OPPORTUNITIES: FACILITIES/MISSIONS
Facilities
NSF’s Daniel K. Inouye Solar Telescope (DKIST) will be the largest solar telescope in the world,able to view features on the Sun as small as 70 km across. Using adaptive optics technology, DKIST’s
4.2-m primary mirror and five major instruments will provide the sharpest views ever taken of the solar
surface, with the spatial, temporal, and spectral resolution and dynamic range needed to measureelemental magnetic structures at and above the photosphere. When DKIST is fully operational, there will
be unprecedented data revealing the roles played by magnetic fields and the embedding plasma ingenerating and transporting solar activity. DKIST is ideally suited to studying the transfer of energy fromthe solar interior to the outer atmosphere, particularly the partially ionized, high-to-low  chromosphereand its magnetic connection to the hot, fully ionized corona. In combination with space missions such as
SDO, IRIS, PSP, and Solar Orbiter, DKIST will be a powerful tool for characterizing the Sun’smagnetized plasma properties and the physical processes behind coronal heating and eruptive activity.
First solar light will be in late 2020. The committee encourages the DKIST team to enable open access to
DKIST observations to the greatest possible extent, consistent with U.S. space data practices.
Radio frequency observations have probed the solar wind and the ISM for many years, revealing
key properties of turbulence, coherent structures, and waves. However, the lack of a ground-based radio
interferometer with the appropriate combination of sensitivity, frequency coverage, and angular resolution
has been a barrier to exploiting these phenomena more effectively. NSF’s next-generation Very Large
Array (ngVLA) will permit pioneering studies of the solar wind and ISM, measuring the solar-windspatial spectrum from tens of meters to 1,000 km. Intensity scintillation tomography will map fast- andslow-wind velocity fields and their fluctuations in the critical corona-inner heliosphere transition,complementing direct sampling by PSP. Faraday rotation and dispersion-measure observations ofpolarized background sources and pulsars can reveal the overall density structure and magnetic field of
the outer corona and inner heliosphere. By making global measurements of the solar wind properties,
turbulence, and transients with radio propagation diagnostics, the ngVLA would be highly
complementary to in-situ measurements made by proposed next-generation heliospheric missions such as
Helioswarm. For the ISM, the ngVLA will characterize interstellar turbulence, with the same instrument
using the same technique (angular broadening), over a wider spectral range than ever before.
Nonetheless, to expand the renaissance that solar radio astronomy has undergone in the past
decade, significant observational advances are required. High-cadence microwave imaging, as currently
obtained by EOVSA and the JVLA, probes coronal reconnection sites, regions where high-energy
electrons are accelerated and propagate, and the elemental structure of the quiet chromosphere. While the
JVLA and EOVSA have served as platforms for developing, testing, and demonstrating the potential of
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broadband imaging spectropolarimetry at radio wavelengths, there is still a need for a high-performance,solar-dedicated radioheliograph designed to fully mine the rich information content of solar radio
emission. The high-level requirements for such observations are: extremely broad, continuous coverage
from 50 MHz to 20 GHz with high spectral resolution, time resolution as short as 10 ms, full polarimetry,full-disk microwave imaging, a field of view out to several solar radii at lower frequencies, and wide
dynamic range (~104). These requirements are met by the Frequency Agile Solar Radiotelescope (FASR),
a next-generation radioheliograph recommended as a priority by previous Astronomy and Astrophysics
and Heliophysics Decadal Surveys. FASR is a low-cost, low-risk, and high-reward facility that would
play a unique and productive role in serving the wider solar community.
Although the case for more extensive laboratory experiments and development programs related
to SAP science is made forcefully in most decadal studies, little progress has resulted. LMAP, theheliophysics laboratory program recommended in the 2014 Heliophysics Decadal Survey, has not yet
been implemented by NASA. A related but very modestly funded program, the Heliophysics Technology
and Instrument Development for Science, includes some laboratory plasma studies of chemical,
spectroscopic, and nuclear measurements supporting observations and models. U.S. federal laboratories
managed by DoD and DOE could be excellent resources for the SAP community, which lacks access tothese capabilities. In return, the laboratories gain expertise in previously underexplored plasma regimes
and opportunities to compare laboratory results with cosmic plasmas. For example, major laboratory
facilities such as UCLA’s LAPD and NRL’s SPSC currently offer limited but vital opportunities for SAPrelated experiments. A comprehensive program that facilitates coordinated experiments between federal
laboratories and the SAP community should be developed and implemented across NASA, NSF, DOE,
and DoD.
Missions
New missions offer great opportunities for discovery SAP science. Solar Orbiter, a European
Space Agency mission with some U.S.-built components, was launched on 10 February 2020. Its primaryscience goals are to perform close-up, high-resolution studies of the Sun and its inner heliosphere, while
orbiting at 0.3-0.9 AU from the Sun. The combination of Solar Orbiter and Parker Solar Probe will
provide unprecedented opportunities to investigate multiscale phenomena in the corona and solar windfrom separate vantage points, through complementary in-situ and remote-sensing observations. Solar
Orbiter will address the following fundamental questions:How and where do the solar wind plasma and magnetic field originate in the corona?
How does solar activity drive heliospheric variability?
How do solar eruptions produce energetic particles that traverse the heliosphere?
What drives the solar dynamo and its connections between the Sun and the heliosphere?

The Ionospheric Connection Explorer (ICON) will investigate the connections between theneutral atmosphere and ionosphere, with three instruments that measure temperature, velocity, andcomposition of gases far from the spacecraft and a pair of identical in-situ instruments that characterize
the plasma around the spacecraft. Its local measurements will complement the global imaging obtained by
GOLD. ICON will determine, for the first time, how dynamic terrestrial weather events, such as cyclones
and El Niño, affect the ionosphere. ICON was launched on 9 October 2019, and is currently in its
commissioning phase.
Geospace Dynamics Constellation (GDC) is an ambitious space-mission concept recommended
by the 2013 Heliophysics Decadal Survey for implementation as the next NASA Heliophysics LWS
mission, which is currently undergoing an implementation study in preparation for the Announcement ofOpportunity. GDC will address crucial questions pertaining to the dynamic processes active in Earth’s
upper atmosphere; their local, regional, and global structure; and their role in driving and modifying
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magnetospheric activity. GDC will be the first mission to address these questions on a global scale with aconstellation of spacecraft that permit simultaneous multi-point observations of a critically undersampled
region of the ionosphere and thermosphere. This investigation is central to understanding the basic
physics and chemistry of the upper atmosphere and its interaction with Earth’s magnetosphere, and will
provide insights into space weather processes throughout geospace. According to the recent Science andTechnology Definition Report for GDC, the primary goals are to understand:

how the high-latitude ionosphere-thermosphere (IT) system responds to variable solar wind/magnetosphere forcing; andhow internal processes in the IT system redistribute mass, momentum, and energy.

Because spatial scales are vast and energetic-particle kinetics and charge exchange areparticularly important, no current models comprehensively describe the heliospheric system fully.
Physical understanding is hampered by the very limited set of observations. To remedy this gap, theInterstellar Mapping and Acceleration Probe (IMAP), an integrated and coordinated suite of 10
instruments, was selected last year by NASA for launch in 2024. IMAP addresses two critical problems in
SAP physics: the acceleration of energetic particles in interplanetary space and the interaction of the solar
wind with the local interstellar medium. IMAP’s science objectives are to:

improve understanding of the composition and properties of the LISM;
advance understanding of the temporal and spatial evolution of the dynamic boundary between thesolar wind and the ISM;
identify and advance understanding of processes governing the interactions between the magnetic
field of the Sun and the LISM; andidentify and advance understanding of particle injection and acceleration processes near the Sun, inthe distant heliosphere, and in the heliosheath.

The HelioSwarm mission concept is a constellation of small spacecraft with a wide range ofspatial separations that would simultaneously sample key physical parameters in the turbulent solar wind.
By measuring properties that relate directly to the cascade of energy across scales to where energy is
dissipated, and into different physical regions, a constellation mission in the solar wind will enable directtests of current conflicting models for the spectral and spatial distributions of turbulent power, thusincreasing our understanding of turbulent SAPs.
An Interstellar Probe was one of the top-10 priorities recommended as new imperatives forNASA by the 2013 Heliophysics Decadal Survey. A NASA-funded study for a “Pragmatic Interstellar
Probe” showed that speeds at least three times that of Voyager 1 were possible using available/near-term
technology, enabling the Probe to reach the pristine LISM within 50 years. An augmented Interstellar
Probe would address not only plasma physics of the heliosphere but also fundamental planetary scienceand astrophysics, as outlined by the following science goals:Understand our heliosphere as a habitable astrosphere.
Investigate the plasma physical processes and global nature of the outer heliosphere, the boundary
regions, the VLISM and beyond to the pristine LISM.
Understand the evolutionary history of the solar system. Explore dwarf planets and Kuiper Belt
Objects through flybys observing atmospheric and surface properties. Determine the large-scale
distribution of the circumsolar debris disk.
Open the observational window to early galaxy and stellar formation. Measure the integrated diffuse
extragalactic background light from redshifted stars and galaxies dating back to ~200 million years
after the Big Bang.

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The primary missions of the recently launched Spectrum-Roentgen-Gamma (Spekrt-RG)
spacecraft are to find and map all massive galaxy clusters in the observable universe at X-ray
wavelengths, and to search for other cosmic X-ray sources, including active galactic nuclei, star formation
regions, and stellar activity. Several astrophysical satellites that probe hot cosmic plasmas with highenergy emissions are planned: for example, the Athena X-ray observatory, the Hard X-ray Modulation
Telescope, the Imaging X-ray Polarimetry Explorer, and the X-ray Imaging and Spectroscopy Mission. In
parallel, radio and millimeter-wavelength observatories that probe nonthermal emission from relativistic
magnetized cosmic plasmas have been recently updated, are developing new capabilities (e.g.,interferometric observations by the Event Horizon Telescope of the plasma orbiting the M87
supermassive BH; Figure 7.2), or are in the final design stages (e.g., the upcoming multinational SKA
radiotelescope scheduled for completion in 2025). These technological advances will ensure a flow of
new discoveries and new physical insights from a wide range of astrophysical plasma environments.
INTERNATIONAL
Comparison of International PSE Community to United States
Active non-U.S. SAP research programs exist throughout the world, with the largest groups foundin China, India, Russia, several European countries, the UK, and Japan. Scientists everywhere havebenefitted from NASA’s open data policy, utilizing observations from heliophysics and astrophysics
missions. The Japan Aerospace Exploration Agency (JAXA) and European Space Agency (ESA)
missions are less generous with their data, in general, although joint missions with NASA typically adopt
NASA’s policies. Data from ground-based facilities such as the Nobeyama Radio Observatory (Japan),the Nançay Radio Observatory (France), and the Low Frequency Array (LOFAR; Netherlands and other
European countries) can be obtained by submitting observing proposals or contacting observatory staff.
Some major plasma physics programs that emphasize SAP simulations and/or data analysis are located at
Katholieke Universiteit (KU) Leuven (Belgium), Max Planck Institute (Germany), Nanjing University(China), Kyoto University (Japan), Indian Institute for Astrophysics and the Physical ResearchLaboratory (India), University of St. Andrews and the Imperial College London (UK), the University ofParis/Meudon Observatory (France), and the Space Research Institute (Russia). Anecdotal evidence
suggests that SAP programs at non-U.S. academic institutions are attracting more students than U.S.
institutions, and that faculty positions at these international institutions are more plentiful than in the
United States. China in particular has sent many graduate students and postdoctoral associates to study atinternational universities and laboratories, and has expanded the number of SAP faculty positions
substantially in the past decade.
Since 2010 the number of countries launching/developing SAP space missions and building orplanning new ground-based facilities has grown. India is preparing to launch Aditya-L1 in 2020, a
mission that will observe the Sun's photosphere (soft and hard X-ray), chromosphere (UV) and corona(visible and near-infrared light); study the solar particle flux, reach the L1 orbit, and measure magnetic
field strength variation around L1. SMILE, a Chinese/ESA collaborative mission under development, willobserve the global structure of Earth’s magnetosphere in soft X-rays. Solar C is planned as a successor to
Hinode by JAXA in collaboration with ESA and NASA. This mission will focus on high-resolution VUVspectroscopy and multichannel EUV solar imaging from the chromosphere to the corona. As noted above,
the Russian Space Agency, in collaboration with the Max Planck Institute for Extraterrestrial Physics inGermany, launched the Spektr-RG high-energy astrophysics space observatory to galaxy clusters andactive galactic nuclei.
As a result of these international activities, the United States is beginning to lose its leadership in
SAP studies, missions, and facilities. Other nations, such as China and India, are prioritizing science to adegree far above that in the United States. The reasons are multifaceted. The United States is building andlaunching spacecraft with SAP payloads too infrequently, training too few U.S. students, especially in
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instrumentation and computation; and placing increasing barriers to retaining foreign nationals at U.S.
institutions (particularly government facilities). Current policies make it difficult for the United States toattract and retain excellent scientists from other countries. In addition, the increasing cost of large
missions needed for breakthrough science are not easily affordable for a single national space agency
without affecting adversely other essential programs. Resolving the dilemma of maintaining leadershipwhile expanding international collaborations is a difficult but crucial task facing the PSE community andits sponsors. The findings and recommendations summarized in Chapter 7 point to some solutions.
Importance of United States to Current Collaborations
SAP research relies heavily on international collaborations, particularly in the era of open data
policies for space missions. The United States has led the way in opening access to NASA mission data.
Most space agencies in other nations have not yet fully adopted the same approach. The growth of
publicly accessible virtual observatories, software repositories, broadly accepted data standards, and othercommunity-based resources has enabled researchers worldwide to download and analyze multiwavelength and multi-messenger observations more easily than ever before. Ground-based networks also
are essential for global coverage of geospace and solar phenomena, as well as long-baseline
interferometry.
These necessary and desired international collaborations can be difficult to establish andmaintain. Most successful international programs have been enabled by professional organizations suchas the United Nations, the International Council of Scientific Unions, and the International Astronomical
Union, often without commensurate funding. One recent example is the International Space Weather
Action Teams (ISWAT) program managed by the Committee on Space Research, a grassroots effort thathas brought together self-funded working groups to tackle key problems in all facets of space weather
science. Among other international programs, NSF provides opportunities for researchers with active NSF
awards to apply for supplemental funding for research visits to collaborate with PIs funded through theEuropean Research Council. In addition, establishing an internationally accessible environment forcollaborative model development would accelerate building essential tools for SAP research. Greater
participation and financial support by U.S. agencies, and collaborations with their foreign counterparts,
would enable more rapid advances in understanding all aspects of space and astrophysical plasmas, andlead to crucial societal benefits.
Space technology exchanges are often restricted by U.S. International Traffic in Arms Regulation(ITAR) based on technology transfer with potential defense-related applications. Given the international
advances that have already been independently made, ITAR restrictions on exchange of SAP data mayneed to be revisited to ensure that these are limiting exchange of non-sensitive data.
FINDINGS AND RECOMMENDATIONS
NASA funding for plasma-related research comes largely from its ability to support missions. Basic codeand simulation development, theory, and novel data-analysis techniques vital to science missions are
infrequently supported by NASA. New initiatives (e.g., DRIVE Science Centers) typically fund a few
large research programs, while the smaller grants are too small and short-term to enable thesecomputational developments.
Finding: A lack of support for basic code and simulation development, theory, and novel dataanalysis techniques has long been a barrier to advancing our understanding of SAPs andpredictive capabilities.

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In addition, the growing trend toward open-source requirements would impose an unfunded mandate on
developers to make their codes publicly available and user friendly, and does not provide for user support.
Coordinated multi-agency and multidisciplinary funding for development of theory, plasma codes with
open source versions, numerical algorithms, and new data-analysis tools (e.g., machine learning) would
maximize scientific return from current and future heliophysics and astrophysics observations andsimulations.
Finding: Unfortunately, the level of funding for the highly successful NSF/DOE Partnership in
Basic Plasma Science and Engineering has lagged that recommended by the 2000 Plasma
Decadal Review, despite its very central role in discovery plasma science and its capacity tocreate effective multidisciplinary bridges within plasma science.
The recent NSF/NASA Next Generation Software for Data-driven Models of Space Weather with
Quantified Uncertainties is an example of a focused SAP-oriented collaboration.
Recommendation: NASA should join the NSF/DOE Partnership in Basic Plasma Scienceand Engineering to expand interdisciplinary basic plasma research that would benefit SAP.
This expanded partnership would leverage strategic contributions from each agency toenable breakthrough progress that benefits a wide range of PSE activities (see Table 1, #3#5).
The contributions of NSF and DOE to the partnership are approximately $4 million to $5 million per year
per agency. NASA joining the partnership with an equivalent contribution by NASA’s Science Mission
Directorate without impacting other programs would significantly increase its scientific impact.
Finding: Solar, heliospheric, magnetospheric, and ionospheric physics, and astrophysics haveuntapped synergies with laboratory plasma experiments, with the common goal of understanding
ambient plasma conditions and chemistry.
SAP examples include ionospheric studies with incoherent scattering radar, chemistry in giant molecular
clouds in the interstellar medium, chromospheric and coronal plasmas, and the very local interstellar
medium. Such laboratory SAP experiments are typically not supported by NASA whereas those agencies
that have the capability to perform such experiments do not necessarily address the most critical SAP
topics.
Finding: Strategic funding from NASA and agencies supporting experimental facilities would
enable more ambitious, innovative joint projects than a single source could support.
A successful model to emulate is NASA’s Living with a Star Focused Science Team program, whichinvestigates major heliophysics questions by assembling teams of small groups that each address selected
aspects of the science.
Recommendation: NASA and NSF should lead an effort with DoD (especially ONR and
AFOSR), DOE, and other stake-holders (see Table 1, #6 and #24) should develop a
collaborative program that enables SAP scientists to collaborate with laboratory plasma
experimentalists and advance both fields by leveraging their different needs and knowledge
bases.
As noted by the 2016 National Academies report Achieving Science with CubeSats, CubeSats andsmallsats offer novel and transformational opportunities to explore geospace and the heliosphere with
unprecedented spatial and temporal coverage, as needed to resolve fundamental plasma physics problems
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requiring multipoint observations—for example, solar wind turbulence and magnetosphere-ionosphere
coupling.
Finding: Clusters of CubeSats and smallsats carrying in-situ and remote-sensing instruments are
the best observing platforms for tackling many basic unsolved questions of multiscale SAPs (e.g.,reconnection, turbulence, and shocks), and provide essential research and training opportunities
for university faculty and students.
Finding: Existing procedures for developing, building, and operating missions are traditionally
geared toward large missions, and can pose unnecessary obstacles for single spacecraft and multiplatform missions employing smallsats and CubeSats.
NSF initiated the CubeSat program, which has become an important gateway for students intoexperimental heliophysics and astrophysics. NASA currently provides CubeSat launches for NSF and will
launch 10 NSF CubeSats in the future. The committee lauds this level of collaboration in a program that
effectively combines workforce development and exciting plasma research.
Recommendation: With NASA and NSF as lead agencies, NASA, NSF, and DoD, as theprimary sources of space missions, should explore avenues, including rideshares,
international partners, and partnering with commercial launch providers, for reducing
costs, lowering barriers, enabling higher-risk missions, and boosting launch opportunities
for these pioneering investigations using Cubesats, smallsats and cluster of these satellites.
(see Table 1, #7).
Finding: NSF, despite having a limited investment level in their Cubesat program, has broad
access to universities and undergraduate and graduate students. This access may be important inproviding basic training in PSE relevant to CubeSats. The recent solicitation for a cross-cutting
NSF Ideas Lab Program focused on CubeSat innovations to push the envelope of space-based
research capabilities is an example of one approach.
Recommendation: In view of their limited level of investment, NSF should identify a clearerrole and “identity” in their CubeSat program that distinguishes it from its NASAcounterpart. To ensure cost and resource efficiencies, NSF and NASA should coordinate
further on funding opportunities.
Finding: Increased support is needed to meet the challenge of designing and constructing
compact plasma and remote-sensing instrumentation suitable for Cubesats and smallsats.
Recommendation: Current NASA programs such as H-FORT, H-TIDES, and the IDP(Instrument Development Program) should be augmented to meet the growing demand forcompact plasma and remote-sensing instrumentation suitable for Cubesats and smallsats.
SAP research, as in other STEM fields, is an international endeavor that often requires efforts and funding
greater than any one country can support. Open data policies maximize scientific progress by expanding
international community access to SAP plasma data, which is especially important for multiwavelength/multi-messenger data sets.
Finding: The SAP community needs to agree on data standards, formatting, and processing
levels for publicly available data.

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Recommendation: Federal agencies that support ground-based and international spacefacilities (NSF, NASA, DoD, NOAA) should adopt similar open data policies and minimize
barriers to international collaboration except where national security is of concern.
Recommendation: NSF should convene a workshop co-sponsored by NASA and DoD tomake recommendations for how to establish and maintain open data policies.
Recommendation: Once established, maintaining and updating the open data standards
should be the responsibility of governing federal organization such as one of the major
contributors (NASA, DoD, NOAA) or a more specialized agency for standards such as
NIST.
Hiring plasma-knowledgeable scientists within universities, national laboratories, and other institutions is
critical to the long-term health of SAP and the development of the future STEM workforce. Traditionally,
university physics and astronomy departments have rarely hired faculty in plasma heliophysics andplasma astrophysics, despite the highly interdisciplinary and fundamental nature of the discipline. The
existing NSF program that supports the hiring of space and solar physicists, in partnership with university
departments, has been quite successful, sponsoring one hire every few years.
Finding: A faculty partnership program introduced by NASA, NSF, and DOE—similar
to that presented in the Finding and Recommendation section of Chapter 1 (see Table1.1)—is needed to strengthen SAP hiring in universities and federal research facilities.

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Appendixes

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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

A
Statement of Task
As part of the Physics 2020 decadal assessment and outlook for physics, the National Academiesof Sciences, Engineering, and Medicine will conduct a study of the past progress and future promise ofplasma science and technology and provide recommendations to balance the objectives of the field in asustainable and healthy manner over the long term. Specifically, the study committee will:
1.

2.
3.
4.
5.
6.
7.
8.
9.

Engage stakeholders in government, the plasma sciences communities, and industry tocollect perspectives on the major achievements and challenges of the past decade and themost exciting and promising areas of plasma research anticipated for the next 10 years, aswell as how plasma research impacts and is impacted by adjacent areas of science andtechnology.
Assess the progress and achievements of plasma science over the past decade.
Identify and articulate the major scientific questions and new opportunities that define
plasma science as a discipline, noting connections to and the influence on otherdisciplines.
Discuss the nature and importance of the U.S. role in multi-national plasma research
activities.
Assess the scope of international research across the breadth of plasma science anddiscuss the relative standing of U.S. activities.
Discuss how plasma science has contributed and will likely contribute to U.S. national
needs both in and beyond plasma science, including workforce development, economic
prosperity, national defense, and other applications.
Assess whether the present plasma science workforce and training opportunities arecommensurate with future workforce needs.
Assess and comment on the present role of, and future opportunities for, universities
within large national programs organized around major research instruments orcommunity assets (i.e., user facilities, satellites, telescopes, etc.).
Assess whether the structure, program balance, and level of the current U.S. research
effort in plasma science across the federal and private efforts are best positioned torealize the science opportunities.

The study committee’s recommendations should not alter recommendations from the Decadal
Strategy for Solar and Space Physics, the mid-decadal assessment of that report, or the ongoing study on
Strategic Plan for U.S. Burning Plasma Research. The committee may make recommendations or offer
comments on organizational structure, program balance, and funding, as appropriate, with discussion of
the evidentiary bases.

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B
Findings and Recommendations

The committee offers the following findings and recommendations on the scientific front ofplasma physics and on government support for plasma science. The committee supports each
recommendation with a set of findings that the committee has made during the course of this study. These
recommendations can be taken to strengthen our responses to specific grand challenges and to broadly
advance the entire scientific frontier of plasma science.
CHAPTER 1 RECOMMENDATIONS
Stewardship and Advancement of Interdisciplinary Research
Finding: Plasma science and engineering (PSE) is inherently an interdisciplinary field of research. Whilethe underlying science has common intellectual threads, the community is organized into sometimes
isolated sub-disciplines.
Finding: What may be narrowly perceived as duplication is actually critically necessary collaboration inorder needed to address the complex science challenges in PSE while rapidly translating results tosociety-benefiting outcomes.
Finding: Institutional barriers between sub-disciplines of PSE make mutually advantageous interactionsdifficult, yet interactions between sub-disciplines have led to important advances that would have beendifficult to produce otherwise and should be encouraged.
Finding: A more unified voice for the field would create opportunities for interdisciplinary andtranslational research, and initiate activities that exploit synergies among different subdisciplines of PSE.
Recommendation: Federal agencies directly supporting plasma science and engineering (PSE) andthose federal agencies benefiting (or potentially benefiting) from PSE should better coordinate theiractivities. This coordination, which extending into offices and directorates within larger federal
agencies, would provide a more unified voice for the field, and create opportunities forinterdisciplinary and translational research, and initiate activities that exploit synergies among
different subdisciplines of PSE.
Finding: Fundamental research in PSE can and does rapidly translate to the development of societally
relevant technologies, the benefits of which cut across the missions of many federal agencies.
Finding: The interdisciplinary and multidisciplinary strengths of PSE are not being fully utilized. Thissituation is to the detriment of the fundamental plasma research and to the detriment of the intended
applications.
Finding: Interagency (and inter-program) initiatives would fully exploit the interdisciplinary andmultidisciplinary potential of plasma science and engineering (PSE) in both fundamental and translational
research if properly stewarded.
Recommendation: Federal agencies and programs within federal agencies that are separately
focused on fundamental plasma research, and those that are focused on science and technologies

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Plasma Science: Enabling Technology, Sustainability, Security, and Explorationthat utilize plasmas, should jointly coordinate and support initiatives with new funding
opportunities.
Finding: The potential is enormous for PSE to contribute to one of society’s greatest challenges—
sustainability. The contributions that PSE could make extend from fusion-based, carbon-free electrical
power generation to electrification of the chemical industry.
Finding: The translational nature of fundamental research in plasma science and engineering (PSE) needs
to be formally recognized at NSF.
Recommendation: The Engineering Directorate (EngD) of the National Science Foundation (NSF)
should, as a minimum, consistently list PSE in descriptions of its relevant programs andconsistently participate in the NSF/Department of Energy (DOE) Plasma partnership.
Recommendation: More strategically, NSF should establish a plasma-focused program in theEngineering Directorate. that would advance engineering priorities across the board, including
advance agricultural systems, energy and environment, chemical transformation, advanced
manufacturing, electronics and quantum systems.
Finding: Public-private partnerships (PPP) have long been a benefit to PSE, largely in the form of SBIR
(Small Business Innovative Research) and STTR (Small Business Technology Transfer) programs.
Finding: With there being few U.S. governmental programs designed to translate industrially relevant
fundamental science to practice, U.S. industries are at a competitive disadvantage internationally.
Recommendation: Federal agencies focused on plasma research, and DOE in particular, should
develop new models that support the translation of fundamental research to industry. Programs
that support vital industries depending on plasma science and engineering (PSE) should be
developed through relevant interagency collaborations.
The Plasma Science and Engineering Community
Finding: The multidisciplinary approach has been at the heart of the success of the field, while
simultaneously working against the long-term viability of the field in academia.
Finding: Lack of a critical mass of faculty in PSE inevitably will lead to an erosion of U.S. capability in
PSE. At the same time, the university leadership in PSE is rapidly aging and will need renewal in the
coming decade.
Recommendation: Federal agencies—for example, Department of Energy (DOE), National Science
Foundation (NSF), National Aeronautics and Space Administration (NASA), and Department of
Defense (DoD)—should structure funding programs to provide leadership opportunities touniversity researchers in plasma science and engineering (PSE) areas and to directly stimulate thehiring of university faculty.
Finding: Plasma-specific educational and research programs that also provide opportunities to diverseand less advantaged populations are needed to ensure a critically populated PSE workforce.
Finding: Plasma-specific intern programs and summer schools are needed for undergraduate andgraduate students, as are programs supporting students with incomplete preparation to progress in plasma
physics, such as the American Physical Society Bridge Program.

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Finding: Requiring students to know early in their undergraduate years that plasma physics is a careergoal has limited the number of students continuing in plasma physics in graduate school and has excluded
less advantaged populations.
Finding: Support for junior faculty, for course development, and for curricula enhancement (e.g.,
inclusion of plasma physics in other courses) are necessary to enable students from a wide range ofinstitutions to enter the field.
Finding: The committee regards multi-agency investment in education, whether through directly
supporting undergraduate and graduate students or programs, or through faculty, and resource
development, as being critical. The more “duplication” of effort in these areas can only further strengthen
PSE.
Recommendation: Funding agencies (e.g., NSF, DOE, NASA, DoD) should structure funding tosupport undergraduate and graduate educational, training, and research opportunities—including
faculty—and encourage and enable access to plasmas physics for diverse populations.
The Research Enterprise in Plasma Science and Engineering
Finding: Given these strong international investments, incremental progress in facilities in the UnitedStates is insufficient to maintain leadership.
Finding: A spectrum of facility scales is required by the sub-fields of PSE to address their sciencechallenges and translational research.
Finding: Mid-scale facilities (e.g., in the $1 million to $40 million range, depending on agency) offer
particularly good opportunities for broadening participation within academia.
Recommendation: Federal agencies (e.g., NSF, DOE, NASA DoD) should support a spectrum offacility scales that reflect the requirements for addressing a wide range of problems at the frontiersof PSE.
Finding: Investment in facilities without the concurrent support of research and operations is not
optimum
Recommendation: Federal agencies whose core missions include plasma science and engineering(PSE)—for example, Department of Energy (DOE), National Science Foundation (NSF), National
Aeronautics and Space Administration (NASA), and Department of Defense (DoD)—should
provide recurring and increased support for the continued development, upgrading, and operationsof experimental facilities, and for fundamental and translational research in plasma science. A
spectrum of facility scales should be supported, reflecting the requirements for addressing different
problems at the frontiers of PSE.
Finding: Computational Plasma Science and Engineering (CPSE) has become essential across PSE forexperiment and mission design and diagnosis, idea exploration, probing of fundamental plasma physics
processes, and prediction.
Recommendation: Federal agencies should support research into the development of computationalalgorithms for plasma science and applications for the heterogeneous device computing platformsof today and upcoming platforms (e.g., quantum computers), while also encouraging mechanisms to
make advanced computational methods, physics-based algorithms, machine learning, and artificial
intelligence broadly available.

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Better Serving the Community
Finding: Although the majority of the FES budget is still devoted to supporting fusion science, thepresent office title does not now accurately reflect its broader mission. The present title may, in fact,
impede the ability of FES to collaborate with other offices within DOE and with other federal agencies,
including impeding its ability to garner support for non-fusion plasma research.
Finding: The national interest as a whole would be better served by renaming the office to better reflect
the broader mission of FES, maximize its ability to collaborate with other agencies and to garner nonfusion plasma support.
Recommendation: Consistent with our recommendations to broaden the impact of plasma science,
the Department of Energy (DOE) Office of Fusion Energy Science (FES) should be renamed tomore accurately reflect its broader mission, and so maximize its ability to collaborate with otheragencies and to garner nonfusion plasma support. A possible title is Office of Fusion Energy and
Plasma Sciences.
CHAPTER FOCUSED FINDINGS AND RECOMMENDATIONS
The committee offers the following findings and recommendations on the scientific front ofplasma physics and on government support for plasma science. The committee supports each
recommendation with a set of findings that the committee has made during the course of this study. These
recommendations can be taken to strengthen our responses to specific grand challenges and to broadly
advance the entire scientific frontier of plasma science.
Chapter 2: The Foundation of Plasma Science
Finding: The theoretical PSE workforce is not large enough to meet our current needs and will become
even less able to do so in the future without deliberate measures.
Recommendation: In developing their research agenda, federal agencies supporting plasma science(e.g., NSF, DOE, DoD, NASA) should make deliberate efforts to support theory.
Finding: Investigations of fundamental plasma science provide the understanding of these complex
processes that underpin the behavior of plasmas across the entire realm of plasma science and engineering(PSE). Studies of fundamental processes tie together seemingly disparate phenomena across the PSE
discipline and provide a unifying perspective to the vast array of PSE applications.
Finding: A widening gap between fundamental studies and application-inspired research impedes
progress in both fundamental studies and application-inspired research and slows the rate of translational
research that leads to societal benefiting technologies.
Recommendation: Federal agencies that fund PSE should forge partnerships with other plasmafocused agencies as well as agencies focused on applications benefiting from plasmas (or programs
within agencies) to close the widening gap between fundamental plasmas science research andtranslational research leading to applications.
Finding: There has been a general loss of broad collaborative activities within the PSE community overthe last decade.
Finding: In both experimental and theoretical/computational areas, the creation of teams with the criticalmass to address important and complex issues in basic plasma science are needed.

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Finding: Center-type activities can provide opportunities that strengthen the overall health of the PSE
community while providing important incubators for the development of the PSE workforce.
Recommendation: The DOE should broaden its support of Plasma Science Centers throughrecurring solicitations at critical funding levels to provide both new opportunities to advanceimportant areas of plasma science as well as to improve the impact of the plasma science
community.
Finding: While many of the basic plasma science facilities are aging, the last decade has seen importantinvestments in several new or expanded facilities in the range of $1 million to $4 million.
Finding: Many U.S. plasma science facilities were built during the last decade with funding provided by
the NSF Major Research Instrumentation program, and many of these facilities provide opportunities forexternal researchers to conduct collaborative experiments with the host institutions. However, theexperimental facility needs of different communities that are pursuing basic plasma science can vary
widely.
Finding: Today, facilities at a spectrum of scales and reflecting the requirements for addressing different
problems at the frontiers of plasma science (in the range $1 million to $20 million) are needed.
Recommendation: NSF, DOE, NASA, and other federal agencies with an interest and programs inplasma physics should provide regular opportunities for the continued development, upgrading andoperations of experimental facilities for basic plasma science at a spectrum of scales.
Finding: Many potential users of these experimental facilities would benefit from small levels of support
to gain experience with and obtain initial data for proof-of-concept demonstrations that are usually
expected in a full proposal to PBPSE. A mechanism to provide one time-short term funding to performthese experiments would address this critical need.
Finding: In addition, to a shared funding resource for user support, a network of basic plasma sciencefacilities might also coordinate on proposal selection, users groups, and outreach activities, thereby
addressing the STEM pipeline into plasma science.
Finding: A network of basic plasma user facilities that would provide opportunities for access to new andupgraded plasma science facilities needs more coordination and support than currently exists.
Recommendation: Federal agencies, particularly DOE-FES and NSF-MPS, should implement a
program for one-time, short-term funding for users of basic plasma science facilities.
Recommendation: A community wide workshop led by a partnership of DOE-FES and NSF-MPS
should define the parameters and participation of such a program and network of user facilities.
Finding: Plasma simulation is not optimally accessible to the wide range of potential users, including
experimentalists and industrial users.
Finding: Funding agencies have not traditionally supported code usability to the extent needed to makeresearch codes user-friendly, support users of codes, or to transition existing codes to new computing
architectures.
Recommendation: Funding agencies, and in particular DOE and NSF, should support mechanisms
for making computational plasma software more widely accessible to non-computing experts, andto transition current codes to new computing architectures.
Finding: At the time of this writing, opportunities for machine learning (ML) and artificial intelligence(AI) that impact computations (and experiments) are only beginning to be realized. This is an extremely
rapidly developing field. Leveraging these advances may require new approaches to computation.

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Recommendation: To assure that PSE computations take advantage of advances in ML and AI, aperiodic workshop should be held to share best practices, jointly sponsored by NSF, DOE andNASA.
Finding: There is a lack of modern educational and review material in computational PSE that addresses
the methods of computation and how to make effective use of computations.
Finding: With the rapid growth of interdisciplinary research in plasma physics, it is time to consider theestablishment of an annual journal that reviews major developments in all areas of plasma physics, much
like the Annual Reviews of Astronomy, for example.
Recommendation: Computational PSE, supported by NSF, should include projects for writing
textbooks and developing courses to train the current and next generation of computational plasma
scientists, and to enable non-computer experts to make optimal use of computations.
Chapter 3: Laser-Plasma Interactions
Finding: Compact plasma accelerators, X-ray sources, and optics were invented in the United States.
However, as reported in the NAS Opportunities in Intense Ultrafast Lasers: Reaching for the Brightest
Light, the United States has lost dominance in high-intensity laser research and related research that isessential to plasma science, accelerators, and their applications.
Finding: There are strategic opportunities in the next 10 years to build scientific facilities that can leapfrog international competition and enable the United States to maintain a leadership position in laserplasma interactions.
Recommendation: To restore U.S. leadership, DOE and other agencies should formulate a national
strategy to develop and build new classes of high-intensity lasers that enable now inaccessible
parameter regimes.
Facilities constructed through the strategy above would produce the technologically highest intensities toopen up new regimes in high field physics and ion acceleration, having repetition rates at and beyond 1
kHz, with shaped pulses enabling precision control, and with active feedback and machine learning foracceleration and plasma optics.
Finding: Plasma acceleration and controlled laser-plasma optics are rapidly advancing, driven by newly
available capabilities in short pulse/broad bandwidth lasers.
Finding: Applications require robust, compact drivers. A long-term plan and resources for developing
technologies that can leverage science advances into society benefiting applications are needed.
Recommendation: DOE and NSF should lead a collaborative effort with other agencies to develop
an extended stewardship program for long-term, application-oriented research to enable thedevelopment of revolutionary laser sources that translate to applications.
Finding: Collaboration between agencies focused on source development (DOE, NSF) and potential user
agencies (e.g., NIH, DoD) is needed to ensure that advanced laser capabilities are developed.
Finding: There is need for multiple programs and approaches in experiment, theory and computation,
ranging in scale from single investigator experiments to user facilities and dedicated mission focusedfacilities or centers.
Recommendation: Agencies focused on the fundamentals of LPI (NSF-MPS, DOE-FES, DOENNSA) should collaboratively augment and create programs in plasma acceleration and optics that
support a range of scales and multiple efforts and that coordinate research, user access, andeducational support.
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Finding: A blend of science innovation (e.g., development of new physics regimes in high field science)and long-term engineering efforts to develop new facilities has been essential to progress in laser-plasmainteractions.
Finding: Together with support from other agencies and DOE support concentrated at the National
Laboratories, NSF support devoted to LPI at universities is essential to the field.
Recommendation: NSF-MPS, DOE-SC, and DOE-NNSA should strongly support research in thefundamental physics of plasma optics, high field acceleration and laser sources in collaboration
with other agencies. This includes research, centers, and mid-scale infrastructure.
Finding: Computation and theory has been essential to the development of the field of Laser-Plasma
Interaction (LPI), providing insights and crucial input into experiment design. U.S. computation, once
dominant, has lost that advantage.
Finding: A range of needed computational tools, both fluid-based and DSMC-PIC, is also needed formodeling plasma sources.
Finding: The innovation that comes from healthy competition would help restore U.S. leadership incomputations for LPI.
Recommendation: NSF-MPS, NSF-CISE, and DOE-SC should support a diversity of computational
and theoretical efforts to help restore U.S. leadership in computations for LPI.
Chapter 4: Extreme States of Plasmas
Finding: Innovative diagnostics and diagnostic techniques have enabled developing a detailed picture of
ICF plasmas and imploded target cores with unprecedented precision, and enabled the investigation of
HED matter at previously unattainable conditions.
Finding: Diagnostic innovation is an ongoing need.
Recommendation: The DOE-NNSA, DOE-FES, and NSF-MPS should increase resources fordevelopment of new diagnostics and analysis methodologies to address needs for ongoing
innovation in HED physics.
Recommendation: The current NNSA ICF National Diagnostics Working Group charter andworkshops should be expanded to explicitly include HED diagnostics, interaction with mid-scale
facilities, and data analysis and data mining techniques.
Finding: While significant progress in HED science has been made in the last decade, more advances areneeded to improve predictive capability.
Finding: Improving our understanding of LPI is essential for continued progress toward validated
predictive capabilities, which are necessary for ignition and gain.
Recommendation: To achieve the goal of ignition and improve the quality of HED science, DOENNSA, DOE-FES, and NSF-MPS should expand and strengthen numerical simulation capability,
focusing in particular on improved atomic and kinetic modeling (including equation of state),
improved radiation transfer (including opacity), improved LPI (laser-plasma-instability)
understanding, uncertainty quantification and machine learning.
Recommendation: Where possible the National Laboratories should contribute their unclassifiedstate-of-the-art simulations codes to collaborations with academic and commercial efforts, andsupport training of qualified users.
Finding: Federal support of HED sciences at universities is essential to the health of HED science.
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Finding: The current paucity of mid-scale pulsed power facilities is a potential danger for the field.
Recommendation: Federal support of HED at universities and mid-scale laser facilities should
continue to expand, not only to benefit HED physics but also to maintain the critically needed HED
workforce.
Recommendation: Mid-scale pulsed-power facilities accessible to universities should be established,with leadership of these new facilities drawn from university researchers and the national
laboratories.
Finding: The basic science programs at NIF, Omega, and Z-machine have resulted in significant
scientific results despite having a small fraction of the available facility time.
Finding: The high visibility of these basic science HED experiments increases the ability to recruit new
talent while improving the understanding of the universe and the science underpinnings of other HED/ICF
research.
Finding: Guidance is required for how best to leverage and expand the basic science programs. This
guidance could come from a new HEDP Basic Research Needs report.
Recommendation: DOE-NNSA, DOE-FES, and NSF-MPS should continue and increase support
for basic HED science programs at large facilities in collaboration with universities.
Recommendation: The science program direction and the appropriate level of funding and facility
support should be guided by the DOE-NNSA, DOE-FES and NSF-MPS collaboratively
commissioning a new HEDP Basic Research Needs report for the HEDP community.
Chapter 5: Low-Temperature Plasmas
Finding: The success of the DOE Low Temperature Plasma Science Center program underlines that there
is a need to sustain LTP research directions for a sufficient period of time (5 to 10 years) and size withsupport on the level of ~$2 million per year to enable scientific impact and translation of research into
society benefiting applications.
Finding: The increasing scope of the LTP field into new materials and biotechnology requires fullparticipation of researchers that are traditionally funded by different agencies not focused on plasma
science. This is particularly the case for electrification of the chemical industry.
Finding: U.S. funding agencies are often ill prepared to support initiatives that overlap multiple agencies
and should actively pursue synergistic opportunities between agencies to maintain U.S. leadership in LTP
in line with the recommendation in Chapter 1.
Recommendation: DOE-FES should establish and coordinate a multi-agency Low Temperature
Plasma Science Center Program to support multidisciplinary research teams and to establish thescientific basis of emerging application areas of low temperature plasma science.
Finding: Based on the funding level for the LTP science center program, a possible minimum level of
support of $20 million over 5 to 10 years for each topical initiative would be appropriate.
Finding: Advances in plasma-materials processing are challenged by the need to choose operating andplasma device designs from the enormous set of possible operating and design conditions.
Finding: There is a serious need for a more detailed understanding of the fundamental processes
underpinning plasma-surface interactions that will enable us to develop predictive capabilities.
Finding: Advances in our understanding of LTP interactions with materials will enable the control ofplasma-surface interactions at the atomic level which in turn will enable the next generation of materials
for quantum computing, new communication and sensor technologies, and energy storage and harvesting.
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Recommendation: DOE-FES and DOE-BES should develop a synergistic collaborative program tofocus on the intersection of plasma and materials.
In addition to FES and BES, initiatives could be coordinated and funded between plasma-focused andmaterials-focused programs in federal agencies that would lead to advances in the science and technology
of both fields.
Industry support could also be leveraged to stimulate fundamental research through public - private
partnerships e.g. with the semiconductor industry. This public-private partnership could take the form of
the federal government supporting more fundamental interdisciplinary research and industry co-funding
more translational research.
Finding: The fundamental research performed in LTP is intrinsically interdisciplinary with societal
benefits occurring most rapidly when that fundamental research is guided by applications.
Finding: Although the NSF/DOE Partnership in Basic Plasma Science and Engineering is a strong
supporter of LTP research, the translational and convergent nature of LTP research often transcends thescope of the NSF/DOE partnership.
Finding: Support for translational and convergent research in LTP by the NSF Engineering directorate
has not been consistent, has not been long term and has not kept pace with the opportunities described inthis report. Deliberate actions are needed to empower these interdisciplinary opportunities.
Recommendation: NSF-MPS and NSF-ENG and funded at a level of $6 million per year, should
establish interdisciplinary and inter-directorate support for emerging LTP science topics that leadto translational research.
Finding: Continuing initiatives like the DOE Low Temperature Plasma Science Center program will help
sustain an internationally competitive LTP community in the United States.
Finding: LTP research at U.S. universities remains highly dispersed and it is not uncommon to find only
one faculty member involved in LTP research in an entire university. This situation underlines the needfor research networks and student training opportunities.
Finding: There are no multi-institutional, networking programs in the United States focused on LTPs.
Training of a new generation of scientists in fundamental LTP science, including diagnostics andmodeling, is a critical need for the coming 10 years, and would benefit from such programs.
Finding: Many U.S. PhD students working in the LTP field are trained with an exclusively application
perspective. To sustain the field, more fundamental LTP science training opportunities for early career
researchers are needed.
Recommendation: NSF should support LTP research networks in the United States by providing
funding for graduate students and postdoctoral researchers to participate in exchanges between
U.S. universities, and for international research experiences for junior scientists.
Finding: Fundamental research in LTP has declined in the United States over the last decade.
Finding: The demographics in the LTP field show that the leadership class will retire within the next
decade with an insufficient number of early career faculty available to assume leadership positions.
Finding: There are currently too few early career LTP-oriented faculty in the United States. The hiring of
faculty within universities in the 21st century needs to be viewed from an interdisciplinary perspectivethat recognizes the intellectual diversity of a field that spans multiple colleges and departments and would
benefit from investment by federal agencies.
Recommendation: To strengthen LTP research at universities, NSF and DOE should establish
specific programs that fund the creation of faculty positions similar to the NSF Faculty
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Development in Space Sciences program to address the urgency of losing key expertise andleadership in low-temperature plasma science over the next decade.
Finding: The vast majority of laboratories for the study of low temperature plasmas consist of tabletop
scale devices—often surrounded by a suite of diagnostic tools.
Finding: Based on its established track record, it is clear that the LTP community does not generally
require nor is there demand for large, single purpose centralized user facilities having a single plasma
source to make societal impact.
Finding: Leveraging the flexibility and interdisciplinarity of individual laboratories should be considereda valuable asset of LTP community, rather than comparing that style of research to large facilities in otherareas of plasma science, and declaring that mode of operation a weakness.
Finding: There is a need to support the flexibility and interdisciplinarity of individual LTP laboratories
perhaps through a mix of user facilities concentrating on diagnostics and improving diagnostic and source
capabilities in individual laboratories that could form a distributed user facility.
Recommendation: NSF and DOE should expand opportunities to develop and acquire diagnostics,
plasma sources, numerical models and reaction mechanisms in support of low temperature plasmas
science, perhaps through the NSF/DOE Partnership in Basic Plasma Science.
Chapter 6: Magnetic Confinement Fusion Energy
Finding: While the United States is still a major contributor to international MFE efforts and benefits
from these collaborations, the U.S. program has lost ground and is at risk of losing leadership in several
areas of MFE research.
Finding: The absence of a consensus strategic plan for fusion research in the United States is an
important factor in our falling behind on international developments, a situation compounded by the lackof vetted designs for new experimental facilities.
Finding: A roadmap is needed that is enabled by new experimental MFE facilities in the United Stateswith opportunities across a range of scales when appropriate,
Finding: To enable proper planning and to enable creation of a roadmap, ongoing feasibility and facility
design activities are essential.
Recommendation: DOE FES should undertake regular strategic planning, led by the U.S. MFE
community, as recommended in the NAS Burning Plasma Report.
Recommendation: Aligning with the NAS Burning Plasma Report, DOE FES should develop aroadmap for the development of commercial fusion power in the United States.
Finding: Declining participation by universities in the MFE program reduces the level of innovation in
the program and is a direct threat to the health of the field. It is essential that the MFE program respond to
this crisis.
Finding: Renewing and growing new efforts at universities could be enabled by providing university
researchers opportunities to participate in and, more importantly, lead the most important research
programs in the field.
Finding: There is a need to grow efforts in fusion engineering and an opportunity exists to stimulate
university programs in this area using both the indirect and direct mechanisms discussed above.
Recommendation: DOE FES should structure funding opportunities in MFE to provide leadership
opportunities to university researchers and to directly stimulate the hiring of university faculty.
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Finding: A recent Office of Management and Budget decision targeted at limiting duplication in
education and outreach programs in funding agencies caused the loss of discipline specific graduate
fellowships and outreach programs in DOE Office of Science (SC).
Finding: These programs are important but lack the effectiveness of the former graduate fellowship andNUF program in attracting new talent into the MFE field.
Finding: The NUF program and the graduate fellowship could be used as a tool to enhance diversity
within the MFE research community.
Recommendation: The DOE Office of Science should restore discipline-specific graduate
fellowships and undergraduate research programs that support MFE research at U.S. universities
as a vehicle for attracting new and diverse talent into mission-specific areas such as MFE, and formaintaining a presence in university science and engineering programs.
Finding: There has been significant growth in non-traditional support of MFE research, i.e., support otherthan that provided by DOE FES, including privately funded fusion companies, philanthropic
organizations, and DOE-ARPA-E.
Finding: There is a danger that the knowledge base, including that generated by former DOE FES
supported research, could become increasingly fragmented. Some challenges, for example thedevelopment of key technologies and materials, are similar even if the fusion configurations are distinct.
Solving these challenges through separate efforts increases overall cost and timescales.
Recommendation: Federal agencies funding the development of MFE science and technology(DOE-FES and DOE-ARPA-E) should leverage privately and philanthropically supported fusion
research and vice versa.
Chapter 7: The Cosmic Plasma Frontier
Finding: A lack of support for basic code and simulation development, theory, and novel data-analysis
techniques has long been a barrier to advancing our understanding of SAPs and predictive capabilities.
Finding: Unfortunately, the level of funding for the highly successful NSF/DOE Partnership in Basic
Plasma Science and Engineering has lagged that recommended by the 2000 Plasma Decadal Review,despite its very central role in discovery plasma science and its capacity to create effective
multidisciplinary bridges within plasma science.
Recommendation: NASA should join the NSF/DOE Partnership in Basic Plasma Science andEngineering to expand interdisciplinary basic plasma research that would benefit SAP. This
expanded partnership would leverage strategic contributions from each agency to enablebreakthrough progress that benefits a wide range of PSE activities (see Table 1, #3-#5).
Finding: Solar, heliospheric, magnetospheric, and ionospheric physics, and astrophysics have untappedsynergies with laboratory plasma experiments, with the common goal of understanding ambient plasma
conditions and chemistry.
Finding: Strategic funding from NASA and agencies supporting experimental facilities would enable
more ambitious, innovative joint projects than a single source could support.
Recommendation: NASA and NSF should lead an effort with DoD (especially ONR and AFOSR),
DOE, and other stake-holders (see Table 1, #6 and #24) should develop a collaborative programthat enables SAP scientists to collaborate with laboratory plasma experimentalists and advanceboth fields by leveraging their different needs and knowledge bases.
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Finding: Clusters of cubesats and smallsats carrying in-situ and remote-sensing instruments are the best
observing platforms for tackling many basic unsolved questions of multiscale SAPs (e.g., reconnection,
turbulence, and shocks), and provide essential research and training opportunities for university faculty
and students.
Finding: Existing procedures for developing, building, and operating missions are traditionally geared
toward large missions, and can pose unnecessary obstacles for single spacecraft and multi-platformmissions employing smallsats and CubeSats.
Recommendation: With NASA and NSF as lead agencies, NASA, NSF, and DoD, as the primarysources of space missions, should explore avenues, including rideshares, international partners, andpartnering with commercial launch providers, for reducing costs, lowering barriers, enablinghigher-risk missions, and boosting launch opportunities for these pioneering investigations using
Cubesats, smallsats and cluster of these satellites. (see Table 1, #7).
Finding: NSF, despite having a limited investment level in their Cubesat program, has broad access touniversities and undergraduate and graduate students. This access may be important in providing basic
training in PSE relevant to CubeSats. The recent solicitation for a cross-cutting NSF Ideas Lab Program
focused on CubeSat innovations to push the envelope of space-based research capabilities is an example
of one approach.
Recommendation: In view of their limited level of investment, NSF should identify a clearer roleand “identity” in their CubeSat program that distinguishes it from its NASA counterpart. To
ensure cost and resource efficiencies, NSF and NASA should coordinate further on funding
opportunities.
Finding: Increased support is needed to meet the challenge of designing and constructing compact
plasma and remote-sensing instrumentation suitable for Cubesats and smallsats.
Recommendation: Current NASA programs such as H-FORT, H-TIDES, and the IDP (Instrument
Development Program) should be augmented to meet the growing demand for compact plasma andremote-sensing instrumentation suitable for Cubesats and smallsats.
Finding: The SAP community needs to agree on data standards, formatting, and processing levels for
publicly available data.
Recommendation: Federal agencies that support ground-based and international space facilities(NSF, NASA, DoD, NOAA) should adopt similar open data policies and minimize barriers tointernational collaboration except where national security is of concern.
Recommendation: NSF should convene a workshop co-sponsored by NASA and DoD to makerecommendations for how to establish and maintain open data policies.
Recommendation: Once established, maintaining and updating the open data standards should be
the responsibility of governing federal organization such as one of the major contributors (NASA,
DoD, NOAA) or a more specialized agency for standards such as NIST.
Finding: A faculty partnership program introduced by NASA, NSF, and DOE—similar to that presented
in the Finding and Recommendation section of Chapter 1 (see Table 1.1)—is needed to strengthen SAP
hiring in universities and federal research facilities.

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C
Survey Data Gathering Events

November 6, 2018
60th Annual Meeting of the APS Division of Plasma Physics, Oregon
January 23, 2019NASA Goddard/University of Maryland, Maryland
January 2019
Dusty Plasma Workshop, Germany
April 15, 2019
University of Colorado-Boulder, Colorado
April 18, 2019
Princeton Plasma Physics Laboratory, New Jersey
May 16, 2019
Laboratory for Laser Physics/University of Rochester New YorkMay 28, 2019
Southeastern (Huntsville, AL)
May, 2019
Southern California
June, 2019
Lawrence Livermore National Laboratory, California
Lawrence Berkeley National Laboratory, California
June 24, 201947th IEEE International Conference on Plasma Sciences, Florida

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COMMITTEE MEMBER BIOGRAPHICAL INFORMATIONMARK J. KUSHNER, Co-Chair, is the Haddad Collegiate Professor in the Electrical Engineering &Computer Science Department at the University of Michigan, and holds appointments in the Nuclear
Engineering and Radiological Science Department, Chemical Engineering Department, and Applied
Physics Program. He is director of the Michigan Institute for Plasma Science and Engineering and theDepartment of Energy Center on Plasma Interactions with Complex Interfaces. Dr. Kushner received his
Ph.D in Applied Physics from the California Institute of Technology in 1979. He served on the staffs at
Sandia National Laboratory and Lawrence Livermore National Laboratory (1980-1983), and as Directorof Electron, Atomic and Molecular Physics at Spectra Technology (1983-1986), before joining the
University of Illinois at Urbana-Champaign (1986-2004). At UIUC, he was the Founder Professor ofEngineering and held several administrative roles. Prof. Kushner was Dean of Engineering and Melsa
Professor of Engineering at Iowa State University (2005-2008), before joining the University ofMichigan. Dr. Kushner’s research interests are in low temperature plasmas, addressing the generation andtransport of charged and chemically reactive species, their interactions with surfaces for materials
modification, and the development of plasma-based devices. Dr. Kushner has served in several national
and international leadership roles, including editor in chief of Plasma Sources Science and Technology,
and served on several National Academies’ studies, including the last plasma science decadal survey. Dr.
Kushner has received numerous awards, including the APS Allis Prize, AVS Medard Welch Award,
IEEE C. K. Birdsall Award, IEEE Plasma Science and Applications Award, Semiconductor Industry
Association University Research Award, and election to the National Academy of Engineering.
GARY ZANK, Co-Chair, is the director of the Center for Space Plasma and Aeronomic Research(CSPAR), University of Alabama Board of Trustees Trustee Professor and Aerojet/Rocketdyne Chair inSpace Science, an Eminent Scholar and Distinguished Professor, and Chair of the Department of Space
Science (SPA) at the University of Alabama in Huntsville. Dr. Zank’s research interests extend acrossspace physics, plasma astrophysics, and plasma physics. Although his research is related primarily totheory, modeling, and simulations, Dr. Zank is involved in numerous experimental and observational
programs. Some areas of research include the interaction of the solar wind with the partially ionizedinterstellar medium. Dr. Zank received his Ph.D in applied mathematics from the University of Natal inSouth Africa in 1987. He has been recognized in his field through the receipt of numerous honors andawards throughout his career. In 2017, he was named the first University of Alabama Board of Trustees
Trustee Professor, was elected in 2016 as a member of the National Academies of Sciences, Engineering,and Medicine, was recognized internationally in 2015 with the AOGS Axford Medal, the highest honor
given by the Asia Oceania Geosciences Society (AOGS). Other awards include his being a fellow of theAmerican Geophysical Union, the American Physical Society, and the American Association for the
Advancement of Science. In 2017, he was also elected an AOGS Honorary Member and was chosen by
the International Space Science Institute (ISSI) to be the 2017 Johannes Geiss Fellow. Dr. Zank has
served on a number of National Academies’ ad hoc and standing committees.
AMITAVA BHATTACHARJEE is Professor of Astrophysical Sciences and Head of the Theory
Department of the Princeton Plasma Physics Laboratory. He also serves as co-director of the Princeton
Center for Heliophysics. He received his Ph.D. at Princeton University (1981) in theoretical plasma
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physics from the Department of Astrophysical Sciences. He has taught previously at Columbia University(1984-93) in the Department of Applied Physics, at the University of Iowa (1993-2003) in the Departmentof Physics and Astronomy, and the University of New Hampshire (2003-12), where he served as Paul
Professor of Space Science. At the University of Iowa, he received the James Van Allen Natural Sciences
Fellowship (1996), the Faculty Scholar Award (1997-2000), and the Michael J. Brody Award (2003). He
has served as senior editor of the Journal of Geophysical Research-Space Physics, as chair of the Divisionof Plasma Physics of the American Physical Society, and as founding chair of the Topical Group in
Plasma Astrophysics of the American Physical Society, and on various prize and fellowship committees.
He is a fellow of the American Physical Society, the American Association of the Advancement of
Science, and the American Geophysical Union. His research interests include magnetic reconnection,
turbulence and singularity formation, kinetic theory, free-electron lasers, and complex (or dusty) plasmas.
PETER J. BRUGGEMAN is a Professor and Associate Department Head of Mechanical Engineering at
the University of Minnesota. He is also the director of the High Temperature and Plasma Laboratory andassociate director of the Department of Energy Center for Low Temperature Plasma Interactions with
Complex Interfaces. His primary research interests are in low temperature plasmas including plasma
diagnostics, plasma-liquid and materials interactions and non-equilibrium plasma kinetics and chemistry
applied to plasma processes for environmental, biomedical and renewable energy technologies.
Previously, Dr. Bruggeman was on the faculty of Eindhoven University of Technology (the Netherlands)
in the Department of Applied Physics. He is a recipient of several awards including the 2012 Hershkowitz
Early Career Award, the 2013 International Union of Pure and Applied Physics Young Scientist Medaland Prize in Plasma Physics, the 2016 U.S. Department of Energy Early Career Award and the 2018 Peter
Mark Memorial Award of the American Vacuum Society. He earned his PhD in Applied Physics fromGhent University (Belgium). He serves as section editor for low temperature plasmas of the Journal of
Physics D: Applied Physics (Institute of Physics Publishing) and as elected member of the board of
directors of the International Plasma Chemistry Society.
TROY CARTER is a Professor of Physics at the University of California, Los Angeles. He received B.S.
degrees in physics and nuclear engineering from North Carolina State University in 1995 and a Ph.D. inastrophysical sciences from Princeton University in 2001. Prof. Carter is the director of the Basic Plasma
Science Facility (BaPSF), a national user facility for plasma science supported by DOE and NSF. He is
also the director of the Plasma Science and Technology Institute (PSTI), an organized research unit at
UCLA. His research focuses on experimental studies of fundamental processes in magnetized plasmas
and is motivated by current issues in magnetic confinement fusion energy research and in space andastrophysical plasmas including magnetic reconnection, turbulence and transport in magnetized plasmas,
and the nonlinear physics of Alfvén waves. He was a co-recipient of the 2002 APS Division of Plasma
Physics Excellence in Plasma Physics Research Award and is a fellow of the American Physical Society.
Prof. Carter has served on a number of advisory committees, including the DOE Fusion Energy Sciences
Advisory Committee, the Fachbeirat for the Max-Planck Institute for Plasma Physics, and programadvisory committees for the DIII-D tokamak, the Alcator C-Mod tokamak, and the NSF Physics FrontierCenter CMSO.
JOHN CARY is a professor of physics at the University of Colorado, Boulder and CEO of Tech-X
Corporation. Dr. Cary's research focuses on the discovery of new methods for accelerating charged
particles, heating and transport of magnetically confined plasma, dense plasma focus, and advanced
computation on new computer architectures. His research interests are concentrated in beam/accelerator
physics, plasma physics, nonlinear dynamics, and computational physics. Dr. Cary’s accelerator/beamphysics interests are currently in advanced accelerator concepts: the generation and use of large (10-100GV/m) fields through laser-plasma interaction. His plasma physics interests are currently in thesimulation of the nonlinear interactions of radio frequency electromagnetic fields with plasma as
occurring in plasma heating. In recent years, he has devoted extensive effort to computational methods,
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including algorithm development. He is the originator of the arbitrary-dimensional, parallel, hybrid,
plasma simulation code, VORPAL. Dr. Cary received a Ph.D. and M.S. in physics at University ofCalifornia Berkeley in 1979 and 1975 respectively, and bachelor’s degrees in physics and mathematics at
the University of California, Irvine in 1973. He is a senior member of IEEE and a fellow of the APS
Division of Plasma Physics, which he chaired 2017-2018. He is a recipient of many awards, such as theIEEE NPSS Particle Accelerator Science and Technology Award. His other service includes being
Associate Editor of the Reviews of Modern Physics and other journals and being on the organizing andprogram committees for the Annual Meeting of the Division of Plasma Physics, the Particle Accelerator
Conferences, and other national and international conferences in plasma and beam science.
CHRISTINE A. COVERDALE is a plasma physicist at Sandia National Laboratories. Dr. Coverdale
joined Sandia in 1997 and in 2011 was named a distinguished member of the technical staff. She has been
involved in a broad range of experiments at the Saturn and Z pulsed power facilities centered aroundnuclear weapons certification and other national security projects. She also works on radiation detection
systems and diagnostics to assess warm and hard X-rays from Z-pinch plasmas. Dr. Coverdale has adoctorate in plasma physics from the University of California, Davis, and has authored or co-authoredmore than 120 papers, and regularly presents at conferences. She served three terms on the executive
committee of the IEEE Plasma Science and Applications Committee and has served as the technicalprogram chair or co-chair for the IEEE International Conference on Plasma Science in 2009, 2010, 2012,2015, and 2021. She also served a four-year term on the IEEE Nuclear Plasma Sciences Society
Administrative Committee. Dr. Coverdale was on the Executive Committee of the American PhysicalSociety (APS) Division of Plasma Physics and severed for several years as the senior editor for HighEnergy Density Physics for IEEE Transactions on Plasma Science. She has served on multiple awardscommittees for IEEE NPSS and APS-DPP, including fellowship committees and is a fellow of both theIEEE and APS.
ARATI DASGUPTA is a senior research physicist at the Naval Research Laboratory. Dr. Dasgupta
received her BS in physics with Honors, MS, and PhD from the University of Maryland before joining theNaval Research Laboratory in 1986. She is a Section Head leading basic and applied research programs in
atomic processes in laboratory and astrophysical plasmas that span pulsed power radiation sources,
inertial confinement fusion (ICF), laser-matter interaction, plasma spectroscopy, low temperature plasma
processing, and ultra-short wavelength lasers. Presently her research focus is on non-local thermodynamic
equilibrium kinetics modeling and simulation of HEDP experiments of multi-keV plasma radiation
sources on Sandia’s Z machine and National Ignition Facility (NIF) at LLNL, ICF using symmetry
capsule (Symcap) implosion on NIF, magnetized plasma on Jupiter Laser Facility at LLNL, and radiation
physics for high ZA elements on the NRL NIKE laser in support of ICF. She is a Fellow of the APS andthe Washington Academy of Sciences. She is a member of several science panels, and served on DOE’s
Fusion Energy Sciences Advisory Committee (FESAC) and was part of a committee in writing
OFES/DOE’s Strategic Planning report in 2014 and DOE’s ReNeW report on HEDLP in 2009. Currently
she is a member of the APS Committee of Status of Women in Physics and chair of its awards subcommittee. She is also a member of the advisory committee (AdCom) of IEEE’s Nuclear and Plasma
Sciences Society. She has served on several APS committees including fellowship committees of
DAMOP and DPP, and chaired Women in Plasma Physics Committee of the DPP. She is the author (oninvitation) of a chapter in a book titled “Blazing the Trail; Essays by Leading Women in Science” andpresented a public lecture at the University of Wisconsin, La Crosse, in their yearly Public Lecture Series
featuring prominent women in physics, astronomy, and engineering.
DANIEL DUBIN is a professor of physics at the University of California San Diego. His principal area of
research is theoretical plasma physics, focused mainly on nonneutral plasmas (pure electron plasmas, pureion plasmas, positron plasmas, etc.) This work has also led to research in the physics of dusty plasmas,
strongly coupled plasmas, 2D fluid dynamics, and nonequilibrium statistical mechanics. Dubin received
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his Ph.D. in plasma physics from Princeton in 1984. He was elected a fellow of the American PhysicalSociety, Division of Plasma Physics, in 1994, and in 2000 he received the American Physical Society
John Dawson Award.
CAMERON G.R. GEDDES is a Senior Scientist at Lawrence Berkeley National Laboratory, and Deputy
Director of the laboratory’s BELLA center focusing on study of laser driven plasma waves and theirapplications compact particle accelerators and photon sources. He leads Center experimental efforts
creating new accelerator techniques to extend the future reach of high-energy physics, for novel radiation
sources in the X-ray to THz bands, for high energy density physics and for applications across medical,
industrial and security spaces. He also leads a project developing plasma based accelerators as compact
sources of near-monochromatic MeV photons for nuclear material detection and characterization.
Previous positions have spanned a range of plasma physics including Thomson scattering measurement ofdriven waves in inertial confinement fusion laser-plasma interaction at LLNL, wave mixing in Omega
laser experiments via Polymath Reseach, and small aspect Tokamak equilibria at the University of
Wisconsin. He received the Ph.D. in 2005 at the University of California, Berkeley, supported by the
Hertz Fellowship, where he received the Hertz and APS Rosenbluth dissertation awards for demonstrationof a laser driven, plasma based electron accelerator producing mono-energetic beams. He received the
B.A. degree from Swarthmore College in 1997, and received the APS Apker Award and Swarthmore
Elmore Prize for work on Spheromak plasma magnetic equilibria. He is a fellow of the American
Physical Society Division on Plasma Physics and a recipient of the Society's Dawson award, and of two
LBNL Outstanding Performance awards. Previous community planning exercises have include Frontiersof Plasma Science (2015, FES), Snowmass (2013, HEP), and the HEDLP ReNeW panel (2009).
S. GAIL GLENDINNING is a technical staff member at Lawrence Livermore National Laboratory,
where her research currently includes designing experiments for the National Ignition Facility onradiation transport and hydrodynamic instabilities. She received her B.A. in experimental physics from
Middlebury College in 1973 and her Ph.D. in experimental nuclear physics from Duke University in
1980. Following post-doctoral work at Duke, she worked for the nuclear fuels division of General Electricin Wilmington, NC and San Jose, CA, designing monitoring systems for low-level radioactive waste. She
joined Lawrence Livermore National Laboratory in the Inertial Confinement Fusion program in 1985. Her
work on ICF focused on the study of hydrodynamic instabilities in planar systems using both direct andhohlraum drive. She is a recipient of the Excellence in Plasma Physics award (1995) for her work onhydrodynamic instabilities and has been a fellow of the American Physical Society Division of Plasma
Physics since 1998. She served for six years on the NAS Plasma Science committee, and for 3 years on
the DPP Executive Committee.
DAN M. GOEBEL is a Jet Propulsion Laboratory Fellow and senior research scientist, an adjunctprofessor of Electrical Engineering and Aerospace Engineering at University of California Los Angeles
and an adjunct professor of Electrical Engineering at University of Southern California. At NASA/JPL heis responsible for the development of advanced electric propulsion systems and spacecraft technologies,
and is the chief engineer of the NASA Psyche Mission that will launch in 2022. Previously he was a
research scientist at HRL Laboratories in Malibu, CA, and Principal Scientist at Hughes/Boeing EDD in
Torrance, CA where he was the supervisor of the Advanced Technology Group for microwave tube
development and the lead scientist of the XIPS ion thruster program for commercial satellite station
keeping. He received a NASA Engineering Achievement Medal in 2011, the IEEE John R. Pierce Award
for Excellence in Vacuum Electronics in 2014, the UCLA Engineering Alumni Professional Achievement
Award in 2016, and the NASA Space Technology Award in 2015 and 2018. He earned his Ph.D. inapplied plasma physics from the University of California, Los Angeles. Dr. Goebel is a member of the
National Academy of Engineering, a fellow of the National Academy of Inventors, a fellow of theAmerican Institute of Aeronautics and Astronautics, fellow of the Institute of Electrical and Electronics
Engineers, and a fellow of the American Physical Society. He is the author of over 135 technical journal
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papers, 150 conference papers, one book entitled Fundamentals of Electric Propulsion: Ion and Hall
Thrusters, and holds 53 patents.
DAVID B. GRAVES is a professor of chemical engineering in the Department of Chemical and
Biomolecular Engineering in the College of Chemistry at the University of California at Berkeley. At
UCB, Dr. Graves has been a leading figure in research associated with semiconductor manufacturing
applications of low temperature plasma. His research interests include plasma modeling and simulations,plasma-surface interactions dusty plasmas, and novel applications of plasma in biology, agriculture andmedicine. He is a fellow of the American Vacuum Society and the Institute of Physics and was therecipient of the Electrochemical Society Young Author Award, the NSF Presidential Young InvestigatorAward, the Tegal Plasma Thinker Award, and the Plasma Prize of the Plasma Science and Technology
Division of the AVS. He was named the Lam Research Distinguished Chair in Semiconductor Processing
at UC Berkeley for 2011-16. He received the Allis Prize for the Study of Ionized Gases from theAmerican Physical Society in 2014 and the 2017 International Symposium of Dry Processes Nishizawa
Award. He earned his Ph.D. in chemical engineering from the University of Minnesota, USA. He acted asco-editor for the Report on Data Needs for Plasma Processing (1995-96). He was co-editor of the Low
Temperature Plasma Science Challenges for the Next Decade. (2008) He is currently senior editor of theIEEE Transactions on Radiation and Plasma Medical Science.
JUDY KARPEN is a research astrophysicist in the Space Weather Laboratory, Heliophysics Science
Division, NASA Goddard Space Flight Center, and the Chief of the Space Weather Laboratory. Her
primary research interests include analytical and numerical modeling of dynamic solar and heliosphericphenomena, and applications of plasma physics and magnetohydrodynamics to solar/heliospheric activity
and space weather. Her current research is focused on solar prominences, coronal mass ejections/eruptive
flares, coronal/heliospheric jets, and magnetic reconnection. Previously Dr. Karpen was a researchphysicist in the Solar-Terrestrial Relationships Branch, Space Science Division, Naval ResearchLaboratory. She has served on numerous committees for the American Astronomical Society and theAmerican Geophysical Union, and on several advisory panels and committees for NASA and the
NASEM, including the NAS/NRC Committee on Solar and Space Physics (1997-2000) and the
NAS/NRC Solar-Heliospheric Panel of the Solar and Space Physics Decadal Survey (2001-2002). She
earned her PhD in Astronomy from the University of Maryland in 1980, and a BS in Physics from the
University of Michigan in 1974.
MAXIM Y. LYUTIKOV is a professor of physics and astronomy at Purdue University His researchinterests include high-energy astrophysics, compact objects, extragalactic astrophysics, cosmic rays, andplasma astrophysics. He earned his M.S. in theoretical physics from Moscow Engineering Physics
Institute and his Ph.D in theoretical astrophysics from California Institute of Technology in 1998. He has
been awarded as a Simons Fellow in Theoretical Physics, and received the CITA National Fellowship, theAllan T. Moffett Fellowship, and the Van Maanen Fellowship throughout his career.
JOHN S. SARFF is a professor of physics at the University of Wisconsin-Madison. His research interests
are fusion energy and basic plasma physics related to toroidal magnetically confined plasmas. He served
as the Director of the Madison Symmetric Torus (MST), which is one of the world’s largest reversed field
pinch (RFP) experiments. The MST facility is used for fusion research on the RFP and tokamak magnetic
configurations as well as exploration of self-organizing plasma dynamics and their connections toastrophysical plasmas through processes such as magnetic reconnection, particle heating and energization,and turbulence and transport. Prof. Sarff has served on numerous committees and panels for the APS
Division of Plasma Physics and FESAC. He has also served on the advisory committees for the UnitedStates’s major user facilities for magnetic fusion research. He is the current President of the University
Fusion Association, and he is one of the co-chairs for the APS-DPP Community Planning Process. Prof.

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Sarff earned his Ph.D. from the University of Wisconsin-Madison. He is a fellow of the American
Physical Society.
ADAM B. SEFKOW is an assistant professor of mechanical engineering and physics at the University ofRochester, with a secondary appointment as a senior scientist at the Laboratory of Laser Energetics. He
earned his B.A. in physics with honors from Northwestern University and his M.A. and Ph.D. in plasma
physics from Princeton University. Before joining the University of Rochester in 2016, he was a principal
member of the technical staff in the Pulsed Power Sciences Center at Sandia National Laboratories. His
primary research interest is to improve predictive capability in computational plasma physics. Prof.
Sefkow has made scientific contributions to magneto-inertial fusion, direct- and indirect-drive inertial
confinement fusion, short-pulse and long-pulse laser-plasma interaction physics, and intense chargedparticle beam transport. He currently leads the development effort of a particle-based hybrid fluid-kinetic
multi-physics simulation code. He has authored or co-authored about 100 papers, and has served as areviewer and committee member for numerous journals, agencies, and conferences. Prof. Sefkow
received the U.S. Department of Energy Office of Science Early Career Research Program Award, theFusion Power Associates 2017 Excellence in Fusion Engineering Award, and the National Nuclear
Security Administration Defense Programs Award of Excellence, in recognition of his scientificcontributions on a range of topics.
EDWARD THOMAS JR. is the Charles W. Barkley Endowed Professor of Physics and the Associate
Dean for Research and Graduate Studies in the College of Sciences and Mathematics at Auburn
University. He earned his Bachelor’s degree from the Florida Institute of Technology, a Master’s Degreefrom MIT, and a PhD from Auburn University. Prof. Thomas began his research career studying edge
particle transport in fusion plasmas. Over the years, his work has become centered in basic plasma
physics where his group conducts experimental plasma physics research on dusty (complex) plasmas,
magnetized plasmas and plasma diagnostic development—with an emphasis on the particle, wave, andenergy transport in low temperature plasmas. Most recently, he has led the development of theMagnetized Dusty Plasma Experiment (MDPX) device. Previously, Prof. Thomas was a faculty member
at Fisk University in the Department of Physics. He is an elected member of the International Union ofRadio Science (URSI), Commission H, and is a fellow of the American Physical Society and the National
Society of Black Physicists. He has served as a member of numerous advisory committees for theAmerican Physical Society, National Science Foundation, Department of Energy, National ResearchCouncil, European Space Agency, and several research centers in the United States, Europe and India—
including the National Academies Plasma Science Committee and the Department of Energy’s Fusion
Energy Sciences Advisory Committee.

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Acronyms

AFOSR

Air Force Office of Scientific Research

AFRL

Air Force Research Laboratory

ARO

Army Research Office

ARPA-E

Advanced Research Projects Agency–Energy

ASCR

Advanced Scientific Computing Research

BES

Basic Energy Sciences

DARPA

Defense Advanced Research Projects Administration

DHS

Department of Homeland Security

DoD

Department of Defense

DOE

Department of Energy

DOE-HEP

Department of Energy Office of High Energy Physics

DOE-SC

Department of Energy Office of Science

DTRA

Defense Threat Reduction Agency

EERE

Energy Efficiency and Renewable Energy

EPA

Environmental Protection Agency

FAA

Federal Aviation Agency

FES

Fusion Energy Sciences

HEP

High Energy Physics

NASA

National Aeronautics and Space Administration

NASA-HEOMD

NASA Human Exploration and Operations Mission Directorate

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NASA-SMD

NASA Science Mission Directorate

NCI

Cancer Institute

NIAID

Allergy and Infectious Diseases

NIAMS

Arthritis and Musculoskeletal and Skin Diseases

NIBIB

Biomedical Imaging and Bioengineering

NIDCR

Dental and Craniofacial Research

NIGMS

General Medical Sciences

NIH

National Institutes of Health

NINDS

Neurological Disorders and Stroke

NNSA

National Nuclear Security Administration

NOAA

National Oceanic and Atmospheric Administration

NRL

Naval Research Laboratory

NSF

National Science Foundation

NSF-BIO

NSF Directorate for Biological Sciences

NSF-CISENSF Directorate for Computer and Information Science

NSF-DMRNSF Directorate for Materials Research

NSF-GEONSF Directorate for Geosciences

NSF-ENGNSF Directorate for Engineering

NSF-MPSNSF Directorate for Mathematical and Physical Sciences

ONR

Office of Naval Research

USDA-NIFA

U.S. Department of Agriculture National Institute of Food and Agriculture

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