OFFICE OF DEFENSE PROGRAMS

2015 Review of the Inertial Confinement
Fusion and High Energy Density Science
Portfolio: Volume I
May 2016

DEPARTMENT OF ENERGY | NATIONAL NUCLEAR SECURITY ADMINISTRATION | DEFENSE PROGRAMS [NA-10]

DOE/NA-0040
Initial release:
Second release:

May 3, 2016
June 8, 2016 – Minor technical edits

EXECUTIVE SUMMARY
In September 2012, at the conclusion of the National Ignition Campaign (NIC), the NNSA
committed itself to conducting a review of the progress toward ignition three years later. NNSA
called upon twenty subject matter experts to independently review and comprehensively
assess the progress and program plans for the Inertial Confinement Fusion (ICF) and HighEnergy Density (HED) science portfolio within the Stockpile Stewardship Program (SSP). A
review that included all major program elements of this portfolio had not been conducted in
more than 15 years.
This effort covered three main topics:
1. ICF and Ignition. An assessment of the scientific hypotheses that guide the ICF Program,the prospects of achieving ignition with existing scientific facilities, and an evaluation ofprogram balance between the three main ICF approaches.
2. The ICF/HED Portfolio and Long-Term SSP Goals. An assessment of the alignment of the
ICF/HED portfolio with SSP requirements; the contribution to the SSP in the science
portfolio in the near, medium, and long term; the scientific and programmatic progress
and plans in the ICF Program to meet the goals of the SSP; and, the long-term
requirements for “high-yield” capabilities at laboratory scale.
3. Improving Scientific Foundations in ICF/HED Physics. The identification of opportunities
to improve the underlying physics and the impact of simulations, models, and codes; toincrease the integrated rate of progress of ICF/HED programmatic deliverables throughnew experimental capabilities (including targets and diagnostics); and, to identify areas
where partnerships with academia, industry, and other government partners may bestrengthened to support these opportunities.
This report summarizes the reviewers’ comments and includes a series of conclusions that wereassembled by the Office of Inertial Confinement Fusion and the Office of Research andDevelopment, the authors of this report.
An overview of the reviewer comments follows.
ICF and Ignition• The ICF Program has achieved the milestones set forth in the “Path Forward” reportpublished in 2012. In particular, the program has: (1) identified leading candidates for
impediments to ignition on the National Ignition Facility (NIF); (2) nearly doubled theshot rate on the NIF; (3) improved diagnostics capabilities on all its key facilities; (4)made progress in laser-driven direct drive ICF efforts at the University of Rochester’sOmega Laser Facility (Omega), and; (5) made progress in magnetically driven fusion at
Sandia National Laboratories’ Z Facility (Z).
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•

There are clear SSP drivers to study the properties of robust thermonuclear burning
plasmas, to pursue multi-megajoule fusion yields (which requires ignition), and to
ultimately pursue high yield.
Barring an unforeseen technical breakthrough and given today’s configuration of the NIF
laser, achieving ignition on the NIF in the near term (one to two years) is unlikely and isuncertain over the next five years. Although performance of NIF ignition targets
continues to improve and simultaneously making contributions to the SSP, currently
there is no known configuration, specific target design, or approach that will guarantee
ignition on the NIF.
The ICF Program has identified and begun exploration of key hypotheses to explain gaps
between calculated and measured performance of NIF implosions, however, the present
approach is too broad and diverse, and needs better focus. Neither Z nor Omega were
designed to achieve ignition, however, they both may be used along with the NIF tounderstand limitations in NNSA’s understanding of physics of ICF implosions, particularly
during hot-spot assembly and stagnation. While efforts are improving, there is currently
no published “roadmap” to coordinate cross-platform activities.
Collaboration between researchers and institutions has improved since the conclusionof the NIC. Priorities for further collaborations include: (1) transformative diagnostics,
including spatially, spectrally, and temporally-resolved imaging and spectroscopic
diagnostics to observe “stagnation” at low, medium, and high convergence; (2)obtaining cross-platform data for fundamental physics validation of models/codes while
improving access to codes/models, where appropriate; (3) reviving development efforts
for codes to model Laser-Plasma Interactions (LPI); (4) increasing the number ofdesigners and experimentalists working on magnetically-driven implosions and laserdriven direct drive programs; and, (5) enhancing peer review by academia and otherinstitutions.
There are areas where program direction should be reassessed, including: (1) pursuing
the study of long length-scale LPI using partial Polar Direct-Drive (PDD) configuration on
the NIF versus pursuing PDD ignition; (2) revising the charter for the laboratory-staffed
ICF Council, which is composed of laboratory researchers; and, (3) reviewing the balanceof focused versus integrated experiments.

ICF/HED Portfolio and Long-Term SSP Goals• The ICF Program is well aligned with the weapons program. The HED science portfolio
has delivered important data to the SSP, demonstrated the validity of theoretical,
computational, and experimental methods important to evaluating the safety, security,
and reliability of the stockpile in HED regimes, and demonstrated the competence and2015 Review of Inertial Confinement Fusion and High Energy Density Science Portfolio

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credibility of technical staff to work in these regimes without additional nuclear
weapons testing.
There is a strategic plan that describes how research efforts will evolve over the next
decade from radiation transport, to boost science, and eventually, to outputs andeffects.
Applications for fusion yields produced on existing platforms are under development.
Higher yields (those approaching ~100 kilojoules) are needed for burn physics relevant
experiments.
The long-term requirements case for “high yield” has not been revisited in nearly twenty
years. It is not clear how this case has evolved for enhancing predictive capabilities fornuclear weapons performance or for nuclear survivability qualification of components.
While there are presently no clear drivers for new major (>$100 million) facility
investments, support is needed for diagnostics and facility improvements over the next
five years.

Scientific Foundations in ICF/HED Physics• The United States (U.S.) leads the world in HED science. Internationally, a number offacilities are being developed that exceed some U.S. capabilities, such as the highintensity ultrashort pulse laser being developed at the ELI Facility in the Czech Republic,
the existing FLASH X-ray Free Electron Laser (XFEL) at the DESY Facility in Hamburg,
Germany, and the follow-on European XFEL, scheduled to come online in 2017, also at
DESY.
• All HED capabilities (domestic and international) must be considered as NNSA defines
the means by which it will execute SSP-related experiments.
• Cross-platform validation experiments (experiments to elucidate similar physics
executed on different platforms such as Z and NIF, for example), are instrumental toadvances in HED physics. These efforts should take priority.
• Special attention over the next five years should be given to developing a robust cadreof top researchers in key areas of atomic physics, spectroscopy, laser plasma
instabilities, and low-energy nuclear physics. NNSA must shape its’ academic programs
to ensure resources are optimally deployed.
Reviewers were not asked to consider resource constraints when providing comments orrecommendations. To affect all recommendations contained herein would exceed current
budget profiles. The principal next step is for NNSA to identify specific resource requirements toprioritize these recommendations within existing budgets. This prioritization process will begin
in FY 2016.

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CONTENTS
EXECUTIVE SUMMARY ......................................................................................................................i
Statement from the Acting Deputy Administrator for Defense Programs ..................................... v
1

Motivation, Objectives, and Structure for the 2015 ICF/HED Portfolio Review ..................... 1
1.1

Report Authorization and Recipients ............................................................................... 1

1.2

Primary Objectives of the Review .................................................................................... 1

1.3

Structure of the Review ................................................................................................... 2

2

Evolution of the National ICF/HED Program since the National Ignition Campaign............... 4

3

Review Topics .......................................................................................................................... 5

4

3.1

ICF/HED Contributions to the Stockpile Stewardship Program ....................................... 5

3.2

The Prospects for Achieving Ignition................................................................................ 8

3.3

Technical Challenges in Inertial Confinement Fusion ...................................................... 9

3.4

Experimental Diagnostics and Computational Resources ............................................. 23

3.5

Improving Scientific Foundations in HED ....................................................................... 27

3.6

Academic Programs and External Partners.................................................................... 32

3.7

Program Direction .......................................................................................................... 35

Next Steps.............................................................................................................................. 39

Acronyms, Abbreviations, and Terms List .................................................................................... 40

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Department of Energy
National Nuclear Security Administration
Washington, DC 20585

Inertial Confinement Fusion (ICF) and High Energy Density (HED) science are core technicalcompetencies within NNSA’s Stockpile Stewardship Program (SSP). The overwhelming majorityof the yield from a nuclear weapon is produced in the high energy density state withtemperatures and pressures rivaling that of the sun. Understanding these fields is critical toensuring current and future stockpiles are safe and reliable.
The ICF effort has the unique challenge of achieving fusion “ignition” and developing
corresponding HED experimental platforms while, at the same time, regularly delivering shortterm contributions to support stockpile Annual Assessments, Significant Finding Investigations,and stockpile modernization. In 2012, the ICF Program outlined its three-year path forward
toward the development of an ignition capability and committed itself to conduct a review of
the Program at its conclusion. What follows in the report fulfills that commitment and, in fact,
expands its scope to encompass the full ICF/HED portfolio.
This review process led to the identification of nearly 40 recommendations that covermanagement, technical, and programmatic issues. These recommendations vary in scope andurgency. One area already identified as being of immediate importance for the ICF effort is the
pursuit of advanced diagnostics that will enable the exploration of ICF implosions at higher
levels of fidelity required to uncover and quantify important phenomena that lie beyond ourpresent understanding. In the non-ICF HED portfolio, the immediate priority is the study of theboost process, which reaches temperatures and pressures that we are only now able to explorewith recent advances at the National Ignition Facility, the Z Facility, and the Omega Laser.
While ignition remains a significant technical challenge, its pursuit and achievement remains
important to the SSP into the foreseeable future. Accordingly, I have directed the Office ofInertial Confinement Fusion and the Office of Research and Development to review andimplement the findings and recommendations as appropriate.
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This page intentionally left blank1 Motivation, Objectives, and Structure for the 2015 ICF/HED Portfolio Review
At the conclusion of the National Ignition Campaign (NIC) in September 2012, the Departmentof Energy’s (DOE) National Nuclear Security Administration (NNSA) committed to conducting acomprehensive review in three years to assess the progress toward ignition – stating in the2012 Path Forward report that a program assessment will occur at the end of FY 2015. As 2015
approached, it was recognized that the Inertial Confinement Fusion / High Energy Density(ICF/HED) physics portfolio would need to be more fully assessed. The NNSA assembled agroup of 20 diverse technical subject matter experts and conducted the review between May
and September of 2015. The review assessed past and current efforts, but particularly
emphasized future plans and opportunities to strengthen the long-term health of the Stockpile
Stewardship Program (SSP). Reviewers individually submitted observations, findings, andrecommendations to NNSA. This report was written by the Office of Inertial Confinement
Fusion (ICF) and Office of Research and Development (R&D) and was reviewed by the Office ofAdvanced Simulation and Computing (ASC). These three offices are within NNSA’s Office of
Research, Development, Test, and Evaluation (RDT&D). This review was not a Federal Advisory
Committee Act activity.
Section 1 presents the motivation, objectives, and structure for the review. Section 2
summarizes the evolution of the program since the conclusion of the NIC, as well as
achievements and challenges that emerged during the NIC. Section 3 addresses the major
observations of the individual reviewers. The report concludes with Section 4, Next Steps. The
Appendices can be found in Volume 2. Appendix A includes documentation associated with thereview process. Appendix B contains the reviewers’ reports as submitted to NNSA. Appendix C
contains additional reference documents.
1.1 Report Authorization and Recipients
The audience for this report are federal and laboratory/site leadership and management within
NNSA’s Defense Programs, particularly those with equities in the ICF/HED portfolio. This
includes the Office of Research, Development, Test, and Evaluation (NA-11), the Office ofStockpile Management (NA-12), and the Office of Major Modernization Programs (NA-19).
Consideration was given to the interest of external stakeholders in the overarching conclusionsof the review and the subsequent direction of the program.
1.2 Primary Objectives of the Review
Individual aspects of the ICF/HED portfolio have been extensively reviewed since the 1980s (seeAppendix C.2). These past reviews have primarily focused on the ICF Program or on the NIF.
Two unique features set this review apart:
1. The major facilities that achieve high energy density conditions are multi-mission.
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mission context. This necessitated simultaneous evaluation of the ICF Program and the
HED aspects of the R&D portfolio 1. This type of all-encompassing review had not been
conducted in 15 years 2.
2. The majority of the previous reviews of the ICF Program focused on achieving ignitionon the NIF. This review included each ICF approach. The result was a comprehensive
review that included all major program elements that comprise the ICF Program.
The review was an independent technical assessment of the program of record as of May 2015.
NNSA asked reviewers to provide their individual recommendations to improve current efforts,
strengthen the three- to six-year program plans, and perhaps most importantly, identify areas
for sound strategic investments over the next 10 to 20 years. The charge to the reviewers isprovided in Appendix A.3.
1.3 Structure of the Review
The review was initiated on May 18, 2015 with reviewers attending a three-day overview of the
program at which the ICF/HED leadership from the laboratories presented their respective
programs. Reviewers were divided into three groups along the elements of the charge. In July
2015, the reviewers had briefings at Lawrence Livermore National Laboratory (LLNL), Sandia
National Laboratories (SNL), Los Alamos National Laboratory (LANL), the University ofRochester’s Laboratory for Laser Energetics (LLE), the SLAC National Accelerator Laboratory(SLAC), and at DOE in Washington D.C. The laboratories which participate in the ICF Program
generated fifteen white papers to prepare reviewers for their visits. Reviewers held discussions
with laboratory leadership and management, attended presentations by laboratory staff
scientists, and met with established laboratory scientists and early-career scientists for further
discussions. Additional details of the review process can be found in Appendix A.
Group 1 – Progress Toward Ignition
Group 1 assessed the potential for achieving ignition through existing scientific capabilities andfacilities. The scientific hypotheses that guide today’s ICF Program were evaluated across thethree established ICF approaches: Laser-driven Indirect Drive (LID), Laser-driven Direct Drive(LDD), and Magnetically-driven Direct Drive (MDD). This group assessed the effectiveness of
the ICF Program’s cross-platform and cross-laboratory collaborations.
Federal Lead: Lois Buitano, NNSA
Meeting locations: LLNL, LLE, SNL
1

The HED aspects of the R&D portfolio are categorized into four areas: Nuclear (materials properties,hydrodynamics), Thermonuclear (mix, burn), Radiation (radiation transport and opacities), and Output and Effects(weapons effects, generating hostile/survivability environments). Over the last five years, significant progress has
been made to improve NNSA’s understanding of energy balance, boost initial conditions, and secondary
performance.
2
High-Energy-Density Physics Study Report, 2001, National Nuclear Security Administration
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Reviewers: Jerry Chittenden, Imperial College
Siegfried Glenzer, SLAC
Jim Hammer, LLNL
Nelson Hoffman, LANL
Warren Mori, University of California, Los Angeles
Andrew Randewich, Atomic Weapons Establishment
Sean Regan, LLE
Bob Rosner, University of Chicago
Susan Seestrom, LANL, Retired
Steve Slutz, SNLGroup 2 – Non-Ignition HED Science and Long-Term PlanningGroup 2 assessed current and future HED contributions to the SSP, and evaluated the long-term
requirements for the ICF Program including the requirements for a “high-yield” fusion platform.
Federal Lead: Njema Frazier, NNSA
Meeting locations: LLNL, SNL, LANL, DOE-HQ
Reviewers: David Crandall, NNSA, Retired
Jill Dahlburg, Naval Research Laboratory (NRL)John Harvey, U.S. Department of Defense (DoD), Retired
Jeffrey Quintenz, NNSA, Retired
Group 3 – Scientific Foundations
Group 3 examined the fundamental science of the ICF Program and progress made inunderstanding the physics relevant to ICF/HED sciences: material equations of state,hydrodynamics, thermonuclear burn, opacity, and radiation transport. Group 3 focused on the
ICF Program’s partnerships with external organizations in these areas. The group assessed thefundamental science experiments currently being executed and the status and contributions ofuniversity programs. Lastly, Group 3 assessed current diagnostics and computational modelingcapabilities.
Federal Lead: Kirk Levedahl, NNSA
Meeting locations: LLNL, SLAC
Reviewers: Sean Finnegan, Office of Fusion Energy Sciences, DOE
Yogi Gupta, Washington State University
Stephanie Hansen, SNL
Richard (Dick) Lee, University of California, Berkeley
John Sarrao, LANL
George Zimmerman, LLNL

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2 Evolution of the National ICF/HED Program since the National Ignition Campaign
The NIC was an integrated national effort consisting of partnerships between national andinternational labs, academia, and industrial partners to achieve ignition and robust
thermonuclear burn on the NIF by the end of FY 2012. During the NIC, 84 of its 86 level one andlevel two milestones were completed. The two milestones not achieved were thedemonstration of limited “alpha heating” and demonstration of ignition. Although the world’s
most powerful laser, NIF, was constructed and successfully transitioned to routine operations,
ignition on the NIF was not achieved by the end of the NIC.
As the NIC was concluding, a workshop was held in May 2012, to “discuss science that had beenlearned during the NIC, identify new science questions that had arisen, and begin to lay thelines of experimental and theoretical inquiry that could address these over a multi-year timeframe.” 3 The workshop identified six Priority Research Directions (PRDs) that address key
physics issues preventing the attainment of ignition on the NIF.
In December 2012, the NNSA and ICF Program scientific and technical community partners
submitted to Congress the, “Path Forward to Achieving Ignition” Report. It proposed a pathforward and ICF Program goals for achieving ignition on the NIF and improving understandingof relevant physics to be explored at the other major ICF/HED facilities (Z at Sandia National
Laboratories, Omega at University of Rochester) over the three years following the conclusion
of NIC. The report presented specific programmatic and technical goals to be pursued at eachof the facilities: the LID Program predominantly conducted at the NIF; the LDD Program
predominantly conducted at Omega, but with elements on the NIF; and, the MDD Program
predominately conducted at Z. These goals became level two milestones for the ICF Program
and were accomplished in the 2012-2015 timeframe. A summary of the milestones is provided
in Appendix C.3. In addition, a summary of major accomplishments over that timeframe in the
ICF/HED portfolio that were not specifically part of the “Path Forward” is provided in Appendix
C.4.

3“Science of Fusion Ignition on NIF Workshop,” May 22-24, 2012, LLNL-TR-570412

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3 Review Topics
Each of the 20 reviewers submitted individual written reports that are available in Appendix B.
While many reviewers addressed the charge given to their assigned group, NNSA encouraged
reviewers to provide comments on all aspects of the program. Upon review of the individual
reviewer inputs, the authors of this report sorted the reviewer’s comments into the following
topics:
•
•
•
•
•
•
•

ICF/HED Contributions to the SSP
The Prospects for Achieving Ignition
Technical Challenges in Inertial Confinement Fusion
Experimental Diagnostics and Computational Resources
Improving Scientific Foundations in HED
Academic Programs and External Partners
Program Direction

The sections of the report are organized using this structure, with each topic beginning withbackground, followed by a segment that captures the major themes contained in the reviewer
comments, and closing with a summary of the NNSA program office perspective and next steps.
3.1 ICF/HED Contributions to the Stockpile Stewardship Program
Summary of Reviewer Comments
With the cessation of underground testing in 1992, the U.S. nuclear weapons program could nolonger directly develop and exercise the expertise of nuclear weapon scientists and the broader
nuclear security enterprise (full scale manufacturing, engineering, production, etc.) throughnuclear explosive tests. Established in 1994, the Stockpile Stewardship Program (SSP) was
created to maintain confidence in the stockpile and sustain the nuclear deterrent in theabsence of nuclear explosive testing. The SSP relies heavily on the NNSA laboratories tomaintain expertise in technical areas relevant to nuclear weapons design and performancethrough leading-edge, science-based programs, thereby providing confidence that the UnitedStates has a safe, secure, and effective nuclear weapons stockpile. As captured in the January
20, 2015 laboratory directors’ letter to the NNSA Administrator, found in Appendix C.1, “HEDscience remains a core technical competency for the Nation’s Stockpile Stewardship Program
for the foreseeable future.” In particular, the “pursuit of fusion yield in the laboratory is critical
for the long-term health of the Stockpile Stewardship Program.” The scientific grand challengeof achieving ignition at laboratory scale attracts top scientists from around the world to theweapons laboratories. It is also recognized that the study of thermonuclear burning plasmas isimportant to develop and validate computational models that are used for the annual
assessment of the stockpile and to resolve issues encountered during weapon surveillance.

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P a g e |5Experimental platforms specifically developed for ICF applications have been adapted andapplied to mature predictive capabilities for studying material properties, opacity andtransport, hydrodynamics and burn, and outputs and effects. There is significant overlap in theskills associated with conducting complex and highly-integrated experiments in the ICF Program
and those needed to conduct a nuclear explosive test. Specific skills include the ability to
conduct diagnostic development and manage many different interfaces through design,
fielding, and analysis. This expertise is important because one goal of the SSP is to maintain theintellectual acuity of the designers, scientists, and engineers who must remain cognizant of
nuclear weapons design, development, and operation. SSP scientists, engineers, and designers
rely heavily on modeling and simulation. Models and the overall simulation approach must be
validated through experimentation. Predicting the results of an experiment, then conductingthat work and analyzing the results and confirming or rejecting the related hypotheses andassumptions is an important learning experience: it is key to establishing experimentally
validated confidence in those models and simulations, and understanding their limitations.
Now, 20 years later, the ICF/HED facilities are the critical tool for providing confidence in thecodes and their limitations in the high-energy regime.
NNSA and its laboratories value the ability to conduct cutting-edge research to attract andretain new employees while also advancing HED science that is critical to the nuclear weapons
program. The NNSA laboratories embrace ICF/HED capabilities to test and train the next
generation of stockpile stewards. LLNL and SNL are more pro-active in using the ICF/HED
facilities in training their stockpile stewards. Since LANL lacks its own major HED facility, young
designers at LANL should be incentivized to carry out experiments at the NIF, Omega, and Z
facilities as part of their training in nuclear design.
By designing and executing experiments, scientists can experience elements of the design
process from hypothesis, to experiment, through complex data interpretation and analysis.
This enables development of validated understanding and design in the HED regime that is
applicable to many NNSA mission areas.
Recent advances in HED science testify to the scientific and technology value that the ICF/HED
portfolio is providing to the SSP. Contributions to SPP include providing equation of state (EOS)
materials data and observing the lattice structure of plutonium under dynamic conditions at Z
and NIF; resolving “energy balance” through experiments at the HED facilities; improving
opacity models and equations of state of other materials of relevance to nuclear weapons;developing x-ray and neutron sources to test electronic components and shock reentry
body/vehicle
materials;
and,significantly
improvingtheunderstandingofradiation/hydrodynamic instabilities, an area that is very difficult to probe experimentally.

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P a g e |6Experimental platforms have been developed for the NIF that achieve fusion yields greater than
10 kilojoules (104 joules). Studies of thermonuclear burn physics become possible as yields
increase to the ~100 kilojoule regime. Exploring burn physics in support of the boost science
effort is the primary focus for applications of yield over the next decade. 4 A multi-megajoule
capability (>> 1 megajoule) would be used to extensively study burn physics and to develop an
intense radiation source with an appropriate spectrum to support precise assessments ofnuclear survivability and vulnerability and to validate nuclear weapons effects codes.
While the pursuit of ignition is valuable on many levels, significant challenges remain for theattainment of “high-yield” laboratory fusion. The pursuit of high yield will test the innovationof designers in ways that few other technical pursuits can. Higher yields enable experiments totest the validity of current nuclear weapon codes in temperature, pressure, and density regimes
closer to nuclear weapons operating conditions, serving as a key means 5 to train the newgeneration of nuclear weapons scientists and engineers who have no experience preparing,fielding, or observing an actual nuclear explosive test. Although there is an inadequate
technical basis today for thinking that high yield from laboratory inertial fusion can be obtainedon existing facilities, the ultimate goal of high yield provides direction and shapes program
decisions many years in advance of the perceived need. Assessing the need for high-yieldcapabilities at laboratory scale should be a long-term goal of the ICF/HED Program.
Guarding against technological surprise is another significant driver for the ICF/HED Program.
Given the unique capabilities and the role of the ICF/HED Program in the SSP, continuing andbroadening DOD and Congressional support for the program through improved communication
is vital to the strength of the SSP and to ensuring national security.
••

NNSA Program Office Perspective and Items for Future Prioritization & Action
NNSA will conduct a gap analysis to determine the ways the ICF/HED experimental
program may be better developed to test weapon’s designer skills and judgement.
Additionally, reviewers commented that better intra-laboratory integration may be awelcomed step in this direction. For example, LANL should build upon recent successes
to improving integration between the HED physics team and the Theoretical Design
Division (XTD).
The three laboratories must strengthen the integration of ICF/HED capabilities(particularly NIF and Z) with the weapons effects and hostile environment communities.
Future Live Extension Programs for stockpiled weapons will inevitably have componentsthat will need to be certified for evolving Stockpile-to-Target-Sequence (STS)4Ten-year National HED Strategic Plan, January 30, 2015, COPD-2015-0003, LA-CP-15-00064
In addition, for example, to sub-critical experiments executed at the Nevada National Security Site (NNSS) andhydrodynamic experiments executed at the Dual-Axis Radiographic Hydrodynamic Test (DARHT) Facility at LANL.
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P a g e |7•requirements. NNSA will pursue an effort to assess the near term and long term
requirements for ICF/HED capabilities in the areas of outputs, environments, andeffects.
Working with laboratory leadership, NNSA will explore how the ICF/HED portfolio can bebetter balanced to avoid technological and geopolitical surprise over the long term.

3.2 The Prospects for Achieving Ignition
Summary of Reviewer Comments
Barring an unforeseen technical breakthrough and given today’s configuration of the NIF laser,achieving ignition on the NIF in the near term (one to two years) is unlikely and uncertain in the
mid-term (five years). The focus of the LID Program over the next five years should be on theefficacy of NIF for ignition. The question is if the NIF will be able to reach ignition in its current
configuration and not when it will occur. The focus of integrated experiments in the LID
Program should not be on high-gain capsules simply because codes and models predict they will
perform well. The codes and models themselves are not capturing the necessary physics tomake such predictions with confidence. A lack of appreciation for this combined with a failed
approach to scientific program management, led to the failures in the NIC.
There are areas of physics that are not well understood or not properly captured in models,codes, and current simulation approaches. Therefore, it is important to probe high energy
density states and the systems that create HED conditions as a function of energy density andchanges in that energy density. This requires a systematic experimental program to explore
factors that impact ICF implosions, and novel ways to measure the physics of the drive
conditions (laser-target interactions) and the implosion characteristics throughout the time of
the implosion.
Despite the failure to achieve ignition during the NIC, there are clear SSP drivers to study theproperties of robust thermonuclear burning plasmas, to pursue multi-megajoule fusion yields,
and to ultimately pursue high yield. This places significant onus on the NNSA, the laboratories,
and the sites to take a different approach to ensure that the significant technical challenges tolaboratory ICF will be met with the best possible science, within fiscal constraints.
Recent program management changes discussed in section 3.7, and sound scientific andstructural groundwork, increase the odds for achieving ignition at the NIF and multi-megajoule
fusion yield on a potential future laboratory driver. Nationally, a reorganization of the ICF
Program has been implemented and is highly effective; providing capable leadership, greater
functionality, and better alignment of the ICF Program with the broader weapons program. The
new research paradigm of the ICF Program is not an open-ended scientific program or an
exercise in systems engineering; but is a balance of integrated experiments, ignition sciencethat pursues focused experiments, and physics integration.
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P a g e |8Although buoyed by the contributions of ignition-driven and high-energy density experiments,
the SSP must be prepared for the possibility that there is no existing experimental driver thatwill achieve ignition. Due to this uncertainty and the challenge in achieving ignition atlaboratory scale, approaches to ignition in LDD and in MDD systems must be strengthened. The
Z and Omega Facilities (which are not designed to achieve ignition), along with the NIF, canstudy the physics of the assembly and “stagnation” of thermonuclear burning plasmas, which
benefits the development of all ICF approaches. The National Implosion Stagnation Physics
Working Group (NISP) is in the process of identifying specific ways to do this. A summary fromthis Working Group’s first meeting is located in Appendix C.5.
Ignition is an important step toward multi-megajoule fusion yield, not an end in itself. ICF
Programs in Russia and China are pursuing platforms that may surpass current U.S. capabilities.
High yield must remain a long-term goal for the ICF Program, even if ignition is not reached on
the NIF. In an extended era without nuclear explosive testing, driving towards a fusion sourceof 500 megajoules or greater will be essential for the health of the program.
Scientific exploration the efficacy of the NIF for ignition is an important endeavor for the SSP
and for broader scientific community in the United States. If the NIF achieves ignition,
applications of fusion yield would be of immediate relevance to the SSP. 6 If it does not achieve
ignition, the reasons for this must be understood and each major ICF facility play a could role indeveloping this understanding. The following sections detail the technical challenges facing
each approach to ignition and the technical challenges they share.
3.3 Technical Challenges in Inertial Confinement Fusion
This section summarizes technical observations in the following areas:••••

Laser-driven Indirect-Drive (LID), predominantly executed at the NIF
Laser-driven Direct-Drive (LDD), predominantly executed at Omega
Magnetically-driven Direct-Drive (MDD), predominantly executed at Z
Shared Technical Challenges between LID, LDD, and MDD
Laser-Driven Indirect-Drive (LID)

3.3.1.1 Summary of Reviewer Comments
During the last three years on NIF, LID achieved hotspot densities and temperatures with lower
convergence and higher adiabat capsule implosions, sufficient for about half of the total fusion
yield to come from alpha particle plasma heating. Trends can be observed in these results, as
the implosions have demonstrated better reproducibility than past implosions. Although thefusion yield is improved, it remains significantly lower than predicted by unperturbed (1-D)
6“Applications of Ignition 90-Day Study,” February 29, 20122015 Review of Inertial Confinement Fusion and High Energy Density Science Portfolio

P a g e |9calculations and a significant fraction of the laser energy (up to 200 kJ) remains unaccounted
for in gas-filled hohlraums.
The volume of high quality published research resulting from experiments during the last three
years is impressive. These articles have concentrated on the ‘high-foot’ platform, where scalar
yield performance has more closely matched predictions. This platform – which uses the same
capsule as the NIC point design with a larger laser prepulse (the “foot”) – has achieved close to1016 DT fusion neutrons (~26 kJ). This result is important and encouraging, because significant
alpha heating is a critical first step toward ignition launching a nuclear burn wave followed by a
rapid 10-fold increase of temperatures and thermonuclear burning of the surrounding dense
fuel. The fusion community has recognized this as a significant achievement.
New NIF diagnostic capabilities, focused experiments, and the ability to simulate the multidimensional effects of perturbations have improved the ability to discern which factors aremaking the most significant contributions to performance degradation. Principal degradation
sources are thought to be time-dependent drive asymmetry due to laser-plasma interactions
and shell perturbations caused by capsule mounting features (commonly known as the “tent”).
In addition, high convergence implosions suffer from mix, non-uniform fuel areal densities, andshell-break up.
Despite the success of the ‘high-foot’ design, the fusion yield remains significantly lower than
predicted by unperturbed (1-D) calculations. Producing adequately symmetric implosions of
indirect-drive ignition capsules has proven to be much more difficult than expected on the NIF.
Laser Plasma Instabilities (LPI), such as Stimulated Raman Scattering (SRS) and Cross Beam
Energy Transfer (CBET), are obstacles to creating the necessary time-dependent drive
symmetry. Time-dependent drive multipliers are applied in simulations to the x-ray drive tomatch the trajectory of the imploding shell. There appears to be a correlation between the
shape of the tent’s contact with the capsule and the structure of the capsule observed inradiography images. Other contributing factors to reduced performance of the high-foot design
include the fill tube, hot electron preheat, and inaccuracies in the equation of state ofdeuterium which impacts target design.
These are also major issues for the ‘low-foot’ design with a higher convergence ratio, whereinhydro instabilities and mix are known to be larger than in the ‘high-foot’ design. Low-adiabat
implosions, known as low-foot implosions, show areal densities close to simulations and to
those needed for high-fusion gain implosions. The experiments have shown low fusion yields,
however, suggesting that the hot spot of the implosions is not forming adequately.
Importantly, x-ray radiographs have shown evidence for shell perturbations caused by thecapsule “tent” that holds the capsule in place inside the radiation cavity, i.e., the hohlraum.

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The LID Program has stepped back from a singular focus on a monotonic increase of yield, but it
has also become diverse. This has led to reviewers’ concern that there is a slowing and dilutionof progress due to pursuit of too many scientific paths at once. The number of experimental
fronts pursued at the NIF grew at first but has recently decreased. This was viewed byreviewers as commendable, as focus is required for progress. Activities have been undertaken
to ensure that the diversity of ideas is not lost; ingenuity and ideas are desirable even if they
are ultimately discarded. Ideas that survive initial analysis may lead to short, targeted
experimental campaigns on Omega or Z to determine feasibility before progressing to the NIF.
Predicting the physics of implosions through simulations is extremely challenging. While some
aspects of the symmetry of imploded capsules is reproducible under small changes in initial andboundary conditions, computational capabilities for LPI are not yet fully predictive andhydrodynamics calculations have never been validated for the final stages of hot-spot assemblyand fuel “stagnation.”
It is unclear which path is more likely to eventually lead to ignition of the hot spot and cold fuel,and the odds of success. It is also unclear at this time whether this multi-platform approach is
better than one that focuses on fewer options at a time, in greater depth. It can take five to ten
experiments or shots to adequately study one concept on the NIF. Currently, there are only
~30 high-energy shots per year. Deciding which matrix of experimental campaigns to pursue is
not simple and requires constant planning, technical peer-review, and some degree of
flexibility.
3.3.1.1.1 Physics Issues Specific to LID
Incremental improvements in yield in LID have been achieved through an approach thatcircumvents problems, rather than by understanding and addressing them directly. While thishas created a baseline for future design efforts, there are underlying physics issues thatconsistently emerge and that need to be addressed. Significant limitations to predictive
capability remain. This means that the experimental exploration of parameter space isempirically-led or constrained to incremental departures from places of known performance.
Investing in diagnostics and other efforts in this area could adequately constrain models,particularly hohlraum models.
Cross beam energy transfer (CBET) was one of the first problems encountered during earlyexperiments on the NIF. There has been little attention given to assessing the time dependenceof the radiation symmetry that is responsible for introducing swings in the capsule shape during
implosion. It may be possible to use different pulse shaping on the inner and outer beams toprovide some time-dependent control of CBET, to design a shimmed capsule with a gradedablator, or to vary dopant thickness to mitigate swings in capsule shape during the implosion. It

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is also possible that gas-filled hohlraums will provide the only path to ignition on the NIF andneed to be understood.
The low- and high-foot campaigns experienced significant SRS from the inner beams. In fact, atleast 20 percent of the energy was reflected after including the CBET. Perhaps more
importantly, when comparing 15 shots with the same nominal target and laser conditions,
there were variations of 15 to 20 percent in the back scatter energy. In addition, there
continues to be variation in the amount of light absorbed or rescattered as it reflects back to
the laser entrance hole.
The lack of control over the time dependence of the CBET within the gas-filled hohlraums has
led to the development of alternative hohlraum designs with lower gas fill pressures. The
reduction of the tamping effect of the gas introduces a new set of challenges and requires
accurate modeling of the plasma expanding from the hohlraum wall, and modeling of thecollision of plasma expansion with the blow off from the capsule. These issues can be mitigatedby the use of denser ablator materials such as high density carbon or beryllium. These would
require a shorter radiation drive pulse and allow the laser energy to couple to the hohlraum
before it is filled by high density blow-off plasma.
A significant number of limitations remain that hinder predictive capability and inevitably meanthat the experimental exploration of parameter space is constrained to incremental departuresfrom a place of known performance. With the perturbation amplitudes apparent in current
experiments, the stagnation process is intrinsically three-dimensional. In places wherediscrepancies lie between experimental observation and 3-D simulation, it is unclear if theseare due to deficiencies in the way in which the hotspot is modeled or if the discrepancies arise
before the start of the deceleration phase. Simulations of the emitted neutron spectra are an
important predictor for whether or not key indicators of the hotspot temperature and velocity
are observable. Anisotropy of the neutron spectrum is a clear indication of a net center of mass
velocity in the hotspot. This is indicative of a low mode asymmetric implosion. Differences
between the DD and DT ion temperatures inferred from neutron spectra indicate that thecalculated spatial temperature distribution may be incorrect.
3.3.1.1.2 The Future LID Program
The LID research program is pursuing integrated experiments, focused experiments tounderstand the ignition science, and a physics integration effort with codes and models. Thisapproach will explore many different ideas and iterate on multiple platforms such as:•

Pushing ‘high-foot’ designs toward ignition through different gas fill, ablators, hohlraum
sizes and shapes, walls and drive profiles,

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••Lowering convergence ratios further and pushing to higher velocities and larger hot
spots so that the hot spot itself has enough mass to provide greater than 100 kJ yield,
andIncreasing the laser energy.

Within each focus area, the goal is to find an experimental platform for which there isagreement with 1-D calculations and to use this as a jumping off point and gradually pushtoward higher yield and ignition. The hohlraum/capsule configuration should be modified to
improve symmetry without the need for CBET. This will require larger hohlraums with areduced gas fill density. Larger hohlraums require more energy to maintain a given radiation
drive temperature. Some of this energy may be obtained through reduced LPI and backscatter,but it is probable that adequate symmetry will only be achieved at lower radiation drive
temperatures.
The LID Program should emphasize hypothesis-driven focused experimental campaigns that are
adjudicated through the interpretation of the data. It is important that experiments test thephysics models used in the radiation-hydrodynamic codes. Understanding the target physics ofa few focused areas is more important than executing an exhaustive experimental campaign ofmany permutations of ablator, capsule mount, and hohlraum gas fill.
Ideas for reducing the effect of the capsule support structure should be pursued, with the goalof identifying an improved alternative to the current tent. Many promising concepts for lessintrusive support structures have been presented and should be investigated. Since high yield
can be degraded by many effects, it is necessary to conduct these experiments under
stringently optimized and reproducible conditions (e.g., with good ice surfaces and wellcontrolled laser pulses). Engineering solutions designed to reduce perturbation levels can bedirectly evaluated through inflight radiographic diagnostics. The relative stability of the current
best performing capsules means that the perturbation induced by the capsule mount will be at
the limit of diagnostic resolution when the implosion is approaching the axis.
The pursuit of reduced convergence implosions is an important new feature of the program andshould be given a high priority. The so-called ‘big-foot’ design increases hot spot rho-R at theexpense of the cold fuel. The results will provide an important test of the new figure of merit
replacing implosion velocity with capsule convergence. If validated, this result will haveimportant consequences for future planning and will motivate fielding designs on the NIF todeliver yields approaching 100 kilojoules. One risk with this thinner ice-layer design is that mix
at the fuel-ablator interface, previously undetected in earlier experiments, could expose higher
Z material to the hot spot.

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Beryllium (Be) and other alternate ablators must be tested with hohlraums and laser pulses
optimized for them. It will be necessary to develop beryllium target designs in hohlraums that
demonstrate the expected desirable features, in order to fully evaluate and benefit from theproperties of beryllium that make it a potentially appealing ablator. This will require intensive
computational design and experimental efforts. Possible directions include large lowtemperature hohlraums optimized for capsule absorbed energy or drive symmetry, or higher
temperature hohlraums with the capsule optimized for hydrodynamic stability. It must be
ensured that these designs are optimized before ranking the ablator’s performance relative toother optimized target designs using other ablators.
LANL is pursuing alternate designs including double-shells, wetted foams, and Be ablators.
Double-shell capsules have two advantages over the single shell designs. The requiredradiation drive temperature in double-shell capsules is lower and the wall motion will be easier
to control due to the short pulse length requirement. It is not clear if double shells will be lesssusceptible to drive asymmetries due to the overall high convergence and the fabrication of
double shell targets is more complex. Target fabrication issues are presently impeding progress
on wetted foam designs.
LANL’s innovative designs are worth exploring, but are in need of a strategy. LLNL must work
more closely together to define the roadmap and decision processes for these designs.
3.3.1.2 NNSA Program Office Perspective and Items for Future Prioritization &Action• A specific effort to better understand all aspects of LPI, including CBET and SRS
independent of each other and in combination, is needed to measure, model andpredict the time-dependent drive symmetry in gas-filled hohlraums. NNSA will assessways in which this may be accomplished with a special focus on engaging the broader
scientific community.
• Mitigation of the effects of the tent is one obstacle to improved performance in LID
implosions. LLNL should identify a tractable number of alternate capsule support
structures, and the plans to experimentally assess those should be externally peerreviewed. For planning purposes, the program of experiments to investigate capsule
support features should conclude on approximately a twelve month horizon.
• A focused campaign with precision measurement of 1-D implosions, especially withlarge case-to-capsule ratio experiments, is a priority. This campaign should be
integrated into fiscal year 2016 planning.
• Beryllium and other ablators or concepts must be evaluated using a hohlraum and laser
pulse combination optimized for the ablator under investigation. A strategy, roadmap,
and decision process for alternate ablators and designs should be developed.
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••More resources should be dedicated to 3-D simulations using codes that are capable ofresolving the physics they are meant to simulate. This would provide insights into theresidual kinetic energy in the compressed shell, hot spot assembly, and stagnation
phase of the implosion.
An evaluation should be made to determine the optimum balance between high-energy,
highly-integrated ICF experimental campaigns, and lower-energy, discovery experimentson the NIF.
Laser-Driven Direct-Drive (LDD)

3.3.2.1 Summary of Reviewer Comments
The LDD effort has demonstrated a series of precision cryogenic implosion experiments on the
Omega laser with inferred hot spot pressures of ~50 gigabar (GB), and initial NIF experiments inthe polar direct-drive configuration have begun. Since direct-drive ICF target designs couple
more energy to the capsule than LID target designs, the required hot-spot pressure andconvergence ratio is lower for LDD target designs (~150 GB hot spot pressure for LDD versus
350-400 GB for LID, and convergence ratios of less than 25 versus ~35 for LID). However,relaxing the plasma pressure requirements in the proposed way makes it harder to meet driverand experiment fielding requirements. Requirements on the laser, such as drive uniformity,laser colors, and power balance, and requirements on fielding experiments, such as a fast
shroud retractor for the cryostat, target alignment, and vibration control are more stringent
than for LID implosions. In addition, the Two Plasmon Decay (TPD) instability will need to be
mitigated.
The LDD Program consists of two major components. The first is a program using a partial Polar
Direct Drive (PDD) configuration at the NIF to investigate LPI and other laser-target physics. The
second is a scientific study of Symmetric Direct Drive (SDD) implosions at Omega, where thegoal is to demonstrate high pressures in the low volume Omega targets. The demonstration ofgreater than 100 GB pressures on Omega DT implosions would be a significant result;calculations using LLE’s in-house codes suggest that performance may be extrapolated to NIFscale implosions to produce ~100 kilojoule yields.
Simulations of higher convergence and lower adiabat implosions indicate that mix due to socalled target debris or capsule impurities is affecting inferred hot spot pressure. The LDD effort
is actively investigating 3-D effects due to low-mode asymmetries induced by, e.g., laser power
imbalance, target offsets, and beam miss-pointing effects. LLE uses an in-house code for the
calculations of 3-D effects. No benchmark calculations, or comparisons with otherhydrodynamic simulations or with experimental data are presently available.

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3.3.2.1.1 Physics Issues Specific to LDD
A potential limitation for LDD is LPI at NIF scale-lengths. The LDD Program has made significant
progress in understanding the effects of CBET and the TPD instabilities relevant to LDD.
Currently, the predicted CBET for NIF-scale coronas in direct drive targets makes ignition
impractical even with 1.8 MJ of laser energy using SDD without mitigation.
As the capsule implodes and becomes smaller than the laser spot sizes, there is increased
overlap of the beams and an increased level of CBET. To counter this effect for SDD, LLE isdeveloping ‘zooming’ phase plates on the five-year timescale. The present program of work
using the PDD configurations on the NIF should instead concentrate on the use of an increased
range of laser wavelengths as the approach to CBET mitigation. The beam zooming option is
being explored on Omega and the wavelength detuning option is being explored on NIF.
TPD drives large-amplitude electron-plasma waves that cause hot electron preheat effects on
the fuel, affecting compressibility and laser-target coupling. Mitigation of CBET could itself giverise to plasma conditions where the TPD instability generates significant hot electron preheat.
Methods of reducing the impact of these effects will be addressed in focused experiments in
the SDD configuration on Omega and in the PDD configuration on the NIF by introducing layersof intermediate Z material. It is important to adequately address the threshold and scaling for
TPD with laser intensity, plasma-scale length, and for zoomed laser beams. The mid-Z layer iseffective in raising the coronal plasma temperature that in turn will lead to increased Landau
damping of plasma waves and consequently reduced hot electron preheat. The predicted
increase in temperature has been observed with Thomson scattering. A complete assessmentof mid-Z layers must analyze the effects on shock timing and possible generation ofreverberating shock waves in the ablator and exacerbated hydrodynamic instabilities.
The LDD effort has benefitted from extensive experience and computational capabilities that
support the modeling of CBET and TPD preheat, benchmarked against experiments on Omega.
The density scale lengths are a factor of four larger in SDD on NIF compared to Omega.
Predicting the behavior of LPIs in these plasmas will stretch the capabilities of these models. It
is therefore important that data from PDD on NIF is obtained to validate models that may be
used for extrapolation to SDD on the NIF.
Naval Research Laboratory (NRL) researchers have shown experimental results from Nike, a 2.5
kJ krypton fluoride laser located at NRL, of laser imprint reduction using thin gold overcoat
layers on planar targets, as well as alternative laser beam smoothing schemes. NRL is currently
extending their gold overcoat campaign to the Omega Laser System.

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3.3.2.1.2 The Future LDD Program
3.3.2.1.2.1 Polar Direct Drive on the NIF
PDD experiments on NIF are an key component of the LDD Program, but are unlikely to lead toignition. As such, this program should discontinue preparing the NIF for PDD implosions. For
example, it is not clear that 48 quads of Smoothing by Spectral Dispersion (SSD) are required if
PDD ignition attempts will not be pursued.
The principal aim of PDD experiments on the NIF is to provide a platform to test strategies for
CBET mitigation on density scale lengths that are significantly larger than can be obtained on
Omega and are within a factor of two of those that will ultimately be encountered in SDD
experiments on NIF. The focus is on experiments and diagnostics leading to high fidelity testsof LPI physics (particularly CBET and TPD) at the correct scale lengths and plasma conditions
relevant to ignition with SDD on NIF. The bulk of these could be planar and hemisphericalexperiments and include tests of high-Z overcoats or buried mid-Z layers as described in the
program plan. Tests of imprint for ignition SDD conditions should be included. Smoothing on
enough quads to enable high fidelity tests would be needed, but the deployment could be
paced by experimental progress.
The LDD Program will need to employ and develop simulation tools that have been tested
extensively against data. For example, for applications that will use the code HYDRA it will be
important to further develop the code and to implement CBET ray tracing to make quantitative
predictions. These tools should be tested against NIF experiments.
3.3.2.1.2.2 Symmetric Direct Drive on the NIF
The LDD strategy is based on the concept of demonstrating “hydro-equivalence” or assumingthat hydrodynamics that lead to high inferred pressures on Omega at 60 kilojoules will scale to
NIF implosions at 1.8 megajoules. The original papers on hydro-equivalence noted that there
are many physics phenomena that will not scale. This includes CBET, LPI, and heat transport inthe conduction zone, thermal conduction in the hot spot, and the mean free path to hot spot
size for the equilibration of the deuterium and tritium ions.
The goal for SDD integrated DT cryogenic shots on Omega is the demonstration of an implosionthat is hydrodynamically equivalent to a SDD implosion on the NIF at 1.8 MJ. Fuel pressures ofabout 120 GB will be needed for a direct drive ignition capsule on NIF to ignite. Similarpressures will have to be demonstrated on Omega. The plan is to increase the fuel pressure by
mitigating CBET, using thicker shell capsules, and improving beam pointing (symmetry).
Proving the scientific case for investing in SDD on the NIF, and in particular, proving that the
known issues such as CBET can be mitigated, represents a significant scientific challenge. This isparticularly challenging in cases where not all of the physical conditions necessary for such a2015 Review of Inertial Confinement Fusion and High Energy Density Science Portfolio

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test can be accessed with existing facilities. It is inevitable that when scaling up a design to alarger platform, not all of the parameters ranges that will be encountered can be fully explored
beforehand. It is therefore important that the data obtained in both PDD on NIF and SDD on
Omega are utilized to inform and constrain theoretical and computational models that will beessential for underwriting the scientific case for SDD on the NIF.
3.3.2.2 NNSA Program Office Perspective and Items for Future Prioritization &Action• NNSA will consider establishing a working group on hydro-equivalence with researchers
from across the LDD, LID, and MDD efforts. The group should rank the areas of scientificconcern with the hydro-equivalence argument, and decide what physics needs to be
explored/added to the design codes.
• The LDD Program, with representatives from both LLE and LLNL, should develop a multiyear plan that describes the deliverables and milestones that would be required totechnically justify a decision to convert the NIF to SDD illumination; in essence, develop
a decision tree, including a time-scale for determining the cost and impact of thisconversion.
• The NIF PDD experimental plan should focus on understanding the physics that does notscale hydrodynamically from Omega SDD experiments, primarily LPI.
• SDD implosions on Omega should be simulated using validated 3-D codes. Better
integration is needed between LLE and LLNL in this area, which is discussed in section
3.4.2.
• Diagnostics to better quantify “mix” should be developed for Omega and experiments
should be conducted to constrain simulations.
• Beam smoothing for LDD should be limited to a subset of NIF quads until/unless a
decision is made to convert NIF to SDD. An assessment of the minimum quantity ofbeam smoothing to study LPI-related physics on the NIF is needed, to support decisions
for potential future investments in SDD.
Magnetically-Driven Direct-Drive (MDD)
3.3.3.1 Summary of Reviewer Comments
The MDD approach provides an intriguing alternative to LID and LDD. Considerable progresshas been made in the development of the Magnetized Liner Inertial Fusion (MagLIF) concept in
the last few years. The achievement of fully integrated shots incorporating liner implosion,
magnetization, and laser preheat represents a significant milestone. The MDD approach has
lower implosion velocity, thick imploding shells, and lower required peak fuel pressure than thelaser-driven approaches. There is a much smaller experimental and computational databaseand less is known about the potential issues. Similar to other inertial fusion concepts, the first2015 Review of Inertial Confinement Fusion and High Energy Density Science Portfolio

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fully integrated MagLIF experiments produced fusion yields significantly lower than thosepredicted by 2-D Magnetohydrodynamics (MHD) simulations.
The first MagLIF experiments at the Z Facility have reached DD fusion yields of ~4 x 1012
neutrons at temperatures of ~2.5 keV. It is thought that conditions suitable for 100 kilojoulesof DT fusion yield with a pressure-time product (P∙τ) of greater than 5 GB-ns and a magnetic
field-radius product (B∙r) of greater than 0.5 MG-cm can be achieved on Z. DT fusion yield
estimates are based on experimental demonstrations of DD equivalent yield; use of tritium on Z
is not expected in the foreseeable future.
3.3.3.1.1 Physics Issues Specific to MDD
A number of mechanisms are thought to be inhibiting the fusion performance, based on
experimental observations and 3-D MHD simulations. These include the non-uniformity andreduced efficiency of the laser energy absorption, hydrodynamic mix of the liner and fuel, massloss through the Laser Entrance Hole (LEH), enhanced radial heat flow due to extended Ohm’s
law effects, and reduced convergence due to 3-D asymmetry at stagnation.
Much of the unpredictability of past experiments is explained by insufficient laser beam
propagation in the target. In current experiments, the Z Beamlet (~2 kilojoule laser) with atarget filled with D2 fuel produce laser heating temperatures of 200 eV. Initial simulations of
this process using LASNEX and HYDRA significantly over-predicted the fraction of laser energythat would penetrate the LEH foil and be deposited in the target. In addition to reducing thefraction of the beam that penetrates the LEH foil, LPI potentially causes the beam to filamentand spray. Filaments that heat the electrodes or the liner could mix this material into the fueland degrade the yield. This is supported by a recent experiment with beryllium electrodes that
performed significantly better than a number of previous experiments that had used aluminumelectrodes. An additional factor that complicates the modeling process is the presence ofembedded magnetic fields. Collaborations have been formed between SNL, LLE, and LLNL toperform dedicated studies of the laser heating process at Omega and, soon, at the NIF.
A significant risk to the MagLIF concept is the mix of material, either liner, window, or dense DT
fuel, into the hot fuel. The conventional wisdom is that at stagnation MagLIF is more prone tomix than laser-driven ICF because MagLIF designs have lower hot spot ρR than laser-driven ICF.
This translates into a longer burn duration to generate enough fusion heating to ignite.
Additionally, other poorly understood phenomena play crucial roles in the operation of a
MagLIF target, including the implosion of a magnetized liner/plasma assembly undergoingmagnetic flux loss, and magneto-hydrodynamic instabilities such as magnetic Rayleigh-Taylor
and electro-thermal instability. The limited existing capability for experimental diagnostics andpredictive simulations prevents sufficient understanding of target performance in these areas.

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3.3.3.1.2 The Future MDD Program
The MDD Program is largely concentrated on evaluating a single computational design,
primarily because experiments on Z occur at a lower repetition rate than laser experiments andthe program has a limited number of shots. While many of the design aspects for MagLIF areconstrained by the generator and available laser parameters, the main constraint appears to be
operational as the present program has insufficient experimental opportunities and lacks
availability to a sufficient number of designers and experimentalists to thoroughly evaluate
more than one design. This is a cause for concern as there would be a limited selection of
mature alternatives if current performance limitations ultimately prove insurmountable. Given
the current constraints, it is not immediately clear how alternative designs that go beyond
simple variations on a theme could grow from a nascent idea to a viable alternative.
As with the other inertial fusion approaches, it is extremely difficult to directly diagnose hotspot
conditions. This is made even more difficult due to the large ρR of the liner surrounding thefuel at stagnation. Results from the NIF have shown that there is a wealth of information
embedded within the neutron spectra. Progress on this has been made at SNL withmeasurements of primary DD spectra and secondary Triton reactions. However, theintroduction of tritium handling capabilities at Sandia would mark a considerable improvement
through increased yield and by introducing a range of new diagnostic options for assessing
hotspot ion temperature, plasma motion, and beam-target contributions. The ability to add
tritium or 3He to the fusion fuel and measure the fusion gamma rays produced in DT or D3He
reactions would allow observation of the fusion reaction history in the implosion, placing
constraints on model development.
The program could use more 3-D modeling to develop mitigations of instability features in the
implosion. This would complement the fielding of improved diagnostics of axially resolved
imaging, spectroscopy, and x-ray scattering to measure the conditions and allow forcomparison with simulation data. Simulation tools and models (including reduced models) withmagnetic fields will need to be developed and tested with focused experiments.
The MDD Program would benefit from the inclusion of LPI experts from across the complex toaid understanding of the laser plasma interactions of the preheat beam. Considering that thelaser preheat is an integral part of the MagLIF research, SNL should consider hiring a postdoctoral researcher to develop in-house expertise for the laser preheat stage of the implosion.
The decades-long goal of the magnetically-driven liner fusion effort is to produce yields
approaching a gigajoule. It is projected that this would require a driver with at least 130
megajoules of stored energy. The decision to turn away from the use of wire array Z-pinches
for indirect drive experiments came as something of a surprise to some in the community as
progress was being made using double-ended vacuum hohlraums and dynamic hohlraums. In
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retrospect however, this decision now seems logical as exploration of the X-ray driven indirectdrive concept is being pursued effectively at the NIF. In addition, more is known now about zpinch-driven hohlraums than when SNL actively pursued indirect drive a decade ago.
There is an opportunity to explore alternative indirect drive designs with larger absorbed
energies on a future larger-scale pulsed-power facility. As was identified in the mid-2000s, themain challenges of an MDD approach includes demonstrating enough pulse shape control tohave the requisite reproducibility and drive symmetry. It is important that the scientificcapability to resolve these issues be reestablished. This capability would enable a logicaltransition from LID to MDD in the future, should the SSP pursue “high-yield” fusion atlaboratory scale.
3.3.3.2 NNSA Program Office Perspective and Items for Future Prioritization &Action• The MDD Program’s highest priority is to demonstrate laser beam propagation andheating on Z which must include collaborations with LPI and laser experts across thecomplex.
• A comprehensive diagnostic plan for characterizing plasma properties during MagLIF
preheating and during implosion must be developed, with a focus on understanding
stagnation.
• A second beam line would enable simultaneous laser preheating of the target andradiographic backlighting, providing extremely important diagnostic information fromexperiments. A cost and schedule estimate for the development of a second beam line
on Z should be prepared for consideration.
• The ability to add tritium or 3He to the fusion fuel and to measure the fusion gamma
rays produced in DT and D-3He reactions should be a high priority.
• Shot opportunities on Z should be increased. The MDD Program should dedicate moreexperiments for understanding and optimizing the power flow in the driver-target
coupling, and understanding the scaling of MagLIF performance as a function of design
parameters such as current, fuel preheat, magnetic field, fuel density, liner aspect ratio,
and liner material over as large a range as possible at the Z Facility. There should also be
more experiments that pursue alternative concepts to MagLIF.
• Additional ICF resources should be prioritized to the MDD effort to build a stronger
cadre of designers, experimental physicists, and diagnosticians.
Shared Technical Challenges between LID, LDD, and MDD
3.3.4.1 Summary of Reviewer Comments
The ICF Program has traditionally been a ‘driver–centric’ research field. While the drivers
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remarkably similar. It is refreshing to see the creation of working groups such as The National
Diagnostic Group and the National Implosion Stagnation Physics Working Group (NISP) toadvance the understanding of the physical processes common to all three ICF approaches.
Measurement of and the creation of diagnostics for laser-plasma interactions, preheat, andcompression and burn physics, are excellent areas for collaborations among the ICF Program
elements.
All three ICF approaches must address laser plasma instabilities. LPI has been actively studied
within the context of ICF for more than 40 years. The community has made some progress in
its study of LPI, however, it needs improved understanding. These processes are being
modeled with codes that are reduced models such as PF3D. There have been claims that thesecodes have been validated against experiment, but they need to be validated against codeswith additional physics. While the assumptions might be reasonable at lower laser energy, they
could be different at higher laser energy, and at different plasma temperatures, densities,
temperatures and density scale lengths, and mixes of material. For example, none of these
reduced models can include the effects of self-generated or imposed magnetic fields. Fully
kinetic models such as Particle In Cell (PIC) codes have shown that the reflectivity from SRS is in
short bursts, and can exceed unity for short times.
The LPI effort was a major driving force in the development of PIC codes. PIC codes are now
widely used throughout the plasma physics community and are currently in limited use within
the ICF effort. This recent precipitous reduction in the LPI effort is due largely to the inability ofeliminating it and the hope that LPI issues could be engineered away. Unfortunately, LPI,
including CBET, is arguably the biggest obstacle to high-yield designs. This philosophy has led toa significant decline in expertise on fully kinetic modeling of LPI at and outside the ICF
laboratories, and has led to insufficient diagnostics for LPI on NIF.
There is the increasing realization that the stagnation phases of all three approaches are
intrinsically 3-D processes. 3-D simulations could provide physical insights for many aspects of
the implosion stagnation, especially in cases where there may be turbulence and where energy
is flowing as a result of asymmetries. Importantly, experimental efforts focused onunderstanding physical processes are imperative for each approach. The NISP could help
identify these specific areas.
3.3.4.2 NNSA Program Office Perspective and Items for Future Prioritization &Action• The NISP should develop a comprehensive plan for using the NIF, Z, and Omega, andvarious computational capabilities, as a scientific tool set to advance fundamental
understanding of the physics of the stagnation process and the state of the fuel andablator near and at stagnation.
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•A working group should be formed for LPI physics similar to the NISP in its structure andcharge.

3.4 Experimental Diagnostics and Computational Resources
Diagnostics
3.4.1.1 Summary of Reviewer Comments
Adequate diagnostic instrumentation at NNSA’s ICF facilities is needed to assess progress,
develop theoretical understanding, and validate computational simulations. New diagnostics
are often the driver for making new scientific discoveries and reducing uncertainty. The overall
rate of scientific progress can often be directly linked to levels of diagnostic investment.
Previous experimental efforts under the NIC were frustrated by the inability to distinguish key
differences between experiments. An improved diagnostic suite has enabled many of theadvances since the NIC, in particular the ‘high-foot’ design described earlier. For example, newdiagnostics have revealed structures that were not known to exist transforming theunderstanding of the structure of the plasma.7
The National Diagnostics Plan, first published in February 2015, was the result of interlaboratory cooperation and presents a national strategy for the systematic improvement of
diagnostics techniques across all ICF platforms. The plan is divided into three categories ofdiagnostics – transformative, broad, and local; and incorporates international scientific andengineering expertise to define the diagnostic development requirements for ICF research. The
plan presents a reasonable timetable for instrument development and deployment, andidentifies eight transformative diagnostics that will revolutionize the data obtained fromcurrent ICF facilities. In addition to benefitting ignition efforts, improved diagnostics will
provide precision measurements for single physics experiments to improve codes and models
for the broader HED portfolio. Diagnostics development is a fertile area for university
collaboration, student training, and the recruitment of new staff. A technical working group
established by NNSA monitors diagnostic development at every stage from concept, to analysisof alternatives, to scientific use. The scientific, engineering, and fabrication tasks of diagnostic
development are divided among LLNL, LANL, SNL, LLE, NRL, and other partners, based on theefficient use of resources.

7

Important diagnostic platforms now in place at the NIF include: re-emission balls, keyhole VISAR, 2DConA
radiography, self-emission x-ray images, primary and down-scattered neutron images, ∆ρR from FNADS, andoutgoing shock imaging. Besides these, other diagnostic platforms under development include foam balls, 5-axis
keyhole, gated SXI, late-time 2DConA, early time self-emission, higher resolution imaging at stagnation including
KBO (Kirkpatrick Baez Optic) and penumbral imaging, Compton radiography at stagnation, and co-aligned neutronand x-ray imaging.
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While there are common needs across all facilities, the implosion geometry at Z provides
unique challenges. The MDD Program has succeeded in delivering excellent data forcompression and burn. Future improvements in temperature measurements with x-ray
scattering and down-scatter from beryllium or deuterium are a priority. There is a need todevelop further a diagnostic plan for the MDD effort to characterize plasma properties during
preheating and implosion, with a focus on understanding mix.
There is a need to improve the understanding of LPI, making optical Thomson scattering
instrumentation a high priority on the NIF. At the very least, two more Near Backscatter
Imagers (NBIs) should be added on NIF, one at a new azimuthal angle and another at the
opposite pole. Adding another Full Aperture Backscatter (FAB) diagnostic at one of theseangles would be useful.
For all ignition approaches, the time between peak velocity of the shell and stagnation is key;when inflowing kinetic energy is converted to thermal energy of the hotspot and fuel, and thewhole assembly is brought to its maximum density. Imaging diagnostics to measure hot spot
formation and resulting residual kinetic energy, including imaging and spatially, spectrally, andtemporally resolved spectroscopy, should be a high priority.
3.4.1.2 NNSA Program Office Perspective and Items for Future Prioritization &Action• The implementation of the National Diagnostics Plan is a high priority. NNSA is placingemphasis on improving spatial, temporal, and spectral resolution for increasingly
stringent tests of theory and simulations.
• Advanced diagnostics to address the needs for fundamental physics should be among
the highest priorities. This includes, for example, the observation of the Doppler
broadening from x-ray emission lines to produce velocity maps and accurate
measurement of residual kinetic energy; the use of particle and x-ray scattering
methods to measure the physical properties of dense matter (e.g., by observing
Compton and plasmon features); and spatially, spectrally, and temporally resolved
focusing spectroscopy.
• Measurements that must be pursued in a sustained and meaningful manner include:
accurate P-V and temperature measurements spanning a large region of densitytemperature space and measurements that can directly examine the microscopic
structure of the HED states.
Computational Resources
3.4.2.1 Summary of Reviewer Comments
Ignition will not be achieved without multi-physics design codes that have sufficient predictive
capability to guide complex, integrated physics experiments. More detailed physics will need to2015 Review of Inertial Confinement Fusion and High Energy Density Science Portfolio

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be included in codes and models as new concepts are investigated and proven, and as newexperimental data – utilizing improved, transformative diagnostics – are acquired. Across LID,
LDD, and MDD, there is an incomplete knowledge of the physics being included in various
models/codes, the equations being solved, and the physics packages being utilized in specificcalculations. Some codes have been developed with little or no external peer review. There is
duplication of code and modeling efforts and impediments to accessing codes andcomputational resources by sites other than the primary site where the capability wasdeveloped or resides.
Considerable funds are spent developing ICF design codes. Code and modeling efforts should
be coordinated across the laboratories and external partners should be included or considered
as potential leads for these efforts. To the extent possible, codes should be available to all ICF
researchers with a “need to know” and the proper clearance, both for simulation purposes andfor code development. At a minimum, there should be a reduction in restrictions for code-use
and source-code availability (at least among the ICF laboratories). This would increase thescrutiny on the constituent models and algorithms that comprise “the code,” and create
opportunities for interactions from outside the originating code development team. While
integrated codes are likely to remain the domain of the labs in general, it would be valuable topromote university-led microphysics code development for the validation of physics packages
in integrated ICF codes, perhaps through the Stewardship Science Academic Programs.
Ultimately, the codes should not be considered the property of a particular laboratory or
person.
A widely-held view is that a code has been validated once it provides agreement with anexperiment. However codes involve complex and nonlinear couplings among choices of
reduced physics models with fitting parameters and numerical approximations. Furthermore,each reduced model should be validated against meso- and/or micro-scale physics to haveconfidence in the results. Additional considerations include the range of applicability for thecode (is the simulation being set-up, run, and analyzed properly for the application at hand) andthe 3-D nature of the features observed in LID, LDD, and MDD experiments. The ICF Program
would greatly benefit from routine use of 3-D simulations. These advanced validation efforts
are complementary to the fielding of spatially, temporally, and spectrally resolved imaging,
spectroscopy, and x-ray scattering diagnostics to measure the conditions and allow forcomparison with higher-fidelity simulations.
Many experimentalists, as well as theorists, modelers, and designers, use the HYDRA code to
calculate results. Therefore, it is important to further develop the HYDRA code and to
implement CBET ray tracing to make quantitative predictions. A wide range of ICF-relevant
physics packages are developed and implemented in HYDRA, and the code has been tested
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against a large database of integrated and focused experiments. The continued developmentof the code, particularly the inclusion of direct drive-relevant physics, and ensuring its suitability
for use with high performance computing benefits the ICF Program and its’ SSP mission.
There are many areas where the physics packages need to be further developed or better
integrated into the codes. LPI physics is not adequately integrated into ICF codes. Kinetic
effects, which are important to properly model hohlraums and may be important in MagLIF
targets, are not sufficiently characterized. Particle In Cell (PIC) codes, now widely usedthroughout the plasma physics community, are in limited use within the ICF Program. VlasovFokker-Planck (VFP) codes now include fully parallelized architectures that expand the
distribution function into an arbitrary number of spherical harmonics with implicit field solvers
that can use very large cell sizes. PIC and VFP codes can be used to test physics packages or be
integrated into the hydro codes. PIC codes can now model more spatial and temporal scales
and can run on 1,000,000+ cores and on GPUs and Intel® Xeon Phi™ processors, allowing forthe study of some hydrodynamics on relevant scales.
The ICF Program should address the following areas: the relative immaturity of LDD-related
physics in some ICF codes; duplication and inefficiency in integration of the Advanced
Simulation and Computing (ASC) Program and ICF Program efforts at SNL; optimization of usetime for LLNL ASC resources between capability and capacity platforms; access by LLE and SNL
to codes developed at LLNL; and, reinvigoration of LPI efforts. The ICF Program relies heavily on
investments made by the ASC Program, so it is worth examining the challenges emerging as aresult of constraints imposed by the pursuit of exascale computing and platforms. The move at
LLNL to a new computer architecture for the next generation is, in general, a challenge for theSSP.
3.4.2.2 NNSA Program Office Perspective and Items for Future Prioritization &Action• ICF codes and models have been largely developed in a compartmentalized manner.
The ICF Program Office will conduct a deeper review of: (1) the prioritization ofcomputing resources; (2) ways to eliminate historic site boundaries that impede
progress, and; (3) opportunities to engage external/academic groups to lead or
participate in computational efforts where appropriate. A set of workshops, similar tothe successful MHD workshop in August 2015, are needed to evaluate the best pathforward for code development, particularly for fully kinetic LPI codes.
• The ICF Program Office will work with the ASC Office to conduct an assessment of the
impact to the ICF/HED Program of the transition to next generation computerarchitectures and the pursuit of exascale.

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3.5 Improving Scientific Foundations in HED
Summary of Reviewer Comments
New experimental capabilities are providing opportunities to improve codes and models used
to support NNSA’s ignition and weapons physics efforts, and to improve scientificunderstanding of phenomena relevant to a broad range of fields such as laboratory
astrophysics and high-pressure physics. The community is now acquiring enough systematic
data to discriminate between physics models in regions of interest, an improvement from theprior reliance on single measurements.
Because the interpretation of HED experiments depends on radiation-hydrodynamic
simulations, the ICF Program, in close coordination with the Office of Research andDevelopment and the Office of Advanced Simulation & Computing, will need to integrate thebest possible physics models into these codes. Plasma transport models must be able to treat
mixtures of elements accurately, and models must be extended to include non-Local
Thermodynamic Equilibrium (non-LTE) effects through tables or algorithms that can run on
future high performance computing architectures. Models for materials behavior, opacity, andtransport coefficients must be self-consistent.
In most ICF/HED experiments, the laser or pulsed power driver nonuniformities imprints onto
the response of the target. The nature of that interaction needs to be fully characterized
before the experiment can be completely understood. The disparate temporal and spatial
scales associated with characterizing and understanding interactions of radiation with matter,particularly when compared to hydrodynamic scales, make the simulation of this problem
intractable. As a result, this aspect of ICF/HED physics is often oversimplified or entirely
ignored.
HED experiments are deeply connected to the method of energy delivery, and each driver has
its own idiosyncratic energy delivery, native efficiency, and diagnostic challenges. HED results
are best validated through comparing data from different platforms or drivers. This was
highlighted in the early 2000s by the controversy over the equation of state for deuterium, as
determined from data obtained at Z and Nova. Recent anomalous iron opacity measurements
on Z will require validation by NIF experiments. Z and NIF are natural partners for crossplatform validation.
X-ray Free Electron Lasers (XFELs), such as the Linear Collider Light Source (LCLS) at SLAC,
uniquely allow for decoupling volumetric heating from the probing of the plasma. For instance,data sets were successfully obtained for Al, Si, and Mg, due to XFEL emission at wavelengths
that are not emitted thermally, even though the system is hot. XFELs provide the ability toobtain data on femto-second time-scales with a probe tunable to greater than 10 keV.

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A strategy of tolerance or avoidance of deleterious instabilities was used during the NIC. This isunderstandable given the complexity of the problem. However, laser-plasma interactions andthe assembly of hot spot at “stagnation” are fundamental to ICF. Dedicated experiments, newmodeling tools, and theory must be used to address this challenging problem head-on.
To establish priorities for planning integrated and focused experiments, it is important todevelop a simulation database that evaluates performance degradations of DT implosions due
to possible errors and uncertainties in the microphysics. Such calculations might also aid theunderstanding of existing experimental databases. An important area of focus is bridging
between atomistic microphysics and integrated hydrodynamics. Appropriately diagnosed andfocused experiments can provide insight into continuum lowering and the ionization state ofdense plasmas. This would allow the validation of calculations of physical properties such as
conductivity, pressure, and ionization balance used in the radiation-hydrodynamic modeling of
implosions.
3.5.1.1 Equation of State physics
NIF, Z, and Omega are producing conditions within materials that only exist in nuclear weapon
explosions or at the cores of astrophysical objects. Recent experimental and theoretical results
have shown that Thomas-Fermi modeling provides a poor approximation to the EOS ofextremely dense materials. Better approximations can improve the fidelity of future ICF
designs. Resolved measurements capable of distinguishing between theoretical models will
advance the field toward understanding and, ultimately, the appropriate use of simulation tools
for predictive capability. Complementary facilities such as the LCLS and APS are providing theopportunity to diagnose the transition of materials through phase changes, with a level ofprecision capable of distinguishing between advanced theoretical models. Researchers aretaking full advantage of these new capabilities to generate experimental data to constrain EOS
models in ICF/HED codes.
High pressure EOS studies are relevant to the study of the formation of planetary cores,
creating opportunities to engage with researchers outside of the ICF/HED Program. It is clearthat the development of high quality equations of state, self-consistent with structure andstrength and implemented into global models with phase transitions accurately captured, will
challenge researchers for decades to come.
HED experiments and modeling should explore the time-dependent phase transitions and theeffects of departures from thermal equilibrium, such as unequal electron and ion temperatures.
Most modeling assumes that pressure and energy can be specified as a function oftemperature, density, and composition in equilibrium. A multiphase model has the potential toinclude time-dependent phase information, once supplemented with the appropriate transition
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dependency. Unequal electron and ion temperatures exist in HED experiments, but models
assume that the pressure is separable into electron and ion components without consideringcorrelation effects, such as screening effects of ion temperature on electron pressure. Current
non-LTE radiative models required to simulate hohlraums and doped fuels provide EOS
quantities that do not agree with equilibrium models. Dependency on simplistic concepts, suchas degree of ionization, should be reduced in favor of more fundamental modeling approaches.
The scientific field of materials modeling relevant to EOS is progressing in an efficient manner.
The codes being developed provide reasonably accurate results, in agreement withexperiments conducted at several NNSA facilities; and EOS models along the Hugoniot, basedon shock wave experimental data, are well in hand. Remaining challenges are the lack of
accurate independent temperature measurements in high pressure experiments, and the limit
in phase space explored as much of the data collected is from diamond anvil cell platforms oralong the Hugoniot in shock wave experiments.
3.5.1.2 Opacity and Transport
Opacity and transport studies are foundational to the field of high energy density physics, andunderpin the ability to model and predict ICF system performance. The availability of facilities
such as NIF, Z, and LCLS and the development of high performance computing platforms areenabling scientists to improve the understanding of microphysics and atomic processes inextreme conditions.
Opacity models that are based on the assumption of Local Thermodynamic Equilibrium (LTE)agree with one another better than they agree with experimental data. For example, codes
predict that the ionization state of carbon in the dense ablator plasma of an ICF implosion isclose to two. However, advanced modeling and experiments suggest that the correct ionization
state is four, which has consequences for opacity and heat transport. This illustrates the needfor advanced models with detailed configuration accounting, non-LTE physics, and continuum
lowering physics that are validated through experiments.
Measurements of emission and absorption non-LTE opacity are difficult, as are measurementsof plasma transport coefficients such as thermal conductivity, electron-ion coupling, andstopping power in a uniform plasma of known temperature. Experiments designed to measurethese properties are highly integrated, and are best suited to validating theoretical models. The
recent measurements at the Z Facility of the opacity of iron indicate that the opacity isapproximately twice the average calculated by the best models. If the Z data are correct, theapproach to modeling opacity needs to be rethought.
The research community clearly understands the significant challenges and opportunities thatexist to advancing the understanding of the physics of opacity. Researchers are making
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excellent use of multiple NNSA experimental facilities and DOE facilities such as the LCLS, to test
theoretical models and predictive capability. Data from the Z Facility are in excellent
agreement with models of some materials, such as nickel, and are in striking disagreement forother materials, such as iron. The discrepancies between observations and theoretical models
are clear opportunities to advance NNSA’s understanding.
As with opacity research, scientists studying transport properties are making excellent use ofexperimental facilities in NNSA and outside NNSA, such as LCLS and the Advanced Light Source(ALS) at Lawrence Berkeley National Laboratory. There is limited experimental data in ICFrelevant regimes, but this is changing; precision measurements are now providing data that ischallenging the state-of-the-art microphysics modeling in codes such as DFT-MD and
Purgatorio.
Accurate modeling of non-LTE population kinetics, which likely dominates the ionization stateand distribution of atomic configurations in virtually all laser-plasma experiments, is anenormous challenge for simulation codes, as the number of levels can become intractable forhigh-Z plasmas. Benchmarking opacity calculations with experiments has been a low priority.
There have been several attempts over the last 35 years to create data to benchmark radiative
properties, such as line shapes, population kinetics, and collision physics. These efforts havebeen thwarted by difficulties with the plasma gradient structure; creating a uniform
volumetrically heated sample to diagnose is challenging.
Magnetic fields affect electron thermal conduction, which then affects plasma density gradientsand hydrodynamic instability growth rates. Routinely running 3-D simulations at adequate
resolution with magnetic fields is resource intensive. Incorporating the possible need fortransport modeling, in place of flux-limited diffusion, is a grand challenge. The validity of using
a single fluid hydrodynamic model is questionable for simulating performance in low density
hohlraums and exploding pusher targets.
The diminishing numbers of scientists trained in the fields of opacity and high temperature,high energy density atomic physics, and spectroscopy is a big concern. There is a severe
shortage of young talent in opacity modeling at the national labs, and if left unaddressed, will
erode NNSA’s strength in this core competency.
3.5.1.3 Hydrodynamics and Burn
The importance of hydrodynamic and burn physics to the ICF/HED Program cannot be
overstated, and the program’s portfolio is unmatched in its breadth, depth, and standing.
However, a systematic approach to enhanced predictive understanding appears to be lacking.
The program lacks sufficient diagnostics for the conditions of an imploding ICF capsule, andresearch is dependent on numerical modeling to characterize these conditions. Because
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outputs from numerical simulations are routinely used to infer the properties of imploded
targets (such as the hot spot temperature used as an initial condition for inferring fundamental
properties), it is important to be able to accurately diagnose the hydrodynamic and kinetic
behavior in converging targets, including 3-D flows and viscosity.
Experiments focused on hydrodynamic instability growth are well matched by simulation, but
the community seems overly focused on hydrodynamic growth and its impact on implosion andignition, and not on the underlying general coupled multi-physics problem. A key issue is theinability to assess accurately the full impact of the driver on initial conditions, such as CBET and
hot electron pre-heat. This may be more important than the relatively well settled issue ofpredicting the growth of hydrodynamic instabilities, such as Rayleigh-Taylor (RT), Richtmyer–
Meshkov (RM), or Kelvin–Helmholtz (KH) at low or high mode number.
Instabilities can combine in ways that are difficult to predict; but are apparent in astrophysicalphenomena, ICF/HED experiments, and nuclear detonations. Much can be learned fromastrophysical phenomena, however weapon scientists need more information than can beobtained from astrophysics, and this was clear during the review discussions. LANL scientists
have developed a shock-shear platform that demonstrates complex plasma instability behavior
in a controlled manner. Used on Omega and NIF, this platform is providing data of value tofundamental science and has value towards answering specific weapons performancequestions. Other fundamental science efforts by labs and university groups explore colliding
plasmas and various plasma hydrodynamic phenomena, and are of value to the weaponscommunity. New diagnostics, coupled with more sophisticated models, create opportunities topursue previously unresolved fundamental questions.
Many of the challenges inhydrodynamics and burn are common to the ICF/HED Program and other scientificcommunities, presenting opportunities for generating innovative ideas through collaborations.
In layered implosion simulations, all unstable wavelengths can be resolved in the highly
resolved spatial representation of the material structure in the calculation. This provides anopportunity to advance understanding of the evolution of these instabilities into turbulencewith the resulting mixing of materials in the target. For example, LES and RANS models areneeded to simulate turbulent mixing in deuterated carbon mix experiments. Unfortunately,
these models have not been successful in correctly predicting all three DD, TT, and DT reaction
yields. Most capsule simulations are done in 2-D using diffusive energy transport and without
self-generated magnetic fields.
A growing body of data enabled largely by the nuclear diagnostics developed by MIT suggests
the importance of kinetic processes. Developing understanding of these processes will
challenge experimental platform development, diagnostics development, and development ofmulti-scale modeling capabilities. The integration of kinetic or microphysics effects into the2015 Review of Inertial Confinement Fusion and High Energy Density Science Portfolio

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modeling of integrated systems in a self-consistent way is a grand challenge and will push thefrontiers of high performance computing.
Although “strength models” are used to model time-independent, inelastic deformation ofsolids, this may not be the correct way to represent the physics of Resistance to Deformation(RTD) under dynamic loading. But the determination of material strength or RTD needs to go
beyond time-independent, phenomenological approaches. Understanding RTD or developing
accurate strength models applicable to a wide variety of load paths remains a significant
challenge and is important. Plane shock wave or ramp compression data are not sufficient todiscriminate between different strength models.
••

NNSA Program Office Perspective and Items for Future Prioritization & Action
Regarding fundamental science efforts, the ICF Program Office will:o Support individual investigators at laboratories who are pursuing fundamental
physics research, through capture of specific goals into program plans andannual implementation plans to emphasize this work.
o Pursue of theoretical quantum molecular dynamics and other approaches fordevelopment of equations of state, transport properties, radiation properties(particularly line shapes), and non-LTE physics. Emphasis will be placed on
experimental observables that can be used to post-process simulations for direct
and detailed comparisons with data.
o Support university investigators working in the area of HED physics through bothexperimental time on HED facilities and financial support for graduate students,
postdoctoral fellowships, and research costs.
The ICF Program Office will specifically seek opportunities to validate physics models
directly by utilizing all available experimental platforms, making cross-platform
comparisons, and developing complementary platforms and diagnostics. This includes:
o Validating the recent Fe opacity experiments on Z through further experiments
on Z and conducting experiments on the NIF, ando Understanding and utilizing the unique and complementary characteristics of the
LCLS for HED investigations.

3.6 Academic Programs and External Partners
Summary of Reviewer Comments
Partnerships with academia and private industry are instrumental to success in HED science,
particularly for ICF. Scientific engagement with partners outside the NNSA laboratories lessens
insularity and reduces the potential for group think. Therefore it is important to maintain avibrant community of researchers external to the national laboratories to serve as a pool ofcollaborators and as a scientific system of checks and balances.
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The DOE Office of Science (SC) and NNSA share an interest in nurturing partnerships anddeveloping researchers in HED science. The interests of emerging scientists should influence
program planning in SC and NNSA; the pending retirement of professors in the field makes thissomewhat urgent and strengthens the importance of the ICF Program PRDs. The PRDs provide
a link between basic and applied science in ICF, and help to establish more effective ties
between the academic community and laboratory scientists.
The ICF/HED Program maintains a world-leading set of experimental facilities, from modest
facilities such as Trident, Jupiter, and Nike, to larger facilities such as the National Ignition
Facility, Z Facility, and the Omega Laser Facility. These facilities enable research at the frontierof discovery science in HED and ICF and attract many of the best and brightest researchers into
the field with the opportunity to study matter in the laboratory at states that otherwise only
exist in astrophysical systems.
The availability of new facilities provides an extended set of capabilities that NNSA must
consider when executing its mission. For example, facilities like LCLS operate on the basis of
the peer group proposal process, with the best proposals awarded beam time. ICF should
support newer capabilities being built around the world, such as petawatt lasers generating
relativistic electrons and other extreme conditions, high energy swift heavy ion sources, andsub-picosecond, intense hard x-ray free electron lasers (XFELs), and use these new capabilities
to build new partnerships, provide relevant benchmark data, and recruit from a broader pool ofhigh-quality students.
The Z Facility and the NIF are not considered typical user facilities. At both facilities, in order foran external (non-NNSA) user to conduct an experiment, there must be strongly engaged NNSA
laboratory scientists with the understanding and requisite savvy to efficiently support theexperiments as well as a genuine interest in the science being explored. They must have astrong scientific interest, the time, the experience, and the stature in the facility to help theacademic partner succeed. It is important to provide some open experimental time through acompetitive peer review process to capture the full potential for fundamental science on thesefacilities. Although only a limited amount of time is made available, every fundamental science
experiment provides tremendous value to the researcher, student, or partnering agency.
Although NNSA requirements necessarily limit the amount of experimental time dedicated touser-driven discovery science, there is broad agreement among the reviewers that it is an
important component of the suite of experimental activities. Another important aspect of user
access is for that access to be multi-year with commensurate funding needed for graduate
students to complete their work and for laboratory staff to support the experiments. Finally,
access to codes by external researchers is needed for experimental design, to broaden the codeuser base, and to level the playing field for leading edge research.
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The state-of-the-art ICF/HED research facilities and the grand challenge of ignition makes NNSA
laboratories attractive to talented young researchers and helps to retain the highly-competentstaff who contribute directly to the SSP. One strategy to broaden the pipeline is to engage nearneighbor disciplines. Many leading professors with good track records of supplying students to
NNSA laboratories are nearing retirement. At some universities there is no clear succession
plan and the path to sustain the research program and the student pipeline is not apparent.
NNSA invests in university HED science through multiple programs: the Stockpile Stewardship
Academic Programs, which includes the Stewardship Science Academic Alliance (SSAA)
Program, the National Laser Users’ Facility (NLUF) Program, and the Joint Program in HighEnergy Density Laboratory Plasmas (JPHEDLP); and through support of users groups such as the
Omega Laser Users’ Group (OLUG) and the NIF Users’ Group. More could be done to support
the academic programs that train the next generation of scientists and to recruit them, bycreating and strengthening partnerships between the national laboratories and universities,
grant programs, graduate student fellowships, and by providing more access to experimental
facilities. The talent pipeline should be monitored to ensure that individuals with relevant skill
sets are available in sufficient quantities; so that the program is better informed to makedecisions regarding investments in academic programs.
•

•

•

•

•

NNSA Program Office Perspective and Items for Future Prioritization & Action
A call for Centers of Excellence, which includes the current HED Centers, is scheduled forsummer 2016. Academic investments for the HED portfolio will be selected, informedby the results of the 2015 ICF/HED Review, with consideration given to partnering with
SC and industry. A Center structure with scientific independence is envisioned, but with
exposure to the national laboratories for students, with fellowships and collaborative
projects, and with critical skills developed through incentivizing key scientific areas.
NNSA will consider a sabbatical program through which national laboratory or university
scientists could spend dedicated time at another lab or university to foster scientificcollaborations.
NNSA will review ways to better use the full breadth of SC and worldwide scientificcapabilities that can achieve the HED conditions for the SSP mission. This will include
identifying ways to reward scientists at the laboratories for developing and fostering
successful collaborations with researchers at universities and private companies.
NNSA will explore metrics to measure the health of the staff pipeline, tracking both thenumber of students entering the laboratory system and the schools and faculty training
them. Ideally, future funding decisions will consider this data.
The NNSA will explore potential user models for the ICF/HED facilities that balance
mission-specific requirements with the desire for access from the broader scientificcommunity.

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3.7 Program Direction
Summary of Reviewer Comments
3.7.1.1 Integrated Strategic Roadmaps
Since the publication of the 2012 Path Forward Report the program has considerably
strengthened the impact and linkages to the SSP. SNL has shifted the majority of the use of Z
Facility time from ICF to stockpile-relevant plutonium materials research, opacity studies, andradiation effects science. At the end of the NIC, facility time on the NIF shifted from 85 percent
ICF to approximately 50 percent HED experiments, each of which is reviewed and approved by
the HED Council – the multi-site body of technical experts and cognizant program managers
that provides recommendations as to the use of experimental resources dedicated to HED
experiments, in accordance with SSP priorities. The recent reorganization at LLNL has aligned
the management and research for ICF with the Weapons & Complex Integration (WCI)
Directorate, and this has effectively enforced the appropriate balance of priorities at the NIF.
The resulting organizational structure needs time to stabilize to tackle the challenges with thetools and people that are being developed.
The HED Council has been a welcome influence on the direction of research on the ICF/HED
facilities. The HED Council has expanded participation in experimental planning andprioritization, and has made a concerted effort to direct experiments to the most appropriate
facilities without the past institutional biases. The HED portfolio is producing outstanding
results for the SSP and it has a sound strategic plan.
The mission drivers for the ICF Program are quite clear. Pursuing thermonuclear burn in thelaboratory, achieving ignition, and multi-megajoule fusion yield have important implications tonational security. Achieving ignition in the laboratory is arguably one of the preeminentscientific challenges of our time and would represent an extraordinary demonstration of U.S.
excellence in science and technology relevant to nuclear weapons. It would further NNSA’s
scientific capabilities, assure allies, and deter potential adversaries. Some of the excellent
young scientists and engineers drawn to ignition research at NNSA’s state-of-the-art HED
facilities will move to nuclear weapons design work. The HED Council plays a key role inplanning and decision-making for the non-ICF portfolio. ICF Program planning could be
improved and the roles and responsibilities of the ICF Council – the multi-site body of technicalexperts and cognizant program managers that perform a cursory review of plannedexperimental activities for each ICF facility – could be revised/retooled to be more useful.
Establishing improved roadmaps and decision processes would help to focus the workforce on
the research priorities.
Program planning for the near term is critical, but it is also important to define the program 10
to 20 years from now. Ignition is one important step along the path and not the final end point.
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Over the long term, the program is aimed toward a high-yield capability whether or not ignition
is reached on the NIF, and major facility upgrades must be considered over a long time-scale. A
fusion source on the order of 500 megajoules or greater will be important for the health of the
program in an extended era without nuclear tests. Such a source is unlikely to be achieved in
the next decade, but maintaining high yield as an ultimate goal should guide program thinking
and direction in the interim.
The sophistication of approach, roadmaps, and decision processes varies widely among thethree approaches to ICF ignition. The LID approach presented overarching goals to improveunderstanding and models of ignition target behavior to either demonstrate ignition or showwhat is needed in capability and understanding to ignite a target. However, there were few
details on how a finding would result in a change in program direction. There was also a threatof dilution of intellectual energy as the number of sub-approaches increased. The LDD
approach showed a roadmap and decision process based on goals for the hot-spot pressure andmitigation of cross beam energy transfer, but little to no peer review of that approach hastaken place. The MDD approach presented a range of goals over the next five years aligned to
the PRDs, but like the LID Program, a detailed roadmap and decision process still needs to be
developed. Unlike the LID Program, however, the MDD Program suffers from a narrow
research focus mostly due to resource constraints.
The roadmap for each approach (LID, LDD, and MDD) must be woven into an overarchingroadmap driven by the vision described in the directors’ letter at five-, 10- and 15-year
waypoints. This roadmap should meet mission requirements, be inspirational, and be
appropriately paced and balanced given the many technical challenges in ICF.
3.7.1.2 The Naval Research Laboratory
Over 50-years, the Naval Research Laboratory's (NRL) scientists, engineers, codes, diagnostics,
and facilities have acted as a science and technology bridge between the DOD and DOE. It has
provided expertise and “corporate memory” for ICF and weapons physics, pulsed power
science, high power electron and ion beams, dense z-pinches, nuclear weapons effects testing,non-LTE physics, and related theories, codes, and diagnostics. NRL contributes in many areas to
ICF and laser physics: in LDD and hybrid x-ray/direct drive approaches using coated capsules,
investigating CBET and LPI at Nike, developing diagnostics including the Virgil M-band
spectrometer for the DANTE at the NIF, and experiments and calculations in non-LTE atomic
physics for nuclear weapons effects (K-shell) on Z. Scientific leadership by the NRL might bestrengthened by focusing on a smaller number of high impact efforts, and through better
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3.7.1.3 Additional Opportunities for Technical Leadership
Independent of the small percent of funding that the ICF Program provides to academic
programs for activities described in Section 3.6, NNSA should consider funding independent
researchers focused on high-risk, high-impact applied science with concrete deliverables to theprogram. These independent researchers could lead working groups and teams of external andlaboratory researchers focusing on key physics issues such as:••••

Novel diagnostics to probe non-LTE plasmas,
Advancing the kinetic theory of plasmas and computational capabilities for laser plasmainteractions,
Developing diagnostics to spatially, spectrally, and temporally resolve the physics of hot
spot assembly and stagnation, andPhysics validation of existing models in ICF codes in multiple areas, such as LPI and MHD.

Additionally, the ICF Program would benefit from increased competition in integrated
experiments to encourage laboratory researchers within the ICF Program and researchers
external to it, to propose novel ideas, have those ideas reviewed, and be awarded experimental
time and funding to support their research.
•

NNSA Program Office Perspective and Items for Future Prioritization & Action
The 2015 ICF/HED Review has informed and matured the National ICF Program
Framework. The four-element Framework is as follows:o Ten-year High Energy-Density (HED) Sciences Strategic Plan. This classified
requirements document outlines deliverables for the ICF/HED Program in three-,five-, and ten-year time frames, and is derived from the 25-year SSMP.
o National Transformative Diagnostics Plan. This resource-loaded plan describes
eight transformative diagnostics that benefit all ICF approaches. Local and broad
diagnostics are managed within the next two elements of the Framework.
o Integrated Experimental Campaigns. This element, frequently depicted as a
Gantt-chart, contains the approach-specific experimental campaigns for highly
integrated experiments with the primary goal of achieving thermonuclear
burning plasma conditions and that push the limits of NNSA’s capabilities andfacilities. Typically progress is assessed by demonstrating improvements in
integrated performance parameters, such as yield and shape. The five-year goalof this element is to determine the efficacy of NIF for ignition and a credible
physics scaling to multi-megajoule yields for all ICF approaches.
o The ICF Priority Research Directions (PRDs). This approach-specific six-part work
breakdown structure enables cross-approach coordination and opportunities forexternal collaborations at the working level. The PRDs enable the development2015 Review of Inertial Confinement Fusion and High Energy Density Science Portfolio

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of physics-based milestones that integrate compendiums of experimental
research executed at each ICF/HED facility with the overall efforts to improvemodels, codes, and simulations. The PRDs are:
 Driver-target Coupling Target Preconditioning
 Implosion Hydrodynamics
 Stagnation and Burn Physics
 Intrinsic and Transport Properties
 Measurement, Modeling, Validation, and Approximation

•

•

•

The Framework will be used to develop a roadmap in fiscal year 2016 with priorities,
metrics, milestones and deliverables, as well as specific “decision trees” to support outyear investments. NNSA will periodically sponsor workshops on the progress towardignition, covering all three ICF approaches. The next major workshop, related to the
PRDs, will be held in June 2016 in Santa Fe, NM.
The ICF Council Charter will be revisited to assess Council roles, responsibilities,
accountabilities, authorities, and overall value. One additional role for the ICF Council
could be to host a review process to award facility time for new ideas outside themainline ICF Program efforts, as is done for general use time at SC facilities.
NRL’s portfolio will be reviewed to identify the highest impact activities and torecommend new opportunities, such as strategic collaborations in atomic physics andspectroscopy or building collaborations with LLNL and LLE in the area of radiation source
development, with supporting experiments at NIF and Omega.
In addition to the SSP-driven requirement to maintain exceptional scientific capabilities
in HED science, NNSA will stand up efforts in fiscal year 2016 to assess long-term
requirements in five major areas:o Maintaining proficiency in secondary design and the ability to assess
performance in the long term in the context of no new nuclear testing.
o Evaluating the long-term experimental needs for threat-condition hostileenvironments and nuclear survivability of non-nuclear components.
o Coalescing the vision for future capabilities for NNSA dynamic material
properties research to enable safe, high-hazard materials science experiments.
o Defining a clear experimental program in burn physics to support boost science.
o Avoiding technological surprise.

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4 Next Steps
The 2015 ICF/HED Review identified nearly 40 areas for future prioritization and action. In fiscal
year 2016, NNSA plans to develop an “after actions” plan and a schedule for implementation.
Several areas have been identified where priorities should be re-evaluated, including:
•

•
•
•
•
•
•
•
•
•

Transformative diagnostics, including spatially, spectrally, and temporally-resolved
imaging and spectroscopic diagnostics to observe “stagnation” at low, medium, and highconvergence.
Obtaining cross-platform data for fundamental physics validation of models/codes while
improving access to codes/models, where appropriate.
Reviving development efforts for codes to model Laser-Plasma Instabilities (LPI).
Increasing the number of designers and experimentalists working on magneticallydriven implosions and laser-driven direct drive programs.
Enhancing peer review by academia and other institutions.
Developing applications for fusion yields produced on existing platforms.
Assessing the long-term requirements case for “high yield”.
Identifying methods such that all HED capabilities (domestic and international) may beconsidered as NNSA defines the means by which it will execute SSP-related experiments.
Developing robust cadre of top researchers in key areas of atomic physics, spectroscopy,
laser plasma instabilities, and low-energy nuclear physics.
Shaping academic program investments to ensure resources are optimally deployed.

Reviewers were not asked to consider resource constraints when providing comments orrecommendations. To affect all recommendations contained herein would exceed current
budget profiles. The principal next step is for NNSA to identify specific resource requirements toprioritize these recommendations within existing budgets. This prioritization process will begin
in FY 2016.

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Acronyms, Abbreviations, and Terms List
A-C
Al
ALS
APS
ASC
Be
B⋅r
CBET
D-E
DANTE
DARHT

Aluminum
Advanced Light Source, Lawrence Berkeley National Laboratory
Advanced Photon Source, Argonne National Laboratory
Advanced Simulation and Computing Program
Beryllium
The product of the magnetic field, B, and the radius, rCross Beam Energy Transfer

EOS
eV

Soft X-ray spectrometer used to measure radiation drive temperatureDual-Axis Hydrodynamic Radiographic Test Facility, Los Alamos National
Laboratory
District of Columbia
Deuterium-Deuterium
Deutsches Elektronen-Synchrotron, a national research center inGermany
Density Functional Theory-Molecular Dynamics
Deuterium - Helium-3
Department of Defense
Department of Energy
Deuterium-Tritium
Extreme Light Infrastructure, Laser User Facility with facilities in the
Czech Republic, Hungary, and Romania
Equation of State
electron Volts

F-G
FAB
Fe
FLASH
FNADS
FY
GB
GB-ns
GPUs

Full Aperture Backscatter
Iron
A free-electron laser at DESY that generates soft X-rays
Flange Nuclear Activation Diagnostic System
Fiscal Year
gigabar
Gigabar - nanosecond
Graphic Processing Unit(s)D.C.
DD, D2DESY
DFT-MD
D3He
DOD
DOE
DT
ELI

H-I

3He, He-3

HED
HYDRA
ICF

Non-radioactive isotope of helium with two protons and one neutronHigh Energy Density (Physics)
LLNL multi-physics simulation code
Inertial Confinement Fusion

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ICF Laboratories
ICF/HEDIntel® Xeon Phi™

The NNSA Laboratories, the Laboratory for Laser Energetics, and theNaval Research Laboratory
Inertial Confinement Fusion/High Energy Density
Intel® Xeon Phi™ Coprocessor, from Intel Corporation

J-K
Jupiter
KBO
keV
KH
kJ
K-shell

Jupiter Laser Facility at LLNL
Kirkpatrick Baez Optic
kilo electron Volt
Kelvin-Helmholtz Instability
kilo Joule
The first shell of electrons surrounding the nucleus of an atomL
LANL
LASNEX
LCLS
LDD
LEH
LEP(s)
LES
LID
LLE
LLNL
LPI
LTE
M
M
MagLIF
M-bandLos Alamos National Laboratory
Computer code used in ICF that simulates interactions and effects
between x-rays and a plasma.
Linac Coherent Light Source, at SLAC National Accelerator Laboratory
Laser-Driven Direct Drive
Laser Entrance Hole
Life Extension Program(s)Large Eddy Simulation, model for turbulence
Laser-Driven Indirect Drive
Laboratory for Laser Energetics
Lawrence Livermore National Laboratory
Laser-Plasma Interaction(s)Local Thermodynamic Equilibrium

MDD
Mg
MG-cm
MHD
MIT

Millions
Magnetized Liner Inertial Fusionrefers to the spectra from M-band emissions, x-rays in the 1.5 to 6.0 keV
range
Magnetically-Driven Direct Drive
Magnesium
Mega gauss-centimeter
Magnetohydrodynamics
Massachusetts Institute of Technology

N
NA-10
NA-11
NA-12
NA-19

Defense Programs, within NNSA
Office of Research, Development, Test, and Evaluation, within NA-10
Office of Stockpile Management, within NA-10
Office of Major Modernization Programs, within NA-10

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NBI
NIC
NIF
Nike
NISP
NLUF
NNSA
NNSS
non-LTE
Nova
NRL
O-P
OLUG
Omega

Near Backscatter Imager
National Ignition Campaign
National Ignition Facility, located at LLNL
Krypton fluoride (KrF) Laser, located at NRL
National Implosion Stagnation Physics Working Group
National Laser Users’ Facility, at Omega Laser Facility, LLE
National Nuclear Security Administration
Nevada National Security Site
non-Local Thermodynamic Equilibrium
High-power laser located at LLNL, built in 1984 and dismantled in 1999
Naval Research Laboratory

Purgatorio

Omega Laser Facility at University of Rochester’s LLE
Omega Laser Facility at the Laboratory for Laser Energetics, University ofRochester
A laser-plasma interaction (LPI) code used to simulate experiments
Particle in Cell
Priority Research Direction(s)The product of the plasma pressure, P, in atmospheres, and the energy
confinement time, τ, in seconds. This product is called the Lawson
Criterion.
LLNL microphysics code

Q-R
RANS
rho-R, ρ-R
RM
RT
RTD

Reynolds-averaged Navier-Stokes Equations
Product of the mass density and radius in the hot spot of an ICF implosion
Richtmyer-Meshkov Instability
Rayleigh-Taylor Instability
Resistance To Deformation

PF3D
PIC
PRD(s)
P-tau, P-τ

S
SC
SDD
Si
SLAC
SNL
SRS
SSAA
SSAP
SSD
SSMP
SSP

Office of Science, U.S. Department of Energy
Symmetric Direct Drive
SiliconSLAC National Accelerator Laboratory at Menlo Park, CA (originallynamed Stanford Linear Accelerator Center)
Sandia National Laboratories
Stimulated Raman Scattering
Stockpile Stewardship Academic Alliances Program
Stewardship Science Academic Programs
Smoothing by Spectral Dispersion
Stockpile Stewardship Management Plan
Stockpile Stewardship Program

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STS
SXI

Stockpile-to-Target-Sequence
Static X-ray Imager

T-U
TPD
TR
Trident
TT
U.S.

Two Plasmon Decay Instability
Technical Report
Trident Laser Facility at LANL
Tritium-Tritium
United States

V-W
VFP
VISAR
WCI

Vlasov-Fokker-Planck Model
Velocity Interferometer System for Any Reflector
Weapons and Complex Integration (WCI) Directorate at LLNLX-Y
XFEL, XFELs
XTD

X-ray Free Electron Lasers
X Theoretical Design (XTD) Division at LANLZZZZ Pulsed Power Facility at SNL
atomic number of a chemical element

1-D
2-D
3-D
2DConA∆ρR

One dimensional
Two dimensional
Three dimensional
Two Dimensional Convergent Ablator, one of the Horizontal and Vertical
Axis Radiography Platforms on the NIF
Variation in ρR in an ICF implosion

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This page intentionally left blankOFFICE OF DEFENSE PROGRAMS

2015 Review of the Inertial Confinement
Fusion and High Energy Density Science
Portfolio: Volume II
May 2016

DEPARTMENT OF ENERGY | NATIONAL NUCLEAR SECURITY ADMINISTRATION | DEFENSE PROGRAMS [NA-10]

DOE/NA-0040
Initial release:
Second release:

May 3, 2016
June 8, 2016 – Minor technical edits

Appendix A Review Materials
A.1
Reviewers
Group 1 - Progress Toward Ignition
Federal Lead: Lois Buitano
Name
Jerry Chittenden

Imperial College

Siegfried Glenzer

SLAC National Accelerator Laboratory

Jim Hammer

Lawrence Livermore National Laboratory

Nelson Hoffman

Los Alamos National Laboratory

Warren Mori

University of California, Los Angeles

Andrew Randewich

Atomic Weapons Establishment

Sean Regan

Laboratory for Laser Energetics

Bob Rosner

University of Chicago

Susan Seestrom

Los Alamos National Laboratory, Retired

Steve Slutz

Sandia National Laboratories

Affiliation

Group 2 - Non-Ignition HED Science and Long Term PlanningFederal Lead: Njema Frazier
Name
Dave Crandall
NNSA, Retired

Affiliation

Jill Dahlburg

Naval Research Laboratory

John Harvey

DOD, Retired

Jeff Quintenz

NNSA, Retired

Group 3 - Scientific Foundations
Federal Lead: Kirk Levedahl
Name
Sean Finnegan

Affiliation
Office of Fusion Energy Sciences

Yogi Gupta

Washington State University

Stephanie Hansen

Sandia National Laboratories

Dick Lee

University of California, Berkeley, Retired

John Sarrao

Los Alamos National Laboratory

George Zimmerman

Lawrence Livermore National Laboratory2015 Review of Inertial Confinement Fusion and High Energy Density Science Portfolio

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A.2

Review Schedule
Review Kickoff Meeting – Washington D.C.
May 18, 2015
08:00 AM
Coffee08:30 AM

Welcome & Introductions

08:45 AM

2015 Review Summary

Keith LeChien

09:00 AM

Federal HED Program Perspective

Keith LeChien

09:30 AM

10-year Strategic Vision

10:15 AM

Break

10:30 AM

Laboratory Leadership Panel: Design Agency
Perspectives on ICF/HED and the National Program

11:45 AM

Lunch

12:45 PM

Scientific Hypotheses: Laser-driven Indirect Drive
Priority Research Directions

John Edwards

02:00 PM

Scientific Hypotheses: Laser-driven Direct Drive
Priority Research Directions

Craig Sangster

03:15 PMBreak

03:30 PM

Scientific Hypotheses: Magnetically-driven Direct
Drive Priority Research Directions

04:45 PM

Alan WanCharlie Nakhleh,
Keith Matzen,
Charlie Verdon

Dan Sinars

ICF Program laboratory panel: Approaches, progress, John Edwards,
collaborations, and outlook in National Program
Craig Sangster,
Don Haynes,
Dan Sinars

05:30 PM

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May 19, 201508:30 AM

Coffee09:00 AM

Welcome & Recap

09:15 AM

Sustaining Stockpile Confidence with HED Science

10:00 AMBreak

10:15 AM

Plutonium Science

Scott Crockett

10:55 AMHED and Boost Science

Frank Graziani

11:35 AM

Secondary Physics

12:15 PM

Lunch

01:00 PM

Addressing UGT Anomalies

01:40 PM

Outputs, Environments and Effects

02:20 PMBreak

02:35 PM

Understanding Fundamental Processes WhichSupport Both Ignition and Weapons Science

03:35 PM

Cross Program and Platform Integration

04:20 PM

Wrap Up2015 Review of Inertial Confinement Fusion and High Energy Density Science Portfolio

Keith LeChien
Alan WanJohn Scott

Steve MacLaren
Brent Jones

Rip Collins
Charlie Nakhleh,
Keith Matzen,
Charlie Verdon

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May 20, 201508:30 AM

Coffee09:00 AM

Next Steps Overview

Keith LeChien

09:30 AMGroup Breakouts - Define Deep Dive Topics andFormatFederal Leads
Moderate

10:30 AM

Break

10:45 AMGroup Breakouts - Continued

11:45 AM

Lunch

12:30 PM

Outbriefs

01:30 PM

Wrap Up2015 Review of Inertial Confinement Fusion and High Energy Density Science Portfolio

Federal Leads
Moderate

Keith LeChien

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Laboratory Site Visits
Group 1: Progress Toward Ignition
Date
Site

Site Leads

July 28 – 29, 2015

Sandia National Laboratories

Dawn Flicker,
Dan Sinars

July 30 – 31, 2015

Lawrence Livermore National Laboratory

John Edwards,
Alan Wan

August 3 – 4, 2015

Laboratory for Laser Energetics

Craig Sangster,David MeyerhoferGroup 2: Non-Ignition HED Science and Long Term Planning
Date
Site

Site Leads

July 14 – 15, 2015

Lawrence Livermore National Laboratory

John Edwards,
Alan Wan

July 16, 2015

Los Alamos National Laboratory

Don Hanes,
Steve Batha

July 17, 2015

Sandia National Laboratories

Dawn Flicker,
Dan Sinars

July 23, 2015

DOE Headquarters with Presentations by
the Laboratory for Laser Energetics andthe Naval Research Laboratory

Craig Sangster,David Meyerhofer,
Tom Mehlhorn

Group 3: Scientific Foundations
Date
Site

Site Leads

July 14 – 15, 2015

Lawrence Livermore National Laboratory

John Edwards,
Alan Wan

July 16, 2015

SLAC National Accelerator Laboratory

Michael Dunne,
Siegfried Glenzer

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A.3

Reviewer Instructions

FY 2015 ICF/HED Review
Guidance to Reviewers
Please use the attached template as a guide to provide your findings, comments, andrecommendations to the Group Lead for your assigned Group.
The findings, comments, recommendations will be published in the Appendix of the Summary
Report for the Review, and will include only minor edits, as appropriate. Note that commentsthat you do not want published should be provided in the section labeled “Specific comments for
HQ only”.
You may provide comments and recommendations on the other Group sections. In that case,your input will be provided to the appropriate Group HQ Lead for consideration and possible use.
If you have questions, contact any of the Group Leads or Keith LeChien.
Your input is due on Tuesday September 1, 2015. Send your completed review via email
attachment to the ICF Director and all of the HQ Group Leads:
Keith LeChien,
ICF Director
Lois Buitano,Group 1 HQ Lead
Njema Frazier,Group 2 HQ Lead
Kirk Levedahl,Group 3 HQ Lead
CLASSIFIED findings, comments, and recommendations must be prepared and submitted inaccordance with Security Policies. Please submit classified portions of your review to the ICF
Director and HQ Group Leads via the NESAN system. If it is not possible for you to provide
classified through NESAN, please contact Daniel Jobe to make other arrangements.

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P a g e |62015 ICF/HED Review
Group: 1 – Progress Toward Ignition
Reviewer Name: _______________________________
Charge for Group 1:
The primary charge is an assessment of the scientific hypotheses that guide today’s ICF Programof work, and prospects of achieving ignition with existing scientific capabilities and facilities, or,if indicated, by specifying what would be required to do so, based on quantitative scientificanalysis. We also request an evaluation of program balance among ICF approaches.
Provide findings and recommendations related to experimental and computational efforts that
address scientific hypotheses related to the development of robust and reliable burning plasmas.
Assess the effectiveness of the ICF Program’s cross-platform and cross-laboratory collaboration.
Specific Comments for HQ only.
I. Assess the scientific hypotheses and the prospect for achieving ignition with existing scientificcapabilities and facilities; or, if indicated, what would be required to achieve ignition andsupporting analysis. Provide an evaluation of program balance among ICF approaches.
Ignition Approach: Laser-driven Indirect Drive
Findings:
Comments:
Recommendations:
Ignition Approach: Laser-driven Direct Drive
Findings:
Comments:
Recommendations:
Ignition Approach: Magnetically-driven Direct Drive
Findings:
Comments:
Recommendations:
Roadmaps and Decision Processes
Findings:
Comments:
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Program Balance
Findings:
Comments:
Recommendations:
II. Assess the integration of experiments and codes
Diagnostics
Findings:
Comments:
Recommendations:
Computational Models and Predictive Capability
Findings:
Comments:
Recommendations:III. Assess cross-platform and cross-laboratory collaborations
Findings:
Comments:
Recommendations:IV. Specific comments for HQ only

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Group: 2 – Non-ignition HED and Long Term Goals
Reviewer Name: _______________________________
Charge for Group 2:
The primary charge is an assessment of the alignment of the ICF/HED program with stockpile
stewardship program and the broader nuclear weapons program. Assess the contribution to
stockpile stewardship in the non-ignition HED sciences in the near, medium, and long term.
In their January 20, 2015 letter, the laboratory director’s described several specific multi-decadegoals for the ICF/HED program within the context of the broader stockpile stewardship program.
Assess both the scientific and programmatic progress – and plans – in today’s ICF Program tomeet those goals.
The formal title of the ICF Program is “Inertial Confinement Fusion and High Yield.” “High-yield”
at laboratory scale is more than a decade away, but having this ultimate goal shapes program
decisions many years in advance of their perceived need. Assess the need of “high-yield”
capabilities at laboratory scale as a long term goal of the ICF/HED program given evolving nuclear
threats, and the overarching boundary condition of no additional nuclear testing.
Specific Comments for HQ only.
I. Alignment of ICF/HED program with SSP and broader weapons program
Workforce Development
Findings:
Comments:
Recommendations:
Program Management
Findings:
Comments:
Recommendations:II. Planning associated with tri-lab Director’s letter
Long-Term Direction
Findings:
Comments:
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Applications of Yield
Findings:
Comments:
Recommendations:IV. Specific comments for HQ only

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Group: 3 – Scientific Foundations
Reviewer Name: _______________________________
Charge for Group 3:
The ICF/HED program is highly applied and focused on programmatic deliverables, but the fieldof high energy-density science is quite exploratory. The primary charge is to identify opportunities
to improve the underlying physics; the impact of simulations, models and codes; and experimental
capabilities (including targets and diagnostics) to best increase the integrated rate of progress on
programmatic deliverables.
Identify areas where partnerships with external entities (academia, industry, other government,international, etc.) may be strengthened to support these opportunities.
Specific Comments for HQ only.
I. Underlying physics understanding and integration.
EOS
Findings:
Comments:
Recommendations:
Opacity and transport
Findings:
Comments:
Recommendations:Hydro and burn physics
Findings:
Comments:
Recommendations:Global and driver physics
Findings:
Comments:
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Community: codes
Findings:
Comments:
Recommendations:
Community: Experiments
Findings:
Comments:
Recommendations:
Community: Collaborations
Findings:
Comments:
Recommendations:III. Specific comments for HQ only

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Appendix B Reviewer Reports
B.1
Group 1 Reviewer Reports
Reviewer Report: Jeremy Chittenden
I. Assess the scientific hypotheses and the prospect for achieving ignition with existing scientific capabilities andfacilities; or, if indicated, what would be required to achieve ignition and supporting analysis. Provide anevaluation of program balance among ICF approaches.
Ignition Approach: Laser-driven Indirect Drive
Findings: The last three years has seen a period of significant scientific progress in inertial confinement fusion experiments on
the National Ignition Facility. The volume of high quality published research that has emerged over this period has been mostimpressive. To a large part this has been achieved by concentrating on the use of higher adiabat, lower convergence shots, whose
performance more closely matches the predictions of simulations, such as those characterized by the ‘high-foot’ radiation pulse.
This is to be contrasted with the lower adiabat, higher convergence experiments undertaken during the National Ignition
Campaign where the susceptibility to instability growth led to a shot-to-shot irreproducibility which removed systematic trends
from the data. The densities and temperatures achieved in the hotspot within ‘high-foot’ capsule implosions are sufficient for alarge fraction of the plasma heating to come from alpha particle fusion products. This has been quite rightly recognized by thefusion community as a significant achievement. The high adiabat of the fuel however means that the hotspot density which canbe achieved in these implosions is too low to allow these designs to be used directly as high yield platforms. The ‘high-foot’platform does however present a well-established ‘base-camp’ design from which to progress towards higher yields along
different trajectories in parameter space which avoid many of the issues experienced during the National Ignition Campaign.
Despite the successes of the high-foot design the fusion yield remains significantly lower than predicted by unperturbed
calculations. Continuous improvements both to the diagnostic capabilities on the NIF and the ability to simulate the multidimensional effects of perturbations, have improved the overall ability to discern which factors are making the most significant
contributions to the degradation in performance. Principle amongst these are thought to be the time dependent radiation drive
asymmetry arising from Cross Beam Energy Transport (CBET) in the hohlraum and perhaps to a lesser extent the imprint on thecapsule surface formed by the capsule support tent.
The lack of control over the time dependence of the CBET within the gas filled hohlraums has led to a program to develop
alternative hohlraum designs with lower gas fill pressures as a means of mitigating this issue. The reduction in the tamping effectof the gas introduces a new set of challenges into the design of these hohlraums and requires accurate modelling of the plasma
expanding from the hohlraum wall and the collision of this with the blow off from the capsule, as well as the impact this has onlaser propagation and the potential for the late onset of CBET in the blow off plasmas. These issues can in turn be mitigated by
the use of denser ablator materials on the capsule such as high density carbon or beryllium, which require a shorter radiation
drive pulse and therefore allow the laser energy to couple to the hohlraum before it is filled by high density blow off plasma. A
program is also underway for advanced hohlraum designs which reduce the plasma expansion velocity and which also have thepotential to produce a more Planckian radiation spectrum with reduced high photon energy
Comments: Much of the progress that has been achieved can be attributed to a fairly pragmatic approach where problems whichappear insurmountable are circumvented rather than tackled head-on. This was the case with the adoption of higher adiabat
lower convergence targets to improve stability and again with the development of the low gas fill hohlraum to reduce CBET. Suchan approach is laudable and doubtless offers the path to most rapid progress. It is possible however that such problems mayneed to addressed once again should they be encountered again on various possible paths of progression from the stable ‘basecamp’ of the high foot design towards higher yields.
It is tempting to believe that the factors limiting performance in the highest yielding designs are well established, indeed theevidence for time dependent radiation drive asymmetry and associated swings in capsule shape is fairly compelling. Similarly
there does appear to be a correlation between the shape of the tent’s contact with the capsule and the structure of the capsuleobserved in radiography images, although the variation in performance with tent thickness is perhaps not as well understood.
There remain however a number of other effects which may also be contributing to reduced performance such as the fill tube,

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hot electron preheat, inaccuracies in the equation of state of deuterium etc. Such effects could well prove to be important, but
do not necessarily provide clear diagnostic signatures. The present approach of first addressing the demonstrably large amplitude
perturbations arising from drive asymmetry and the capsule mounting before attempting to evaluate other effects whose
contribution might be masked by these larger effects therefore appears reasonable.
The issue of cross beam energy transfer was one of the first problems to be encountered during early experiments on the NIF. At
the time a series of work arounds were introduced into the design tools and the experimental beam energy balance that produced
a radiation drive that was symmetric in a time integrated sense. Other issues such as the capsule instability then became theprinciple limiting factors in performance. Having eliminated or circumvented these issues, the program has now returned to apoint where CBET, or rather the time dependent radiation drive asymmetry which arises from it, is again the limiting issue.
Viewfactor experiments, where one laser entrance hole is removed to allow end-on soft X-ray imaging, have concentrated on
addressing assessing the efficiency of converting laser energy to X-rays as well as the time integrated symmetry of the radiation
emission from the hohlraum wall. There has been little attention given in such experiments to assessing the time dependence ofthe radiation symmetry which is responsible for introducing swings in the capsule shape during implosion. It is not clear to me
whether all of the options to try to mitigate time dependent drive asymmetry have been fully explored. Perhaps it is possible touse different pulse shaping on the inner and outer beams to provide some time dependent control of CBET, or to design ashimmed capsule with a graded ablator or dopant thickness? Whilst the effects of the capsule mounting tent on performance
may not be as significant as the time dependent radiation asymmetry, engineering solutions designed to reduce perturbationlevels can be directly evaluated through inflight radiography diagnostics. The relative stability of the current best performing
capsules means that the perturbation induced by the capsule mount will be at the limit of diagnostic resolution when the
implosion is approaching the axis. Measurements to evaluate symmetry improvements from different capsule mounts will
therefore be considerably enhanced by improvements to diagnostic imaging systems for the 2DConA or other back-lighters.
Alternatively the capsule may have to be re-designed to increase instability growth in order to enhance the amplitude of theperturbation to diagnosable levels
Choosing to address the CBET issues by concentrating on low fill hohlraums has brought about the need for development
programs not only for the hohlraum platform itself but also for capsule designs based on high density carbon and beryllium
ablators. The relative immaturity of these designs compared to the gas filled hohlraum and the CH ablator capsule, means thatthese development programs represent a significant fraction of the overall ICF campaign over the next 3-5 years. Whilst there is
optimism that initial experiments have demonstrated reduced radiation asymmetry with low fill hohlraums, there is no guarantee
of increased overall yield in integrated experiments. In addition to their suitability for use in the low fill hohlraum, high density
carbon and beryllium ablators offer improved stability properties compared to CH and therefore provide the potential to broaden
accessible parameter space by allowing higher implosion velocities or higher convergence ratios to be used. Importantconsiderations for the design of the next generation of hohlraum wall materials are not only reductions in wall blow off plasma,
but also a reduction in m-band or other high photon energy components which will reduce the need for dopant layers within thecapsule and maximize the stability benefits of choosing a high density ablator.
Considerable progress in the theory and simulation of indirect drive has been driven by the large volumes of high quality
diagnostic data provided by the NIF. There remain however a significant number of limitations to predictive capability which
inevitably mean that the experimental exploration of parameter space is constrained to incremental departures from a place ofknown performance or is in some way empirically led. Areas where the biggest uncertainties lie are the hohlraum modelling andthe stagnation phase. In hohlraum modelling it is difficult to be quantitative about the degree of laser plasma instability and crossbeam energy transport, which means that the X-ray conversion efficiency and symmetry are typically dealt with using either adhoc multipliers or semi-empirical fixes. These approaches provide a good representation of experiments where minor variations
are made from a base design, but must be re-calibrated when more significant changes in design are made. With the perturbation
amplitudes apparent in current experiments, the stagnation process is an intrinsically three dimensional process. Where
discrepancies lie between experimental observation and 3D simulation, it is not clear whether these are due to deficiencies in
the way in which the hotspot is modelled or whether the discrepancies arise before the start of the deceleration phase, i.e. themodels of the stagnation phase are simply working from the wrong set of initial conditions. Simulations of the emitted neutron
spectra are an important prediction for whether key indicators of the hotspot temperature and velocity may be observable.
Anisotropy of the neutron spectrum is a clear indication of a net center of mass velocity in the hotspot which is indicative of alow mode asymmetric implosion. An isotropic distribution does not eliminate the possibility of higher mode asymmetry giving2015 Review of Inertial Confinement Fusion and High Energy Density Science Portfolio

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rise a more turbulent residual velocity at stagnation. Differences between the DD and DT ion temperatures inferred from neutron
spectra indicate that the calculated spatial temperature distribution may be incorrect.
Recommendations: There will always be a need for a balance in programs such as this between keeping the number of designs
to a manageable level where they can be systematically investigated within the resources available and the need to maintain theflexibility to be open to new ideas. Within some parts of the program there is a potential to only taking small steps away from aregime that is known to work. This is a conservative approach which will only follow a trajectory through parameters space if thepath is a contiguous series of positive results. Scientifically I find this approach admirable, but my concern would be whether thisleads to incremental progress which would limit the exploration of parameter space over the 3-5 year time frame.
The low gas fill hohlraum designs and the high density ablators represent a logical, relatively low risk approach to tackling theprincipal factors limiting performance over the next few years. At this stage there is no way to accurately predict the performanceof integrated experiments, but in the event that these designs reach a similar performance ceiling to the current high foot shots,then it is important that alternative concepts, which may be higher risk in nature, are sufficiently matured to be then considered.
It is encouraging to see that alternative concepts based on radically different capsule designs or which are not targeted at highgain yields, such as the double shell and Big Foot designs are coming forward. I think it is important to maintain a balanced
portfolio of options at different stages of readiness and with different levels of risk and payoff. It is also important to encourage
input from a broad and diverse range of contributors into the development of new ideas and to maintain the flexibility tointroduce new concepts into the shot plan.
Ignition Approach: Laser-driven Direct Drive
Findings: Laser driven direct drive provides a intuitively complimentary approach to indirect drive which offers advantages forincreased energy delivery to the hotspot and therefore reduces the convergence required for ignition. The quoted program goal
for laser driven direct drive is to scientifically and technically justify the reconfiguration of the NIF for Spherical Direct Drive. Thisis being pursued through spherical direct drive (SDD) illumination experiments on the Omega laser at LLE and polar direct drive(PDD) illumination experiments on the NIF at LLNL. In this regard PDD is not being directly pursued as a path to ignition itself but
rather as a platform to assess the scientific case for adopting SDD on the NIF. The laser driven direct drive program has seen somesignificant achievements over the last three years. The implementation of the PDD platform on the NIF is a major accomplishment
as is the attainment of 50 Gbar hotspot pressure on the Omega laser.
Amongst the principle objectives of the program are goals related to both hydrodynamic implosions and to cross beam energy
transport (CBET) arising from laser plasma instabilities (LPI). For hydrodynamic implosions, the goal for SDD integrated DT
cryogenic shots on Omega is the demonstration of an implosion which is hydrodynamically equivalent to a SDD implosion on the
NIF at 1.8MJ. For PDD experiments on NIF the aim is to perform a high convergence ratio (Cr~20), non-cryogenic implosion. It is
progress towards the understanding and mitigation of energy losses due to CBET however which appears to be the principle
driver in determining overall progress towards the program goal. In particular, as stated in the laser direct drive white papers, itappears that without significant CBET mitigation, there is no credible concept for direct-drive ignition at NIF-scale energies. For
this reason the principle aim of PDD experiments on the NIF is to provide a platform to test strategies for CBET mitigation on
density scale lengths which are significantly larger than can obtained on Omega and are within a factor of two of those which will
ultimately be encountered in SDD experiments on NIF.
The strategy for mitigation of the CBET in PDD on the NIF is different to that in SDD on Omega. As the capsule implodes andbecomes smaller than the laser spot sizes, there is increased overlap of the beams and hence an increase in the level of CBET. To
counter this effect, in the near term LLE are developing ‘zooming’ phase plates which produce a reduced focal spot late in time
as well as a full-aperture zooming system based on a grating with an axicon, over the 3-5 year timescale. PDD shots on the NIF
will instead concentrate on the use of increased range of laser wavelengths as the approach to CBET mitigation. Should the NIF
be reconfigured to SDD however the CBET mitigation strategy would instead be more closely aligned with that on Omega andwould employ combination of zooming and wavelength detuning.

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Mitigation of the CBET could itself give rise to plasma conditions where the two plasmon decay (TPD) instability generates
significant hot electron preheat. Methods of reducing the impact of these effects will be addressed in focused physics experimentin SDD on Omega and in PDD on NIF by introducing layers of intermediate Z material.
Comments: Proving the scientific case for investing in SDD on the NIF and in particular proving that the known issues such as
CBET can be mitigated represents a significant scientific challenge particularly where not all of the physical conditions necessary
for such a test can be accessed with existing facilities. Significant investment in the PDD platform on the NIF will be required inorder to enhance the ability to explore mitigation of CBET through wavelength detuning approaches. In the event of conversion
of NIF to SDD however, the approach to CBET mitigation would be different and would require the extrapolation of zooming
techniques developed on Omega to plasmas of much larger density scale lengths. It is inevitable that when scaling up a design toa larger platform, not all of the parameters ranges that will be encountered can be fully explored beforehand. It is therefore
important that the data obtained in both PDD on NIF and SDD on Omega are utilized to inform and constrain theoretical andcomputational models which will be essential for underwriting the scientific case for SDD on the NIF.
The direct drive program has extensive experience and computational capabilities for the modelling of CBET and TPD preheat
which are benchmarked against extensive data sets from experiments on Omega. Predicting the behavior of LPIs in plasmas withdensity scale lengths which would be a factor of four larger in SDD on NIF will stretch the capabilities of these models. It istherefore important that full use of the data from PDD on NIF is made in benchmarking the extrapolation of the models to the
midpoint between Omega SDD and NIF SDD. Similarly it is clear that high quality computational capabilities exist at LLE to model
the hydrodynamic convergence of SDD implosions on Omega in both 2D and 3D. What is less clear is the level of confidence inthe ability to model polar direct drive experiments with the added complexity that the variation in incidence angle has on lasertransport and ablation processes as well as CBET. It is possible that improved convergence of simulation and experimental
observation for PDD will require larger scale 3D simulations to resolve the combined impact of these effects on laser imprint andimplosion symmetry.
Recommendations: Reconfiguring the NIF for spherical illumination direct drive experiments, would require not only a substantial
financial investment but also a significant interruption to indirect drive research as well as a range of other non-fusion programs.
The bar will therefore be set very high for the scientific case to be sufficiently persuasive to undertake this change. The current
timetable for direct drive for the next five years is well matched to the objectives of exploring CBET mitigation and moderate
convergence shots in PDD on the NIF as well as developing zooming techniques and achieving high pressures in hydrodynamicallyequivalent shots in SDD on Omega. Meeting these objectives however will not necessarily provide a complete and compellingcase for SDD on the NIF and it may be that such a decision point would not be reached until further into the future. Should it
prove necessary however to bring forward such a decision point then this can only be achieved by investing sufficient funds toallow an acceleration of both the SDD program on Omega and the PDD program on NIF.
Ignition Approach: Magnetically-driven Direct Drive
Findings: The last few years have seen considerable progress in the development of the MagLIF fusion concept at Sandia. The
achievement of fully integrated shots incorporating liner implosion, magnetization and laser preheat represents a significant
milestone. A central component of the MagLIF design is the magnetization of the fuel which reduces heat losses from the fuel tothe liner in the present experiments on Z and could also reduce the requirements for ignition on a next step facility by providing
confinement of the alpha particles.
In common with other inertial fusion concepts, the first fully integrated MagLIF experiments produced fusion yields which weresignificantly lower than predicted by 2D MHD simulations. Whilst these yields were also low compared to those other fusion Zpinch plasmas at similar currents (such as deuterium gas puff experiments on Z), the MagLIF experiments were the first to
demonstrate reasonable yields in a small plasma volume, dense enough and magnetized enough to provide a scalable path toignition.
A number of candidate mechanisms thought to be inhibiting the fusion performance have been identified, based on experimental
observations and 3D MHD simulations. These include the non-uniformity and reduced efficiency of the laser energy absorption,2015 Review of Inertial Confinement Fusion and High Energy Density Science Portfolio

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hydrodynamic mix of the liner and fuel, mass loss through the laser entrance hole, enhanced radial heat flow due to extended
Ohm’s law effects and reduced convergence due to 3D asymmetry at stagnation.
Sandia have presented an extensive program plan and set of goals to investigate these effects through diagnostic andcomputational improvements as well as targeted physics experiments.
Comments: The decision to turn away from the use of wire array Z-pinches for indirect drive experiments came as something ofa surprise to some in the community as significant progress was being made at the time with double ended vacuum hohlraums
and dynamic hohlraums. In retrospect however this decision seems logical as exploration of the X-ray driven indirect drive
concept is now being pursued very effectively on the National Ignition Facility. Nevertheless, should it prove that the pursuit ofignition and high yield using indirect drive on the NIF is ultimately limited by the maximum energy that can be coupled to thetarget, there may still be an opportunity to explore alternative indirect drive designs, with larger absorbed energies, on a future
larger scale pulsed power facility. It is important that the scientific capability to mount such a campaign in the future is retainedat Sandia.
The change in direction of the fusion program at Sandia to magnetically driven direct drive has led to the development of a viable
alternative approach to laser driven approaches which uses the efficient coupling of energy to the fuel to good effect. The larger
scale of the targets involved in this approach means that there is potential for relatively high yields (100kJ) in non-igniting
experiments on the current Z facility and very significant (GJ level) yields should an ignition experiment be successful on a 5070MA class driver.
The MagLIF fusion program at Sandia is largely concentrated upon evaluating a single computational design. Whilst many of thedesign aspects for MagLIF are constrained by the generator and laser parameters available, the main constraint appears
operational in that there are insufficient shots available to thoroughly evaluate more than one design. This is a little concerningin that should the current limitations to performance ultimately prove insurmountable, there would be a limited choice of mature
alternatives. It is not immediately clear to me how alternative designs, which go beyond simple variations on a theme, could begrown from a nascent idea to a viable alternative given the current constraints.
Whilst there is a broad program designed to address those factors so far identified as potentially limiting performance, much of
the initial emphasis has been placed on measuring the fraction of the laser energy absorbed by the deuterium gas during thepreheat phase. This is perhaps not surprising since this issue can be addressed relatively straightforwardly in offline experiments
in collaboration with LLE. It is important however that sufficient resources are applied to developing the diagnostics required toaddress the other concerns in parallel, so that these are well underway should the laser absorption issue prove not to be solely
responsible for the present performance. It is also important that other approaches to heating can be considered should the
problem with the laser heating prove insurmountable. Just as an example, I have found through my own simulations of MagLIF
that an end-on dynamic hohlraum provides a more energy rich and isotropic heating source than a laser.
Recommendations: Delivery of increased currents, magnetic fields and laser energies to MagLIF are important goals for the futureof the concept and for the ongoing development of the facility, but it is important they are not the principle drivers for assessing
success. In the present experiments the fusion yield remains a small fraction of that predicted by 2D MHD design calculations. If
this fraction remains the same in experiments at higher drive parameters, then little will be achieved either in terms of improved
understanding or in the viability of a next-step generator. As with the other approaches to ICF, assessment of progress towards
improved understanding of those factors currently limiting performance will be more important than milestones based on
numerical metrics. As with the other inertial fusion approaches, direct diagnosis of the hotspot conditions is extremely difficult.
This is made even more so by the large ρR of the liner surrounding the fuel at stagnation. Results from the NIF have shown that
there is a wealth of information embedded within the neutron spectra. Sandia have made considerable progress in this regard
with measurements of primary DD spectra and secondary Triton reactions. The introduction of Tritium handling capabilities at
Sandia however would mark a considerable improvement not only through increased yield, but by introducing a range of new
diagnostic options for assessing hotspot ion temperature, plasma motion and beam-target contributions.
Over the past few years Sandia has assembled a portfolio of compelling arguments for the benefits of building a next step pulsed
power facility based on results in material science, pulsed neutron and X-ray sources and fusion platforms. If such a project is to2015 Review of Inertial Confinement Fusion and High Energy Density Science Portfolio

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succeed, it is critical that there is sufficient investment in programs to evaluate the pulsed power technology in the near term, inorder to be able to design and build a new facility in a few years’ time. The construction of large scale LTD modules in the nearterm is essential for the assessment of not only the scalability of such technology to the currents and voltages required, but also
the economy of scale in the manufacturing of large numbers of modules which will be a major driver for determining the cost of
a new facility. Similarly experiments to either assess the ability of present or alternative designs for the convolute, diode stackand MITL to withstand the additional power flow requirements, will need to be undertaken in the near term.
Roadmaps and Decision Processes
Recommendations: The major decision point which is visible on the horizon will be how long to continue with indirect drive on
the NIF in its current configuration. At present there is a clear and well thought out program for the next 3-5 years to address
intuitive approaches to improving the fusion performance. There is a high confidence in the ability of the program to continuously
deliver high quality and high profile work which will provide a steady improvement in our understanding of the science. Whatcannot be assured at this stage is that the current set of designs will not encounter similar performance ceilings to those designs
already tried and therefore the maximum yield obtained may not increase during this time. In several design scenarios reduced
performance can often be compensated for by increased drive energy. Should the energy available from the NIF prove to be an
ultimate limit then options for increasing the energy coupled to the capsule include reengineering the laser to operate at green
wavelengths or reconfiguration of the facility to spherical direct drive illumination. The scientific case for adopting any proposed
alternative approach would already need to be well established in order to be able to inform the decision making process. The
timescale for developing a compelling scientific case for implementing direct drive on the NIF is at present determined by the five
year program to evaluate mitigation strategies for CBET. It is possible however a significantly longer program will be required tocomprehensively provide all of the information required to inform a decision. It is important therefore to consider whether thesetimescales are sufficiently short to meet the required timetable for informing a decision about reconfiguring the NIF.
At present there is no capability worldwide which can completely asses the scientific feasibility of direct drive ICF using sphericalillumination at the scale required for ignition. One discussion which has surfaced a number of times within the European IFE
academic community is whether there is a need for intermediate scale (sub-ignition class) laser facility of the order of a few
hundred kJ which could thoroughly test the scientific issues associated with a spherical direct drive approach. This conversationarises because the absence of any existing ICF implosion capability of the scale of Omega within Europe makes the extrapolation
to PDD experiments on LMJ more problematic than in the case of NIF. Should the decision point for implementing SDD on the
NIF however be pushed back to well beyond the 5-10 year timeframe it might be worth considering whether evaluation ofdifferent approaches to addressing the current issues were better undertaken at a larger scale. This would strengthen the caseand reduce the risk associated with conversion of the NIF to spherical direct drive.
Magnetically driven inertial confinement offers a viable alternative approach to achieving high yield fusion in larger scale
cylindrical implosions with the possibility of a different class of GJ high yield experiments. Sandia has in place a detailed program
to address current factors limiting fusion performance in the present MagLIF design and to maximize the current, magnetizationand laser heating available on Z. Should these experiments prove successful, there would be a fair degree of confidence that the
MagLIF concept could be extrapolated to provide significant fusion yields on a higher current pulsed power driver. It is important
to note that there are a number of other valuable applications of a next stage pulsed power driver in material science and X-ray
sources where there is also confidence in the extrapolation to higher current. In addition there are other fusion concepts such as
high yield indirect drive or non-igniting pulsed neutron sources such as deuterium Z-pinches which could also be exploited on alarger scale pulsed power driver. It is important that sufficient resources can be applied to assessing the pulsed power technologyof large scale LTD drivers in the near term in order to provide a mature design that could inform the decision process on the sametimescale that MagLIF experiments on Z are anticipated to reach their design yields.
II. Assess the integration of experiments and codes
Diagnostics
Findings: The National Diagnostic Plan is an excellent example of inter- laboratory cooperation to establish a national strategy forthe systematic improvement of diagnostics technique across all ICF platforms.

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Comments: In the words of Lennon and McCartney - “Living is easy with eyes closed. Misunderstanding all you see”. There are
numerous examples where the development of a new diagnostics has revealed structures that were not known to exist
beforehand and have transformed our understanding of the structure of the plasma. In the absence of a fully predictive
computational model, it is the development of new diagnostics which is the principle driver for making new discoveries andreducing uncertainty. It is often the case that the overall rate of scientific progress can be directly linked to level of diagnostic
investment.
The list of eight priority diagnostics identified by the National Diagnostic Plan management group are indeed transformative inthat they would revolutionize the quality of data and the ability to inform and constrain models on all three approach to inertial
fusion.
At present one of the principle limits to our understanding of the stagnation phase on the NIF is knowing the exact form of theperturbation of the dense fuel during the last few hundred microns of the implosion. This structure determines the pressure of
the hotspot that will form and the symmetry of the dense fuel that must confine it and retains a fossil record of the drive
asymmetries and capsule defects which have provided a source for the perturbation. Improvement of the spatial and temporal
resolution of radiography at this phase of the implosion can have a critical impact on constraining 3D models of the stagnation
phase.
Computational Models and Predictive Capability
Comments: There has been an increasing realization that the deceleration and stagnation phases of all three approaches are
intrinsically three dimensional processes. In some sense this is good news as three dimensional models with suitable
perturbations tend to fit the experimental data better than 2D. The degrees of freedom in a 3D perturbation are however far
greater than in 2D and the data required to constrain the form of the perturbation is much harder to quantify. 3D models do nottherefore offer predictive capability and are unlikely to do so without being constrained by more high quality diagnostic data.
Recommendations: It is important to maintain a range of different code capabilities. There is a case to be made that if all designers
are using the same general purpose radiation hydrodynamics code, such as HYDRA then this maximizes the user base andenhances the overall experience level as well as code development. This approach has to be tensioned against the need for codes
to be cross checked against other models with alternative computational methodologies and physics packages. Maintaining ahealthy diversity of different models is essential, as is maintaining the capability to develop independent code capabilities. Thereis also a need to maintain specialist codes for specific problems such as laser ray trace hydrodynamics at LLE and MHD at SNL.
III. Assess cross-platform and cross-laboratory collaborations
Comments: High Energy Density Physics is a notoriously ‘driver –centric’ research field. All too often researchers will adopt thethought process of ‘what can I do with the machine I have?’ rather than ‘which machine can I use to access the physics I’minterested in’. Whilst there are many differences in the drivers themselves, the physical processes involved in achieving fusion
through implosion are remarkably similar. It is therefore most refreshing to see an approach developing between the US labs
involved where working groups such as The National Diagnostic Group and the National Implosion Stagnation Physics Group are
established to help advance the understanding of the physical processes common to all approaches.
Recommendations: Each of the three approaches to inertial fusion is presently engaged in a scientifically driven research
campaign where it is the progress achieved in understanding the physical processes at work and how these influence the fusion
performance which is the principle measure of the success of the program. Milestones based on purely numerical metrics are notnecessarily the most effective way of assessing the performance of such a program. Non quantitative measures of progress whichassess improvements in the level of understanding can however be subjective and inaccurate. It is only through an active peer
review program that independent assessment of the quality of the research can be achieved. Peer review should not be limited
to purely retrospective assessment of achievements but should be seamlessly built into processes for evaluating new concepts,
determining the balance between campaigns and assessing priority research directions. It is only by providing the transparency
which is brought by external participation in the decision making process that a complete appreciation of prioritizations within
the ICF program can be recognized by the external HEDP community.

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Reviewer Report: Siegfried H. Glenzer
I. Assess the scientific hypotheses and the prospect for achieving ignition with existing scientific capabilities andfacilities; or, if indicated, what would be required to achieve ignition and supporting analysis. Provide anevaluation of program balance among ICF approaches.
DOE-NNSA has made significant investments in major facilities and high performance computing to ensure present and futurescientists have the means to successfully execute the Stockpile Stewardship Program. Of high importance is the demonstrationof ignition and burning fusion plasmas in the laboratory. The laboratory directors have expressed that the demonstration of fusionin the laboratory is a high-priority goal and have pointed out the importance for the US to be the first nation to succeed. The
program is pursuing three viable approaches: laser-driven indirect drive, direct drive, and magnetic direct drive implosions. During
the review, the ICF programs have clearly communicated their present understanding of the physics issues in each area and havedescribed their experimental plans that are based on precision experiments and designs using computations with state-of-the art
radiation-hydrodynamic modeling. The complete program that was laid out gives reasons for optimism that significant progress
will be made in the near future. If successful, fusion yields due to alpha heating in indirect dive implosions on NIF will increase
towards conditions favorable for nuclear burn waves that will approach physics regimes important for nuclear weapons.
Summary statements on the specific question for each ignition approach
For Laser-driven Indirect Drive: What understanding/performance metrics/criteria are used to measure progress/determine
endpoint for HDC, Be, CH ablators target designs, and for vacuum/near-vacuum hohlraum designs? What is the path to high yieldand high areal density implosions?
The highest priority of the indirect drive program should be the demonstration of 100 kJ yield in indirectly driven implosions.
These plasmas will test our understanding of alpha heating physics and are critically important for measuring alpha stopping andinitiation of nuclear burn for achieving high DT fusion gain. The program has developed lower convergence high-velocity
implosions that are suitable candidates; it is recommended to develop 2 platforms in parallel to achieve this goal within the next
3 years. A precision implosion diagnostics program should be pursued vigorously to quantify what it will take to launch a burnwave. The path to high yield and high areal density will require additional improvements in hohlraum drive symmetry andradiation hydrodynamic modeling that will need to be pursued in parallel.
For Laser-driven Direct Drive: Is 80 Gbar hot-spot pressure in OMEGA DT layered cryo implosions, in and of itself, a reasonable
go/no-go metric for proceeding to NIF experiments? What are good understanding/performance metrics/measures of success forsymmetric/polar direct-drive? What are the scientific questions that need to be addressed and decision path for the choice forpolar drive and/or symmetric drive ignition on NIF?
Demonstration of 80 Gbar pressure on Omega DT implosions will be a very significant result. This result would be a reasonable
metric in favor of symmetric direct drive implosions on the NIF provided that a) progress in yield and pressure of indirectly driven
implosions is slow and struggles at delivering 100 kJ yield, and b) radiation-hydrodynamic and laser-plasma interaction predictions
for direct drive implosions are successfully tested with adequately performing cryogenic polar direct drive implosions.
The direct drive laser approach promises ignition and significant fusion yield for plasma conditions that appear to be easier met
than indirectly driven implosions. However, relaxing the plasma pressure requirements in the proposed way makes driver andexperiment fielding requirements significantly harder to meet. An aggressive campaign of the direct drive program on the NIF isin order to assess the full scope of performing these extremely challenging experiments.
For Magnetically-driven Direct Drive: The path to ignition with MDD appeared to be based upon driver enhancement goals (everlarger/higher power facilities). What are the scientific benchmarks or understanding goals underpinning the MagLIF approach toignition?
The present approach promises ignition and significant fusion yield on future facilities for plasma conditions at much lower
pressures than required for indirectly driven implosions that are presently being performed on the NIF. The costs of fusion with
reduced plasma pressure requirements in MDD implosion are higher experimental complexity and the need to develop predictive

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modeling that will need to include 3-D physics with magnetic fields. This task is extremely challenging and will require close
collaboration between the laboratories.
At the highest priority, the MDD program must demonstrate laser beam propagation and heating on Z. The goal is to deliverintegrated performance with effective kilojoule-laser heating of the fusion target. Much of the non-predictive behavior of somepast experiments is presently being explained by insufficient laser beam propagation in the target. This factor will need to beruled out to enable future optimization studies and to determine the scaling to high yield. To make quantitative measurementsof implosions will require simultaneous laser heating and laser backlighting experiments.
Ignition Approach: Laser-driven Indirect Drive
Findings: Since 2010, two experimental laser-driven indirect drive campaigns have been completed on the National Ignition
Facility at Lawrence Livermore National Laboratory. The teams executed series of indirectly driven layered DT implosions withthe goal to achieve fusion burn in the laboratory and demonstrate fusion gain that exceeds 1 MJ yield (~3 x 1017 DT fusion
neutrons). As of today, these experiments have not reached the burn regime, but significant progress has been made, mostimportantly the first unambiguous demonstration of alpha heating. The highest fusion yield shots have achieved close to 1016 DT
fusion neutrons in implosions with 26 kJ of fusion yield. Half of the yield is from alpha heating. This result is important andencouraging because a plasma regime with significant alpha heating is a critical experimental step needed to launch a nuclear
burn wave followed by rapid 10-fold increase of temperatures and large fusion yields from burning the surrounding dense fuel.
It is important that the NIF experiments have used laser and target parameters that were very close approximations of the laserplasma interaction and radiation-hydrodynamic design calculations for ignition. These findings indicate that predicting the physics
of ignition through simulations is much more challenging to than previously thought. Low-adiabat implosions (so-called low-footimplosions) show large areal densities close to simulations and close to those needed for high-fusion gain implosions. However,
the experiments have resulted in low fusion yields (~1015 DT fusion neutrons) suggesting that the hot spot of the implosions is
not adequately forming. Specifically, hydrodynamic mix or shell break-up occurring during the final compression phase from radiiof 100 microns to about 25 microns are leading candidates to explain the behavior. Utilizing highly accurate target implosion
diagnostics and focused experiments have led the way towards providing measurements of 1) mix from comparisons of x-ray andneutron yield, 2) non-uniform fuel areal densities from variations in scattered neutrons, and 3) x-ray radiograph images of shell
perturbations. These measurements have helped providing the hypothesis for explaining low yield in low-foot implosions.
Importantly, the x-ray radiographs have shown evidence for shell perturbations caused by the capsule tent, which holds thecapsule in place inside the radiation cavity, i.e., the hohlraum.
Significant progress has since been made and alpha heating has been observed when switching to higher-adiabat DT implosions(so-called high-foot implosions). This strategy trades large areal densities with conditions that have significantly smaller growthfactors for hydrodynamic mix and thus behave more favorably for hot spot formation. These implosions have resulted in thehighest neutron yields so far from laboratory experiments of ~1016. Focused experiments have corroborated the picture thatthese implosions are more stable by showing no or reduced capsule tent features in 2-D radiographic imaging and direct growth
factor measurements have validated the low-growth rate scenario for mix. These experiments have shown good agreement withsimulations and post-shot simulations agree with yield data to within a factor of ~2. However, when using high-foot implosions
to further heat the hot spot by increasing implosion velocity and convergence the capsules start to fail and the fusion yield has
been observed to decrease. The leading hypotheses for the failure are hohlraum drive asymmetries and perturbations seeded by
the tent. Without any further improvements and developments the high-foot implosions would need ~3x more energy in the fuelto ignite. Although improvements in optics will occur over the next 5 years, significant progress towards ignition on the NIF should
be expected with the existing scientific capabilities and facilities.
The indirect drive experimental program is presently pursuing 4 goals with high priority. The first thrust area takes advantage ofthe knowledge base generated during the low-foot and high-foot campaigns and will be fielding so-called big foot implosions on
the NIF. These experiments will test the hypothesis that high convergence results in shell breakup due to hohlraum drive
asymmetries. Due to lacking of an optimized hohlraum, these shots will use near vacuum hohlraums with diamond ablators thatshow very little laser-plasma interaction physics effects and where the total hohlraum radiation drive is close to predictions fromradiation hydrodynamic modeling. The goal is to demonstrate stable implosions with adequate hot spot formation at a limited

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convergence ratio of ~20. The shots should achieve high implosion velocity of 450 km/s at high adiabat with 100 kJ of DT fusion
yield.
As high priority, the indirect drive ICF program will be developing a predictable hohlraum with improved symmetry control toultimately achieve high convergence implosions for a burning fusion platform. The phase space consists of variations in fillpressure, case-to-capsule ratios and capsule ablator materials including CH, Be and HDC. The design space is large and it will bechallenging to make progress without detailed measurements of the shell behavior close to stagnation in non-layered implosions.
Other effects could confuse the answer especially effects from the capsule tent, or variations in laser-plasma interactions
especially for targets with different materials and scale lengths.
It is recognized that the program will need to develop and field precision diagnostics of the hohlraum plasma conditions and drive
symmetry. This includes imaging, spectroscopy, x-ray and particle scattering measurements. These diagnostics are expected togreatly improve knowledge of the implosion by visualizing shell break-up and the effects on hot spot formation and resulting
residual kinetic energy. Importantly, the diagnostics are expected to provide new insights into the modeling of the high-energy
density science experiments. In addition to measuring the conditions of fully integrated DT implosions they will provide
capabilities for critically testing predictions of the modeling and theory in focused experiments. For example, accurate
measurements of the hohlraum temperature near the laser entrance hole with Thomson scattering will allow distinguishing
between competing models for the hohlraum plasma and drive parameters and will contribute resolving the issue of missing
energy in the hohlraum.
The program has committed to the long-term development of the radiation-hydrodynamics code HYDRA for the design ofimplosions. A wide range of ICF-relevant physics packages is being developed and implemented. The code has been tested against
a large database of integrated and focused experiments. This knowledge is kept in a configuration-controlled database. The
continued development of the code, its future capability for use with high performance computing, and the inclusion of directdrive-relevant physics will benefit the whole National ICF program and is of general importance for the stockpile stewardshipmission.
Comments: The pursuit of big foot implosions, or more generally of implosions with reduced convergence, is an important newfeature of the program. Investigating a regime that is better understood and where the integrated performance data follow moreclosely the radiation-hydrodynamic modeling appear to be the correct strategy for improving fusion yield performance andpossibly isolating important physics mechanisms. Improving the physics models in the design codes is critically important forsuccessful ignition attempts. This thrust reflects the change in the guiding principles of the indirect drive program away fromhigh-yield high-gain implosions to a regime that is better understood and that allows steady progress towards ignition. Preparing
implosions that use wetted foams or double shells follow a similar idea of making implosions more 1-D like by reducing
convergence. However, while important for future directions, wetted foam targets are challenging to build and the big footimplosions will likely test the performance of low convergence ratio implosions first. Similarly, the plan to pursue double shell
implosions sounds attractive, but the program will need to build more confidence with focused experiments before investing
significant resources in target fabrication and before new precision diagnostics are ready to make quantitative measurements inthis more challenging regime. A key question is to resolve if sufficient drive can be generated on NIF to successfully implodedouble shell capsules.
The development of a more predictable hohlraum is an important activity. However, a detailed plan will need to be developedthat includes milestones and success criteria. Without performing large case-to-capsule implosions it will not be clear how 1-D
implosions really look like on NIF and if other performance cliffs are important. This area of research includes many variables
calling for the need to develop a clear direction that defines the main program and provides focus and priorities for resources.
The pursuit of new ideas should be encouraged and managed with well-defined finite shot resources.
Importantly, the poor performance of implosions with Be ablators give raise to concern that laser-plasma instabilities, i.e., CBET,
stimulated Brillouin scattering, stimulated Raman scattering and hot electron generation are a dominating factor. The issue of Be
ablators and the differences in performance compared to near vacuum hohlraums will need to be better understood. There are
doubts about the early interpretation of the missing radiation drive in hohlraums; view-factor experiments have led to theconclusion that it is more important to focus on the physics of the hohlraum’s conversion of laser light into x rays as opposed to2015 Review of Inertial Confinement Fusion and High Energy Density Science Portfolio

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the ablation model for the capsule. This early conclusion is questionable since subsequent experiments in near vacuum hohlraums
show no discrepancies with the x-ray drive models. This is not a surprise because the hohlraum drive model was motivated by alarge experimental database that included empty hohlraum shots. More importantly, the view factor shots have shown thatlaser-plasma interactions in gas-filled hohlraums are not well understood and implosions in near vacuum hohlraums will deliver
more drive to the capsule.
Alternatively, the lack of predictability of implosions could be explained by capsule tent perturbations. Solving this issue seems
to have taken a back seat during the high-foot campaign. Preparations for improving the capsule mounting should be moreadvanced and better prepared with radiation-hydrodynamic simulations of various realizations for the capsule mounts.
There are other trends in the current experimental database that are not completely understood. Examples are pressure versus
coasting time or the pressure data from the adiabat shaping experiments. It is important to develop hypotheses and to pursue
experimental tests that should be preferably performed with near vacuum hohlraum implosions and with improved capsulemounts.
Recommendations: Fielding big foot implosion experiments on NIF should be pursued at highest priority. The results will provide
an important test of the new figure of merit replacing implosion velocity with capsule convergence. If validated, this result will
have important consequences for future planning and will motivate fielding designs on NIF to deliver 100 kJ DT yield in the next
three years. At a minimum, two independent 100 kJ designs should be pursued, for example, high-density carbon in near vacuum
hohlraums and a high-foot beryllium design.
It is a high priority to vigorously pursue the National target diagnostic plan. This program has delivered a plan to develop, build,and field a new generation of precision diagnostics to measure hohlraum and implosion performance. In particular, future
experiments will need to accurately measure the hohlraum plasma conditions to test radiation-hydrodynamic modeling of drive
symmetry. Further, future diagnostics must measure the integrity of the shell during the formation of the hot spot. Importantly,
the program should develop advanced diagnostics that can measure the residual kinetic energy with Doppler spectroscopy andtest the microphysics modeling used for the dense plasmas of the implosion utilizing particle and x-ray scattering methods. New
diagnostics specifically aimed for providing precision data on novel future implosions for NIF such as double shell targets ordirectly driven implosions should also be within the scope of the program.
The ICF program should put a high bar on focused physics campaigns to make sure that the results are not masked by othereffects (laser-plasma interactions, tent etc.). It is important that shots deliver critical experimental tests of the physics models
used in the radiation-hydrodynamic codes. In addition to examples mentioned above, a focused campaign with precision
measurements of 1-D implosions especially with large case-to-capsule ratio experiments should be a priority.
The ICF program will need to implement the best possible physics models into the radiation-hydrodynamic simulations. New
experimental and theoretical results from other experimental programs have shown that orbital free (Thomas-Fermi) modelingprovides a poor approximation. This is a challenging area where better approximations appear possible with the potential toproduce results that will affect future ICF designs. Further, many calculations of NIF capsule implosions result in an ionization
state of carbon in the dense ablator plasma close to 2 while advanced modeling and experiments have shown Z=4. Possible
consequences on opacity and heat transport will need to be investigated. In particular, advanced models such as those that use
detailed configuration accounting, non-LTE physics, and continuum lowering physics should be routinely used and tested inexperiments, possibly at Omega and medium sized facilities.
To develop guides for experiments planning of integrated shots and focused experiments it is important to develop a simulation
database that evaluates performance degradations of DT implosions due to possible errors and uncertainties in the microphysics.
Such calculations should also help to better understand the existing experimental databases. An example where assessments areneeded is the difficult regime of Warm Dense Matter where uncertainties in the heat conductivity could affect the growth ofRayleigh Taylor instabilities. In addition, simulations of hot-spot formation and burn truncation could be affected as a result oflarger conduction losses than calculated with present models.

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Ignition Approach: Laser-driven Direct Drive
Findings: The direct drive ICF program has demonstrated significant progress in their understanding of crossed beam energy
transfer (CBET) that has led the team to successfully field a series of precision cryogenic implosion experiments at the Omega
laser facility resulting in significant hot spot pressures of 56 ± 7 Gbar. These pressures are the result of recent additions including
improved illumination uniformity using SG-5 phase plates and a “poor-mans” form of zooming by turning off Smoothing by
Spectral Dispersion (SSD) at the peak of the laser drive. The experimental DT fusion neutron yield has reached 45% of the clean
calculated 1-D value. Especially in the regime of moderate convergence ratios (<17) and moderate fuel adiabats (α > 3.5) theexperimental pressure values are very close to 1-D performance. In this regime, pressure values of 90% and areal density valuesof 100% of 1-D calculations are reported.
Higher convergence and low-adiabat implosions show performance cliffs. Simulations indicate that mix due to so-called target
debris or capsule impurities is affecting the attainable hot spot pressures. A reduction of up to a factor of 5 was found. Further,
the program is actively investigating 3-D effects due to low-mode asymmetries induced by, e.g., laser power imbalance, target
offsets, and beam miss-pointing effects. Comparisons with simulations indicate burn truncations significantly reducing theattainable pressure. In general, the database shows distinct trends that are not completely understood. For example, smaller
capsules with 800-micron diameter show the best performance while larger diameter capsules perform poorly despite the factthat CBET is reduced for larger diameter targets. Reducing the target diameter will come at the cost of reduced fuel andconsequently less overall yield. If scaled to full-scale ignition experiments this trend will make it harder to get to alpha heating.
The direct-drive team has developed a project and campaign plan to reach implosions with peak pressures of 80 Gbar at the
Omega laser. If this performance is achieved it would provide a major impetus to become a candidate for the development of aburning fusion platform. The main technological advances needed include sub-aperture and full-aperture zooming to increase
the kinetic energy of the implosion. Also, reductions of low-mode and high-mode mix, and optimizations of the capsule adiabat
to increase the hot spot pressure are important. In addition, the program is pursuing high-Z capsule coatings and dopants to
reduce mix.
The predictions for direct drive ignition on NIF (gain of 1) show that the target requirements are in a significantly less challenging
hydrodynamic regime than current indirectly driven capsules. The design use a convergence ratio of less than 25 and hot spotpressures of about 150 Gbar where our current understanding from indirectly driven NIF experiments suggest that stable wellperforming implosions are feasible. On the other hand, the requirements on the laser, e.g., drive uniformity, laser colors, power
balance, and on target and target fielding, e.g., fast shroud on cryostat, target alignment, and vibration control are much more
stringent than for indirect drive implosions. In addition, the two-plasmon decay (TPD) instability will need to be mitigated.
Comments: TPD remains a key physics risk factor for direct drive implosions. This deleterious laser-plasma instability drives largeamplitude electron-plasma waves that cause hot electron preheat effects of the fuel affecting compressibility and laser-target
coupling. It is important to adequately address the threshold and scaling for TBD with laser intensity, plasma scale length, andfor zoomed laser beams. The current strategy is to mitigate TPD by utilizing mid-Z layers in the ablator. The mid-Z layer is effectivein raising the coronal plasma temperature that in turn will lead to increased Landau damping of plasma waves and consequently
reduced hot electron preheat. The predicted increase in temperature has been observed with Thomson scattering. Despite theobvious attraction of the mid-Z layer strategy, it appears to kick the can down the road. For once, it will require use of fill tubes
where very little modeling expertize exists for direct drive implosions. Further, there is a lack of existing performance data to
support the viability of direct drive implosions that use capsules with fill tubes. A complete assessment must further analyze theeffects on shock timing and possible generation of reverberating shock waves in the ablator and exacerbated hydrodynamic
instabilities.
Assuming that TPD can be mitigated either through mid-Z layers or with laser beam smoothing at moderate laser intensities it
must be of high importance to prepare directly driven layered DT implosions on NIF. The NIF Polar Direct Drive (PDD) working
group has adopted a program to work on shock timing, PDD phase plates, laser imprint studies (Multi-FM), and wavelength
detuning experiments. The solution of these issues will require facility development efforts. These modifications are under way
at a moderate level. However, the scope of work falls short of what is actually required for a successful direct drive program on
NIF.

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A NIF shot request of 12 shots on 5 days in FY16 does not match with the ambitions of the program and is not consistent with thegoal to develop a directly driven burning fusion platform.
Direct drive implosion physics and the experimental campaigns on Omega are well prepared with radiation-hydrodynamic
modeling and laser-plasma interaction calculations. At this point, LLE uses a no-name code for the calculations of 3-D effects; thequality of the results and the predictive capabilities of this tool have not been demonstrated. No benchmark calculations,comparisons with other hydrodynamic simulations or with experimental data are presently available.
Recommendations: The direct drive program will need to move much more aggressively towards delivering quantitative
experiments on NIF. The direct drive program will need to develop an integrated experimental and facility plan that will result inthe technical feasibility demonstration of cryogenic precision implosions on NIF with the correct color separation, beamsmoothing, zooming optics, fast cryogenic shroud, and layering with fill tubes. The program must develop milestones and showthat the performance matrix can be met in integrated experiments. This includes control of target debris, CBET mitigation, andlaser power balance. In addition, engineering solutions will need to be developed on the NIF to meet the laser and target pointing
and vibration requirements.
The direct drive program should further move towards developing and demonstrating effective TPD mitigation for NIF plasma
scale lengths, plasma temperatures, and laser pulse durations. Mitigation strategies that include modifications of the baseline
direct drive ignition target such as mid-Z payers or fill tubes will need to be addressed with simulations and experiments. The
plan will further need to assess all DD facility modifications and test the performance with laser and target experiments wherever
possible.
Further, the team must pay special attention to areas where the direct drive requirements are most stressing to the NIF laser andwhere they go significantly beyond present capabilities. New mitigations must be developed if power balance of 2.5% on target
or beam and target pointing offsets of < 5 µm, or the fully requested wavelength tuning range cannot be delivered.
The experimental effort on the NIF will need to match the quality of experiment preparation, experiment performance and postshot analysis at Omega. For NIF implosion studies, detailed simulations must be performed for actual experimental fielding
scenarios. Sensitivity studies that include pointing offsets, power balance etc. will need to be performed to guide theexperimental team with realistic pre-shot predictions. These shots must be an integral part of the NIF direct drive plan discussed
above with the expectation to deliver answers to specific milestones. The results of experiments should then form the bases fordeveloping optimized sets of requirements for attempts at alpha heating and ignition.
For this purpose, the program will need to employ and develop simulation tools that have been tested extensively against data.
For example, for applications that will use the code HYDRA it will be important to further develop the code and to implement
CBET ray tracing to make quantitative predictions. These tools should be tested against experiments on NIF.
Extensive LPI modeling of CBET will be required and NIF experiments that directly measure the coronal plasma conditions at thelocation of the CBET process should be performed. The team should further develop experiments to make quantitative
measurements of CBET on NIF to test the models that are presently applied with fair success at Omega.
Extensive LPI modeling of TPD will be required and NIF experiments that directly measure the effects of hot electrons such as
hard x-ray imaging or x-ray fluorescence measurements should be developed.
Extensive hydrodynamic modeling of the effects of fill tubes will be required and NIF experiments that directly measure theeffects on neutron yield and areal density should be developed.
Hydrodynamic modeling of mix will need to be put on solid footing. This includes benchmarking against other codes and data.
Experiments at the Nike laser could help testing the models. The development of mix mitigation strategies in directly driven
implosions such as Au layers will need to be carefully conducted to assure that all other requirements on adiabat, velocity, TPD
and CBET instability are met.

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Ignition Approach: Magnetically-driven Direct Drive
Findings: The magnetically-driven direct drive ICF program is a recent development of the National program that combines
magnetization, laser heating, and implosions to reach fusion plasma conditions. Specifically, the Z-pinch discharge magnetizes
the fusion fuel and a beryllium liner with a magnetic field of 10-30 T in axial direction. The role of the field is to provide early
confinement by inhibiting thermal conduction losses and magnetization of the ions, and to help stabilizing the main compressionof the liner. Between magnetization and compression an optical laser heats the fusion fuel with a kilo-joule beam (2-10 kJ).
Current experiments with D2 fuel indicate temperatures of 200 eV due to the laser heating. The heating effect largely reduces therequirements on compression and simulations show that fusion temperatures can be reached with a radial compression ratio of
about 30. This translates into implosion velocities of 100 km/s for at 100 Mbar magnetic drive pressure to achieve stable andquasi-adiabatic compressions. The current system can couple 100 kJ energy into the heated fuel.
With high priority, the program is pursuing the physics of driver-target coupling including target pre conditioning, implosion
experiments, stagnation and burn, modeling and simulations. This includes focused and integrated implosion experiments on
multiple facilities and the development of new diagnostics and simulation tools. At a lower priority the program is developing thescaling to high pressures on Z and possible high yield gas and ice burning physics on future facilities.
The first experiments on the Z facility have resulted in remarkably good performance reaching D-D fusion yields of 2-4 x 1012 attemperatures of ~2.5 keV. On Z, it is thought that conditions suitable for 100 kJ DT fusion yield with a pressure-time product ofP-tau > 5 Gbar-ns and a field-radius product of BR > 0.5 MG-cm can be achieved (for the foreseeable future, DT fusion yield
estimates are based on experimental demonstrations of DD equivalent yield). An important milestone is to deliver a 25 MA
current to a successful target; if successful, a significant increase in yield is expected over the presently fielded 18 MJ current
shots.
For 50:50 DT implosions, possible fusion yields from gas (~5 MJ) and ice burning (~ 1GJ) ignition are exciting prospects, but not
attainable with present facility capabilities. On Z, a five-year schedule was presented to demonstrate performance with DT fuelat the 1% percent level of tritium. A 50:50 DT fuel shot would imply utilizing a significant amount of radioactive fuel and is statedas a longer-term goal.
The MagLIF experimental team has fielded a series of shots with the goals to improve the performance and fusion yield ofmagnetized implosions. However, it became apparent that variations of laser beam propagation and small laser heating of thefuel is a limiting factor for improving integrated implosion performance. The team has developed a strategy to demonstrate laser
beam propagation at Omega and NIF with the goal to subsequently field optimized experiments on Z.
Other experiments have investigated implosion performance after some modifications were made to the Z-pinch discharge.
Examples include coated wires and different gap distances; these studies have shown that the performance of the implosion is
not fully predictable. This could be a reflection of variations in laser heating performance. However, modifications could also giveraise to failures; in one example problems due to impurities were reported.
Comments: The time scales in the 5-year planning for fielding experiments with tritium to study fusion gain and alpha heating are
too long. To benefit from progress of our understanding of NIF and Omega implosions and to provide leadership in compression
and burn physics it will be important to increase the fusion gains from MagLIF implosions as quickly as possible.
Z pinch implosions provide a harsh environment making development of diagnostics a very challenging task. The program has
succeeded in delivering excellent data of compression and burn. The program is an important contributor to the National
Diagnostics program. Future improvements of temperature measurements with x-ray scattering and down-scatter from beryllium
or deuterium are a priority.
The program would greatly benefit from the use of 3-D modeling to develop mitigations of instability features in the implosion.
These developments should go along with fielding improved diagnostics of axially resolved imaging, spectroscopy and x-ray
scattering to measure the conditions and compare with simulations. Importantly, simulation tools and models with magnetic
fields will need to be developed and tested with focused experiments. Collaboration on HYDRA is an obvious choice. Magnetic
fields also need to be included in reduced models, for example in the isobaric pressure model.

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Recommendations: It should be the highest priority to field experiments with effective and reproducible laser heating as quickly
as possible. Laser beam propagation is not a new problem and has been solved by NIF Early Light experiments in 2007. The laser
beam smoothing requirements are well understood. Well-tested analytical models and 3-D simulations are available. The teamshould take advantage of the capabilities that exist within the National complex and use the tools to reduce the scope of thelaser-plasma interaction investigations by designing phase plates and polarization smoothing optics. An integrated test should bedemonstrated within less than 1 year.
Further, availability of a designated expert on laser-plasma interactions may be helpful to the program. This expertize could bein form of a designated laboratory expert, collaborator or a scientists at a University.
Also at high priority, the magnetically driven direct drive program must develop predictive modeling of the integrated implosion.
Experiments on Z occur at a lower repetition rate than laser experiments and the program has access to a limited number ofshots. It must be a priority to field 2 laser beam lines (one for backlighting, one for laser heating) to deliver extremely importantdiagnostic information on every shot.
II. Assess the integration of experiments and codes
Diagnostics
Findings: The National Diagnostics program has developed a well thought-out plan to develop new diagnostics for measuring
critically important quantities whose knowledge will allow major progress towards ignition. The program has brought together
the scientists from all areas of the NNSA science complex and contributions of all programs and researchers have been vetted inseveral National Diagnostics workshops. This process has led to the first eight foundational diagnostics that will provide
unprecedented information on implosion physics and compression and burn regimes, map out the plasma conditions created byboth laser and pulsed power drivers, and enable dynamic information over a range of relevant conditions on the properties ofmaterials utilized in nuclear weapons. The data provided by these diagnostics will validate and improve the physics contained
within the multi-dimensional simulation codes developed by the ASC Program and both uncover and quantify importantphenomena that lie beyond our present understanding.
Comments: The first eight foundational diagnostics span a wide range of capabilities addressing a range of critically important
physics questions. The new capabilities will allow assessing the performance of integrated implosion experiments and support
focused physics experiments that aim to measure single parameters or quantities that determine the physical and structuralproperties of fusion plasmas conditions. It will be important that the diagnostics are precise enough to critically test theory ofdense plasmas achieving an accuracy of the data that can clearly distinguish between the results of simulations and different
theoretical models. In addition, the diagnostics must visualizes the evolution of the compressed material and determine nuclear
fuel assembly and hot spot formation.
It will be important to continue pushing the boundaries towards improved precision, higher resolution and diagnostics
information that is based on fundamental physical principles. For example, new techniques will need to be considered thatobserve the Doppler broadening from x-ray emission lines to produce velocity maps and accurately measure residual kinetic
energy. Further, particle and x-ray scattering methods should be adopted that allow measurements of the physical properties ofdense matter by, e.g., observing Compton and plasmon features. Applications of these techniques in focused experiments canprovide insight into density functional quantum molecular modeling, continuum lowering and the ionization state of dense
plasmas. These methods are suitable to test calculations of physical properties (conductivity, pressure, ionization balance) to be
used in radiation-hydrodynamic modeling of implosions.
The availability of precision diagnostics will be important to deliver the program with the best possible understanding of the
behavior of integrated experiments and of the underlying physical processes. The availability is critical to remove multipliers andsolve missing energy problems that still await a resolution. In the past, imaging and scattering methods have removed many
uncertainties in our fundamental understanding of laser-plasma interactions and fusion plasma conditions. This is expected toalso apply in present fusion experiments. In particular, competing modeling and resolution of missing laser energy in hohlraums
appear possible with accurate temperature measurements of hohlraum plasma conditions with Thomson scattering.

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Recommendations: The implementation of the precision diagnostics proposed in the National Diagnostics Plan should be pursued
at high priority. The program serves as a major attraction of talent in experimental physics and provides a conduit to pursue
unprecedented explorations of plasmas and material conditions critical to the missions of DOE/NNSA.
Computational Models and Predictive Capability
Findings: The commitment towards developing radiation-hydrodynamic codes and in particular of HYDRA by the ICF program at
LLNL should be of great benefit of the community. Examples for testing the models and database that goes into the code havebeen discussed in comments above. Importantly, the code development includes physics critical to direct drive such as CBET andmagnetic fields.
Comments: It will be important to perform benchmark calculations of the conditions for all three ICF implosion geometries andmake the results available for researchers of the national program. Similarly to the analysis and archiving of the experimental
database from NIF experiments it appears that the program would benefit from a dedicated person who keeps track of simulation
performance with changing drive and as improved physics models become available. It was noted that several experimental plots
from NIF performance data were shown without simulations results.
Recommendations: The continued development of HYDRA is a critically important activity that should be pursued at high priority.
III. Assess cross-platform and cross-laboratory collaborations
Findings: The extremely challenging measurements and diagnostics of laser-plasma interactions, preheat, and compression andburn physics are an excellent area for intense collaborations between the ICF program elements. The development of the eightfoundational diagnostics demonstrate that collaborations on diagnostics are a very important area for pushing the boundaries ofexperimental physics, assuring quality measurements among the laboratories, and making critically important measurementsthat inform future designs for ignition.
The development of radiation hydrodynamics modeling is an equally important area for cross-laboratory collaborations.
Comments: Platforms for determining parameters of subsequent ignition shots are too specific to each specific approach and are
not necessarily informing the other campaign. However, focused physics experiments on physical properties such as conductivity,
opacity, EOS etc. are important for all approaches and are possible areas of collaboration among the scientists of the complex.
Recommendations: Besides including the relevant physics into HYDRA it is important to make predictions for problems that affectmultiple laboratories. Effects of the fill tube in direct drive and comparisons to indirect drive, or laser beam propagation in MagLIF
target and in indirect ICF hohlraums are examples that need accurate assessment and simulation predictions.
The collaboration on focused physics experiments to determine physical and structural properties or models thereof areimportant for ICF and have wide impact into related fields of science such as laboratory astrophysics and high-pressure physics.
It provides an excellent opportunity to test assumptions and methods against those used in other fields of science and tocollaborate on developing accurate physics models.

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Reviewer Report: James Hammer
I. Assess the scientific hypotheses and the prospect for achieving ignition with existing scientific capabilities andfacilities; or, if indicated, what would be required to achieve ignition and supporting analysis. Provide anevaluation of program balance among ICF approaches.
General remarks: The prospect for achieving ignition with existing capabilities remains uncertain. The groundwork being laidin the current program, however, does make it possible that ignition and substantial yield will eventually be achieved on either
an existing device or a future laboratory driver. Reaching that goal will, of course, depend on the structure and level of support
for the program. Many of the needed structural changes have already taken place, but the trends toward improving the scientificunderpinnings and inter-laboratory collaboration should continue to be strengthened. A commitment by the NNSA for steadysupport of the program, with neither draconian cuts nor crash “success-oriented” programs, will be essential for fostering theneeded climate and ensuring long term success.
We simply do not know enough at the present to define a guaranteed ignition-capable driver, or even whether the required
technology is laser or pulsed-power based. The reason for that uncertainty is because of the core nature of the ignition challenge.
Creating ignition conditions at the energies available from laboratory drivers requires extreme concentration of that energy,
which in turn requires a high degree of control and precision in implosions in order to reach high convergence. To ignite, someof the fusion fuel must be hot enough for thermonuclear burn, but also it must be dense enough and long lasting enough thatthe release of fusion energy will heat surrounding fuel to burning conditions. These requirements lead to a connection between
how much energy is needed, and the extent to which the energy must be concentrated or converged. If energy is plentiful in the
imploding fuel, a fairly modest degree of convergence can reach ignition, or conversely, an energy-starved system will require
extreme control and high convergence. Ignition has not been achieved on the NIF predominately because, given the amount ofenergy available, the control of the imploding fuel has not been precise enough to reach the needed convergence. The causes ofthat lack of control are incompletely known, and the scientific program to unravel the causes will dominate the indirect drive
program for the next few years. Success at identifying and curing these problems would make ignition on the NIF much more
likely. The other major stumbling block, aside from concentration of the energy, is the tendency for cold fuel or other material tomix into the hot, burning fuel and quench the burn. Control of this phenomenon is another challenge for all ignition concepts,
although mix does not appear to be dominant in recent NIF experiments.
The energy-convergence connection is at the heart of the concepts competing with indirect drive. Direct laser drive is more
efficient at converting incident laser light into imploding fuel energy, so the convergence requirements are less. On the other
hand, direct drive has additional sources of non-uniformity, such as imprint of laser non-uniformities on the implosion. These
are not yet well enough understood to know if direct drive wins out over indirect drive. Until recent years, the lack of control ofmagnetically-driven implosions had eliminated pulsed power as a contender, even though pulsed power is by far the most energyrich technology. Pulsed power drivers with more than ten times the energy of NIF are readily imaginable. Recent advances incontrol of metal liner implosions have put pulsed power into contention as a path to ignition and high yield. In the case of all
three drive methods, the question comes down to the quantitative issue of whether the precision in controlling implosions
matches the available energy.
The optimal approach to ICF ignition is not, at one extreme, an open-ended scientific program, or at the other extreme, an
exercise in systems engineering where the fundamental science is believed to be sufficiently understood to march step by stepto ignition. The National Ignition Campaign failed by hewing too close to the latter approach with excessive confidence in theexisting physics understanding. The optimal balance point is where the emphasis is on finding a “good enough” physical model
to guide the integrated ignition experiments. This balancing entails focused experiments to help isolate the important physics,
model improvements, and integrated experiments that start from well-behaved sub-ignition “base camp” designs then take smallenough steps to avoid extrapolating beyond the limited predictive power of the models. A base camp, in analogy with mountainclimbing, is a starting place for the assault on ignition, which in our case means two things: 1) a design where the existing models
have demonstrated predictive power in the sense of small changes have predictable effects and 2) the models predict that ignition
could be reached by a series of incremental changes away from the base camp. Though likely incorrect in detail, if models show
no path to ignition for a design, then experience shows that is probably the case, i.e. the models are unlikely to be pessimistic.
Some might argue that a base camp design simply hides physics which will prevent modified versions from reaching ignition. In
a sense this is true, but the main reason for the incremental approach is to be able to sort out what effects dominate degradation

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as changes are made. When the design is “over the cliff” in several ways simultaneously as occurred in the National Ignition
Campaign, then it is very difficult to attack the problem. Also, the point of the base camp strategy with small steps is not risk
aversion so as to avoid experiments that “fail”, i.e., give lower performance. The point is to approach failure modes in a way that
can help teach us how they fail.
Because the target designs require the interaction of many complex physical processes, the fate of an ignition approach rests
largely on the fidelity of the multi-physics models used to design experiments and help interpret data. The complexity and theneed for precision and high convergence rule out a purely empirical approach. The models in the design codes are necessarily
approximate, with many simplifications, idealizations and often numerical “knobs” that are adjusted to cover unknown orunresolved physics. There are also many choices in model parameters, types of model and mesh resolution made by the design
physicist using the code, so the accuracy and effectiveness depend on the skill of the user as much as the code itself. The choices
and models represent what has been judged by design physicists and code developers to be “good enough” to serve as design
tools for experiments, and as a consequence must be closely tied to experimental validation. The issue of getting the right answer
for the wrong reason is always very present when using codes calibrated in this way. In fact, one could say the codes always get
the right answer (when they do) for the wrong reason, and it is simply a matter of degree of “wrongness.” Still, these codes in
the right hands can be powerful tools for designing experiments, and for many problems the degree of “wrongness” isinsignificant. The codes work best when the extrapolation is small from what has been experimentally validated. They failed to
predict capsule behavior in the National Ignition Campaign because the extrapolation from the earlier validated parameter
regimes was too great. Prior to the National Ignition Campaign, there was significant disagreement within the design physics
community about whether the required extrapolation was too large. The pessimists have been vindicated. One of the tasks now
for indirect drive is to use experiments much closer to the ignition regime to find the weak points in the earlier model choices
and idealizations, repair the deficiencies, then use the codes to steer integrated experiments closer to ignition in small steps
consistent with their predictive power. The situation for the alternates to laser indirect drive is analogous. Experiments thatprobe our ability to model implosions and ignition-relevant physics can test and validate the models for both laser direct driveand magnetically-driven implosions. Those validated models should enable modest experimental extrapolations for thoseconcepts on the path toward ignition.
A well-proven target design strategy that complements the model-improvement strategy is to alter the experiment until theexisting model becomes valid. A recent example of this strategy is the decision of the indirect drive campaign to focus on designs
with shorter laser pulses and near-vacuum or low-gas-fill hohlraums. It appears that CBET (cross beam energy transfer) and laserbackscatter are significantly reduced for these designs, making the hohlraum easier to model in some respects. Whether thisstrategy by itself can lead to ignition remains to be seen. The prudent approach is to work in both directions: change the design
to reduce undesirable complex phenomena while at the same time improve our understanding of such phenomena.
Following the National Ignition Campaign, the indirect drive program regrouped and pursued a base camp strategy starting witha more conservative implosion, the High Foot design, along with the “small steps” philosophy described above. This strategy
proved effective on two fronts: 1) capsule performance improved over an order of magnitude, breaking into the fusion alphaparticle heating regime; and 2) experiments revealed the importance of symmetry control as a dominating factor in limiting
performance. The second revelation has highlighted the need for better hohlraum models (the model-improvement strategy) as
well as the design change strategy noted above. These two strategic elements, applied to all concepts, are the best chance forsuccess but may not lead to rapid improvements in performance. Following the incremental path requires taking the long viewon the part of program leadership. Improving models is time and labor intensive, with new focused experiments needed, as wellas the painstaking analysis of an extensive suite of data, a certain amount of trial and error, and potentially new theoreticalframeworks to account for neglected physics. An alternative strategy – identify a potential “magic bullet” fix and launch an
integrated ignition campaign around that fix – has been tried without success. I strongly recommend the long haul, three pronged
strategy of 1) data driven model improvement, 2) changing as needed to more model-friendly designs and 3) taking small steps
away from reasonably well understood base camps in ignition attempts. Progress along this path cannot be measured solely by
numerical figures of merit such as yield or stagnation pressure, but should also be assessed with the time honored and morenuanced method of peer review.
The small-steps approach applies to designs on the ignition path. In parallel, the program should be exploring new design features
or concepts that could be integrated into a new or modified ignition-relevant base camp. A reasonable amount of risk-taking is2015 Review of Inertial Confinement Fusion and High Energy Density Science Portfolio

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warranted in trying things that are far afield from the usual designs. A potential example is the use of foam liners or shine shields
in hohlraums. I should disclose that I have been participating in a Laboratory Directed Research and Development project onalternative hohlraums employing foams. Since the ICF design space is large and many things could be and have been proposed,
the highest priority new concepts should be those that could potentially improve or reduce the importance of the mostdeleterious behaviors, e.g., uncontrolled asymmetry in indirect drive implosions. Experiments exploring new design features
should be similar to other focused experiments where the goal is to test understanding of the underlying physics and ability ofmodels to capture relevant behavior. Combined with the other experimental activities, tests of new design features can gradually
increase the design physicist’s “bag of tricks,” i.e. techniques that can be employed with confidence in integrated designs. On
occasion, the increasing “bag of tricks” may enable a qualitative leap in performance or control. Such leaps cannot be forecast
or planned for, but the program can choose to create a climate that invites innovation.
Finally, on the note of program balance and collaboration, it makes good sense that the ICF program diversify since it is not clearthat laser indirect drive on the NIF will reach ignition. Since LLNL represents the largest part of the program, it is reasonable thatsome of the first steps in diversification would come from increased involvement of LLNL scientists in laser direct drive andmagnetically-driven implosions. Here let me disclose that I am involved in an existing collaboration between LLNL and SNL on
magnetic drive. I can attest that the LLNL investment in codes, diagnostics and target fabrication are already being heavily
leveraged to the benefit of magnetically-driven implosions and that we hope to increase that interaction. Similar interactions onlaser direct drive could also be launched. Feedback in the other direction can be expected as well. Experience with fuelmagnetization at SNL may help motivate NIF magnetized fuel experiments. The extensive expertise at LLE in the control of laser
uniformity and bandwidth has already influenced direct and indirect drive experiments at NIF and will continue to do so.
Over the long term, I believe the program should be aiming toward a high-yield capability, whether or not ignition is reached on
NIF. I base that belief on my understanding of the long-term needs of the Stockpile Stewardship Program. In my opinion, a fusion
source of 500 megajoules or greater will be essential for the health of the program in an extended era without nuclear tests.
Such a source is unlikely to be achieved in the next decade, but keeping high yield as an ultimate goal can still guide our thinking
in the interim, e.g., driver technology choices could be made consistent with the high yield goal. Ignition is one important stepalong that path, but not the final end in itself.
Ignition Approach: Laser-driven Indirect Drive
Findings:
1.

The change in the program after the National Ignition Campaign has born fruit through the High Foot campaign in two
important ways: by accessing the alpha heating regime and through the greater clarity about what is preventing further
advances, i.e., low mode asymmetry.
2. Improvements to the diagnostic suite over the last few years have had large positive effects on the program. Striking
examples include the 2DConA imaging experiments which revealed the tent feature and the great wealth of information
coming from neutron diagnostics.
3. Progress in numerical figures of merit, such as yield and the Lawson criterion, are likely to be episodic, given the natureof the program. For instance, the High Foot campaign appears to have taken advantage of comparatively low-hanging
fruit in capsule performance, and further improvements could require more fundamental improvements in hohlraum
radiation symmetry.
4. The new structure of the indirect drive program is a step in the right direction with 3 focus areas: integrated
experiments, ignition science that pursues focused experiments, and physics integration.
Comments:
Physics integration covers the effort to analyze data and extract physically meaningful information, as well as improve models.
This is a crucial activity that was not previously given enough attention. Before the restructuring, too many scientists were in“feed the beast” mode where a great many calculations were done to support upcoming shots, and the fidelity of those
calculations was of secondary concern.
Each time a new diagnostic is fielded, unexpected structure emerges. These revelations have proven very useful and informative,
and a steady pace of development of new diagnostics should be a priority for the program.

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Even after the conclusion of the National Ignition Campaign, there was a tendency toward “ignition fever” in the program wheresome felt that ignition was just over the horizon and could be reached if only a particular feature of the implosion were tweaked.
This led to substantial expenditure of shots and resources without corresponding benefit. The more humble but effective methodof establishing base camps with incremental steps is preferable.
Recommendations:
1.
2.
3.

4.

5.

6.

7.

8.

Measure progress first and foremost through peer review assessment of scientific progress rather than numericalmetrics such as yield.
Continue a three-pronged strategy of 1) data driven model improvement, 2) changing as needed to more model-friendly
designs and 3) taking small steps away from reasonably well understood base camps in ignition attempts.
I encourage design physicists in both the integrated experiments area and physics integration to pursue more hohlraum
model variations, especially those that can be tied to observations other than drive and hot spot shape. For instance, in
hohlraums the gold bubble may intermix with the gas (or ablator for near-vacuum hohlraums) in a way not captured bystandard hohlraum calculations due to Rayleigh Taylor instability or finite mean free path effects. Applying mix models
to the gold–gas interface could change both laser propagation and the volume and location of x-ray emitting matter,hence the capsule symmetry. Viewfactor and other hohlraum imaging experiments may be able to constrain thesemodels by comparing data to synthetic images. It is already known that the standard model does not accurately predict
emission images in some cases.
Pursue the “BigFoot” design that increases hot spot rho-R at the expense of the cold fuel. One risk of this design is thatmix at the fuel-ablator interface may have gone undetected in earlier experiments but the thinner ice layer could expose
higher Z material to the hot spot. X-ray and potentially nuclear diagnostics capable of detecting hot spot- ablator mix
should be fielded.
Examine implications of backscatter variation on stagnation symmetry. The observation that, for gas filled hohlraums,
non-reproducible variations in inner beam backscatter are more than three times the incident beam variation, suggests
this could be an important contributor to radiation drive non-uniformity and stagnation asymmetry, e.g. as observed on
the FNADS nuclear diagnostic. The backscatter variation is especially of concern if the observed shot to shot variation is
also representative of non-reproducible quad to quad variations. Improving backscatter variation measurements could
be justified if models suggest the inferred variation is a problem, e.g. by instrumenting another inner beam quad withbackscatter diagnostics.
Consider a large case-to-capsule, sub-ignition experiment that reduces drive asymmetry to levels that would not
dominate performance. Such an experiment could answer the question: is it possible to get 1D performance from asymmetric implosion at greater than convergence 30? The answer could offer a preview to the next stumbling block
after hohlraum symmetry is improved for ignition designs, or conversely, give more confidence that ignition will be likely
once adequate symmetry is obtained.
Encourage innovation that could enable creation of new base camps. This would entail exploring more ways to increase
the design physicist’s “bag of tricks.” Foam features in hohlraums are already being considered along with magnetizing
capsules and hohlraums. A broader suite of modifications to the laser itself could be explored, e.g., new methods ofmodulating the laser to decrease CBET and backscatter.
Foster a robust basic science effort in important physics areas underpinning ignition. This would include, among others,
non-LTE (Local Thermodynamic Equilibrium) atomic physics, computational fluid dynamics, kinetic theory of plasmas
and Laser Plasma Interactions (LPI). The community has despaired of making significant headway in LPI but it remains a
critical concern and 1) taking the long view, new experimental approaches and computational capabilities may arise and2) as in target design it may be possible to change the experiment. An example of the latter would be rapid modulationof the laser with high contrast (factor of ~ 100), to make theory more applicable.

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Ignition Approach: Laser-driven Direct Drive
Findings:
1.

Direct drive experiments on OMEGA have continued to make steady progress in performance metrics such as stagnationpressure, and should be robustly supported as the main experimental capability for integrated spherical direct drive(SDD) experiments over the next five years.
2. Since NIF polar direct drive (PDD) implosion experiments appear to have low chance of reaching ignition, and the cost
and time required to prepare for PDD are substantial, NIF direct drive experiments should shift toward assessing thepotential of SDD on NIF.
Comments:
Several factors drive the finding regarding PDD: the belief, as expressed by LLE management, that PDD is unlikely to be a path toignition; the desire to diversify the program over the next five years to include laser indirect drive, laser direct drive and magnetic
direct drive; and the guidance from NNSA to expect roughly flat budgets over the next several years. Committing to fully equip
NIF, within three years, with hemispheric detuning, SSD and PDD phase plates on all quads would require many tens of millionsof dollars. The effect in a flat budget environment would be to narrow rather than diversify the program since that substantial
sum would need to be extracted from the rest of the effort. Much of the effort expended on PDD would not apply to SDD, e.g.
phase plates, and the resources expended on PDD implosions would distract from getting the best possible understanding of the
LPI and imprint issues which will dominate the ultimate decision on SDD. Focusing on SDD physics would require fewer costly
changes to the laser, i.e. smoothing on less than the full complement of NIF beams, and give SDD its best chance of building astrong physics case. The proposed early steps on the NIF direct drive program are already (and appropriately) aimed in the
direction of understanding LPI and imprint issues. Further efforts to improve LPI could also be of major benefit to laser indirectdrive and MagLIF. Changing the NIF direct drive program to focus on SDD would not be an irrevocable decision. If at any point
the prospects for PDD ignition are found to improve, the program plan could be modified and the SDD-focused research that had
taken place would undoubtedly be of benefit to future PDD experiments.
SDD on NIF would offer the best chance for ignition with direct drive, but the decision to reconfigure NIF for SDD will undoubtedly
require a high bar given the cost and impact on the HED program. It is difficult to foresee all the elements that will drive thatdecision, but progress on the OMEGA SDD experiments and a good understanding of SDD relevant LPI and imprint are clearlyrequirements. Focusing on those two things for the next five years would seem to be the most prudent use of resources.
Recommendations:
1.
2.

3.

4.
5.

Measure progress first and foremost through peer review assessment of scientific progress rather than numericalmetrics such as yield. Major decision points, such as reconfiguring NIF for direct drive should require advances in
performance metrics, such as stagnation pressure and the Lawson parameter as well.
Discontinue experiments preparing for NIF PDD implosions (shock timing, hemispheric detuning, 48 quads of SSD andpolarization smoothing) and increase the number of NIF shots and diagnostics leading to high fidelity tests of laser
plasma interaction (LPI) physics (CBET and TPD) at the correct scale lengths and plasma conditions for ignition SDD. The
bulk of these could be planar and hemispherical experiments and include tests of high Z overcoats or buried mid Z layers
as described in the program plan. Tests of imprint for ignition SDD conditions should be included. Smoothing on enoughquads to enable high fidelity tests would be needed, but the deployment could be paced by experimental progress.
Develop improved LPI diagnostics at NIF, e.g. Thomson scattering at short time scales for a more detailed
characterization of LPI processes. Laser direct drive is so intimately tied to LPI that decisions on SDD or PDD ignition
experiments will need the strongest possible foundation. A focused LPI effort as part of SDD research with better
diagnostics to both characterize LPI and study mitigation could also be of major benefit to the laser indirect drive and
MagLIF efforts.
Encourage innovation that could enable creation of new ignition base camps.
Increase multi-laboratory collaboration on laser direct drive in the areas of target design, diagnostics, data analysis, andtarget fabrication as well as underlying science in these areas.

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Ignition Approach: Magnetically-driven Direct Drive
Findings:
1.

Magnetically driven implosions (MDIs) have made great strides in recent years in their ability to concentrate energy
effectively and in producing hot, dense, thermonuclear plasmas.
2. MDIs are at an earlier stage of maturity than laser indirect drive, but stand to benefit greatly from the ICF program
investment in codes, diagnostics and target fabrication.
3. The potential for pulsed power technology to deliver large total energy opens the possibility of ignition at lower
implosion quality than required for lasers, as well as high total yields.
Comments:
As acknowledged by the proponents, the greatest risk of the MagLIF concept is the mix of material, either liner, window or evendense DT fuel into the hot fuel which could quench the burn. This can occur early in time due to filamentation of the laser, laser
ablation of adjacent material or swirling of the gas caused by non-uniform heating. Late in time, the stagnation is also more
prone to mix than standard ICF. The reason for that greater sensitivity is that igniting designs have lower hot spot rho-R thanstandard ICF, which translates into a longer burn duration to generate enough fusion heating to ignite. The ratio of required burntime to the sound transit time of the hot spot is inversely proportional to the hot spot rho-R. Accordingly, the low MagLIF hot
spot rho-R means there might be significantly more time for hydrodynamic mixing than in standard ICF.
The space of potential MDI designs is large, however, with different strengths, sensitivities and failure modes than MagLIF. That
breadth of possibility combined with the potential of the technology for reaching much greater implosion energy than lasers
makes MDIs an area of new opportunity that should be exploited by the national program.
Recommendations:
1.
2.
3.
4.
5.

Measure progress first and foremost through peer review assessment of scientific progress rather than numericalmetrics such as yield. Major decision points, such as construction of a higher current driver should require advances in
performance metrics such as stagnation pressure and the Lawson parameter as well.
More completely flesh out a diagnostic plan for characterizing plasma properties during MagLIF preheating andimplosion, with a particular focus on understanding mix.
Increase multi-laboratory collaboration on MDIs in the areas of target design, diagnostics, data analysis, and target
fabrication as well as underlying science in these areas.
Encourage innovation that could enable creation of several ignition base camps.
Consider an (initially modest) effort to explore magnetically driven indirect drive. More is now known about z-pinchdriven hohlraums than when SNL actively pursued indirect drive a decade ago, and such an effort would benefit fromwhat has been learned in the laser indirect drive program on NIF. Estimates suggest that scaling up the mass, energy
and size of a High Foot capsule, while preserving the demonstrated implosion quality (convergence ratio, shock history,
stagnation pressure, etc.) would lead to ignition at about 3 times the energy of NIF. Construction of a pulsed powerdevice at 3 (or even as much as 10) times the NIF x-ray energy appears to be manageable. The high efficiency of pulsed
power and absence of expensive and fragile optics tends to give it a large advantage over lasers in cost per unit energy.
Some of the main challenges of a magnetically-driven indirect drive approach would include demonstrating pulse shapecontrol, reproducibility and symmetry.

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Reviewer Report: Nelson Hoffman
I. Assess the scientific hypotheses and the prospect for achieving ignition with existing scientific capabilities andfacilities; or, if indicated, what would be required to achieve ignition and supporting analysis. Provide anevaluation of program balance among ICF approaches.
Ignition Approach: Laser-driven Indirect Drive
Findings: It has proven much more difficult than expected to produce adequately symmetric implosions of NIF indirect-drive
ignition capsules. This fact is viewed by the LLNL leadership as the main impediment, so far, to achieving ignition at NIF. While
the symmetry of imploded capsules is reproducible, and varies systematically under small changes in initial and boundary
conditions, it has not been predictable by numerical simulations. This finding applies generally to ignition-scale low-foot and highfoot capsules in high-density gas-filled hohlraums (0.96 mg/cm3 < ρgas < 1.6 mg/cm3). The unpredictability is believed to result
from the strong effect of cross-beam energy transfer (CBET) in such hohlraums, and the high sensitivity of CBET to the details of
local conditions, e.g., the temperature, density, and composition of the rapidly evolving plasma in the hohlraum. CBET moves
significant energy from the outer beams to the inner beams in the hohlraum, but there is not a reliable predictive model for thephenomenon. The result is that laser energy is deposited in unpredictable (albeit reproducible) locations in the hohlraum, giving
rise to an unpredictable (albeit reproducible) pattern of radiation drive falling non-uniformly on the capsule surface.
It furthermore seems clear that the asymmetry in a capsule implosion, induced by the non-uniform radiation drive, is exacerbatedwhen the capsule is required to implode to a very small radius, i.e., a very high convergence ratio (CR). This fact is intuitively
reasonable, born out by simulations, and verified in experiments.
Alternative ignition designs will receive greater emphasis in the near future. Given the difficulty in achieving adequate implosion
symmetry in NIF hohlraums, the indirect-drive ICF design community at LLNL and LANL is reducing its emphasis on highconvergence capsules, with their tendency to exacerbate drive asymmetry. There is instead a new emphasis on capsule designs
that sacrifice convergence and high gain in favor of robustness at lower convergence, with lower gain. The first LLNL high-velocity“Bigfoot” capsules (CR ≈ 25) will be tested in August 2015, while the LANL wetted-foam high-vapor-pressure capsules (CR ≥ 15)
will be tested in the first half of FY2016, and six shots have been requested for LANL double-shell capsules (pusher CR ~ 10) in
FY2016. These capsules all employ shorter laser pulses than past ignition-scale low-foot or high-foot implosions, and it is believedthat the resulting lower density plasma environment will result in more predictable radiation drive symmetry.
Additional physics phenomena may play important roles. Other difficult-to-predict phenomena have emerged as possible
significant obstacles to ignition at NIF. These include (1) laser-plasma instabilities and associated scattered laser light, likely
accompanied by hot electron production, transport, and x-ray generation; (2) hydrodynamic perturbations induced by the capsule
support structure (“tent”), which can be modeled only approximately in moderate-resolution simulations; and (3) non-LTE atomic
physics processes involved in x-ray production in the gold plasma and the mixed gold-helium-ablator plasma. Interestingly, one
often-invoked phenomenon that is believed to have been ruled out as a limitation on the performance of the high-foot capsules
is the hydrodynamic turbulent mixing of ablator material into the hotspot.
In retrospect, perhaps NIF should have been designed with 45% of its energy in the inner beams. The difficulties involved in innerbeam propagation in high-fill long-pulse hohlraums, uncovered through extensive work on hohlraum performance, modeling,and simulations over the past several years at NIF, have led LLNL researchers to conclude that a better design would have put
45% of NIF’s energy in the inner beams. As actually designed, NIF has 33% of its energy in the inner beams. The coming generationof improved hohlraum designs, using lower gas fills, is expected to make optimum use of the 33% as-built fraction.
Comments: Hohlraums with intermediate gas fill (ρgas ≈ 0.6 mg/cm3) may not be as easy to understand as is hoped. We should
be skeptical that complex systems (e.g., hohlraums) can be easily understood in small regions of parameter space embedded inlarge parameter regions that are baffling. Reviewers were told that high-density-gas-filled hohlraums (ρgas ≥ 0.96 mg/cm3) were
hard to understand because of CBET and LPI scattered light, leading to more oblate implosions than simulations predict.
Reviewers were also told that low-density or near-vacuum hohlraums (ρgas ≤ 0.03 mg/cm3) were hard to understand because of
the likelihood of long-mean-free-path (kinetic) interpenetration of ablated capsule and hohlraum wall material, leading to moreprolate implosions than simulations predict. Then reviewers were invited to believe that hohlraums with intermediate gas density

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(ρgas ≈ 0.6 mg/cm3) represent a “sweet spot” between the extremes, where the effects of CBET and kinetic plasmas are both smalland “symmetry is reasonably well modeled”, in the sense that the 0th-order shape, and its sensitivity to small variations arounda baseline, are predictable. But this appears to be a rather optimistic interpretation of the data. It seems at least equally plausible
that, at intermediate gas density, the oblate-tending effect of LPI and CBET simply offsets the prolate-tending effect of kinetic
interpenetration. If this is true, then the apparent ability to predict symmetry in this regime is fortuitous, and larger parametervariations in this vicinity may give unexpected results.
It is doubtful that any advantages of beryllium ablators will manifest themselves, as long as beryllium ablators are tested withhohlraums and laser pulses optimized for other ablators. To derive maximum benefit from the properties of beryllium that makeit potentially appealing (such as its high ablation pressure at a given drive temperature), it will first be necessary to develop
ignition-relevant beryllium target designs in hohlraums (e.g., with large size and low temperature) that are tailored to exhibit thedesirable features of beryllium. For beryllium to warrant continued investigation, it will be necessary that these designs besuperior in significant respects to optimized target designs using any other ablator. The superiority must be apparent first “onpaper” (i.e., during the computational design stage), and then ultimately borne out in experimental tests.
Recommendations: Hohlraums with low to intermediate gas fill (ρgas < 0.6 mg/cm3) should be thoroughly characterized, guarding
against unjustified optimism. The improved in-line CBET model should continue to be developed, and a corresponding effort indeveloping models for plasma motion in hohlraums is needed. The low- and intermediate-fill regimes should be investigatedthoroughly with a skeptical view of their predictability, until compelling evidence is accumulated. It is commendable that LLNL
researchers are continuing to improve their ability to model CBET by developing an in-line CBET model, to replace the unwieldy
present model that depends on post-processing an initial hohlraum simulation to derive CBET estimates for input to a second
hohlraum simulation. But it appears that a commensurate effort on models for kinetic plasma motion and interpenetration is
also warranted. Examples of such models already exist in at least one LLNL radiation-hydrodynamics code. In the “Hohlraum Era”,
research on this kind of enhanced physics modeling capability should be paramount.
Beryllium ablators should be tested with a hohlraum and laser pulse optimized to exhibit a clear advantage over other ablators, if
such designs can be found. Designing new beryllium-specific hohlraums will require intensive computational design effort,
followed by experiments. Possible directions could include large low-temperature hohlraums optimized for capsule absorbed
energy or drive symmetry, or higher temperature hohlraums with the capsule optimized for hydrodynamic stability. Then, if suchdesigns can be found, the experimental process of hohlraum qualification and validation of the optimized target design should
follow. The validation process alone is not cheap; LLNL hohlraum designers estimate that characterizing a new hohlraum andlaser pulse requires about 1 year, 12 NIF shots, and a team of about four computational designers, not counting experimenters.
Ideas for reducing the effect of the capsule support structure should be pursued, with the goal of identifying an improved
alternative to the current “tent”. Reviewers were presented with many promising concepts for less intrusive support structures.
These concepts should be investigated, with the expectation that an unambiguous signature of improved performance, namely
higher yield, will be clearly apparent. Since high yield can be spoiled by many effects, it is necessary to conduct these experiments
under stringently optimized and reproducible conditions (e.g., with good ice surfaces and well controlled laser pulses).
In the Hohlraum Era, new kinds of hohlraum diagnostics should be investigated. LLNL researchers are to be commended for
initiating novel experiments, such as the ViewFactor series, that have provided a clearer picture of the behavior of hohlraums
and the conditions within them, including the behavior of the laser spots and laser entrance holes. But more efforts in this area
may be required, in order to adequately constrain hohlraum models. For example, thin-wall hohlraums would allow timedependent imaging of the most brightly emitting portions of the wall, important in accounting for radiation drive asymmetry.
Marshak-wave arrival measurements at the outside of the wall would show directly the rate of energy absorption by the wall,
important in accounting for the energy budget in the hohlraum. These and other techniques should be considered as possible
future initiatives, as the predictive capability for hohlraums continues to mature.

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Ignition Approach: Magnetically-driven Direct Drive
Findings: The MagLIF target concept being investigated at Sandia is an intriguing but complicated approach to fusion ignition.
Extensive research will be necessary to adequately assess, let alone realize, its prospects for success. The MagLIF concept is rather
new, with less than ten years of research focused on it to date. In certain attributes (low implosion velocity, thick imploding shells,
low required peak fuel pressure) it appears to be a more conservative approach to laboratory fusion than laser-driven approaches.
However, several poorly understood phenomena play crucial roles in the operation of a MagLIF target, including high-intensity
laser heating of a deuterium plasma, implosion of a magnetized liner/plasma assembly undergoing magnetic flux loss, andmagnetohydrodynamic instabilities such as magnetic Rayleigh-Taylor and electrothermal instability. The present limited
capability for experimental diagnostics and predictive simulations cannot yet give the depth of understanding of target
performance that would allow confident extrapolations to larger scale facilities. But Sandia researchers, with collaborators fromLLNL and academic institutions, have a well thought-out, detailed plan to address the long list of physics issues and developments
needed to move the MagLIF concept closer to fruition. They have recently leveraged their on-going NNSA-funded research withsupport from ARPA-E.
Comments: At current funding levels, progress on MagLIF will be somewhat slow, but increased funding is probably not warranted
unless certain key advances can be demonstrated. Given the long history of research in laser-driven ICF approaches, and thecomparatively nascent stage of MagLIF, it makes sense to continue the present program balance for the near and intermediate
future. But Sandia MagLIF researchers have identified a set of ambitious goals that, if achieved at Z, might compel a revised
national strategy, or at least a high-level review of fusion progress with that end in mind. These goals (to be achieved at Z unlessotherwise indicated) include:
•
•
•
•
•
•
•

coupling more than 2 kJ into the magnetized fuel with Z Beamlet, compared to the present level of ~0.2 kJ;
demonstrating ~30 kJ preheating at NIF;
achieving burn-averaged ion temperature greater than 4 keV;
achieving yield greater than 100 kJ;
demonstrating a continuous, nearly uniform stagnation column at CR > 20;
determining the non-thermal component of fusion yield;
controlling the seeds for acceleration and deceleration instability, and demonstrating the ability to simulate theirevolution in 2D and 3D;•
demonstrating a validated capability to simulate magnetic flux loss (Nernst-Ettingshausen terms) and current flow in
low-density plasmas;•
demonstrating predictable scaling of yield as drive conditions are varied;•and numerous other goals as well.
Recommendations: Addition of a capability to perform laser preheating and backlight imaging on the same shot would be a major
step forward and should be pursued with high priority. The state of the preheated fuel (including, for example, its density andtemperature distributions, Bz, and induced velocity fluctuations) probably exerts a strong influence on the later evolution of the
implosion. Observing it will require a simultaneous preheating/backlighting capability.
The capabilities (1) to add tritium or 3He to the fusion fuel and (2) to measure the fusion gamma rays produced in DT or D3He
reactions would allow observation of the fusion reaction history in the implosion, and should be pursued with high priority. At
present there is no capability at all to observe the reaction history in a MagLIF implosion. Such a measurement will provide ahugely important constraint on models and understanding of the implosion.
Roadmaps and Decision Processes
Findings: Summary of some hypotheses motivating Roadmap and Decisions in indirect-drive ignition research. Since our primarycharge is to make “an assessment of the scientific hypotheses that guide today’s ICF program of work”, it is useful to try to list
what some of those hypotheses are. I did not see an aggregation of specific hypotheses explicitly presented at any sites, but thissection seems like a good place to begin such a list.
Hypothesis I: The past poor predictability of NIF ignition-scale capsule implosions stems largely from poorly predicted drive
asymmetry arising from several sources including the tent perturbation, aggravated by high convergence.

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Hypothesis II: New shorter-pulse low-convergence target designs, such as Bigfoot, high-vapor-pressure wetted foams, and double
shells, together with lower hohlraum gas density, will behave more predictably than past longer-pulse high-convergence designs,
and conform more closely to simulations.
Hypothesis III: Hohlraums with gas fill density in the intermediate range around 0.6 mg/cm3 will be largely free of various difficultto-understand phenomena limiting our predictive capability at present, such as LPI, CBET, and kinetic plasma interpenetration.
Hypothesis IV: Ablator materials such as high-density carbon and beryllium provide attractive alternative paths to an ignition
design.
II. Assess the integration of experiments and codes
Diagnostics
Findings: Researchers have made truly remarkable progress in developing and using advanced diagnostics for understanding laserdriven ICF implosions. Ambitious progress on additional diagnostics is on-going at NIF. Considering just diagnostics for asymmetry
in capsule implosions, for example, a wide range is already in place, including re-emission balls, keyhole VISAR, 2DConA
radiography, self-emission x-ray images, primary and down-scattered neutron images, ∆ρR from FNADS, and outgoing shock
imaging. Besides these, other diagnostics under development include foam balls, 5-axis keyhole, gated SXI, late-time 2DConA,
early time self-emission, higher resolution imaging at stagnation including KBO (Kirkpatrick-Baez Optic) and penumbral imaging,Compton radiography at stagnation, and co-aligned neutron and x-ray imaging.
Recommendations: For NIF implosions, the all-important epoch between the time of peak velocity and the time of stagnation
deserves highest priority in the development of new diagnostics. New diagnostics focusing on this time window (late-time 2DConA,
early time self-emission) should receive the greatest emphasis, as this is the crucial period during which inflowing kinetic energy
is converted to thermal energy of the hotspot and fuel, while the whole assembly is brought to its maximum density. This is also
the time period when low-mode asymmetry probably exercises its greatest deleterious effect. Yet this period has received little
diagnostic emphasis so far (probably because capsule conditions, including brightness and optical thickness, are changing so
rapidly), which may be why understanding it has proved elusive.
III. Assess cross-platform and cross-laboratory collaborations
Findings: There are numerous good examples of highly effective cross-platform and cross-laboratory collaboration. These include
the participation of LANL scientists in developing new diagnostics (e.g., neutron imaging and gamma-ray measurements) andfielding experiments at NIF, and in designing new kinds of ignition capsules, such as those with beryllium ablators or low
convergence ratios (e.g., high-vapor-pressure and double-shell designs). Academic researchers, including the groups at MIT andat LLE, have likewise developed vitally important diagnostics, such as high-resolution spectrometers for charged particles,
neutrons, and x rays. Another example is the participation of LLNL scientists in the Sandia MagLIF effort, through developing MHD
computational capability, investigating the mechanisms of laser preheating, and simulating and analyzing the performance ofmagnetized targets, while performing relevant experiments at other facilities. Regarding cross-platform collaboration, theOMEGA laser has been absolutely crucial in allowing new diagnostics to be tested and optimized, and then rapidly implemented
at NIF. Huge savings in terms of NIF shots and program costs have undoubtedly been realized as a result.

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Reviewer Report: Warren Mori
To: Keith LeChien
Lois Buitano
Njema Frazier
Kirk Levedahl

ICF Director
Group 1 HQ Lead
Group 2 HQ Lead
Group 3 HQ Lead

From: Warren Mori
Re: Group 1 Progress towards ignition for the 2015 ICF/HED Review
This is an individual report based on attending three separate deep dive presentations held respectively at Sandia National
Laboratory (July 28 and 29), Lawrence National Laboratory (July 30 and 31) and the Laboratory for Laser Energetics (August 2 and
3). I was not able to attend a the May 18-20 meeting at NNSA headquarters because my clearance had not yet been processed;
however, I met with some of you at NNSA headquarters at a later date to obtain details of the planning of this review as well as
to read through the presentations from this original meeting. My report is also based on documents provided online to themembers of Group 1 as well as on private conversations with some scientists from the NNSA laboratories.
The primary charge of our Group is an assessment of the scientific hypotheses that guide today’s ICF program of work, andprospects of achieving ignition with existing scientific capabilities and facilities, or, if indicated, by specifying what would be
required to do so, based on quantitative scientific analysis. This includes a request for an evaluation of program balance among
ICF approaches and an assessment of the effectiveness of the ICF Program’s cross platform and cross-laboratory collaboration.
I believe that achieving ignition through inertial confinement fusion is a worthy goal from a purely science based view. With threemajor experimental facilities currently operational (NIF, OMEGA, and Z) this is a very exciting time for HED science. Significant
progress continues and this progress is due to the experiments generating data and the improvement in diagnostics. This leads
to new hypotheses and the design of new experiments and the identification of where codes need to improve. The ICF programis generating large numbers of peer reviewed publications and, with the delays in ITER, it is in a strong position to recruit talented
PhD graduates as well as to entice entering graduate students into HED science. In this report, I will offer recommendations inareas I think the program can be improved and not comment on the many areas in which the program is working very effectively.
I was very impressed with the breadth of activities and science being conducted at each facility. I was also happy to hear fromand meet numerous young staff and post-doctoral researchers at each laboratory. Personnel at each laboratory were very
responsive and helpful in answering questions. It was my impression that the research staff of each laboratory believe in what
they are doing and are optimistic about the success of their respective ICF concepts. Although I spent 6 days visiting the sites,
heard numerous presentations, talked to lab researchers, read through numerous documents, and read some peer reviewed
publications, it is still not possible for me to assess with confidence the likelihood of ignition. It is clear that within the next 5
years, ignition can only be achieved with ID on NIF. Both DD and MD need new facilities to demonstrate ignition, SDD on NIF andZ+ at SNL. Currently, laser plasma instabilities (Stimulated Raman Scattering) and cross beam energy transfer (CBET) remain an
obstacle to creating the necessary drive symmetry (time dependent) that would provide the needed fuel conditions for ignition
for the high foot design. These are also major issues for the low foot design (higher convergence ratio), where hydro instabilities
and mix are also an issue. Achieving ignition using either the high or low foot designs are exacerbated by the lack of predictive
ability in modeling individual effects of CBET and SRS, or their combination. The tent, which holds the capsule in place, is also isbelieved to effect surface perturbations when it explodes. I feel that this issue can be fixed somehow.
The strategy being employed at LLNL is to explore “many” different ideas and iterations. They fall under three categories, eachof which is believed could ignite the hot spot. Within each category the goal is to find an experimental platform for which there
is agreement with “1D” calculations and to use this as a jumping off point to then gradually push towards higher yield and thenultimately ignition. The first category is based on pushing the high foot concept towards ignition by experimenting with different
gas fills, ablators, hohlraum sizes and shapes, hohlraum walls, and drive profiles. The second category is to go to even lower
convergence ratios, higher implosion velocities, and larger hot spots where the hot spot itself has enough mass to provide greaterthan ~100kJ (a starting point) of yield. The third category is to increase the laser energy (there were other ideas along this energypath). Some hydroequivalence arguments could be made regarding how present results might scale. I do not recall seeing these.

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In addition, although not discussed the 2ω operation for both a near vacuum (NVH) or a low gas filled (LGF) hohlraum could beconsidered.
Even with all of the information, LLNL scientists cannot say with certainty which path is more likely to eventually lead to ignitionof the hot spot and cold fuel and the odds of success. An attempt to assess the overall “risk” of a new path was presented in theform of a spreadsheet. Changes from existing platforms are listed in columns, an each change is assigned a low, medium, or highrisk based on the confidence level of the understanding of its effectiveness. It was stated that to adequately study one “concept”
takes at least 8 shots. Unfortunately, there are only ~30 high energy shots per year. For example, while going to near gas or low
gas filled hohlraum (NVH and LGF) did eliminate some issues with respect to time dependent symmetry, symmetry issues remain.
The levels of SRS for gas fills less than .6mg/cm-3 is not believed to be important. It may be too early to argue that LPI is a nonissue for NVH and LGF. As expected, even with the shorter laser pulse lengths, wall motion is an issue without the gas fill (wallbubbles form). Furthermore, a lack of agreement between codes and experiments also remains. It is believed that a major sourceof this disagreement is due to the interpenetration of the wall and the ablating material. Eliminating LPI/CBET from the hohlraum
should make modeling “exponentially” easier, as the LPI is not in play. Using the NVH and LGF to “validate” some of the hydrocodes should be a high priority. If the design codes cannot accurately model these designs it seems unlikely it is difficult for theID effort to move forward. There are many ideas on how to mitigate the wall motion with LGF however, with the limited shot
rate a solution will only be found with predictive code capability.
There were presentations on capsule only simulations where the x-ray drive included 2D and 3D asymmetries. These show how
asymmetric implosions get worse at large convergence ratios presumably because of lost energy into RKE and increased heatcondition from the larger surface area of the perturbed hot spot surface. These showed that 3D (including the azimuthal andpolar angles) is worse than simple 2D (only the polar angle) asymmetries. There were also hohlraum simulations in which thetime dependence on the laser energy in different cones is altered to see how the results compare to data. Both of theseapproaches should be continued as they will help to determine where in time and space the LPI/CBET needs to be more closely
examined. Another issue that was discussed in several talks is the understanding of the stagnated fuel conditions. These talks
illustrate the tremendous progress on diagnostics and how the increased knowledge narrows the window for the predictions forthe codes. I did not hear in any presentation about how the time dependent asymmetry (or lack of symmetry in the early part ofthe pulse) leads to asymmetry to the entropy (and a higher average entropy) which will make compression more difficult. It seems
that this is also an issue.
Currently, the predicted CBET for NIF scale coronas in direct drive targets makes ignition not feasible even with 1.8 MJ of laser
energy using symmetric direct drive (SDD). The strategy for progressing towards ignition being employed by LLE is morestraightforward since gas fill, hohlraum size, and drive profiles are not in play. The proposed path forward is to attempt to mitigate
CBET on OMEGA (first using zooming and then a graxicon), and increase Phs and Ehs to values which, when scaled to NIF energy (afactor of 30) using hydroequivalence, lead to ignition. This requires hot spot pressures of ~>120 GBar. Currently, pressures of~60GBar are being seen without CBET being mitigated. This path forward assumes that any physics that does not follow
hydroequivalence does not affect the drive pressure, the symmetry of the implosion, and the implosion itself. This includes CBET,
LPI, heat transport in the conduction zone, thermal conduction in the hot spot, and the mean free path to hot spot size for the
DT ions. My impression is that LLE believes that the biggest issue with hydroequivalence is CBET and LPI (hot electrons from 2ωp)so they have put forth a program to study these for NIF scale targets using polar direct drive (PDD) shots on NIF. However, thesestudies will still have shorter density scale lengths than that expected in an SDD ignition sized target. Other “nonhydroequivalence” physics could be important so it is important to capture some of these in 3D simulations. As was learned from
NIF, scaling some physics to higher energy is not simple.
The long term (decades) goal of the magnetically driven liner fusion effort is to produce yields of ~GJ per shot which it is projected
would take at least a 130MJ pulsed power driver. The nearer term goal is to develop the scientific case to build Z+ which would
be a 50MJ facility that could produce ignition (more output energy than is absorbed [3-5MJ]). The 24MJ Z facility couples about.5MJ on target. The MagLIF concept is much newer than laser driven ICF and there is a smaller experiment and computational
database. Therefore, less is known about the potential issues. Therefore, the next 5 years are very important and the proposedplan does include a well thought out list of physics uncertainties, diagnostic needs, and modeling challenges. These are broken
up into driver target coupling (moving towards 26MA of current), preconditioning (preheating the fuel), implosion (understandwhat leads to non-uniform compression and how this effects the stagnated properties), stagnation and burn, and modeling and2015 Review of Inertial Confinement Fusion and High Energy Density Science Portfolio

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simulation. An important part of this last topic is developing scaling and some hydro-equivalence. The topics are vast and theycannot all be studied with existing manpower. Experiments are critical to indicate where to focus the computational and follow
on experimental efforts. Integrated experiments are beginning to be undertaken at Z with the goal to demonstrate Br greaterthan .5MG-cm, 4 keV ion temperatures, pressures exceeding 5 Gbar, and Pgreater than 5 Gbar-ns. A major obstacle has been
the coupling of the preheating of the gas by the laser. In current experiments the Z Beamlet (~2kJ laser) is used. This needs to be
improved to >6kJ to achieve the pressures and Pto detect enough neutrons for the diagnostics. More than 20 kJ needs to becoupled in the Z+ designs so possible experiments at NIF (30kJ) or on OMEGA-EP (6.5kJ) can also be carried out. Since there seems
to be flexibility in pulse length, they should be able to make progress by lowering the average laser intensity and using“smoothing” techniques. This effort could benefit extensively from the techniques used to mitigate LPI in laser driven ICF as well
as from the experimental infrastructure. It should be mentioned that some LPI codes may not be able to straightforwardly model
plasmas with embedded magnetic fields.
The effort on diagnostics seems well organized and well designed. There is a National Diagnostic Plan (NDP) is a living documentwith ongoing collaborations. It has a management group and is based on input from user groups, HED science workshops, anddiagnostic centered workshops. However, if developing a path towards ignition is viewed as a top priority then I argue strongly
that additional backscatter diagnostics as well as Optical Thomson Scattering are needed urgently. These diagnostics are notgoing to be a priority of HED science users of NIF. I believe that for the most part the NDP and the process seem very well thought
out. Progress, theoretical understanding, and simulation validation can only be achieved with adequate (sometimes duplicated)diagnostics. This coordination should be duplicated by the design code efforts.
Finding: Based on document 62_WP_ALL_ Group _1, the balance of the program in terms of FTEs is reasonable to zeroth order.
Comments: The categories of manpower are broken up into experimentalists, designers, code developers, and theorists (notethat the numbers at LLNL for code development and theory are switched, it should be 6 code developers and 4.5 theorists). To
accurately assess the correct balance it would be useful to know the meaning of the designer, code developer, and theorist. For
example, how many designers and code developers also do theory and do theorists use codes? The power of computer
simulations is to study the changes to an output due to changes to an input as well as changes to physics packages, while being
able to have perfect diagnostic capability. Is this type of exploratory simulation (not modeling a particular experiment) done bydesigners, theorists, or both? In which category do those doing LPI belong? It is noteworthy that there are 6 code developers at
LLNL while 7.3 at LLE. Furthermore, at LLNL these are broken up into those working on Hydra and Lasnex. What about PF3D orother LPI related codes? Who is carefully looking at the results from design calculations and ensuring that the models within thecodes are “validated”? I will comment on this later. It also seems to me that having only .3 FTE on code development at SNL
seems low, unless the needs of MD ICF on code development are being met through the 6 code developers at LLNL. There is muchknowledge at LANL in ICF. Based on what was presented at the deep dives it seems that it would be useful to engage this expertise
more. There is also much knowledge and expertise at NRL on DD. The role of this effort in the ICF program should be better
defined.
Recommendation: The management at each lab should attempt to allow FTEs to have at least 2 days a month to think freely
about other ICF concepts and new concepts, and new theories. This is in addition to any realignment in activities agreed to by lab
management. For example, designers at LLNL should also be able to work on DD and MD during these 2 days a month. Experts
on SRS at LLNL and LANL (more on the LANL effort on LPI later) should be able to study SRS on DD scale targets on NIF and experts
at LLE on 2ωp be able to study 2ωp for ID plasma and laser conditions. I also do not feel that the designers and hydro codedevelopers have the necessary understanding of LPI. The efforts across experiment, design, code development, and theory,
should not be as compartmentalized as they appear. This could be improved through interlab sabbatical programs as well as
having “designers” work on some LPI problems and LPI “theorists” work on some design problems. In some cases,“experimentalists” should be encouraged to run design codes as this can help them better understand how to interpret data andallow them to know when code results can be trusted.
Finding: LPI has been actively studied within the context of ICF for over 40 years. In fact this effort was a major driving force inthe development of PIC codes. PIC codes are now widely used throughout plasma physics and are currently in limited use within
the ICF effort. This recent precipitous reduction in the LPI effort (particularly at LLNL and LANL) is due largely to the inability ofeliminating it, and the hope that LPI issues could be engineered away. Unfortunately, LPI including CBET is arguably the biggest

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obstacle to high yield designs. This philosophy has led to a significant drop off in the expertise on fully kinetic modeling of LPI (atand outside the ICF laboratories) as well as led to insufficient diagnostics of LPI on NIF. However, laser plasma interactions(including cross beam energy transfer) remain a major issue for each ICF concept (ID, DD, MD). Without a critical mass of effort,
LPI is not being adequately understood or addressed (experimentally, computationally, and theoretically). It is worth noting that
there is now minimal effort at the labs on PIC calculations. Until very recently LANL had a strong effort on PIC modeling of LPI but
it no longer appears to be supported.
Comments: For example, in the low and big foot campaigns, there was significant (at least 20% of the energy was reflected after
including the CBET) SRS from the inner beams. Perhaps more importantly, when comparing 15 shots with the same nominal
target and laser conditions, there was 15-20% variations on the back scatter energy. In addition there are variations of in theamount of light absorbed (or rescattered) as it moves back to the laser entrance hole. So there is a ~10% variation in the amountof light hitting the wall which is 5 times greater than the variation of the laser from shot to shot. The natural assumption is that
this variation exists on a single shot across the various inner beams. The angular variation in SRS and plasma conditions could
have been known on single shots if more NBIs and FABS were added. CBET in direct drive and the hot electrons from two plasmon
decay (and the high frequency hybrid instability [HFHI]) are currently believed to be biggest challenges for hydroequivalence. In
MD, propagating and absorbing the heater laser without it hitting the walls and backscattering is believed to be one of the biggest
challenges. Importantly, these processes are modeled with codes that are reduced models (such as PF3D and LSPE [ZAK]). There
have been claims that they have been validated against experiment (I comment more on this later with respect to all codes).
While I sympathize with the need for codes to model time and space scales needed to make statements on experimental
measurements, these codes and their assumptions need to be “validated” against codes with more physics. While theassumptions might be reasonable at lower laser energy they could very well not be at higher laser energy, different plasma
temperatures, different densities, different temperature and density scale lengths, and different mixes of material. For example,
none of these reduced models can include the effects of self-generated or imposed magnetic fields. Fully kinetic models such as
PIC codes have shown that the reflectivity from SRS is in short bursts and can in fact exceed unity for short times. This is in contrast
to reduced model LPI codes. Such intense bursts of reflectivity can lead to rescatter and a spectrum of plasma waves that canlead to more energetic hot electrons. While the average reflectivity (the experimental measurement being used to validate acode) might be similar between PIC and a reduced model, the details can lead to very different conclusions regarding the insideof the hohlraum and the symmetry of the drive. The reduced models attempt to add some kinetics back by including a kinetic
damping term (or a nonlinear frequency shift) in the time envelope operator. However, these are local operators, and the physics
is not local. The reduced models do help to identify physics such as cooperation of plasma waves from overlapping beams.
Validating the reduced models on smaller time and space scales against the more kinetic models would be useful. Despite thesedifferences which point to a need to keep kinetic modeling capabilities in the mix, there has been a decline in PIC efforts on LPI
at the labs. It should also be stressed that not all PIC codes are the same. I could list many more areas where the reduced models
may miss physics. It is very likely that LPI will remain unpredictable and a problem, unless one can find a fully saturated nonlinear
state that is not deleterious (need more laser energy) or determine mitigation strategies that keep it in the noise in a linear
regime, e.g., STUD pulses. For example, even if 2ωp/HFHI is found to not be a problem on OMEGA scale plasmas, it may be a
problem on NIF SDD scale plasmas (600um scale lengths). At this scale length (and temperatures) it will likely be far above
threshold, and it will turn on earlier in the pulse. In addition SRS may occur. Even if SRS leads to a few percent reflectivity this
could leave an imprint on the target. It is also worth noting that as today’s computers get bigger, the capability of PIC gets greater(the best PIC codes scale to 1,000,000 cores). The 3D simulations done with the ZAK/EMZAK (where the overlapping beams areshown to be important) can be carried out with a 3D PIC code using 10,000,000 core hours per 5ps. On a computer with 300,000
cores, this would only take 30 hours (about a day to complete). Such simulations will only get better on future machines with
GPUs and Intel Phis.
Recommendation A: There should be a reconstitution and reinvigoration of the LPI efforts. These efforts should be coordinatedacross the labs. It should include having joint/coordinated code development efforts and making the lab codes open source (oropenly shared within the labs) using Github or an equivalent. This would also allow outside groups at universities to participate.
For example, EMZAK under the LPSE will be able to model SRS and SBS in underdense plasmas. This code does not envelope thespatial derivatives or the ion acoustic wave equation. Results from EMZAK could be compared against PF3D for some volume.
Within the ZAK models of LPSE, electrons (and ions) are pushed through the full fields (the fast component at ωp is added backto the fields) and test particles are pushed through them (I do not believe that collisional effects are included in this process).

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This evolves a distribution function that is globally averaged and then used to estimate Landau damping of the plasma wake ateach k component. In reality, the evolution of plasma waves depends on the local distribution function. Pockets of expertise in
kinetic modeling exist within the university community. This includes PIC as well as Vlasov Fokker Planck. Engaging this expertiseto study specific parameters of relevance to ICF should be encouraged. A small working group should work to develop test
simulations for comparing codes against each other where possible and working to understand why they do or do not agree. Thiscan be time (FTE time) consuming, so this must be factored into the prioritization of what is to be studied. There should be aneffort at ensuring that these codes are easy to use so that non LPI experts such as designers could run them. The Anomalous
Absorption Conference should be supported and by NNSA and the ICF labs. A small workshop on LPI theory and modeling shouldbe held where common and unique issues for ID, DD, and MD are discussed and hopefully a consensus on some priorities isformed. Ideas which may eliminate LPI such as STUD pulses should be explored and discussed.
Recommendation B: Additional viewing angles for backscatter should be implemented as soon as possible on NIF. At the very
least two more NBIs should be added, one at a new azimuthal angle and another in the opposite pole. Adding another FAB at oneof these angles would also be useful. Adding Optical Thomson Scattering capability should also be given top priority. To
understand LPI and its true effects it is necessary to know the plasma conditions as well as the angular variability of thebackscatter (time and frequency resolved). I realize that there is a National Diagnostic Plan (which as I noted earlier is very wellthought out), however, I cannot think of a reason why the backscatter diagnostics should not be a high priority. If the cost isformidable then a working group should be formed to find a solution.
Finding: Ignition will not be achieved without multi-physics design codes that have some degree of predictive capability to guideexperiments. Furthermore, as new concepts are investigated, new experimental data is acquired, and diagnostics improve, thenmore physics will need to be included. There appears to be lack of true coordination in code development across the labs. This
leads to a duplication of efforts as well as an incomplete knowledge of what physics is being included, what equations are being
solved, and what physics packages have been implemented.
Comments: We heard about a multitude of codes and duplication of efforts. Some codes are 2D while others are 3D. Some scalebetter on parallel computers. In addition, while there is much in common there are important differences in the physics that isneeded to be included between ID, DD, and MD ICF. Due to different priorities, code developers responsible for a code that has
primarily been used for ID may be delayed in including physics needed for another concept. We also heard claims that certain
packages are better in certain codes. These two issues lead to others using less desirable codes or developing their own code.
The development of design codes needs to be better coordinated and more transparent.
Recommendation: The equations for each code should be widely disseminated within the ICF complex and to the extent
possible should be published in the peer reviewed literature. To the extent that classification is not an obstacle, the details of thephysics packages (non-LTE, flux limiters, inclusion of magnetic fields) should be described. A National Design Code Plan (withclassified and unclassified parts if necessary) with a management team should be generated. The first step would be a workshop
focusing on short term and long term priorities. It appears that the code of choice moving forward is Hydra. However, MD (aswell as ID and DD) requires magnetic field generation and transport. Within Hydra, what is the form of Ohm’s law? Does it contain
Nersnt and Gran n x Grad T terms etc.? What are the details of the non-local heat transport? Does it include transport across B
and along B? Researchers at LLE are not using Hydra because they need better ray tracing and non-local heat transport models.
They are running their own 3D code (we do not know what equations are being solved) but as I understand it, it assumes asymmetric corona and adds an imprint to the extent possible the codes should be managed using Github or an equivalent. Afterthe NDCP is generated, then a sabbatical program that allows researchers from other labs to have extended visits (three months
to a year) at another lab to work side by side (this is the only way that joint work will truly occur) to improve the software. I heard
arguments that it is good for each lab to have their own version of codes or to have two or more codes. I am sympathetic to thisargument, as I too have argued that monolithic codes can be dangerous. However, as codes get very complex and more physics
needs to be added, the real challenge is validating each package (and not the whole code) and then verifying that they have been
integrated into it properly. Furthermore, computer power is improving at the expense of hardware therefore it is too FTE
intensive to maintain more than one large code that will run effectively on next generation hardware. Software engineering anddata structures are chosen such that new physics packages can be added without these developers worrying about parallelizationand the hardware.

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Finding: Much of the DD strategy for moving forward is based on the concept of hydroequivalence. The idea is to scale OMEGA
results at 60kJ to NIF at 1.8 MJ. This can also be used for ID concepts (and with modifications MD concepts) if the laser energy isscaled to higher energy or to 2ω operation. As noted in the original papers on hydroequivalence there is much physics that will
not scale. This includes among other things, CBET, LPI, heat transport in the conduction zone, thermal conduction in the hot
spot, and the mean free path to hot spot size for the equilibration of the D and T ions.
Recommendation: A small workshop on hydroequivalence with researchers across DD, ID, and MD should be held to rank theareas of concern and decide what capabilities need to be in the design codes to better quantify and include their effects.
Finding: There appears to be a widespread view that a “code” is validated when it provides agreement with experiment.
However, these codes involve complex (and nonlinear) couplings between choices of physics packages with fitting parameters aswell as numerical choices.
Comments: Modeling ICF is a very challenging problem. However, some form of predictive capability on ICF ignition using codes
may only be achieved if each physics package is validated against more “accurate” models (those that make less approximations
or assumptions). This is true across the entire spectrum of codes used. For example, while there is a current attempt to include
inline SRS backscatter and hot electron models using ray tracing, this cannot provide true predictive capability. This will provide
additional knobs (such as flux limiters, CBET limiters,…) to change to tune the agreement and it will allow one to see how thereflectivity feeds back onto the plasma conditions which then modifies the backscatter. There is merit in this so that designers
can develop an intuition of the complex interplay of physics. However, this cannot lead to true predictive capability, as SRS (orother LPI processes) cannot be accurately modeled in this fashion. Unless each reduced model is validated against meso- and/or
micro-scale physics models for SRS/CBET, non-local heat transport, magnetic field generation, interpenetrating fluids, etc. thenthe integrated result cannot be correct in general. There has been tremendous advances in kinetic modeling (Vlasov Fokker Planck[VFP] and PIC). VFP capability now includes fully parallelized codes that expand the distribution function into an arbitrary numberof spherical harmonics. There are implicit field solvers such that very large cell sizes can be used. These codes can be used to test
physics packages or even be integrated into the hydro codes. PIC can model more and more spatial and temporal time scales(they can run on 1,000,000+ cores and on GPUs and Intel Phi processors) such that some hydro processes can be studied withtime and space scales of relevance.
Recommendation: Efforts should be made to free designers, LPI researchers, HED plasma theorists time so they can try tovalidate each physics package, i.e., to improve them or to better understand their limitations. A small workshop on identifying
relevant problems to test a package (a unit test) should be held. This can be time consuming, so this must be factored into theprioritization of packages. A workshop in which discussions on what it means exactly when there is agreement between
simulations and experiments would also be useful. For example, it is often claimed that there is agreement between a simulation
and an experiment but only a 2D code is used. If a 3D simulation is performed it will undoubtedly be different.
Finding: Although there is an apparent spirit of cooperation between the labs, more should be done to promote cooperation
across theory, target design, experiments (including diagnostics), code development, and computation.
Comments: True collaboration and focused effort arises when people sit down and work side by side.
Recommendation: The labs should develop a Sabbatical program for lab or university personnel to spend dedicated time atanother lab or university.
Finding: Sometimes there is a lack of computational resources on open computers.
Comments: There was concern about running simulations on 2000 cores for 4 weeks or 4000 cores for 2 weeks. These are verysmall simulations (100,000 core hours). I have heard mixed answers regarding the ability of Hydra to be run in the open only in
the Restricted Zone or on open computers at national leadership class facilities such as Blue Waters and Titan.
Recommendation: This should be clarified and if non NNSA DOE and NSF facilities can be used then LLE researchers should
apply of computer time at these facilities through the DOE INCITE program.

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Reviewer Report: Andrew Randewich
Introduction
The findings from this review are focussed on the balance, metrics and decision making of the Inertial Confinement Fusion (ICF)
and High Energy Density (HED) Programme. They span from the working level shot selection on NIF, Z and Omega through to themechanisms for making National decisions on the overall Programme direction.
The review has been primarily informed by: briefings given in Washington DC May 18 to 22, “The National HED Strategy – Vision2032” by Alan Wan, Discussion with Alan Wan at JOWOG32S June 3, The Programme Balance white paper by Richard Town, atelecon with John Edwards July 13, and discussion with Bill Goldstein June 10. The reviewer is also a member of the NIF
Management Advisory Committee (MAC).
Ignition
Regarding the charge from part I. “assessments of … prospects of achieving ignition”.
This review is about ICF and High Energy Density physics in general rather than Ignition per se, but the group charge explicitly
raises questions on the latter. It must be emphasised that Ignition is a hard problem! Today it remains impossible to state withauthority whether or not it will be possible to achieve Ignition on NIF. Nevertheless the position is far from negative. Of significant
note is that nationally, but in particular at LLNL, reorganisation has been implemented. The new Programme, capable leadershipand functional organisation are highly effective and it is explicitly noted that the alignment of the ignition and other Stockpile
Programmes as separate from NIF operations is to be commended. The resulting structure needs to be given stability to tackle
the challenges with the tools and people that are being developed. Reviews often happen when change is required but this one
is happening immediately after substantial upheaval; it may provide advice and guidance, but continuous change must be
resisted.
Recommendation: Resist making multiple successive changes to the HED Programme; rather allow the leadership to exploit
the beneficial effect of previous changes.
Importantly, improvements in the tools for calculation are enabling understanding that was not previously possible; an example
would be the influence of the capsule support “tent”. Nevertheless the approximations that must be made in calculations remain
significant (in all three fusion approaches), resulting in the endurance of design “knobs” and leaving a truly predictive capability
a distant possibility at best. Improvements in tools for calculation will be discussed later.
Looking at NIF in particular, the diagnostics are now much better than those available to the early National Ignition Campaign(NIC) Programme, which had a minimal set. Diagnostics will also be discussed more in the section on Balance between Codes andExperiments. The improvements in codes, experience and diagnostics together have allowed a significant demonstration in thehigh-foot campaign. High-foot achieved the first laboratory plasma where alpha heating resulted in significant yieldenhancement, but this is secondary to the fact that it demonstrated an ability (absent in NIC) to evolve a platform through controlparameter space and demonstrate a smooth response in diagnosed outputs. Such control is precisely what is required if an
ignition design is to be developed, although it is also the case that physics must line up favourably. There is further cause to bepositive in the latter regard, as the potential phase space is very wide when a step back is taken from the original point design.
At the same time the range of options causes potential problems for the Programme if it becomes too diverse, as explained in
the section on Incentives, Metrics and Shot Planning.
Strategic GovernanceRegarding the charge from part I. “evaluation of program balance among ICF approaches” and from part III. “effectiveness of the
ICF Program’s cross-platform and cross-laboratory collaboration”.
At the current time it is not readily apparent that there is a system to allow major decisions to be taken on the overall Z, Omega
and NIF HED Programme. An example would be making a cost-benefit decision on whether to move NIF to a Direct Drive
configuration or perhaps to switch it to green light. It is important that this governance mechanism for technical direction exists,

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as lack of such will lead to de facto continuation of the as-is Programmes; the only sufficiently powerful imperatives for large
scale change would then be political rather than technical. The required governance does in fact exist, and has been
demonstrated by the recent (January 20th) “Lab Directors’ letter”. However perception is important; governance must not only
exist, but also be clearly and publicly seen to exist. Apparent ungoverned continuation of the status quo could drive decision
making by those less technically equipped to make such decisions.
Recommendation: A visible forum of lab directors to steer fusion for the Stockpile Programme is essential. The “Lab Directors’letter”, showing commitment to a single National Programme, should not be an anomalous event.
Detrimental tension between teams from different labs has previously been obvious. However it is perfectly possible to have ahealthy tension with rational debate on issues. No one actually knows today which fusion solution will achieve Ignition or provide
the most effective long-term input to the Stewardship Programme. It was therefore heartening to see presenters across fusion
approaches and across the labs standing shoulder-to-shoulder and presenting a coherent overall picture of their work to thereviewer. The discussion will later touch on mutual support for inter-lab campaigns of experiments spanning multiple facilities,
which are commended. Omega, for example, is not just about demonstrating Direct Drive, nor about proving extrapolations to
NIF scale (which NIC showed us were fraught). It is about mutually closing down phase space on science and materials issues, andmany of the findings are pertinent to multiple threads of the fusion Programme.
The degree to which Governance can be applied to balance the Programme is actually not great. The capital cost of the major
facilities and their operational costs are dominant over the small amount of funding which delivers the beneficial outputs. A point
worth making for such “entry level” situations is that a small amount more Programme can lead to significantly enhanced
productivity from the facilities and this can be an opportunity. It also means that there is often not much scope for large-scale
rebalancing of the Programme. The Programme balance between Ignition and non-Ignition is discussed in the next section as is
the question of whether the Stewardship Programme effectively locks NIF into Indirect Drive mode.
Link from Strategy to Programme
Regarding the charge from part I. “scientific hypotheses that guide today’s ICF program”. Note that this discussion has
commonality with the Group 2 charge.
The review considered the link between the recently published HED Strategy and the Programme. Firstly it must be stated thatthe links from Stockpile drivers to types of HED experiment are clear and strong; having a Strategy that lays out what is required
and why is a very important step forward and is commended. However, the priorities that thereafter inform the generation of
the Programme Plan (what topics are most important or urgent) have not been documented. An explicit example would be thethree year NIF ICF Plan, where the link to the Strategy is clear, but the origin of the planned order of activities is not shown. As
an aside, due to the Stockpile being the driver for the HED Programme, although the UK and US Strategies are similar, the priorities
are different, hence differences exist between the Programmes. This serves to illustrate the importance of prioritisation.
Leaving priorities unstated could certainly generate problems. One point that clearly comes out of the Strategy is that while
Ignition will lead to important new classes of Stewardship experiments, there are also large elements of the Stockpile Stewardship
Programme (SSP) that do not require Ignition, and much of this work is already being pursued. These experiments include
developments in code validation, methods of code application and use of grand challenges to develop designers as well as
material data experiments. Furthermore some source experiments are enabled by the alpha-heating regime that has alreadybeen demonstrated on NIF. If the highest probability path towards Ignition requires a major change of configuration on one of
the facilities, it is not obvious that the information is in place to make the judgement on that change. An example is whether the
SSP effectively “locks” NIF into an Indirect Drive configuration.
Of course, in reality the capability to do, and therefore the feasibility of, different experiments depends on many factors such as
facility capability, people capability, target deliverability, modelling and calculation maturity, radiation source availability such as
Ignition and diagnostic availability. These constraints frequently dominate the planning process over and above the SSP priority.
Furthermore, as described already, it may not even be possible to rebalance an entry level Programme more than slightly.

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Although the Programme is dictated by reality, the expression of priorities in the Strategy would be beneficial to the enterprise.
As a minimum the Strategy should indicate whether the expectation is for short or long term delivery. It would be particularly
beneficial if it can be shown how different types of experiments might best be used to burn down Stockpile risks, since maximisingtechnical risk reduction for the Stockpile will allow minimisation of the overall cost of the Programme, and makes simple any
business case for HED investment.
Recommendation: It is acknowledged that Stockpile Stewardship priorities have to be combined with realism such as the timingof available capabilities in derivation of the HED Programme plan. Furthermore the plan may need to change when these realities
are better understood (for example when Ignition becomes feasible). Prioritisation absolutely does occur, and there is a process.
Nevertheless, it is recommended that the Strategy should state the relative priority for the activities from a Stockpile Stewardship
perspective, and that when reality is subsequently factored into the planning that this is also explicitly documented.
Incentives, Metrics and Shot Planning
Regarding the charge from part I. “evaluation of program balance among ICF approaches”.
While Strategic Governance has been discussed already, it is also important that the labs are led to maximally exploit their capital
facilities. Such exploitation is incentivised by metrics, but these must be mindfully selected; it is often said “be careful what you
measure”. NIF, for example, is measured on the number of shots fired per year, but this will not in itself optimise the balance ofshots within the Programme to deliver benefit to the Stockpile. Even within a single Programme such as Ignition, the balance
between layered cryogenic shots and low power platform and diagnostic development shots would not be well served by assimple a metric as “number of shots fired”.
In fact the NIF shots are now allocated via a thorough Governance model. There is indeed a drive to fire more, lower energy,
shots, but this is due to the need to preserve the NIF optics rather than the “number of shots” metric. High energy shots are
therefore carefully allocated between Programmes. These shots are required because scaling from small to large hohlraums is
not yet possible by calculation alone, particularly for rugby hohlraums. Shots are also allocated in order to maximise benefit to
the designers who are being developed (this is a major aim of the Programme) and there is only so much data analysis that each
designer can do.
Recommendation: Plan with performance metrics, but ensure that they motivate the right Programme. There are many
benefits to facility shots. A good metric might be “how many of the best and brightest engineers and scientists stay or are losteach year”.
Of course the method of deciding which experimental campaigns to schedule is not simple. NIC experienced tension between
pushing for higher yield and trying to understand more about the underlying science. Because the enabling science work hascorrectly stepped back from trying to achieve Ignition it has become diverse and (as noted from the previous section) lacks
priorities, potentially slowing progress on each front. It was stated that the breadth of phase space available to the Ignition
Programme on NIF is heartening, but a concern is that this leads to attempts to progress on too many fronts at once, in whichcase effort is spread quite thinly. There is a necessity to inform selection of future directions, but with tunes being played on thelaser pulse length and number of shocks, the ablator material, the hohlraum gas fill or lack of it, and the hohlraum size, shapeand material the progress on each front may be limited.
The number of fronts that NIF has been working has decreased recently, and this is commended as focus is required; it takes
several years to play out any campaign and that cannot be allowed to stretch. To balance this, a separate activity is being
undertaken to ensure that diversity of ideas is not lost; ideas are desirable even if they are quickly discarded. Ideas that survive
initial analysis may lead to science on Omega before progressing to NIF, where relatively short, targeted campaigns can be used
to determine feasibility. The integrated use of the three major facilities to support each other in this way is commended.
Recommendation: The number of fronts being pursued on NIF has been, arguably, too large, and the current refocus is lauded,
as is the initiative to maintain diversity of ideas with the best prospects leading to limited campaigns. This approach should besustained.

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The Balance between Codes and Experiments
Regarding the charge from part II. “experimental and computational efforts”.
It has been noted that the beneficial part of the Programme is significantly smaller than the capital and operational costs of the
major facilities, and so it does not make sense to really compare the scale of these investments to the modelling effort; the former
necessarily dwarfs the latter. However given that the facilities are open for business, the question can be posed whether themodels are being developed with appropriate balance between experiment and calculation. On the face of things, the codedevelopment effort deployed at the three labs is meagre compared to experiment. Actually it is not as imbalanced as it seems,
since much code development work is done in support of other Programmes, so the numbers that the group reviewed should
not be considered in isolation. Nevertheless, it is the reviewer’s opinion that more effort on code development would be
beneficial, particularly for the Z Programme. Perhaps surprisingly, code development is also squeezed from the other side.
Considerable funding is committed to the procurement of the latest, most powerful, High Performance Computers in the world.
While such procurements are essential, these machines are themselves difficult to exploit, and drive a large amount of computerscience effort in order to port codes to the new platforms. The Programmes relating to the addition of new physics models andnew methodologies for modelling with them are relatively small (in other words beneficial application is being squeezed again).
Recommendation: HPC and experiments dominate costs, and the balance should be swayed (slightly) towards codedevelopment, specifically to adding new required physics to the codes and developing their applicability. In particular, it isrecommended that Z is supported with more computational effort.
Although there is a need for some rebalancing, one experimental area should be protected, even enhanced if possible. That isthe development of new diagnostics. History tells us that on NIF the experimental Programme was all but futile under NIC because
the diagnostics were (in retrospect) insufficiently capable to discriminate between shots. Many of the advances since NIC, inparticular the high-foot campaign as described earlier, have only been possible because of the improved diagnostic suite
available. The current hypothesis regarding NIC, for example, is that drive asymmetry and capsule support were dominating yielddegradation. New codes and diagnostics made derivation of this hypothesis possible, and further improvements will be crucial toprove or disprove it and measure the next steps forward.
Recommendation: Diagnostics are an important part of the Programme; on NIF in particular, the plan to increase diagnostic
capability should be protected and given high priority even if at the expense of, for example, shot rate.
Conclusions
This review benefitted from the time and attention of a range of lab staff, and the reviewer would like to thank them for theirconsideration. Equally the NNSA employees who enabled the process are thanked and commended. Overall the decision-making
processes from top to bottom of the fusion Programme are not unsound, but enhanced publicity and documentation will lendthem more credibility. The Programme is well balanced and there is limited scope for change, but enhanced physics codedevelopment is important and diagnostic development is vital. Finally, there are two pleas. Firstly, the leadership across theProgramme is outstanding, and will succeed in delivering exceptional benefit to the Stockpile Stewardship Programme if given
time and scope; do not perturb the system unduly! Secondly, this Programme is closely scrutinised, and rightly so, but reviews
must avoid too much duplication; it loads work on those reviewed and communicates a lack of trust. Instead reviews should use
each other’s findings and outputs.

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Reviewer Report: Sean P. Regan
I. Assess the scientific hypotheses and the prospect for achieving ignition with existing scientific capabilities andfacilities; or, if indicated, what would be required to achieve ignition and supporting analysis. Provide anevaluation of program balance among ICF approaches.
Ignition Approach: Laser-driven Indirect Drive
Findings: Research for laser-driven, indirect drive inertial confinement fusion is the most mature of the three ignition approaches.
The failed ignition attempts by the low-adiabat implosions of the National Ignition Campaign (NIC) were followed by a highadiabat campaign that demonstrated experimentally evidence of alpha heating. The maximum primary neutron yield of the highadiabat campaign fell just short of breaking the 1 x 1016 goal. The energetics of the gas-filled hohlraum is not understood fully.
The capsule mounting tent seeds an ablation-front hydrodynamic instability. A significant fraction of the laser energy (up to 200kJ) cannot be accounted for in the energetics of gas-filled hohlraums. Multipliers (<1) are applied to the x-ray drive to match the
trajectory of the imploding shell. Implosion symmetry control in the presence of cross beam energy transfer (CBET) is notdeterministic. In contrast, the energetics of near vacuum hohlraums is closer to predictions, but implosion symmetry is
challenged by the un-tamped motion of the laser deposition region in the converging Au plasma from the inner wall of thehohlraum. The thrust of the current research is to establish a more fundamental understanding of hohlraum energetics,
implosion symmetry, and hot-spot formation. Reducing the gas fill density in the hohlraum alleviates the laser plasma instabilities
and provides an opportunity to study the implosion hydrodynamics in a more straightforward manner. The overarching goals forindirect-drive ICF over the next five years of understanding the limitations on convergence ratio, implosion velocity, andstagnation and heating of the DT fuel are on the mark. The strategy of developing 1-D implosions on NIF, focused experiments,
diagnostic/computational/facility capabilities should improve the understanding and modeling of ignition target behavior. The
move away from the high-pressure (>1.0 mg/cm3), gas-filled hohlraum is reasonable, especially since these gas-filled hohlraums
are very complicated to understand. This research will lead to a better understanding of the hohlraum and implosion, but an
ignition design based on the near vacuum hohlraum does not exist yet. What happens if the outcome of this research is that thehigh-pressure, gas-filled hohlraum is needed to achieve the high areal density and high yield needed for ignition? The program
should have some level of hohlraum research investigating the energetics of the high-pressure, gas-filled hohlraums. The LANL
program is adding to the LLNL-led, mainline research program alternate designs including double-shell implosions, wetted foam
designs, and Be ablators. These innovative designs are worth exploring, but they are sorely in need of a strategy. The challenge
is to define the roadmap and decision processes that streamline these innovative concepts into the mainline research within theconstraints of limited resources. LANL needs to work with LLNL to define the roadmap and decision processes. LLNL has themost sophisticated 3-D simulation capability for ICF; however, it is very limited. More resources need to be dedicated to 3-D
simulations. These simulations would provide insights to the residual kinetic energy in the compressed shell and hot spot.
Comments: Understanding the target physics of a few focused areas is more important than executing an exhaustive
experimental campaign of many options of ablator, capsule mounting and hohlraum gas fill.
3-D simulations for every NIF implosion should become routine. Currently it is a heroic effort to complete a single 3-D NIF
implosion simulation.
Diagnosing the plasma conditions in the hohlraum plasma using x-ray spectroscopy and eventually optical Thomson scattering(OTS) is critical for indirect-drive ICF.
The gas-filled hohlraum may be the only path to ignition. Energetics research on the gas-filled hohlraum should continue todevelop understanding.
Develop an ignition design based on the near vacuum hohlraum and the lower gas-fill hohlraum.
It is essential to chart the progress of indirect-drive ICF using the generalized Lawson criterion for integrated, indirect-drive DT
cryogenic implosion experiments on NIF.
At this point, the achievement of ignition with laser-driven, indirect-drive ICF using a 1.8 MJ driver is a stretch.

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Recommendations: Continue to perform hohlraum energetics research on gas-filled hohlraums.
Increase the amount of resources dedicated to 3-D implosion simulations. The goal should be to make routine 3-D simulations
for each NIF implosion.
Define a strategy for down-selecting the number of ablator materials.
Reduce the number of possible capsule supports to a tractable number for testing.
Define a roadmap and decision processes for the innovative double-shell implosions, wetted foam design, and Be ablators. A
clear strategy operating within the resource constraints needs to be articulated.
Maintain a reasonable number of integrated, indirect-drive DT cryogenic implosions on NIF to chart the progress of indirect-drive
ICF using the generalized Lawson criterion.
Ignition Approach: Laser-driven Direct Drive
Findings: Research for laser-driven direct drive inertial confinement fusion is conducted on the OMEGA laser system using
symmetric direct drive (SDD) of layered, DT cryogenic implosions and on the National Ignition Facility using polar direct drive(PDD). Cross beam energy transfer (CBET) has been identified as a primary physical mechanism limiting the ablation pressure
and consequently the hot-spot pressure. The Laser Plasma Simulation Environment (LPSE) code was developed at LLE for a
predictive capability of multi-beam laser plasma interactions. The early predictive results are very promising. CBET mitigation
has been proposed using beam zooming on OMEGA and wavelength detuning on NIF. Target designs that couple more energy
to the hot spot have a clear advantage for achieving ignition in the laboratory. Since direct-drive ICF target designs couple moreenergy to the hot spot indirect-drive ICF target designs, the required hot-spot pressure and convergence ratio is lower for the
direct-drive ICF target design (CR<25 vs. CR=30-40; 150 Gbar vs. 350-400 Gbar). Hydrodynamically-scaled symmetric implosions
can be conducted at the 30-kJ-scale on OMEGA to test energy coupling, laser imprint, and preheat. Current implosion
experiments have achieved a hot-spot pressure over 50 Gbar. Experiments are needed on NIF to test the energy coupling, laser
imprint and preheat on ignition-scale coronal plasmas having longer density scale lengths and higher electron temperatures.
Significant resources would be needed to change the beam layout on NIF to achieve a symmetry laser drive on a direct-drive
target. In the next decade, NIF may explore the symmetric direct-drive option, but no decision has been made to convert NIF tosymmetric beam geometry. Consequently, the only practical option available for laser-driven, direct-drive ICF on NIF today is
PDD. LLE has designed phase plates for PDD on NIF, but resources have not been allocated to produce a full set of NIF PDD phase
plates. Unlike other laser facilities that have phase plates tailored for particular experiments, NIF only has a single set of phase
plates optimized for indirect-drive ICF research. Current PDD experiments use the indirect-drive phase plates in defocused beamgeometry to optimize the laser uniformity on target, which works for many of the focused experiments and for low convergence
ratio PDD implosions. The PDD experiments on NIF provide an experimental platform to examine preheat, laser imprint, andenergy coupling for ignition-scale, coronal plasmas. The coronal plasma of the NIF PDD implosion provides an important
experimental platform to test CBET mitigation schemes. Focused experiments are conducted to study preheat from the twoplasmon decay instability using planar targets; to study the early time energy coupling at the pole and equator using a multi-axis
VISAR target; and to study laser imprint using cone-in-shell x-ray radiography targets. Integrated PDD implosion experiments on
NIF require facility improvements to achieve high convergence ratio (CR=20) PDD implosions. The improvements include a set ofintermediate PDD phase plates, multi-FM smoothing by spectral dispersion, and possibly polarization smoothing. LLE proposes
to have PDD phase plates available on NIF late in FY18 to demonstrate low-mode control of high convergence ratio PDD
implosions, and to decide in FY19 whether PDD or SDD is the viable path forward. The cryogenic hardware needed for directdrive on NIF depends on this PDD vs. SDD decision. NRL researchers presented experimental results from Nike of laser imprint
reduction using thin Au overcoat layers on planar targets, as well as alternative laser beam smoothing schemes. NRL is extending
the Au overcoat campaign to the OMEGA laser system.
Comments: A demonstration of CBET mitigation is essential for laser-driven, direct drive ICF. The beam zooming option is being
explored on OMEGA and the wavelength detuning option is being explored on NIF.

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The PDD vs. SDD decision for NIF hinges on the availability of NIF PDD phase plates to test high convergence PDD implosions(CR=20).
3-D implosions for low-mode drive nonuniformities could greatly benefit the direct-drive ICF research, especially understanding
the residual kinetic energy in the compressed shell and hot spot.
Ignition with laser-driven, direct-drive ICF may be more likely to be achieved than it is with indirect-drive, since direct drive cancouple more energy to the hot spot.
Recommendations: Fabricate the NIF PDD phase plates to perform high-convergence ratio (CR=20) implosion on NIF.
Integrated PDD implosion experiments are proposed to diagnose CBET mitigation techniques. Explore the possibility ofdeveloping a focused experiment to test CBET mitigation techniques.
Develop laser scattering diagnostics on NIF optimized for PDD implosions.
Explore more PDD implosion designs that demonstrate alpha heating, but do not ignite. These high yield shots have HED
applications on NIF.
Train scientists across the complex to use the Laser Plasma Simulation Environment (LPSE) code to study multi-beam laser plasmainteractions.
Develop collaborations across the complex to develop a predictive capability for CBET, multi-beam SRS, and the two-plasmon
decay instability.
A clear understanding of the effects of the thin Au overcoat layer on the laser imprint and the target adiabat should beestablished. The team at NRL should lead this effort.
Ignition Approach: Magnetically-driven Direct Drive
Findings: Magnetically-driven Direct Drive is the newest research program of the three ignition approaches. Magnetized Liner
Inertial Fusion (MagLIF) offers the possibility of a DD equivalent of 100 kJ of DT yield in the near term on Z with modest upgrades
to the existing capability. Target designs and pulsed power architecture for future Z300 machine to produce alpha-dominatedplasmas and for Z800 to produce burning plasmas were presented. The magnetically-driven, direct-drive ICF presented a rangeof goals over the next five years covering the critical areas of research including: drive-target coupling, target pre-conditioning,magnetic implosions, stagnation and burn, modeling, simulation and scaling, and diagnostic development. SNL staff leads all of
the research except for the laser preheat. SNL relies on laser plasma interaction experts at LLNL to understand the laser preheat
phase. The MagLIF research at Z is challenged by the limited shot opportunities, as well as by the limitations of having only asingle laser beam. The computational effort often lags the experimental effort. The laser beam can be used either for laser
preheat or for x-ray backlighting. The laser-driven, MagLIF experiments conducted on OMEGA and OMEGA EP in collaboration
with LLE broadens the scope of the magnetically-driven, direct-drive research approach. The MagLIF experiments planned for
NIF will provide an early test of the laser preheat for an ignition-scale target.
Comments: The MagLIF research at Z is challenged by the limited shot number and the limitations of having only a single laser
beam.
The laser-driven, MagLIF experiments conducted on OMEGA and OMEGA EP in collaboration with LLE greatly expand themagnetically-driven, direct-drive research approach.
The MagLIF experiments planned for NIF will provide an early test of the laser preheat for an at-scale ignition target.
Recommendations: SNL is wise to involve LLNL LPI experts in the understanding of the laser plasma interactions of the preheat
beam. It is a good use of resources across the complex. However, considering that the laser preheat is an integral part of the2015 Review of Inertial Confinement Fusion and High Energy Density Science Portfolio

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MagLIF research, SNL should consider hiring a post-doctoral researcher to develop in-house expertise for the laser preheat stageof the implosion.
SNL should add another laser beam to the Z machine to increase the scientific output from each shot.
SNL should dedicate more experiments to understand and optimize the power flow in the driver-target coupling.
Roadmaps and Decision Processes
Findings: The sophistication of the roadmaps and decision processes for the three approaches varied widely. The laser-driven,indirect-drive ICF showed a broad research program with few details on roadmaps and decision processes. Overarching goals toimprove understanding and models of ignition target behavior to either demonstrate ignition or show what is needed in capability
and understanding to ignite a target were discussed for the indirect-drive approach. The laser-driven, direct-drive ICF showed aroadmap and decision process based on goals for the hot-spot pressure and mitigation of cross beam energy transfer. The
magnetically-driven, direct-drive ICF presented a range of goals over the next five years, but like the indirect-drive research
program a detailed roadmap and decision process was not presented. The goals are related to drive-target coupling, target preconditioning, magnetic implosions, stagnation and burn, modeling, simulation and scaling, and diagnostic development.
Comments: Roadmaps and decision processes help to focus the workforce on the research priorities.
Recommendations: All three approaches should present a concise one page Gantt chart highlighting their roadmap and decision
processes over the next five years.
Program Balance
Findings: The number of full time equivalent personnel working on ICF ignition provided by LLNL, LANL, SNL, LLE, NRL clearly
showed that LLNL has the most FTE’s in just about every category---experimentalists, designers, code developers and theorists.
Comments: The main area of concern for program balance is hydrodynamic simulations, especially 3-D simulations. Laser-driven,
direct-drive ICF and Magnetically-driven, direct-drive ICF are clearly understaffed.
Recommendations: Program balance for the three approaches should be considered, especially in the area of 3-D simulations.
II. Assess the integration of experiments and codes
Diagnostics
Findings: The National Diagnostics Plan led by J. Kilkenny, G. Rochau, C. Sangster, S. Batha is divided into three categories:
transformational, broad, and local. J. Kilkenny does an outstanding job leading this effort, which incorporates worldwide
scientific/engineering expert input to define the diagnostic development requirements for ICF research. Diagnostic workshops
are routinely held for this purpose. The structure of the plan is dynamic; it is fully capable of adapting to evolving diagnostic
needs. J. Kilkenny oversees the diagnostic development at every stage from concept to scientific use. The scientific, engineeringand fabrication tasks of diagnostic development are divided between LLNL, LANL, SNL, LLE, and NRL based on the efficient use ofresources. The ICF program greatly benefits from the National Diagnostics Plan.
Comments: Encourage other ICF research areas to adopt a similar mode of operation to the National Diagnostics Plan.
Recommendations: There should be a succession plan for the leadership of the National Diagnostics Program. Mentoring thenext leader is crucial for ICF research.
Computational Models and Predictive Capability
Findings: There is a wide range of computational models and predictive capability for the three ignition approaches. LLNL has
the biggest work force and leads the way with the 3-D simulation capability. All three ignition approaches use HYDRA. LLNL
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ray tracing algorithms for direct-drive ICF applications. There seems to be a big knowledge gap or disconnect between LLE andLLNL and SNL and LLNL regarding the successful execution of 3-D simulations.
Comments: 3-D simulations could provide physical insights for many aspects of the implosion, especially for the residual kinetic
energy in the shell and hot-spot. More resources should be dedicated to 3-D simulations.
Recommendations: LLNL should provide source code assess for HYDRA to collaborators at SNL, LLNL and LLE. There needs to bea national representative for code development similar to the role of J. Kilkenny in the National Diagnostics Effort. LLNL should
provide more support than current level for 3-D simulations of laser-driven, direct-drive ICF implosions and for MagLIF
experiments. Hydrodynamics codes need to be written to exploit fully high-speed computing hardware.
III. Assess cross-platform and cross-laboratory collaborations
Findings: An impressive list of cross-platform and cross-laboratory collaborations is outlined in one of the joint white papers (LLE
White Paper #3: Cross Platform and Laboratory Collaborations) prepared for this review. The collaborations are divided into thefollowing categories: diagnostics development and collaboration, code development and use, capability enhancements,
collaborative experiments, and target development. Some of these collaborations provide support to the academic researchcommunity, which brings more students and researchers into the field of ICF.
Comments: These collaborations are crucial for the ICF research program.
Recommendations: Continue to seek and maintain further collaborations.

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Reviewer Report: Robert Rosner
Roadmaps and Decision Processes
Findings:
1.

There has been a remarkable change for the better in the overall ICF effort over the past 2 years, a change directly
attributable to the change in leadership at LLNL. It is evident – from the top at the labs – that there is genuine interestin building a common front to the challenge of achieving ignition.
2. However, I did not see any evidence for a coordinated approach – a ‘unified roadmap’ across the 3 competing
approaches to ignition. What seems to be missing is a definition of the milestones and “performance gates” needed tomake the crucial – and hard – decisions about how to proceed: For example, at what point will we be in the position tosay, “indirect drive-based ignition is on the way to success, so that the alterative efforts can be put on a back burner”?
Or, at what point will we be able to say “indirect drive ignition cannot be achieved by NIF in its current configuration”?
In the absence of such a coordinated plan, it is hard to see how the Labs and NNSA will confront some key decision
points coming up over the next 5-10 years: What are the key criteria used to decide to modify NIF for polar direct drive?
For full direct drive? For abandoning the purely laser-driven inertial approach and moving to magnetically-confined
direct drive?
Recommendations: NNSA needs to push the labs to construct an overall ICF roadmap that defines critical milestones and“performance gates” for the three competing ICF approaches. This is the time to take advantage of the fact that the current
leadership of the 4 NNSA labs has demonstrated that they can – and do – collaborate.
Program Balance
Findings: While the current allocation balance of funds to the 3 competing ICF approaches appears to be reasonable, it is entirely
unclear how this balance will be adjusted in the future – see my comments about Roadmaps and Decision Process immediately
above. The key elements to sensible program balance are (a) a set of performance gates applied to the three competing
approaches and (b) a hard-nosed willingness to readjust program balance if performance gates are not passed.
Recommendations: NNSA needs to put in place an agreed-upon ICF program plan and roadmap – this is an essential prerequisite
to any effort to define a sensible program balance.
II. Assess the integration of experiments and codes
Diagnostics
Findings: The diagnostics capabilities of the ICF program are finally getting the attention it so badly needed; and the National
Diagnostics Plan presented by Kilkenny at LLNL was everything one could have hoped for. The Plan’s focus on the science needs– as opposed to an approach focused parceling out funds to facilities – is to be highly commended; and the National Diagnostics
Plan’s timetables for instrument development and deployment seem very reasonable. The diagnostics area is a fine example ofwhat can be achieved across the NNSA lab complex if one puts the right person in charge.
Recommendations: NNSA should ensure that the National Diagnostics Plan’s timetables for instrument development anddeployment can be achieved – meaning that the necessary funding should be put in place. Timely progress towards deciding
between competing ICF approaches will require this, for the obvious reason that diagnostics are at the heart of a science-based
approach to ignition – independent of the path ultimately chosen.
Computational Models and Predictive Capability
Findings:
1.

2.

There has been a substantially increased attention at all of the labs to validate the simulation codes against
experimental data, and so substantially improving the physics capabilities – and whence the predictive capabilities – ofthese codes. This is a direct reflection of moving towards a more science-based roadmap towards ignition, rather thanthe engineering-based approach that the NIC typified.
In some areas, there remain substantial gaps in our understanding of the fundamental physics, resulting in the use ofcalibrated phenomenological models to fill these gaps. This is highly unsatisfactory because it limits the predictive

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capabilities of the codes. I comment in more detail on this issue in the section of Computational Models and Predictive
Capability immediately following.
3. In some physics areas, especially in the domain of laser-plasma interactions and mix, the existing fundamental/firstprinciples understandings remain incomplete, and the ICF codes are not really capable of a first-principles physics-based
predictive capability in such domain. The substantially greater involvement of the weapons program scientists in the ICF
effort has been a boon for the ICF simulation effort, as it has enabled direct comparison of codes whose methodology
and origins differ substantially. This is especially true for questions regarding turbulence and mix in converging
geometries.
4. The LLNL ICF code effort is very limited in the domain of direct drive, and a real effort at a complete V&V program
involving the LLNL ICF code (e.g., HYDRA) at Rochester seems to be in the planning stage, and is only now getting a real
start. This has been a huge handicap for the direct drive program because Rochester has only full access to validated 2D codes; its code building capabilities (especially for 3-D) are simply insufficient (both in terms of funds and manpower
available) for a credible effort, and so depend on the HYDRA team at LLNL for support; and its use of HYDRA iscompromised by the fact that they have limited access to the code development effort.
5. It is striking that in the simulation domain, there is no comparable effort to the National Diagnostics Plan (and there
certainly is no National Diagnostics Program). This is a major failing, because it means that the synergies that could
emerge as scientists from the 4 NNSA labs collaborate are simply missing; and it is especially amazing that no simulation
plan exists across the labs because the predictive codes are an intimate and essential part of the roadmap to ignition.
This failure shows up in a number of areas, three of which exemplify the problems that emerge when no real plan is put
in place:a. It is simply unacceptable that ICF design codes are treated as “black boxes” by subsets of NNSA scientists, asituation that exists at Rochester, which does not get access to the source code for 3-D LLNL ICF designcodes they need to run. It is difficult to understand how any good scientist can accept the results fromcodes to which he/she does not have full access; and given sufficient care in limiting access (say, only toscientists with sufficient security clearance), I cannot see any reasonable argument for maintaining thecurrent “black box” regime for these codes. (I might add that what we heard about HYDRA at the LLNL andRochester deep dives differed significantly.)b. The LLNL effort at building an entirely new predictive capability (based on a new framework and an Eulerian
scheme), which was discussed at LLNL, appeared to be news to folks at the other labs – certainly this wasnews to folks at Rochester.
c. A looming issue is the move at LLNL to a new computer architecture for the next generation leadershipmachine, a machine that is very unlikely to run the existing design codes efficiently – indeed, there isevidence that the wall-clock time to solution will degrade, and in the absence of sufficient funding for retooling the design codes (very likely), this may be a serious problem. This will affect code efforts at all of the
NNSA labs because the LLNL machine will be the leading edge “capability” (as opposed to “capacity”)
machine for the NNSA for a number of years to come.
Recommendations:1.

It may be time for a “laser-plasma science” initiative that is separated from the roadmap to ignition, and has a separate
funding line – this may be the only way to get focused attention on a fundamental physics issue that bedevils both direct
and indirect drive. Similarly, it may be useful to establish a “mix” initiative – again separate from the main-line ICF
effort; in this case (unlike the laser-plasma case) there would be substantial science overlap with the weapons design
program.
2. There is a crying need for a “National Simulation Code Plan” – the existing regime is really not the optimal solution tobuilding a first-rate predictive capability. As part of such a Plan, NNSA should focus on three issues in particular:a. Building and maintaining codes is expensive – we know this from the ASC /ASCI days. If NNSA is serious
about building and maintaining ICF-capable design codes, sufficient funding needs to be made available sothat the codes can evolve effectively as the dominant computer architecture evolves.
b. At minimum, there needs to be a clearing house approach to code developments, so that scientists at all
NNSA labs are aware of what is going in this domain at all the labs.
c. NNSA should force the Labs to go to an “open source” code approach, at least within the classified domain.
This would go a long way towards opening up the code efforts to effective collaboration across all of thelabs.
III. Assess cross-platform and cross-laboratory collaborations
Findings: The extent of collaboration between the three weapons labs and Rochester on ICF has increased substantially over the
past 2 years. This is true especially in the area of magnetically-driven direct drive, where Rochester is clearly developing a very
active collaboration with Sandia. The direct drive effort at NIF remains modest, with a few LLNL scientists now getting involved

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in the polar direct drive design effort. Finally, LANL has substantially increased its involvement at NIF, which is highly desirable,
given that LANL’s approach to modeling (including its simulation design codes) is not the same as LLNL’s.
Comments: A significant impediment to increased collaborative activities is the limited funding available to support suchactivities. In an environment in which funding is limited, scientists will tend to work on those programs that are best (and mostreliably) funded. So, to no surprise, LLNL and LANL scientists will (by and large) work on indirect drive, Rochester scientists will
largely work on direct drive and Sandia scientists will largely work on magnetically-driven direct drive.
Recommendations: The obvious recommendation of simply suggesting more funding is clearly not the right answer, primarily
because it is so unlikely to occur. But perhaps NNSA could consider starting a competitive “ICF innovation fund”, with areasonable level of funding (perhaps in the range of $5M-$10M), that supports cross-platform and cross-laboratory work. I
suspect that some of the very best scientists at the 4 labs will go after this sort of funding – and the program as a whole mightthen benefit well out of proportion to the amount of money actually spent.

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Reviewer Report: Susan Seestrom
My comments on the program are essentially limited to program issues. I think that the program is GREATLY improved from inthe past. It appears to be more open, it attempts to address a broad set of scientific issue that are relevant to achieving ignition.
In the past it seemed to me that the program was always grasping at a single issue that would be the key to ignition, and the
projections of performance were based on the most optimistic possible calculations, ones which many members of thecommunity would think incredible.
That said, there still seems to be a danger of putting too much focus on the next big thing (e.g. vacuum hohlraums and/or STUD
pulses) or worse, jumping onto direct drive as the best path. It is essential that the program lay out a roadmap of all the issues
that must be addressed to achieve ICF predictive capability, and create a balance program to address these issues. The national
diagnostic plan will be an essential part of this plan. I am also concerned about the present role of Los Alamos. It was telling that
there was no deep dive held at LANL given the number of science areas that are ones of historic LANL strength (like LPI) and thefact that if NIF/ICF do not become significant tools for designers at LANL there truly is NO national program.
Finally - I have a concern regarding the LLE program. It is not clear to me whether weapons physics done with an igniting Direct
Drive system would be as relevant as one provided with indirect drive. Further, since the real weapons codes are not and cannot
be used model the LLE work it is difficult to see how it will provide an important test of predictive capability relevant to theweapons program.

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Reviewer Report: Stephen Slutz
I. Assess the scientific hypotheses and the prospect for achieving ignition with existing scientific capabilities andfacilities; or, if indicated, what would be required to achieve ignition and supporting analysis. Provide anevaluation of program balance among ICF approaches.
Ignition Approach: Laser Indirect Drive (LID)
Findings and comments: The National Ignition Campaign (NIC) was a tightly focused effort based heavily on numerical simulations
to obtain fusion ignition in the laboratory. Many scientists outside of NIC believed that too much confidence was placed on
numerical simulation and this is ultimately why ignition was not achieved. I believe the story is more complicated and is still
unfolding. In particular scientists within the NIC recognized that numerical simulations were not accurate enough to completely
determine all the parameters of the design and that experimental tuning would be required. As an example, very accurate shock
timing (<100 ps) is needed to keep the fuel on the low adiabat required to reach ignition within the energy constraints of the
National Ignition Facility (NIF) laser. Numerical simulations are not accurate enough due to uncertainties in physical quantities
such as the equation of state (EOS). Shock timing was successfully tuned using the keyhole target configuration and low adiabat
implosions were produced during the NIC. Drive symmetry is another example that requires tuning, but in this case the required
symmetry has still not been achieved. In principle a sufficiently large hohlraum could provide the required radiation drive
symmetry, but the larger the hohlraum the more laser energy required to reach sufficiently high radiation temperatures to drive
the capsule. High-energy lasers are expensive so the hohlraums designed for the NIC were just large enough to provide adequate
symmetry according to numerical simulations. Since there is not much space between the capsule and the hohlraum wall, thedesign included a helium gas fill to mitigate hohlraum wall motion. Early in the NIC it was discovered that the opacity and thermal
conductivity models were not adequate. Modeling the hohlraum with Detailed Configuration Accounting (DCA) for opacity andeither nonlocal transport or a large flux limiter for electron thermal conduction (the high flux model HFM) resulted in much better
agreement with experiment. Calculations using the HFM result in somewhat colder He gas fill and consequently stronger inverse
bremsstrahlung absorption and Laser Plasma Instabilities (LPI) of the laser beams. Consequently the inner cones did not deliver
enough energy to the midplane of the hohlraum, which resulted in pancake shaped implosions. The solution adopted during the
NIC was to adjust the wavelength difference between the laser cones to enhance Crossed Beam Energy Transport (CBET) fromthe outer cones to the inner cones. This approach led to more symmetric images of the stagnated fuel, but has not led to asymmetric drive over the complete duration of the implosion. NIF capsules require high convergence ratios (>30) to obtain
ignition. It has been shown numerically [V.A. Thomas and R.J. Kares PRL 109, 075004 (2012)] that small asymmetries are amplified
by high convergence implosions and result in turbulent flow. Such turbulent flow [Residual Kinetic Energy RKE] does not transfer
to thermal energy fast enough to heat the fuel at stagnation. Consequently a high level of symmetry is required throughout the
implosion. It is now recognized that it will difficult to adequately control CBET in the high gas fill (HGF) hohlraums when the innercones need to be boosted by more than 50%. Consequently lower gas fill densities are being considered. Since this will result in
more hohlraum wall motion, larger hohlraums are also being considered.
In addition to inadequate hohlraum drive symmetry; the NIC capsules were not adequately robust to instabilities such as theRayleigh-Taylor (RT) and the Richtmyer-Meshkov (RM). This was demonstrated by the High Foot design, which obtained yields
much closer to the 1D simulated yields. It has also been discovered that the thin films (tent) used to position the capsule within
the hohlraum leaves scars that seed the RT instability, which grows to large amplitudes during the implosions. Due to insufficientzoning resolution, simulations performed before the experiment did not predict this scarring. The effect is more pronounced on
the low adiabat NIC capsule implosions and could have degraded performance as much or more than the asymmetric drive. Morerecent high-resolution simulations have been performed that capture the effect of tent scarring. Several approaches have been
proposed to position the capsule without detrimental scarring. These approaches will be simulated and tested experimentally.
Recommendations: A means to position the capsule without detrimental scarring must be found, but given the number of options
this should not pose a fatal flaw.
The hohlraum/capsule configuration should be modified to improve symmetry without the need for CBET. This will require larger
hohlraums with a reduced gas fill density. Larger hohlraums require more energy to maintain a given radiation drive temperature.
Some of this energy may be obtained through reduced LPI and backscatter, but it is probable that adequate symmetry will only
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at lower drive temperatures than either plastic or High Density Carbon (HDC) ablator capsules. The implosion time of a Beryllium
capsule is shorter than a plastic capsule making it more compatible with hohlraums with low fill densities. Furthermore, it isrelatively easy to dope Beryllium which enables the control of hard x-ray preheat. Consequently, high priority should be given to
the study of Be capsules.
There is presently not enough information to know if ignition can be achieved on NIF. Hohlraum designs need to be found withlow enough gas fill that LPI is minimal. These hohlraums must be large enough so that wall motion is tolerable. Power balance tothe laser cones can then be used tune the low mode symmetry without the use of CBET. Diagnostics need to be developed toaccurately determination of the radiation drive asymmetries on the capsule over the entire implosion. Once control of the lowmode drive symmetry is obtained Big Foot and wicked foam experiments should be used to determine what convergences are
possible with near 1D performance. 3D asymmetries from the finite number of lasers in each cone may limit the 1D likeconvergence to a value below that needed for ignition and larger hohlraums would be needed to smooth out such asymmetries.
The minimum hohlraum size should be found such that ignition relevant high-convergence implosions have 1D like behavior. The
laser energy needed for ignition could then be determined with confidence.
Magnetization of the gas within the hohlraum should result in higher temperatures and thus reduce absorption and LPI.
Magnetization of the capsule could also reduce ignition requirements. Both of these options should be studied.
Double shell capsules have two advantages over the single shell designs, which are presently being studied. The required radiation
drive temperature is lower and the wall motion will be easier to control due to the short pulse length requirement. On thenegative side it is unlikely that double shells will be less susceptible to drive asymmetries due to the overall high convergenceand the fabrication of double shell targets is more complex. If the study outlined above indicates that single shell designs will notlead to ignition on NIF double shells might provide 1-2 MJ yields, but there does not seem to be a high-yield option.
Ignition Approach: Laser Direct Drive (LDD)
Findings: LDD can deliver five times the energy to ICF capsules as LID. This should increase margin, but there are associateddisadvantages. Increased beam smoothing is required to avoid imprinting because the laser beams are in direct contact with thecapsule. In addition energy can transfer from a beam going toward the capsule to a beam going away from the capsule. This isreferred to as cross beam energy transfer (CBET). This process reduces the fraction of the laser energy that is actually depositedin the capsule. Most of the CBET occurs from beams at impact parameters equal to or slightly larger than the capsule radius. Thus
simply decreasing the size of the beam focus reduces CBET, but at the expense of increasing drive nonuniformities. Studies
indicate that adequate uniformity and reduced CBET can be obtained when the beam spot size is about 80% of the capsulediameter. A conceptually simple approach to CBET modification is to keep the laser spot size roughly 80% of the capsule diameteras it implodes. Producing a time-dependent laser spot size is referred to as zooming. Plans have been made to use this approachon Omega. The zooming will be accomplished using a two-region phase plate. The central region will focus the early part of thebeam to a spot size appropriate for the initial diameter of the capsule and the outer region of the phase plate will produce asmaller laser spot size appropriate later in the pulse when the capsule has begun to implode. Another approach is to shift thelaser wavelength of opposing beams to keep the CBET process out of resonance. This is the approach that is being tested on NIF.
Experiments on Omega indicate that CBET and LPI can be modeled adequately. However, LDD NIF capsules will be significantly
larger and LPI becomes stronger with longer plasma scale lengths. NIF experiments are planned to determine if CBET and LPI are
still understood and well modeled for larger capsules.
LLE is pursuing hydro equivalence as a metric to determine the expected performance of direct drive capsules on NIF. Fuelpressures of about 120 GB will be needed for a direct drive ignition capsule on NIF. Similar pressures will need to be demonstrated
on Omega. This is significantly larger than the 56 GB that has been demonstrated on Omega. The plan is to improve that number
by mitigating CBET, using thicker shell capsules, and improving beam pointing (symmetry).
Comments: Symmetric direct drive SDD on the NIF will require a reconfiguration of the laser. This will be expensive and would
preclude indirect drive experiments at full laser energy while the laser is in this symmetric configuration. Since laser-driven
hohlraum experiments are useful for weapons physics experiments, the decision to make such a transition will be difficult.

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Recommendations: In addition to achieving high pressures (>100 GB) with SSD, polar direct drive PDD should be studied on
Omega. If these studies are favorable, the NIF could be converted to PDD much less expensively than to SDD. The additionalsmoothing of the lasers needed for PDD will only improve LID experiments. If PDD direct drive does not work the decision toreconfigure NIF to SDD will be better informed in knowing that it is necessary for direct drive.
Independent of whether PDD or SDD is recommended for NIF experiments, the method of CBET mitigation that will be used on
NIF should be tested on Omega with hydro equivalent capsules that obtain the high pressure (>100 GB) needed for direct drive
NIF ignition capsules.
Ignition Approach: Magnetic Direct Drive (MDD)
Findings: Magnetically driven implosions are highly efficient when compared to either laser drive options. The challenge is create
fusion conditions for cylindrical implosions, which are significantly slower (~100 km/s) than is typical of conventional ICF (>300km/s). Magnetized Liner Inertial Fusion (MagLIF) is an intriguing approach to magnetic direct drive. Initial experiments havedemonstrated that the approach can create fusion conditions and sufficiently compress the magnetic field to trap α-particles,
but much more research is needed to determine the ultimate potential. The process of heating the fuel with a laser is not wellunderstood or modeled. Initial simulations of this process using Lasnex and Hydra significantly over predicted the fraction of laser
energy that would penetrate the Laser Entrance Hole (LEH) foil and be deposited within the foil. This disagreement is probably
due to LPI that is not modeled sufficiently well by either of these two design codes. In addition to reducing the fraction of thebeam that penetrates the LEH foil, LPI probably causes the beam to filament and spray. Filaments that heat the electrodes or theliner could mix this material into the fuel and degrade the yield. This is supported by a recent experiment with beryllium
electrodes that performed significantly better than a number of previous experiments that used aluminum electrodes. Note thatMagLIF implosions are particularly susceptible to mix due to the long implosion times.
Collaborations have been formed between SNL, LLE and LLNL to study the laser heating process. Experience within LLE and LLNL
indicates that beam smoothing is critical the controlling LPI. Z Beamlet has no beam smoothing, since it is not required forbacklighting, which was its original purpose. Random phase plates are being prepared to smooth the Z Beamlet laser. Controlledlaser preheating of the fuel will allow the study of MagLIF scaling with current, laser preheat, and the initial magnetic field.
Comments: Magnetically driven direct drive has the potential to be a technical surprise. Russia has plans to build a 50 MA pulsed
power machine with the goal of obtaining 25 MJ yields. The Z machine can provide at most about 27 MA. China has built a scaled
down version of the Z machine and is in the process of copying most of the published Z experiments. It is presently unknown
when they will build a larger machine.
Simulations indicate that very large yields (~ 10 GJ) and gains (~1000) could be possible with ice burning MagLIF, albeit onmachines producing much larger currents than Z. Certainly such a platform would be desirable for weapon physics experiments.
Sandia has developed future pulsed power machine designs based on LTD technology, which is significantly more efficient thanMarx based pulsed power machines. Calculations indicate that approximately 9% of the capacitively stored energy could bedelivered to a MagLIF liner as compared to about 5% using Z. An LTD design generating 48 MA could fit into the existing Z building.
2D Lasnex simulations of MagLIF driven by such a pulsed power machine produce 18 MJ yields with a simple gas-burning target.
Recommendations: Numerical simulations indicate that MagLIF could produce DT yields of ~ 100 kJ when driven by a peak currentof 25 MA, with a fuel preheat of ~6 kJ, and an initial field of 30 Tesla. The MDD program should work toward achieving these
conditions in the next 5 years on Z. Achieving such a goal may require the development of liners that are benign to mix. This could
be accomplished by forming a thin (several m) layer of DD or DT ice on the inside of the liner.
More importantly, the MDD program should work toward understand the scaling of MagLIF performance as a function of design
parameters (current, fuel preheat, magnetic field, fuel density, liner aspect ratio, and liner material) over as large a range as
possible on the Z facility. This scaling will be needed to determine if at some future date a next generation pulse power machine
should be built to study MagLIF at higher drive currents.

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Program Balance
Findings: Indirect drive on the NIF is and should be the main effort, but not to the exclusion of alternatives. The total number of
FTEs working at the laser laboratories is 55.5 at LLNL, 30.6 at LLE, 19.8 at LANL, and 13 at NRL for a total of 118.9. The number of
FTEs working on pulsed power is 16 at SNL. The magnetic direct drive effort is less than 12% of the total ICF effort.
Recommendations: Pulsed power is less expensive and much more efficient than lasers. MagLIF has the potential for high yields
with affordable costs. A larger fraction of the effort should be directed toward this approach
II. Assess the integration of experiments and codes
Computational Models and Predictive Capability
Findings: LPI physics is not adequately integrated into the design ICF codes such as Lasnex and Hydra, even though LPI physics
affects all three ignition approaches. Kinetic effects can be important in near vacuum hohlraums and may be important in MagLIF
targets. Current driven systems are not well modeled. In particular vacuum regions have to be treated with artificial density andmagnetic floors.
Comments: ICF is the arena for testing weapons designers, experimenters, and diagnosticians. In the attempt to achieve ignition
on NIF we have learned that our codes do not predict ICF implosions adequately. Is this due to physics particular to ICF (LPI or
kinetic effects) or something more basic? The physics particular to ICF experiments will have to be modeled better to answer thisquestion.
The nation spends considerable funds developing design codes. These codes should be available to all ICF researchers with needto know and the proper clearance, both for simulation purposes and for code development. They should not be considered theproperty of a particular laboratory or person.
Recommendations: LPI physics needs to be improved in the ICF designs codes. This is critical to all three ignition approaches.
Better modeling of kinetic effects is needed for low gas density hohlraums. Extended MHD is needed to model magnetic directdrive. This includes modeling transport such as the Nernst effect and removing density floors so that current paths can be moreaccurately calculated.
Within the constraints of need to know and clearance level, design codes should be shared more readily among the laboratories.
III. Assess cross-platform and cross-laboratory collaborations
Findings: Collaborations across both platforms and laboratories have been increasing. This trend should be encouraged. Suchcollaborations result in cross-fertilization of ideas and provide a means to balance efforts on the various approaches without
actually hiring, firing, or moving people.
Comments: It is my impression that many weapons designers are content to reanalyze old experiments repetitively rather thanengage in experiments on the ICF/HED facilities. Although there is certainly some value in being the custodians of historicalexperiments, in my opinion it is not sufficient to truly understand how difficult it is to use simulation tools to design and predictthe performance of actual experiments. If at some time substantive changes to the stockpile were needed, I would hope theresponsible designers have had their metal tested on real experiments.
Recommendations: Collaborations between the laboratories and platforms should be encouraged. Weapons designers should bestrongly encouraged to participate in HED/ICF experiments to sharpen their skills.

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B.2
Group 2 Reviewer Reports
Reviewer Report: David H. Crandall
Summary:
The Inertial Confinement Fusion (ICF) program and related High Energy Density (HED) science is following the “NNSA’s Path
Forward to Achieving Ignition in ICF” known as the “path forward” plan issued in 2012. In addition a number of changes havebeen made at the weapon laboratories (LLNL, LANL, SNL) to focus value from ICF on the weapon interests of the Stockpile
Stewardship Program (SSP). The alignment of the ICF sub-program with needs and interests of science-based SSP has never been
better. This conclusion is consistent with the letter from weapon laboratory Directors to NNSA Administrator Frank Klotz ofJanuary20, 2015. This is the overarching finding:
The ICF program is fulfilling its role as a primary instrument for science basis in Stockpile Stewardship.
From the beginning of the SSP in the 1990s, the vision was that the ICF program and its major facilities, the National Ignition
Facility (NIF), the Omega laser and Pulsed Power (Z), would provide physics insights and data for warhead analysis and would
provide nuclear burn challenge to partially replace nuclear explosive device testing. In the program planning, it was originally
articulated that nuclear warhead designers would be trained and tested by designing and conducting inertial fusion experiments.
That direct value to training and testing designers was not strongly followed by the US design laboratories until now. It was
expected from the beginning that the grand challenge of fusion ignition was to be a primary attractor for the talent needed in
SSP.
As recently as 3 years ago, this vision appeared to be in jeopardy. The ICF program was unsuccessfully seeking “ignition” (morefusion energy released by implosion of miniature deuterium-tritium filled pellets than input by lasers into the target at NIF). And,foolishly, the primary focus of this effort appeared to be getting enough energy gain to become the basis for a major Inertial
Fusion Energy (IFE) program with nuclear-weapon-related interests being secondary to that IFE direction.
Now, through change in laboratory management at all of the labs, especially at LLNL, and through technical inventions at thelaboratories, the program direction has completely changed. The failure to obtain ignition was a critical catalyst. A clear reminder
was delivered to the SSP that codes predicting nuclear explosion cannot yet be trusted outside a tested range; a lesson ofimmense value. In addition, the next step in progress at the NIF, the “high foot” target implosion with notable and predictableyield, was achieved by weapon designers. Further, new concepts for using fusion yield (even at today’s levels) at ICF facilities toclarify “boost physics”, to observe material behavior in weapons-relevant conditions, to help interpret past nuclear tests and toprovide tests of nuclear weapon effects, have been developed. The alignment of ICF program management with nuclear weapon
program interests within each major lab and among all of the ICF laboratories has become by far the strongest ever. While thesenew program aspects are nascent and not yet fully proven, ICF research of direct value to SSP is underway, credible and highly
promising.
The critical manpower to realize the potential of ICF/HED is growing now. The integration of ICF design and nuclear weapons
design has improved the role that ICF/HED has in manpower development for SSP. At LANL the funding for ICF/HED is sufficiently
constrained that some important ICF design work that has this symbiosis with nuclear weapon design is languishing. This can beredressed with modest funding enhancement at LANL.
The young researchers we met at the labs are potential stars for SSP and the supply of new talent from high energy density
physics programs at universities is continuing with healthy competition for the brightest and best graduating students. However,there is concern that the leading professors at places like MIT, Cornell, Michigan, Washington State and other universities arenear retirement without clear replacements and the intent to sustain these programs is not apparent at some of the universities.
Also, the funding of these university programs is under pressure and is too lean to sustain these programs, a problem that can beredressed by relatively minor adjustments to programs in NNSA and the DOE’s Office of Science.

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With regard to manpower the finding is:Current manpower, required to realize the value of ICF/HED for SSP and to develop future nuclear weapon
designers, is healthy and strengthening, but near term increments for LANL and the universities are required tosustain manpower supply.
The long-term development of ICF for SSP is unclear. Since the 1980s there has been a vision of quite high laboratory fusion
yields (500 to 1000 Mega Joules of fusion energy release) to address interests of the SSP in an environment without nuclear
explosive device testing. However, in spite of ICF program advancement, there is inadequate technical basis today for thinking
that such levels of yield from laboratory inertial fusion can be obtained. The potential value for SSP in such high yields remains
valid but may be at least partially addressed at lower yields through the inventions of new approaches now occurring at the labs.
Science-based SSP can progress significantly with ICF yields from 10s of Kilo Joules (KJ) to 10 Mega Joules (MJ). About 30 KJ ofyield is obtained at the NIF today, but 10MJ requires ignition and gain of about 5. With continuing support and anticipatedtechnical progress, over the next decade, experimental results and predictive computer code advancements will evolve to clarify
what is possible.
Intent to support the ICF/HED endeavors for up to a decade within SSP is critical for national security and is recognized as a
substantial US government commitment of several billions of dollars over that time. During that time warhead requirements
may also evolve and new threats may emerge. The evolution of the US stockpile and its role in national security is likely tocontinue to change over this decade. In order to analyze emerging nuclear threats from antagonists against the US and to mitigate
nuclear explosive device threats that may occur, the need for nuclear design expertise may grow over this decade. Given theselikely changes and uncertain progress in ICF, new evaluation of ICF for SSP should occur about a decade from now withappropriate checkpoints during the decade. During this decade, the ICF program can play a critical role in sustaining andadvancing nuclear design expertise essential to national security. ICF/HED has value for fundamental science and long-term
fusion energy potential and that value is likely to grow during this decade if there is increasing ICF capability of current facilities
and manpower. All of these factors lead to uncertainty as to the long-term value of ICF for national security interests with great
dependence on the progress made in ICF during the next decade.
Thus the finding on long-term value of ICF is:
ICF can lead in development of nuclear design expertise over the next decade, retaining ignition as an important
goal and applying the experimental approaches and code development underway at the laboratories. The role of
ICF for SSP, and other applications, beyond the next decade remains unclear with great potential dependent on
progress within ICF.
Background: This report is prepared for the National Nuclear Security Administration within the Department of Energy undercontract with TechSource, Inc. as part of the “2015 IFC/HED Review” Group 2 on Programmatics. The analysis and opinions
expressed are solely those of the author. The “Charge to Review Group” was supplied in May 2015 to the selected reviewers.
In conducting this review, the author participated, with others, in 3 days of presentations at NNSA headquarters from NNSA
leaders and the weapons Laboratories; LLNL, LANL and SNL. An additional 5 days of “deep dive” discussions were held at the 3laboratories and at a meeting at NNSA headquarters that included representatives from Laboratory for Laser Energetics,
Rochester New York and Naval Research Laboratory, Washington, DC. Specific agendas for those meetings can be supplied by
NNSA. In addition some time was spent reviewing a number of ICF and Stockpile Stewardship program planning documents andreports (classified and unclassified) and requested “white papers” from the ICF laboratories; all documents are available from
NNSA. This was a highly organized and appropriate process with particularly detailed attention by Njema Frazier of NNSA, Alan
Wan of LLNL, Don Haynes of LANL, Dawn Flicker of SNL and Craig Sangster of LLE.

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Full Report:
Alignment of ICF with Stockpile Stewardship:
Alignment Background: Since nearly 2 years ago a process of realignment of the ICF program, particularly at LLNL, has been
underway. The failure to achieve ignition at NIF was a critical catalyst. An intense program element called the “National Ignition
Campaign (NIC)” was conducted during FY 2010 through FY 2012. The campaign had control of the completed NIF and benefitted
from marvelous capability in target fabrication and fielding and steadily increasing diagnostic capability at the NIF. This wasleading edge science in a physical regime never achieved previously in the laboratory. Arguably, the NIF with associated targets
and diagnostics is the most complex engineering accomplishment ever by mankind and the science was expected to be a “grandchallenge”. Never the less, optimism was high that ignition (release of fusion energy exceeding the NIF laser energy supplied tothe target that contained an imploding capsule of deuterium and tritium in a frozen shell with central gas) would be achieved
through systematic engineering of the laser properties and target attributes. The overall ICF endeavor had been underway since1960 with ever increasing sophistication but with unfulfilled expectations at times along the way. The detailed codes andtechnological capability achieved by 2010 gave observers and participants in the ICF program confidence that rapid progressmight occur. However, the NIC failed; a final report of a review initiated by DOE Under Secretary for Science, Steve Koonin andcompleted with Koonin’s reviewers, concluded that “the NIC was completed on Sept. 30, 2012 having achieved all project goals
with the exception of its grand challenge scientific goal of achieving ignition”. The yields achieved were about 1000 times lessthan predicted by simulations. The Koonin reviewers thought that the capsule did not maintain geometrical integrity for the highconvergence of ~35 to 40 times used in the NIC and felt strongly that the capsule implosion cases that did match prediction mustbe found and experiment direction then determined in part through simulation excursions from those cases.
During the NIC, leadership at LLNL, particularly NIF Director Ed Moses, raised expectations of a rapid (10-15 year) developmentof LIFE (Laser Inertial Fusion Energy based on ignition at NIF). While inertial fusion energy (IFE) is a laudable goal and plausible
on a longer term, the expectations raised for LIFE appeared silly, as advertised, to most knowledgeable observers. In part becauseof the LIFE initiative, Under Secretary Koonin established a review of IFE by the National Academy of Sciences/National ResearchCouncil. Their sanguine report in February of 2012 is detailed and lengthy and useful in the long term; it contains the statement“the Committee judges that the potential benefits of inertial fusion energy justify it as a part of the long-term US energy R&D
portfolio, recognizing that the practical realization of fusion energy remains decades away”. The DOE’s policy on inertial fusionenergy established by Secretary Watkins in 1992, following advice from the Fusion Policy Advisory Committee, remains valid; thenuclear weapons program seeks fusion ignition that can support inertial fusion energy as well, if achieved.
In the meantime, the nuclear weapons program did achieve some important results (such as data applying to “energy balance”
in nuclear explosions) at NIF during the NIC but the weapons program was highly limited in operation time and was left to explain
confidence in nuclear warheads in spite of the NIC failure. The weapons program leaders made that explanation patiently andconvincingly, and, as well, initiated less ambitious experiments with less compression of the NIC capsules but with results thatlargely matched predictions and achieved an order of magnitude increase in fusion yield over that typically obtained during the
NIC. Current experimental results show clearly that both hydrodynamic instability distortion of the capsule and laser plasmainteractions, that interfere with the x-ray drive of the capsule during the laser pulse, caused the failure of the NIC. Current
research seeks to mitigate those dynamic distortions. It would be appropriate for the LLNL/NIF web sites to have an explanationof the failure of NIF that informs the interested public of the state of knowledge about ignition experiments at NIF.
Over the past 3 years the ICF endeavors have focused appropriately on physics challenges and focused physics experiments witha mix of seasoned scientists and engineers with young and imaginative researchers. Also, during the past 2 years, increased
attention has been given to development and application of computer codes to predict ICF performance (even more attention
may be appropriate) and to development of new means of using the results from ICF to test specific physics of nuclear explosive
devices. It is these elements of physics focus and technical progress, along with management changes for programs at all 3
weapons laboratories but particularly at LLNL, that have led to the significant change in alignment of the ICF program with nuclear
weapon needs.

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Management realignment:
Integrating designers: at both LLNL and LANL the ICF designers are now part of the nuclear weapons organizations and managed
in common with nuclear weapon designers, breaking 40 years of traditional separation. And, it is expected that designers will
participate in both ICF experiments and warhead design activities. This may be the most critical of the management realignmentsthat have occurred. This enables the practice of training and testing of nuclear explosive device designers through ICF
experiments. That practice was discussed positively at both design laboratories and is under way but specific outcome examples
are yet to be developed and are needed.
Developing and testing designers: new technical leaders of the nuclear weapon design teams at both design labs have knowledge
of ICF and appreciation of how it can apply to developing and testing of nuclear warhead designers. There are some healthy
differences between the 2 labs in how this approach may be expanded, but a common sense of purpose in applying this approach.
The technical leaders must give this approach continuing attention and assessment for its potential to be realized. It is easy toargue that this change should have been made long ago, but more important to nurture it now. This mixing of designers andtechnical design objects is a difficult management challenge but one that cannot be improved from outside the lab teams.
Evolving the role of ICF: during the “deep dive” discussions at LANL there was specific discussion of the value of ICF design
experience versus the prototyping of modified nuclear warheads for development of nuclear weapon designers. Both can havesignificant value. ICF designs are not nuclear weapons so lack tests of critical attributes but nuclear weapon designs are unlikely
to get developed far enough to truly test the designers. As clearly stated by Michael Bernardin at LANL, “nuclear weapons design
is about energy multiplication” and ICF designs can be also through nuclear processes. ICF designers can experience the full range
of design ideas completed in specific engineered hardware with outcome tested; an integrated experience necessary for
confidence in nuclear weapon designers. A specific ICF design and test may require about $10M for one case while a nuclear
warhead prototype design with some component testing requires more like $300M. There is no conclusion to the question ofwhich activity has greatest value, and there may never be, but the value of ICF design activity is becoming clearer and should beapplied and evaluated at LLNL and LANL.
Planning: the Directors’ letter to Klotz of January 20, 2015 initiated some more integrated planning among the laboratories. Theysaid, “We and our delegates will be meeting regularly in 2015 to ensure progress towards this integrated and coordinatedNational HED effort”. Some meetings have occurred but not regularly and not fully coordinated. The Director intent needs to be
more urgently acted upon. The willingness of the ICF laboratory community to do this appears high; the important participationof Sandia, LLE, NRL, General Atomics and Schafer is possible and those institutions do have some appreciation and understandingof the new alignment of ICF with the weapons program. Some issues like the role of the new “priority research directions (PRDs)”
in ICF program execution remain unclear and need the integrated planning promised. Again, it is important that the laboratory
technical leaders conduct and own this process; NNSA can observe and encourage this planning but it needs to be owned bypeople conducting the program.
All of these management factors of integrating designers, developing designers, evolving the role of ICF and integrating planningare critical to the new alignment of ICF with weapon program interests. Progress is nascent but needs continuing leadership
attention.
New technical factors:
Use of low yield: invention of methods to use HED and ICF for weapon analysis has been critical. In the original conception of therole of ICF in Stewardship, a central theme was to provide robust ignited fusion capsules that could be degraded or caused to failby modifications that were nuclear warhead relevant. The concept of ignition was central but its applications to weapon interests
were not developed in sufficient detail. Along with the failure of NIC, some new, classified, ways to use yield at levels less thanignition, for weapon-specific results, have been developed. Useful examples were presented during the May 18-20 meeting at
headquarters and at the deep dives at the laboratories in July. Some of these experiments will examine degradation of yield byspecific modifications of the target; up to about 10MJ, additional experiments of this nature are possible as yield increases. At
LLNL, specific experiment designs made clear that “boost-relevant” physics can be studied with yield that is now obtained at NIF.
Most of the weapon physics at NIF and much of the weapon effects studies at NIF and Z are now based on yield rather than

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ignition per se. Experiments are being initiated using today’s yield at NIF and similarly experiments using yield at a Z-like device
are being conceived. These approaches were not known in detail when ICF was included in Stewardship planning, but are now
the basis for ICF application for nuclear weapon interests.
Materials behavior: experiments on materials behavior when high energy density is applied are being done at NIF, Omega and Z
and other facilities. The advent of short duration intense lasers and other light sources (one example, the Linear Coherent Light
Source at Stanford) and the improved intensity and control of Z-pinch discharges allow laboratory study of higher pressures andhigher energy density in matter than previously possible. Some of these experiments are of fundamental science interest and anumber are directly for weapon applications. As stated by Rip Collins during the review, “all of the kids want to know if life canexist on other planets, controlled by the melt curve of Iron, but they are not so much interest in melting of Plutonium”. The
science is similar and requires similar specialized techniques. Through these experiments ICF both contributes to fundamental
science and benefits from such science. ICF facilities can both apply high energy density to materials and examine the fast time
responses of the materials. Experiments at Z and NIF on Plutonium are yielding unprecedented details of the response of thisunique material to high pressure and high energy density. Of course, these data are of high value in analysis of the detonationof nuclear devices. These non-ignition experiments were not known to be possible when Stockpile Stewardship was conceived
but are a notable part of its success today.
Hydrodynamic behavior of plasma: measuring the evolution of plasma instabilities and dynamic plasma behavior is importantfundamental science. Plasma instabilities often are combined or integrated in intricate ways, difficult to predict, but apparent inastrophysical phenomena, HED/ICF experiments and nuclear detonations. A lot can be learned from astrophysical phenomena
but discussions during the review made clear that weapon designers need more than can be obtained from astrophysics. LANL
scientists have developed “shock-shear” experiments on ICF facilities that give combined plasma instability behavior in acontrolled manner providing data of fundamental science value and specific value for particular nuclear weapon performancequestions. Other experiments by labs and university groups explore colliding plasma and various plasma hydrodynamic
phenomena at the ICF facilities – fundamental science of value to the weapon applications.
Test Readiness: experiments at ICF facilities are in concert with substantial advanced diagnostic development that is critical to
ICF progress. Many of these diagnostic devices can be applied in any future nuclear device tests. And, these activities develop
the people that would be required for obtaining data of scientific value from any nuclear tests. Along with subcritical tests in
Nevada, these ICF activities make it possible to gain scientific value from testing of nuclear explosive devices should that ever
become necessary in the future.
Improving the computer codes: during the review, a definition of Stockpile Stewardship was offered by Frank Graziani, “In theabsence of testing, define and test computational procedure that is accurate enough to do the job”. An important element indoing that and in having confidence that it is being done is HED/ICF. Both open and classified computer codes are applied toresults of experiments in HED/ICF. Some codes are developed specifically for ICF ignition others deal with various HED
experiments, and others deal with specifics of nuclear explosions. Code development is both learning to apply fastercomputational capability and including specific improved physics models and material data. More effort on codes is needed now
and is made meaningful by having new data from HED/ICF. The more integrated planning of ICF should have value in planning ofcode development. This is another area where technically knowledgeable leadership at the labs is critical.
The challenge of ignition: while it is ICF yield more than ignition per se that is applied for weapon issues, the challenge of ignition
stimulates the program and attracts the needed people. This is as true now as it has been over the first 20 years of Stockpile
Stewardship. In addition yields in the 1-10MJ range would enable more advanced weapon applications of ICF and such yields are
only achievable in the near term from ignition at the NIF. Ignition is itself weapon physics. Thus the drive for nuclear ignition andburn in the laboratory remains central to Stockpile Stewardship and critical to future value of ICF for Stewardship.
Weapon Effects: experiments at a number of NNSA’s pulsed power facilities and at NIF provide x-rays for valuable weapon effects
testing on electronics and even re-entry bodies. Valuable x-ray and gamma-ray tests continue using ICF facilities and expertise.
The end of use of the Sandia Pulsed Reactor (SPR) meant that fewer means of testing effects of neutrons are available. Yield at
NIF, and potentially at Z, can provide sufficient neutrons for some weapon effects tests. Invention of ways to use these neutrons
in a more physics-based way, testing codes, would be valuable in weapon effects assessments. Yields in the few MJ range would

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be quite useful, particularly if greater volume of neutron flux is also achieved. At LANL, Michael Bernardin commented that oneof the most significant challenges that he sees coming is qualifying the function of our new and modified nuclear warheads inradiation environments; all rebuilt nuclear warheads will inevitably have changed electronic controls with potentially changed
sensitivity to radiation. He highly values what could be achieved within ICF for this application. The convincing and more
complete tests of weapon effects could be achieved if the full vision of 500 to 1000 MJ yield were achieved through ICF
approaches. However, such high yields remain highly uncertain, requiring ignition success, significant new facilities and at least
decades of progress and construction; this cannot be a sensible part of concrete Stewardship planning now. So the near term
development of means to use yield at NIF and possibly Z should be the focus of effort for weapon effects interests.
Overall: Technical invention of means to conduct experiments using ICF facilities has enabled a new range of weapons physics andeffects and meaningful tests of advancing computer codes. These ICF-related technical advances are critical to science-based
Stockpile Stewardship.
The combination of management changes aligning ICF with Stewardship and technical advances allowing a wider range ofexperiments, especially including those with lower yields, leads to the overarching conclusion:
The ICF program is fulfilling its role as a primary instrument for science basis in Stockpile Stewardship.
Planning and development of manpower: In order to continue and strengthen the remarkable realignment of ICF with nuclear
weapon interests there are important considerations for NNSA and the weapon laboratories. Nothing could be of greater value
than technical progress toward ignition and yield above 1MJ. No great increase in funding for ICF is needed now but some funding
adjustments are needed and future progress could change the funding needs. It is critical that NNSA have the intent to support
HED/ICF at about the current level for a decade.
The integrated planning of the ICF community for the 3 approaches to inertial fusion burn (indirect laser drive, direct laser drive,and magnetic compression at Z) is critical. The facilities, particularly NIF, have become more efficient at providing shots andexperiment time which enables more results and better planning. The laboratories need to lead in making the integrated planningmore meaningful and this is a matter of some urgency.
As technical progress occurs in ICF critical new questions may arise such as investing in more laser energy at NIF or reconfiguring
NIF for symmetric drive or investing in a more advanced Z facility. None of these new investments are justified today, but
technical progress is difficult to predict and could happen rapidly or slowly. The ICF program is poised to pursue the needed
progress intently and in a coordinated manner.
White papers about manpower were supplied to the group by the weapons labs, LLE and NRL. Each of these papers documents
the trajectory of 10s of young researchers in recent years at each laboratory. These papers show that ICF/HED has been a clear
attractor of talent for the Stewardship program. That remains true today and new and talented young researchers continue tobe recruited to the labs from university-based HED programs today. There is not a manpower crisis today.
Some near-term funding adjustments are critical for long-term manpower development and supply. At LANL the integrated
approach to design in ICF and nuclear weapons needs increased support. Work on topics like double shell ICF and Beryllium
ablators for NIF capsules is languishing for lack of a few million dollars. This work is important to the use of ICF design for training
and testing weapon designers. A modest increment (a few million $) in HED/ICF funding at LANL is important.
NRL has had a long-term role in the ICF program developing techniques and concepts for laser direct drive and supplying specificscience expertise and data valuable to Stewardship. NRL needs modest funding increase (a few million $) to sustain this role. It
is clear that NRL has played a useful role in the program.
At the universities the HED science that develops new talent for Stewardship faces financial hardship and change. The science isof high quality and attractive to capable young scientists and engineers as indicated by their participation and papers at technicalconferences. Both the Office of Science and NNSA have interest in nurturing this area; the science and the interest of young
scientists should influence program planning in both parts of DOE. Additional funding (about $20M increase) for basic high energy
density science at universities could pay great dividends, both in new quality science relevant to materials behavior, fundamental

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plasma physics, astrophysics and nuclear science, and in retaining the interest of young scientists and stimulating intent of
universities to continue their programs. The NNSA and the DOE Office of Science should strengthen their university programs in
HED in a joint manner for the benefit of fundamental science and national security. The potential retirement of so many leading
professors in the field makes this somewhat urgent.
The manpower finding is:Current manpower, required to realize the value of ICF/HED for SSP and to develop future nuclear weapon
designers, is healthy and strengthening, but near term funding increments for LANL and universities are required
to sustain manpower supply.
Long-term value of ICF for SSP: Yogi Bera might have said, “planning is difficult when you don’t know the answer”. The questionof “high yield” (500 to 1000 MJ in a laboratory) does not have an answer now. Even the question of ignition and modest gain at
NIF (1 to 10 MJ yield) does not now have an answer. This makes the long-term answer to the question of value of ICF for the SSP
unclear. In discussions at the laboratories, specific weapon-relevant experiments to use gains up to 10MJ were presented. There
were no current clear examples of experiments or needs for yields in the range 10 to 100 MJ. Above 100 MJ yields (beyond thepotential capability at any existing ICF facilities) there were clear concepts for weapons physics and weapon effects experimentsthat opened. These concepts are classified but clearly supported utility to SSP of high yield, which has been a long-term goal for
ICF. High yield can be retained as a goal for ICF but it has no useful meaning if considerable progress toward ignition is notachieved. Within about 10 years the answers, that could give meaning to planning for high yield, may be obtained. In theintervening 10 years it is clear that ICF will have significant value for Stockpile Stewardship in training and testing designers andin providing physics insights (for example boost physics) and specific data (for example Plutonium response to high pressure) for
Stewardship and other science and national security interests, and in challenging and attracting bright scientists and engineers.
Strong support for ICF within Stewardship is easily given now, but the long-term is not clear.
ICF can lead in development of nuclear design expertise over the next decade, retaining ignition as an important
goal and applying the experimental approaches and code development underway at the laboratories. The role of
ICF for SSP, and other applications, beyond the next decade remains unclear with great potential dependent on
progress within ICF.
Closing comment: The alignment of ICF with SSP has never been better in more than 50 years of ICF history. The diverse ICF
program participants have never been more unified in their pursuit of the scientific goal of ICF ignition and burn in the laboratory.
These changes are quite remarkable and are to the credit of a great number of people; technically astute leadership at the weapon
laboratories and willing integration of talents is key. Management attention at the labs is critical to retaining this newenvironment and realizing its value. New technical inventions are allowing better use of ICF capabilities for weapon interests.
However, new technical progress in the quest for ICF ignition and burn is also required to maintain this momentum. That progress
is not assured and is difficult to predict. It will likely take as long as a decade to understand and assess this quest. Along the way
checkpoints are needed; some type of technical review of ICF should occur every 2 or 3 years. Early progress, anytime during thedecade, on the fusion front could call the question of choosing some form of upgrade or modification at NIF or Z in order tosustain progress; there is insufficient basis for such upgrades or modifications now. The SSP and the ICF subprogram are strong
and dynamic; sustaining that is the challenge.

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Reviewer Report: Jill Dahlburg

28 August 2015

Jill Dahlburg, PhD, SESSpace Science Division Superintendent
Naval Research Laboratory Code 7600
Washington, DC 20375

Njema Frazier, PhD
Office - Inertial Confinement Fusion [O-ICF]
NA-112, Defense Programs
Department of Energy [DOE]
National Nuclear Security Administration [NNSA]
1000 Independence Avenue, SW
Washington, DC 20585
Dear Dr. Frazier,The 2015 Review of the ICF / HED (High Energy Density) Physics for Stockpile Stewardship first convened on 18-20 May 2015 at
DOE NNSA Headquarters [HQ]. Group -2 of this Review, which addressed "Non-ignition HED and Long-term Goals," convened aspart of this 18-20 May event, and also convened on two other occasions: 14-17 July 2015, for deep dives at the three NNSA
Laboratories; and, for a deep dive, to discuss the Naval Research Laboratory [NRL] ICF program and the University of Rochester
Laboratory for Laser Energetics [LLE] program, at DOE NNSA HQ on 23 July 2015. With the exception of the deep-dive day at Los
Alamos National Lab [LANL] on 16 July 2015, and the deep dive day at Sandia National Lab [SNL] on 17 July 2015, I personallyparticipated in all of the Group -2 convenings, i.e.: the 18-20 May event, the days 1 & 2 of the 14-17 July event, at Lawrence
Livermore National Laboratory [LLNL]; and, the entirety of the day at NNSA HQ on 23 July. Note: For the NRL portion of the 23rd,
because of my 1985-1999 affiliation with the NRL ICF program within NRL's Plasma Physics Division [PPD], and my ongoing
employment at NRL as Superintendent of the NRL Space Science Division [SSD], which is a sister division to the PPD and in anotherdirectorate at NRL, I offered to recuse myself. This offer was deemed unnecessary by the Group -2 members and by the DOE
personnel present, so I participated in this portion of 23 July's event also.
This letter summarizes my independent review, from a Group-2 perspective. At the start of the review, on 18 May, Keith Le Chien,
Director, ICF, NNSA, introduced the review topics and purpose. This review was a promise made by NNSA to Congress, to conduct
a comprehensive review in 2015 on the "progress towards ignition" and the broader HED physics program that ICF facilities enable
within the NNSA Stockpile Stewardship Program [SSP]. Specific Group-2 duties were to: (I) assess the alignment of the ICF / HED
program with SSP and the broader Nuclear Weapons Program [NWP], with emphasis on workforce development and program
management; (II) assess the long-term direction planning associated with the tri-Lab Directors' Letter; and, (III) assess the needfor "high-yield" for the SSP. My assessments, following, include four (4) findings and also four (4) actionable recommendations.
(I) Assessment of the alignment of the ICF / HED program with SSP and the broader NWP in the near, medium, andlong term, with emphasis on workforce development and program management.
During the Cold War era, the U.S. effectively provided a validated NWP strategic deterrent, designing, building, testing, anddeploying numerous nuclear warheads of various designs. This deterrent was in the product -- the stockpile -- and its delivery
vehicles. And, the deterrent was also in the development and production Complex which encompassed: the staff; the RDT&E
programs; and, the facilities, including the Labs and the factories.
The moratorium of nuclear testing that began in 1992 ushered in a new era for the deterrent. The product passed into a mode
primarily of maintenance, which had immense implications for the development and production complex. Now nearly a quarter2015 Review of Inertial Confinement Fusion and High Energy Density Science Portfolio

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of a century into the moratorium, and nearly three quarters of a century from when the deterrent was first realized, no active
researcher directly remembers a time before the advent of the deterrent, and few have experience from the active phase of thedeterrent -- the Cold War era.
The primary function of the Complex is refurbishment of existing warheads and associated, with objective to guarantee deterrent
effectiveness in the event that it is ever needed.
Maintaining a state of peak but static readiness is very difficult, in part because this goal is seen as achieved and abiding by all
constituents of the Complex. The central core of the Complex, around which all else could be rebuilt should that need ever arise,is the knowledgeable and experienced staff. In the context of a fixed definition of readiness, static can become passive, leading
to analysts and analyzers where -- for a reliable deterrent into its next century -- designers and experimentalists are needed
instead. It is in this area that the ICF / HED program can and should provide significant mitigation to a central risk in readiness,
which is that our nuclear weapons will fail to perform as expected, due to staff misapprehensions arising from complacency as
result of insufficient experience with empirical, real-world effects, AKA the unpredictability of "Mother Nature."(F-1) Finding: The designers at the NNSA NWP Labs have demonstrated that lack of sufficient experimental, empiricalinformation can lead to unexpected and profound errors, as evidenced by the lack of success of the National Ignition Campaign[NIC] to achieve ignition.
(R-1) Recommendation: The NNSA should ensure that the design and experimentation skills of the NWP staff are regularly
exercised, including by innovative exploitation of ICF and HED facilities available to the staff. For example: high-Z metal targets
with deuterium-tritium gas fill may offer promising routes to laboratory ignition and burn, including on the National Ignition
Facility [NIF], relative to the conventional plastic capsules of the NIC and immediate follows-on. Additions of imposed,
compressed magnetic fields could enhance the ignition margin, and should also be studied. These designs would challenge staff
in key areas of modeling and simulation, materials and target fabrication, and diagnostics, and should be experimentally exploredin the near- and mid-term, and if promising also in the far-term.
In addition to stagnation is the danger of staff insularity. As early as the KD-0 decision point for NIF, circa 1992-1993, informed
ICF researchers external to the tri-Lab (LLNL, LANL, SNL) complex recognized, promulgated, and documented all of the majorhydro failure modes of what became the NIC baseline capsule [REF: "Shell Implosion Modeling (U)," Defense Research Review(1994), Jill Dahlburg,* Stephen Bodner,* John Gardner,* Andrew Schmitt.* *(NRL)].
This (REF) work was presented to the DOE NNSA Inertial Confinement Fusion Advisory Committee [ICFAC] during the KD-0
decision time period. Had this information been properly evaluated by the tri-Lab ICF staff, at the time, many years of more
effective research could possibly have been achieved in the intervening nearly quarter century.
During the years from 1992 to the present, both of the non tri-Lab ICF organizations -- NRL and LLE -- have contributed significantly
to the Complex. These include myriad successful experimental campaigns on Omega and on Nike, new concepts and capabilities
both realized and proposed, and key staff transitions to the tri-Lab cadre, among them Dr. Charles Verdon from LLE to LLNL and
Dr. David Meyerhofer from LLE to LANL. In addition, the contractor ICF organizations General Atomics and Schaffer Corporation
have provided tremendous target fabrication and related ICF technology support as well as beneficial staff transitions.
(F-2) Finding: The tri-Lab NWP has benefited by inclusion in the ICF / HED cadre of organizations outside of the tri-Lab institutions,in substantive and documented ways.
(R-2) Recommendation: The NNSA should reliably cultivate appropriately broad partnerships with the ICF / HED community
beyond the tri-Lab cadre, including with Laboratories in other Agencies, Universities, and private Corporations. For example: the
NNSA could define and promulgate an ICF / HED experimental challenge intended for participation by the tri-Labs and also byother ICF/ HED organizations. The challenge should be scoped so that it could be executed on these (and possibly also other)
facilities: Z at SNL; Trident at LANL; NIF at LLNL; Nike at NRL; and Omega & Omega-EP at LLE.

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(II) Assessment of long-term direction planning associated with the tri-Lab Directors' Letter.
From a Group-2 perspective, the Letter is a good start. The above-discussed issues of staff possible stagnation and insularity arealso the purview of the tri-Lab NWP management as represented by this Letter, and their subordinates. It is a sadly oftenrecognized fact that truly good management is not appreciated until it is gone. The NNSA NWP Complex at present is extremely
fortunate with excellent tri-Lab Directors and also with outstanding -- by any measure -- NWP / ICF/HED management: at SNL (Dr.
Keith Matzen); world-leading overall management at LANL (Dr. Charles McMillan); and, perceptive and thoughtful, outstanding
NWP management at LLNL (Dr. Charles Verdon). In particular, Dr. Verdon's recent reorganization of A-, B- and ICF areas of LLNL
is to be applauded.
(F-3) Finding: Suitable management is in place at all three of the NNSA Labs to enable next beneficial steps for the advancementof the NWP cadre, as intimated by the tri-Lab Directors' Letter.
(R-3) Recommendation: NNSA should formally recognize this NWP / ICF/HED management (McMillan, Verdon, and Matzen)
excellence, and request this management to build from the posture described in the Letter, and work together to develop aroadmap for NWP designers' and experimentalists' career development, across the tri-Lab Complex. The roadmap: should
included detailed description of a tri-Lab vision that describes what the community of designers and experimentalists should look
like at both 5-year and 15-year points in the future; should delineate the necessary attributes of this designers andexperimentalists community; and, should include definitive discussion of how ICF/HED experimental research will help tocultivate and hone these attributes, at all three Labs.
Consequence of no near-term action: The time during which all three of these personally knowledgeable and manageriallyoutstanding leaders currently available to the NNSA will pass, and a rare window of opportunity to utilize their combined expertisefor tri-Lab joint workforce advancement will disappear.
(III) Assessment of the need for "high-yield" for the SSP.
The near-total lack of ability to test the reliability of a nuclear warhead's components in a relevant environment presents a riskthat cannot be understated. No current capability enables broad assurance of refurbished components in already-known threat
environments, and as new threats evolve, the risks increase. High yield under controlled conditions would enable retirement ofmany of the known and envisioned risks. This is much needed.
Further, designing for high-yield exercises an NWP designer's innovation skills in ways that few other non-proscribed technicalactivities achieve.
(F-4) Finding: High yield is needed for the SSP, technically, and it is also beneficial for workforce development across the NNSANWP Complex.
(R-4) Recommendation: The NNSA should continue to encourage development of high yield designs. In consideration of the factthat ignition is not yet achieved on NIF, and also that high yield would not be supportable by the NIF Facility, these designs should
be encouraged to be as innovative as reasonable, so as to stretch the design capabilities across equation of state, radiationtransport, hydrodynamics and magnetohydrodynamics, thermal conduction, and turbulence modeling. At the same time, thedesigns should be arguably feasible to fabricate. For more promising designs that may require novel geometric configurations orproperties (e.g. metal foam), a modest amount of target fabrication collaborative research could be very beneficial, to keep themodeled design grounded in reality.
I welcome requests from your office to elaborate or clarify.
Sincerely,

Jill Dahlburg
Naval Research Laboratory2015 Review of Inertial Confinement Fusion and High Energy Density Science Portfolio

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Reviewer Report: John R. Harvey
Introduction
The primary focus for NNSA’s HED facilities (NIF, Omega, Z) must be to advance nuclear weapons stockpile stewardship. 1 In thisregard, their role is two-fold:
These facilities are unique in enabling experiments to test the validity of (and thereby provide means to improve) existing nuclear
weapons codes in the temperature, pressure and density regimes in which nuclear weapons operate.
Probably more so than for other modern experimental facilities in NNSA’s weapons complex, they provide primary means toreplace nuclear testing as a training tool for a new generation of nuclear weapons designers and engineers.
Both objectives are essential for the future success of stockpile stewardship. How well these three facilities, and the scientists
and engineers who operate them and carry out complex experiments, meet these objectives is the focus of more detailed remarksthat follow.
I. Alignment of ICF/HED program with SSP and broader weapons program
NNSA’s HED facilities have made essential contributions to the nuclear weapons program over the past five years. Non-ignition
HED experiments have made important contributions to our understanding of how nuclear weapons operate in the areas ofenergy balance (a major breakthrough), boost, secondary performance, and warhead radiation output and associated weapons
effects (relevant to qualification of non-nuclear components of the W76 and B61-12 LEPs). Achieving ignition has important
implications for weapons work as well as for providing long-term energy solutions for our nation. Very importantly, ignition
experiments confirm that our computer codes do not model with sufficient precision ICF capsule implosions designed to achieve
the temperature, pressure and density regimes for sustained thermonuclear burn. 2 That said, the conclusion of the ignition
campaign has permitted a desired increased focus on important weapons physics that can be addressed in non-ignition
experiments. Other key findings regarding HED workforce development and overall program management follow.
Workforce Development – It’s the people, stupid!
For two decades officials have wrestled with the problem of how best to ensure that the next generation of nuclear weapons
designers and engineers is ready to take over from those who honed their skills during nearly five decades of nuclear testing. As
time passes, loss of knowledge resulting from the departure of the older generation, and the need to transfer critical skills basedon that knowledge, heighten the urgency of this effort. Lab directors have expressed concerns about the “shifting to the right”
of the peak of the age distribution of working-level weapons scientists and engineers. This relates not just to the ability to develop
a modern warhead or field a new or different military capability if required in the future, but to the judgment to ensure that theexisting stockpile remains safe and reliable. Bringing highly-capable young scientists and engineers to the laboratories has been
and will continue to be driven by access to world-class scientific facilities producing path-breaking research, and the ability towork on complex technical problems involving the security of the nation whose importance is communicated clearly by its leaders
in both words and actions.
Importance of HED Experiments with Advanced Diagnostics

1

These notes reflect my perspective on the state of NNSA’s ICF/HED physics program after participating in a “deepdive” review organized by NNSA’s NA-10 organization. Although a physicist, I have not been immersed in thisprogram. My remarks however reflect 35 years experience working nuclear weapons and national security issues,
first at Lawrence Livermore National Laboratory, then at Stanford University’s Center for International Security andArms Control and in senior government positions in the Departments of Defense (twice) and Energy. I carried out
this work for NNSA under a consulting agreement already in place with the Los Alamos National Laboratory. As
stated, these notes reflect my own views and are not necessarily those of Los Alamos or the NNSA.
2
Indeed, the high convergence implosions characteristic of HED capsule experiments stress the weapons codes inways that modeling a generic nuclear explosion do not.
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The challenge of training weapons designers and engineers is evolving due to the absence of nuclear testing and availability ofnew, extraordinarily powerful computing capabilities. More so than their predecessors, young designers rely heavily on computer
simulation, modeling and calculations, tending towards overconfidence in the quality of the weapon physics embedded in thecodes. One senior designer noted that “the codes always lie” and the job of the designer is figure out where they can be wrong
and when.
Predicting the results of an experiment ahead of time, whether a nuclear test in Nevada or an HED physics experiment, has beenand remains an important learning experience for a young designer. Finding out why the codes do not work in certain instances
creates knowledge that builds judgment. In addition to greatly advancing our understanding of how nuclear weapons work, theNIF, Omega and Z facilities, coupled with advanced experimental diagnostics capabilities, provide opportunities for young
weapons designers to build skills and judgment through the understanding gained when the results of their calculations are—orare not—confirmed by Mother Nature.
To achieve these training objectives require some adjustments in ongoing programs. Funding shortfalls and other priorities
prevent young scientists from fully exploiting these facilities. For example, because LANL does not have a resident large-scale
HED facility, LANL secondary designers, in order to access temperature and pressure regimes unique to secondaries, must conduct
experiments at a remote facility. All three facilities are open to outside users, but LANL designers tend to rely less on HED
experiments in honing skills than do those at LLNL. Indeed, LANL’s HED program is relatively modest by comparison. 3 LANL’s
leadership recognizes the problem and is working to address it, among other things, by shifting the culture at the lab to reinforce
the idea that HED physics is an integral part of stockpile stewardship. LANL’s HED program, unlike LLNL’s which has a strong
ignition component, is totally focused on non-ignition weapons physics. Significant work, and training, can therefore be carriedout at Omega where it is cheaper to operate. Still, with the conclusion of the ignition campaign, more high-value NIF weapons
shots can be allocated to LANL, which is steadily ramping up its work at NIF. To fully exploit opportunities at NIF, however, will
require a corresponding increase in associated LANL funding.
Program Management
Program management should seek to promote tight coupling between HED experimental work and the needs of nuclear weapons
design and modeling efforts in support of upcoming LEPs. This is a work in progress with some noteworthy disconnects. For
example, there are concerns that the scientific knowledge gained from HED experiments is not being exploited rapidly enough in
updating nuclear weapons design codes. Indeed, in one case at least, this had led to different codes being used for ICF capsulesand for weapons. There may be good reasons for two sets of codes (e.g., the high convergence implosions characteristic of ICF
capsules referred to earlier), or for delay in updating weapons codes (e.g., concerns about data quality), but ideally it seems
desirable to strive to use the same codes to model the same physics.
In the past year or so, to promote greater linkages between weapons and HED physics work, LLNL has integrated primary andsecondary design teams, and the ICF capsule designers, into one weapons design division. Notwithstanding a speed bump or two
in the ensuing culture clash, this is the right approach. LANL, which had already integrated primary and secondary design teams
and the computational physics folks into one division, should explore the benefits of further integration with the HED physics
team (aka Experimental Plasma Physics division).
Recommendations•

More fully utilize existing HED facilities. Tight budgets are a fact of life; we must get “more bang for the experimental
buck” by operating more efficiently and by managing safety risks rather than seeking, fruitlessly and at high cost, toeliminate them. Such efficiencies can augment other resources to bolster LANL’s HED physics program.

3

Only 10% of LANL’s secondary designers are actively involved in HED experiments. LANL’s share of the total
FY15 ICF/HED budget for experimental work related to stockpile support and ignition is also about 10%. An LLNL
white paper notes that training in HED science is essential for all of its designers and suggests that a much higher
fraction are involved in associated experiments.

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•
•
•
•

Provide young LANL designers with stronger incentives to carry out experiments at NIF, Omega and Z facilities in theirtraining and later design work. To promote this, strive to make NIF more “user friendly” to outside users. Among otherthings, clarify the process through which work funded by LDRD can compete with other users for NIF shots.
Continue to challenge young weapons scientists at all the labs to brief and document their predictions on the results ofexperiments before they are carried out. This process provides opportunities to fail and, thus, is a vehicle for building
judgment.
All labs should strive to strengthen integration of HED programs and weapons design teams or, in the case of Sandia,
with those working nuclear effects. LANL should explore integrating its HED physics team with its single nuclear design
division.
Implement timely updates to weapons codes based on validated physics results from relevant HED experiments. As agoal, each nuclear design lab should maintain a single set of codes (independently developed to facilitate peer review
assessments of the other’s work) to model both nuclear explosions and HED experiments.

II. Planning associated with Tri-Lab Directors’ letter
The January 2015 letter sent to NNSA Administrator Frank Klotz by the three weapons lab directors highlights the importance of
the ICF/HED program for stockpile stewardship. 4 It states:
The overwhelming majority of the yield of the Nation’s nuclear weapons is generated when the conditions within the nuclear
explosive package are in the high energy density (HED) state. This requires that proficiency in HED science remains a coretechnical competency for the Nation’s Stockpile Stewardship Program (SSP) for the foreseeable future.
It calls for a review of the overall effort on ignition:. . . the HED program in the United States is at an important juncture where we must assess the appropriate balance between
pursuit of ignition and the other uses of HED research in stewardship.
. . . the pursuit of fusion yield in the laboratory, is critical for the long term health of the stockpile stewardship program.
It identifies specific goals for the ICF and HED scientific programs:
In the absence of new nuclear tests and the attrition of nuclear test experience, looking forward the nuclear weapons laboratories
will need the ability to (1) test nuclear designers in high energy density (HED) experimental design, (2) access material pressureand density regimes that are presently inaccessible to other experimental techniques, (3) generate and utilize thermonuclear
burning plasmas, (4) develop commensurate high-fidelity diagnostics and experimental platforms that help to assure ourweapons are safe, secure, and effective, and ultimately, (5) create and apply multi-mega joule fusion yields to enable enduring
stockpile stewardship.
Finally, the letter calls for “regular meetings in 2015 to ensure progress towards this integrated and coordinated HED effort . . .”IgnitionWith the conclusion, in 2012, of the scientific campaign to produce ignition, the trend has been to increase the proportion of NIF
shots devoted to non-ignition weapons physics experiments. This is an important development because much can be learned
about weapons physics at NIF absent ignition. It also provides an opportunity to increase the number of shots that can beallocated to training young designers. At the same time, pursuit of ignition remains important to stockpile stewardship for several
reasons:••

If we don’t achieve ignition conditions in capsule implosions, we need to understand why so we can adjust the weapons
codes accordingly.
If ignition is achieved, our understanding of weapons physics (e.g. secondary performance) will be further advanced by
the study of how variations in capsule design and initial drive conditions affect performance. Hardening/vulnerability

4

Letter to Frank Klotz, NNSA Administrator, from Charles McMillan (LANL), William Goldstein (LLNL), and Paul
Hommert (Sandia), 20 January 2015.

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assessments of military hardware will benefit from the intense neutron environments produced from burning DT
plasmas.
•Achieving ignition in the laboratory—arguably one of the preeminent scientific challenges of our time—would represent
an extraordinary demonstration of U.S. excellence in science and technology related to nuclear weapons. As such, itwould augment an important component of our overall capabilities to assure allies and deter potential adversaries.
•
Some of the excellent young scientists and engineers who are drawn to state-of-the-art HED facilities to work on ignition
will at some point in their careers move to nuclear weapons design work.
All this argues for continued strong effort on ignition but at what level? In recent years, the number of NIF shots devoted toignition on an annual basis dropped from about 90% to about 50% of total shots. Weapons-related non-ignition shots have taken
up the slack. This overall trend is desirable and, indeed, somewhat overdue. The details of shot allocation, however, can best be
addressed by the technical community with clear guidance from NNSA that the needs and priorities of stockpile stewardship are
to be the principal driver in shot allocation.
Long-Term Direction
NIF weapons physics experiments, supplemented with related work carried out at Omega and Z, have contributed to resolving
some of the scientific puzzles (e.g. energy balance) discovered, but not explained, during the days of underground nuclear testing.
There is reasonably wide agreement within the weapons community that the next “grand challenge” for HED physics research,and one that does not require ignition to achieve significantly increased understanding, is in boost physics. Remaining challenges
involve more precise understanding of plutonium EOS, secondary performance and weapons output. These can be addressed inparallel with lower priority.
Although there has been significant progress in Sandia’s work at Z, another key focus for future work must be on source
development for exposing military hardware to intense X-ray (both hot and cold) and neutron environments.
The Laboratory Directors’ letter rightfully calls attention to “avoiding technological surprise” as a key mission driver for NNSA.
Indeed, we must ensure that the U.S. nuclear weapons enterprise, and the security it provides, is resilient to unforeseen adverse
contingencies whether geopolitical or technical in nature. In our “deep dive” meetings at the laboratories, we (certainly I) did
not hear a clear articulation of how a balanced HED program contributes specifically to avoiding surprise. Of course, maintaining
the capabilities of scientific and technical personnel, the experimental tools, and manufacturing infrastructure—if directed by the
President—to develop and field modern warheads or warheads with new or different military capabilities is an importantcomponent of hedging against surprise. But it would benefit this program, by broadening support for it in the DoD and Congress,
to develop the story for how the results from HED experiments specifically contributes to avoiding surprise.
Establish Coordinated National Roadmap/Decisions Making/Metrics for Progress
Finally, the letter calls for further meetings in 2015 to scope out a balanced national HED program. When several of us asked forwhat had been done on this (i.e. as of July 2015), the answer in essence was “not much so far.” A ramp up in this activity seems
needed.
Important Role for Omega and NRL
Work at the University of Rochester (Omega) and the NRL provide important contributions to the nation’s ICF/HED program.
These facilities are smaller and cheaper to operate and therefore provide efficient means to develop experimental platforms,
associated diagnostics, and target fabrication to support the work of larger facilities. Training benefits because graduate students
at the U of R have opportunities to take a greater role than they could at NIF, for example, in developing and fielding experiments.
Both labs are involved with innovative approaches (e.g., direct drive, hybrid drive) that could hedge against failure of otherapproaches. The NRL, as a source of expertise within the DoD, can help convey the importance of HED physics for stockpile
stewardship to other parts of DoD—often a harder sell for the DOE folks. Finally, these two centers of HED expertise provide animportant means for independent peer review.

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Recommendations:•

The pursuit of ignition is important for weapons. We must therefore (as I sometimes do!) avoid characterizing HED
experiments as either “ignition” or “weapons-related non-ignition.” To best advance weapons program interests, thefocus of future ignition work (as it seemingly was not during the ignition campaign) must be to understand why thefundamental physics embedded in the codes has so far not aligned with Mother Nature.
•
A “national HED effort” must focus on the needs and priorities of stockpile stewardship. It can best be achieved with aninclusive process in which weapons program leaders from all three NNSA facilities and the NRL create a program thatleverages each other’s work and identifies a proposed associated resource allocation within an overall total budget levelprovided by NNSA.
•
In line with the Lab Directors’ letter, ramp up activities/meetings in the second half of 2015 in advancing a national HED
program.
•
Articulate (in a monograph. or equivalent. written for the layman) how a balanced HED program and associatedexperiments can provide a hedge against technological and geopolitical surprise.
•
In advancing a national program at the NNSA facilities and NRL, invest in a broad range of ideas involving both direct andindirect drive as well as innovative capsule designs (e.g., metal capsules, double-shell designs, etc.)
III. High Yield (multi-Mega joule) for Stockpile Stewardship
Previous discussion has addressed the benefits for stockpile stewardship of achieving ignition in the laboratory (e.g., gains in therange of 1-10) and the relative balance between ignition and non-ignition weapons-related experiments. The question here is
the relative degree to which ignition experiments and associated platforms that achieve very high gain (hundreds of MJ) areessential, desirable but not essential, or not that important at all for stewardship. Of course, achieving ignition and burn at theselevels has important implications for the nation’s long-term energy future, for example, or in the national security arena in regard
understanding the potential for advanced new types of nuclear weapons. In regard to today’s stockpile stewardship needs, theprincipal benefit would seem to be in providing an intense source of radiation with an appropriate spectrum to support precise
assessments of the hardness and vulnerability of military hardware as well as to validate nuclear effects codes. It is unclear tome the degree to which very high-gain experiments would provide a more complete understanding of the grand challenges ofboost physics and secondary performance. In any case, once ignition is achieved work should continue to reach high gain.
Increased funding for such experiments, outside the weapons program, might well follow. Until ignition is achieved, however,there does not seem to be much justification for allocating substantial funding to plan for such experiments.
Recommendation: Maintain planning for high-gain experiments, and associated platforms, at a relatively modest level pendingachievement of ignition.

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Reviewer Report: Jeffrey P. Quintenz
The primary charge is an assessment of the alignment of the ICF/HED program with stockpile stewardship program and thebroader nuclear weapons program. Assess the contribution to stockpile stewardship in the non-ignition HED sciences in thenear, medium, and long term.
Given that the overwhelming majority of the yield of a nuclear weapon is generated when the conditions within the nuclear
explosive package are in the High Energy Density (HED) state 5, HED science and understanding are unquestionably critical elementsof the nuclear weapons program. From its inception, the Inertial Confinement Fusion (ICF) program has advanced ourunderstanding of nuclear weapons; indirectly at first and more directly in recent years. ICF research places significant challenges toour understanding of fundamental physics of relevance to a nuclear weapon. For example, data obtained on ICF facilities havemeasurably improved tables for opacity and equation of state in relevant materials and conditions. In my opinion, the alignmentof the ICF program with the broader weapons program has always been there but has markedly improved since the completion of
the National Ignition Campaign (NIC). The balance between dedicated experiments primarily exploring specific issues related toignition and experiments more broadly addressing weapons physics and engineering has shifted with roughly 50% weapon centric
at the National Ignition Facility (NIF) and a greater percentage at Z. In my opinion this is about the right mix, though as the needfor higher yield becomes more apparent, I believe that more effort should be placed on exploring the limits of fusion yield using
magnetic drive and below I have included a recommendation to that effect. The Z effort on ignition and yield seems suboptimal
though the split in utilization (ignition/ICF vs. direct weapons work) is appropriate. More ICF effort on Z would likely require more
operational funding or offloading some materials work as discussed later in this report.
In the past, ICF facilities, and data obtained thereon, have contributed to a better understanding of nuclear weapons. Specificexamples include the energy balance question and properties of relevant materials at extreme conditions of temperature, density,and pressure. In the near term, data from these experiments will be used to further improve understanding of opacity, equationof state, various coupled radiation/hydrodynamic instabilities, and other properties of matter under conditions relevant to nuclear
weapon operation. These data and improved understanding are being incorporated in numerical simulation codes and provide abasis for improved confidence in their predictions. In the longer term, ICF should produce a burning plasma allowing for the firsttime the study of these conditions in a laboratory environment with precision diagnostics and providing further insight into boost
physics. A high yield facility would allow new capability that has long been recognized as opening unprecedented opportunity to
study aspects of weapon physics not available short of resumption of underground nuclear testing. More about this history andthe requirements for high yield are referenced in the classified appendix to this report.
I.

In their January 20, 2015 letter, the laboratory director’s described several specific multi-decade goals for the ICF/HED
program within the context of the broader stockpile stewardship program. Assess both the scientific and programmatic
progress – and plans – in today’s ICF program to meet those goals.
The laboratory directors expressed their strong support for an enduring program to maintain proficiency in HED science, “a coretechnical competency for the Nation’s Stockpile Stewardship Program (SSP)”. The letter is short on specifics regarding multi-decadegoals but in broad brush terms they expressed the needed ability to test nuclear designers in HED experimental design, accessmaterial pressure and density regimes that are presently inaccessible to other experimental techniques, generate and utilize
thermonuclear burning plasmas, develop diagnostics and platforms, and create and apply multi-megajoule fusion yields. Progresshas been made in each of these areas but significant challenges remain ahead. For example, we have yet to achieve the alphaheating goal on the NIF (though we are very close to the 1016 neutron goal). A careful facility and laboratory inclusive study
identified several transformational diagnostics that were needed to continue to advance our understanding of the HED
environments produced on these facilities. We are short of ignition, the predecessor to robust burning plasma platform, and nocurrent facility can credibly be predicted to reach the multi-megajoule yields as indicated in the director’s letter.
The directors expressed their “view that the U.S. must continue to strive to be the first nation to demonstrate ignition and highyield in the laboratory” to both support the SSP “but also to send a strong signal to others regarding our Nation’s scientific andtechnical capabilities”. In my opinion, the U.S. remains far ahead of the rest of the world in creating and utilizing HED platforms.
It is unlikely that any nation will soon duplicate the capabilities of NIF or Z. Even the French, with their significant investment in
Laser Mègajoule (LMJ), are several years away from full design operation. The Chinese and Russians have announced plans to build
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substantial HED facilities but, in particular for the Russians, these plans have been around for more than a decade with little evident
progress. The Chinese are reported to be building a Z-like machine based largely upon published Z material. I am not aware of any
recent results from the Chinese but close attention to their progress would be prudent as I expect they could move faster than the
Russians in this area even though Russian scientists have been quite innovative in fast pulsed power research and design.
In commenting on the progress toward the goals laid out in the director’s letter I would first acknowledge the work being done byGroup 1 and Group 3. Progress made toward ignition and go forward plans in continuing to “strive to be the first nation todemonstrate ignition and high yield in the laboratory” are the purview of Group 1. Group 3 will likely include some discussion ofpresent diagnostic capabilities and needed improvements in that area. For HED science as required by and applied to the SSP more
directly, I suggest that progress has been substantial and has recently accelerated. Sandia has been increasing the utilization of Z
fraction from ICF to more directly relevant weapons work for many years to good effect. After the end of the National Ignition
Campaign (NIC), the effort on NIF has also shifted with approximately 50% of the experimental time devoted to HED Council defined
experiments. The HED Council has been a welcome influence on the direction of research on the ICF/HED facilities. The Council has
expanded participation in experiment planning and prioritization and has made a concerted effort to direct experiments to themost appropriate facilities without the past institutional biases.
Funding for the ICF program has come almost entirely from the weapons program. From its inception, the quest for ignition andhigh yield has been justified by applications to weapons science. This justification has been repeatedly documented in classified
and unclassified venues. ICF presents a significant scientific challenge with many aspects directly related to understanding neededby weapons designers. The significant investments made to construct the world leading HED facilities are paying dividends on
multiple fronts. Conditions of pressure, temperature and density heretofore unavailable in the laboratory are now routinely
produced and exquisitely diagnosed. New data on opacity, EOS, radiation flow, etc. are being used to challenge our understanding
and weapons code predictions. There are many examples that can be found in the references at the end of this report. In large partdue to the available facilities and challenging work, the ICF program has been a main attractor to the laboratories of new stewards.
This program provides the weapon stewards with new tools to test their ideas. The laboratories did express concern that thepipeline of university students was at risk due to the loss, or potential loss, of several professors who have a good track record of
supplying students with the desired background for work on nuclear weapons. They also stated that with the smaller pool ofgraduating students, there is at times unhealthy competition for these students between the laboratories. NNSA should address
this concern soon given the time required to educate a future steward [see recommendation below].
In short, many of the promises of a sustained investment in ICF/HED have already been realized even without the achievement of
ignition and gain.
The formal title of the ICF Program is “Inertial Confinement Fusion and High Yield.” “High-yield” at laboratory scale ismore than a decade away, but having this ultimate goal shapes program decisions many years in advance of theirperceived need. Assess the need of “high-yield” capabilities at laboratory scale as a long term goal of the ICF/HED
program given evolving nuclear threats, and the overarching boundary condition of no additional nuclear testing.
High yield has been an ICF objective from the very beginning of the program. Even while underground nuclear testing was ongoing,
nuclear explosive package and non-nuclear weapon component designers alike recognized the utility of a laboratory facility that
could produce significant fusion yield. “High” is a relative term and there are likely differences of opinion about what constitutes
high yield. A report written in the early 1990s and reinforced during this review suggested that several 10s of Megajoule fusion
yield were required for some interesting applications 6. Designers have proposed experiments that would be enabled at successive
increases in yield. All proposed experiments would provide data that could be used to further understanding, improve codes, andtest designer’s skills and judgments. The two NEP design laboratories each have listed underground nuclear tests (UGT) they would
propose should that testing be allowed. It is highly unlikely that any UGT will be forthcoming, so the question to be answered is
how is the current HED/ICF program effort being directed to improve understanding, reduce uncertainty, and increase confidence
in our deterrent? The program of work as defined by the HED Council and coordinated with the ICF program leadership is, in myopinion, doing a very good job of prioritizing the work to be done. The Council helps to identify and prioritize research needed tosupport the NSE objectives and in large part is the source of input to define the SSMP goals and milestones. There is much workthat can be done on existing facilities and that work could realistically be expected to last for many years. Designers are clever andII.

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will propose many different and important experiments to be done on these facilities. The HED Council has a formal process to sort
through the proposals and define the plan to execute. I am encouraged that the HED Council and the newly formed ICF Council arecoordinating efforts on these shared facilities. By identifying the opportunities for improved understanding, determining priorities
and appropriate timeframes, and setting realistic goals, the Council adds significant value to NNSA program management. When
asked what yield is needed, the designers will almost always answer that nothing they don’t already have access to is needed toassess the current stockpile. They will also say, however, that more yield is better.
It is important to recognize that even after ignition is achieved, yield of a few megajoules will be needed to provide the robust
ignition platform required to perform desired experiments in this low yield regime. Robust in this context implies yield sufficiently
beyond the “ignition cliff” to distinguish between the physics of interest and the physics of ignition. Near the cliff, capsule
performance can vary widely as small changes or accumulated errors can dud an implosion or confuse the desired physics data.
Robust also implies reproducibility. It is likely that more yield will also require more margin. More margin will likely result in morepredictable yields and better reproducibility.
I. Alignment of ICF/HED program with SSP and broader weapons program
Workforce Development
Findings: The laboratories expressed concern that the pipeline of university students was at risk due to the loss, or potential loss,of several professors who have a good track record of supplying students with the desired background for work on nuclear
weapons. They also stated that with the smaller pool of graduating students there is, at times, unhealthy competition for thesestudents between the laboratories.
Comments: Given the time required to educate a future steward (7-10 years post graduation), there is the potential for an
unfavorable change in demographics at the laboratories if not corrected soon. In the past, due to the vagaries of hiring freezes
and bad publicity, reductions in the number of staff with certain years of experience have been created and these “holes” in theexperience distribution tend to propagate over the course of time. While budgets and bad publicity can’t be reliability predicted,
it is certain that a lack of qualified students in relevant fields will create future “holes” if not addressed.
Recommendations: NNSA should address this concern soon by establishing metrics to quantify and track the problem and byincentivizing new faculty and students to enter the relevant fields of study. This may require rebalancing funding within HED and
ICF programs. bv
Findings: The challenge presented by ICF attracts and helps to retain highly competent staff who can and often do contributedirectly to stockpile stewardship. Potential loss of future talent is a threat to the entire NSE and demands action.
Recommendations: NNSA, not solely NA-11, should identify additional funds for university research and target those funds
toward developing new professors and their students. Funding decisions must be based upon data. NA-11 should lead in thedevelopment and tracking of these metrics.
Findings: The HED facilities provided by the ICF program are critical instruments used in the training and testing of new stewards
in the SSP. All three NNSA laboratories recognized the importance of ICF/HED experiments in training new staff and keeping moremature staff current.
Comments: LLNL and SNL were more explicit in their statements about training using ICF facilities but LANL talked to the value of
testing designer judgment using these complex experiments and having to “think in an integrated way” with emphasis on
interfaces throughout the process. In May, the LANL representative was asked how much HED instruction was included in the
TITANS program and he answered “probably not enough”. When pressed later during the LANL deep dive session, the answer
was refined to state that there is no specific HED module in the TITANS program and, given that it is more aimed at broader
issues, it would not be appropriate. For example, there is no module dedicated to DARHT experimental capability either.
Recommendations: Since the DPAC is focusing its first study on Workforce and several other recent studies external to NNSA are
making recommendations in this area, I would only add that the ICF/HED programs should take seriously the recommendations

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from these studies. NNSA should compile a list of recommendations from the various recent studies, evaluate its performance,
and implement changes as warranted. NA-112 and NA-113 could jointly develop a report that highlights the workforce
development attributes of ICF/HED. This report could include a description of the various university and mentorship programs
sponsored in whole or in part by NA-11.
Findings: All three NNSA laboratories commented upon emerging threats and the need to be responsive.
Comments: No detail was presented but the need for highly trained, competent and experienced scientists and engineers toquickly address an emergent threat cannot be overstated. HED/ICF is, and will continue to be, a key asset in this area.
Recommendations: It is recognized by most that attracting and retaining skilled talent in the weapons program is an imperative
to our National deterrent. Staff within the HED/ICF programs are well equipped to address many of the questions that arise as
new technologies are developed or new threats arise. These programs should retain the flexibility to assign personnel to joint
projects with other NNSA organizations as the need arises. The flexibility could include rebalancing program budgets andschedules. These efforts to prevent technological surprise and address emerging threats have proven to offer excellent straining
opportunities for weapon stewards
Findings: Concern was expressed that we are turning engineers/scientists into analysts.
Comments: Analyzing past UGT data will eventually run its course. Engineers and scientists need the challenge of “white sheet”
design to practice innovation and to exercise the myriad of interfaces between design, prediction, manufacture, execution,
analysis,… The inherent complexity of experiments conducted on ICF facilities requires exercising many aspects of “white sheet”
design. Hypotheses are developed, pre-shot simulations performed, targets manufactured, diagnostics employed, and data
analyzed to support or refute the hypotheses. With the exception of hydrodynamic experiments, these HED/ICF experiments may
be the closest thing we have available to exercising and testing designer Skills, Knowledge, and Abilities (SKA).
Recommendations: The ICF/HED programs use of the ICF facilities is, for the most part, appropriately balanced between pursuitsof ignition/fusion and non-fusion applications. The main exception in my opinion is that more fusion directed work should bedone on Z. A suggestion about how to accomplish this is found in a later recommendation. Given that the balance is about right,
I would not recommend a change to the process that has successfully arrived at the balance. The HED and ICF Councils together
with NNSA and laboratory leaderships have found a management approach that seems to work. The non-fusion activities advanceunderstanding in weapons relevant areas and/or contribute to fundamental science that can be an attractor for future stewards.
All of the above activities help to maintain or advance designer SKA. In the days of UGT, there was significant pre-work done
above ground before the experiment was ready to go down hole. Peer review, diagnostics development, calibration, experimental
planning, etc. An experiment on NIF or Z has many of the same elements. A good example is a cryogenic capsule experiment on
NIF. In order to maximize the opportunities for innovation and “white sheet” design, NNSA must continue to support breadth in
the program and encourage the exploration of new ideas.
Findings: LLE provides a unique opportunity for steward development.
Comments: Because of its university affiliation and the Omega facility, LLE is able to attract and help train current and futurestewards in the weapons program. LLE has a long and proven record of educating students who have later gone on to become
valuable contributors to the SSP. Omega also provides a cost effective test bed for proposed experiments and diagnostics on NIF
and Z. Through the laboratory basic science program, LLE provides the nuclear weapons laboratories scientists time to do nonprogrammatic research which in turn acts as an attractor to and helps to retain these staff at the NNSA laboratories.
Recommendations: Given the stress on other university participation in developing future stewards, NNSA should continue astrong relationship with LLE and encourage laboratory staff engagement in experimental research on Omega. Sabbaticals mightmake sense to strengthen the ties.
Program Management

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Findings: The HED Council is the model for laboratory direction setting and prioritization in this field. It is referenced as the model
to be followed by the ICF Council and the Subcritical Experiments Council. The HED Council, together with NNSA, have constructeda robust program management system that aligns program activities with the larger goals and objectives of the SSMP.
Comments: The HED Council is working well. The ICF Council is in definition and its value is yet to be realized. The Councils,
working with NNSA, have balanced the experimental efforts on the ICF facilities and at present that balance appears to beappropriate to make reasonable progress on the various SSMP objectives.
Recommendations: NNSA should assess the evolution of the ICF Council in comparison to the model of the HED Council. Due tothe facility centric nature of the three ICF approaches, the ICF Council will likely have much less impact upon program direction
than the HED Council has had on HED science. In my opinion, to this point in time, the ICF Council has not worked at the required
level of detail to make recommendations for or reach consensus on research paths that go beyond very generic questions. For
example, LLE is unlikely to advise SNL on the next best MagLIF experiment to conduct on Z. I do not recommend forcing the ICF
program into the mold of the HED program. They have different organizing principles. An exception to this observation is thegood work done to arrive at consensus on the National Diagnostic Plan. As long as the balance between and within the ICF and
HED efforts remains consistent with NNSA overall program priorities, and I believe that they are today, NNSA should assume aconcurrence role in reference to Council recommendations. The required balance changes with time and judgement must be
regularly applied. It is difficult to be quantitative about the right balance but it was very clear that during the waning days of the
NIC, the balance of activities on NIF was too heavily toward ignition with little room for non-ignition SSP experiments. (You willknow it when you see it.) NNSA ultimately has the accountability for overall program performance and has the authority to nonconcur should that be needed.
Findings: There is no common view about the ICF Council role nor the advisability of combining the ICF and HED Councils.
Comments: The ICF program is organized along three approaches to fusion and these are highly facility (NIF, Omega, Z) specific.
The HED program in contrast is organized along PRDs and is largely facility agnostic. Both programs make heavy use of the ICF
facilities so there is some discussion about combining the two Councils. Some are of the opinion that the ICF Council adds novalue when it comes to prioritizing experiments. If there is common understanding between the laboratories and NNSA about
the respective roles of each Council, it was not apparent during the review. (The answer to a similar question about the need to,or value of, combining NA-112 and NA-113 to better coordinate efforts was unanimous that there was no need to combine theorganizations and, in fact, it could be detrimental to the overall effort.)
Recommendations: NNSA should work with the laboratories to revisit the ICF Council charter and to gain a common
understanding of its role and value. Decide if the HED and ICF Councils are duplicative efforts and, if so, combine. If not, thenmore clarity in the ICF Council charter, roles and responsibilities is warranted.
Findings: Tremendous value was derived from the May 2012 review of the ignition program at NIF, the June 2014 HED workshop,
and the more focused review of NIF experiments and plans in August of 2014. The progression toward more community
involvement and openness was evident with each new event.
Comments: The value of these events was enhanced by the organizers who invited a wide range of expertise, set high goals forthe events, made a record of the conclusions and discussion and reported out the results afterwards.
Recommendations: NNSA should, as currently planned, periodically sponsor similar events. A workshop on progress towardignition that addresses all three ICF approaches is in planning. A workshop on approaches to high yield would make sense soon
as well.
Findings: Progress in evaluating the magnetic drive approach to ICF has been slowed due to the high demand for materials workon Z and the lowered ICF budgets at Sandia.
Comments: Sandia has suggested that much of the materials work could be offloaded from Z to a dedicated and specificallydesigned accelerator and that would allow a doubling of the ICF effort on Z in addition to reducing the risk of damage to the Z2015 Review of Inertial Confinement Fusion and High Energy Density Science Portfolio

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order to help plan for a high-yield future, the magnetic drive approach needs to be evaluated at a faster pace.
Recommendations: NNSA should establish an independent review of Sandia’s proposal. If the review substantiates Sandia’s
expectations for the new accelerator and the claim that the fusion effort could be doubled, then NNSA should fund thisinvestment. A major application of this facility would be driven by the NA-80 Counterterrorism and Counterproliferation program.
NA-11 should explore the possibility of a partnership with NA-80 and possibly AWE. For example, shared development andoperating costs and possibly the construction of two accelerators (one for SNL and one for AWE).
Findings: The cost of change of station is prohibitive and presents a barrier to program integration.
Comments: Encouraging broad cross-laboratory participation in experiments on ICF facilities is in the best interest of the ICF/HED
programs. These are complex facilities and considerable time is invested in successfully executing each experimental series. LANL
described the issue of utilizing NIF effectively. They believe that a change of station, especially an on-site engineer, is very helpful
but the rules for those assignments make them unattractive. It seems that the rule makers are being penny wise and pound
foolish given the goals of the program and the expensive facilities being utilized. Encouraging is the fact that LANL has grown its
NIF experimental effort through the HED Council from 6 to 40 shots recently in spite of this difficulty.
Recommendations: NNSA should revisit this issue in light of the barriers this rule poses to collaboration and utilization of thesefacilities. If the rules originate within NNSA, they should be rewritten. If the rules are driven by forces outside NNSA, NNSA must
be the advocate for change.
Findings: The budget level in HED/ICF is impeding the rate of progress.
Comments: Budget issues were common throughout this review. LANL suggested that their budget was insufficient to sustain
HED but followed with a suggestion that ASC should fund some of their HED code development work that is presently funded by
the ICF/HED program. Sandia would like more ICF experimental time on Z and suggested that it could be accomplished byoffloading materials work to a new accelerator (cost TBD). NRL said their budget was below their requirements case but that
requirement has been reduced from a 2011 level of $12M to $9M today. To my recollection, LLNL and LLE were silent on budget
issues.
Recommendations: NNSA should continue to enhance coordination between the HED/ICF efforts and the ASC program. A major
objective of the SSMP is the improvement and validation of nuclear weapon simulation codes. Several components required inthis code development and validation effort (HED, ICF and ASC) fall within the purview of NA-11. NA-11 has the ability to address
the LANL recommendation if needed and should take an active role in determining the appropriate balance. As NA-80 requests
more time on ICF facilities, NNSA should look to that program to help support the operational costs.
II. Planning associated with tri-lab Director’s letter
Long-Term Direction
Findings: The laboratory director’s letter is a strong statement of the need to sustain world leadership in HED science. Further,
the letter reaffirms the need for continued development of the science of HED/ICF and the pursuit of ignition and high yield.
Comments: The letter is long on vision and short on specifics but that is to be expected. It is encouraging that the three NNSA
laboratories found common ground and pledged to work together towards an “integrated and coordinated National HED effort”.
The HED Council has gone a long way to defining that effort where HED science is concerned. The ICF effort is not as far along
and needs some emphasis at this point. It is not clear to me that the ICF Council can provide that emphasis alone and NNSA may
need a stronger hand at this point.
Recommendations: NNSA should establish a regular forum to report on and monitor progress toward the “integrated andcoordinated “effort promised in the director’s letter. NNSA should drive the ICF Council to establish roles, responsibilities,
authorities and accountabilities that are acceptable to all elements of the program or should decide that this Council does not
fulfil a need and put its efforts elsewhere.

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Findings: HED/ICF experiments are advancing the Nation’s test readiness posture.
Comments: There is significant overlap in the skills associated with conducting complex, highly integrated, and expensive
experiments on the ICF facilities and those needed to conduct a nuclear test. Specifics include diagnostic development andfielding and managing many different interfaces through design, fielding and analysis. As long as maintaining the capability totest remains a National imperative, these HED/ICF experiments will help to demonstrate that capability.
Recommendations: NNSA should direct its laboratories to develop a report to document the skills overlaps between ICF/HED
experimentation and UGT. This does not need to be a long report but would be useful to have in response to inquiries on this
topic.
III. High Yield for SSP
Applications of Yield
Findings: The value of a laboratory high yield capability was recognized very early on in the ICF program history and has repeatedly
been affirmed as a worthy goal that would be put to very good use should it be available for weapons experiments.
Comments: The difficulty of maintaining Congressional support during the construction of NIF and continuing through the ignition
effort, caused some to lose track of the initial goal for the program to provide high yield (several 10s of Megajoule). The unstatedargument was that defining a capability need beyond what NIF could reasonably be expected to provide would be fatal to theproject. Why build NIF when we need something bigger? NIF and ignition were initially recognized to be a necessary step toward
high yield but, in part because of the difficulty of achieving ignition, the high yield goal suffered from diminished visibility. One
senior program leader even stated that “there never was a requirement for high yield”. I am encouraged that NNSA is once again
seriously considering the ultimate goal of its ICF program. Certainly high yield is decades away and necessarily follows
demonstration of ignition but there is no existing facility (or approach, short of a nuclear weapon) that can credibly promise highyield today.
Recommendations: NNSA and its laboratories should acknowledge the ultimate ICF goal of high yield in the laboratory and thenecessary first step of ignition. In my opinion, serious consideration should be given toward determining a conceptual design for
the next ICF facility and what physics and engineering uncertainties need to be addressed before any decision to begin the processof justification or design. The goal would be to establish a research path beyond the existing capabilities and create the next big
vision for the NNSA RD&T HED experimental program.

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B.3
Group 3 Reviewer Reports
Reviewer Report: Sean M. Finnegan
I. Underlying physics understanding and integration.
EOS
Findings: High pressure equation of state (EOS) microphysics is a frontier scientific endeavor. Experimental tools like the NIF are
producing conditions within materials that only naturally exist at the cores of astrophysical objects and thus have never before
been studied in the laboratory. Similarly, facilities such as the LCLS and APS are providing the opportunity to diagnose theevolution of materials as they transition through phases with a level of precision capable of distinguishing between our mostadvanced theoretical models. Researchers are taking full advantage of the emergence of these capabilities to generate
experimental data capable of constraining EOS models for use in ICF codes.
It is clear that the development of high quality, phase-aware, EOS which is self-consistent with both structure and strength andits implementation into global models such that phase transitions including solid-solid transitions and refreezing are accurately
captured will challenge researchers for decades to come.
While it was not necessarily discussed explicitly during the review, high pressure EOS studies are also relevant to researchers
studying the formation of planetary cores. This broader application beyond ICF will generate opportunities to engage withresearchers outside of the field of ICF which could pay significant dividends in terms of broadening the number of program stakeholders.
Comments: The physics underlying high pressure material equation of states (EOS) is fundamental to the field of HEDP and its
application to ICF. Like every aspect of HED and ICF science, resolved measurements of microphysics, capable of distinguishing
between theoretical models, will advance the field toward the development of a truly predictive capability.
Recommendations: The NNSA HED/ICF program is encouraged to:•••Continue to utilize all available experimental platforms (including cross-platform comparisons), and potentially develop
new complimentary platforms and diagnostics, to directly validate micro-physics.
Develop and field diagnostics capable of directly measuring temperature.
Continue to develop and validate new techniques.

Opacity and transport
Findings: Regarding opacity research, there appears to be a clear understanding within the research community as to where thesignificant challenges/opportunities exist for progress in advancing our understanding of underlying physics in the coming decade.
This seems to be true for both LTE and non-LTE environments. Additionally, researchers are making excellent use of multiple
experimental platforms both within the NNSA portfolio (e.g. Z, NIF, OMEGA) and more broadly in the DOE portfolio (e.g. LCLS) to
test theoretical models and predictive capability. Excitingly, experimental data from the Z machine at Sandia are bothdemonstrating excellent agreement with models of some materials (e.g. Ni) and striking disagreement for other materials (e.g.
Fe). Such discrepancies between observations and theoretical models are clear opportunities to advance our understanding.
Perhaps the single biggest concern in the area of opacity is the diminishing availability of scientists trained in the field of hightemperature (high energy density) atomic physics and spectroscopy. If left unaddressed, loss of such expertise stands toeventually erode the NNSA’s core competency in this area.
As with opacity research, scientists studying transport (electric, thermal, radiation, particle, etc.) in HED/ICF systems are making
excellent use of a wide variety of experimental facilities both within the NNSA portfolio and more broadly (e.g. LCLS, ALS, etc).
Quit surprisingly though, there is limited experimental data in ICF relevant regimes, though this appears to finally be changing. It
will be exciting to see how precision measurements on world-class facilities challenge the state of the art micro-physics modeling(e.g. DFT-MD, Purgatorio, etc.).

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Comments: Like EOS, both opacity and transport studies are foundational to the field of high energy density physics particularly
as they underpin our ability to model and make predictions about ICF system performance. The availability of facilities like NIF,
Z, LCLS, etc. along with the continued development of high performance computing platforms are enabling scientists to challenge
our understanding of micro-physics and atomic processes in extreme states of matter with unprecedented precision andresolution.
Recommendations: The NNSA HED/ICF program is encouraged to:••

Evaluate the developing workforce situation concerning the availability of scientists trained in HED atomic physics andspectroscopy. If it is determined that the situation is at a tipping point, the NNSA should consider creating a center of
excellence in HED atomic physics that engages in HED research as it pertains to both ICF and astrophysical systems. This
could serve as a natural way of tapping into the much larger field of observational astronomy/astrophysics. Such a
coupling could significantly improve workforce availability in this area and introduce new innovations into the program.
Continue to utilize all available experimental platforms (including cross-platform comparisons), and potentially develop
new platforms, to resolve outstanding problems in both opacity and transport studies.

Hydro and burn physics
Findings: It is difficult for me to determine if uncertainties in predicting the growth of hydrodynamic instabilities (RT, RM, or KH
at low or high mode number) in ICF experiments stems from gaps in our underlying understanding of these instabilities or rather
from gaps in our fundamental knowledge of the particular material EOS, transport, or simply the inability to accurately assess thefull impact of the driver in altering the initial conditions on (and in) the target (e.g. CBET, hot electron pre-heat, etc.). In ICF, it
seems to me to be driven more by the latter rather than the former and as such those opportunities for improvement are
discussed in other sections.
There does, however, appear to be significant opportunity to advance our understanding of the evolution of these instabilities toa turbulent state and the resulting mixing of materials in the target. In recent years there is a growing body of data suggesting
the importance of kinetic processes, enabled largely by the nuclear diagnostics developed by the MIT group. Developing acomplete understating of such processes will challenge all three phases of research: experimental platform development,
diagnostics development, and the development of multi-scale modeling capabilities. In fact, the integration of kinetic or microphysics effects into the modeling of integrated systems in a self-consistent way is a grand challenge for the program and will push
the frontiers of high performance computing.
The importance of accurately capturing the complete hydrodynamic and kinetic behavior at all scales (including 3D flows andviscosity) in converging targets is highlighted by the fact that outputs from numerical simulations are routinely used to infer theproperties of imploded targets (e.g. hot spot temperature). In the absence of appropriate diagnostics, numerical modeling is ournext best option to understanding behavior of these systems and as such the multi-scale problem needs to be met head-on.
Comments: It is near impossible to understate the importance of hydrodynamic and burn physics to the HED/ICF program. It istherefore no surprise that the portfolio of research supported by the HED/ICF program has no equals and is unmatched inbreadth, depth, and standing. Many of the problems faced by the HED/ICF program in this area are also challenges for othercommunities (albeit in different geometries e.g. divergent as opposed to convergent systems) which may present an opportunity
to bring in new innovative ideas.
Recommendations: The NNSA HED/ICF program is encouraged to:•••

Explore introducing a “common” rad-hydro code, openly accessibly to the broader research community that will server
to reduce the barrier to entry for collaborating on research projects and designing experiments for the NIF. There would
be significant benefit to making the source code available for the community to develop and introduce new packages fortheir own purposes. In this way the code would become a living tool capable of growing and expanding with theresearch needs of the community in real-time.
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Global and driver physics
Findings: In many, if not most, HED/ICF experiments in the laboratory, the driver (often laser light) imprints itself on the responseof the target, in ways both intentional and unintentional, and as such the nature of that interaction often needs to be fully
characterized before the focus of the experiment can be completely understood. While this statement is seemingly obvious, thedisparate temporal and spatial scales associated with characterizing and understanding Laser Matter Interactions (LMI),
particularly when compared to hydrodynamic scales, makes this problem largely intractable. As a result this aspect of HED/ICF
physics is often oversimplified if not ignored entirely.
This seems to be particularly true for performance driven pursuits like the National Ignition Campaign. Rather than emphasizing
study and understanding of laser matter interactions (a process critical to the deposition and distribution of energy in thehohlraum), a strategy of avoidance and tolerance of deleterious instabilities was adopted. Again, this is understandable, to adegree, given the complexity of the problem. However, laser-plasma interactions are so fundamental to laser-driven ICF that thischallenging problem needs to be addressed head-on in a comprehensive way (i.e. dedicated experiments, new modeling tools,
and theory).
Lastly, it appears that the number of U.S.-trained research scientists working in the area laser-plasma interactions continues todiminish. This reality could present a problem in the future as it is unlikely that laser drivers will be replaced any time soon.
Comments: I specifically chose to focus my comments on laser-plasma interactions as it is potentially the most relevant andimportant element of driver physics with opportunities to improve our underlying understanding and to improve our physics
modeling. The reason is simple, most HED/ICF platforms supported by the HED/ICF program are laser driven and all threemainline efforts pursuing the achievement of ignition in the laboratory involve laser-plasma interactions. The subject is quite
simply unavoidable and tolerance may be unacceptable.
Recommendations: The NNSA HED/ICF program is encouraged to:••

Support research to understand the statistical, self-organizing nature of LPI at multiple scales in laser driven ICF systems
to place realistic bounds on mitigation strategies. This includes the development of new multi-scale kinetic modelingtools and dedicated experiments.
Engage the broader academic community. The absence of a diverse research community working on laser-plasmainteraction problems means that there is no community to peer-review the efforts of the national laboratories indeveloping strategies for mitigation or exploitation.

II. Partnerships with external entities
Community: codes
Findings: A potentially significant barrier to collaboration between researchers at the NNSA laboratories and scientists atuniversities, both domestic and international, is access to a common set of “codes” which are used to model laboratory
experiments. This is particularly true for radiation hydrodynamics codes. The rad-hydro modeling code of choice by researchersat the NNSA laboratories has increasingly become HYDRA. Export control however limits access to this tool, effectively
marginalizing researchers outside of the NNSA laboratories. Furthermore, pre-shot simulations are becoming increasingly
important in experiment design on the major facilities, particularly the NIF. As such, researchers who do not have access to codes
which are implicitly endorsed by the facilities are at a significant disadvantage in terms of experimental design and ultimately
being awarded shot time through a competitive proposal and peer review process.
Furthermore, integrated codes, such as HYDRA, are built upon sets of interconnected physics packages, the accuracy and validityof which often needs to be verified with well diagnosed single-physics (or as close to single-physics as possible) experiments.
Where possible, I believe that the university community is best positioned to deliver on this need, as the academic environment
incentivizes basic science.
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exercise caution when simulations are used to infer statistical properties of matter (e.g. temperature of the hot spot of an
imploded ICF capsule, temperature in hohlraum plasma) in experiments when no physical measurement is actually made. I fearthat this may lead to a false sense of confidence in our understanding of highly integrated systems and distract from the fact that
there is no substitute for actual measurements.
Lastly I would like to comment on the danger of running ever bigger calculations on increasingly more processors for the sake of“big science”. While I appreciate the public relations value that such calculations can yield as well as the potential to capture thefull 3-dimensional spatial nature of a problem, they also cost both significant time and money and the overabundance of
information which is generated can be immensely difficult to interpret or even provide a false sense of understanding. I therefore
encourage researchers to work “smarter” and not necessarily look toward the crutch of size, speed, and power. Bigger is notalways better.
Recommendations: The NNSA HED/ICF program is encouraged to:••

Explore introducing a “common” rad-hydro code, openly accessibly to the broader research community that will server
to reduce the barrier to entry for collaborating on research projects and designing experiments for the NIF. There would
be significant benefit to making the source code available for the community to develop and introduce new packages fortheir own purposes. In this way the code would become a living tool capable of growing and expanding with theresearch needs of the community in real-time.
Specifically, seek to engage the university community in the validation of physics packages in integrated codes, throughexperimentation and diagnostic development.

Community: Experiments
Findings: While the leadership-class machines like the NIF, Z, Omega, and Omega-EP are well supported and maintained, theenabling facilities like Trident and JLF appear to be eroding in their capabilities due to lack of budget priority. Facilities such asthese play an important role in the experimental “ecosystem” as the relative cost per shot and shot rates afford the opportunity
to test and vet high risk – high reward ideas and diagnostics before being fielded on the leader-ship class systems.
Support for a healthy “ecosystem” or hierarchy of machines is important to cost effectively maximizing scientific yield from thepremier facilities. At present the HED/ICF program supports a complete set of facilities which utilize lasers as the principle target
driver, with the National Ignition Facility as the crown jewel. However, the set of pulsed power machines is far from complete.
Unlike with laser systems, the hierarchy of pulsed power machines is incomplete as there is no intermediate scale machine to aid
in the development of ideas before they are fielded on the Z machine.
The health and vitality of the HED/ICF field is enabled by, and depends critically on, the programs experimental capabilities. More
importantly, the existence of a university community and their ability to meaningfully collaborate with and contribute to HED/ICF
research, including workforce development, depends critically on open access to the facilities supported by NNSA.
Comments: The HED/ICF program maintains a world-leading set of experimental facilities at multiple scales ranging from modest(e.g. Trident, Jupiter Laser Facility, Nevada Terawatt Facility, etc.) to massive (National Ignition Facility, Z machine). These facilities
continue to collectively push and expanded the frontier of discovery in HED and ICF science. Moreover, these facilities attract
many of the best and brightest researchers into the field as they offer the opportunity to study matter in the laboratory in a state
which has often never before been created on Earth and only naturally exists in astrophysical systems. Providing open
experimental access through a competitive peer review process is critical to capturing the full potential for discovery on thesefacilities. While only a limited amount of time is made available on these machines for open discovery-class science (i.e. nonprogram), each and every experiment represents tremendous value for the researcher, student, or partnering agency.
Recommendations: The NNSA HED/ICF program is encouraged to:••Continue to maintain and provide access to their world-class facilities at all scales through competitive, peer reviewed
selection processes.
Regularly engage the user groups of NNSA facilities to solicit feedback regarding operations procedures, facility needs,
and future diagnostics.

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P a g e | 87•Thoroughly evaluate the portfolio of laser facilities at the bottom of the “ecosystem” and consider possible reductions
or closures in order to support the most impactful facilities fully.
•
Consider developing an intermediate scale pulsed power system.
In addition to the above, the NNSA should explore partnering with other funding agencies to jointly develop or maintain facilities
at the small and intermediate scale where it is of significant mutual benefit. It is not clear that the NNSA can continue to bear
this burden alone.
Community: Collaborations
Findings: It is clear that the NNSA recognizes the value of collaborative partnerships to both problem solving through innovationand scientific discovery, as well as workforce development. The level of collaboration between the three NNSA laboratories
appears to have increased in recent years (since 2012), particularly in research areas of importance to the ICF program. While
there is still plenty of room for improvement, this is a significantly positive step forward for the program. In the absence of thelaboratories actively competing with each other to solve identical sets of problems, the best way to innovate and make progress
is for them to work collaboratively.
In addition to cross-laboratory collaboration, the HED/ICF program also supports collaborations between the national
laboratories and university researchers through grants programs, graduate student fellowships, and providing access to theworld-class experimental facilities operated by the program. Scientifically, the existing set of collaborations has been particularly
successful in developing new and innovative diagnostic tools which have proven critical to gaining deeper insights into the kinetic
physics behavior in ICF targets. Perhaps the greatest benefit to the HED/ICF program from collaborations between the national
laboratories and universities has been workforce development.
Regarding workforce development, the HED/ICF program continues to successfully use partnerships between the National
Laboratories and universities, both domestically and internationally, as a “pipeline” to train and recruit the next generation of
HED scientists. As stated previously, this is accomplished through maintaining grants programs, graduate student fellowships,
and providing access to NNSA operated experimental facilities. All three of these elements are essential to meeting the workforce
needs of the program, and should be maintained.
Lastly, it is important to maintain a vibrant community of researchers external to the national laboratories to serve not only as apool of potential collaborators, but also as a scientific system of checks and balances. The value of such an external community
was not capitalized upon during the National Ignition Campaign, and provided important insights after the fact through their
participation in the Science on Fusion Ignition Workshop (San Ramon, May 2012).
Comments: Diversity in collaborative partnerships encourages and fosters innovation and the development of creative solutions
to both near-term and long-term problems. This is true at all scales (micro: individual researcher, meso: institutional, and macro:federal agencies) and across scientific sub-fields. I see tremendous opportunity for the HED/ICF program to leverage their worldleading computational and experimental capabilities to not only maintain existing partnerships but to also establish new valueadded relationships at all levels to deliver on its mission. Without continued collaborative engagement with a diverse set ofpartners, the program is likely to see stagnation in innovation, discovery, and an inability to recruit and retain a workforce withthe talent necessary to accomplish the mission.
Recommendations: The NNSA HED/ICF program is encouraged to:•••

Maintain existing competitive grants programs, graduate fellowships, and access to experimental facilities by
researchers external to the NNSA national laboratories.
Promote diversity in the number of institutions (university, national laboratories, private companies) collaborating withNNSA laboratory researchers on solving fundamental HED and ICF science and technology (i.e. diagnostics, drivers, etc.)
problems.
Reward scientists at the laboratories for developing and fostering successful collaborations with researchers atuniversities and private companies by directly supporting their time an effort to engage in those activities. Positive
career development incentives will ensure that researchers actively seek out opportunities to collaborate.

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Reviewer Report: Yogendra M. Gupta
This report is organized in the following four parts: Overall Comments; HED Science; the ICF Program; and External
Partnerships. Please note that I am making a distinction between HED Science and the ICF program. To me, the former is ascientific endeavor while the latter has well defined goals that utilize the knowledge gained from the various HED scientificactivities.
I.

II.

Overall Comments
A. Observations
1.
The three NNSA Laboratories are interacting in a positive and synergistic manner. Despite theirdifferent approaches, they recognize that achieving ignition is an enormous scientific challenge. Healthy,
competitive/collaborative dialogues and interactions were evident.
2.
Although a significant amount of information was provided by the Laboratories about what they havebeen doing and are doing (in various write ups and in the presentations), I would like to have seena succinct listing of the important and foundational science needs/challenges that should be addressedto achieve ignition in the Laboratory. Perhaps, the enormity of the highly coupled, nonlinear
problem does not lend itself to succinct definitions of the different challenges.
3.
What states of matter does High Energy Density refer to? A better definition of HED states would be very
useful in discussing the relevant scientific issues and questions that need to be addressed.
4.
The linkage between fundamental science activities and the ICF Program needs was not obvious.
5.
The highly coupled (or integrated) nature of the physical phenomena “on the path to ignition” necessitates
the use of complex codes and raises the following question: how feasible is it to “untangle” the physicalphenomena of interest and examine them through a less integrated approach?
6.
The scientists involved in the ICF Program are extremely talented, aware of the enormous S&T challengethat they have embarked on, and their passion and commitment toward the “ignition” goal came through.
B. Comments/Recommendations
1.
NNSA (HQ) and the Laboratory Directors should do everything reasonable and possible, even in times oftight budgets, to encourage and ensure that the healthy competitive/collaborative spirit is maintained wellinto the future.
2.
Laboratory Ignition is truly a scientific “Grand Challenge”! The United States – through the DOE/NNSA –must remain committed to this extremely ambitious goal and develop a long-term investment
strategy that is both appropriate and sustainable.
3.
Despite the highly coupled nature of the problem, it would be useful for the experts to link the ICF goal
to foundational scientific challenges. Such a link would help establish more effective ties between theacademic community and the Lab. scientists, and will greatly benefit the ICF program in the long run.
4.
Regarding the definition of HED states, I offer some suggestions in part II.
5.
The foundational scientific challenges that constitute the hurdles to achieving ignition in the laboratoryneed to be articulated and prioritized as much as possible.
6.
It would be useful (though likely difficult) to define some fundamental science experiments that examineand evaluate different parts of the simulations being used to design and analyze experiments.
7.
The leadership at NNSA (HQ) and the leadership at the Labs need to chart out a sustainable path toencourage and foster a sense of intellectual inquisitiveness and excitement among the scientists working in
the ICF program.
HED Science
A. Definition of HED states
Not having a clear definition of HED states makes it difficult to discuss the relevant scientific phenomena
and issues in a meaningful manner. Some of the definitions in current usage are: pressures above 1 Mbar orexperiments carried out at HED facilities (Omega, Z, NIF) or experiments carried out using high intensity
lasers. None of these definitions are satisfactory. Clearly, 1 Mbar in tantalum is not the same as 1 Mbar inhydrogen. Perhaps, the First Law of Thermodynamics can be used to define HED statesdE = dW + dQ
HED means a large internal energy increase in a small volume. Since mechanical work is primarily due to volume
compression, it would be better to define HED states in terms of volume compression and temperature. The
latter could be defined in terms of the Fermi Temperature. I recognize that the appropriate definition of HED

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In short, HED states need to be defined in terms of volume compression and temperature, and a lower
bound needs to be agreed upon for defining HED states.
B.

EOS
Often the term EOS is used (incorrectly) to denote a P-V relation. The development of an accurate EOS (notjust an isotherm or a Hugoniot) for a material is a central need because so much of the rest of the material
response depends on the accuracy of the EOS. Although there is a broad agreement within the HED
community regarding this need, experimental data to provide fundamental insights and to discriminate
between different EOS models are lacking. Accurate temperature measurements over the broad range ofcompressions and temperatures relevant to HED states remain an important need. This long-standing needfor accurate temperature measurements simply has not received the concerted and sustained investment
needed to ensure reliable determination of temperature. Temperature measurements are important discriminantsin evaluating different EOS models.
Over the past 20 – 25 years, there has been a very large increase in publications that report EOS developments
using increasingly sophisticated theoretical methods. In contrast to the calculations, accurate experimental data
(even P-V data), outside of the Hugoniot data, are quite sparse. Deuterium, central to fusion, offers aninteresting example. A recent paper by Sandia researchers (published in Science at the end of June) reported
metallization of deuterium by sampling P-T space through ramp (or shockless) compression preceded by shockcompression. The experimentally determined phase boundary for this insulator-metal transition was very
different from the many published theoretical calculations. The differences among the various theoretical
calculations were also extremely large. The obvious question is: why the very large spread in the theoretical
calculations and why are they so different from the experimental calculations?
Because an accurate EOS (spanning a broad range of density-temperature space) is central to all other aspects of
HED science, the following measurements need to be pursued in a sustained and meaningful manner.
•••

Accurate P-V measurements spanning a large region of density- temperature space
Accurate T measurements over a large region of density-temperature space
Measurements that more directly examine the microscopic nature of the HED states

It is important that multiple platforms (e.g. pulsed power, lasers) and different diagnostic capabilities (fortemperature measurement) be used to ensure consistency and accuracy of these measurements.
C.

Material Strength
Material strength models are commonly used to represent time-independent, inelastic deformation of solids.
Though convenient, time-independent, “strength models” may not be the correct way to represent the actual
phenomenon of interest – Resistance to Deformation (RTD) under dynamic loading.
Irrespective of the above comments, it is not clear why material strength – used to describe inelastic deformation
in solids – is important at HED conditions. Of course, this statement depends on the definition of HED states.
Although the study of inelastic deformation under dynamic loading is an important need for materials related
issues (Campaign 2), its relevance to the ICF program or at HED conditions is not obvious.
If inelastic deformation is indeed important for HED states of matter, then the determination of “material
strength” or RTD needs to go beyond time-independent, phenomenological approaches. Without going into a
lot of details, let me state that understanding RTD or developing accurate strength models that are applicable fora wide variety of load paths remains a significant challenge and an important need. Plane shock wave or ramp
compression data are not sufficient to discriminate between different “strength” models, which themselves
depend on the assumptions being made (in the models) and the EOS being used.

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III. ICF ProgramBecause of a lack of scientific expertise in this area, I don’t feel qualified to offer any substantive comments.
A general comment/question: is there a way to break the very integrated approach into smaller elements so that the same canbe examined using simpler or fundamental science experiments?
IV. External Partnerships
The discussion period with external constituencies (almost exclusively academic faculty members) was very helpful inunderstanding the relevant issues related to academic involvement at the HED facilities.
The Sandia/UT (Austin) collaboration on the astrophysics work at Z is a great success story. Alan Wooten’s strong interest androle in making this happen deserves special mention.
It is clear that Z and NIF are not typical user facilities. Both at Z and NIF, there have to be strongly engaged Lab scientists who are
genuinely excited about the science outcome and have a good understanding (including the requisite savvy) of how to getexperiments completed in a timely manner. In short, the Lab person has to have the strong scientific interest, time, and stature(within the Lab) to help the academic partner.
Several issues that have hindered stronger academic engagement were brought up in the discussions and the same are listed
below.
1.

2.

3.
4.
5.

Export control: Academic partners not being able to access codes to design potential experiments at the HED facilities
was viewed as a major hindrance by all academic attendees. According to some individuals, the export control
restriction was unnecessary.
The academic community needs to be certain that multi-year (and not just one year) access to the facilities will beavailable when their project is selected to receive time at the facility. This is needed for graduate students to do theirwork and, evidently, is not the norm at all facilities.
The time that the Lab scientists can spend on University/Laboratory partnerships was brought up as a challenge forthe Lab scientists involved in such partnerships.
Facility time by itself is not sufficient. There needs to be funding for the academic partners to cover other costs.
The national diagnostic plan needs to be broadly disseminated and discussed with the academic community.

Summary/Recommendation (External Partnerships)
Although one meeting is not sufficient to really understand all the relevant issues and to develop a path forward, the above
comments need to be discussed between the appropriate individuals at NNSA (HQ) and at the Labs to develop a clear andtransparent path forward to engage the academic community in a meaningful manner.
I am not advocating more meetings or forming more committees. Instead, each NNSA Lab that wants to engage the academic
community at their HED facility should inform the interested users about the ground rules for being involved: selection criteria
for projects; proposal template; how will the non-facility costs be covered; will multi-year access be guaranteed for selected
projects; Lab PI for each project, etc. Also, the Lab has to interact with NNSA (HQ) to ensure that sufficient resources can becommitted to academic partnerships.
At the end of the day, the Lab management and scientists (with NNSA’s support) have to be very clear in their own minds about
the strong commitment to meaningful academic partnerships. They have to be realistic about these commitments in the face ofvarious programmatic demands and budget uncertainties.
As a university faculty member, my final comments regarding this matter are as follows. In establishing meaningful Lab/University
partnerships, expectations for both sides need to be carefully defined and agreed upon at the beginning. Subsequently, theexpectations need to be carefully managed through the completion of the research project. The academic institutions have a lot
to offer to this field. But the disparate scientific cultures between the National Labs and the Universities will require care on bothsides to ensure a successful outcome.

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Reviewer Report: Stephanie Hansen
Executive summary:
We are poised at the brink of a golden age for fundamental High-Energy-Density (HED) science in the United States. Withextraordinary experiments at world-class facilities creating extreme states of HED matter, unprecedented simulation andcomputing capabilities, advancing instrumentation enabling ever-more stringent tests of those capabilities, and the highly visible
failure of a scientific approach that is over-reliant on numerical simulations, we have both the tools and motivation to strengthen
the foundations of HED science. Progress will be most rapid in a research environment that encourages deep interaction between
simulation, theory, and experiment, values curiosity-driven investigations informed by programmatic goals over results-driven“engineering” tasks, and offers a stable funding outlook to facilitate challenging long-term projects and substantive university
interactions. Without this environment, we risk squandering the present opportunities for progress in basic HED science andmore deeply embedding a false confidence in our understanding of complex HED systems.
The state of HED science
Like any scientific endeavor, fundamental high-energy density science progresses by bringing its models of the world into
harmony with the voice of nature, which is expressed through experiments and mediated by measurements. Applications suchas credible ignition and weapon designs are built on a foundation of scientific understanding, the integrity of which requires welldiagnosed, repeatable experiments and well-founded, falsifiable models. Here the field of HED science faces unique challenges:
HED experiments are complex, with profound transience and gradients that make measurements difficult to perform andinterpret. Frontier HED experiments are expensive, making repeat experiments and cross-platform comparisons rare. The
simulations that help design and interpret these experiments are extraordinarily intricate, tracking the flow and interaction ofmaterial and energy over enormous variations in length scales. And both simulations and diagnostics are deeply intertwined withtheoretical models of material properties that remain largely untested at the extreme pressures and temperatures thatcharacterize HED material.
In the face of these challenges, the nation’s recent investments in HED facilities, diagnostics, and computing capabilities have set
the stage for an era of discovery in HED science. Experimental facilities like the NIF at LLNL, Omega at LLE, the Z machine at SNL,
Trident at LANL, NIKE at NRL, and the LCLS x-ray free-electron laser at SLAC concentrate energy in space and time to produce
states of matter at extreme conditions never before studied on earth. While such “exotic” states of matter compose most of thevisible universe, active laboratory interrogation is much more informative than passive observation of distant astrophysicalobjects. Laboratory plasmas are diagnosed with ingeniously designed instruments that can resolve spatial, temporal, and energy
dimensions rich with information. These measurements help inform both fundamental HED theory and simulations, which areboth enabled by advanced computing power. Fundamental HED theory is moving towards first-principles quantum modeling of
the atomic- and nano-scale properties of material at extreme conditions, providing essential information to the massively multiscale simulation tools that are used to inform our understanding of plasmas on laboratory and even astrophysical scales. Withsufficient understanding of foundational HED science, these simulation tools could be used much like the simulation tools of
aerodynamics or other engineering disciplines to design and control complex systems with practical applications. Unlike
engineering tools, they will also provide insight into the nature and evolution of the visible universe. But unlike engineering tools,
HED simulations are not yet securely coupled to established scientific foundations.
There is a necessary element of bootstrapping in any emergent field of scientific investigation by which informed predictions are
made, tested, and refined. Large steps away from well-established ground – such as that taken in going from Omega’s 40 kJ to
NIF’s 2 MJ – are predictably uncertain. While the failure to achieve ignition on NIF was painful for the HED community, it wasprobably the best possible outcome for the health of fundamental HED science in the United States. This is not primarily because
NIF provides a marvelous platform for HED science (although it does) or because NIF is now operating with ever-more efficiency
as integrated ignition experiments cede limited ground to focused, well-diagnosed HED science experiments (although it is), but
because the failure to achieve ignition on NIF has reminded us that we are a community of scientists, not engineers. Our tools
are not yet the tools of engineers. In addition to the failure of our integrated simulations to even now explain the results fromthe original NIF target designs, we are finding disturbing disagreement between high-precision experimental data and our basic
theoretical models of x-ray absorption, transport, and the pressure response of materials in extreme conditions. As we increase
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increasingly clear. With this acknowledgment and the extraordinary scientific infrastructure now at hand, we are better
positioned to make real progress in fundamental HED science than we have been since the advent of the science-based stockpile
stewardship program in 1995.
And this progress appears to be well underway: A survey of recent technical publications in the high-profile journals Science andNature indicates a vibrant and growing field, with the publication rate of HED-relevant topics more than doubling from about 4
per year in 2010-2011 to more than 10 per year in 2012-2015. (For comparison, there are 1-2 MFE-related publications per year
in these journals.) About 30% of the high-profile HED publications report on results obtained at facilities outside the U.S., ~20%
each are from Omega and LCLS, and ~7% each are from NIF, Z, Trident, and a combination of several smaller U.S. laser facilities.
Excluding the significant contributions from international facilities and LCLS to focus only on publications from NNSA-fundedfacilities, we find that roughly 40% of the high-profile publications originate from work at Omega and 15% each originate from allother facilities. Although NIF, Z and Trident also conduct classified research not represented in the open literature, the scientificoutput from NNSA facilities measured in this way does not track closely with NNSA funding allocations (roughly 65% for NIF, 15%each for Omega and Z, and 2-3% for Trident, Nike, and Academic Alliance programs). While the topical areas of the surveyed
publications are broad, ranging from high-pressure materials science to laser-matter interaction and atomic physics, the drivers
are dominated by optical lasers. Strong connections to astrophysics and condensed matter physics are evident. The affiliations
on the surveyed publications indicate reasonably healthy collaborations among the U.S. facilities, with LLNL-LLE and MIT-LLE
connections being particularly strong and LCLS collaborations particularly ecumenical, reflecting the science models in place atthe various facilities. While collaborations among the NNSA laboratories are increasing, there are only a handful of strong
University interactions. And while there is energetic and rigorous interaction between experiments and theory (particularly
Quantum Molecular Dynamics), simulations often appear less connected to experiments; either being treated as quasiexperiments themselves or serving merely as rough guides to help interpret experimental data.
The Group 3 activities in summer 2015 presented a similar impression of the overall health of HED science: Intense interest anda deep engagement between theory and experiment was evident in discussions of focused, fundamental physics topics such as
equation of state, transport, non-equilibrium physics, and (to a lesser extent) opacities. For integrated fusion experiments, too,
there was a sense of excitement and collaboration among designers, experimentalists, and diagnosticians. But on topics ofintegrating fundamental data into simulation codes, extending simulation capabilities (e.g. by introducing native laser-plasmainteraction, magnetohydrodynamics, or kinetic effects), or even rigorous testing of particular physics packages (e.g. mix models,diffusion) by comparing simulation predictions to data from tailored experiments, there appeared to be much less generalenthusiasm. While the development of predictive simulation tools for complex HED systems is an extraordinarily complex task, itcannot become isolated from the experimental and theoretical facets of the HED community without losing credibility – acredibility that transfers to U.S. science-based stockpile stewardship. Only when we achieve consistent, detailed, and rigorous
agreement between our modeling and our measurements can we be confident that we understand the physical processes thatdrive the hearts of stars, the costs of viable fusion reactors, and the operating margins of thermonuclear weapons.
Findings and actionable recommendations
1.

In comparison with other scientific communities, HED has an extended design-experiment-analysis cycle of many
months to years. In a corporatized research environment driven by demands for bottom-line improvements (e.g.
neutron or x-ray output), the analysis part of that cycle is easily short-circuited: rather than analyze data from failures,designers begin looking for the next tweak that might enhance performance. This approach can work in an engineeringcontext with reliable simulation tools, short experimental cycles, and cheap data, but it leads to enormous waste in ascientific environment where simulation tools offer limited guidance and data is dear. In frontier science, a research
environment closer to the oft-derided “sandbox” model that encourages pulling the threads on curious or anomalous
data and deeply analyzing failures is much more productive than a forced march towards a prescribed goal.
Recommendations: Recognize that funding stability is essential for the long research cycles of HED science. Because target
fabrication is one of the major causes of long experimental cycles, encourage innovation in target materials and flexibility
in target design. Explore flexible scheduling options at large facilities to permit follow-up studies on compressed
timescales for at least simple targets. Encourage and explicitly fund time for data analysis.

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2.

In comparison with other scientific communities, HED has developed a deep reliance on simulations to both design andinterpret experiments. In a field where experiments are complex, expensive, difficult to diagnose, and not often
repeated, it is tempting to use simulations to fill in the gaps in our understanding. But it is all too easy for a flawed but
familiar tool to become oracular, and this carries a significant risk of misleading or even retarding progress in realscientific understanding.
Recommendations: Reduce code-use and source-code restrictions (at least among the laboratories) to increase scrutinyof code components and enhance opportunities for contributions from outside core developer teams. Support tri-lab code
comparison workshops and outreach to external communities with less general but more locally rigorous tools (e.g.
particle-in-cell methods, line-by-line radiative transfer, extended MHD). Encourage and reward engagement between
code developers and users (designers) throughout the laboratories. Encourage and reward engagement of codedevelopers and designers with theoretical and experimental scientists through focused experiments that test particular
aspects of the simulation codes, particularly driver physics, non-hydrodynamic transport, and mix. Encourage repeatedexperiments to ensure meaningful code verification metrics.

3.

In comparison with other scientific fields, HED science rests on an extraordinary interdependence among experiments,
diagnostics, simulation, and theory. While there are a limited number of focused-science experiments that produce
relatively uniform and quiescent HED samples, most HED plasmas have large spatial and temporal gradients that require
simulations to provide least qualitative guidance for data analysis. Simulations are of course informed by atomic-scale
theory through constitutive models, but the diagnostic signals from even uniform HED plasmas are also intimately
connected to theory: imaging depends on detailed atomic-scale emission, absorption, production rates, and stopping
powers; energy-resolved measurements sample line shapes and scattering processes. Very little HED theory has been
independently benchmarked – indeed, as we better control experiments and refine our diagnostics, we find few
experiments that do not surprise us. Worse, there is a persistent circularity in even the most sophisticatedbenchmarking experiments (e.g. line shapes from simple ions are used to characterize the conditions that produce
complicated opacity signatures from recent experiments on the Z machine; X-ray Thomson scattering is used tocharacterize the conditions of samples on Omega to provide benchmark stopping powers – but both scattering andtransport use a common electronic structure model).
Recommendations: Continue to support basic HED science experiments on platforms that emphasize sample uniformity
and extensive diagnostics for cross-validation. In particular, because the disagreement between Z experiments andtheoretical iron opacities has significant implications for atomic-scale theory, cross-platform experiments on NIF must be
supported along with continuing opacity experiments on Z. Continue support of the national diagnostics plan to provide
higher spatial, temporal and energy resolution for increasingly stringent tests of theory and simulations. Explicitly fundtheoretical development of quantum molecular dynamics and other approached for equation of state, transport, radiation(particularly line shapes) and non-LTE physics, emphasizing experimental observables that can be used to post-processsimulations for direct and detailed comparisons with data.

4.

Platform diversity is essential to the health of HED science for validation of basic science at the frontiers of HED, risk
mitigation through flexibility in the mode and efficiency of energy delivery, and the diverse research opportunities
afforded by various facility scales and access models. The importance of cross-platform validation for fundamental HED
science was highlighted in the early 2000s by a controversy over the deuterium equation of state as measured on Z and
NOVA, and NIF measurements will be essential to resolve the iron opacity problem raised by recent experiments on Z.
The fact that Z and NIF are natural partners for cross-platform validation underscores the importance of diverse drivers:
Because HED experiments are deeply connected to the method of energy delivery, each driver carries its own
idiosyncrasies in energy delivery, native efficiency, and diagnostic challenges. Optical laser drivers deliver energy cleanly,
but their wall-plug efficiency is inherently low and laser-plasma interaction can further limit and distort the intended
energy delivery. Pulsed-power drivers provide a harsh environment for diagnostics but are highly efficient, with energy
delivery limited by breakdowns in the current feed and the induction of the target itself. Platform diversity may be a key
for progress in ICF as well as basic HED science: because energy delivered to the target appears to be the critical factor
in achieving ignition, the efficiency of pulsed power drivers makes them an appealing option for a future facility. Today’s

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20 MA Z machine delivers ~0.5 MJ of energy to its targets – similar to NIF’s ~2 MJ – and can credibly produce similar
numbers of thermonuclear neutrons. Looking beyond NNSA facilities, X-ray lasers like LCLS offer unique options forcreating and probing HED material, the value of which is reflected in the extraordinary scientific output of the OFESsupported Matter at Extreme Conditions (MEC) endstation at LCLS. Like LCLS, Omega is a user facility that is also highly
productive in basic HED science, supporting the importance of maintaining a diversity of facility access models. It isnotable that while there are a plethora of small- and mid-scale laser facilities at U.S. universities that operate at
intensities similar to NIF, there are only a handful of small-scale (~1 MA) pulsed-power drivers and no mid-scale or userbased pulsed-power facilities. Thus the most efficient HED driver operates at a significant disadvantage, with a muchsmaller workforce pipeline and very limited opportunities for scaling studies.
Recommendations: Maintain driver diversity in large-scale facilities and encourage cross-platform basic HED science.
Explore options for a mid-scale (~10 MA) pulsed power facility to enhance the user base, workforce pipeline, and scientificcontributions of pulsed power science; such a facility would also help verify scaling arguments for a potential high-yield
pulsed power facility. Engage OFES and other agencies to leverage NNSA-supported ICF and basic HED science.
5.

HED has natural resonances with other scientific communities, particularly those of magnetic fusion, condensed matter,
atomic physics, and astrophysics. All of these fields have a broad university base and thus could each contribute to the
HED pipeline, especially if given increased access to major HED facilities and codes. While the magnetic fusion
community has served as a training ground for many leaders of today’s HED community, the unique physics associatedwith high densities often makes the transition from classical plasmas to HED difficult. Connections with the universitybased condensed-matter community appear to be growing in HED. This is valuable for two reasons: First, increasing thetemperature of natively dense systems offers a critically independent test of traditional plasma-based approaches that
increase the density of classical plasmas. This is particularly important in the regime of warm dense matter, which is oneof the most fundamentally difficult regimes of HED – and one that is amenable to rigorous study on university-scale
facilities. Second, the condensed matter community is natively uncomfortable with the large uncertainties that are often
accepted as a matter of course in HED science and will push for higher precision. The atomic physics community would
also seem a natural partner to HED, but its focus in the U.S. has largely shifted towards cold systems. This has led to avery limited number of university interactions in atomic physics and an atrophying of the HED-relevant atomic physics
capabilities that inform both diagnostics and simulations. Critical capabilities like opacity and atomic structure codes,
line shape modeling, and atomic physics databases are currently sustained by a small handful of scientists, with about
half of them near retirement. The astrophysical community includes scientists with experience in multi-scale modelingand non-local effects like beams, fields, and radiation transport in regimes of high temperature and density. However,the HED community has, in general, developed more sophisticated models than the astrophysical community andinteractions are currently quite limited. Increased interactions would broaden the applicability of HED science, provide
critical data for the astrophysical community, and widen the HED pipeline, but their immediate impact on fundamental
understanding of HED science and the fidelity of HED simulations is likely to be modest.
Recommendations: increase university funding opportunities for focused, high-precision experimental studies in warm
dense matter and for theoretical model development, particularly in atomic physics. Critical topical areas for ICF/HED
science are transport physics (particularly thermal conductivities) in warm dense matter and radiation physics (particularlyline shapes and non-LTE kinetics) in hot plasma; both play major roles in energy transport and instability development.
Explore ways to increase university access to large facilities. Sandia’s “Z Astrophysical Plasma Properties” program is an
exemplary model that engages both university researchers (including promising students) and the astrophysicalcommunity. Explore ways to broaden the user base of lab codes.

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Reviewer Report: Richard W. Lee
TO:

Keith LeChien,
Lois Buitano,Njema Frazier,
Kirk Levedahl,

ICF Director
Group 1 HQ Lead
Group 2 HQ Lead
Group 3 HQ Lead

I. Underlying physics understanding and integration.
EOS
Findings: The discussion of the equation of state modeling indicated that this field is, with respect to the wider scientificcommunity, being developed in an efficient manner. The codes that have been and are being developed seem to provide
reasonably accurate results in agreement with the experiments carried out at several facilities in the NNSA complex. The
work that is largely dominated by matter shocked along the Hugoniot is well in hand.
Comments: My view of the status would be that it is slightly subtler than the Findings overview. High pressure is not actuallythat well known: you have a choice - static experiments, for example Diamond Anvil Cells (DAC), which are limited inpressure, along an isotherm, or dynamic, which gives data along the Hugoniot. Nature allows you to do that by responding
appropriately. It could be said that because we do not have independent temperature measurements yet, one does not
actually have benchmark high pressure data except along those two particular paths. To put this in perspective one would
have to agree that this situation is much better than, EOS’s counterpart, i.e., Opacity data, but only because nature is
helping you. The big challenge will come when one attempts to go off-Hugoniot and find a method to measure thetemperature,
Recommendations: I would strongly recommend that the EOS effort be encouraged to continue pretty much without
interference. As the editor of the special topic journal “High Energy Density Physics” I get to see contribution from the
NNSA complex and all the other laboratories doing work in this area. It is quite clear that at this time the EOS effort madehere are amongst the leading efforts. Further, the level of collaboration in both theory and experiment (including
instrumentation, data analysis, etc.) is impressive. This openness should be
encouraged – possibly by leaving theseresearchers to do their job.
Opacity and transport
Findings: The situation for Opacity and Transport is definitely distinct from that of EOS. I note that the scientific issue is
Opacity, which once known, would be used in radiative transfer codes to provide a description of the radiation field intensity.
So, I deal here with opacity. In current practice, from my understanding in the discussions, the last thing the code developers
want to put into their codes is an accurate model of non-LTE population kinetics, which I am pretty sure dominates theionization in virtually all laser-plasma experiments. This is understandable as the number of levels can quickly become
intractable for high- Z plasmas for any current computer. On the other hand, this does not excuse the lack of effort put into
this area when it comes to experiments. [Okay, I admit that this is the field I have worked in roughly forever.] The trouble
has been that there are only a few benchmarks in the field of Opacity.
Comments: I don’t think that radiative properties have been hard to benchmark because the processes involved are on the
microscopic –or atomic– scale but because there have been no methods of creating an appropriately uniform volumetricallyheated sample, and one has the complication for opacity of requiring a separate source and target laser. In contrast for theisotherm for high pressure DACs you don’t heat, and for the Hugoniot, nature conveniently does it for you, lapping up thatentropy you are producing, and only by definition digests exactly the right amount to reach the ‘correct’ state. For radiative
properties, i.e., line shapes, population kinetics, collision physics, etc., there have been several attempts over the last 35
years to create bench mark data for laser-plasmas and the difficulties
arising from the plasma gradient structure havethwarted these efforts. That obtaining a benchmark is central to the advancement of the field can be evidenced by thecontinued use of the plasma benchmark we have from W.L. Weise, D.E. Kelleher, D.R. Paquette,(Phys. Rev. A6, 1132

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(1972)) which was a long time ago. Indeed, using this data it has been recently determined in a comparison of line shape
theories, that one of them is incorrect. Without a benchmark the true nature of the problem would remain uncertain.
The second benchmark comes from the use of the X-ray Free Electron Laser at SLAC’s LCLS. This data was taken in an x-ray
heated aluminum sample which has virtually no thermal gradients. The data was used to determine the incorrectness of thestandard Ionization Potential Depression, which has been used since the 1960’s and was chosen for the APS Division of
Plasma Physics Dawson prize this year. This effort was led by an international team from Oxford, LLNL, LCLS, European
XFEL, DESY, STFC (UK), UCB, LBNL.
Recommendations: I believe that the efforts in the area of Opacity have been extremely well served by the work being
performed at Sandia. The group there arguably has the best assemblage of researchers in HED plasma spectroscopy in theworld and has provided a new impetus for the field by making measurements that are broadly interesting to the scientificcommunity. This effort should be maintained and further encouraged.
Further, I think the X-ray FELs are unique and can be important as they allow researchers, for the first time, to decouple
volumetric heating from the probing of the plasma. That is to say one could argue along the lines of the x-ray FEL providing
the perfect probe. All the success of the data on Al, Si, Mg etc. has arisen because the x-ray FEL is producing core holes, toallow emission at wavelengths that are not emitted thermally, even though the system is hot. While this gives one a hugeparameter space to explore, we assume researchers will need to rethink the X-ray FEL experimental designs once theyattempt to interrogate a system at a wavelength where it is emitting thermally, and not just owing to the core holes
generated. X-ray FELs will provide the possibility of data taking on the 10fs time scale with a probe tunable to greater than
10 keV.
Hydro and burn physics
Findings: The performance of the hydro codes associated with the ICF complex has been continuously impressive. The
reported results though when compared to the results of experiments is less accurate than one would have hoped for. Thisis exceedingly troubling. Further, again probably due to my lack of detailed knowledge of what was being done in supportof ICF, the reliance on 1-D models without burn etc. makes no sense, as the addition of burn seems to have worsened theagree between the experiments and the simulations. This is difficult to grasp, much less understand.
Comments: The number of efforts being pursued to understand the complex behavior of the HED plasma generated in the
ICF experiments seems to me to be an indication that the pursuit of indirect laser-driven fusion is not scientifically ripe atthis time and will require high quality experimental results that can be used to benchmark the codes. The codes that need
to be developed would include all the disciplines that have been discussed in the NNSA Laboratories’ reports. The list islong and provides an outline of all the areas of physics that require concerted effort before one could hope to have acomplete simulation capability that can be relied upon to obtain valid prediction.
Recommendations: I believe that the best one can do is to take the lead by enlisting as many high quality researchers as
possible to take on the challenges of the ICF program. Room may be in the budget to develop a set of Academic Centers of
Excellence tin HED Science to aggressively develop both experimental and theoretical approaches to find the solutions to
the outstanding issues.
Global and driver physics: (I assume the Global physics addresses the experimental-scale performance of the codes,
including integration of the atomic- and micro-scale physics
Findings: It is clear the there are many gaps in the necessary knowledge base needed to pursue the calculation of the physicalprocesses required to understand ICF/HED.
Comments: The concepts that require addressing are numerous and were well outlined in the discussions and white
papers provided by the laboratories. However, there are many researchers worldwide working on the same or similar
problems. The global ensemble is large but the inability of the group to effect improvements in the simulations could arise
from the need to adhere to the program plan, which in hindsight was well off the mark.

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Recommendations: Figure out how to redirect some of the funds appropriated for laser-driven fusion to Centers of
Excellence in HED science which could be focused on the larger view of HED science including aspects of astrophysics,
planetary physics, the microphysics that can be accessed by the x-ray FELs. This would provide a substantial increase incollaborations and manpower working on the central problems related to ICF/HEDS.
II. Partnerships with external entities
Community: Codes
Findings: The codes developed within the NNSA complex have been well received scientifically and remain at the center of
the ICF/HED field. The work previously performed to incorporate improvements in the codes seems responsive to theprogrammatic needs. On the other hand, it is clear that servicing those needs was not sufficient to improve the predictive
capability of the simulations
Comments: At the risk of being repetitive, I do not have a way to explain the many areas where the codes need improvement,
but were still used to support the program plan. This is unfathomable to me.
Recommendations: The best one can do in a situation of this kind is to re-evaluate the influences the program planner hadon those developing the codes and thus on those performing the experiments. A better organizational structure should becreated to address the fact that this large scale project must have had tell-tale signs of unsatisfactory results. Yet there was
no indication that corrective actions were taken given the continuous evolution of the ICF program. I apologize if myperception is incorrect due to my distance from the program’s oversight.
Community: Experiments
Findings: The small facilities broadly speaking allow more rapid progress due to the obvious advantages of being lessexpensive to run, provide an ease of genuine continuity for training students, who through eagerness and novel views canprovide much benefit to smaller scale research teams. The larger the facility, the more expensive the effort, the slower the
progress. On the other
hand, the larger facilities can access much wider ranges in the HED phase space than smaller
facilities– the NIF clearly dominates the the largest range of the HED space and will do so for many years. Careful
coordination amongst the facilities in a national program may be able to optimize the opportunities, but this form of
coordination requires much effort, intelligent management, and zeal.
Comments: In the end the number and type of facilities need to be responsive to the program needs. I assume here that
one needs to accommodate Indirect Drive, Direct Drive, and Magnetically driven implosions in the plan. The fir st two
are of a kind, while the third is sufficiently different to provide a test bed to test the creation of high density, hightemperature environments. In this regard there are a reasonable set of facilities to achieve this goal.
Given my sense that direct and indirect drive are quite similar I would say that there is much exchange of information
and a similarity of techniques. On the other hand, magnetically-driven systems would be difficult to compare with
the Laser-based ICF methods, unless these are fundamental studies where a particular quantity is extracted fromthe experiment – at that point the comparisons again become straightforward.
Recommendations: A coordinated effort to provide redundancy in a particular measurement has never been actively
pursued. When is the last time that you remember an experiment being performed on a different platform tocompare results because the different facilities have differing diagnostics and approaches toward achieving theconditions of interest? This is rarely done on mid- and large-scale facilities due the nature of competition and theresistance of management to attempt duplicative experiments. This, again, would require directions from above.
Wherever that may fall in the organization.
To clarify these points: I believe that the diversity of experimental approaches is reasonable but the cross-checking
is close to zero. Also, the exchange of results happens within DoE NNSA as it does outside of NNSA, i.e., largely throughthe literature and professional meetings. I am obviously not including in this comment those topics that are not2015 Review of Inertial Confinement Fusion and High Energy Density Science Portfolio

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communicated in open forums.
The “User Facility” model should not be expanded within the NNSA community, as there are several highly
functioning facilities However, there should be a substantial effort to incorporate other facilities aggressively into the
HEDP arena. This would be a cost-effective way to benefit the larger international community, as HEDP has
numerous hard-to-solve problems and could become a focus of a larger scale efforts. The newer capabilities, e.g.,petawatt lasers generating relativistic electrons and other extreme conditions, high energy Swift Heavy Ion sources,
and sub-picosecond, intense hard x-ray free electron lasers, which are being built in various places around the world
can make an important contribution to the longer term success of ICF through a deeper understanding of HED
science. These facilities have nascent HEDP efforts, which would be supported and could be excellent partners withthe ability to recruit high-quality students and provide benchmark data.
Following on from the above, the construction of numerous facilities is ongoing around the world, tapping into thisvast resource base would be a far more effective way to resolve the potential problem of facility redundancy, provide
for an enhanced interest in HEDP together with a much expanded work force.
Community: Collaboration
Findings: The health of the laboratories’ scientific efforts is enhanced by the numerous collaborations that have beendeveloped over many years. These collaborations are important as they allow researchers to interact with a wider set of
their peers. These collaborations also make it possible to perform experiments on other facilities around the world, which
requires a great deal of interaction, coordination and much data.
Comments: The extension of the collaborations with researchers outside of the NNSA complex should be encouraged. It isa cost effective way to
expand the data being generated and has the advantage of bringing novel techniques, newresearchers and their idea into the system.
Recommendations: Allow collaborations to expand within the constraints of the governmental oversight. The developmentof new facilities around the world will provide an extended source of information for NNSA. The facilities, like LCLS at SLAC
operate on the basis of the peer group proposal process which mean that the “best” proposals get beam time. This meansthat the cost to NNSA would be the researchers and their equipment. Thus the “User Facility” model should not be
expanded within the NNSA community, but there should be a substantial effort to incorporate other facilities
aggressively into the HEDP arena. This would be a cost effective way to benefit the community, as HEDP has
numerous hard-to-solve problems and could become source of a new focal point for HED science. The newer
capabilities, e.g., petawatt lasers generating relativistic electrons and other extreme conditions, high energy Swiftheavy ion sources, and sub-picosecond, intense hard x-ray Free electron lasers, which are being built in various places
around the world. These facilities have nascent HEDP efforts, which should be supported and could be excellent
partners with the ability to recruit high-quality students and provide benchmark data.

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Reviewer Report: John Sarrao
General Comments
In general I found the review to be quite stimulating. There is an energy and a spirit of collaboration within the ICF/HED
community that is much more evident than it was just a few years ago. This is dramatically positive. At the highest level, my
advice is keep doing what we’re doing. I don’t get the sense that ignition or some other field-changing breakthrough is at the tipsof our fingers, and therefore a near-term, budget increase in order to ‘surge’ to the finish line seems premature. On the other
hand, it would seem to be a significant mistake to dial back the effort now, given the current momentum and future high potential
for impact. As discussed specifically above, there was some variability by subfields in the focus/excitement of the respective
communities. In general, those areas that were focused on particular microphysics topics were most energetic, especially whena significant fraction of the leadership was now from beyond LLNL. This is not to say that Livermore scientists are not doing greatscience, rather it’s just the opposite – success would not be coming if not through LLNL leadership; however, a broader community
is key for the competition of ideas that drives good science. On the other hand, the sessions that focused more on integrated
codes and performance were less stimulating and rather more LLNL dominated, presumably due to e.g., the large code base thatis closely held by LLNL. Continuing to grow and diversity the community and to move the intellectual center of mass beyond
Livermore remains an important opportunity and challenge.
It was quite valuable to spend a day at SLAC. The cultural differences between SLAC and LLNL were obvious, even when LCLS has
a relatively low ‘shot’ rate and its campaign approach is relatively similar to NIF. Again, keeping the shot rate up at NIF andensuring beam time availability at LCLS will do wonders in stimulating the community for future success. Further, the geographic
proximity of SLAC and LLNL provides an opportunity to enhance Bay Area leadership in HED science, spanning SC and DP and
including broader elements of the community, including at Berkeley.
I. Underlying physics understanding and integration.
EOS
Findings: The community is benefiting from a new generation of experimental tools, both in terms of what quantities aremeasured and the extremes in which these measurements occur. The state of theory and computing feels solid and is pushingitself into new regimes. This is an emerging area of science in which we know we know less than we did 5 years ago, which is apositive sign for future breakthroughs that will not only advance the frontiers of science but also directly impact NNSA mission
needs.
Comments: A key opportunity is cross-platform and cross-diagnostic comparisons. The community is now acquiring enough datathat discriminating tests in regions of interest become possible, in contrast to single, isolated measurements. More data will
surely lead to more internal inconsistencies; resolving these apparent conflicts will impact positively our predictive capability. An
important area of focus will be bridging atomistic micro-physics and integrated hydrodynamics.
Recommendations: Continue to invest in and pursue the articulated diverse science strategy, including synergistic opportunities
enabled by LCLS as well as NIF.
Opacity and transport
Findings: While this has been and continues to be an important area of science, the community seems to have less ‘vision’ thanother communities. The staffing pipeline seems challenging here because there are not a lot of ‘near neighbor’ disciplines withwhich to engage.
Comments: The community would benefit from some ‘fresh blood’ leadership and a forward-leaning strategic plan.
Recommendations: Working to grow the number of university partners and new contributors to the field should be a community
priority.

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Hydro and burn physics
Findings: This is an important area of science, but the community seemed overly focused on hydro growth and its impact on
implosion/ignition, and not the underlying general coupled multi-physics problem. New diagnostics coupled with moresophisticated models create an opportunity to pursue previously unresolved fundamental questions.
Comments: To the non-expert, it’s not clear if there is a systematic approach to enhanced predictive understanding in thecommunity or if it’s limited to an approach along the lines of pick your favorite candidate uncertainty and work to reduce it.
Recommendations: Ensure that the community embraces a vision of not only better thermonuclear burn but also a broader
understanding of instability physics.
Global and driver physics
Findings: The academic community interested in LPI seems to have shrunk to a level that may be unsustainable.
Recommendations: As the community moves beyond on a singular focus on ignition, the opportunity to pursue ‘crazy’ ideas
should be enhanced in order to challenge understanding and to test/train designers.
II. Partnerships with external entities
Community: codes
Findings: Barriers continue to exist, especially for integrated codes, in providing the best available codes to the academic
community. The arrival of exascale computing will present both opportunities and challenges for this community.
Comments: Integrated codes are likely to remain the domain of the labs in general and LLNL in particular, but further growth inuniversity-led micro-physics codes would be valuable.
Recommendations: Work to find ways to leverage the PSAAP centers in diversifying and expanding the suite of integrated andsingle-physics codes
Community: Experiments
Findings: Opportunities exist to bridge the “LCLS culture” and the “NIF culture.” Success will enhance the visibility and foster thegrowth of the ICF and HED communities.
Comments: Target fabrication remains a challenge for the academic community which needs to be addressed to ensure the mosteffective scientific agenda.
Recommendations: As the LCLS- and NIF-based communities continue to grow, direct funding support is needed to foster the
emergence of university groups until they reach a state of maturity similar to the materials-synchrotron community in which
other funding modalities are possible. It is also important to continue support for staff scientists at the facilities to foster andgrow new members of the community and to facilitate their initial success.
Community: Collaborations
Findings: HED science would seem to be a frontier for the interface between Office of Science and NNSA, and synergistic
partnerships should be actively pursued.
Comments: A number of collaboration and funding models are currently being used, e.g., by Omega, Z, and NIF, as well as LCLS.
At the moment, maintaining this diversity (rather than picking a particular answer) is probably healthy for the community
Recommendations: Given the significant change that has come to the HED community in the last several years with the
emergence of LCLS and the dramatic changes in NIF shot rate, one should be patient in not forming judgments about thecommunity too quickly.

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Reviewer Report: George Zimmerman
I. Underlying physics understanding and integration.
EOS
Findings: Besides thermodynamic quantities as a function of density and temperature, HED experiments and modeling should
explore the time variable (phase transitions) and also effects on EOS due to departures from thermal equilibrium such as unequal
electron and ion temperatures.
Comments: Most current modeling assumes that pressure and energy can be specified as a function of temperature, density andcomposition in equilibrium. A multiphase EOS has the potential to include time dependent phase information but needs to besupplemented with the appropriate transition rate data. Strength models are usually inconsistent with the EOS and do notprovide for a time dependent loss in strength. HED requires the EOS of materials with unequal electron and ion temperatures,
yet we assume that the pressure is Pe(ρ,Te)+Pi(ρ,Ti) without considering, for example, the screening effects of the ion
temperature on the electron pressure. Non-LTE radiative models required to simulated hohlraums and doped fuels provide only
very crude EOS quantities which do not agree with equilibrium models when they should. Dependence on simplistic concepts,
such as degree of ionization, should be reduced in favor of a more fundamental modeling approach.
Recommendations: Small scale experiments (with high data rates) and related modeling efforts should be encouraged to extend
EOS models into these non-equilibrium situations. This is an opportunity to get academic engagement and workforce
development. Goals should be experimentally validated non-equilibrium EOS models which agree with the equilibrium EOS whenappropriate.
Opacity and transport
Findings: LTE opacity models agree with each other much better than they agree with experiment. There is a severe shortage ofyoung talent in opacity modeling coming into the labs. Plasma transport coefficients and non-LTE atomic physics are essentially
not measured at all.
Comments: The recent SNL measurement of the opacity of Fe is ~2x that calculated by our best opacity models. There may besomething wrong with this experiment, but if not, we will need to seriously rethink these models. Measuring non-LTE opacity(both emission and absorption) and plasma transport coefficients (thermal conductivity, electron-ion coupling, and stopping
power) in a uniform plasma of known temperature are very difficult experiments. They may always be integrated experiments,
better suited to validating theoretical models then providing fundamentally independent data. Non-LTE opacity generation inhydro code simulations is already expensive and will become much more so before the non-LTE modeling will reduce to the best
LTE opacities when they should.
Recommendations: Repeat the SNL Fe opacity measurement on NIF varying parameters to capture trends with T, ρ and Z if
possible. Extend simulations of plasma transport coefficients to include mixtures of elements. Research methods toapproximately tabulate non-LTE effects as well as develop non-LTE algorithms on future GPU architectures. Strive to establish
consistency in the modeling for EOS, opacity and transport coefficients.
Hydro and burn physics
Findings: In layered implosion simulations all unstable wavelengths can be resolved on the mesh, but LES and RANS models stillneed to be in HED codes to simulate other capsules such as the CDMixCap series. These models do not yet get all three DD, TT
and DT reaction totals correct. Most capsule simulations are done in 2D using diffusive energy transport and without selfgenerated magnetic fields. Experiments focused on hydro instability growth are well matched by simulations.
Comments: Magnetic fields affect electron thermal conduction which affects plasma density gradients which affect hydrodynamic
instability growth rates. We may know all the equations, but routinely running 3D simulations at adequate resolution including
magnetic fields is a tall order. Toss into that the possible need for transport instead of flux-limited diffusion and you have a truly

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grand challenge problem. The validity of a single fluid hydrodynamic model is questionable in low density hohlraums andexploding pusher targets.
Recommendations: Incorporate magnetic fields in simulations as soon as they can be done robustly. Perform a small number of
3D “kitchen sink” simulations in which all known asymmetries are included. Look into slightly extending hydrodynamic (andMHD) simulations toward longer ion mean-free-paths by incorporating ion species diffusion/separation, multiple fluids, multiple
ion temperatures and/or pressure tensor evolution, benchmarking against Fokker-Planck and LSP simulations.
Global and driver physics
Findings: LPI is a classic multiscale problem requiring subzone models for backscatter and cross beam energy transfer. If wecannot get around LPI then it may be important in all three: direct drive, indirect drive and MagLIF. Measuring the plasma
conditions, rather than relying on hydro simulations, might help clarify the role of LPI. Large circuit models for Z do not yet model
the load current well. Experimentalists spend 90% of their time setting up shots and 10% understanding results.
Comments: If simple circuit models for Z can model the load current, then large (many element) models should be able to as
well. Perhaps we can understand and fix this problem during the MHD modeling workshop August 24-26, 2015 at LLNL. We must
understand expensive experiments at better than the 10% level. Getting more students involvement might be an answer.
Recommendations: Continue to develop Thomson scattering measurements of hohlraum plasma conditions. If possible measurebackscatter with <10 ps time resolution to provide additional information to LPI modelers.

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Appendix C Supporting Documents
C.1

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C.2
Summary of Previous Reviews
It was not an objective of this study to evaluate the importance or the necessity of an ICF/HED
program, although this has been extensively studied over the past 30 years. Below is a list ofrecent studies for reference:1986 – Review of the Department of Energy’s Inertial Confinement Fusion Program, National
Academy of Sciences.
1989 – Laboratory Microfusion Capability Study Phase I, Department of Energy (DOE/DP-0069).
1990 – Second Review of the Department of Energy’s Inertial Confinement Fusion Program,
National Academy of Sciences.
1990 – Performance of Participants in DOE’s Inertial Confinement Fusion Program, Government
Accountability Office (GAO/RCED-90-113BR).
1990 – The Nike Laser Program at the Naval Research Laboratory, Department of Energy.
1990 – Fusion Policy Advisory Committee, Department of Energy.
1992 – The Nike and Mercury Programs, Department of Energy.
1993 – Laboratory Microfusion Capability Study Phase II, Department of Energy (DOE/DP-00 1 7).
1993 – NIF Justification of Mission Need, Department of Energy.
1994 – Review of Science Based Stockpile Stewardship, JASON Committee (JSR-94-345).
1994 – Independent Cost Estimate – The National Ignition Facility Conceptual Design, Foster
Wheeler USA (DOE Contract No. DE-ACO 1-94PR I 00 1 6).
1994 – Approval of Key Decision One for the NIF, Department of Energy.
1995 – The NIF and the Issue of Nonproliferation, Department of Energy.
1996 – Inertial Confinement Fusion Review, JASON Committee (JSR-96-300).
1996 – NIF Title I Design Review, Department of Energy.
1996 – Programmatic Environmental Impact Review for Stockpile Stewardship and Management,
Department of Energy (DOE/EIS-0236).
1997 – Review of the Department of Energy’s Inertial Confinement Fusion Program – The
National Ignition Facility, National Academy of Sciences.

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1997 – Independent Cost Estimate – The National Ignition Facility Title I Design, Foster Wheeler
USA
2000 – National Ignition Facility: Management and Oversight Failures Caused Major Cost
Overruns and Schedule Delays, Government Accountability Office (GAO/RCED-00-271).
2000 – Final Report of the NIF Laser System Task Force, Secretary of Energy Advisory Board.
2001 – High-Energy-Density Physics Study Report, National Nuclear Security Administration.
2003 – Frontiers in High Energy Density Physics, National Academy of Sciences.
2005 – Preliminary Results of Review of Campaigns to Provide Scientific Support for the Stockpile
Stewardship Program, Government Accountability Office (GAO-05-636R).
2005 – Assessment of the plan and prospects for achieving ICF ignition at the NIF by 2010, JASON
Committee (JSR-05-340).
2005 – Preliminary Results of Review of Campaigns to Provide Scientific Support for the Stockpile
Stewardship Program
2009 – Addendum: Policy and Scientific Issues for Consideration by Expert Advisory Panels,
JASON Committee (JSR-09-330).
2010 – Actions Needed to Address Scientific and Technical Challenges and Management
Weaknesses at the National Ignition Facility, Government Accountability Office (GAO-10488).
2010 – 2012 – Quarterly Reviews of the National Ignition Campaign (The Koonin reviews).
2012 – Basic Research Directions for User Science at the National Ignition Facility, Office of
Science.
2012 – Science of Fusion Ignition on NIF (San Ramon Report), National Nuclear Security
Administration.

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C.3

Milestones from the 2012 Path Forward
Ignition
Suggested milestone
Platform

Completion Criteria

Status/Update1All

For all fusion approaches, define
the plan and specific goals forscientificandtechnologicalactivities to be performed in
preparation for the FY 2015
review.

For all approaches, identify and document the detailed Completed
experimental, computational, technology development, andother activities required to be performed in preparation for
the FY 2015 review. For PDD, this will include an assessment
in FY 2013 from both the target physics and technology
perspective. Based on this assessment, NNSA, LLE and LLNL
will define a set of PDD tasks consistent with planned
budgets and priorities.

2

All

Review results of all three ignition Review progress of all fusion approaches with respect to the Completed
approaches (LID, PDD, MDD).
program plan defined at end of FY 2013 and out-year plansfor ICF and high yield platforms.

3

LID

Conduct experiments designed to
examine scientific and implosion
performance issues identified
during the NIC campaign.

4

LID

Review alternate x-ray drive Review alternate x-ray drive implosion concepts from both Completed
implosion concepts including a scientific and technology perspective.
technology feasibility.

This milestone will include a campaign of experiments to Completed
look at symmetry and mix issues and will include highadiabat, cryogenic implosions to compare code predictions
and performance.

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5

LID

Conduct physics and integrated DT Assess experiments conducted to determine the level of Completed
implosion experiments to examine experimental and computational understanding of capsuleexperimental and computational drive and hydrodynamic performance.
understanding of capsule drive.

6

LID

Conduct
anexperimental
campaign and assess agreement
between models and simulation of
implosion
compression
andpressure.

Develop and execute cryogenic gas-filled and layered DT Completed
implosions with convergence ratio > 20 as an integrated testof experiment and code performance. Measure fraction ofyield due to alpha heating and report other performanceparameters including DSR, Ti, velocity, and fuel shape.

7

PDD

Complete an assessment of thepredicted implosion performanceusing the measured imprint
efficiency
withmulti-FMsmoothing by spectral dispersion.

Assess the predicted implosion performance on the NIF Completedusing the measured imprint efficiency with 1D multi-FM SSD
on OMEGA EP and compare with measured and simulated
implosion performance using the current laser smoothinglevels on OMEGA.

8

PDD

Perform
integrated
PDD
implosions on the NIF toinvestigate symmetry control and
LPI mitigation.

Using current NIF capabilities, conduct PDD implosions on Completed
the NIF and compare predicted symmetry and laser energy
coupling performance against simulations and OMEGA
experimental results.

9

PDD

Conduct integrated cryogenic DT
implosions on OMEGA to establish
the predictive basis for NIFequivalent hydro performance.

Compare computational predictions of cryogenic DT Completed
implosion performance on OMEGA against a broad
spectrum of design parameters and investigate
discrepancies in the computational models.

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10

PDD

Conduct in-depth external review Includes completion of CD-0. Reference definitions of CD-0 Completedof PDD point design to assess go- and CD-1. Scope and commitments need to be clear andforward program and readiness for consistent with budgets.
CD-1

11

MDD

Demonstrate initial capability for Commission initial capability at Z to simultaneously Completed
magnetized and pre-heated fusion magnetize and preheat cylindrical fusion targets on Z withexperiments.
requirements of initial B = 7-10 Tesla and initial laser preheat energy = 1.5–2 kJ. Determine the impact of themagnetic field on current coupling to the target. Conduct
experiments with magnetization and pre-heat separately
and together.

12

MDD

Conduct initial integrated fusion Determine fusion plasma parameters at initial levels of pre- Completed
target experiments and compare heat, magnetic fields, and drive currents. Apply initial
results to simulations.
methods to measure the efficacy of flux compressions by
the imploding liner. Compare results to simulations.

13

MDD

Evaluate fusion performance andstagnation plasma parameters at
enhanced drive conditions andcompare results with simulations.

14

Diagnostics Demonstrate
operationof Complete installation of ARC equipment for one NIF beam Completed
Advanced Radiographic Capability and demonstrate ARC is operational.
(ARC) at NIF using one NIF beam.

Increase magnetic field, laser pre-heat, and drive current Completed
capability. Requirements are B > 20 T, laser pre-heat > 4 kJ,
drive current > 22 MA. Conduct experiments to measure thestagnation plasma parameters and fusion target
performance for all platforms.
Compare results tosimulations and quantify agreement.

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C.4

Major Accomplishments in the ICF/HED Science Portfolio from 2012 – 2015

FY 2012
•
•
•
•
•

•

A NIF layered cryogenic target implosion produced a record neutron yield of 7x1014 witha 3.7 keV ion temperature.
The Omega laser facility performed its 20,000th target shot.
Proof of principal experiments for future NIF platforms to study radiation transport were
demonstrated on the Z Facility.
The Argon gas puff was developed and fielded on the Z Facility enabling a new class ofsources for radiation effects to assess nuclear survivability of components.
High pressure tantalum strength experiments on Z measured higher yield strength than
predicted by most existing theoretical models, with some experiments indicating higher
sensitivity to microstructure at Z strain rates than was expected.
LANL conducted a set of colliding shock/shear experiments at Omega to study turbulence
and mix.

FY 2013
•

•
•

•
•

•

•
•

Completed operational qualification of the first set of ignition regime-relevant diagnostics
and installed capabilities to support cryogenic target implosions on the National Ignition
Facility (NIF).
A record peak pressure exceeding 50 Mbar was demonstrated in an isentropic
compression of carbon experiment on the NIF.
Completed first set of NIF experiments to tune and control the shape, implosion velocity,
compressed fuel density, and mix of implosions and demonstrated layered tritium‐hydrogen‐deuterium (THD) and deuterium‐tritium (DT) cryogenic layered implosions.
A record yield of 2x1013 was obtained from a direct drive cryogenic implosion on Omega
using new polar drive phase plates.
Demonstrated improved hydrodynamic efficiency in direct-drive implosions on Omega
using beryllium ablators and quantitatively showed the effects of A/Z (atomic
mass/charge) on the conversion of absorbed laser power into shell kinetic energy.
A load current record of 26.4 Mega‐Amperes (MA) was achieved on Z, and routine
operation at 85 Kilovolts (kV) Marx charge was demonstrated, allowing higher energy
densities to be obtained routinely on Z.
Experiments on Z provided comprehensive characterization of materials relevant todevelopment of multi-point-safety options for the stockpile.
After completing Omega experiments to develop he platform, the LANL shock-shear
platform was moved to NIF to study mix.

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•

•
•

NIF experiments were performed in the Pleiades collaboration between AWE and LANL
for measuring radiation transport through a silicon aerogel foam. Spectral data of theburn-through was obtained.
Experiments were performed on Omega EP to develop an HED platform to infer equationsof state by measuring target release.
SNL completed a comprehensive study of foam under shock compression. Foams arewidely used to protect components in high impact applications.

FY 2014
•
•

•
•
•

•
•

•

•
•
•

The NIF high-foot campaign delivered a record neutron yield of 9.5x1015.
A new experimental platform validated the improved hydrodynamic stability of the highfoot design relative to a NIC target, dispelling a hypothesis that 5X larger than predictedhydrodynamic instability growth rates were responsible for capsule degradation during
the NIC.
NIF experiments on the ramp compression of diamond are the cover article for the July
18 edition of Nature.
The first beryllium capsule experiment was successfully completed on August 30 on the
NIF.
First highly resolved full sphere 3D ICF capsule simulation capability was demonstrated
that enabled detailed post-shot modeling, eventually leading to calculations that
reproduced some aspects of the capsule degradation observed during the NIC.
LLE validated implosion energetics modeling using backlit radiography and ablation front
shadowgraphy using Polar Direct-Drive implosions on the NIF.
SNL, in collaboration with LANL, executed the 14th plutonium (Pu) experiment on Z,
utilizing an innovative load design to reach 80% higher pressures in shocklesscompression then previously attained.
Joint Sandia/LANL opacity experiments on Z, with multiple materials and twotemperature/density conditions, revealed significant discrepancies between most atomicmodels and the data. Tests to understand the experimental platform over several years
have not yet revealed any flaws in the experimental methodology.
Magnetized Liner Inertial Fusion (MagLIF) first demonstrated thermonuclear neutron
production and fuel magnetization, opening a broad space of potential ICF designs.
A NIF experiment in the complex hydrodynamics campaign was completed measuring
symmetry of the shock wave produced in a copper foam ablator in a vacuum hohlraum.
A LLNL, SNL, AWE collaboration performed shots to measure system generated
electromagnetic pulses (SGEMP) produced by a laser-generated x-ray source on NIF.

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FY 2015
•
•
•
•
•
•
•
•
•

•
•
•

Observed the lattice structure of plutonium under extreme pressure and temperature
conditions on the NIF.
Safely executed the 17th plutonium experiment on Z to study shockless loading at low
pressure in order to span the full equation-of-state phase space.
Increased the number of shots on NIF from 191 in FY2014 to 356 in FY2015 with fixed
funding.
Achieved the 25,000 shot on Omega, a seminal achievement in the facility’s 45 year
history.
The detailed analysis of the first fully-integrated Magnetized Liner Inertial Fusion (MagLIF)
experiments on Z were published and the initial results were reproduced.
LLE made the first direct measurements of the conduction zone length and mass ablation
rate in direct-drive implosions.
Achieved record 50-gigabar pressures in capsule implosions on the Omega Laser. These
capsules are designed to inform future decisions for facility investments at the NIF.
Identified the two major causes that have limited performance of NIF implosions; capsuledrive asymmetry and capsule support engineered features.
Executed the first experiments for a campaign on NIF to characterize the measured
radiation transport in SSP relevant regimes. Obtained excellent results for validating ASC
models.
NIF completed a four-shot radiation transport campaign to study Marshak wave
propagation in complex configurations.
LLE performed absolute EOS measurements of foam targets using OMEGA EP x-ray
radiography.
Executed Z shots to develop neutron sources and study neutron radiation effects insemiconductors.

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C.5
Summary of First National Implosion Stagnation Physics Working Group (NISP)
Meeting
A summary of the first NISP workshop, Oct 27-28, 2015
1. Agenda:
Tuesday, October 27, 2015, B481, Room 2005
8:00amGathering and refreshments
8:30amWelcome and opening remarks
8:40amCharter and deliverables
9:00am
MDI
12:30pm
Lunch (will be provided)
13:30pm
DDI
16.00pm
Day 1 wrap-up discussions
Wednesday, October 28, 2015, B481, Room 2005
8:00amGathering and refreshments
8:30am
IDI
12:00pm
Lunch (will be provided)
13:00pm
Workshop wrap-up discussions
15:00pm
Generate report out

K. LeChien
J. Frenje/S. Regan
K. Peterson (discussion lead)
R. Bahukutumbi (discussion lead)All

P. Patel (discussion lead)All
All

Attendees:
A. Schmitt, S. Velicovich, R. Bahukutumbi, J. Knauer, V. Goncharov (web), A. Simakov, T.
Murphy, M. Gomez, P. Knapp, K. Peterson, B. Spears, P. Patel, T. Ma, A. Pak, I. Nobuhiko, D.
Casey, C. Yeamans, R. Mancini, B. Appelbe, J. Chittenden, M. Gatu-Johnson, W. Hsing, J.
Kilkenny, J. Edwards, B. Sims, K. Levedahl, K. LeChien, S. Regan and J. Frenje.
Summary of the Magnetic-Drive Session
Sandia’s highest priority with the MagLIF Program is to develop a well understood and repeatablepreheating platform. Currently, the initial conditions of the preheated fuel and the observed
conditions at burn and stagnation are not well understood. At peak burn, an electron
temperature of 2-4 keV, a density of ~0.1 to 0.5g/cc, a burn duration of 1-2 ns, a height of 5-10mm, a width of 50-100 um, a B-field of 5-15 kT (at stagnation), a peak liner velocity of 70-100km/s are observed, which correspond to an inferred stagnation pressure of ~1 GBar, whereas
clean 2D simulated values predict values of 2.2 GBar assuming optimal laser energy coupling to
the fuel.
Magnetic Drive: Hypotheses for the Observations
Several hypotheses explaining the observations and discrepancies to modeling were discussed.
These are:•Low laser energy is coupled to the fuel, with little to no mix of the liner/endcap/window.
The implosion is also essentially 1D (accounting for end losses) in nature at stagnation.

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••Simulations of the early MagLIF experiments explain the observables assuming only ~200
J (10%) of laser energy couples to the fuel. This hypothesis may explain the initialintegrated experiments that used relatively thick (3 μm) LEH windows.
A moderate amount of laser energy (~50%) is coupled to the fuel, while a few percent of
the liner/endcap/window material is mixed into the fuel. The observables can be
described by near-1D (accounting for end losses) modeling of the implosions at
stagnation. This may explain integrated MagLIF experiments that used thinner (1.5 μm)
LEH windows where the expected laser energy transmission increased significantly, but
neutron yields dropped 10×. Recent experiments have shown that integrated
performance is significantly degraded with Al endcaps compared to Be, implying endcap
mix is important in experiments with improved laser coupling.
In contrast to hypotheses #1 and #2, the observed helical structure at stagnation
represents a significant departure from a 1D stagnation description and results ininefficient conversion of kinetic energy, inadequate confinement, and the presence ofresidual flows. This hypothesis is based on 3D simulations, which can also describe
experimental observables with a moderate amount of laser energy (~50%) coupled to thefuel with minimal amounts of liner/endcap/window mix.

These hypotheses were formulated with one or more of the following assumptions:
•
•
•
•
•

The stagnation column is contiguous and the axial magnetic field lines follow perturbation
contours at stagnation.
Non-symmetric laser heating generates vorticity, enhanced scrape mix from liner walls
and limits compression.
Hard X-ray diagnostics are adequate surrogates for neutron burn history.
Sufficient magneto thermal insulation has been obtained. Transport models arereasonably accurate and thermal conduction losses are not significantly degrading
implosion performance.
Axial mass/flux losses are not degrading performance more than expected fromsimulations and analytic estimates.

Summary of the Direct-Drive Session
A major goal with the direct-drive program at LLE is to demonstrate a well-understood and wellmodeled cryogenic implosion reaching a pressure in excess of 100 Gbar. To date, the highest hotspot pressure inferred from x-ray and nuclear diagnostics is 56±7 Gbar for an α∼3.3 implosion ofa layered DT target, which should be compared to the 1-D simulated value of ∼90 GBar. The 1-D
simulation includes cross beam energy transfer, which reduces the target absorption andresulting ablation pressure of direct-drive ICF targets. Relative to 1-D simulations. 3-D
simulations suggest that low-mode distortion of the hot spot seeded by laser-drive nonuniformity and target-positioning error truncates the neutron rate and reduces the hot-spotpressure. This trend is consistent with the measured neutron rate and the hot-spot pressure.
When burn truncation is taken into account the 1-D simulations for implosions with aconvergence ratio CR≤17 and α≥ 3.5 are in closer agreement with the experimental values of the2015 Review of Inertial Confinement Fusion and High Energy Density Science Portfolio

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hot-spot pressure and the compressed areal density. In addition, ion temperatures (Ti) measured
with neutron-time-of-flight detectors, positioned in different locations around the implosion,indicate significant variations in cryogenic implosions (generally displaying ∼10-14% rms, but up
to 50% variations are occasionally observed), which should be compared to room-temperature
implosions with a Ti variation of ∼2.8% rms. In cryogenic implosions, the observed burn rate
generally tracks the 1-D simulated rates but then deviates from experiment (burn truncation)prior to the 1-D bang time. To effectively address these issues, better diagnostic information(time resolved and viewed from different directions) about the compressed core including the
hot spot and cold shell is required.
Direct Drive: Hypotheses for the Observations
Reasons for reduced hot-spot pressure in the cryogenic implosions include:• Long-wavelength growth during deceleration phase that can result in low-mode hot-spot
distortion, incomplete stagnation, an increased hot-spot volume, and consequently adecrease in hot-spot pressure.
• Too much mass in the vapor before deceleration.
o Decompression of the rear surface of the shell, which could be due to 1D effects
such as additional rarefaction waves, EOS, opacity uncertainties etc.
o Short wavelength growth at the ablation surface.
The evidence for these hypotheses are: a lower inferred hot-spot pressure compared to the 1-D
simulation is observed for experiments with CR≥16; 3D simulations that include the effects ofbeam-to-beam laser imbalance and target positioning offset (long wavelength non-uniformities)
also indicate the same trend; Measured burn rate tracks 1-D simulations and then truncates prior
to the 1-D simulated bang time, which is reproduced in 3-D simulations.
Summary of the Indirect-Drive Session
Discussions focused on hot-spot shape, hot-spot flow, hot-spot temperature and fuel/ablator
areal density and asymmetry.
Hot-Spot Shape
Hypothesis: Hohlraum drive asymmetry, especially time-varying asymmetry, due to CrossBeam-Energy Transfer (CBET) or wall-induced spot motion is driving asymmetric (oblate) andincomplete stagnation.
Evidence:• Multiple line-of-sight measurements of x-rays and neutron self-emission broadly
indicate that the size of x-ray and neutron images (P0) are similar on a ~10% level, buthigher modes can be different.
• The variation in P2 from ConAs (shell) to hot spot emission (hot spot) appears to dependon design (gas fill and case-to-capsule ratio). The late-time shape swings are notunderstood and are difficult to predict due to the uncertainties in CBET in high-gas fill
hohlraums, and Au wall expansion in near-vacuum hohlraums.
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•Understanding the evolution of the hot-spot shape during the 'missing time window'
between the 2D ConA radiography and self-emission imaging measurements will beessential.

Hot-Spot Flow
Hypothesis: An unknown source of one-sided drive asymmetry is generating hot-spot flow andincomplete stagnation. Flows from this and other drive imbalances (see 3.1) lead to incomplete
stagnation and a loss of hot-spot internal energy to unconverted kinetic energy in the shell andhot spot.
Evidence:• A similar picture of the fuel bulk motion (translational velocity) is provided by neutronand x-ray measurements. It is also observed in x-ray data that the bulk motion isfunction of signal contour suggesting that differential motion of brightly emitting
regions within the hot spot can be determined. Source of bulk motion is not understoodat this point. It is clear from simulation that this type of translational imbalance
produces damaging hot-spot flow and incomplete stagnation.
• Ti measured with different neutron-time-of-flight detectors, positioned at various
locations around the implosion, indicate a fairly isotropic temperature distribution (<400 eV). However, post-shot simulations with sizable asymmetries show temperature
distributions that vary about 200 eV. The data isotropy and the code-predicted level ofanisotropy are not consistent.
• Using an energy balance model, the total residual kinetic energy in the dense shell andhot spot is estimated to be in the range of 70-100% and 0-30%, respectively.
Uncertainties in the modeling are large, of the order of several kJs.
Hot-Spot Temperature
Hypothesis: The differences in DD and DT Ti differences and the associated DD/DT yield ratios
are caused by 3D asymmetries that produce both hot-spot flows and distortions of the angular
fuel areal density distribution.
Evidence:• The observed differences in the DT and DD Brysk Ti are larger than expected for a static,
equimolar, Maxwellian fluid.
• Measured DT to DD neutron yield ratio is also larger than expected on the basis ofmeasured Brysk Ti and a simple model to account for the difference in down-scatter
fractions. Fuel stratification cannot be an explanation as this would drive the ratio in the
opposite direction. One hypothesis is that the simple down-scatter corrections are notaccurate due to significant 3D distortions of the fuel.
• The observed electron temperatures (Te) are currently not accurate enough to evaluate
the effect of bulk flows on the Brysk Ti.
Fuel/Ablator Areal Density
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Hypothesis: Time-varying drive asymmetry and engineering support features are damaging thecold fuel configuration leading to large areal density variation.
Evidence:• Time-varying, low-mode drive asymmetries and the tent perturbation are believed to be
the dominant factors affecting the implosion performance. In high-foot implosions, theyield reduction due to low-mode drive asymmetries and tent perturbation is estimatedto be 20× and 5×, respectively, while in low-foot implosions the yield reduction isestimated to be 5× and 10×, respectively.
• Significant areal-density asymmetries are often inferred from FNADS data. This datameasures the composite effect of hot-spot neutron source distribution and out-scatteringof primary neutrons by cold fuel areal density. The areal density is believed to dominate
the angular variation. From fits to FNADS data, the areal density is generally much higher
at the poles, resulting in 1-1.5g/cm2 asymmetries.
Summary of Hypotheses
We hypothesize that the stagnation phase of IDI implosions is compromised by non-sphericaleffects. The evidence suggests that both the hot spot and cold shell show 3D asymmetries.
Measurements further suggest that the hot spot is incompletely stagnated and consequently
suffers a reduction in internal energy due to residual flows.
Incomplete stagnation is likely due to two effects:• Hohlraum drive asymmetry• Perturbation from the support tent
Hohlraum drive asymmetry, especially time-varying asymmetry, is likely due to CBET or wallinduced spot motion. Drive asymmetry contains both P1 and P2 components (and likely otherlow modes). Further perturbations from the support tent lead to areal density variation in theconfining cold fuel as well as additional damage to hot spot stagnation.
List of Action Items:• Non-radial flow: emphasis on nTOF analysis, with peer review by LLE and LLNL. Sandia will
look for precision requirements• X-ray emission analysis: compare images and resolutions at LLE and LLNL. Are the images
different (smooth, lumpy). Sandia might offer a non-spherical analysis perspective• Compare consensus on image shapes and Ti variation. Shouldn’t round images andisotropic temperatures go together?
• Scrutinize and compare current analysis of the pressure.
• Measurements of Te: Sandia, LLNL do nearly same differential filtration. Compare. Also
compare to continuum spectrometry at LLE. Potentially develop a comparison with
continuum and ross pairs at Omega• Cold fuel analysis: think about cold fuel, dark region and hot spot. Can we backlight theshell, compare to hot spot?
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••DD/DT yield ratios to understand scattering, species separation…
Compare Te and Ti to understand thermal/non-thermal contributions.

1. Date and Agenda for the Second NISP Workshop
The second NISP workshop is planned to be held the week of March 7, 2016. At this workshop,
action items 1-4 in Section 4 will be addressed.
Appendix: Questions/Suggestions by Panel
Magnetic Drive• How stable is the Image plane of the ZBL laser?
• What is the radial and axial field distribution and how does this effect triton/alphatrapping?
• What effect does the observed morphology have on stagnation pressure, density,
temperature, and confinement?
• How do we define the convergence ratio in the presence of a helical stagnation?
• Explore options for a burn history diagnostic on Z. Could we put a sacrificial scintillator
within roughly a meter of the load to measure the burn history?
• Develop stronger collaborations with LLE and LLNL to learn potential ways to use ourneutron diagnostics more effectively (better ion temperature measurements – axiallyresolved Ti? higher nTOF moments, Be back-scatter, environmental effects, DT spectral
analysis, IRF effects, forward analysis, etc.)
Direct Drive• Can we reduce the timing uncertainty for the NTD on OMEGA to make a better case forburn truncation as opposed to an overall reduction in neutron rate?
• Are we confident that other sources of non-uniformity (ice roughness etc.) are notresponsible for the degraded performance?
• Hot spot radius is measured from a different direction compared to the areal density. So
should there be consistency between the hot spot radius and areal density?
• Can a phase velocity of x-ray emission be extracted from the time-resolved hot spot
images by using an indexed SEM grid instead? Or x-ray Doppler velocimetry can be used
to extract RKE?
• Can fNADS be investigated for areal density anisotropy in areal density?
• Is there a correlation between Ti variations and the areal density variations between the
MRS and nTOFs?
• Is there a correlation between neutron yield and Ti variations? In other words, canscattering from various fixtures etc. contribute to the Ti variations?
• Is there a correlation between CR and Ti variations?
• Is there a scenario from simulations where hot spots images including motion blurring,
instrument response etc. are quasi round but there is significant Ti variations?
• Can deliberate non-uniformities such as increased power balance or increased offset bestudied in cryogenic implosions?
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edge, how can you correct for that background when inferring areal density frombackscattered neutrons?

Indirect Drive• What are we learning from the calculations– 3D simulations low mode/high mode?
• What is not being done with the codes?
• What about density measurements of hot spot?
• Is a neutron temporal diagnostic possible on NIF?
• Is the Te inferred from time-integrated, Ross-filtered images measuring the same hotspot plasma as the Ti inferred from nTOF diagnostic?
• Has a Fourier analysis of the DIXI hot-spot images been performed to study the evolutionof the modal structure?
• How do magnetic fields in the hohlraum affect the drive asymmetry?
• Regarding nTOF calibration data, are hard x-rays a good surrogate for neutrons.

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