Perspectives on Burning Plasma ResearchCharles M. Greenfield, Director
Amanda E. Hubbard, Deputy Director
US Burning Plasma Organization
National Academies Burning Plasma Committee
June 5, 2017

This work is supported by the US DOE under DE-FC02-04ER54698.
DISCLAIMER
This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any
legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product,
process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors
expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

1706-0101

Disclaimer• We would like to claim this talk is comprehensive, deep,
and balanced. But we can’t. That talk would take weeks to
prepare and hours to present.
• We have not had time to solicit input from USBPO
membership to prepare for this meeting, so this talk should
be taken as our personal perspective.
• As you may know, we have been collecting input from
USBPO membership with the intention of preparing one ormore white papers for your committee. We hope to havean opportunity later to present and discuss that input.

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NAS Burning Plasma | C.M. Greenfield | June 5, 2017

You asked us to address three questions
1. What advancements in fusion science and technology haveoccurred since the release of the previous Burning Plasma
Report (2004)?
2. Have any advancements or developments altered theimportance of burning plasma research to the U.S. fusion
research program?
3. During the next decade, what are the important scientific andtechnical problems to be addressed in the U.S. burning plasma
research program?
We will focus our comments (mostly) on fusion science – the Virtual
Laboratory for Technology (VLT) may be better positioned to brief
you on fusion technology.
We will give a more complete answer to #3 later, based on USBPO
member input.
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This talk will address advances since 2004, andthose yet to be made, in fusion science• Advances since 2004 and next steps for burning plasma research– Transients: ELMs and Disruptions– Plasma-material interactions:Power and particle exhaust,PFCs, core-edge coupling– Integrated simulations– Operating scenarios– Heating and current drive– Diagnostics– Plasma control– Energetic particles– Transport and confinement• The role of international collaboration• Have any advancements or developments altered the importance ofburning plasma research to the U.S. fusion research program?
• A few comments on ITER

Focusing on the tokamak, but most of this is applicable to otherconfigurations, e.g. stellarator

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Fusion Science and Technology Has a
Medium-Term and a Long-Term Target

1. Ensure that ITER can successfully
carry out its mission. ITER is largely
designed, with a rapidly closing
window for design changes.
Emphasis is needed on validating
and optimizing use of the alreadyspecified hardware and to makethe very few remaining hardware
decisions.
1706-0101/ 5

2. Prepare for post-ITER devices that are stilllargely undefined. They will undoubtedlypose new and greater technicalchallenges than ITER, but also present
unconstrained opportunities to develop
new tools. Research will continue throughthe next decade or more.

NAS Burning Plasma | C.M. Greenfield | June 5, 2017

The state of research in most of the highest priority
areas was captured in the 2015 community workshops• Workshops documented recent progress and identified near-term
research opportunitiesY
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Recommended reading!

ce• Many, but not all, of the topics we will discuss today are described in
more detail in these reports• Other source material includes 2009 ReNeW and several recent FESAC
studies
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NAS Burning Plasma | C.M. Greenfield | June 5, 2017

The Transients Workshop Addressed the Most
Immediate Challenges for Burning Plasmas
Challenge

ApproachEdge-Localized Modes (ELMs) • Suppression with resonant magnetic
inflict a repetitive, pulsed heat
perturbations (RMP)
load to the divertor in H-mode • ELM pacing
plasmas in tokamaks and• Naturally ELM-free operating
scenarios (QH-mode, I-mode)
stellarators
Disruptions can rapidly release •all of the plasma’s magnetic
and kinetic energy during a•fast termination, primarily intokamaks••

Disruption prediction (proximity tostability limits)
Active avoidance via plasma
control
Passively stable operating scenarios
Mitigation by injecting impurities
into the plasma core

These are areas in which the U.S. is a clear leader
There has been a great deal of progress in these areas since 2004, but
additional work is still needed for ITER
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NAS Burning Plasma | C.M. Greenfield | June 5, 2017

ELM Mitigation Compatible with High Performance
Operation is a Requirement for ITER and Future Reactors
Requirements
1. Reduce peak heat flux from
ELMs by factor 50-100x
2. Replace ELM’s impurity removal
mechanism
Goals of current research• Demonstrate effective ELM
control solutions in ITER & SS
regimes• Test and validate model
predictions for extrapolation toreactorsbN
Icoil

PegasusDa

2004: Quantitative understanding of ELMs lacking, only rudimentary
mitigation (pellet pacing) achieved, naturally ELM-free QH-mode
obtained but required strong counter-NBI
2017: ELM limit understood and predictable as peeling-ballooning mode,
several different approaches demonstrated to control. I-mode.
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RMP ELM suppression demonstrated
in DIII-D and ASDEX-U• First demonstrated in DIII-D in early
2000s• Previous: ASDEX-U only able to accessmitigation (decreased size) rather thanELM elimination as seen in DIII-D• Result on DIII-D suggested lower
collisionality on AUG is key• Follow on experiment on AUG achieved
ELM suppression• Encouraging result for ITER
• Research carried out as ITPA joint
experiment

DIII-D n=3 RMP
164361

bN
I(kA)
Da

AUG n=2 RMP
33353

bN
I(kA)

Internal coil (I-coil)in DIII-D produces
n=3 RMP field

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Da

NAS Burning Plasma | C.M. Greenfield | June 5, 2017

Shape overlay
DIII_D/AUG

d≈0.3

ELM Control Coils for ITER are based on
DIII-D experience• ELM control coils for ITER are based on empiricalextrapolation from DIII-D– water-cooled “picture frame” coils• mineral insulated conductor– Geometry : 9x3 coils (powered independently)• toroidal symmetry n=3 or 4
– Current: max 90 kAturns (6 turns)• To do:– Physics largely understood, but predictive capability not yet achieved– ELM suppression at ITER relevant low torque in baseline scenario
remains elusive• Has been achieved in hybrid scenario– RMP ELM suppression in helium plasmas not well established• Question: Is the physics the same?
– Reduced pedestal gradient ➔ reduced global confinement• Need to quantify and optimize.
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NAS Burning Plasma | C.M. Greenfield | June 5, 2017

ELM mitigation with pellet pacing• Inject pellets into pedestal at higher rate than natural ELM rate withexpectation that ELM frequency increases with concomitant decrease in
ELM size• First demonstrations in early 2000s at ASDEX-U and others• Recent results with fuel (D2) pellets in DIII-D: Peak heat flux at or better
than 1/fELM expectation• Effect also seen with impurity pellets (carbon, lithium)• To do:– Quantify dependencies, e.g. is divertor detachment and fuelingaffecting the ELMs?
– Results across devices not consistent – need to understand why– How does this affect confinement?
– Does this extrapolate to ITER? Beyond ITER??
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NAS Burning Plasma | C.M. Greenfield | June 5, 2017

Naturally ELM-free operating scenarios
offer the promise of a simplified solution• QH-mode discovered in 1999 in DIII-D– Early results required strong counter-NBI– More recently, obtained with co-NBI andsustained (not yet accessed) with ITERrelevant low torque• I-mode more recently discovered in C-Mod– Energy but not particle barrier.
– Requires toroidal field oriented for the ∇Bdrift to point away from the active x-point• Both are sustained with MHD activity near theboundary that prevents access to the ELM limit• To do:– QH-mode is a candidate scenario for ITER,
but access with little or no applied torque isstill to be developed– I-mode requires reversed B, not in ITER plans• Subsequent devices could be designed
to allow this.
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NAS Burning Plasma | C.M. Greenfield | June 5, 2017

Disruptions in tokamaks can release all of theplasma’s thermal and magnetic energy• Anatomy of a disruption– Can be triggered by crossing a stability
limit or by hardware failure
1. At the thermal quench (TQ), theplasma’s kinetic energy is rapidly
released➞Localized heating of PFCs
2. At the current quench (CQ), theplasma current ramps down, releasing
magnetic energy and generating alarge toroidal electric field➞Large EM forces
3. The toroidal electric field canaccelerate electrons creating a multiMeV runaway electron (RE) beam
➞Localized beam strike on PFCs
• Each of these phases can cause device
damage if not prevented or mitigated– Requires a multi-layered strategy ➞1706-0101/ 13

NAS Burning Plasma | C.M. Greenfield | June 5, 2017

MYTH: Disruptions are inevitable in tokamaks• Operating scenarios are characterized by their “safety factor” q, which
varies as B/I.
– ITER baseline scenario operates at q~3• Passively stable operating scenarios can be achieved– Higher q ➞ less likely to disrupt, even at high b (pressure)!
– High performance scenarios, such as Advanced Inductive (“Hybrid”) andhigh qmin steady-state scenarios rarely disrupt in present-day experiments– Note: This does not preclude a disruption caused by hardware failure(control fault, PFC breakage,…).
• Active stability control ➞ high performance operation near stability limits– Plasma control system must be able to predict an oncoming disruption
and take measures to restore stability or shift to a more stable (albeit lower
performance) operating point– As a last resort, the PCS will need to trigger mitigation measures

2004: Disruptions thought by many to be a random and unpreventable
event
2017: Progress in understanding, prediction, avoidance, and mitigation
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NAS Burning Plasma | C.M. Greenfield | June 5, 2017

Disruption prediction and avoidance:
Where we are, where we need to go• Empirical disruption predictors (including neural nets) have beendeveloped on NSTX, JET, etc.
– Already in routine use in JET to protect “ITER-like” tungsten/beryllium
first wall
• Rudimentary disruption avoidance already a part of routine operation– DIII-D “dud detector” can trigger safe rampdown or measures tosuppress instabilities including neoclassical tearing mode or resistive
wall mode• To do:– Empirical approaches: Need to demonstrate portability, e.g. can anempirical predictor developed/trained on one device be ported to a
new device with minimal new training or calibration?
– Real-time stability calculations becoming a reality– Develop increased sophistication of PCS• Need to include off-normal (“not plasma physics”) event response

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NAS Burning Plasma | C.M. Greenfield | June 5, 2017

We have active control techniques in
hand for the most common instabilities• Neoclassical tearing modes (NTM)– Magnetic islands form and locally depress bootstrap current– Can lead to mode locking and disruption– Successfully suppressed by replacing current in magnetic island withelectron cyclotron current drive (ECCD)• Resistive Wall Mode (RWM)– Instability occurs when above the “no wall” b limit – most applicable toadvanced/higher performance scenarios– Rarely disruptive, but can result in loss of a desirable operating point– Successfully suppressed with application of external magnetic fields (fromsame coil system used for RMP ELM suppression)• Error fields– Can arise from tokamak assembly defects of application of external field
perturbations– Can impact confinement and stability (interacts with above instabilities)– Correction of n=1 component of error field routinely done in tokamaks– Recent: Discovery that higher order error field components are important
too – more advanced error correction techniques can address this1706-0101/ 16

NAS Burning Plasma | C.M. Greenfield | June 5, 2017

Instability control, continued• To do:– NTM• Continue to develop “catch andsubdue” technique that minimizes
effect on Q by only applying ECCD
when and where instability appears– Error fields and RWM• More work is needed to determine
optimal use and placement ofinternal and external coils• Continue to develop techniques
using these coils to correct error
fields with n=1, 2, 3,…
• Includes dynamic error field control
applicable to RWM suppression

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NAS Burning Plasma | C.M. Greenfield | June 5, 2017

The last resort: Radiate away theplasma’s energy harmlessly (mitigation)• Usual approach: inject impurity particles during or before the TQ– Massive Gas Injection (MGI): C-Mod, DIII-D,…
– Shattered Pellet Injection (SPI): DIII-D; JET (2018)• Chosen for ITER Disruption Mitigation System (DMS)– Capable of mitigating the heat andelectromagnetic loads of the TQ and CQ• Both theory and present experiencesuggest RE beam not solved• To do– Complete testing to qualify SPI for ITER
• DIII-D (2017): Use of multiple injectors,
requirements for injection direction• DIII-D & JET (2018): Data to extrapolate to ITER
– Develop solutions for RE beam
• Requires advances in theory• ITER can accept alternative concepts with mature designs up to 2030
• No shortage of ideas, but only a few being tested– Need international cooperation
Not just an ITER issue – needed for all future tokamaks
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NAS Burning Plasma | C.M. Greenfield | June 5, 2017

FUSION ENERGYSCIENCES WORKSHOP

!

!

!

!

!

ON PLASMA MATERIALSINTERACTIONS
Report on Science Challenges and Research
Opportunities in
Plasma Materials Interactions
MAY 4-7, 2015

The Plasma Materials Interactions Workshop
Was More Future-Focused

Fusion Energy Sciences

Challenge

Approach

Power exhaust and particle
control

Understand, develop, anddemonstrate innovative solutions for:• Dissipative/detached divertor• Main chamber wall components

Plasma facing components(PFCs)••

Interplay between boundary •conditions and core
performance•

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Develop understanding ofmaterial behavior under reactor
conditions
Identify limits for solid and liquid
PFCs
Develop understanding andcontrol of core-edge coupling.
Use to optimize scenarios(including ITER)

NAS Burning Plasma | C.M. Greenfield | June 5, 2017

Plasma exhaust and particle control
Nucl. Fusion 53 (2013) 093031

For ITER:• Heat flux width characterized, but scaling to ITER ismuch narrower than had been expected,
increasing the challenge.
• Progress made in understanding conditions for
detachment.
• Diagnostics allowing increasingly sophisticatedmodel validation exercises• Heat fluxes studied at ITER level in C-Mod,
reduction to need levels by seeding
Figure 3. Poloidal magnetic field at the outer midplane versus
power fall-off length (λ ). The solid line gives the result of
demonstrated
regression #14 and the dashed lines the error bars.
• To do:– ITER hardware is set, but more progress inunderstanding detachment conditions andextrapolation of heat flux width is still needed– Model validation in present-day tokamaksq

2004: Radiative divertors assumed in future tokamaks, but not muchdetailed thought to how it could be achieved.
2017: Heat flux width characterized. Diagnostic sets primed to makeprogress.
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NAS Burning Plasma | C.M. Greenfield | June 5,
2017
Figure 4. Comparison of power spreading factor (S) versus power
fall-off length (λq ).

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Plasma exhaust and particle control
Beyond ITER, to DEMO
• Challenge is much greater, may well need new
divertor geometries.
• Several divertor geometries have been tested or
modifications are underway now• Simulations of detachment predict detachmentwith much less impact on core plasma
To do: Validate models, optimize divertor geometry,
test more options, at high heat flux.

2004: Rudimentary comparisons of open and closed divertors carried out
with sparse diagnostic sets
2017: Simulations and tests of several divertor configurations underway andplanned.
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NAS Burning Plasma | C.M. Greenfield | June 5, 2017

Plasma-facing components• Most experience and databases gained with carbon-walled tokamaks.
ITER will have tungsten divertor and beryllium main chamber– Adopted by JET• Performance in metal-wall devices has not been as good as with carbon– New optimizations being performed, e.g. impurity injection• To do:– Optimize performance with metal walls (needed for ITER). JET ismaking progress.
– For post-ITER devices, development of new materials may be required
to meet reactor challenges• Simultaneously address tritium retention, heat flux tolerance,
radiation tolerance,…
2004: Carbon walls in most tokamaks (Mo in C-Mod)
2017: Several tokamaks changed to metal walls, especially JET with its“ITER-like” wall
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NAS Burning Plasma | C.M. Greenfield | June 5, 2017

Core-edge coupling

Snyder, Hughes, TTF17

EPED Predicted Pedestal Height for ITER Baseline
160
140

Pedestal Height (kPa)• The core and edge communicate with eachother through the H-mode pedestal• EPED can predict the pedestal based on
peeling-ballooning setting stability (ELM)
limit and kinetic ballooning mode driving
transport• New C-Mod data, fills in to ~90% of ITER’s
expected pedestal pressure• To do:– Full pedestal still not predictable… EPED
predicts pressure, but not density andtemperature– Progress would greatly improvepredictability ➞ shorten time (number ofshots) to make progress in ITER andsubsequent devices

120
100
80
60

EPED (Super H-Mode)
EPED (H-Mode)

40
20
0
4

Intermediate (unstable branch)
68

10 12 14 16 18 20 22 24 26 28

Pedestal Density * Zeff1/2 (1019 m-3)

2004: H-mode pedestal largest uncertainty in predicting performance
2017: Theoretical understanding makes many (but not all) features of thepedestal predictable, including ELM limits
1706-0101/ 23

NAS Burning Plasma | C.M. Greenfield | June 5, 2017

The Integrated Simulations Workshop
Identified Numerous Opportunities• Identified gaps and challenges in the areas of:– Disruption physics, including prevention, avoidance, and mitigation– Plasma boundary, including the pedestal, scrape-off layer, andplasma-materials-interactions– Whole device modeling (WDM)• New opportunities identified in– Interaction of fast particles with thermal plasma waves and instabilities– Steady-state plasma modeling with strong coupling of core transport
to sources and MHD– Whole-device modeling (WDM)• Inclusion of multiscale turbulence• Development of a fast WDM capability for real-time simulation,
numerical optimization, and uncertainty quantification• Use of probabilistic WDM to assess the likelihood of key physicaltransitions or states occurring
Integrated simulation in concert with experimentation has been and willcontinue to be a hallmark of our burning plasma research
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NAS Burning Plasma | C.M. Greenfield | June 5, 2017

Operating scenario development is progressing withincreasing fidelity to burning plasma conditions• Operating scenarios for burning plasmas (e.g.
ITER) developed mostly in tokamaks with co-NBI– Strong rotation and ion heating contrasts
with expectations in BP• Recent research exploring access in morereactor-relevant conditions• Conventional tokamak– ELMing H-mode – ITER baseline scenario– Stability at low rotation a concern• Hybrid/advanced inductive– Self-organized core maintains qaxis>1 (avoids sawtooth instability)– Demonstrated with low torque and combined with RMP ELM suppression– Higher q ➞ lower incidence of disruption– Projects to Q=10 in ITER at lower current• Steady-state– Higher q, with all current provided by bootstrap and external sources– Confinement reduced in some recent experiments due to energetic
particle instabilities– Rarely disrupts– Lower Q due to requirement for external current drive
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NAS Burning Plasma | C.M. Greenfield | June 5, 2017

Operating scenarios, continued• To do:– All scenarios: Continue to work toward demonstrations that include:• Integration of first wall, boundary, pedestal, and core
• Reactor-relevant applied torque and (primarily electron) heating• ELM control – via RMP, pacing, or coupling core scenario with QH-modeor I-mode edge
• Heat flux within PFC limits.
– Conventional tokamak (“ITER baseline”)• Address instability at low rotation – some recent success in DIII-D• RMP ELM control needs to be established at low rotation and in helium
plasmas (addresses ITER non-activated operational phase)– Hybrid/advanced inductive• Work to establish as viable alternative ITER baseline scenario– Steady-state• Address energetic particle instability issue– Broader issue in a burning plasma with alpha heating• Establish at low rotation and with ITER-relevant heating and current drivemix (for ITER Q=5 steady-state mission)• Scenario optimization to maximize bootstrap/minimize need for externalcurrent drive• Establish physics basis for steady-state DEMO operation
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Heating and current drive
C-Mod, S. Wukitch• Have made good progress, particularly in RF.
• Has become clear that electron heating (ECH or
ICRH) is critical for controlling high Z impurities.
• ICRH:– Impurity generation is a major issue. Now muchbetter understood, and options demonstrated togreatly reduce source. Field-aligned (FA)antenna on C-Mod, new design on AUG.
– Still some unanswered questions on physics
mechanisms, impurity transport.
• Much improved– US leads in simulation, through SciDAC. New RF
performance
schemes, relevant to ITER, have been predictedpredicted with highand demonstrated. (eg 3-species, on C-Mod andfield side launch, for
JET, generates high energy ions). W7X will use.
both ICRF and LHCD.
• LHCD:(see PMI workshop)
20-3– High CD efficiency demonstrated to ~10 m
Requires testing as(C-Mod). Improved understanding of limiting
option for devices
mechanisms at higher density.
beyond ITER.
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NAS Burning Plasma | C.M. Greenfield | June 5, 2017

Diagnostics• Status– A steady progression of diagnostic developments accelerated in the
1990s, and continues to the present day• A hallmark of the US fusion program– To do:• Many present-day diagnostics will not work in a burning plasma
environment due to radiation, heat, long-pulse operation, andaccess limitations• Work already in progress to develop new techniques for ITER
• New classes of diagnostics needed for confined and lost alphas in
ITER, including velocity space distribution• Post-ITER devices even more challenging– Example: Magnetic pickups, ubiquitous in present-day devices,
may not be applicable in a reactor• Need to establish minimum set of diagnostics for reactor control

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NAS Burning Plasma | C.M. Greenfield | June 5, 2017

Plasma Control• Status– Real-time plasma control becoming increasingly sophisticated,
including multiple sensors and multiple actuators– Real-time profile analysis allowing control of profile shapes (not just 0-D
control anymore!)• To do:– Include possibility of a single actuator doing multiple things– Burn control – alpha particles will be dominant source of heating
power in a burning plasma– Determine minimum sets of measurements and actuators for a powerplant

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NAS Burning Plasma | C.M. Greenfield | June 5, 2017

Energetic Particles• Status– Longstanding mysteries of transport of energetic particles (EPs) by
Alfvén eigenmodes (AEs) are being solved through innovative
experiments, diagnostics, and modeling• Impacts beam ions in present and future devices, alpha particles inburning plasmas– Innovative measurements providing opportunities for model validation• To do– Heating physics of alphas, including alpha channeling– NBI heating and current drive physics in ITER
– Linear and nonlinear understanding of AEs– EP interaction with non-AE MHD instabilities– Safe termination of high-Q burning plasma discharges• A burning plasma experiment is essential for understanding alphatransport since NBI is unable to recreate the isotropic alpha distribution

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Transport and confinement• Status– Strong modeling program combined with unique set of turbulencemodels has led to• Understanding and improved predictive modeling of heat transport• Understanding of the L- to H-mode mechanism• Impurity transport through neoclassical simulations and experiments• Advances in understanding moment transport• To do:– The focus needs to shift to addressing transport in plasma regimes thatare relevant for burning plasmas, with no ELMs, strong radiative
divertor, current drive,…
– Build confidence that we can achieve high confinement, including
core-edge integration– Need capability to predict within a reasonable time and withreasonable accuracy how plasmas will behave in future experiments
and future devices• Will be instrumental to the operation of ITER (or any burning plasma
device)1706-0101/ 31

NAS Burning Plasma | C.M. Greenfield | June 5, 2017

International collaboration will accelerate
fusion energy development and scientific understandingJET

ASDEX-U

MAST-UITER

JT-60SAA strong U.S. domestic
program is vital

DIII-D

NSTX-U

WEST

TCV

SST-1

EAST

KSTAR

Not a one-way progression from US to foreign devices – collaborations canand must go in both directions!
1706-0101/ 32

International collaboration will accelerate
fusion energy development and scientific understanding• US is a major participant in ITPA due in large part to technicalcontributions from our tokamaks• Research leading toward and beyond ITER should take advantageof the complementary nature of US facilities and those of ourinternational partners– Example: long-pulse superconducting tokamaks can work
together with more flexible, but shorter-pulse, US devices todevelop and qualify long pulse operating scenarios• In some cases, international facilities can provide opportunities toextend research beyond US capabilities– Example: DT experiments in JET
Not a one-way progression from US to foreign devices – collaborations canand must go in both directions!
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Have any advancements or developments altered the importanceof burning plasma research to the US fusion research program?

NO

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NAS Burning Plasma | C.M. Greenfield | June 5, 2017

Have any advancements or developments altered the importanceof burning plasma research to the US fusion research program?

NO“The study of burning plasmas, in which self-heating from fusion reactions dominates plasma behavior, is at thefrontier of magnetic fusion energy science. The next major step in magnetic fusion research should be a burning
plasma program, which is essential to the science focus and energy goal of fusion research… ITER offers an
opportunity for the study of burning plasma physics in conventional and advanced tokamak configurations for long
durations with steady state as the ultimate goal, and would contribute to the development and integration ofplasma and fusion technology”
2002 Snowmass meeting press release; later endorsed by FESAC• Nothing has happened to make this statement less true
• The importance is the same
• Our readiness has advanced

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NAS Burning Plasma | C.M. Greenfield | June 5, 2017

The ITER project is moving ahead and making progress
toward the burning plasma laboratory we envisioned in 2002
• The ITER construction project will produce
a scientific instrument that can achieve
its specific technical goals– Q=10 for hundreds of seconds– Q=5 in steady-state-capable scenarios
for thousands of seconds– Provide a unique laboratory to study
the physics and technology of burning
plasmas and provide a significant partof the basis to proceed to a DEMO
• The results will inform US efforts toward afusion energy DEMO
• There is still work to be done
– The US FES program has the assets inplace to prepare for a successful ITER
program – we are world-leading inmany areas
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NAS Burning Plasma | C.M. Greenfield | June 5, 2017

Burning plasma is still the next frontier –as it has been since Snowmass• Advancements and developments since 2004 have only increased ourreadiness to take the burning plasma step
• International collaboration (present-day and an international burning
plasma experiment such as ITER) can leverage our research, but astrong domestic program is needed• ITER construction is on track – I believe that the best path to provide aburning plasma laboratory for the US and the world is to complete ITER
and carry out its research program– There have always been viable alternatives to ITER, but it seems
unlikely that a US-only burning plasma experiment with similar mission
could be available sooner or at a lower cost to the US– ITER is a science experiment and should not be taken as a prototype
power plant; other fusion devices will be needed and we also need toprepare for them1706-0101/ 37

NAS Burning Plasma | C.M. Greenfield | June 5, 2017