A reinvigorated US fusion energy program

S. Prager
Princeton University
Reﬂec%ng, in part, discussions with T. Carter, R. Fonck, M. Haynes, D. Maurer,
D. Meade,G. Navra%l, G. Tynan, D. Whyte

The commi:ee charge is large and expansive• To advance the US to world leadership in fusion research• To develop fusion energy as a priority for the US• Projec?ng both near- and long-term
This is a crucial and %mely opportunity for the US fusion research(and for the ﬁeld of plasma physics)

Fusion research at mid-life iden?ty crisis
Several paradoxes• Technical• Timeline• US standing

Technical paradox
Remarkable progress• Tokamak performance, fusion plasma physics, fusion engineering• Construc?ng ITER - a reactor-scale, burning plasma experiment
But,• More scien?ﬁc and engineering challenges lie ahead,• Challenges of steady-state, disrup?ons, high performance arepersistent
ITER embodies the strengths and challenges of tokamak
conﬁnement (Q = 10, but for 8 minutes),
EU DEMO embodies current knowledge base -> large, pulsed

Timescale paradox• Now there is a societal desire to achieve fusion urgently
But,• The ?me to fusion power is paced by facility construc?on ?mes(fusion cannot be proven/developed at small scale, then scaled up)

US leadership paradox
The US workforce is at the world forefront (although narrowing)
But,
The US research program is not(more later)A redeﬁned US program can alleviate all 3 paradoxes by• Resolving technical hurdles, emphasizing innova?on forimprovements• Accelera?ng the ?me to fusion landmarks and fusion power• Bringing the US to the world forefront

The interim charge – assess current status of US research– issubstan?ve and important
Substan?ve: Deserves a frank and accurate assessment of thehealth and stature of the US program
Important: Deﬁnes the landscape from which a new strategicplan will be launched
Not been previously ar?culated “oﬃcially”

US has been a world leader in nearly all areas of fusion research• Built upon major investments in 1980 – 2000
(TFTR, DIII-D, NSTX, CMOD, coupled to strong base program)• One metric is the US share of interna?onal research prizes
Nuclear Fusion prize – 8 out of 11 to work led by US scien?sts
Alfven Prize, EPS – US scien?sts won 8 out of 17 years, mainlyfor fusion researchThis metric is a lagging indicator of investments built up over decades

US is losing research leadership and vitality for 2 coupled reasons• No current strategic plan for fusion energy
absence of DOE-sanc?oned community process,no considera?on of slip in ITER ?meline (20 yrs to DT opera?ons)• Lack of major investment in new US research facili?es and capabili?es
20 year gap in major investments (~$ 1B) in US facili?es,
recent closure of CMOD (2016), closure of TFTR (1997) leaves only
DIII-D (1986) and NSTX-U (1999/2019)

This contrasts sharply with our interna%onal partners

Our ITER partners have roadmaps to DEMO
European roadmap
Fusion Electricity
A roadmap to the realisation of fusion energy

EU roadmap in a nutshell
1. Plasma opera-on

Induc-ve
Steady state

European MST+ IC

2. Heat exhaust

MST = Mid-scale tokamak
IC = Interna-onal Collabora-on
DTT = Divertor Test Tokamak

Baseline

And similarly for China, S. Korea, Japan
Advanced conﬁgura-on and materials

European MST +linear plasma + DTT + IC

3. Materials

Tri-um(the4. US
isbreeding
dis?nct in its absence of a fusion roadmap)……
ITER Test blanket programme
Parallel Blanket Concepts

CFETR (CN)FNS (US)

5. Safety

DEMO decision

6. DEMO

CDA +EDA

7. Low cost

Low capital cost and long term technologies

8. Stellarator

Stellarator op-miza-on

2010

Construc-on

2020

Fusion electricity
Opera-onBurning Plasma
Stellarator

2030

2040

2050

1

Scien?ﬁc facili?es are increasing across the world
China: superconduc?ng tokamak (2006)

New major facili?esIn Asia
Japan: superconduc?ng tokamak (2019)

Korea: superconduc?ng tokamak (2008)

Scien?ﬁc facili?es are increasing across the world
Germany: superconduc?ng stellarator (2016)

In the European Union
France: ITERFrance: SCtokamak (2016)

The world has entered the era of superconduc?ng facili?es (steady-state)
A leading indicator

Collabora?on on facili?es abroad• An important, valuable opportunity for the US (and host labs)• But, interna?onal collabora?on is not a subs?tute for US
leadership.

All fusion research sectors not suﬃciently healthy
Universi?es:A cri?cal situa?on. Prospects for faculty posi?ons weak, despitescien?ﬁc interest. Due to decline in research projects and gov’t
long-term commitment. (see UFA report, D. Mauer talk)
Na?onal labs:
Similar causes led to few na?onal labs with MFE as priority
Industry:
Li:le involvement in DOE program (except GA), but new
phenomenon of fusion startup companies

But the stage is set for the US to transi?on to a dynamic, leading
fusion program• We have a world-leading workforce• With many innova?ve and important ideas ready to pursue

A new fusion strategy
Vision:Employ new scien%ﬁc advances for an improved fusion powersystem and an accelerated path to fusion energy,building upon the exis%ng knowledge base and interna%onal
ac%vi%es

A new fusion strategy
Vision:Employ new scien(ﬁc advances for an improved fusion powersystem and an accelerated path to fusion energy,building upon the exis%ng knowledge base and interna%onal
ac%vi%es

Note: the following strategy is described programma?cally; the underlying fundamental
science is implicit, but not ar?culated

Three premises for strategy
1. Pursue ideas to improve the fusion vision and accelerate its pace
New opportuni?es have emerged within physics and engineering forimprovements and solu?ons to remaining challenges,
Allow for higher risk tolerance
2. Builds on and leverages the US and world tokamak/ITER program
Accommodates tension between staying with proven performance vsexploring new ideas

3. Incorporates a US DT program (and facility) as an integra?ng goalWith a mission that complements ITER, and includes advances
since the ITER design and those that accrue through #1

Features of above strategy• A dis?nct US approach that complements, and beneﬁts from, theworld program;departs from the dominant ITER -> DEMO -> Reactor framework(both too risky and leads to too large a reactor)• Requires a substan?ally restructured, reinvigorated, US program• Would restore the US to a world leadership posi?on in fusion

Examples of major new research elements suitable to anew strategy

Program mission elements
1.

Create fusion plasma corehigh gain, steady-state, disrup?on-free, compact

2.

Tame the plasma-wall Interface
survivable materials, plasma control

3. Harness fusion power
tri?um breeding, structural materials, energy
conversion, environmental a:rac?veness4.

Establish an integrated fusion power concept that iscommercially a:rac?ve
economic, reliable, high availability

In each area,• There are “big ideas,” many pioneered in the US, not being
explored signiﬁcantly, that can have large impact• Most ideas have “moderate cost” next steps and “substan?alcost” integra?ng/demonstra?on steps;
the strategy is rela?vely robust to funding level• Many ideas, no one “silver bullet” for fusion

Create the fusion plasma core
1. Realize a smaller, steady-state tokamak visionHigh temperature/high ﬁeld SC magnets
Low aspect ra?o tokamak
Improved opera?ng regimes
2. Develop new 3D magne?c conﬁgura?ons for intrinsic steady-state
Op?mize stellarator for high performance
Aim toward DT facility
3. Establish a program for high risk, high payoﬀ exploratory concepts
With an evalua?on structure with metrics

Create the fusion plasma core
1. Realize a smaller, steady-state tokamak visionHigh temperature SC magnets
A new ac%vity,Low aspect ra?o tokamak
Improved opera?ng regimes poten%ally transforma%ve
2. Develop new 3D magne?c conﬁgura?ons for intrinsic steady-stateOp?mize stellarator for high performance
Aim toward DT facility
3. Establish a program for high risk, high payoﬀ exploratory concepts
With an evalua?on structure with metrics

Pushing fusion to smaller size
fusion power~ (pressure)2
where β = p/B~ β2B4~ (κβNB)4 for ﬁxed bootstrap frac?on2(βN = β/(I/aB) ,κ = elonga?on )Increase β,κ bypushing physics(spherical tokamak)

Increase B by pushingtechnology(e.g, high Tc superconductors)“Compact” fusion pilot plant/FNSF
Generates net electricity,breeds tri%um, high neutron ﬂuence
ST design (PPPL)ARC design (MIT)
Major radius = 3 m
High Tc SC for high ﬁeld
and/or smaller magnets

Volume within cryostat about 1/3 that of ITER

Advancing the High Magne?c Field Approach• High Tc magnet R/D for fusion (3 – 5 years)
Prototype coil tests (incl. for 3D systems)
Develop demountable joints(Moderate cost)• Enables a compact conﬁnement experimente.g., divertor test tokamak, DT experiment(Substan?al cost)

Create the fusion plasma core
1. Realize a smaller, steady-state tokamak visionHigh temperature/high ﬁeld SC magnets
Low aspect ra?o tokamak
Improved opera?ng regimes
2. Develop new 3D magne?c conﬁgura?ons for intrinsic steady-state
Op?mize stellarator for high performance
Aim toward DT facility
3. Establish a program for high risk, high payoﬀ exploratory concepts
With an evalua?on structure with metrics

Super-op?mizing plasma conﬁnement (stellarators)
3D magne?c ﬁeld: no symmetry
huge magne?c design space
Merges most advanced physics and computa?onW7-X

Can vary: symmetries (helical, toroidal), no symmetry, magne?c shear,curvature, aspect ra?oOp?mizes: thermal conﬁnement, energe?c par?cle conﬁnement,
MHD stability, turbulent transport…....
Result: Steady-state, disrup?on-freeWell-conﬁned
High fusion energy gain

Challenges:
Experimental valida?on
Find op?mumAdvancing the stellarator• Begin a na?onal op?miza?on/design study now
Focused on design that complements interna?onal eﬀort(e.g., quasisymmetry, incorporate new ideas such as turbulent
transport op%miza%on, magnet simpliﬁca%on, energe%c par%cle
conﬁnement, strong ﬂow…..)• Construct a mid-scale facility to test these ideas~ moderate cost
• Advance toward a world-leadership-scale experiment
design could be similar or complementary to mid-scale facility,(substan?al cost)

All new and poten?ally transforma?ve2. Tame the plasma-wall interface• Develop liquid metal boundaries• Explore and deploy new advanced magne?c divertor topologies• Linear test stands – materials exposed to plasma ﬂux• Explore addi?ve manufacturing for advanced solid walls

2. Tame the plasma-wall interface• Develop liquid metal boundaries
New and poten?ally transforma?ve• Explore and deploy new advanced magne?c divertor topologies
Exis?ng program, but many addi?onal opportuni?es• Linear test stands – materials exposed to plasma ﬂux
New program, moving beyond exis?ng facili?es• Explore addi?ve manufacturing for advanced solid walls
Largely unexplored for fusion

Liquid metals for the plasma-facing material
Self-regenera?ng,No erosion, neutron damage, heat overload (if moving)
Highly absorbing (if lithium): no inﬂux to plasma, improves
conﬁnement,
Many science and engineering challenges to establish feasibility

Developing Liquid Metal Boundaries• Broad R&D program: next 5 – 7 years
Surface science studies
Linear test stands
Liquid ﬂow tests
Studies in exis?ng toroidal facili?es(Moderate cost)•

Integrated fusion facility with LM boundary
Integrated viability of liquid surfaces,
Engineering design/construc?on begin in ~ 5 years,
Possibly two stages – divertor, full wall
(Substan?al cost)3. Harness fusion power• Materials and blanket researchcompact neutron source
innova?ve blankets (immersion, DCLL)(moderate cost)• US DT facility: Ini?ate now a community planning process forpossible missions, complemen?ng ITER:
Fusion nuclear science facility (FNSF)
High gain burning plasma science (Q > 10)
Pilot plant (net electricity)(very substan?al cost)

US DT Facility
Next 3-5 years:• Iden?fy mission(FNSF, high gain burning plasma science, net electricity)• Develop op?mal path(s) to a DT experimental program(e.g., AT, ST, high ﬁeld, op?mized stellarator…...)

In 3-5 years:• Review status and decide mission/?ming of DT facility

Increasing opportuni?es in computa?on and theory• Computa?on (at all scales, up to exascale), in concert withtheory, underlies all fusion topics• Tremendous opportuni?es are strongly in line with DOE/
na?onal emphasis on large-scale computa?on

With or Without the US in ITER
• Above strategic vision and goals are unchanged  thestrategy is rela?vely robust• If US not in ITER: aﬀects ?ming and mission of US DT program,decreases emphasis on ITER prep research
Although if the US pulls out, an earthquake could result with unpredictable consequences

This strategy would be a 4th shiz for fusion research
70s/80s:

Surge in tokamak research (facili?es)
Tokamak performance/understanding exploded

mid-90s:

Restructuring: shiz to science founda?ons
CIT/BPX TFTR TPX & US out of ITER,
Succeeded in reinvigora?ng fusion science

mid-2000s:

2018:

Presiden?al ITER ini?a?ve and coordinated world eﬀort
ITER moves forward as focus of world program
but, US domes?c capabili?es wane rela?ve to world
Establish an aggressive program, exploi?ng newinnova?ve ideas, to carry the US to fusion energy:
Re-assert US leadership

Typical fusion plan in other na?ons (simpliﬁed)
Plasma-materialinterface

Solid tungsten (tokamaks and test facili?es)

High performance,steady state

Tokamaks, limited stellarator

burning
plasmas
Fusion nuclear
science
Integra?onITER
Blanket development studies, TBM in ITER, possible IFMIF

Large-tokamak DEMO

A sample new US program in the interna9onal context
Plasma-materialinterface

Solid tungsten (tokamaks and test facili?es)

High performance,steady state

Tokamaks, limited stellarator

burningplasmas
Fusion nuclearscience
Integra?on

Liquid metals (tokamak, test facili?es)

An HTS reduced size tokamak/ST; a unique-design stellarator

ITER
Reduced-cost BPX, FNSF, or Pilot Plant
Blanket development studies, TBM in ITER, possible IFMIF
Compact neutron source, innova?ve blanket designs

Large-tokamak DEMO
More compact DEMO

The above can be described via challenges in fundamental science• A burning plasma is itself a major physics accomplishment – a newcomplex, physical system• The strategy is driven by major ques?ons inplasma physics (turbulence, self-organiza?on, breaking ofmagne?c topology, symmetry eﬀects…..),material science (under extreme condi?ons)• The connec?ons to other areas of science is large and speciﬁc(astrophysics, complex systems, accelerator physics.....)

How should fusion R/D be organized within DOE?
• The Oﬃce of Science (FES) must remain a key sponsor, given theremaining fundamental challenges in plasma physics and materialsciences• The Oﬃce of Science cannot tackle all the cri?cal challenges infusion engineering and technology• Thus, a possible approach is to sponsor fusion energy research inboth OS and an applied energy oﬃce, coordinated from above

Closing comments• A frank assessment of the health of the current program isimportant, and sets the stage from which to grow a new strategy• A new strategy emphasizing innova?ons for an improved fusion
system concept and accelerated path
Can be embarked upon with moderate new funds,
Forms the basis for aggressive roadmap to fusion power,
Builds construc?vely upon the current program,Re-establishes the US as a world leader,
Is scien?ﬁcally exci?ng