Options and strategies towards
fusion net electricity
Dr. Jonathan Menard
Princeton Plasma Physics Laboratory, USANAS Committee for a Strategic Planfor U.S. Burning Plasma Research
Princeton Plasma Physics Laboratory
April 11, 2018

Thank you for the invitation to speak about:• The state and potential of magnetic
confinement-based fusion research in theUnited States and the options and strategies
that may shorten the path to fusion energy…
• …for example, through design andconstruction of fusion energy facility todemonstrate electrical self-sufficiency
2Outline• Overview• Tokamak Pilot Plants• Stellarator Pilot Plants• Summary3Electricity gain Qeng determined primarily byengineering efficiencies and fusion gain Q (=QDT)Qeng 

Electricity produced
Electricity consumedth ( M n Pn  P  Paux  Ppump )= PQeng = th aux Q ×aux

 aux

 Ppump  Psub  Pcoils  Pcontrol(4 M n  1  5 / Q  5 Ppump / Pfus )th  thermal power conversion efficiency
aux  injected power wall plug efficiency
Q  Pfus / Paux = fusion power / auxiliary power5(1   aux QPextra / Pfus )Parameter Assumptions:• Mn = 1.1, Ppump = 0.03×Pth• Psub + Pcontrol = 0.04×Pth• aux = 0.3• CD = ICDR0ne/PCD  0.3×1020A/W/m2
For more details see J. Menard, et al., Nucl. Fusion 51 (2011) 103014
4

Burning plasma demonstration remains essential
ITER: Q = 10Pfusion = 400-500MW
tpulse = 300-500s
R = 6.2 m, a = 2.0 m
BT = 5.3 T, IP = 15 MA•••••

Critical knowledge to be gained:
Non-linear dynamics from turbulence,majority self-heating by -particles
Confinement, stability at low r*, n*High power exhaust handling, both
steady-state and transient (ELMs)
Disruption prediction, avoidance, andmitigation at reactor scale
Nuclear facility: licensing, operation,
diagnostics, plasma control, remotehandling, T processing

5

ITER basis extrapolates to large, pulsed DEMO
• R = 8-10m• tburn =1-3 hrs• Advantage:– Use nearly/existing
physics, technology• Challenges:– Thermal, EM stress– Energy storage– Cost and schedule
for construction
6Some stellarator reactor designs also large R• FFHR-2ml (Japan), LHD-like– R=14m, a=1.73m, B=6.2T, Pfusion=1.9GW• HSR (Germany), W7X-like– R=20m, a=1.6m, B=5T, Pfusion~3GW• ARIES-CS (US), NCSX-like– R=7.75m, a=1.7m, B=5.7T, Pfusion=2.44
Note: These are Pelec~1GWe  higher than largest-R tokamaks on previous slide7

~70% of U.S. electricity from ≤ 500MWe sources

From: Observations on Fusion Power Market Attractiveness
Ryan Umstattd - Deputy Director for Commercialization (Acting)Presented at US Fusion Community Workshop
December 11, 2017 – Austin, TX

8

~70% of U.S. electricity from ≤ 500MWe sources
Characteristics of U.S.
electricity market:• Lower power: 1-500 MWe• Modular / load-following• Low (enough) capital cost
 Challenging for fusion
From: Observations on Fusion Power Market Attractiveness
Ryan Umstattd - Deputy Director for Commercialization (Acting)Presented at US Fusion Community Workshop
December 11, 2017 – Austin, TX

9

Possible high-level fusion development strategy
 Focus research and resources on key science andtechnology drivers that could lead to more compact
and/or efficient fusion systems
1. If above R&D successful, develop small net electricdemonstration (or equivalent) facility (Pilot Plant)
2. AND need substantial fusion nuclear materials andcomponent R&D (Fusion Nuclear Science Facility)• May be possible to combine 1. and 2. into FNSF/Pilot

Performance parameters for strategy
1. Integrate high-performance, steady-state, exhaust QDT = 1-20, 100% non-inductive (tokamaks), Pheat/S ~ 0.5-1MW/m2

2. Fusion-relevant neutron wall loading Gn ~ 1-3MW/m2, fluence: ≥ 6MW-yr/m2

3. Tritium self-sufficiency

FNSF emphasis

 Tritium breeding ratio TBR ≥ 1

4. Electrical self-sufficiency
 Qeng = Pelectric / Pconsumed ≥ 1

Pilot emphasis

Possible to achieve in single device with phased program?

What are key drivers for compact fusion?

Consider tokamaks first….

Fusion gain QDT  H25 from low  high gain

Fix current, field, density, geometry, auxiliary power, P = 0.7:
QDT ≤1  QDT  Q*DT  H2
QDT >>1  QDT  Q*DT2.5  H513Gain vs. physics and engineering constraints• In steady-state, current-driven kink limit weaker constraint than highfBS  no q* dependence  relevant variables are bN / fBS and fgw:
Exponent 98y2 Petty-08
Cb

2.68

2.14

CB

2.98

2.74

Cgw

0.82

0.64

CP-0.38

0.06

CR

1.98

2.04

CC

5.92
1.54

5.04
1.61

• Choose electrostatic gyro-Bohm Petty-08
with no b degradation (JET, DIII-D, NSTX)
Gain depends on (at least) 8 global parameters

C. Petty, et al., Phys. Plasmas 15 (2008) 080501

14

Key parameters for achieving high gain
Optimize: confinement, current drive vs density

Majorradius
Normalized Normalized
GainConfinement

ExternalCurrent Drive
Fraction
Normalized
Density

aspect ratio

Elongation
Toroidalfield inplasma

Normalized
betaInverse
aspectratio
15Potential Innovations for Compact Pilot
Tokamak• Magnets – HTS for higher BT and Jwinding-pack• Confinement – Optimize edge transport barrier• Stability – Disruption avoidance, bN > no-wall limit• Aspect Ratio – Reduced A  higher bN and • Heating & Current Drive – New RF, Negative NBI• Divertors – Advanced / long-leg, liquid metals• Blankets – Liquid metal, high efficiency

High-current-density rare earth barium copper oxide (REBCO)
superconductors motivate consideration of lower-A pilot plants
A ~ 2 attractive at high JWP
Conductor on Round Core Cables(CORC): High winding pack current
Pnet [MWe]150
density at high magnetic fieldJ
JWP ~ 70MA/m2 at 19T

Higher current densities, B likely possible…

WP[MA/m2]

10050

19T

012T

10 mm-5010 mm-100
7 kA CORC (4.2K, 19 T) cableBase cable: 50 tapes YBCO Tapes with 38 mm substrate(Van Der Laan, HTS4Fusion, 2015)

-150
1.5

2.0

2.5

3.0

3.5

Aspect Ratio A

R = 3mTBR ~ 1PNBI = 50MW
100% non-inductivebN (A) at no-wall limit

4.017

A ≤ 2 maximizes TF magnet utilization

JWP = 70MA/m2

Eff. shieldthickness:
0.3m
0.4m
0.5m
0.6m
0.7m

18

A ≥ 3 maximizes blanket utilization
Eff. shieldthickness:
0.3m
0.4m
0.5m
0.6m
0.7m
JWP = 70MA/m219

All R=3m pilots require enhanced confinement
i.e. H > 1 vs. conventional aspect ratio confinement scalings
H98y2 = 1.5-1.8

HPetty-08 = 1.25-1.4
JWP[MA/m2]

Effective inboard WC n-shield thickness = 60cm
20

Example: A=2, R0 = 3m HTS-TF FNSF/Pilot Plant
J. Menard, et al., Nucl. Fusion 56 (2016) 106023

BT = 4T, IP = 12.5MA
 = 2.5, d = 0.55
bN = 4.2, bT = 9%, fgw = 0.8
H98 = 1.75, HPetty-08 = 1.3
HST = 0.7-0.9
fNI = 100%, fBS = 0.76

Cryostat volume ~ 1/3 of ITERStartup IP (OH)~2MA
JWP = 70MA/m2
BT-max = 17.5T
No joints in TF
Vertical maintenancePfusion = 520 MW
PNBI = 50 MW
ENBI=0.5MeV
QDT = 10.4
Qeng = 1.35
Pnet = 73 MW

Wn = 1.3 MW/m2
Peak n-flux = 2.4 MW/m2
Peak n-fluence: 7MWy/m2
TBR  121

Example: A=2, R0 = 3m HTS-TF FNSF/Pilot Plant
J. Menard, et al., Nucl. Fusion 56 (2016) 106023

BT = 4T, IP = 12.5MA
 = 2.5, d = 0.55
bN = 4.2, bT = 9%, fgw = 0.8

Pfusion = 520 MW

H98 = 1.75, HPetty-08 = 1.3
HST = 0.7-0.9

but potentially
QDT = 10.4
favorable
Qeng
1.35
ST=non-inductive
atPnetsustainment= 73 MWhigh performance2
Wnremains= 1.3 MW/m
to be
Peakdemonstrated
n-flux = 2.4 MW/m2

fNI = 100%, fBS = 0.76
Startup IP (OH)~2MA
JWP = 70MA/m2
BT-max = 17.5T
No joints in TF
Vertical maintenance

PNBIST= 50
MW
confinement

scaling
uncertain,ENBI=0.5MeVPeak n-fluence: 7MWy/m2

TBR  1
Cryostat volume ~ 1/3 of ITER
Understanding ST confinement, sustainment = drivers for NSTX-U – See Gerhardt talk22

Advanced / long-leg divertors, and/or fast-flow
liquid metal likely required to enable compact Pilots
Long-leg / Super-X divertor

Shorter leg LM divertor

Geometry also compatible with“vapor box” concepts (Ono / Goldston)

9 MW/m2

21 MW/m2
23

Benefits of shorter-leg liquid metal divertor:• No top PF coil or separate cryo-stat  simplified maintenance

453
2

6178

• Significantly reduce outboard PF coil current, force, structure• If liquid lithium, wall pumping could help increase H-factor
Power handling, mass control/removal, pumping drivers for LM – See Jaworski talk24

Liquid metal / molten salt blankets offer potential forhigh thermal efficiency, modular design
HTS ST-FNSF/Pilot

ARC (MIT)
JointedTF

FLiBe:
600-900ºC

L. El-Guebaly, et al., Energies, 9 (2016) 632

PbLi
450-750ºC

SiC / PbLi
1000ºC

Dual-coolant Lead-Lithium (DCLL) blankets,
20 vertical sectors: th = 30-45% (55% SiC/SiC)

FLiBe liquid immersion blanket, single
component/removable: th = 40-50%25Outline• Overview• Tokamak Pilot Plants• Stellarator Pilot Plants• Summary26

Stellarator strengths, challenges for FNSF/Pilot• No current drive required / intrinsically steady-state– Lower recirculating power, smaller wall penetrations• MHD-stable without active feedback control– Reduced diagnostic and actuator needs– No coils inside blanket/shield, internal stabilizing shells,
disruption mitigation systems, or runaway electron risk
– Thinner first wall, improved T breeding• Challenges:– Thermal / fast particle confinement, complex coils / blanket /maintenance, 3D power / particle exhaust, compactness

272010-11: Size of compact stellarator (CS) pilot driven bymagnet technology and neutron wall loading, but not Qeng

Qeng6.0=1.1 accessible at HISS04 ≥ 1.1 (~L-mode)
6

Bcoil = 14T

B [T]

B [T]

= Pilot design point

1.1

5.0

5

1.5

H-ISS04=2

b=6%

H-ISS04=1.5

HISS04 = 2

H-ISS04=1.1

th = 0.3

44.0

433
55
66
4MajorRadius[m]
HISS04=2
 QMajor=2-3,high[m]QDT (~H-mode)eng
H=Radius
2, b = 6%53646.064.75m

ISS043

BB[T][T]

255.0b=6%

26

Qeng = 1

Qeng=1, Q=9

Qeng=2, Q=264

Qeng=3, Q=70
th = 0.3

4.033

70

QDT = 944Major Radius55[m]Major Radius [m]66• A = 4.5 = 4.75m / 1.05m• BT = 5.6T, IP = 1.7MA (BS)• Avg. Wn = 1.2-2 MW/m2• Peak Wn = 2.4-4 MW/m2

28

New stellarator optimization initiated at PPPL
• Study intended to map out the configuration and physics
program for a future stellarator project• Current topics include (a subset):– Generate a database of starting point equilibria by varying aspect ratio,elongation, bootstrap fraction and beta.
– Include coil force constraints (COILOPT++ code modified)– Neoclassical transport, bootstrap (SFINCS), REGCOIL coupled to STELLOPT– Extend turbulent transport optimization from Quasi-Axisymmetric (QA) to QuasiHelically (QH) symmetric configurations– Develop metrics that will be used in an eventual divertor optimization algorithm
29Recent design efforts: Reactor (not Pilot Plant) designsmodified to improve physics/engineering self-consistency• Increase A = 4.5  6, R=7.75m to 9.4m,
straighten outer legs for vertical maintenance
MC with straight back legs

FreeBoundary

FixedBoundary

ARIES-CS 4.5 AR,
7.75-m Raxis

ARIES-CS 6.0 AR,9.4-m Raxis

High AR device meets targeted
ARIES-CS plasma boundary30

Result: simplified tokamak like vertical maintenance• Future: Need to revisit
design and performance
implications for CS
FNSF / Pilot Plant
31

Potential Innovations for Compact Pilot
Stellarator• Magnets – HTS for higher BT, Jwinding-pack beneficial?
• Confinement – Optimize 3D core, edge, fast-ion• Stability – intrinsically avoid runaways, EM loads• Aspect Ratio – maintenance vs. mass-power density• Heating & Current Drive – New RF, Negative NBI• Divertors – Further design needed, liquid metals• Blankets – Liquid metal, high efficiency
32

Outline• Overview• Tokamak Pilot Plants• Stellarator Pilot Plants• Summary33

U.S. is leader in scoping studies for range ofpossible compact FNSF/Pilot Plants
STLow-A

Quasi-symmetric(QS) Stellarator

Standard-ATokamak

A=3-4, R=4m

A = 1.7
R = 1-2.2m

A~2
R = 3m

A=3
R = 3.3m
A=4, R=4.8m(FESS FNSF)

A ≥ 4.5, R ≥ 3.5m
34

U.S. could / should lead in establishing physics& technology basis for compact FNSFs/Pilots• Integrated experimental demonstrations plus validated
predictive capability to confidently proceed to FNSF/Pilot:– Adequate / elevated confinement - thermal and fast particle– High efficiency CD for tokamaks, steady-state operation (1046s)– Divertor + first-wall solutions for high power (P/S~1MW/m2), highTwall (350-550C possibly higher), mass removal for erosion/dust– ELM & disruption avoidance/mitigation (leverage ITER R&D)

• HTS magnets for higher field, current density, temperature• Radiation-resistant materials, high-efficiency blankets
35

Summary• Extrapolations of present physics and technology basis
appears to lead to large fusion devices which may not bewell matched to U.S. electricity market• For more attractive fusion end-products, innovations areneeded, and several appear very promising• U.S. research to advance compact AT/ST/stellarator
combined FNSF + Pilot Plants could form complementaryand highly impactful contribution to world fusion program36

BackupComparison of low-A FNSF / Pilot Plants

TF coiltypeR

Surf-avg
Ph / Sn-fluence

H98 HPetty HST

x bN bT f BS

1.6

1.25

1.25

0.70

2.75

520

0.82 7.3 3.0

≥6

0.9

1.25

1.1

0.72

2.75

4

16

0.76

0

0.04

0.5

2.3

2.1

0.64

2.30

4

7.1 0.84 7.4

1.0

4-6

0.5

1.8

1.3

0.69

2.50

48.7 0.76

AQeng QDT TBR

1.70.1

1.0

≤ 0.9

6

1.7 1.70.15

2.0

1.01.8

217.3

321.3

10[m]

122
[MWy/m ] [MW/m ][%]I P BT Pfus
[MA] [T] [MW]60

Copper
11 3.0 160
5160

REBCO
13 4.0 510