The High Field Path to COMMONWEALTH Fusion Energy: C-Mod to FUSION SPARC to ARC* SYSTEMS

The High Field Tokamak Path to Fusion Energy: C-Mod to SPARC to ARC*

Earl Marmar1, D. Brunner2, M.J. Greenwald1, Z.S. Hartwig1, A. Hubbard1, J. Irby1, B. LaBombard1, J. Minervini1, R. Mumgaard2, B. Sorbom2, E. Tolman1, D. Whyte1, A. White1, S. Wukitch1, and the MIT PSFC Magnetic Fusion Experiments Team

1MIT Science and Fusion Center, Cambridge, MA 02139 USA 2Commonwealth Fusion Systems, Cambridge, MA 02139 USA

60th Annual Meeting APS Division of Plasma , Portland, OR, November 8, 2018

*Partially Supported by the U.S. Department of Energy, Fusion Energy Sciences Compact High-Performance have Demonstrated High Absolute Performance

JT60 Japan JET 3 Europe Alcator C-Mod 3 Tesla MIT 8 Tesla

2 Compact, High B Tokamak Physics

• C-Mod Completed Operations in 2016 • Pointing to a high field path for future – 23 highly productive years – High Temperature, High Field – Many groundbreaking physics results Superconductors enable compact burning plasma and reactor concepts – Analysis ongoing

3 C-Mod Achieved World Record Core and Pedestal Plasma Pressures

21 High Performance: n≤1.5x10 ; T≤10keV; P≤2.1 atm, Pped≤0.8 atm Pedestal Pressure to 90% of ITER Target[1] X All C-Mod EDA H-mode Super H-mode XX X I-mode XXXX X X X

Compact/High B: R=0.67m; a=0.22m; ≤1.8; B0≤8T • All RF Auxiliary Heating & Current Drive • High Power Density: PB/R ~ 100 MW-T/m, 2 – ICRF: P≤6.5MW, 50 MHz to 80 MHz q||~3 GW/m – LHCD: P≤1.5MW, 4.6 GHz • High-Z Plasma Facing Components – Vertical plate divertor

[1]Snyder, et al., IAEA FEC 2018 EX/2-4 4 ELM Suppressed I-mode High Energy Confinement Regime: Operating Window Widens at High B

• I-mode, primarily studied on C-Mod, has many attractive features: – High energy confinement, low (BxB away from X-point) particle/impurity confinement – Weak confinement degradation with power – No ELMs to challenge the divertor • May be particularly attractive for the high B H-mode approach to reactors – H-mode threshold increases with B, suppressing the I- to H- transition at high power • Some of the remaining challenges L-mode – Power handling and robustness to detachment – Scaling to burning plasma conditions Also see Wilks, et al., IAEA FEC 2018, EX/P6-19; Happel, et al., EX/2-3 5 Non-Inductive Lower Hybrid Current Drive is Challenging at High Density

•C-Mod results[1] show anomalously low current drive efficiency and sharply decreased production of fast electrons at high density, high Greenwald

fraction (fG)

•Increasing Ip at fixed density (and thus lowering fG) reduces the anomaly – Current drive efficiency matches model

[1]Wallace, et al., Phys. Plasmas 2010

6 Reduced Current Drive Efficiency Correlates with Increased Greenwald Fraction

•C-Mod results[1] show anomalously low current drive efficiency and sharply decreased production of fast electrons at high density/high Greenwald

fraction (fG)

•Increasing Ip at fixed density (and thus lowering fG) reduces the anomaly • Directly correlates with reduction in edge turbulence Normalized Hard X-Ray Flux X-Ray Hard Normalized driven particle flux at low fG

[1]Wallace, et al., Phys. Plasmas 2010

Baek, et al., IAEA FEC 2018, EX/P6-28 7 Edge/SOL Density Fluctuations and Cross-Field Particle

Transport Increase Dramatically as fG Increases

•C-Mod results[1] show anomalously low current drive efficiency and sharply decreased production of fast electrons at high density/high Greenwald

fraction (fG)

•Increasing Ip at fixed density (and thus lowering fG) reduces the anomaly • Directly correlates with reduction in edge turbulence [2] driven particle flux at low fG 0.1 0.2 0.3 0.4

[1]Wallace, et al., Phys. Plasmas 2010 Normalized Greenwald Fraction (fG)

[2] LaBombard, et al., Phys. Plasmas 2008 8 Low Greenwald Fraction is not attractive for Power Reactors Possible Solution: High Field Side Launch

• High-field side SOL is quiescent:[1] • Wave accessibility and damping also expected to improved with HFS launch[2] HFS Launcher • Plan to test on DIII-D[3]

[1]Smick, et al., Nucl. Fusion 2013 [2]Bonoli, et al., Nucl. Fusion, 2018 [3]Wukitch, et al., EPJ Web of Conf. 2017; Wallace et al., IAEA 9

FEC 2018 FIP/3-3 C-Mod Results Show that “Eich” Scaling[1] for SOL Power Width Continues to the ITER Poloidal Field

[2] q database Extended with Operation at 8 Tesla

Implies ITER will have

q=0.5 mm

[1]Eich, et al., Nucl. Fusion 2013 [2]Brunner, et al., Nucl. Fusion 2018; Brunner, et al., IAEA FEC 2018, EX/P6-9 10 Original q Scaling Developed for H-mode [1] -1/2 C-Mod Results show q  Pressure for L-mode, I-mode and H-mode

Each confinement regime gives q  1/Bp, but Plasma Pressure unifies all the C-Mod results with different constants of proportionality

[1]Brunner, et al., Nucl. Fusion 2018; Brunner, et al., IAEA FEC 2018, EX/P6-9 11 Divertor Solutions Needed For Reactor Regimes

• Current experiments (and ITER) push to the limits of conventional vertical plate divertor • New solutions will be needed for the ~5x bigger challenge anticipated in reactors

12 Advanced Divertor Concepts are being Developed: Must be Tested at Ultra-High Power Density

Modeling shows great promise for the ADX is a DTT concept that can test many long-leg X-point target concept[1] advanced divertor configurations[2]

Prad and Te contours with Psol= 6 MW (PB/R = 70 MW-T/m)

[1]Umansky, et al., IAEA-FEC 2018 (TH/7-2) [2]LaBombard, et al., 2015 13 REBCO High Temperature/High Field Superconductor: Game-Changer for High B/Compact Fusion Energy Path

• Conventional superconductor (Nb3Sn) limits maximum on-axis B to about 5 tesla (R/a ~ 3) • Development of High-Temp Superconductors (HTS) opens the window for increased B – Field limit is no longer B at the coil, but engineering stresses instead – Higher T (~20 K) operation also has engineering advantages, and may allow for jointed coils

14 SPARC: Concept for Compact, High-Field Burning Plasma Facility

SPARC technical objectives: Size of DIII-D/ASDEX-U, B0=12 Tesla • Burn D-T fuel • Q > 2 (with headroom)

•Pfusion > 50MW • Pulsed with 10s flattop burn (about

2x CR) • ~1,000 D-T pulses, >10,000 D-D full-power pulses • ~1 hr D-T pulse repetition rate • ~15 minutes between D-D shots Desired Schedule: 3 yrs R&D (already started) + 4 yrs construction 15 The H98=1 Confinement Projection Puts SPARC within the Footprint of the Existing Tokamak Database

16 In Plasma Physics Variables, the SPARC Operating Point Is Generally Closer to the Mean of the H-mode Confinement Database than ITER

N * *

q95 n/n . ITERDB data using G criteria from H98 scaling and ITER-like geometry . Exception: some records don’t contain the kinetic information required to calculate * or *

17 For Example, SPARC operates in a well explored region of normalized density

n/nG SPARC baseline operation

ITER operation #of data points #of data points in database

Running comfortably below the density limit The level of plasma fluctuations and convective has a strong impact on the plasma losses are dramatically lower  Less susceptibility to disruptions  Strongly reduced main chamber wall interactions  Easier, generally, to get good confinement  Less scattering of RF waves by edge fluctuations

18 Compact High Field Pilot Plant Concept (ARC)[1] With Advanced Divertor, Jointed Coils, Liquid Blanket[2]

• Recent design concept for a compact, high field, reactor using HTS magnets – incorporates long-leg X-point target divertor for power handling • Joints in TF coil could dramatically ease maintainability

• About the size of JET, but at B0=9.2 T

–Pfusion ~ 525 MW

– Pelectric ~200 MW

[1]Sorbom, et al., Fus. Eng. Des. 2015 [2]Kuang, et al., Fus. Eng. Des. 2018 19 Exciting Path for Fusion Energy

High-Field, High Power Density Plasma ARC Pilot Plant Science Experiments ADX/DTT

Alcator C-Mod

SPARC

Magnet and Fusion Technology, Burning Plasma

20