High Fusion Performance in Super H-Mode Experiments on ...E ~ 30-67 kPa s, nTτ ~ 4 - 8 1020 keV m-3 s Very High Pedestal Pressure, Stored Energy, and Confinement Time in Recent co-I

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High Fusion Performance in Super H-Mode Experiments on Alcator C-Mod and DIII-D

P.B. Snyder1, J.W. Hughes2, T.H. Osborne1, C. Paz-Soldan1, W. Solomon1, D. Eldon1, T. Evans1, T. Golfinopoulous2, B. Grierson4, R.J. Groebner1, A. Hubbard2, A. Jarvinen3, M. Knolker4, B. LaBombard2, F. Laggner4, A. Leonard1, O. Meneghini1, S. Mordijck5, T. Petrie1, S. Scott4, H.Q. Wang6, J.G. Watkins7, H.R. Wilson8, Y.B. Zhu9

Presented at 2018 IAEA Fusion Energy Conference Ahmedabad, Gujarat, India October 22–27, 2018

1 General Atomics 2 MIT Plasma Science and Fusion Center 3 Lawrence Livermore National Lab 4 Princeton University / PPPL 5 College of William and Mary 6 Oak Ridge Associated Universities

7 Sandia National Laboratory 8 York Plasma Institute, University of York, York UK 9 University of California-Irvine, Irvine CA

P.B. Snyder/IAEA/October 2018

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•  This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences, under Awards DE-FC02-04ER54698, DE-FC02-99ER54512, DE-FG02-95ER54309, DE-FC02-06ER54873, DE-SC0014264, and DE-SC0017992, using the DIII-D National Fusion Facility and Alcator C-Mod, DOE Office of Science user facilities. Extensive discussions with the ITPA pedestal group, as well as the numerous contributions of the Alcator C-Mod team, DIII-D team, and OMFIT group are gratefully acknowledged.

•  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.

Acknowledgments

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Super H-Mode Experiments on Alcator C-Mod and DIII-D Achieve High Fusion Performance, Record Pedestal Pressure

•  Super H-mode (SH) predicted in strongly shaped plasmas: high pped, increases with ne [Snyder NF15]

•  Record pedestal pressures (~80 kPa) achieved in C-Mod SH experiments [Hughes NF18] •  Successful tests of EPED model up to ~90% of predicted ITER pped

•  Record DIII-D fusion gain (QDT,eq~ 0.54). QDT,eq/IaB and QDT,eq/(RB)2 highest reported on any tokamak

•  High performance sustained w/ 3D magnetic perturbations to control ne and impurity accumulation •  Predicted to enable high performance on ITER, and be compatible with high separatrix density for

divertor solutions

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TFTR L16MW

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Q=inf, 15MA

2 atm

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JET ITER

TFTR L-Mode

H-Mode

Super H-Mode/NSH

Q=inf, 11MA

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EPED Model Predicts a High Pedestal “Super H-Mode” Solution

•  EPED (Snyder NF11) normally predicts a single pedestal solution –  Intersection of calculated peeling-ballooning (PB) and KBM criticality

–  Predicted using sets of realistic model equilibria w/ self-consistent bootstrap current

•  At strong shaping, fixed input parameters (including density), PB mode can go from stable to unstable (pressure driven) and back to stable again with increasing pressure and current: multiple roots for two “equations”, PB and KBM

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Pedestal Width ( N)

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Illustration of EPED1 Model, Multiple Roots

Peeling-Ballooning

KBM

EPED1 Prediction

S

SU

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EPED Model Predicts a High Pedestal “Super H Mode” Solution

•  Expect only lowest solution to be accessible for these parameters. However, can move in third dimension (eg density) to access higher roots (Super H)

•  SH predicted by theory [Snyder12,15], discovered and explored in counter Ip campaigns on DIII-D [Solomon14, Snyder15, Garofalo15, Solomon16]

2016 C-Mod: L-I-H transition to explore Super H regime access 2017-18: DIII-D: co-Ip SH expts explore performance and core-edge

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Peeling-Ballooning

KBM

EPED1 Prediction

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Pedestal Density (1019 m-3)

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EPED Predicted Pedestal Height vs Density

Super H-ModeH-ModeNear Super H


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High peak performance in Super H-Mode experiments


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Pedestal Density [ne,ped(Zeff /2)1/2 ,1019 m-3 ]

Pede

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Very High Super H Mode Pressure Predicted for C-Mod

•  Alcator C-Mod is a compact, high field device (here Bt~5.3T), capable of high δ –  After discovery of Super H-Mode on DIII-D, predictions were made for C-Mod (right)

•  Test SH theory at high Bt & Bp, zero injected torque (RF), high Z metal wall –  Following the right parametric trajectory should enable very high pressure

•  Need to reach densities much lower than typical for C-Mod H-mode to access Super H •  Challenging to do on a high-Z metal wall device like C-Mod

?


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Access to Super H Mode on C-Mod Achieved via L-I-H Transition

•  Transitioning first to I-mode, then to H-mode leads to a low ne, low impurity H-mode (left) •  As pedestal approaches predicted kink/peeling limit, low n mode observed (center) •  Discharges at 1MA, 5.4T reach SH regime, pped~70 kPa (right)

Hughes et al, NF 58 112003 (2018) Pedestal Density [ne,ped(Zeff /2)1/2 ,1019 m-3 ]

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C-Mod 1160922020, 0.8MA

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Pedestal Density [ne,ped(Zeff /2)1/2 ,1019 m-3 ]

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Pedestal Density [ne,ped(Zeff/2)1/2,1019m-3]

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EPED Predictions 1.4MA (based on 1160930042)

H-ModeNear Super HSuper H-ModeMeasured (C-Mod)

Super H-Mode Experiments on C-Mod Yield ITER-like pped

•  Super H-Mode expt at 1.4MA achieved record 81 kPa pedestal pressure on last day of Alcator C-Mod operations, ITER-like pressure at ITER-like field [Hughes NF 2018] –  EPED model successfully tested over 2 orders of magnitude in pressure on 6 tokamaks

•  No indication of significant variation of model accuracy with ρ* or pped


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•  High pedestal pressure enables good confinement, high global MHD limits –  C-Mod: Bt=5.3-5.8T, Ip=0.8-1.4MA, a=0.19m, R=0.67m, δ~0.5

•  ~ 100-170 kPa, pped ~ 50 - 80 kPa –  DIII-D: Bt=2.1-2.2T, Ip=1.6-2.0MA, a=0.6m, R=1.67m, δ~0.5-0.7

•  ~ 70 – 110 kPa, pped ~ 20 – 32 kPa, Ti,0 ~ 14 -18 keV

Broad Profiles and High Pressure Obtained in Both C-Mod and DIII-D

Electron Density (10 m )

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02468

Ion Temperature (keV)

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DIII-D 177007 @ 2190ms

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C-Mod 1160930042 @ 900ms

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•  Deep access into Super-H regime, good agreement with EPED predictions –  Bt=2.17T, Ip=1.6-2.0MA, a=0.6m, δ~0.5-0.7 –  pped~30kPa, W~2 - 3.2 MJ (highest in present DIII-D config.) at modest Pnbi ~ 8-12 MW –  Peak τ~0.4-0.7s, H98~2.2-2.9, τE ~ 30-67 kPa s, nTτ ~ 4 - 8 1020 keV m-3 s

Very High Pedestal Pressure, Stored Energy, and Confinement Time in Recent co-Ip Super H-Mode Experiments on DIII-D

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Access to High Performance Super H-Mode Regime on DIII-D

H-ModeNear Super HSuper H

t=2.1s

t=2.2st=2.3s t=2.4s


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•  DD neutron rates up to 1.85 1016/s –  ~2/3 thermal, Pfus,DD ~ 22 kW, Pfus,DT,eq ~ 4.8 MW (at Pnbi ~ 9 MW)

High Pedestal Pressure and Ti Enable High Peak Fusion Performance on DIII-D


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•  Equivalent QDT,eq = Pfus,DTeq/Pnbi ~ 0.54. Q*DT,eq=Pfus,DTeq/(Pnbi-dW/dt) ~ 1

–  Previous DIII-D record Q = 0.32, Lazarus96 in negative central shear discharges with 2.2MA, 22m3

–  Achieved at modest B = 2.17T, Ip=2MA, V=20 m3. DTeq Fusion power density ~0.2 MW/m3

High Pedestal Pressure and Ti Enable High Peak Fusion Performance on DIII-D, Record Fusion Gain

Appears to be highest QDT,eq and τ on any medium size (R<2m) tokamak, and highest QDT,eq/IaB or QDT,eq/R2B2 on any MFE device

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Sustainment and Core-Edge Compatibility of

Super H-Mode Regime

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•  High performance condition sustained by applying 3D magnetic perturbation –  Controls density and impurity

accumulation –  Feedback control of pedestal or

average density demonstrated –  Sustained W~1.9MJ, QDT,eq~ 0.15, τ~0.2s, H98~1.6, βN ~ 2.9

–  ~2s sustainment (hardware limited)

Super H-Mode Sustained Using 3D Magnetic Perturbations to Control Density and Impurity Accumulation

High sustained βN

Excellent confinementH98~1.6-2.5, τE~0.2-0.6s

Highest WMHD (~2.3-3.2MJ) since 2002Sustained WMHD~ 2 MJ

i-coil enables stationarydensity, pressure

WMHD

(MJ)

βN

H98


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•  Super H (J-limited) solution predicted not to show degradation of pedestal pressure w/ ne,sep –  P-limited solution degrades with increasing ne,ped

and ne,sep (eg high gas puff in JET ILW)

•  Scan D2 gas rate, and introduce radiative impurities (N2) into the Div/SOL to test predictions on DIII-D –  Use 3D magnetic perturbations (i-coil) to control particle and

impurity accumulation in core

–  Use i-coil feedback to maintain ~constant density in pedestal & core as separatrix, divertor and SOL density are increased

•  Test EPED predictions of sensitivity of pedestal to separatrix conditions

Connecting a High Performance Super H Pedestal & Core to a High Density, Radiative Divertor & SOL

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

J-limited

P-limited


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•  D2 gas scan in Super H mode experiment at Ip=2MA, Bt=2.1T. Gas rate varied ~30x –  Pedestal pressure and τE remain ~fixed, high –  i-coil feedback control of ne,ped ~ 7-8 1019 m-3

successful up to~110 torrL/s of D2 gas –  Separatrix density rises from ~2.5 – 4 1019 m-3

–  Strike point density rises from ~2.5 – 7 1019 m-3

D2 gas Scan Increases Separatrix and Divertor Density while Pedestal Pressure and Confinement Remain High

Both pedestal and separatrix density reach ITER values while maintaining high confinement and pped


Super H-mode compatible with both high fusion performance and high separatrix density for

divertor solutions.

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•  Significant cooling with ~5MW of divertor radiated power using feedback on N2

–  Peak Te near strike point drops more than 3x –  Pedestal pressure and confinement remain

~constant –  Future experiments needed to explore full

detachment and impact of closed divertor

N2 Injection Effective for Cooling Divertor while Maintaining High Performance Core & Pedestal

Outer divertor

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Predictions for ITER, Implications for Compact, High Performance Fusion

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Super H/NSH Regime Access is Predicted for ITER: DIII-D has Achieved Needed βN,ped, ne,sep, ne,ped Consistently

Open issue: Physics of the Greenwald density limit which constrains degree of Super H

access and predicted performance for ITER and DEMO concepts

•  Core-pedestal simulations find ITER high performance (Q>10) at high ne [Meneghini16]

•  DIII-D SH experiments reproduce many characteristics of the predicted ITER regime, including βN,ped~0.8, ne,sep~3-4, ne,ped~7-10. C-Mod produces pped~80 kPa

–  Potential for substantial improvements in ITER performance, consistent with ne,sep

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EPED Predicted Pedestal Height vs Density for ITER Baseline

H-ModeNear Super HSuper H


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Super H and Near Super H Operation Enables Very High Fusion Performance per IpaBt

•  Simple metric of fusion performance (Q or W/P) per IpaBt –  Colored points are observations ( > 50 kPa), red points are SH/NSH experiments –  High Q/IaB enables ITER success, and compact, cost attractive pilot plant

Open issues: Challenges for Super H-mode operation include

sustainment, impurity control, and ELM control.

For JET and ITER, compatibility of strong shaping and nearby

metal walls


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•  Theoretical prediction of Super H Mode has guided successful expts on C-Mod and DIII-D –  Entering new era where theory can enable predictable, higher MFE performance

•  Record pedestal pressures (~80 kPa) achieved in C-Mod SH experiments [Hughes NF18]

–  Successful tests of EPED model up to ~90% of predicted ITER pped

•  Record DIII-D fusion gain (QDT,eq~ 0.54, Q*DT,eq~ 1). QDT,eq/IaB ~ 0.21 and QDT,eq/(RB)2 ~ 0.04

•  Projects (theoretically & empirically) to excellent ITER performance, compact attractive pilot plant

•  High performance sustained w/ 3D magnetic perturbations to control ne and impurity accumulation (DIII-D: W~1.9MJ, QDT,eq~ 0.15, τ~0.2s, H98~1.6, βN ~ 2.9)

•  High performance maintained with strong D2 gas puffing and N2 injection •  Separatrix density reaches ITER values, divertor T reduced by ~3x

High Fusion Performance and Promising Core/Edge Solutions Developed via Super H Theory & Experiment

Super H-mode compatible with both high fusion performance and high separatrix density for divertor solutions. Projects to excellent

ITER performance and compact, attractive pilot plant

Documents

High Fusion Performance in Super H-Mode Experiments on ...E ~ 30-67 kPa s, nTτ ~ 4 - 8 1020 keV m-3 s Very High Pedestal Pressure, Stored Energy, and Confinement Time in Recent co-I