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
1 General Atomics

2 MIT Plasma Science and Fusion Center3 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

Presented at2018 IAEA Fusion Energy Conference
Ahmedabad, Gujarat, India
October 22–27, 2018
P.B. Snyder/IAEA/October 20181

Acknowledgments• This material is based upon work supported by the U.S. Department of Energy, Office ofScience, Office of Fusion Energy Sciences, under Awards DE-FC02-04ER54698, DEFC02-99ER54512, DE-FG02-95ER54309, DE-FC02-06ER54873, DE-SC0014264, and DESC0017992, using the DIII-D National Fusion Facility and Alcator C-Mod, DOE Office ofScience user facilities. Extensive discussions with the ITPA pedestal group, as well as thenumerous 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 UnitedStates Government. Neither the United States Government nor any agency thereof, nor any of theiremployees, makes any warranty, express or implied, or assumes any legal liability or responsibility for theaccuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, orrepresents that its use would not infringe privately owned rights. Reference herein to any specificcommercial product, process, or service by trade name, trademark, manufacturer, or otherwise does notnecessarily 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 notnecessarily state or reflect those of the United States Government or any agency thereof.

2Super H-Mode Experiments on Alcator C-Mod and DIII-D AchieveHigh 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

Fusion Performance Metric (<p>W/PhIaB)• 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 fordivertor solutions
15ITER
DIII-D Super H

DIII-DC-ModSuper H-Mode/NSH

10

Q=inf, 11MA

DIII-D H

Q=inf, 15MA

C-Mod Super H
C-Mod H

Q=10, 11MA
5JET

2 atm

16MW

JET H

ITER
Q=10, 15MA
H-ModeTFTR L

Q=5, 15MA
00.0

0.5

TFTR

L-Mode1.0

1.5

Minor Radius (m)2.02.5

3

EPED Model Predicts a High Pedestal “Super H-Mode” Solution• EPED (Snyder NF11) normally predicts a single pedestal solution• At strong shaping, fixed input parameters (including density), PB
mode can go from stable to unstable (pressure driven) and backto stable again with increasing pressure and current: multiple
roots for two “equations”, PB and KBM

Pedestal Height (pped, kPa)

– Intersection of calculated peeling-ballooning (PB) and KBM criticality– Predicted using sets of realistic model equilibria w/ self-consistentbootstrap current

35

Illustration of EPED1 Model, Multiple RootsUS

Peeling-Ballooning3025KBM
EPED1 Prediction

U20
15
10S

500.00

0.02

0.04

0.06

0.08

Pedestal Width ( N)P.B. Snyder/IAEA/October 2018

4

EPED Model Predicts a High Pedestal “Super H Mode” Solution• Expect only lowest solution to be accessible for theseparameters. However, can move in third dimension (eg density)
to access higher roots (Super H)• SH predicted by theory [Snyder12,15], discovered and explored incounter Ip campaigns on DIII-D [Solomon14, Snyder15, Garofalo15,Solomon16]

Pedestal Height (pped, kPa)

35

Illustration of EPED1 Model, Multiple RootsUS

Peeling-Ballooning
30

KBM
EPED1 Prediction

25U

20
1510S

500.00

0.02

0.04

0.06

0.08

Pedestal Width ( N)2016 C-Mod: L-I-H transition to explore Super H regime access

EPED Predicted Pedestal Height vs Density

2017-18: DIII-D: co-Ip SH expts explore performance and core-edge

Pedestal Height (kPa)

25
20
1510

Super H-Mode
H-ModeNear Super H

50
12345678910

Pedestal Density (1019 m-3)

P.B. Snyder/IAEA/October 2018

5High peak performance inSuper H-Modeexperiments

P.B. Snyder/IAEA/October 20186

Pedestal Pressure (kPa)Very High Super H Mode Pressure Predicted for C-Mod?

Pedestal Density [n e,ped (Zeff /2)1/2 ,10 19 m -3 ]• 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
P.B. Snyder/IAEA/October 20187

720msPedestal Pressure (kPa)

Pedestal Pressure (kPa)

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

790ms
760ms
680ms
C-Mod 1160922020, 0.8MA

Pedestal Density [n e,ped (Zeff /2)1/2 ,10 19 m -3 ]

930ms
850ms
870ms
830ms
790ms
770ms
750ms

Hughes et al, NF 58 112003 (2018)

810ms

C-Mod 1160922032, 1MA

Pedestal Density [n e,ped (Zeff /2)1/2 ,10 19 m -3 ]• 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)

P.B. Snyder/IAEA/October 20188

Super H-Mode Experiments on C-Mod Yield ITER-like pped
Pedestal Pressure (kPa)

120
110
100
90
80
70101

60
5040

H-ModeNear Super H
Super H-Mode
Measured (C-Mod)

3020100

Measured Pedestal Height (kPa)

102EPED Predictions 1.4MA (based on 1160930042)

024681012141618
201/2
19-3
Pedestal Density [ne,ped(Zeff/2) ,10 m ]

22100
100

C-Mod (3, SH expt)
C-Mod (10, ELMing H-mode)
DIII-D (124)
JET (137)
JT-60U (16)Compass (23)
AUG (13)
ITER

101

102

EPED Predicted Pedestal Height (kPa)• Super H-Mode expt at 1.4MA achieved record 81 kPa pedestal pressure on last day ofAlcator 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
P.B. Snyder/IAEA/October 20189Broad Profiles and High Pressure Obtained in Both C-Mod and DIII-D
Electron Density (10 19m-3 )2520
1510508177007.2190.00

Electron Temperature (keV)

6420400

Pressure (kPa)

300

00(Electron)

0.2

Electron Density (1019 m-3 )15Ion Temperature (keV)Electron Temperature (keV)

10(Total)

200100C-Mod 1160930042 @ 900ms

86420864200.40.60.8
Normalized Radius (ψN)

1.05DIII-D 177007 @ 2190ms
000.2
0.4
0.6
0.8
Normalized Radius (ψN )1.0• 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• <p> ~ 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•<p> ~ 70 – 110 kPa, pped ~ 20 – 32 kPa, Ti,0 ~ 14 -18 keV
P.B. Snyder/IAEA/October 201810

Very High Pedestal Pressure, Stored Energy, and Confinement Time in
Recent co-Ip Super H-Mode Experiments on DIII-D
Pedestal Pressure [2*pe,ped, kPa]

Access to High Performance Super H-Mode Regime on DIII-D
35
30

t=2.3st=2.2s25

t=2.4st=2.1s20
15
10H-ModeNear Super H
Super H

503

45678910

1112

Pedestal Density [ne,ped(Zeff/2)1/2,1019m-3]• 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, <p>τE ~ 30-67 kPa s, nTτ ~ 4 - 8 1020 keV m-3 s
P.B. Snyder/IAEA/October 201811

High Pedestal Pressure and Ti Enable High Peak Fusion
Performance on DIII-D
Neutron Rate (10 16 /s)

2.0

1.6

174809Measured

Total(TRANSP)

1.2

Thermal(TRANSP)
0.8

Beam-Target(TRANSP)

0.4

Beam-Beam (TRANSP)
0.0

1.95

2.10

2.25

2.40

Time (s)• 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)

P.B. Snyder/IAEA/October 201812

High Pedestal Pressure and Ti Enable High Peak Fusion
Performance on DIII-D, Record Fusion Gain
0.54

0.32

• 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
Appears to be highest QDT,eq and <p>τ on any medium size (R<2m) tokamak, and highest
QDT,eq/IaB or QDT,eq/R2B2 on any MFE device
P.B. Snyder/IAEA/October 201813

Sustainment and Core-Edge
Compatibility ofSuper H-Mode Regime

14Super H-Mode Sustained Using 3D Magnetic Perturbations to Control
Density and Impurity Accumulation• High performance condition
sustained by applying 3D
magnetic perturbation

High sustained βN

3βN– 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 (hardwarelimited)

2i-coil enables stationarydensity, pressure

103Excellent confinement
H98~1.6-2.5, τE~0.2-0.6s

H98 2
10

WMHD 2(MJ) 1

Highest WMHD (~2.3-3.2MJ) since 2002
Sustained WMHD~ 2 MJ
171322

02000

2500

3000

3500

4000

4500

Time (ms)P.B. Snyder/IAEA/October 201815

Connecting a High Performance Super H Pedestal & Core to aHigh Density, Radiative Divertor & SOL– P-limited solution degrades with increasing ne,pedand 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 andimpurity 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 toseparatrix conditions

P.B. Snyder/IAEA/October 2018

Separatrix density half of pedestal (Bt=2.17T, Ip=1.6MA, tri=0.56)35

Pedestal Pressure [kPa]• Super H (J-limited) solution predicted not toshow degradation of pedestal pressure w/ ne,sep

30

J-limited

25
2015
EPED (H-Mode)

10EPED (Near Super H-Mode)503

P-limited

EPED (Super H-Mode)
4

5

6

78

9101112Pedestal Density [ne,ped(Zeff/2)1/2,1019m-3]

16

D2 gas Scan Increases Separatrix and Divertor Density while
Pedestal Pressure and Confinement Remain High• 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
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 fordivertor solutions.
P.B. Snyder/IAEA/October 201817

N2 Injection Effective for Cooling Divertor while Maintaining
High Performance Core & Pedestal• 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 fulldetachment and impact of closed divertor

Outer divertor
6050 Te (eV)177018,2300−2600ms
177018,3300−3600ms

40302010010819-3ne (10 m )64200.99 1.00 1.01 1.02 1.03 1.04

ψn,outP.B. Snyder/IAEA/October 201818

Predictions for ITER,
Implications for Compact,
High Performance Fusion

19

Super H/NSH Regime Access is Predicted for ITER: DIII-D has
Achieved Needed βN,ped, ne,sep, ne,ped Consistently
EPED Predicted Pedestal Height vs Density for ITER Baseline

Pedestal Pressure (kPa)

160
140
120
100
80
60
40H-Mode

20Near Super H

00

Super H
246810121416

Pedestal Density * (Zeff/2)1/2 (1019 m-3)

18Open issue: Physics of theGreenwald density limit whichconstrains degree of Super Haccess and predicted performancefor 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,sepP.B. Snyder/IAEA/October 201820

Fusion Performance Metric (<p>W/PhIaB)

Super H and Near Super H Operation Enables Very High Fusion
Performance per IpaBt
15ITERDIII-D Super H

DIII-DC-ModSuper H-Mode/NSH

10

Q=inf, 11MA

DIII-D H

Q=inf, 15MA

C-Mod Super H
C-Mod H

Q=10, 11MA
5JET2 atm

16MW

JET H

ITER
Q=10, 15MA
H-ModeTFTR L

Q=5, 15MA
0
0.0

0.5

TFTR

L-Mode

1.0

1.5

2.0

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

2.5

Minor Radius (m)• Simple metric of fusion performance (Q or <p>W/P) per IpaBt– Colored points are observations (<p> > 50 kPa), red points are SH/NSH experiments– High Q/IaB enables ITER success, and compact, cost attractive pilot plant
P.B. Snyder/IAEA/October 201821

High Fusion Performance and Promising Core/EdgeSolutions Developed via Super H Theory & Experiment• 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

Super H-mode compatible with both high fusion performance andhigh separatrix density for divertor solutions. Projects to excellent
ITER performance and compact, attractive pilot plant

P.B. Snyder/IAEA/October 201822