High Fusion Performance in Super H-Mode Experiments on ... · 2 Super H-Mode Experiments on Alcator C-Mod and DIII-D Achieve High Fusion Performance, Record Pedestal Pressure •

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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, 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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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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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

0.00 0.02 0.04 0.06 0.080

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Pedestal Width ( N)

Pedesta

l H

eig

ht (p

pe

d, kP

a)

Illustration of EPED1 Model, Multiple Roots

Peeling-Ballooning

KBM

EPED1 Prediction

S

SU

U


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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

0.00 0.02 0.04 0.06 0.080

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Pedestal Width ( N)

Pedesta

l H

eig

ht (p

pe

d, kP

a)

Illustration of EPED1 Model, Multiple Roots

Peeling-Ballooning

KBM

EPED1 Prediction

S

SU

U

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Pedestal Density (1019 m-3)

Pede

stal H

eight

(kPa)

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

stal

Pre

ssur

e (k

Pa)

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 ]

Pede

stal

Pre

ssur

e (k

Pa)

680ms720ms

760ms790ms

C-Mod 1160922020, 0.8MA

Pede

stal

Pre

ssur

e (k

Pa)

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

750ms

770ms

790ms810ms

830ms

850ms870ms

930ms

C-Mod 1160922032, 1MA


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101

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EPED Predicted Pedestal Height (kPa)

Mea

sure

d Pe

dest

al H

eigh

t (kP

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

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100110120

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

Pede

stal

Pre

ssur

e (k

Pa)

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 )

0 2 4 6 8

Electron Temperature (keV)

02468

Ion Temperature (keV)

0.2 0.4 0.6 0.8 1.005

1015

DIII-D 177007 @ 2190ms

0Normalized Radius (ψ )

19 -3

N

177007.2190.00Electron Density (10 m )

Electron Temperature (keV)

Pressure (kPa)

19 -3

(Total)

(Electron)

C-Mod 1160930042 @ 900ms

Normalized Radius (ψ )N

0.2 0.4 0.6 0.8 1.000

100200300

400

510152025

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•  Deep access into Super-H regime, good agreement with EPED predictions –  Bt=2.1T, 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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Pede

stal

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ssur

e [2

*pe,

ped,

kPa]

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


1.95 2.10 2.25 2.400.0

0.4

0.8

1.2

1.6

2.0174809

Total(TRANSP)

Measured

Thermal(TRANSP)

Beam-Target (TRANSP)

Beam-Beam (TRANSP)

Time (s)

Neu

tron

Rat

e (1

0

/s)

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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

0.54

0.32


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Sustainment and Core-Edge Compatibility of

Super H-Mode Regime

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171322

Time (ms)

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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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stal

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

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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T (eV)

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e19 -3


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

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stal

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Pa)

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


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Extra Slides

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C-Mod H-modes triggered using a sweep in magnetic balance leads to low-ne high-T pedestal evolution

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B×∇B is toward upper divertor

LSN DN

Short I-mode

Phase

H-formation

ICRF on

Te,95

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

•  Peak Te near strike point drops more than 3x, pedestal pressure and confinement remain ~constant

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

N2 + D2

Time(s)Time(s)

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Similar Level of EPED Accuracy with Metal or Carbon Wall

•  Metal: average error=1.46 (14%), correl=0.90, σ=0.19

•  Carbon: average error=1.88 (18%), correl=0.85, σ=0.22

•  No indication of strong effect of wall material on EPED accuracy –  JET ILW has lower impurity levels,

different operational limits than JET C

–  Studying impact of impurities and gas puffing

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Case Number (Ordered by Shot #)

Pede

stal P

ressu

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a)

Metal Walls, EPED1 Comparison (10 C-Mod, 335 JET ILW)

EPED1 PredictionMeasured Ptot,pedMeasured 2ne,pedTe,ped

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Case Number (Ordered by Shot #)

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stal P

ressu

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Carbon Walls, EPED1 Comparison (225 DIIi-D, 137 JET CFC)

EPED1 PredictionMeasured Ptot,pedMeasured 2ne,pedTe,ped

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High Fusion Performance in Super H-Mode Experiments on ... · 2 Super H-Mode Experiments on Alcator C-Mod and DIII-D Achieve High Fusion Performance, Record Pedestal Pressure •