Physics Basis for Advanced ST Plasmas in NSTX

1
Physics Basis for Advanced ST Plasmas in NSTX

• C. Kessel

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Overview

• NSTX Advanced ST Plasma Targets and Tools to
  Reach Them (possibly some sense of when!)
• Review NSTX Experimental Long Pulse Discharges
• Integrated Scenario Modeling on NSTX
• Description of TSC/TRANSP, other analysis
• Simulation of discharges 109070 and 112546
• Scenario calculations targeting fNI 100 for ,
  and experimental progress toward these scenarios
• Scenario calculations targeting high ?, fNI
  100 for.. and experimental progress twoard these
  scenarios
• Conclusion

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NSTX is Targeting High Performance Steady State
Operation
NSTX Experimental Long Pulse Results
NSTX High ?, Non-Inductive Sustained Scenario
NSTX Non-Inductive Sustained Scenario
?13, ?Ngt 5 fNI 100 fBS gt 50 ? 2.5, ?
0.8 H98(y,2) 1.25 tflattop 2 ?J IP 0.8 BT
0.5 T nL controlled NB, NBHHFW
?40, ?Ngt8 fNI 100 fBS gt 50 ? 2.5, ?
0.8 H98(y,2) 1.55 tflattop gt 4 ?J IP 1.0
MA BT 0.35 T nL controlled NB, EBW, HHFW
?15-25, ?Ngt5.9 fNI 60 fBS gt 30 ? 2.4, ?
0.6 H98(y,2) 1.25 tflattop 1-2 ?J IP
0.8-1.2 MA BT 0.45 T nL rising NB
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Scenario Simulations Have Identified the Tools to
Access These Plasmas
NSTX Experimental Long Pulse Results
NSTX High ?, Non-Inductive Sustained Scenario
RWM stabilization
?40, ?Ngt8 fNI 100 fBS gt 50 ? 2.5, ?
0.8 H98(y,2) 1.55 tflattop gt 4 ?J IP 1.0
MA BT 0.35 T nL controlled NB, EBW, HHFW
?15-25, ?Ngt5.9 fNI 60 fBS gt 30 ? 2.4, ?
0.6 H98(y,2) 1.25 tflattop 1-2 ?J IP
0.8-1.2 MA BT 0.45 T nL rising NB
HHFW heating/CD
Plasma shaping
Density control
EBW off-axis CD
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Simultaneous High ? and ? Can Be Obtained from
PF1A Modification(replace with expts)
?2.6,?0.8
?2.6,?0.4
?1.9,?0.8
Shapes with Existing PF Coils
Shape with PF Mod
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High Harmonic Fast Waves (HHFW) Can Be Absorbed
on NBI Fast Ions and Thermal Ions (report new
developments)
Beam ions absorb HHFW power ----gt seen in beam
ion energy on expt. Thermal ions absorb HHFW
power ----gt no expt. verification so far HHFW
power is absorbed before waves reach axis
----gt low k suffers
No CD is assumed from HHFW in scenarios that
include NBI
?k? 5.6 /m Pe Pi Pf Fast,
no therm. 0.16 0.00 0.84 Fast
therm. 0.10 0.44 0.46 No fast,
therm 0.15 0.85 0.00
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NSTX Can Operate for Several Current Relaxation
Times Depending on the TF Field
Accessible TF Coil flattop time
6.0
?J 670 ms Non-inductively Sustained, High ?
5.0
4.0
?J 500 ms Non-inductively Sustained
3.0
Time, sec
?J 230 ms (109070)
4 ?J
2.0
Latest long pulse expts were done here
2 ?J
1.0
0.0
3
3.5
4
4.5
5
5.5
6
Bt (kG)
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Electron Bernstein Wave CD Can Provide Off-axis
Current for J Optimization
EBW Conversion Allows EC Techniques to be Used In
Overdense Plasmas
GENRAY/CQL3D Shows LFS Deposition and Large
Trapped Particle Fraction (Low Aspect Ratio) Lead
to Strong Ohkawa Current Drive
Current Density ( A/cm2 )
G. Taylor, et al., Phys. Plas., 11, (2004), 4733
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Density Control Efforts..Li Pellets
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2002 Discharge 109070 (112546,) Provides a Long
Pulse Baseline for Simulations
IP PNB Te Vloop nL
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2004(5) Run Produced Sequence of Long Pulse
Discharges
IP 0.8-1.2 MA, tflattop 0.85-0.6 s
BT 0.45 T
Early heating/H-mode transition ??? 2.3-2.5,
better Z feedback Glow He shot Glow reduces
density rise somewhat
??? 15-25
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NEW results from 2005 run period from ISD
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Combination of Experiments and Integrated
Scenario Modeling is Critical Component of
Advanced ST Development

• Reproduce expt. discharge behavior, interpret
  plasma evolution
• Establish impact of proposed expt. discharges
• Extrapolate to near, mid and long term plasma
  configurations based on expt. discharges
• Identify the tools required to access the target
  advanced plasma configurations

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Tokamak Simulation Code (TSC) is Used With Other
Analysis --gt TSC/TRANSP
Benchmark performed on 109070 with TSC Density
profile is fixed, magnitude prescribed versus
time Thermal diffusivities spatially fixed
(TRANSP), scaled by IPB98(y,2) global
scaling NBI characteristics (Wbeam, nfast,
HNB(r)) fixed to 109070 (TRANSP), scaled by
power Zeff magnitude and profile fixed to
109070 NBCD benchmarked against TRANSP HHFW CD
from CURRAY, EBW CD from GENRAY/CQL3D
New capability
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TSC Benchmark Simulation Shows Good Agreement
With 109070 (112546,) Expt Data

1. Use L-mode ? model prior to 2 NB sources, t lt 200
   ms
2. Use ?e,i from 109070 derived at t 450 s
   throughout H-mode phase, t gt 200 ms
3. Density profile and magnitude is prescribed
4. In extrapolated simulations, ?e,i are scaled by
   IPB98(y,2) scaling

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Benchmark Simulation ---gt Decrease of q(0) Strong
Suppression of NBCD by Density Rise
Profiles at t 450 ms
Constrained to match discharge
End of discharge, q(0) crosses 1.0
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Scenarios to Obtain fNI 1 for ?flattop gt ?skin
and Experimental Progress Toward Them
Modifications to 109070 discharge
High elongation (to raise IBS) and
triangularity Density control so that
non-inductive current sources can be
optimized Early heating and H-mode transition to
elevate the safety factor, and prolong q(0) gt
1.0 Possibly use HHFW as a heating source in
presence of NBI No HHFW CD assumed
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Significant Improvement Over 109070 for
Prolonging Discharge and Reaching fNI gt 90

• 109070
• ? 2.0, n rising throughout discharge, H-mode
  transition at 200 ms, H98 1.25
• Hi ?, n control
• ? 2.5, n flattoped, H-mode at 200 ms, H98
  1.25
• Hi ?, n control, early heat/H-mode
• 2.5, n flattoped, stronger heating early with
  H-mode transition at 100 ms, H98 1.25
• Same as above higher ?E
• H98 1.5

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Current Profiles from 100 Non-inductive
Sustained Scenarios
fNI 50
109070
t(q 1.0) 0.55 s
t(q 1.0) 0.7 s
fNI gt 90
t(q 1.0) gt 1.5 s
t(q 1.0) 1.4 s
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NSTX Experimental Progress Toward Long Pulse SS
Discharges
109070 Pseudo-112546
Comparison of 109070 and 112546 Shows Impact of
Higher ? and early heating/H-mode Higher safety
factor in 112546 throughout discharge, keeping
q(0), qmin gt 1 NBCD still suppressed by density
rise Bootstrap current in 112546 higher from
higher ?
INItotal INBCD IBS
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Impact of Early Heating/H-mode and Density
Control on 109070
109070 109070 density control early
heat/H-mode
109070 109070 early heat/H-mode
109070 109070 density control
INItotal INBCD IBS
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Density Control for 112546 Could Provide fNI
88
Pseudo-112546 Pseudo-112546 density control
Density control sustains NBCD Density control
removes continuous rise in bootstrap
current NBCD is on-axis, which can drive q(0)
down toward 1 Increasing fNI must be a balance
between fNIon-axis and fNIoff-axis to provide
q(0) gt 1 and stationary behavior
INItotal INBCD IBS
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HHFW Heating Can Improve the Flexibility to
Optimize the J and q Profiles
PNB 4 MW, PHHFW 6 MW, hi ?, n control, early
heat/H-mode
All cases reach 100 non-inductive current
Zeff(0) 2.5 H98 1.30 JNB broader
Zeff(0) 1.5 H98 1.34
Zeff(0) 2.5 H98 1.24
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Scenarios to Obtain fNI 1 at ? 40 for
?flattop gtgt ?skin and Expts Making ..
Modifications to 109070 discharge
High elongation (to raise IBS) and
triangularity Density control so that
non-inductive current sources can be
optimized Early heating and H-mode transition to
elevate the safety factor, and prolong q(0) gt
1.0 Possibly use HHFW as a heating source in
presence of NBI No HHFW CD assumed and Lower BT
to 0.35 T, try to raise IP to 1.0 MA Add 3.0 MW
of EBW heating and CD
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Goals of fNI 1 and q(0) 1.5 Constrain
Lowering of BT and Raising of IP

• Case 1 (IP 800 kA)
• ? 2.6, n control, early heat/H-mode at 100 ms,
  PNB 6.75 MW (ENB 100 keV), EBW off-axis CD,
  H98 1.37
• Case 2 (IP 850 kA, higher ?E)
• 2.5, n control, early heat/H-mode at 100 ms,
  PNB 6.75 MW (ENB 100 keV), EBW off-axis CD,
  H98 1.54
• Case 3 (IP 1 MA, broader JNB)
• ? 2.5, n control, early heat/H-mode at 100 ms,
  PNB 6.75 MW (ENB 100 keV), EBW off-axis CD,
  H98 1.36

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Broader JNB and Off-axis EBW CD Allow Operation
at Lower BT and Higher IP
PNB 6.75 MW, ENB 100 keV, PEBW 3.0 MW
Broader JNB H98 1.36 n19(0) 0.35 IP 1.0 MA
Higher ?E H98 1.54 n19(0) 0.51 IP 850 kA
H98 1.37 n19(0) 0.44 IP 800 kA
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Show results of ISD discharges with BT 0.35
T, progress made in starting to approach this
regime MHD effect on NB current distribution,
can broader JNB be accessed at lower BT
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HHFW Heating and Broader JNB Allows Reduction to
2 NB Sources, q(0) gt 1.5
NBIHHFW JNB narrow H98 1.58 n19(0)
0.33 PHHFW 3 MW PEBW 3 MW PNB 4 MW ENB 80
keV
NBIHHFW JNB broad H98 1.5 n19(0) 0.3 PHHFW
3 MW PEBW 3 MW PNB 4 MW ENB 80 keV
NBI only JNB broad H98 1.36 n19(0) 0.42 PEBW
3 MW PNB 6.75 MW ENB 100 keV
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Integrated Advanced ST Plasmas
PNB 6.75 MW (100 keV), PEBW 3.0 MW, q(0)
1.71, qmin 1.71, IP 1 MA, BT 0.36, ?
42.7, ?N 8.8, n19(0) 0.42, H98 1.55,
Zeff(0) 2.5
PNB 4.0 MW (80 keV), PHHFW 3.0 MW, PEBW 3.0
MW, q(0) 3.0, qmin 2.14, IP 1 MA, BT
0.345, ? 38.0, ?N 7.7, n19(0) 0.30, H98
1.55, Zeff(0) 1.5
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Advanced ST Plasmas Can be Reached in NSTX

• Simulations using experimental data indicate that
  reasonable extrapolations can allow NSTX to
  access
• 100 Non-inductive discharges
• 100 Non-inductive High ? discharges
• Critical upgrades and demonstrations to reach
  these plasmas are
• High elongation and triangularity with PF1A coil
  modification
• Density control to optimize non-inductive CD
  sources
• EBW off-axis CD for profile optimization
• HHFW heating and CD

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Plasma Scenarios and Physics Issues

• 100 Non-inductive scenario
• IP 800 kA, BT 0.5 T, fBS 50, ?N 4.7, ?
  13, H98 1.23
• 100 Non-inductive High ? Scenario
• IP 1 MA, BT 0.35 T, fBS 50, ?N 7.7-9, ?
  38-42, H98 1.55
• Important physics features
• Early heating and H-mode transition
• Energy confinement
• Plasma impurity content
• Peakedness of NB current profile
• Maintaining safety factor gt 1.5 throughout
  discharge