PERSISTENT SURVEILLANCE FOR

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ELM suppression studies with resonant magnetic
perturbations
Presented byT. E. Evans General
Atomics Presented at the NSTX Research
Forum December 5, 2006
PERSISTENT SURVEILLANCE FOR PIPELINE PROTECTION
AND THREAT INTERDICTION
In collaboration with S. Kaye (PPPL) and R.
Maingi (ORNL)
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ELM control studies on NSTX motivation and goal

• Motivation
• Large Type-I ELMs are a serious concern for
  burning plasma experiments (such as ITER)
• A decision is needed soon on internal versus
  external ELM control coils for ITER
• High priority ITPA and US-BPO ITER Issue Cards
• Data is needed from the NSTX EF/RWM coil to
  assess the efficacy of external coils
• NSTX EF/RWM coil is closer to the plasma than the
  DIII-D C-coil ? increased stochasticity
• TRIP3D modeling ? NSTX EF/RWM coil is a more
  effective source of edge stochasticity than
  DIII-D C-coil, see L. Yan, T. E. Evans, S. M.
  Kaye and R. Maingi, Nucl. Fusion 46 (2006) 85
• Goal
• Significantly modify or eliminate large Type-I
  ELMs using n1 and/or n3 EF/RWM coil RMPs

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ELMs are completely eliminated in RMP H-modes
with ITER Similar Shapes (ISS) and pedestal
collisionalities

• Best results with strong n3 I-coil (internal)
  RMPs (density pump out -gt ELM stabilization)
• Off-resonance n3 I-coil produces 5-10x frequency
  ? with 8-10x amplitude ?
• n1 C-coil (external) RMPs produce small
  frequency (2x ?) and amplitude (2-3x ?) changes
  under some conditions (involves destabilization
  of core MHD modes)

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ELMs have been significantly modified with n1
RMPs in JET using an (external) Error Field
Correction Coil (EFCC)
67954 Ip 1.6 MA Bt 1.84 T q95 4.0 d
0.3 ? 1.7 ne 0.085 (at R 3.75m)
q95 (EFIT/Chian1)
ICoilmax 48kAturns (3kA16turns)
IEFCC (IDFA2A1)
WDia (EFIT)
D Wdialt10
Pinputtol
Ohmic LHCD NBI
0.6MW 16.8MW
H98 (SCAL)
bN (EFIT/Dia)
fELMs 28 Hz
117 Hz
Da (AD35) outer divertor
IDalpha reduced by a factor of 10

• EFC-coil n1 RMPs produce higher frequency (?
  3x) lower amplitude (? 10x) ELMs
• Density pump-out, similar to DIII-D n3 I-coil,
  also observed in these experiments

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XP525 discharges with n3 RMP coil currents of
0.5?1.0 kA-turn suggest the possibility of ELM
suppression

• Is the apparent ELM suppression seen in 117142
• due to changes in upper divertor recycling?
• determine recycling recovery time using repeat
  coil off discharges

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ELM control studies on NSTX experimental
approach

• Experimental approach
• Part I - Reproduce XP525 discharge 117142
  ?low0.6, ?2.0 IRWM/EF 0.5 kA-turn with
  reproducible large Type-I ELMs (c.f. 117425,
  balanced DN)
• Assess correlations between ELM suppression and
  upper divertor recycling
• coil off repeat discharges to assess recycling
  recovery
• Part II - Reproduce JET n1, DIII-D n3 low
  collisionality results
• Obtain Type-I ELMing reference discharge with
  ?low0.3-0.4 ?1.7-1.8 and pedestal
  collisionality as low as possible
• - lithium wall coating for density control highly
  desirable
• Apply n3 n1 RMPs with currents of 0.5 kA-turn
  IRWM/EF 3.0 kA-turn and various toroidal
  phases until significant ELM modification/suppress
  ion is observed
• - Is density pump-out observed (as in JET and
  DIII-D)
• Verify reproducibility - coil on/off shots
  (reference and physics documentation data)
• Scan q95 to assess resonant window (using either
  Ip or BT - BT preferred)
• Run days requested 1.5

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Backup

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NSTX resources and desired diagnostics

• Required NSTX resources
• Reference shape 117142
• Ip 0.8 to 1.1 MA
• ITF56 kA (0.35 - 0.55 T),
• ? 1.8 - 2.0,
• Upper/lower ?, 0.6 ? 0.1/ 0.6 ? 0.1 and lower ?
  0.3-0.4
• deuterium gas,
• NBI sources A/B/C (_at_90 kV),
• EF/RWM configured for maximum DC current (n 3
  n 1)
• Desired (required) diagnostics
• bolometer arrays, CHERS, divertor fast camera,
  edge rotation spectroscopy, filterscopes,
  FIReTIP, GPI, infrared camera, Langmuir probes
  (PFC tiles and RF antenna), full magnetics, fast
  lost ion probes, MSE, neutral particle analyzer,
  plasma TV, fixed freq. reflectometer, Thomson
  scattering, soft x-ray, visible brems
• Run days requested
• 1.5 days