Plans for NSTX Edge/Divertor Fixed Langmuir Probes

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Plans for NSTX Edge/Divertor Fixed Langmuir Probes
C. E. Bush, R. Maingi, S. Zweben, L. Roquemore,
R. Kaita, P. Roney, V. A. Soukhanovskii, K.
Williams, et al. NSTX Boundary Physics
Brainstorming Meeting Princeton Plasma Physics
Laboratory Princeton, February 12, 2006
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Probes are installed in divertor, centerstack,
and new electrode

• Flush mounted single probes
• Total of 27 probes, 6 top and 6 bottom divertors
• Some along centerstack
• 5 on new Electrode (fast)
• Have data for vast majority of shots
• Virtually no signal from centerstack probes when
  plasma is diverted
• Some Isat, Te, ne data in Tree

• Tile Langmuir Probes

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Divertor Langmuir Probes
1 R(probe 1) 1.02 m
2 R(probe 2) 0.91 m
3 R(probe 3) 0.80 m
4 R(probe 4) 0.49 m
Strike-point
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Heat Flux Profile Becomes More Peaked with
Increasing NBI Power

• Peak in Isat occurs near peak heat flux
• In general peak Isat is independent of Pb,
  heating power

50
0.306 sec
40

• Isat Probe 3

30
Isat (mA)
20
IsatProbe 2
10
IsatProbe 1
0
R. Maingi
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Radial Variation of Jsat, Te and ne on Divertor
Plate for NBI Power 3 MW
Jsat(R) (Amps)
Te(R) (eV)
ne(R) (/m3)
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Better Probe Coverage Needed for Physics and
Modeling

• Physics of interaction of ELM perturbation with
  divertor and plasma edge depends on the edge
  plasma parameters
• Important data for edge / divertor modeling
• New fast probes (5 probes capable of 100 kHz)
  should provide correlations with GPI blob data
• As blobs move radially outward across the GPI
  view
• Plans to go to PC based data acquisition this run
  for the present probe system
• better time resolution, better IV
  characteristics data
• turbulence data (faster digitization)
• Prelude to installing additional probes

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Approach for Increasing Coverage

• Thermal stress studies
• determine minimum safe distance between probes
• Minimum for next opening
• 1st 5 probes spaced 1 -2 cm apart near outboard
  strike-point
• 2nd 5 probes spaced similarly on inboard
• Longer range - better overall coverage

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EXTRA
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Isat for Probes Divertor GAS InjectorPuff - 500
Torr
60
LRDFIT
With Gas Puffs Isat shows correlation, (1)
between probes, (2) with gas puffs (3) with D?
(4) when probes move to private flux region
Current (mA)
40
Isat(ion)
20
0
Gas Puffs
Probe3
Current (mA)
Isat(ion)
Probe3
0.8
Private Flux
Strike point radius (m)
0.6
Probe4
0.4
Probe5
0.0
0.2
0.4
0.6
Time (s)
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Probe 3 in Private Flux Region at 0.5 secs
Both EFIT and LRDFIT equilibrium codes show Probe
3 to be in private flux region at t 0.5 s
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Requirements and Results

• Obtain probe Te, ne, particle fluxes during
  ELMing discharges
• Compare ELM Types
• Compare turbulence and particle efflux detected
  by fixed probes with GPI and Fast Reciprocating
  Probe
• Main Diagnostics Fixed probes (usual 5 new,
  fast), GPI, reciprocating probe
• Required Runtime
• Reports and Publications Publication with
  emphasis on fixed probe data. Contribution as
  collaborator and co-author of pubs from other
  XPs. Collaboration on modeling.