An HIBP for NSTX Why and How

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An HIBP for NSTXWhy and How

• Paul Schoch, Associate Professor
• Diane Demers, Research Assistant Professor
• Kenneth Connor, Professor
• Electrical, Computer, and Systems Engineering
  Department
• Rensselaer Polytechnic Institute
• Troy, NY

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Why-The Heavy Ion Beam Probe - HIBP

• Probe the plasma with energetic, high mass ions
• Not confined by magnetic field
• Electron impact ionization will produce higher
  charge state ions secondaries
• The change of energy of secondary compared to the
  primary is a measure of the potential at the
  point of ionization
• Steer the sample location across the plasma and
  profiles are obtained.

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Why - Data from 500kV HIBP on TEXT
Power spectra of density fluctuations, potential
fluctuations, coherence and phase shift

• Time variation of the secondary ion energy is a
  measure of the fluctuating potential in the
  plasma, fig (b).
• Time variation of the total signal is a measure
  of the fluctuation of the electron density, fig
  (a)
• These signal can be cross correlated to yield the
  coherence and the phase relation

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Why - Two point TEXT data
Power spectra from density fluctuations using two
detectors

• TEXT system had 3 detector sets
• Alignment of sample volumes is along primary ion
  beam, so typically are displaced both radially
  and poloidally

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Why - TEXT data
The GAM part of the Zonal Flow as measured in
TEXT. It appears as a fluctuation of potential
with m0 mode structure, with little or on
corresponding density fluctuation.
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Why - TEXT data
Higher order spectral analysis showed three wave
coupling. The narrow band potential fluctuation,
GAM, is coupled to the broad band density
fluctuations.
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Proposed HIBP for NSTX

• 500kV accelerator from TEXT in storage
• Maximum operating voltage is 545kV
• Sodium as ion of choice, 545keV very useful,
  900keV offers greater plasma coverage
• Lithium is too light, (requires too high an
  energy.)
• Potassium allows greater coverage or even
  possible use of a 300kV accelerator, but will be
  strongly attenuated for moderate density plasma
• Sodium is best option
• 0.4 resolution for density fluctuations
  (0-500kHz)
• Limited by predicted signal level and detector
  electronic noise
• Electronic noise is broadband resistor noise
• 3Vrms resolution for potential fluctuations
  (0-500kHz)
• Also limited by signal level and electronic noise
• Sensitive to the low wavenumbers, klt3cm-1

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How - HIBP for NSTX
Red is 580kV Na or 345kV for K, BT0.45T, Blue is
930kV Na, 540kV K
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Overlay of EFIT by F. Paoletti Shot 105094,
t241ms ßt 19.5 BT 0.35T
Circled stars represent 350kV Na for BT
0.35T 575kV Na for BT 0.45T 345kV K for BT
0.45T Blue stars represent 550kV Na for BT
0.35T 910kV Na for BT 0.45T
Primary sweep at 1.8, 0, 2.375 Detector at 2.2,
0.8, -0.2
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Same sample locations as previous slide, shows
trajectories at ports Zhang, Schoch, Connor Rev.
Sci. Instrum., Vol. 74, No. 3, March 2003
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HIBP for NSTX

• Attenuation
• 1.6m is an the mean free path for 500keV Na for
  a plasma with ne 3x1019m-3, and Te1keV.
• This gives a nice balance between sufficient Na2
  production and not too much.
• The mfp for K for the same energy and plasma is
  about 0.53m
• Still useful but not optimal
• Allows for greater plasma coverage but reduced
  sensitivity.
• Frequency range (0-500kHz) and resolution
• Frequency range is limited by detector
  electronics
• Noise is dominated by resistor noise in
  transimpedence amplifiers

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HIBP for NSTX

• Wavenumber sensitivity
• Sample volumes are disk shaped with the size
  determined by the ion beam size, the detector
  slit size and the magnetic geometry.
• Predict sample size of about 2cm in the longest
  direction
• Spacing between samples is determined by the
  detector entrance slit geometry and the magnetic
  field.
• Sensitive to the low wave numbers, klt3cm-1

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How -HIBP for NSTX

• 500kV accelerator from TEXT
• Maximum operating voltage is 545kV
• Sodium as ion choice
• Potassium would allow greater coverage or even
  possible use of a 300kV accelerator, but will be
  strongly attenuated for moderate density plasma
• 0.4 resolution for density fluctuations
  (0-500kHz)
• Limited by predicted signal level and detector
  electronic noise
• Electronic noise is broadband resistor noise
• 3Vrms resolution for potential fluctuations
  (0-500kHz)
• Also limited by signal level and electronic noise
• Sensitive to the low wavenumbers, klt3cm-1

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