Beam Modulation Effects on Ion Power Balance XP 737

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Beam Modulation Effects on Ion Power BalanceXP
737

• P.W.Ross

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Basics of XP 737

• The goal of XP 737 is to study the ion power
  balance and the coupling between the injected
  beam and the thermal ions
• Also goal is to minimize known uncertainties in
  power balance such as edge charge exchange losses
  (need edge neutral measurements
• Experimental technique for fast ion response
• Modulate Beam power, modulate 3-gt2 beams
• Evaluate the fast ion response using the NPA,
  SSNPA, FIDA, and SFLIP diagnostics
• Compare diagnostics to TRANSP predictions
• Understand any differences

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ENDD Profile and image
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ENDD shows densities from 1e12-1e14
Preliminary
Seperatrix
The Edge Neutral Density Diagnostic measures the
neutral density in the edge of the plasma.
Typical densities range from 1e12 to about 5e13.
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Problems with the ENDD Diagnostic

• ENDD is heavily dependent on Thomson Scattering.
  
• This is in the region of low temperature (a few
  eV). Slight variations in the temperature causes
  significant changes in the calculated Neutral
  Density
• ENDD profiles behave erratically with edge TS
  (large error bars in the edge).
• Possibility of lithium coating.
• X-rays can cause spikes in the image which need
  to be ignored.

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NPA signal shows lack at certain pitch angles
Rtan50cm
Rtan80cm
Rtan120cm
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NPA signal dependent on Beam Timing

• Shot 125331

• Shot 125332

These shots were very similar. The beam timing
on shot 331 was a mistake, but it showed how the
beam timing affects the NPA signal.
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TRANSP shows NPA modulations at all pitch angles
Rtan 125
TRANSP shows modulations at all tangency radii
that match the beam modulations. This is not
seen in the measured NPA signal, particularly for
Rtan 80, near the magnetic axis. (The measured
NPA signal is not shown)
Rtan 80
Rtan 50
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FIDA shows similar behavior to NPA
This is the overlay of 5 shots with identical
beam timing and plasma parameters. Individual
shots were too noisy to detect a correlation.
When several signals are overlaid from repeated
shots, a small modulation is seen. A similar
effect may be possible with the NPA and other
diagnostics
Shot 125332 showed no distinct signal on the NPA
and shows a similar lack of signal on the FIDA
diagnostic with the beam modulation (Neutron
signal in red, FIDA in black)
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SSNPA and SFLIP Add to the Confusion
SFLIP probe shows loss associated with MHD
activity, but does not show any activity
associated with the beam modulation
SSNPA signal at various energies. No obvious
signal matches beam modulation
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Conclusions and Further Analysis

• The ENDD diagnostic has taken data and initial
  analysis has been performed
• Firm estimates will be available about the effect
  of lithium on the edge neutral density
• XP 737 highlighted the lack of understanding of
  the presence or absence of a strong NPA signal,
  particularly as related to beam modulations
• Shots with 3 beams early have a significantly
  higher absolute NPA signal, but lack the large
  modulations that are apparent in shots without 3
  beams early
• SSNPA, FIDA and SFLIP confirm lack of large
  modulations in fast ion population, although
  overlaying several shots/performing a Fourier
  transform may show low amplitude signals
• We would like to have TRANSP simulate other
  diagnostics, such as the FIDA and SSNPA, which
  would assist in understanding their signals.