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MIT Plasma Science and Fusion Center. DNB Attenuation or “Misuse” of MSE Data continued…. Rachael McDermott, Bill Rowan Thanks to Steve Scott and Howard Yuh for numerous consultations. What and Why?. Using MSE data to find accurate estimates of neutral beam attenuation

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dnb attenuation or misuse of mse data continued

MIT Plasma Science and Fusion Center

DNB Attenuationor“Misuse” of MSE Datacontinued…

Rachael McDermott, Bill Rowan

Thanks to Steve Scott and Howard Yuh

for numerous consultations

what and why
What and Why?
  • Using MSE data to find accurate estimates of neutral beam attenuation
  • These measurements can be used to benchmark beam penetration codes currently in use.
  • Accurate knowledge of neutral density is necessary for calculations of impurity densities in the plasma.
last time we
Last time we…
  • Found a set of channel-to-channel calibration factors for the MSE diagnostic
  • Used these factors to derive relative beam attenuations from the MSE signal for beam into plasma shots

To Do List from last time

  • Understand the calibration at all pressures.
  • Compare the attenuations to standard results from the literature and from our own penetration code
calibration constants
Calibration Constants
  • Due to a calculation error, the calibration constants presented at the last presentation were incorrect. The correct (hopefully) constants are shown above.
  • We still don’t have an explanation for the discrepancies between the pressures. The lowest pressure constants are used for the beam density calculation.
comparison to literature
Comparison to Literature
  • An analytical fit to the stopping cross-section for a neutral beam into a hydrogen plasma as derived by Janev is
  • A theoretical beam attenuation can be derived from this as follows

Janev, R.K., Boley, C.D., Post, D.E. (1989) PENETRATION OF ENERGETIC NEUTRAL BEAMS

INTO FUSION PLASMAS. NUCLEAR FUSION, Vol. 29, No.12, 2125-2139

decay constants
Decay Constants
  • All of the attenuation curves were fit to The values of the parameters for two shots are given in the table below.
  • As the level of impurities is increased in the predicted model so does its agreement with the MSE attenuation.
prediction and experiment
Prediction and Experiment

The predicted beam attenuation for each shot is calculated using the CMOD temperature, and density profiles.

The temperature profile was obtained from ECE.

The density profile was obtained from the Visible Bremsstrahlung diagnostic.

  • An MSE derived beam attenuation along with its corresponding Janev-predicted beam attenuation is pictured above. This is for shot = 1040505029.
conclusions
Conclusions
  • An astonishing 39 of 41 shots fit well to exponential curves and were consistent with predicted results.

To Do List

  • Explain calibration constant variation with pressure. Find another way to derive a channel-to-channel MSE calibration.
  • Include an error analysis in the derivation of the densities.
  • Include a measure of the difference between the calculated and predicted attenuations.
  • Finish writing this program in a “user friendly” form that can be run after each shot.
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