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DNB Attenuation or

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MIT Plasma Science and Fusion Center. What and Why? ... Found a set of channel-to-channel calibration factors for the MSE diagnostic ... – PowerPoint PPT presentation

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Title: DNB Attenuation or


1
DNB AttenuationorMisuse of MSE
Datacontinued
MIT Plasma Science and Fusion Center
  • Rachael McDermott, Bill Rowan
  • Thanks to Steve Scott and Howard Yuh
  • for numerous consultations

2
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.

3
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

4
Calibration Constants
Shot 002 003 004 005 006
Pressure (mT) 2.45 1.215 .5939 .5903 .2697
Channel (m)
.86786 1.00000     1.00000   1.00000    1.00000   1.00000
.85243 0.352164   0.58445     0.717148   0.708050 0.803426
.83575 0.196582    0.55356     0.949377   0.92907     1.23440
.81979 0.039039   0.19822     0.42616     0.414802 0.605755
.78509 0.00438422 0.0736256   0.288886   0.283944  0.542222
.76645  0.00151599  0.0490210    0.260984   0.249218  0.551441
.74647 0.000307003   0.0191607   0.143248   0.133928 0.321710
.72641 0.000171313  0.0213610    0.24522    0.230223  0.664743
.70109 2.73887e-05  0.00777271   0.127916   0.112520 0.347466
.67594 5.02186e-06 0.00373183  0.086171  0.0745174  0.222317
  • Due to a calculation error, the calibration
    constants presented at the last presentation were
    incorrect. The correct (hopefully) constants are
    shown above.
  • We still dont have an explanation for the
    discrepancies between the pressures. The lowest
    pressure constants are used for the beam density
    calculation.

5
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
6
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.

Shot   MSE No Impurities 1C 2C
1040409007 a -0.036409910 -0.078569204  0.071894864 -0.067443145
1040409007 ß  1.1521804     1.1679132   1.1600576   1.1541364
1040409007 ? 0.12570610 0.16726451  0.16841049  0.17047122
1040505029 a -0.13186031    -0.1694330    -0.16218624  0.15475712
1040505029 ß   1.3511533     1.4181084 1.4075826   1.3967821
1040505029 ? 0.15018593  0.13794946 0.13883806 0.13977914
7
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.

8
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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