PlasmaJog MSE Calibration

1
Plasma-Jog MSE Calibration
Scott, Yuh, Granetz, Wolfe, Ko, Beals
Issue MSE calibration based on beam ? gas
with known TF / EF gives wrong
pitch-angle during beam ? plasma.

• Difference is of order 3 degrees versus desired
  accuracy 0.2 degrees
• so this is a big deal.
• MSE cant provide an accurate q(r) measurement
  until we either
• learn how to correct for the difference
  between gas/plasma behavior
• or until we carry out a calibration in
  plasma.
• Same effect, although smaller, was observed on
  TFTR. Attributed to
• difference in p/s intensity from excited
  beam neutral population.
• Qualitatively we understand why effect is
  larger in C-Mod near
• viewing geometry along edge channels
  increases our sensitivity to
• s radiation.

2
Proposed Experiment

• Benign plasma ohmic, L-mode, possibly helium
  (to reduce background light). Prefer
  inner-wall-limited to minimize q? at plasma edge.
• Ramp Rmajor slowly over 500-1000 ms so as to
  sweep plasma edge past each MSE spatial channel
  (70-87 cm).
• Measured field line pitch angle using MSE with
  long pulse DNB. Calibrate against EFIT.
• Take data at 3-4 values of qy at 2.7, 5.4, and
  7-8 Tesla.
• Compare to beam-into-gas data on same day 3
  values of EF for each TF.
• Total shots about 20.