mse spectral analysis on the madison symmetric torus betsy den hartog jinseok ko kyle caspary daniel...

MSE Spectral Analysis on the Madison Symmetric

TorusBetsy Den Hartog

Jinseok Ko

Kyle Caspary

Daniel Den Hartog

Darren Craig

MST RFP is a toroidally axisymmetric current carrying plasma with B ~ B, 0.2 ≤ |B| ≤ 0.5 T

Self-generated currents drive plasma to a relaxed state in which toroidal field is reversed at edge

Motional Stark Effect Overview• H beam atoms experience an

electric field: E = vbeam x B

• H emission stark splitting

• Linear at high fields

• Obtain B┴ from line splitting

• components linearly polarized along E

• components circularly polarized

n=3

n=2

= o2(3/2)(eao/hc)|E|

MSE implementation on MST

Diagnostic Neutral BeamE = 46 keVI = 5.5 ADivergence = 18 mradDuration = 20 ms

On-Axis Views•7 views• all looking at magnetic center• shuttered to look at different time points

Mid-Radius views• 4 views• 2 orthogonal polarizations• 2 time points

On-Axis Analysis• Low Fields of MST Present Challenge - E~ 1 MV/m • Stark components not resolved• use polarizer to block most of and pass radiation• Data is fit to the sum of 9 gaussians based on linear

Stark model – relative I’s taken from Mandl

Note +/- asymmetry. This is typical of MST MSE data.

Analysis considerations

• Linear Stark model not adequate at low

fields

• Need a model which includes Zeeman and

spin-orbit terms (ADAS 605)

• Cannot account for +/- asymmetry, non-

equilibrium populations?

On-axis spectral fitting

400 kA

plasma

200 kA

plasma

Old fit New fitB = 0.41 T B = 0.39 T

B = 0.27 T B = 0.26 T

Mid-radius view – a challenge!

• Two orthogonal polarizers

• Now getting usable data showing

broadening on one polarizer view

• Geometry constraints limit ‘contrast’

between 2 views

Mid-radius view

• and radiation patterns mapped onto the plane of the polarizer

• mid-radius patterns depend on pitch angle

• ellipse lies oriented in same direction as linear – limiting ‘contrast’

pi

Mid-radius view – first cut

pi

fit|B| and pitch angle now both free parameters in fit

|B| = 0.42 ± 0.07 T = 40.3° ± 9.4°

Summary

• Incremental improvement in on-axis analysis

utilizing ADAS 605

• Still have not explained +/- asymmetry - ADAS

development underway may yield insight

• Mid-radius view promising to yield |B| and