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