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## PowerPoint Slideshow about ' MSE Spectral Analysis on the Madison Symmetric Torus' - trapper

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### MSE Spectral Analysis on the Madison Symmetric Torus

Betsy Den Hartog

Jinseok Ko

Kyle Caspary

Daniel Den Hartog

Darren Craig

MST RFP is a toroidally axisymmetric current carrying plasma with Bf ~ Bq , 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 = vbeamxB
- Ha emission stark splitting
- Linear at high fields
- Obtain B┴ from line splitting
- p components linearly polarized along E
- s components circularly polarized

n=3

n=2

Dl = lo2(3/2)(eao/hc)|E|

p+

s

p-

MSE implementation on MST

Diagnostic Neutral Beam

E = 46 keV

I = 5.5 A

Divergence = 18 mrad

Duration = 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 s and pass p radiation
- Data is fit to the sum of 9 gaussians based on linear Stark model – relative I’s taken from Mandl

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

p+

p-

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 p+/p- asymmetry, non-equilibrium populations?

On-axis spectral fitting

Old fit

B = 0.41 T

New fit

B = 0.39 T

400 kA

plasma

B = 0.27 T

B = 0.26 T

200 kA

plasma

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

- p and s radiation patterns mapped onto the plane of the polarizer
- mid-radius patterns depend on pitch angle
- s ellipse lies oriented in same direction as linear p – limiting ‘contrast’

pi

Mid-radius view – first cut

fit

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

pi

|B| = 0.42 ± 0.07 T

g = 40.3° ± 9.4°

Summary

- Incremental improvement in on-axis analysis utilizing ADAS 605
- Still have not explained p+/p- asymmetry - ADAS development underway may yield insight
- Mid-radius view promising to yield |B| and g

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