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 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 = v beam 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  = o 2 (3/2)(ea o /hc)|E|

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  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 fitNew fitB = 0.41 TB = 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 