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MSE Spectral Analysis on the Madison Symmetric Torus

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 f ~ B q , 0.2 ≤ |B| ≤ 0.5 T.

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MSE Spectral Analysis on the Madison Symmetric Torus

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  1. MSE Spectral Analysis on the Madison Symmetric Torus Betsy Den Hartog Jinseok Ko Kyle Caspary Daniel Den Hartog Darren Craig

  2. 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

  3. 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-

  4. 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

  5. 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-

  6. 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?

  7. 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

  8. 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

  9. 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

  10. 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°

  11. 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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