Plasma and Fusion Research

Volume 14, 3402083 (2019)

Regular Articles

Study of Lyman-α Polarization due to Anisotropic Electron Collisions in LHD
Nilam RAMAIYA1), Motoshi GOTO1,2), Tetsutarou OISHI1,2) and Shigeru MORITA1,2)
1)
Department of Fusion Science, SOKENDAI (The Graduate University for Advanced Studies), Toki 509-5292, Japan
2)
National Institute for Fusion Science, Toki 509-5292, Japan
(Received 9 January 2019 / Accepted 22 March 2019 / Published 3 June 2019)

Abstract

We have investigated the polarization of Lyman-α line in the Large Helical Device (LHD). A theoretical model has been developed for a quantitative understanding of the anisotropy in the electron velocity distribution function (EVDF). The present model treats an anisotropic EVDF having different electron temperatures in the directions parallel and perpendicular to the magnetic field. The steady-state time period of an electron cyclotron heated discharge has been analyzed and the comparison between the theoretical and measured polarization degrees suggests that in the edge plasma the difference between these two temperatures is approximately 10%. In addition, the dependence of the observed Lyman-α intensity on the angle of the linearly polarized light has been studied. The obtained results show that in the experimentally observed intensity the inboard side emission dominates over the emission from the outboard side and in the edge LHD plasma the electron temperature in the perpendicular direction to the magnetic field is higher than that in the parallel direction.

Keywords

Lyman-α line, velocity distribution function, polarization degree, VUV spectrometer, Large Helical Device

DOI: 10.1585/pfr.14.3402083

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