Modeling of Lyman-α line polarization in fusion plasma due to anisotropic electron collisions

M Goto,N Ramaiya

doi:10.1088/1742-6596/1289/1/012011

Abstract

We have derived a formula for calculating the polarization state of the Lyman-α line in plasma caused by anisotropy in the electron velocity distribution function. Calculation results under the condition of the magnetically confined fusion plasma show that the longitudinal alignment of 0.01 is caused by approximately 10%–20% difference in the electron temperature in the directions parallel and perpendicular to the magnetic field. It is also found that the polarization decreases with the increasing electron density, ne, due to the collisional population averaging effect over the magnetic sublevels in the range of ne > 1018 m−3 and is virtually extinguished at ne = 1021 m−3.

Highlights

Anisotropy in the velocity distribution function (VDF) is thought to play a key role for determining confinement characteristics of electrons in the magnetically confined fusion plasma [1]
The Lyman-α of neutral hydrogen can be a target of the observation first because hydrogen is the dominant constituent of the fusion plasma and, high emissivities are expected
Confinement characteristics of electrons are dependent on their velocity pitch angle with respect to the magnetic field line

Summary

Introduction

Anisotropy in the velocity distribution function (VDF) is thought to play a key role for determining confinement characteristics of electrons in the magnetically confined fusion plasma [1]. Confinement characteristics of electrons are dependent on their velocity pitch angle with respect to the magnetic field line. This paper describes the outline for calculating the polarization state of the Lyman-α line with anisotropic electron collisions following Fujimoto’s methodology [2], and shows some results of the actual calculation under typical plasma conditions of the Large Helical Device (LHD), which is a fusion experiment machine of magnetic confinement.

Results

Conclusion