Self-reversal in Lyman-α line profile for diagnosis of fusion plasma

M Goto,K Sawada,T Oishi,S Morita

doi:10.1088/1742-6596/810/1/012016

Abstract

We have observed Lyman-α line profile which exhibits the so-called “self reversal” at the line center. A one-dimensional radiation transport equation is numerically solved for simulating the Lyman-α line profile, where the emission and absorption coefficient distributions over the line-of-sight are evaluated based on the Laplace inversion analysis of the Balmer-α line measured simultaneously with the Lyman-α line. While the synthetic profile of the Lyman-α line shows a good agreement with the measured data in the line profile tail, the central part shows a significant discrepancy between the synthetic and measured profiles. It has been known that the neutral density profile in the plasma boundary region derived from the Balmer-α line profile analysis has a relatively large error and the present results shows that the Lyman-α line measurement would play a complementary role to determine an entire neutral density profile from the core to the edge.

Highlights

The neutral atom density in the plasma is an important parameter for evaluating the plasma confinement characteristics because the ionization of neutral atoms is essential in the particle source, and neutral atoms in the plasma cause particle and energy loss through the charge exchange process
This kind of measurement has an essential problem because observed line emissions of neutral atoms are mainly located at the outermost boundary of the plasma and weak line emissions in the core region, if any, are difficult to be detected by a line-integrated measurement with a line-of-sight which passes through both the edge and core regions
We focused on the tail component of observed Balmer-α line profiles and established a method to deduce a spatial distribution of the hydrogen atom density [3]

Summary

Introduction

The neutral atom density in the plasma is an important parameter for evaluating the plasma confinement characteristics because the ionization of neutral atoms is essential in the particle source, and neutral atoms in the plasma cause particle and energy loss through the charge exchange process.Many efforts have been made to determine the hydrogen atom density or the ionization rate in the plasma, most of which are based on spatial inversion of chord-integrated intensities of an emission line such as the Balmer-α line [1] or the Lyman-α line [2]. Many efforts have been made to determine the hydrogen atom density or the ionization rate in the plasma, most of which are based on spatial inversion of chord-integrated intensities of an emission line such as the Balmer-α line [1] or the Lyman-α line [2].

Results

Conclusion