Plasma and Fusion Research

Volume 16, 2406011 (2021)

Regular Articles

VUV Emission Spectroscopy for Evaluation of Optical Thickness in He Cascade Arc Plasmas
Md. Anwarul ISLAM, Ryo SHIGESADA, Takumi YAMAGUCHI, Hayato KAWAZOME1), Naoki TAMURA2), Hiroki OKUNO3) and Shinichi NAMBA
Graduate School of Advanced Science and Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Japan
1)
National Institute of Technology, Kagawa College, Mitoyo 769-1192, Japan
2)
National Institute for Fusion Science, Toki 509-5292, Japan
3)
RIKEN, Nishina Center for Accelerator-Based Science, Wako 351-0198, Japan
(Received 16 November 2020 / Accepted 22 December 2020 / Published 19 February 2021)

Abstract

We have generated a cascade arc plasma with a channel diameter of 8 mm for application to plasma window. Helium arc plasma up to a discharge current of 100 A were generated. We investigated the radiation trapping effect in the high-density He plasmas under various ambient gas pressures. In order to investigate the radiation trapping effect (optical thickness) in the high-density plasmas, we conducted vacuum UV (VUV) emission spectroscopy associated with He I resonance line. By observing the VUV spectrum attributed to He I resonance (1 1S-2 1P) transitions, we compared the emission intensities for different gas pressures. Lyman α intensity was increased by 3 times with a magnetic field due to well confinement of He plasma. The intensity decreased rapidly at high-ambient pressures due to the strong self-absorption. Therefore, the high-pressure arc plasma generated was classified into the optically thick one, and the self-absorption process of the resonance lines drastically influenced the population kinetics and energy transport.

Keywords

cascade arc discharge, radiation trapping, VUV emission, radiative transfer equation, collisional radiative model, optically thick plasma, plasma window

DOI: 10.1585/pfr.16.2406011

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