Temperatures of Neutral Atoms in C-Stellarator Discharges and Charged-Particle Temperatures of the Afterglows

Abstract

The kinetic temperatures of neutral helium and hydrogen atoms in ohmically heated discharges of the C stellarator were determined from measurements of spectral profiles of the λ4921, 21P−41D line of HeI and the Hβ line of hydrogen. The time resolution of the measurements was about 250 μsec, or about 110 of the duration of the discharge. It was found that the neutral atoms were at all times at a temperature much higher than the walls of the discharge vessel, with highest temperatures in the neighborhood of 2 eV. The results are interpreted in terms of energy transfer between electrons and ions through Coulomb collisions, between ions and neutral atoms through resonant charge exchange, and between neutral atoms and the walls through semielastic collisions. In addition, the temperature of the recombining ions in the afterglow of the discharges was determined by the same method, and found to be in good agreement with simultaneously measured electron temperatures.