Dynamic behavior of hydrogen atoms with a boronized wall

Abstract

Dynamic behavior of hydrogen atoms in boron films, which is one of candidate materials of the first wall of fusion devices, has been studied. Hydrogen absorption behavior was investigated with a glow discharge in hydrogen. After a strong absorption in the beginning of the discharge, hydrogen atoms were slowly and continuously absorbed for 10 h without saturation. The slow absorption is due to deeper migration of hydrogen atoms into the film, enhanced by the ion bombardment. A helium glow discharge causes both ion induced desorption and the deeper migration, and thus, hydrogen atoms are accumulated in the film when the H 2 and He discharges are repeated alternately. Most of the retained hydrogen atoms were released by heating up to 400°C. A calculation result based on a simple model was compared with the experimental results. A recombination coefficient was obtained from the analysis of the experimental transient release of the H atoms just after the H 2 discharge. The time behavior at the initial phase of the He discharge was reproduced fairly well with use of a smaller cross-section for the He + ion induced detrapping than that for H 2 +.