DYNAMIC BEHAVIOR OF HYDROGEN-ATOMS WITH A BORONIZED WALL

Dynamic behavior of hydrogen atoms in boron films, which is one of can didate 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 dischar ge, hydrogen atoms were slowly and continuously absorbed for 10 h with out saturation. The slow absorption is due to deeper migration of hydr ogen atoms into the film, enhanced by the ion bombardment. A helium gl ow discharge causes both ion induced desorption and the deeper migrati on, and thus, hydrogen atoms are accumulated in the film when the H-2 and He discharges are repeated alternately. Most of the retained hydro gen atoms were released by heating up to 400 degrees C. A calculation result based on a simple model was compared with the experimental resu lts. A recombination coefficient was obtained from the analysis of the experimental transient release of the H atoms just after the H-2 disc harge. 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(+). (C) 1998 Elsevier Scienc e B.V. All rights reserved.