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Author(s):
K. Tsuzuki, N. Inoue, A. Sagara, N. Noda, O. Motojima, T. Mochizuki, T. Hino and T. Yamashina
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Title:
Dynamic Behavior of Hydrogen Atoms with a Boronized Wall
Date of publication:
July 1997
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Key words:
hydrogen atoms, boronized wall, first wall, fusion device
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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. Boron films were deposited on the whole inner surface of a liner, which acts as a large test piece with a surface area of 7000 cm^2. Hydrogen absorption behavior was investigated with the glow discharge in hydrogen. After a strong absorption into the near surface region, hydrogen atoms were slowly and continuously absorbed for 10 hours without saturation. A helium glow discharge was carried out after the hydrogen discharge to investigate hydrogen desorption by the He ion bombardment. Fifteen percents of the absorbed H atoms were desorbed. The strong absorption was observed at the initial phase of the hydrogen discharge after the He discharge due to the evacuation of the H atoms from the surface during the He discharge. The number of absorbed hydrogen atoms was larger than one desorbed during the He discharge, which indicates that hydrogen atoms accumulate in the film when the H_2 and He discharges are repeated alternately. The slow absorption is due to migration of hydrogen atoms deeper into the film enhanced by the ion bombardment. Depth profile measurements with elastic recoil detection (ERD) give a consistent result. Most of the retained hydrogen atoms were released by heating up to 400 degree C. A possibility of the boron films as a protection wall of tritium permeation is suggested. A calculation based on a simple model was discussed with the experimental results. A recombination coefficient was obtained through the calculation of the 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 by assuming a smaller cross-section for ion induced detrapping.
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