Hydrogen retention properties of low Z and high Z plasma facing materials

Abstract

Hydrogen retention properties of isotropic graphite, B 4C converted graphite, SiC converted graphite and tungsten were evaluated by using a technique of thermal desorption spectroscopy after the hydrogen ion irradiation (5 keV, H 3 +) in an ECR ion source. The ratios of retained hydrogen at RT were 3 2 , 5 6 and 1 10 for B 4C, SiC and tungsten, respectively, when the retained amount of graphite was normalized unity. B 4C or SiC had two peaks due to detrappings of CH bond, and BH or SiH bond in the thermal desorption spectrum. Tungsten had also two peaks in the range below 1000°C. In the annealing temperature dependences of the retained hydrogen, the ratios of retained hydrogen for tungsten, B 4C and SiC more rapidly decreased with the temperature, compared with the case of graphite. In order to reduce the hydrogen retention, the helium ion irradiation (5 keV, He +) and the subsequent thermal desorption experiment were conducted after the hydrogen ion irradiation. The reductions of the hydrogen amount for tungsten and B 4C were larger than that of isotropic graphite. However, the reduction of SiC was smaller, compared with the case of isotropic graphite.