Interaction of plasma facing materials for fusion devices with low energy hydrogen and helium particles

Radiation damage formed in metal specimens exposed to long pulse tokamak pl asmas of TRIAM-1M was examined by transmission electron microscopy. By comp aring these results with those of low energy hydrogen ion irradiation it wa s concluded that the charge exchange energetic neutrals of hydrogen emitted from the core plasma caused remarkable displacement damage. The flux of th e neutrals in the energy range of 0.5-3 keV which were responsible for disp lacement damage, was estimated to be about 1.5-3 x 10(18) H/m(2)/s. These e nergetic neutrals cause not only material degradation at the sub-surface re gion but also change bulk properties of plasma facing components in a plasm a confinement device. Effect of helium plasma was also discussed with empha sis on very strong effects on damage accumulation. Damage by He is a seriou s issue of plasma facing materials.