Plasma-surface interaction effects during high ion temperature long pulse experiments in TRIAM-1M

TRIAM-1M tokamak is very suitable for studies on plasma material interaction because of its very long duration plasma discharges. We have investigated the damage and modification of plasma facing materials by exposing to the plasma in the scrape-off layer (SOL) of this machine and review the recent results in this paper. Dense dislocation loops were formed in Mo and W by exposing to the plasma for a few 10 min. This damage was caused by energetic charge-exchange hydrogen neutrals generated mainly in the lower half of the plasma. The mean flux of responsible neutrals for the damage was estimated to be 3×10¹⁷ m^-2 s^-1 sr^-1. Plasma facing surfaces were covered by an impurity deposit consisting of very fine crystalline grains (about 1 nm in size), whose crystal structure is not normal body-centered-cubic (bcc) structure but face-centered-cubic (fcc) structure. It was found that retention of hydrogen in these peculiar materials is much stronger than `normal' Mo.