TRITIUM TRAPPING IN MULTI-LAYER PLASMA FACING MATERIALS

The influence of damaged surface layer on the permeation and inventory of hydrogen was also examined experimentally. The upstream surface of a vanadium membrane (0.1 mm in thickness) was exposed to hydrogen gas at 640 Pa and 673 K, and the steady state of the permeation was attained. Then. the downstream surface of the membrane was irradiated with He ions. No significant variation of the permeation rate was observed in the initial stage of irradiation. The permeation rate, however, started to decrease at the fluence of 10^<21> m^<-2> with further irradiation. This was attributed to the trapping effect on hydrogen diffusion by radiation defects. The irradiation of He ions was intermitted when the permeation rate decreased to a half of the initial value, and then the ion beam was switched on and off repeatedly. The permeation rate increased promptly by the switching-on and decreased by the switching-off These results clearly indicated that the trapping effect under irradiation is small compared with that in the absence of irradiation.