Effects of high heat flux hydrogen and helium mixture beam irradiation on surface modification and hydrogen retention in tungsten materials

High heat flux experiments using a hydrogen–helium mixture beam have been carried out on powder metallurgy tungsten (PM-W) and ultra fine grain W–TiC alloy (W–0.5 wt%TiC-H2). The energy of is 18 keV. Beam flux and heat flux at the beam center is 2.0 × 1021 atoms/m2s and 7.0 MW/m2, respectively. Typical ratio of He/D ion is 0.25. Beam duration is 1.5–3 s and interval of beam shot start is 30 s. The samples are irradiated up to a fluence of 1022–1024 He/m2 by the repeated irradiation pulses. After the irradiation, surface modification by the irradiation and hydrogen retention, surface composition have been investigated. Surface modification by hydrogen–helium mixture beams is completely different from results of single beam irradiation. In particular, mixture beam irradiation causes remarkably high hydrogen retention.