Dynamic Response of Hydrogen Reemission and Retention from and in Inert Gas Sprayed Tungsten Exposed to ECR Plasmas

Hydrogen reemission and retention from and in the inert gas plasma sprayed tungsten (IPS-W) exposed to the plasma are described. Two kinds of irradiation scenarios are investigated in continuous and cyclic exposures. In the later a recovery phase exists between plasma exposure phases, simulated to the regular tokamak discharges. The H retention at the surface temperature Ts of 600 ~ 900 K was evaluated from 4 × 10²⁰ m^-2 to 2 × 10²² m^-2 at the fluence from 1 × 10²⁴ m^-2 to 1 ×  10²⁶ m^-2 under continuous exposure conditions. For the cyclic exposure, two cases associated temperature variation during the cycle, large T_s > 100 K and small < 40 K, are investigated. The temperature rise T_s dependence of the reemission and retention is observed. When T_s > 100 K, the apparent reemission is triggered by both T_s and irradiation itself, and then after the exposure stops it turns to apparent retention. However, for T_s < 40 K no reemission and retention are observed in the cycle. This fact suggests that the hydrogen reemission is enhanced during the exposure via the surface recombination process depending on T_s or T_s gradient across the specimen.