Surface temperature effects on the retention and pressure variation in continuous and cyclic plasma exposures on the tungsten

Abstract

Hydrogen retention and pressure variation in and from the inert gas plasma sprayed tungsten (IPS-W) exposed to plasmas are described. Two kinds of plasma irradiation scenarios are investigated in continuous and cyclic exposures. The H retained fluence at the surface temperature T s of 470–900 K was evaluated in the range of 4 × 10 20–2 × 10 22 H/m 2 for the bombarding fluence of 1 × 10 24–1 × 10 26 H/m 2 under continuous exposure condition. For the cyclic exposure, it is found that if Δ T s > 100 K during exposure, the apparent re-emission (pressure increase) is triggered by both Δ T s and irradiation itself, and just after the exposure it turns to apparent retention (pressure decrease). However, for Δ T s < 40 K no apparent re-emission 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 Δ T s or T s gradient across the specimen.