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

H. Zush et al.

Fusion Science and Technology / Volume 55 / Number 2T / February 2009 / Pages 9-14

Technical Paper / Seventh International Conference on Open Magnetic Systems for Plasma Confinement /

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 Ts > 100 K and small < 40 K, are investigated. The temperature rise Ts dependence of the reemission and retention is observed. When Ts > 100 K, the apparent reemission is triggered by both Ts and irradiation itself, and then after the exposure stops it turns to apparent retention. However, for Ts < 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 Ts or Ts gradient across the specimen.

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