EFFECT OF LIGHT IMPURITY ELEMENTS ON HYDROGEN TRANSPORT IN HIGH-Z PLASMA FACING MATERIALS

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Retention and the thermal release of D atoms retained in near surface layers of Mo and W crystals were investigated by ion-beam analysis techniques in connection with influences of helium pre-implantation and light impurities such as carbon and oxygen in the surface layer.From the depth profile studies of the retained D atoms and the implantation induced disorder, it may be concluded that the trapping of the D atoms in Mo and W crystals is associated with lattice distortion caused by the implantation induced extended defects such as interstitial loops. This was consistent with the results of ion channeling experiments: D atoms implanted in the W crystal were located near the tetrahedral interstitial site and the lattice distortion may become stable due to the local relaxation by trapping D atoms, especially at room temperature.A large lattice distortion was created by 10 keV He pre-irradiation with about 1x10ィイD119ィエD1 He/mィイD12ィエD1, and the retention of the D atoms in W and Mo was str … More ongly enhanced at room temperature. At higher He dose, the D retention did not depend on the He pre-implantation dose. However, the lattice disorder was significantly accumulated in near surface layer and the thermal release of D atoms occurred at higher temperature in comparison with that for unirradiated crystals.Ion implanted D atoms accumulated in the surface oxide layer of Mo and W with a concentration of 4〜6x10ィイD128ィエD1 D atoms/ィイD13ィエD1 at room temperature. Carbon contained Mo surface layer also strongly enhanced the retention of D atoms in comparison with that for clean Mo surface, however, the D atoms distributed far beyond the carbon-enriched layer and distributed in single crystalline substrate region. Thickness of the oxide layer on the Mo was decreased during successive D implantation and heat treatment. On the other hand, the W oxide layer with high density of D atoms was stable during the annealing up to 800K. Thermal release of D atoms from the carbon containing layer of W and Mo occurred at considerably lower temperatures (〜350K) than that from clean surface. Less