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Tungsten (W) is one of the most promising candidates for plasma facing materials in the fusion reactor. Helium (He) in W can influence the retention of hydrogen isotopes. In the present study, W targets were simultaneously irradiated by He+-H 2 + or He+-D 2 + ion beams with the energies of 1 keV or 3 keV, at fixed temperatures in a range of room temperature (R.T.) to 1073 K. Mechanisms of He and hydrogen interaction in W were discussed, especially from the point of He retention, which was characterized by the high-temperature thermal desorption spectroscopy (TDS) and glow-discharge optical emission spectroscopy (GD-OES) measurements. It is found that He desorption shifts to a lower temperature range for the W simultaneously irradiated by 3 keV He+-1 keV H 2 + at 573 K, under He+ fluence up to 1 × 1022 He+m−2. Transmission electron microscope (TEM) observation and annealing treatment at the temperature of 873–1073 K show that the increased He uptake is caused by the formation of dislocation. Enhanced retention amounts for the hydrogen isotopes were also confirmed. Amounts of the dislocation loops introduced by the H 2 +-only irradiation can be reduced by annealing treatment at 873 K, while that introduced by He+ irradiation are quite stable, which grows larger at elevated temperatures. With an increase of H 2 + energy, Helium uptakes at both weak trapping sites and bubbles are increased, while the amounts of hydrogen retention are decreased. It suggests that hydrogen ion has a significant influence on the He trapping sites at the irradiation temperature up to 573 K, while the hydrogen retention is determined by the distribution of He bubbles and dislocation loops. • Helium was mainly trapped by dislocation loops in tungsten irradiated by 3 keV He+- 1 keV H 2 + at 573 K. • Helium concentration in tungsten under 3 keV He+- 1 keV H 2 + irradiation was decreased at 873 K. • Increased hydrogen isotope uptake in tungsten was found when helium was mainly trapped at dislocation loops. [ABSTRACT FROM AUTHOR]

The purpose of this study is to elucidate helium (He) retention behavior in tungsten (W) under simultaneous He and hydrogen (H) irradiation. Polycrystalline-W was irradiated by He + and H 2 + simultaneously with the energy of 1.0 keV and 3.0 keV. He + fluences were (0.5, 1.0, 10) × 10 21 He + m −2 and H 2 + fluence was 1.0 × 10 22  H + m −2 ,respectively. After irradiation, He desorption behavior was investigated by high temperature thermal desorption spectroscopy (HT-TDS) in the temperature range of R.T.-1773 K. Micro-structure changes of W after irradiation were observed by TEM. It was found that simultaneous irradiation with different H 2 + energy significantly changed He retention behavior. 1.0 keV H 2 + suppressed the He bubble growth and no bubbles can be observed at room temperature. On the other hand, 3.0 keV H 2 + facilitated the formation of He bubbles and increased the He retention due to the additional damage introduction by energetic H 2 + . [ABSTRACT FROM AUTHOR]

Co-deposition of wall material and ions from plasmas occurs on material surfaces in fusion devices. In this study, we focus on tungsten (W) deposition layer in helium (He) plasmas (He-W co-deposition) formed at surface temperatures of 473–773 K. Usually, He irradiation at the surface temperature below 1000 K does not lead to significant morphology changes; we will show from transmission electron microscope observations that the roughness of the co-deposition layer has a significant temperature dependence even when the temperature is less than 800 K. We conducted deuterium plasma irradiation to the He-W co-deposition layer. It was found that the deuterium retention on the He-W co-deposition layer increased significantly with increasing the formation temperature of the co-deposition layer. [ABSTRACT FROM AUTHOR]