Helium and hydrogen interaction in tungsten simultaneously irradiated by He+-H2+ at high temperature

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 x 10(22) 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. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.