Simulation of Experimental Deuterium Retention in Tungsten under Periodic Deuterium Plasma Irradiation^*)

To study the effect of periodic plasma irradiation on deuterium (D) retention in tungsten (W), an irradiation experiment with low-energy (50 eV) and high-flux (~ 10²² m⁻² s⁻¹) ions was simulated through the coupling with collision and diffusion processes of injected D atoms. The irradiation was interrupted over one and two time intervals until the total fluence reached 10²⁶ D m⁻², in order to compare with the continuous irradiation case. The time evolution of the D atoms retained in W was calculated using the observed time variation of the material temperature and the irradiation sequences used in the experiments. After the periodic irradiation, the thermal desorption spectroscopy spectra were calculated, and the retention properties (depths, D/W ratios, and detrapping energies of the trapping sites) were estimated through comparison with the experimental spectra. At a temperature of 573 K, the irradiation with one interruption interval was found to increase the depth of the trapped D atoms and reduce the D/W ratio of the trapping sites with a low detrapping energy, compared with the continuous irradiation case. However, at 643 K, the depth was found to be decreased, and the D/W ratio of the trapping sites with a high detrapping energy was slightly increased; thus, the total retention was also slightly increased.