Modeling and simulation for surface helium effect on hydrogen isotopes diffusion and trapping/detrapping behavior in plasma facing materials

In this study, surface helium (He) effect on hydrogen isotopes diffusion and trapping/detrapping behavior was modelled and integrated into the HIDT simulation code. Effective dynamics properties of hydrogen in tungsten including diffusivity, solubility, recycling and diffusion barrier were considered to reflect the influence of He bubbles. Simulation results showed that total hydrogen retention was reduced with the existence of He bubbles near surface, which was consistent with the reported laboratory experimental results. It was found that the most significant influence came from the diffusion barrier induced by He bubbles. With increasing the barrier factor, total hydrogen retention changed from the tendency of decrease to increase. When the barrier factor was less than 0.3, hydrogen desorption from the implantation surface was dominant, while that from the backside surface became dominant when the barrier factor was greater than 0.4. In the meanwhile, more hydrogen accumulated beyond the He bubble layer was observed. These hydrogen atoms occupied not only in trapping sites, but also in lattice sites. Based on these findings, three desorption stages, namely surface desorption, major desorption and backside desorption, could characterize the TDS spectra with different mechanisms. In addition, our findings were further substantiated by the reported experimental data. This study provides a new perspective to reveal the surface He effect on hydrogen isotopes retention behavior in plasma facing materials.