Exploring the suppression methods of helium-induced damages in tungsten by investigating the interaction between beryllium and helium

Abstract

Helium (He)-induced damages are sensitive concerns for the performance of tungsten plasma facing materials (W-PFMs). Recent experiments have revealed that trace impurities in He plasma can effectively prevent the formation of He bubbles and fuzz on W surfaces. To explore its plausibility and underlying mechanism, we performed a multiscale computational study that combines density functional theory calculations and object kinetic Monte Carlo simulations to investigate the effects of a small quantity of beryllium (Be) on the evolution of He bubbles. It is found that there is strong attractive interaction between He and Be, which can be attributed to the decrease of electron density and the lattice distortion induced by embedded Be atom. Therefore, the co-implantation of Be continuously introduces trapping centers for He. Due to low implantation depth and high migration energy of Be, the Be atoms are located close to the surface, leading to the trapping of the majority of He within the near-surface region and the development of a shielding layer for He permeation. The presence of Be facilitates the dispersion of the trapped He, skewing the He clusters into smaller size. More importantly, the Be trapping centers bring the He clusters closer to the surface, significantly increasing the probability of bubble bursting and the release of He back to the vacuum. These ultimately leads to a lower retention of He in the case of He+Be co-irradiation, compared with the case of He-only irradiation. Consequently, our findings elucidate the suppressive effect of a low flux of Be atoms on the growth of He bubbles, highlighting the need to focus on the synergetic effects between plasma species.