Helium defects interactions and mechanism of helium bubble growth in tungsten: A molecular dynamics simulation

Molecular dynamics simulations have been performed to investigate the interactions between helium (He) and defects in tungsten (W). The binding energy between He and He cluster is shown to be positive, which increases with increasing He cluster size. Both the W self-interstitial atoms (SIAs) and the vacancy can promote the He cluster formation. The binding energies of a He, a vacancy and an SIA W to a He-vacancy cluster (He_nV_m) in W are also investigated, which depend on the n/m ratio. According to these results, we propose the formation and growth mechanism of He bubbles, which involves the procedures of He-vacancy cluster formation, the capturing of vacancies, then He atoms, and vacancies again. The mechanism provides a good reference to understand the initial stage of the He bubble formation and growth in W.