Evolution of helium bubbles below different tungsten surfaces under neutron irradiation and non-irradiation conditions

Studies of the evolution of embedded helium (He) bubbles in tungsten are very important for understanding the failure mechanism of tungsten as a plasma-facing material. In this work, the processes of He bubble evolution under neutron irradiation and non-irradiation conditions have been investigated by molecular dynamics simulations. The influences of temperature, helium/vacancy ratio, and surface crystal orientations on the stability and evolution of He bubbles were discussed. Four evolution cases (standing, expanding, bursting, and oversaturation expanding) of He bubbles under {1 0 0}, {1 1 0}, and {1 1 1} surfaces were found, and the oversaturation expanding case was discussed in detail. In particular, the differences between the stable bubbles bursting from {1 0 0}, {1 1 0}, and {1 1 1} surfaces under neutron irradiation condition were investigated. It was also found that He bubbles can burst from the surfaces (especially from a surface with low crystal face density) more easily under neutron irradiation condition.