Initial growth of tungsten fuzz induced by bubble-driven surface stress layer under helium irradiation

Abstract

Abstract Low-energy, high-flux He exposure to tungsten (W) surface leads to the formation of surface nanostructures and severe morphological changes, which may eventually erode the W divertor and threaten the operation of the reactor. In this study, the response of polycrystalline W under low-energy He+ irradiation at different temperatures has been investigated in order to analyze the early stage of nanostructure formation. It is found that the interactions of high-density over-pressured He bubbles result in the formation of surface stress layers. The significant effect of temperature on the surface stress leads to differences in the incubation dose of W fuzz growth. The interaction between the planar network and the underlying W matrix is weak under surface stress, and the W fuzz grows on the surface once the stress reaches a threshold. Thereafter, tensile stress-driven cracking causes the 3D growth of W nanofibers.