Strain-enhanced helium bubble nucleation and growth in tungsten: atomic-level insights and long-term dynamics

Helium (He) irradiation-induced degradation, particularly through the formation and growth of bubbles, poses a critical challenge for tungsten plasma-facing materials (W-PFMs). In service, these materials often experience tensile strain fields due to thermal cycling and bubble accumulation, yet the underlying physical mechanisms of external strain on the fundamental processes of He bubbles, from self-trapping, nucleation, growth, to long-term evolution, remain unclear. In this work, we systematically investigate these processes under isotropic tensile/compressive strain using multiscale simulations. We reveal that tensile strain induces a counterintuitive behavior: although the He solution energy is lowered under tensile strain, the He–He binding energy is significantly enhanced, a trend opposite to the positive correlation observed across different metals. This originates from the synergistic effect of strain and He, causing the variation in the electronic structure. Furthermore, tensile strain promotes bubble nucleation and growth by facilitating Frenkel pair nucleation and trap mutation. Extending these atomic insights to long-term evolution, we demonstrate how tensile strain accelerates bubble coalescence, rupture, and the early-stage formation of fuzz, consistent with experimental observations of strain-dependent bubble evolution. Crucially, a positive feedback mechanism integrating these findings is suggested: dense bubbles induce a subsurface tensile strain field in PFMs, which in turn further promotes bubble nucleation and growth. The proposed strain-enhanced mechanism informs the development of predictive models for He-induced damage in PFMs under fusion-relevant conditions.