Helium Defect Morphology Governs Impact-Induced Cratering and Ejecta in Tungsten

Tungsten plasma facing components experience simultaneous helium implantation and high velocity dust impacts, yet the coupling between He induced microstructure and impact damage remains unclear. Using large scale molecular dynamics, we quantify how distinct He topologies, sparse and dense bubble arrays, four isolated bubbles, He platelet, alter the response of a W target to normal incidence impacts by a 10 nm W projectile over impact velocities from 3.5 to 4.5 km s⁻¹. We find a robust ordering of retained crater volume and ejecta at 200 ps: pristine W < sparse array < dense array < isolated bubbles ≪ He platelet. Bubble arrays act as a compliant, venting layer that sustains plastic cratering and elevated steady ejecta while platelet undergoes a late time delamination that produces a sudden, large ejecta burst. For pristine and bubble array targets, ejecta kinetics is well described by a stretched exponential form; platelet failure requires an additional step term to capture delamination event. Depth resolved dislocation density profiles confirm localized plasticity in bubble arrays and distributed decohesion in platelets. These results provide an atomistic map from He topology to dust impact outcomes and a compact kinetics description, enabling He aware erosion and lifetime projections for fusion relevant tungsten.