Tungsten, the primary material under consideration as the divertor material in magnetic-confinement nuclear fusion reactors, has been known for the last decade to form âfuzzââa layer of microscopic, high-void-fraction features on the surfaceâafter only a few hours of exposure to helium plasma. Typical molecular dynamics simulations of phenomena relevant to plasma-facing tungsten are based on fluxes of ~1028 mâ2 sâ1, while fluxes in experiments are typically closer to 1021â1023 mâ2 sâ1. Large-scale molecular dynamics simulations of post-implantation helium behavior in plasma-facing tungsten single crystals recently revealed orientation-dependent depth profiles, surface evolution patterns, and other crystallographic and diffusion-related characteristics of helium behavior in tungsten during the first microsecond. This study tackles the issue of the effect of helium flux by way of long-time (500â1000 ns) molecular dynamics simulations of plasma-facing tungsten at fluxes ~1027, 1026, and 1025 mâ2 sâ1, all whilst tracking surface features and helium depth profiles. These calculations serve as important benchmarks for coarse-grained simulations and unveil the relative importance of the transport processes and material deformation process involved in surface evolution in plasma-facing materials.
