(305d) Effects of Flux on Helium Bubble Growth in Plasma-Facing Materials

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 “fuzz”—a layer of microscopic, high-void-fraction features on the surface—after 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 m^−2 s^−1, while fluxes in experiments are typically closer to 10²¹â€“10²³ m^−2 s^−1. 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 (500–1000 ns) molecular dynamics simulations of plasma-facing tungsten at fluxes ~10²⁷, 10²⁶, and 10²⁵ m^−2 s^−1, 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.