(510b) Large-Scale Atomistic Simulations of Low-Energy Helium Implantation into Tungsten Single Crystals

Large-scale molecular dynamics simulations of post-implantation helium behavior in plasma-facing tungsten single crystals reveal orientation-dependent depth profiles, surface evolution patterns, and other crystallographic and diffusion-related characteristics of helium behavior in tungsten during the first microsecond. The flux of implanted helium atoms studied, Γ = 4 × 10²⁵ m^−2 s^−1, is only one order of magnitude larger than that expected ITER, the experimental fusion reactor currently being constructed in France. With simulation times on the order of one microsecond, these results serve to discover of the mechanisms involved in surface evolution as well as to serve as benchmarks for coarse-grained simulations such as kinetic Monte Carlo and continuum-scale drift–reaction–diffusion cluster dynamics simulations. The findings of our large-scale simulations are significant due to diminished finite-size effects and the longer times reached (corresponding to higher fluences). Specifically, our findings are drastically different from findings published previously in the literature for (0 0 1) surfaces under a helium flux of Γ ~ 10²⁸ m^−2 s^−1, which is typical of smaller size and shorter time atomistic simulations. In particular, this study highlights the atomic-scale materials processes relevant to helium entrapment and transport in metals, which have implications not only for nuclear fusion–relevant processes, but also helium-induced embrittlement in irradiated materials such as hospital equipment and fission reactor materials.