Large-scale atomistic simulations of low-energy helium implantation into tungsten single crystals

KD Hammond and S Blondel and L Hu and D Maroudas and BD Wirth, ACTA MATERIALIA, 144, 561-578 (2018).

DOI: 10.1016/j.actamat.2017.09.061

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, Gamma approximate to 4 x 10(25) m(-2) S-1, is about one order of magnitude larger than that expected in ITER, the experimental fusion reactor currently being constructed in France. With simulation times on the order of 1 mu s, these results serve to discover 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 (001) surfaces under a helium flux of Gamma similar to 10(28) 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. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

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