(510e) Modeling of Nano-Fuzz Formation in Helium-Ion-Irradiated Tungsten

Due to its low hydrogen solubility, low sputtering yield, high melting point, and high thermal conductivity, tungsten (W) is considered as a suitable plasma-facing material (PFM) candidate for divertor and first-wall systems, capable of tolerating the extreme conditions of high temperature and particle flux inside fusion reactors. However, experiments have shown that helium (He) from linear and tokamak plasma devices is responsible for the formation of a nanostructure with a fuzz-like morphology on the W surface after a few hours of plasma exposure. We are especially interested in fuzz formation under the operating conditions of temperature, He impact energy, and He flux expected for ITER’s divertor, which affect the reactor performance leading to increases in the nucleation of He bubbles, retention of hydrogen isotopes, and production of high-atomic-number dust.

In this presentation, we focus on obtaining a fundamental understanding of the initial stage of fuzz formation and predicting the surface morphological evolution of helium-ion-irradiated tungsten considered as a PFM based on an atomistically-informed, continuous-domain model that we have developed. According to this model, we have conducted a systematic protocol of self-consistent dynamical simulations of the evolution of the irradiated tungsten surface morphology, focusing on W{110} surfaces, in order to identify the critical range of conditions for nanotendril formation on the surface, a precursor to fuzz-like surface growth. We examine a broad range of operating conditions, including surface temperatures from 1300 to 2300 K, He ion energies from ~10 eV to ~1 keV, and He fluxes over several orders of magnitude from 10¹⁶ to 10²² m^-2 s^-1. We compare our simulation results with recent experimental measurements and find the predicted size and arrangement of nanotendrils to be in good agreement with the experimental observations. We also present the results of a sensitivity analysis of the key model parameters, such as He concentration and He nanobubble size. Future model extensions driven by comparisons of the model predictions with the experimental observations, as well as the anticipated divertor performance, will be discussed.