Modelling of physical sputtering properties during tungsten fuzz growth under various impact energies on NAGDIS-II

Fiber-like nanostructure named fuzz can form on tungsten (W) surface under the irradiation of helium (He) plasma. While the W fuzz growth can be suppressed by the bombardment of energetic He particles. The experiments of tungsten fuzz growth and erosion exposed by He plasma with impact energies in the range of 200 ∼ 500 eV have been conducted on the linear divertor simulator NAGDIS-II. To study W physical sputtering properties during fuzz growth on NAGDIS-II, three-dimensional kinetic Monte Carlo code SURO-FUZZ has been upgraded by including the migration of W adatoms and the deposition of sputtered W particles. By means of the renewed SURO-FUZZ, dedicated simulations of W fuzz growth and erosion under various He impact energies have been performed to reproduce the NAGDIS-II experiments. The simulated fuzz layer thicknesses under erosive regimes show a good agreement with the measurements on NAGDIS-II. The W net physical sputtering yield on W fuzzy surfaces increases with He impact energy according to SURO-FUZZ modelling. Further, the relative W net physical sputtering yields of the fuzzy surface to the smooth surface (Yfuzz/Ysmooth) have been studied under different He impact energies, which reveals that the decay trend of Yfuzz/Ysmooth is mainly dependent on the fuzz layer thickness.