Molecular dynamics simulations on the effect of sub-surface helium bubbles on the sputtering yield of tungsten

Abstract

Tungsten is being considered for the divertor in ITER and for future nuclear fusion reactors because of its high melting temperature and high thermal conductivity. While the sputtering yield of tungsten is generally low, previous observations of surface modification due to plasma exposure raise questions about the effects of surface morphology and sub-surface helium bubble populations on the sputtering behavior. Results of computational molecular dynamics are reported that investigate the influence of sub-surface helium bubble distributions on the sputtering yield of tungsten {100} and {110} surfaces induced by helium ion exposure in the range of 300eV to 1keV. The specific microstructures and incident ion energies have been coordinated with planned experiments, which will be reported in the future. The calculated sputtering yields are in reasonable agreement with a wide range of experimental data, but do not show any significant variation as a result of the pre-existing helium bubbles.