Molecular dynamics simulations of cumulative helium bombardments on tungsten surfaces

Molecular dynamics simulations were performed to study the cumulative bombardments of low-energy (60-200 eV) helium atoms on tungsten surfaces. The behaviour of helium and the response of tungsten surface were investigated. The helium incident energy and tungsten temperature play important roles on the formation and growth of helium clusters. The temperature can promote the coalescence of helium clusters and increase the size of the helium clusters. The rupture of the helium clusters has also been observed. During the formation of helium clusters, the interstitial tungsten atoms are produced and evolve into bundles of <1 1 1> crowdions, which would be constrained around the helium clusters for a long time. However, they will finally move onto the top surface along the <1 1 1> direction, which results in stacking the tungsten atoms on the surface. The complex combination effects of the helium clusters and the interstitial atoms result in the growth of the surfaces. Besides, several tungsten atoms were ejected from tungsten surfaces.