Enhanced erosion of tungsten by atom clusters

Self-sputtering of tungsten, a plasma-facing material candidate in fusion devices, by ionized atoms is a widely studied phenomenon. However, not only single atoms, but also small clusters sputtered from plasma-facing surfaces can be ionized in the sheath and redeposited back on the first wall. Using molecular dynamics simulations we study the self-sputtering of tungsten by small Wn (n=1,2,4) clusters in the energy range 0.2–40 keV/cluster. We show that, in comparison with single-atom sputtering yields, enhanced sputtering yields by clusters are observed at energies higher than about 2 keV/atom. The yields are proportional to the number of atoms in the cluster at 40 keV/cluster. However, cluster bombardment at energies lower than 2 keV/cluster is not self-sustaining and will reduce to single-atom redeposition.