Molecules can be sputtered also from pure metals: Sputtering of beryllium hydride by fusion plasma-wall interactions

The low-energy erosion mechanisms of first-wall materials subject to a fusion plasma are poorly known theoretically, even though they pose a critical problem for the development of tokamak-like fusion reactors. Using molecular dynamics computer simulations and analytical theory, we have examined the fundamental mechanisms of the erosion of first-wall materials, focusing on molecular release from beryllium surfaces. We show that the observed sputtering of BeD molecules from beryllium when exposed to a D plasma can be explained by the swift chemical sputtering mechanism, and that it also can happen in BeW alloys. This demonstrates that pure metals can, in contrast to conventional wisdom, be sputtered chemically. We also link the simulations of BeD sputtering to the plasma impurity transport code ERO, in order to follow the behavior of sputtered BeD species in a plasma. This multi-scale approach enables direct comparisons with experimental observations of BeD sputtering in the PISCES-B facility.