Atomistic simulations of the effect of reactor-relevant parameters on be sputtering

Abstract

Beryllium (Be) is the main plasma-facing material in the present day fusion reactor JET as well as in the upcoming ITER. Thus, the Be erosion plays a key role in predicting the life-time and viability of the reactors. In this work, Be surface erosion and morphology changes due to deuterium (D) irradiation are studied by using molecular dynamics simulations, varying key parameters such as particle flux, surface temperature and impact energy. At low temperatures, the main molecular species among the sputtered particles is BeD due to a low D surface concentration, as the incoming D projectiles cluster beneath the surface. At higher temperatures, the D surface concentration increases and larger species (BeD2, BeD3) dominate the molecular erosion, lowering the BeD to Be ratio. When approaching the Be melting point, D desorbs from the surface, increasing the fraction of Be eroded as BeD. The larger molecules will dissociate as soon as entering the edge plasma, with only a minor contribution to the BeD formation. These findings correlate well with observations at JET. The effect of the incoming D flux on the results is negligible.