Atomistic simulations of Be irradiation on W: mixed layer formation and erosion

Abstract

In the recent ITER-Like Wall experiment at JET, tungsten (W) and beryllium (Be) are used as the first wall plasma-facing materials. Due to the plasma–wall interactions, these materials will erode, be transported, re-deposit and mix. We present the first computational, atomistic, systematic study on the W–Be material mixing under fusion-relevant conditions. To this end, W surfaces were irradiated by Be, varying the impacting energy and angle, followed by annealing the mixed W–Be layers. At low energies, a Be layer is deposited on W, suppressing the W erosion. The materials mix as the W atoms migrate towards the Be layer due to the heat of mixing. Be2 and BeW molecules eroded, both physically (dimer sputtering) and chemically (sputter etching). All the mixed layers show an underlying hcp-like Be structure and the Be : W ratios are close to those in the intermetallic phases (Be2W—Be12W). However, no crystalline alloy structure formed, even after annealing. Further, we present a geometrical model for the angular dependence of the Be reflection, which strongly affects the W sputtering.