Modelling the erosion of beryllium carbide surfaces

Redeposition of beryllium eroded from main chamber plasma facing components of ITER onto the divertor material carbon creates a mixed material, beryllium carbide Be₂C, whose interaction with the plasma is not well known. In this study, we have investigated the erosion of Be₂C by deuterium using molecular dynamics simulations and ERO impurity modelling. We found that beryllium sputters preferentially over carbon and identified the sputtering mechanism in the ion energy range 10–100 eV to be both physical and swift chemical sputtering. In addition to single atoms, different types of small molecules/clusters were sputtered, the most frequently occurring molecules being BeD, Be₂D, and CD. The sputtering threshold was found to lie between 10 and 15 eV. The MD sputtering yields were used in plasma impurity simulations, serving as a replacement for input data obtained with TRIM. This changes the accumulation rate of impurity Be in the divertor region compared to previous estimates.