MD simulations of low energy deuterium irradiation on W, WC and W2C surfaces

According to the present design beryllium (Be), tungsten (W) and carbon (C) will be the plasma facing materials in the ITER fusion reactor. Due to sputtering and subsequent re-deposition, mixing of these materials will occur. In this context, molecular dynamics simulations of cumulative, low energy and high flux D bombardment of pure W and tungsten carbides (WC, W2C) were carried out. The retention and sputtering properties as well as the structural deformation were analysed and comparisons to SDTrimSP simulations were made. Almost no tungsten is sputtered in the energy range considered and the D backscattering is lower in pure tungsten than in any of the tungsten carbides. In WC and W2C, the deuterium is mainly trapped forming small molecules, whereas mostly atomic D is present in pure W. The C sputtering increases with C content in the material, and shows a peak at the bombardment energy ∼50 eV, most likely due to the swift chemical sputtering mechanism. Pure W is seen to lose its crystallinity in the areas where D is present. After the D irradiation, the composition of both WC and W2C is mostly W in the topmost layers, due to preferential sputtering of C, an amorphous D-C mixture underneath and an undisturbed lattice in the rest of the cell.