H Binding Energetics at Near-Surface He-V clusters and Bubbles in Tungsten

We describe results of density functional theory calculations to investigate the interaction and binding energies of H with a wide range of He-V clusters as a function of depth below W surfaces of varying orientation. The results show that the behavior of H below W can be divided into three distinct regions, namely a strong influence region, a transition region and as the depth below the surface increases, the H cluster configurations with lowest energy are similar to those found in bulk W. Additionally, we have evaluated the H trapping energetics at planar He-W interfaces to assess the influence of helium density and surface orientation on de-trapping energies. Our results provide fundamental insight into the energetics of H and He that control the surface morphology and tritium retention behavior in W exposed to low-energy plasma conditions.