The use of bare Reduced Activation Ferritic Martensitic (RAFM) steels has been proposed for the first wall in a fusion reactor. Thus, it is necessary to understand the erosion and surface morphology changes under direct and simultaneous hydrogen and helium implantation of RAFM steels under fusion-relevant condition. Experiments were performed at ion energies of ∼1 keV over the temperature range of 500–900 K, consistent with the anticipated operating conditions of the blanket region. The irradiation fluence was 1 × 1024 m−2 and the He% in the ion beam was 0.5%. Mass loss was measured before and after irradiation to determine erosion. Surface morphology changes were observed by SEM/FIB. RBS was used to quantify the near surface W concentration. From SEM images, surface roughening was observed at T &gt
750 K and complex surface structures formed with peak-to-peak variation in the ∼μm range. Mass loss increased with increasing surface roughening but the loss for simultaneous hydrogen-helium case was systematically higher compared to hydrogen-only case. A corresponding lower surface W concentration was measured for the simultaneous case, indicating Helium has an important role in W surface enrichment process.