Measurement of hydrogenic retention and release in molybdenum with the DIONISOS experiment

Abstract

Molybdenum targets are exposed in the DIONISOS experiment to a deuterium (D) plasma ( Γ D ∼ 10 21 m −2 s −1) at target biases of 30–350 V and target temperatures of 300–700 K while simultaneously diagnosing the D in the surface with a 3.5 MeV 3He ion beam. The 3He diagnostic beam creates displacements in the Mo lattice which can then trap D, allowing retention far beyond the plasma ion implantation range. The conversion of displacements to trap sites averaged over the ion range is non-linear with a scaling (dpa) α, 0.25 ⩽ α ⩽ 0.5. The beam-induced traps are distributed from the surface to the end of range as opposed to the damage (dpa) profile that is concentrated at the end of range. Measurement of the near-surface D time-dependence has allowed inference of an effective surface recombination rate, which is lower than predicted by theory and at the low end of those found in literature.