Deuterium retention in self-irradiated tungsten by D2 gas loading

• Near-surface vacancy clusters trap deuterium and hinder deeper penetration. • Mono-vacancies are the dominant traps in the bulk after room-temperature irradiation. • Rate equation simulations and deuterium desorption confirm vacancy type distribution. • Depth-resolved positron experiments reveal vacancy filling from surface inward. • Trap-limited uptake causes a lag phase and non-classical diffusion kinetics. Deuterium trapping in self-irradiated tungsten was investigated by thermal desorption spectrometry (TDS) and depth-resolved positron annihilation spectroscopy (PAS). Polycrystalline W samples were irradiated at room temperature with 4 MeV W ions up to 0.5 dpa and subsequently gas-loaded in D 2 atmosphere at 473 K for 4–168 h. PAS reveals irradiation-induced open-volume vacancy formation and a progressive, surface-inward filling of those vacancies during gas loading, with no measurable change in the overall vacancy size distribution at the loading temperature. TDS shows that high-binding-energy traps dominate short gas exposures, whereas longer exposures increase the contribution from the lower temperature peak which correspond to mono-vacancies deeper in the material. The combined data indicate a relatively higher fraction of vacancy clusters near the surface up to around 50 nm that capture D and reduce diffusion beyond the 50 nm. Higher irradiation fluence amplifies this effect and hinders deeper permeation. Kinetic rate equation simulations support these trap type distributions and the interpretation of non-Fickian, trap-limited uptake at 473 K.