Hydrogen isotope exchange and deuterium removal in pre-irradiated tungsten: a comparative study of H/He/Ar plasma exposure and H2 gas annealing

• H isotope removal in W was investigated by using a linear plasma device. • D removal efficiency by H plasma exposure was more efficient than inert plasmas. • H isotope exchange can be enhanced by energetic plasma implantation. Experiments on hydrogen (H) isotope removal from tungsten (W) were performed using a steady-state linear plasma device. The W samples were first irradiated with deuterium (D) plasma at 85 eV to a fluence of 2.9 × 10 24 D m −2 at a controlled sample temperature of 513 K, followed by exposure to plasmas of different ion species (H, He, Ar) with identical incident ion energy and fluence. Control experiments of D removal from W under a H 2 gas atmosphere were also conducted for comparison with plasma exposure treatments. Residual D retention in the W bulk after different plasma exposures and after H 2 gas annealing treatments was quantified via thermal desorption spectroscopy (TDS). The results showed that up to ∼89% of retained D was released at an exchanging H fluence of 2.9 × 10 24 H m −2 , marking the highest removal efficiency among all these treatment methods. The D removal efficiency of H 2 gas annealing was lower than that of H plasma exposure, which was attributed to the distinct isotope exchange processes under plasma and gas conditions. Energetic H plasma implantation enables more efficient isotope exchange in the near-surface region, compared with H 2 molecules adsorption and dissociation on the W surface. The minimal D desorption from W under Ar and He plasma exposures arose from thermal release during plasma irradiation, rather than isotope exchange. This resulted in a significantly lower D removal efficiency for He/Ar plasmas than that of H plasma exposure and H 2 gas annealing treatments.