Deuterium trapping in the subsurface layer of tungsten pre-irradiated with helium ions

The effect of He-induced defects in tungsten on the efficiency of trapping of deuterium ions in the subsurface layer was studied using thermal desorption spectroscopy (TDS). The W sample was pre-irradiated with 3 keV helium ions at room temperature and various fluences in the range of 1019 – 5 × 1021 He/m2. Then, it was exposed to a probe fluence of 1019 D/m2 of 2 keV D3+ (670 eV/D) ions, and in-situ TDS was performed. The de-trapping energy for D atoms increased with the increase of the He pre-irradiation fluence. On the other hand, a strong decrease in the D retention was observed if the He fluence increased above 1021 He/m2. At the highest He fluence of 5 × 1021 He/m2 deuterium trapping was possible only after partial release of He atoms. By comparison of experimental TDS spectra with modeling, the de-trapping energies of D atoms from various defects were estimated.