Influence of near-surface helium on the deuterium retention and uptake in tungsten

• Detailed study of the effect of near-surface He on D uptake in tungsten. • Quantitative D and He depth profiling. • Clear proof that D is trapped in the He region. • Reduction of D uptake beyond the He region by 15 times. The effect of near-surface helium (He) on deuterium (D) retention and uptake into the bulk of tungsten (W) was investigated. To quantify the He influence on D uptake, He was implanted close to the surface with 3 keV energy at different fluences and different temperatures. 20 MeV W irradiation was performed at room temperature after He implantation to create defects within the first 2.3 µm. Samples were then exposed to a low flux, low energy (300 eV/D) D ion beam at 450 K. The defects created by W ions trap penetrating D and make it hence possible to quantify D transport into depth below the He layer using 3 He nuclear reaction analysis. Elastic recoil detection analysis enabled us to measure the D and He concentration depth profiles near the surface. Results show that D gets preferentially retained where He is implanted with D concentrations up to 10 at.%. At the same time D uptake beyond the He zone is reduced by a factor of 15 compared to a He-free W sample.