Stabilization of defects by the presence of hydrogen in tungsten: simultaneous W-ion damaging and D-atom exposure

Abstract : The possible synergistic effect and mutual influence of the defect production by W-ion damaging and presence of hydrogen isotopes in the crystal lattice of tungsten is studied. For this purpose we perform modelling of the experimental data where samples were in one case sequentially damaged by W ions followed by D-atom exposure and in the other case simultaneously damaged by W ions and exposed to D atoms. Modeling is performed by the MHIMS (migration of hydrogen isotopes in materials) code in which a model of trap creation due to W-ion irradiation during the D-atom exposures is implemented. With the help of the surface model and the experimental data the migration barrier from the surface to the bulk is determined as a function of exposure temperature. It is shown that there is a temperature dependence of the migration barrier which at high temperatures and low hydrogen atom surface coverages stabilizes at 2 eV being in good agreement with the first-principle calculations. The evolution of trap concentrations with temperature is obtained from fitting the deuterium (D) depth profiles and the thermo-desorption spectra of deuterium gas at different damaging temperatures. In both experiments, the desorption peaks corresponding to induced trap defects are described by two trapping types with energies of 1.83 eV and 2.10 eV attributed to dislocation loops and cavities, respectively. The concentration of the low energy trap is higher in the case of simultaneous W/D exposure as compared to sequential W/D exposure experiment. This gives an unambiguous proof that the presence of deuterium does have an influence of defect evolution in tungsten material and therefore prevents spontaneous annihilation the traps.