New insight on deuterium diffusion, trapping, and desorption in plasma-facing materials during and after irradiation

Integrating Monte Carlo collisional processes with deterministic methods for the thermal processes, we analyzed hydrogen isotope behavior in tungsten and tungsten-based compounds, an important issue for the performance and safety of future fusion reactors. Deuterium retention was analyzed in its dependence on flux, fluence, impurities, and material temperature. We benchmarked our new models against laboratory experiments and DIII-D recent data regarding D trapping sites/defects evolution as well as ion/atom collisions, diffusion, retention, and desorption during and after exposure of D plasma and multispecies D/C plasma fluxes. Comparing modeling and experiments at various irradiation conditions and delay time between exposure and thermal desorption spectroscopy, we predicted the retained and the solute (free) D distribution in material. These simulations explained, for the first time, the effect of material temperature on spatial distribution of trapped D concentration and the four-fold increase in D accumulation at higher (400-500K) W temperatures compared with 300K. Substantial free D in the sub-surface layer of warm target can lead to stress-induced vacancies and voids formation. Low diffusivity at 300K leads to D surface accumulation and significant desorption during and after irradiation.