Modeling and predictions of the effects of plasma characteristics on D-supersaturation induced defects formation in tungsten-based materials*

Mechanisms of defect formation and enhanced D retention in tungsten-based materials were studied and simulated based on W samples irradiated during discharges in the DIII-D tokamak and in laboratory experiments. Modeling predicts the dynamics of D supersaturation (exceeding the solubility limit) depending on the intensity of D and impurity irradiation together with changes in material temperature. This is important in predicting the role and dynamics of vacancies and vacancy clusters/voids formation. This analysis is based on hybrid atomistic and continuum models implemented in the ITMC-DYN package, which include plasma kinetic effects on the surface with details of multiple D trapping in a monovacancy, the effect of multiple D on vacancy formation, and transition regimes to vacancy clusters and bubbles/voids. This analysis clearly predicts that at D fluxes relevant to a fusion device, the high temporal temperature variation and impurities can reduce the effects of D supersaturation on the W surface and enhance D-induced defects in subsurface layers. We also compare the experimentally guided parameters of D diffusivity, desorption, and intrinsic vacancy and vacancy cluster concentrations in our simulations with the theoretical values, showing orders of magnitude difference in predictions for ideal and real material and effects on fuel retention and material degradation.