Development of an analytical hydrogen isotope exchange model in fusion relevant plasma facing components

A simple model for H isotope retention depth profiles in W is developed, which can easily be extended to other plasma facing components (PFCs). This retention model is subsequently used to model how the depth profile changes after H isotope exchange. We calculate how trapping defects in W trap D (or H) inventory as W is being exposed to plasma. The model characterizes each trapping site by a trapping rate and a release rate, where the only free parameters are the distribution of these trapping sites in the material. The filled trap concentrations for each trap type are modeled as a diffusion process because post-mortem D depth profiles indicate that traps are filled well beyond the ion implantation zone (3-4 nm with 100 eV ions). Using this retention model, an isotope exchange rate is formulated. The retention model and isotope exchange rate are compared to low temperature (100 $^{\circ}$C) isotope exchange experiments in W with good agreement. Experimental retention profiles were measured using the D($^{3}$He,p)$\alpha $ nuclear reaction after plasma treatment. We additionally discuss how a uniform damage profile up to 1 micron in W induced by Cu ions using incident energies of 0.5, 2, and 5 MeV affect retention in W and the retention model.