Effect of composition and surface characteristics on fuel retention in beryllium-containing co-deposited layers

We have investigated retention of deuterium in beryllium-containing, laboratory-made films whose properties resemble co-deposits observed on JET-ILW or predicted for ITER. The samples were prepared using High Power Impulse Magnetron Sputtering and Thermo-ionic Vacuum Arc Deposition. We have observed that retention depends on the flux of D atoms on the growing film, but even more prominently on its composition, structure, and morphology. Especially, inclusion of carbon by 10-15 at% in the layers can increase retention by a factor of 2-10. This we attribute to increasing number of defects as well as aromatic and aliphatic C-D bonds in the samples. Other impurities do not significantly alter the D inventory while more D is retained in samples with rough or highly modified surfaces. Our results show that reproducing the reported D concentrations of ∼5 at% in JET-ILW-like deposits requires keeping the sample temperature at 100-200 °C during the production phase and optimizing the uniformity of deposition fluxes. Data from Be-D samples further indicate that fuel retention in more ITER-relevant co-deposits would be around 1-2 at%.