The influence of D 2 pressure on D retention and release from Be co-deposits

Highlights: • Be co-deposit desorption studies are reported that focus on the role of D${}_2$ pressure during layer formation. • A sharp release mechanism, T${}_0$, is found to be predominately inked to pressure. • TESSIM simulations show best ITER bake efficacy when a T${}_0$ fraction is present in the co-deposit. Beryllium co-deposit thermal desorption studies are reported that focus on the effect of D${}_2$ pressure during layer formation, as pressure has been linked in prior work to the formation of a high-retention-capacity sharp-release-feature. A pressure range from 0.3 to 13.3 Pa is explored. Additional insight into what drives the formation of T${}_0$ is established through co-deposit formation parameter variations including deposition temperature spanning 373 K to 608 K, and ion impact energy in the range 10–100 eV. It is found that the formation of the sharp release feature exhibits a multi-parameter dependence, but is predominately favoured by low deposition temperature, higher D${}_2$ pressure, and to a small degree, increased ion impact energy, during deposition. TESSIM simulations of the D${}_2$ thermal release at the ITER bake temperatures of T${}_{b1}$ (513 K) and T${}_{b2}$ (623 K), show that the best efficacy for D removal (defined as the ratio of post to pre bake inventory) is found when the sharp release feature is present. However, when this feature is present, the total retained D inventory tends to be significantly increased.