The influence of D₂ pressure on D retention and release from Be co-deposits

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.