Investigation of deuterium retention in/desorption from beryllium-containing mixed layers

Abstract

This article reports experimental results regarding the deuterium (D) retention and release characteristics of beryllium-containing mixed material layers. The main aim is an assessment of the efficiency of the tritium removal procedure currently suggested for ITER, i.e., wall baking at 513 K (240 °C) for the main chamber walls and 623 K (350 °C) for the divertor.It is observed that the tritium retention as well as the removal efficiency by a following baking procedure will strongly depend on the composition of the deposited layer and the wall temperature during plasma operation. In the case that D is implanted at moderate temperatures (300 to 400 K), which would correspond to the “cool divertor” scenario in ITER, a large fraction of retained D is trapped in states having a low D binding energy and correspondingly low release temperature. Therefore, in this case baking can release a significant amount of retained D. On the other hand, if D is implanted at temperatures above 520 K, which would correspond to the “hot divertor” scenario in ITER, the amount of retained D will be significantly lower, but the retained D is predominantly trapped in high-energy binding states. In such a case, even baking at 623 K might not efficiently remove the retained tritium.