Codeposition of deuterium with ITER materials

Abstract

The levels of retention in codeposited layers of each of the three ITER materials (C, Be and W) are compared. Scaling laws, based on the conditions during the codeposition process (surface temperature, incident particle energy and ratio of the depositing fluxes), are presented to allow prediction of expected retention under ITER conditions. Retention in carbon codeposits scales inversely with incident particle energy, whereas in the metallic codeposits the retention level scales proportionally to increasing particle energy. The differing scaling of retention with incident particle energy provides insights into which material may impact the global retention in ITER depending on where it may form codeposits. In addition to the amount of retention, the release behaviour of tritium from codeposits will influence the tritium accumulation rate within ITER. The thermal release behaviour of T (or D) from codeposits can be used to evaluate the effectiveness of baking at different temperatures as a means of tritium removal. Finally, the desorption kinetics from Be and W codeposits are contrasted. In the case of W codeposits, the duration of the baking cycle is important in determining the removal efficiency, whereas with Be codeposited layers, the maximum achievable bake temperature plays the leading role in determining removal efficiency.