Investigation of damages induced by ITER-relevant heat loads during massive gas injections on Beryllium

摘要

Highlights ? Beryllium specimens were subjected to ITER relevant massive gas injection like heat loads. ? All of the applied loading conditions led to noticeable surface modifications. ? In the worst case, a crater like morphology with molten beryllium and an affected depth of ～340 μm formed in the loaded area. ? The level of damage was highly depending on the absorbed power density, pulse duration, and pulse number. ? The formation of beryllium oxide can accelerate the MGI induced surface destruction. ? The cyclic melting of beryllium can enable a thinning mechanism of the armor tiles. Abstract Massive gas injections (MGIs) will be used in ITER to mitigate the strong damaging effect of full performance plasma disruptions on the plasma facing components. The MGI method transforms the stored plasma energy to radiation that is spread across the vacuum vessel with poloidal and toroidal asymmetries. This work investigated the impact of MGI like heat loading on the first wall armor material beryllium. ITER-relevant power densities of 90-260 MW m ?2 in combination with pulse durations of 5-10 ms were exerted onto the S-65 grade beryllium specimens in the electron beam facility JUDITH 1. All tested loading conditions led to noticeable surface morphology changes and in the expected worst case scenario, a crater with thermally induced cracks with a depth of up to ～340 μm formed in the loaded area. The level of destruction in the loaded area was strongly dependent on the pulse number but also on the formation of beryllium oxide. The cyclic melting of beryllium could lead to an armor thinning mechanism under the presence of melt motion driving forces such as surface tension, magnetic forces, and plasma pressure.