Irradiation experiments of divertor pebbles

A multi-layer coated pebble is the essential component of the pebble drop divertor system. For the test of the integrity of the multi-layer structure, two types of pebble were fabricated and irradiated by high flux beams. The one has a SiC kernel, and the other has a carbon kernel. Each type of pebble had a SiC tritium permeation barrier layer and a graphite plasma facing layer. These pebbles were irradiated by 6.7 MW/m2 of electron beam and 6.2×1021 D/m2 of high particle flux deuterium beam. After the irradiation, they were examined the failure of the coating layers and the sputtering yield of the surface layer. On the carbon kernel pebbles, no cracks and failures of the coating layers were detected after the irradiation. The test results of SiC kernel pebbles indicated there were some failures at the interface between a SiC layer and a surface graphite layer due to the fabrication process.