Pumping performance of pebble drop divertor

The pebble drop divertor concept was proposed for compact and high power density fusion reactors. In this concept, fuel gas can be pumped out by using fuel gas gettering by the surface layer of the pebbles. We are interested in the pumping by using transient hydrogen release from graphite just after ion irradiation. In this study, the pumping performance of the pebble drop divertor by using the transient hydrogen release is experimentally studied. In the experiment, the graphite samples were irradiated by high flux hydrogen beam with a maximum flux of 1×1022 H/m2 s (H3+, 5 keV). Just after the irradiation, hydrogen release from the samples was measured with keeping the sample temperature at the temperature reached by the irradiation. The transient hydrogen release was observed in all cases. The amount of the transient hydrogen release increased with increasing temperature. The amount of maximum transient hydrogen release was 4.4×1020 H/m2 at the temperature of 973 K. From this result, the pumping performance of the pebble drop divertor will satisfy the specification of fuel gas feed needed in steady state operation of ITER.