Steady state wall pumping performance of pebble drop divertor

A pebble drop divertor concept is proposed for future fusion reactor. By using multi-layer coated pebbles, this system can be expected to provide the fuel gas pumping function. In this paper, the pumping performance of the pebble drop divertor is estimated. The transient behavior of hydrogen retained in the surface layer of pebbles in divertor irradiation is calculated using a mass balance equation of hydrogen atoms in the graphite surface. In this calculation, the incident hydrogen flux of 1 x 1023 atoms/m2 s (1.5 keV) and the heat flux of 35 MW/m2, and the width of strike zone of 5 cm are assumed. Range distribution of 1.5 keV hydrogen and ion-induced detrapping cross-section is calculated by TRIM code. From the calculated dynamic hydrogen retention, it is shown that the pebble drop divertor using the pebble with graphite surface layer and BeO kernel can pump out hydrogen by 4.3 x 1022 - 2.2 x 1023 atoms/s from the ITER scale fusion reactor. (orig.)