Hydrogen retention and depth profile in divertor tiles of Jt-60 exposed to hydrogen discharges

Abstract

Depth profile and retention properties of hydrogen in the graphite armor tiles of JT-60 open-divertor used for HH discharge period were investigated by secondary ion mass spectroscopy and thermal desorption spectroscopy. Two tiles were investigated, one at the inner divertor area covered with the re-deposited layers of the largest thickness (70 μm) and the other at the private flux region near the outer divertor striking point hardly covered with the re-deposited layers (only 1–2 μm). In the former, hydrogen was retained uniformly in the carbon re-deposited layers with H/C of 0.03, which was significantly smaller than H/C observed in the re-deposited layers of other tokamaks. Such small hydrogen retention in the re-deposited layers is attributed to the temperature rise of the re-deposited layers during discharges due to their poor thermal contact to the substrate. The latter retained rather large amount of hydrogen only in the shallow surface layers and its depth profile decayed sharply to 1.3 × 10 −4 in H/C of the bulk retention as expected from the very thin re-deposited layers and observed temperature rise above 900 K.