Retention and depth profile of hydrogen isotopes in gaps of the first wall in JT-60U

Hydrogen (H) and deuterium (D) retention in gap side surfaces of the first wall tiles exposed to DD and HH discharges in JT-60U were examined. On the sides of outboard tile, the H and D retention and the deposited amount of boron increased with the gap width. On the sides of inboard tile, thick carbon deposition layer (∼10 μm) was observed. The deposited layers retained rather large amount of hydrogen with ∼0.15 in (H + D)/C atomic ratio compared to that found in the deposited layers on the divertor tiles, most likely due to the lower temperature. The H + D retention on the sides analyzed here was comparable to that of the plasma facing surface.