The Depth Profiles of Deuterium and Hydrogen in Graphite Tiles Exposed to DD Plasma Discharges of JT-60U

Abstract

Depth profiles of deuterium and hydrogen retained in plasma facing graphite tiles placed in the divertor region of JT-60U, and chemical bonding states of carbon on the surface of the tiles, were respectively investigated by SIMS and XPS. The deuterium in the near surface of all graphite tiles was replaced by hydrogen due to exposure to hydrogen plasma in the clean-up stage after the D-D operation. The depth profiles of the H/12C and D/12C signal intensity ratios varied with the location of the tile. The integrated (H + D)/12C intensity ratio, Σ(H + D)/12C, in the outer divertor tile was the lowest at the strike point, and increased with the distance from the strike point. At the inner divertor tile with a thick re-deposition layer, Σ(H + D)/12C was very low (values in the range of 0.01 ~ 0.07). After the removal of the re-deposition layer, the integrated ratios Σ(H + D)/12C and ΣD/12C increased by factors of 4 and 70, respectively. In the cases of the baffle plates and the dome top tiles, Σ(H + D)/12C was higher. The intensity ratios, D/12C and H/12C, were strongly influenced by the temperature of the tile, the existence of redeposition layers or eroded regions, and the fluxes of hydrogen isotope ions and charge exchange particles during the D-D operation.