Depth profile and retention of hydrogen isotopes in graphite tiles used in the W-shaped divertor of JT-60U

Abstract

Depth profiles of deuterium and hydrogen retained in graphite tiles placed in the divertor region of JT-60U were investigated by secondary ion mass spectroscopy. The deuterium in the near surface of all graphite tiles was replaced by hydrogen due to exposure to hydrogen plasmas at the final stage operations. The depth profiles of the H/ 12C and D/ 12C signal intensity ratios varied not only with the location of the tile but also with the existence of redeposited layers. The integrated intensity of (H + D)/ 12C within the depth of 1.7 μm for the deposition dominated tiles was much smaller than that for the erosion dominated tiles. This suggests that thermal contact of the redeposited layer might be too poor to remove the heat loads from plasma to the substrate resulting in the surface temperature of the redeposited layer becoming much higher than that of the substrate.