Distribution of hydrogen isotopes retained in the divertor tiles used in JT-60U

Distribution of deuterium and hydrogen retained in graphite tiles placed in the divertor region of JT-60U with the dual side pumping geometry was investigated by thermal desorption spectroscopy. The retention of hydrogen isotopes was nearly proportional to the thickness of the carbon redeposited layers, though their concentration changes with the poloidal location and orientation of the surface tiles. The least concentration of (H + D)/C (∼0.02) was found in the redeposited layers on the inner divertor tile. Rather high hydrogen concentration was found in the redeposited layers on plasma shadowed area. In particular, the redeposited layers on the bottom side of the outer dome wing tile shadowed from plasma and facing to the pumping slot showed the highest concentration of 0.13 in (H + D)/C. In JT-60U, however, the carbon deposition in the shadowed area is very small, resulting in a smaller total retention in the divertor area compared to other large tokamaks.