Hydrogen isotope behavior in in-vessel components used for DD plasma operation of JT-60U by SIMS and XPS technique

The behavior of hydrogen and deuterium retained in the graphite tiles placed in the dome top unit, the outer divertor unit and the outer baffle plate of JT-60U with W-shaped divertor were investigated by secondary ion mass spectroscopy and X-ray photoelectron spectroscopy (XPS). It was found that deuterium on the surface of the tiles was replaced by hydrogen due to hydrogen discharges at the final stage. The amount of deuterium on the dome top unit largely depends on the location of the dome unit. Especially, the amount of that on the inner side and the center of the dome top units were high compared with that on the outer side. The binding energies of C 1s and B 1s peaks on the surface of the inner side of dome top unit were largely shifted to higher energy by XPS. These results indicate that hydrocarbons and boron oxide might be formed on the surface. It is concluded that the behavior of hydrogen and deuterium and the chemical state of graphite were influenced by the temperature of the surface, the position of the strike point and the flux of the particles during the operation.