Analyses of Hydrogen Isotope Distributions in the Outer Target Tile used in the W-shaped Divertor of JT-60U

Hydrogen isotope distributions of the outer divertor target CFC tile, in the W-shaped divertor of JT-60U where erosion dominated, were analyzed by secondary ion mass spectroscopy (SIMS) to study the correlation between the concentrations of hydrogen isotopes and erosion/deposition rate. The chemical states of the CFC tile surfaces were analyzed by X-ray photoelectron spectroscopy (XPS). The existence of re-deposition layers was observed by scanning electron microscope (SEM). The erosion/deposition depth was also evaluated by a surface profilometer, namely dial gauge. The hydrogen and deuterium retention profiles were compared with the tritium profile obtained by the tritium imaging plate technique (TIPT). It was found that almost all the deuterium once retained in the near surface region of the erosion dominated area was replaced by hydrogen during the final HH discharge and/or exposure to the atmosphere. The hydrogen retention profile was controlled by surface temperature and plasma flux, and the total hydrogen retention was much less than that in the re-deposition layers observed at the plasma shadowed area in this particular tile