Correlation between hydrogen isotope profiles and surface structure of divertor tiles in JT-60U

The present paper is devoted to depth profiles by secondary ion mass spectroscopy (SIMS) of hydrogen/deuterium in tiles taken from the dome unit area of JT-60U. This information is correlated with surface features, particularly from the aspect of erosion and deposition, determined by scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). The outer divertor-facing surface was mostly covered by re-deposited layers a maximum of 10 μm thick, while the inner divertor-facing side was eroded. The deposition profile is opposite to the observation for the divertor area in most tokamaks that the outer divertor side is eroded, while the inner deposited. However, H + D retention was higher for the deposited layers than that for the eroded area. Nevertheless, hydrogen retention seems very small and showed no appreciable effects on C1s spectra of XPS compared to the constituent elements boron and oxygen.