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Abstract: Retention of hydrogen isotopes in the carbon (isotropic graphite) first wall tiles of JT-60U was studied by secondary ion mass spectrometry and thermal desorption spectroscopy. The surface morphology and erosion/deposition profiles of the tiles were characterized using scanning electron microscope and X-ray photoelectron spectroscopy. The upper area is mainly eroded, while the bottom area of the inboard wall is dominated by deposition. In contrast to the divertor area, hydrogen isotope retention in the eroded wall area was generally larger than that in the deposition dominated area. Measured near surface concentrations of hydrogen isotopes in the wall tiles, as well as the D/H ratios, were a little higher than those in the divertor area. This indicates direct implantation of high-energy D from NBI into the first wall. The lower temperature of the first wall relative to the divertor tiles would reduce desorption and/or replacement of implanted D by subsequent D or H impingement. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: Dependence of implantation temperature on chemical behavior of energetic deuterium implanted into WC was investigated by TDS and XPS. 1.0keV ions were implanted into WC samples at the implantation temperature range of 323–873K. It was found that the deuterium retention decreased as the implantation temperature increased. Above 573K, most of the retained deuterium was bound to C, which was less than 20% of the total D retention after implantation at 323K. Above 673K, C was segregated on the WC surface and some of the implanted deuterium was retained in the segregated carbon layer. Additionally, it can be said that the D retention in WC was much less than that in other carbon-related materials, such as graphite and SiC. Hydrogen isotope retention can be reduced significantly when WC is formed on a divertor surface as a redeposited layer. [Copyright &y& Elsevier]

Abstract: Retention profiles of hydrogen and deuterium in graphite tiles placed in the inner divertor region of JT-60U were analyzed by secondary ion mass spectroscopy (SIMS) and thermal desorption spectroscopy (TDS). The difference in hydrogen and deuterium retention behaviour is discussed considering the frequency of the strike-point hit and history of NBI heating power. It was found that most of hydrogen/deuterium was retained in the deposited layers, HH deposition layers/DD deposition layers or co-deposited with carbon. Owing to the higher heating power of DD discharges, the deuterium concentration in the DD deposition layers was much lower than that of hydrogen in the HH deposition layers. On the area showing no deposition, very shallow profile of deuterium dominated hydrogen profile. These results indicate that the tritium retention is strongly influenced by the history of discharge and temperatures. Tritium retention on graphite tiles and deposition layers could be significantly reduced with increasing the operation temperature. [Copyright &y& Elsevier]