Hydrogen Isotope Retentions and Erosion/Deposition Profiles in the First Wall of JT-60U

To investigate retention characteristics of hydrogen isotopes in the first wall tiles made of isotropic graphite of JT-60U, surface morphology, erosion/deposition profiles and hydrogen isotope retentions were examined by SEM, XPS, TDS and SIMS. It was found that poloidal deuterium retention profile was rather uniform, while the thermal desorption behavior of deuterium was quite different depending on the locations of the tiles. Deuterium retained in the upper first wall, which was covered by thick boron layers with high concentration of B, was desorbed at lower temperature than that in the lower area covered by carbon layers with much less B content. Hydrogen retained during the boronization has significant contribution on the total hydrogen retention. D/H ratio in the first wall tiles was appreciably higher than that observed in the divertor tiles. Probably, the lower temperature of the first wall compared to that of the divertor tiles would prohibit desorption of the implanted deuterium and/or its replacement by subsequent D or H impingement. The injection of high energy deuteron originating from NBI into the first wall could have some contribution on the high hydrogen retention of the first wall.