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The cooperative research program between JAERI and universities using the first wall tiles was initiated in 2001 to elucidate the plasma–wall interactions in JT-60U. Various studies have been intensively performed from 2001 to 2002. Major research results obtained in these years were reviewed. Main topics are as follows: (1) Tritium areal distribution on plasma facing graphite tiles was measured by using tritium imaging plate technique and a combustion method. the results were compared to the simulation results for triton orbits, (2) erosion depth and deposition thickness were measured poloidally by using dial gauge and SEM on a set of W-shaped divertor tiles, (3) distribution of hydrogen isotopes and the chemical status of carbon in the divertor region were evaluated by SIMS and XPS, (4) release behavior of tritium from graphite tile samples was studied using thermal desorption, and (5) tritium degassing characteristics in tokamak exhaust were investigated by cleaning discharges. [Copyright &y& Elsevier]

Abstract: Optical absorption/emission spectroscopy is considered to be used for in situ characterization of plasma facing carbon tiles and quantitative evaluation of tritium. In this paper we have applied ex situ laser Raman spectroscopy for carbon tiles used as first wall and divertor in JT-60 exposed to HH discharge plasma to verify the applicability of the technique. The analysis shows that the micro-structure of the carbon tile surfaces is modified in a similar way like damaging by energetic ion irradiation and that one can get information of how graphite structures are damaged by plasma exposure or what kind of structures the redeposited carbon obtains. [Copyright &y& Elsevier]

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: 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]

Abstract: Release behavior of tritium from the graphite tiles used at dome top and inner dome wing in JT-60U was investigated by the thermal desorption method in dry argon, argon with oxygen and water vapor, or argon with hydrogen. It was found that approximately 20–40% of total tritium is left in graphite even after heating to the high temperature above 1000°C in dry argon. The residual tritium could be removed by exposing the graphite tile to oxygen with water vapor or hydrogen at the high temperature above 1000°C. The tritium retention of the dome top tile was quantified as 84–30kBq/cm2. The inner dome wing tile had a steep tritium distribution from 8 to 0.1kBq/cm2. It is observed that a measurable amount of tritium existed in the deep site of the graphite tile. [Copyright &y& Elsevier]

Abstract: Hydrogen retention of dust produced by hydrogen discharges from June 1987 to October 1987 in JT-60 was measured to contribute for the estimation of in-vessel tritium inventory in the next generation of fusion reactor, such as ITER. After venting the vacuum chamber, several types of dust-like pieces, i.e. flake-like carbon dust, graphite, and metal pieces, were found in the vacuum vessel. The amount of retained hydrogen in flake-like carbon dust was two orders of magnitude larger than that in the graphite and metal pieces. However, the hydrogen concentration of flake-like carbon dust was 0.04 in the atomic ratio of H/C, which was one order of magnitude smaller than that of carbon flake produced in JET. One of possible explanations is the difference of the wall temperature between JT-60 and JET. [Copyright &y& Elsevier]

Depth profiles of deuterium and hydrogen retained in graphite tiles placed in the divertor region of JT-60U were investigated by secondary ion mass spectroscopy. The deuterium in the near surface of all graphite tiles was replaced by hydrogen due to exposure to hydrogen plasmas at the final stage operations. The depth profiles of the H/12C and D/12C signal intensity ratios varied not only with the location of the tile but also with the existence of redeposited layers. The integrated intensity of (H + D)/12C within the depth of 1.7 μm for the deposition dominated tiles was much smaller than that for the erosion dominated tiles. This suggests that thermal contact of the redeposited layer might be too poor to remove the heat loads from plasma to the substrate resulting in the surface temperature of the redeposited layer becoming much higher than that of the substrate. [Copyright &y& Elsevier]