Tritium profiles on the surface of graphite tiles used in JT-60U

Tritium Imaging Plate Technique (TIPT) is used to measure the tritium areal distribution on plasma facing graphite tiles of JT-60U. Measurement of the W-shaped divertor region showed that the surface tritium distribution of tiles used under the "both-side pumping" system was similar to that of tiles used under the "inner-side pumping" system. This result suggests that tritium retained in those tiles is not affected by the type of exhaust system because this tritium was implanted with high energy. Thus, tritons produced by D-D reaction were implanted in the plasma facing wall without completely losing their initial energy. The tritium level beneath the redeposited layer on the inner divertor target tile was about three times as high as that of the surface of the redeposited layer. The toroidal surface tritium distribution suggested ripple loss of high energy tritons. These results also indicate that long-term tritium retention in JT-60U was caused by implantation of high-energy tritons.