Tritium distribution measurement of the tile gap of JT-60U

Tritium retention in the gaps or side surfaces of JT-60U divertor tiles was measured by an imaging plate (IP) technique and a combustion method. On the toroidal side surfaces, the retained amount decreased exponentially from the front (plasma facing) end to the rear end with an e-folding length of 3 mm for all tiles. On the other hand, the tritium retention characteristics on the poloidal sides varied depending on the location of the gap. Retention of tritium in redeposited carbon layers was observed in the gaps between inner divertor target tiles and the bottom side of dome outer wing tiles that faced the outer pumping slot. From the extrapolation of these IP and combustion results to the full toroidal direction, the total tritium retention in the divertor gaps was estimated to be around 0.07% of the total tritium produced by D–D reactions or 0.13% of thermalized tritium.