Ion beam analysis of H and D retention in the near surface layers of JT-60U plasma facing wall tiles

H and D retention characteristics in the near top surface of the JT-60U plasma facing carbon tiles were investigated by means of elastic recoil detection analysis. From the result, H was dominantly retained within 1 μm depth because of the H discharges for the wall cleaning carried out before the removal of sample tiles. (H + D)/C ratios were small: it was ∼0.07 at a maximum in the divertor samples except for the deposition on the dome outer wing tile which was ∼0.13, and it was ∼0.15 at a maximum in the first wall samples. The hydrogen concentration in the redeposited carbon layers is strongly influenced by the temperature. Consequently (H + D)/C ratios at the observed low level are a result of the operation of JT-60U at wall temperatures of 300 deg. C or higher