Hydrogen isotope retention of JT-60U W-shaped divertor tiles exposed to DD discharges

Deuterium (D) and Hydrogen (H) retention in carbon tiles exposed to DD and HH discharges in the JT-60U W-shaped divertor has been investigated by means of thermal desorption spectroscopy (TDS) and secondary ion mass spectrometry (SIMS). In the thick re-deposited layers on the outer divertor, hydrogen (H + D) was retained rather homogeneously with its concentration of 0.03 in (D + H)/C atomic ratio, which is attributed to the surface temperature rise above 900 K. Owing to the HH discharges performed after the DD discharges for tritium removal, H-dominated re-deposited layers were added on D-dominated re-deposited layers. In addition D retained in near surface layers were replaced by H both for re-deposited and eroded area. Accordingly deuterium concentration peaked at a little inside behind the H dominated surface layers for all tiles. The temperature increase during the discharge very likely causes the saturation of hydrogen retention even in the re-deposited layers. Accordingly the global wall saturation was observed in JT-60U.