Removal of deuterium from carbon-based codeposits by hydrogen isotope exchange

The use of H2 gas soaks has been studied as a method of removing deuterium from DIII-D and ASDEX-Upgrade (ASDEX-U) codeposit specimens. The current experiments investigate the effectiveness of H2 gas soaks at 350-450 °C and 33 Pa-70 kPa for up to 100 h exposure time on codeposits with varying B impurity content. The range of parameters studied thus includes conditions relevant to the ITER divertor. Results show strong temperature dependence but little pressure dependence of D removal at the test conditions for DIII-D codeposits. At 350 °C and H2 pressures ranging from 33 Pa to 70 kPa, ∼50% of D in DIII-D codeposits was removed in 10-15 h. At 450 °C and similar pressures, ∼84% was removed in 6 h. In contrast, D removal for ASDEX-U codeposits shows little temperature dependence at the test conditions, with 76-80% of D removed after 6 h at 350-450 °C, 20 kPa.