Temperature dependence of D removal from JET codeposits by thermo-oxidation

The present study presents new findings for the temperature dependence of D removal from JET Mark II Gas Box divertor codeposits via thermo-oxidation. D removal efficiencies are presented for oxidation with 21 kPa O2 pressure at temperatures in the range 523–623 K (the 623 K results have been recently published [9,10]). The codeposits analysed in this study have Be concentrations of up to ∼40% Be/(Be + C) and thicknesses ranging from 5.5 to 54 μm. The hypothesis that codeposits are porous in nature is supported by post-oxidation surface analysis and codeposit erosion trends. Initial D removal rates from oxidized JET divertor codeposits vary linearly with inherent D content and codeposit thickness, and are independent of Be content and codeposit geometry. The percentage of recoverable D from the JET divertor codeposits was ∼65% at 523 K, ∼75% at 573 K and ∼90% at 623 K, all at 21 kPa. SIMS and NRA surface analyses confirm the fact that codeposit characteristics vary widely even among specimens cut adjacent to one another. This is true even after aggressive oxidation where in some cases the codeposit is totally depleted of the inherent deuterium without a significant reduction in thickness. However, the overall D removal effectiveness of thermo-oxidation appears to be unaffected by these large variations in codeposit structure and composition.