Ion beam analysis of 13C and deuterium deposition in DIII-D and their removal by in-situ oxygen baking

An experiment was conducted in DIII-D to examine carbon deposition when a secondary separatrix is near the wall. The magnetic configuration for this experiment was a biased double-null, similar to that foreseen for ITER. 13C methane was injected toroidally symmetrically near the secondary separatrix into ELMy H-mode deuterium plasmas. The resulting deposition of 13C was determined by nuclear reaction analysis. These results show that very little of the injected 13C was deposited at the primary separatrix, whereas a large fraction of injected 13C was deposited close to the point of injection near the secondary separatrix. Six of the tiles were put back into DIII-D, where they were baked at 350-360 °C for 2 h at ∼1 kPa in a 20% O2/80% He gas mixture. Subsequent ion beam analysis of these tiles showed that about 21% of the 13C and 54% of the deuterium were removed by the bake.