OEDGE modeling of 13C deposition in the inner divertor of DIII-D

Abstract Use of carbon in tokamaks leads to a major tritium retention issue due to co-deposition. To investigate this process a low power L-mode experiment was performed on DIII-D in which 13 CH 4 was puffed into the main vessel through the toroidally-symmetric pumping plenum at the top of lower single-null discharges. Subsequently, the 13 C content of tiles taken from the vessel wall was measured. The interpretive OEDGE code was used to model the results. It was found that the 13 C deposition pattern is controlled by: (a) source strength of 13 C + , (b) Δ r s , radial location of the 13 C + source, (c) D ⊥ , (d) M ∥ , the scrape-off layer parallel Mach number. Best agreement was found for (a) ∼50% conversion efficiency 13 CH 4 → 13 C + , (b) Δ r s , ∼+3.5 cm (outboard of separatrix) near 13 CH 4 injection location, (c) D ⊥ ∼ 0.3 m 2 /s, (d) M ∥ ∼ 0.4 toward inside.