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

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 13CH4 was puffed into the main vessel through the toroidally-symmetric pumping plenum at the top of lower single-null discharges. Subsequently, the 13C 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 13C deposition pattern is controlled by: (a) source strength of 13C+, (b) Δrs, radial location of the 13C+ source, (c) D⊥, (d) M∥, the scrape-off layer parallel Mach number. Best agreement was found for (a) ∼50% conversion efficiency 13CH4 → 13C+, (b) Δrs, ∼+3.5 cm (outboard of separatrix) near 13CH4 injection location, (c) D⊥ ∼ 0.3 m2/s, (d) M∥ ∼ 0.4 toward inside.