Indications of an inward pinch in the inner SOL of DIII-D from 13C deposition experiments

Abstract 13 C methane puffing experiments were conducted on DIII-D in both L- and ELMy H-mode conditions. The puffing was toroidally symmetric into the crown of a series of well-characterized lower single-null discharges. The hydrocarbon breakup, carbon transport and deposition were modeled using the OEDGE interpretive code. Three separate hypotheses were tested using OEDGE to try to reproduce the experimental deposition: Radial variation of fast parallel flow, erosion of the puffed 13 C deposited in the divertor, and a pinch in the inner scrape off layer (SOL) towards the separatrix. A fast parallel flow was imposed for all hypotheses. The magnitude and the distribution of the 13 C deposition resulting from each hypothesis are compared. A fast parallel flow in the SOL toward the inner divertor combined with a pinch/drift of 10–30 m/s in the inner SOL towards the separatrix roughly reproduces the deposition in both the L- and H-mode experiments.