Interpretive modeling of SOL impurity transport using ¹³C deposition patterns on crown and midplane collector probes in DIII-D

Recent experiments injected deuterated methane with isotopically enriched ¹³C into the outer divertor of upper single null discharges. The far scrape-off layer (SOL) impurity transport code, 3DLIM, was used to reproduce the resulting deposition patterns for multiple collector probes. This has allowed characterization of the near-SOL ¹³C poloidal distribution. The poloidal structure of SOL impurities is inferred using collector probes (CPs) installed on reciprocating drives at DIII-D. The deposition patterns on these CP sets along with the 3DLIM simulations suggest a near-SOL source of impurities that is poloidally bound between the outboard midplane and the outer strike point when operating in an unfavorable magnetic drift direction. This differs from previous observations of tungsten SOL transport, which suggested a near-SOL impurity source in the vicinity of the plasma crown for similar plasma conditions. Specifically, it is found that the deposition profile is influenced by the convective radial carbon velocity, and it is found that the connection length between each CP and surrounding wall structures strongly influences the deposited ¹³C magnitude. These results are providing needed validation studies for understanding and controlling SOL impurity transport.