Interpretive analysis of scrape-off layer carbon transport using DIVIMP and impurity collector probes on DIII-D

DIVIMP simulations based on measurements made using a stable isotopic mixing model (SIMM) were able to quantitively explain the deposition of ¹³C from isotopically enriched methane puffing and background sources on collector probes (CP) in the far scrape-off layer (SOL) of DIII-D. Impurity CPs at the outboard midplane and crown regions were installed to sample impurities in the far-SOL, with resulting ¹³C deposition patterns used to infer near-SOL impurity distributions through the use of the 3DLIM synthetic diagnostic toolset. Experimental measurements and DIVIMP modelling suggest that the OSP launch alone cannot fully explain CP deposition measurements. Measurements made using SIMM suggest at least 40% of ¹³C CP deposition is from a buildup of ¹³C on the plasma facing components. DIVIMP simulations of ¹³C sourcing from the walls and inner divertor must be included along with the OSP injection to create the near-SOL sourcing profiles consistent with CP ¹³C deposition patterns. These findings highlight how a buildup of impurities on plasma facing components can result in migration of the impurity source and impact SOL impurity distributions.