OEDGE modeling of far-SOL tungsten impurity sources and screening in WEST

The WEST tokamak contains entirely W PFCs, and so represents an ideal environment to study W impurity transport. This work demonstrates that the divertor target experiences the highest gross W erosion in the device but is well screened for impurities penetrating into the main Scrape-Off Layer (SOL) plasma, while other plasma-facing component (PFC) regions like the pumping baffle experience lower erosion but can have higher proportional contamination of the near-SOL. The background plasma and impurity transport are modeled using the OEDGE code suite (DIVIMP, EIRENE, and OSM). Target data from divertor Langmuir probes and upstream data from interferometry/reflectometry and reciprocating Langmuir probes are used to create a background plasma solution with OSM and EIRENE. DIVIMP uses a Monte Carlo method to track individual impurities and simulate transport. W-I spectroscopic data from WEST at the lower divertor and baffle is used to estimate the sputtered W flux. Several shots over a power scan with between 1.5 – 2.35 MW reaching the SOL are modelled. Impurity densities near the separatrix are found for each modeled shot. Transport mechanisms for the migration of far-SOL impurities into the near-SOL are analyzed in terms of the force balances in the plasma models. Results indicate that increasing power does not necessarily increase SOL contamination from the baffle source but instead hints at a complex relationship that requires the assessment of how the power scaling affects the balance of friction forces and ion temperature gradient forces on impurities in the SOL. [Maeker, JNM, 2022].