Effect of Main Ion Density on High-Z Impurity Transport in the Scrape-off Layer of DIII-D Using Collector Probes

An interpretive modeling workflow is presented for assessing impurity leakage and scrape-off layer (SOL) transport of tungsten (W) sputtered from the DIII-D Small Angle Slot (SAS-VW) divertor for a range of main ion densities. SAS-VW is a tightly baffled, closed divertor with W-coated plasma-facing components that is intended to reduce impurity leakage while lowering the target density threshold required to induce detachment. Experiments have been designed to perform a series of L-mode discharges in the case where the B X ∇B drift direction is out of the divertor with increasing main ion density in order to approach and slightly exceed the detachment threshold at the target. Impurity collector probes at the outer midplane (OMP) and crown are used to assess the far-SOL impurity content with the aid of the 3DLIM interpretive model. The near-SOL impurity distribution is developed using DIVIMP, which is constrained using W source spectroscopy. The SOL impurity distribution simulations for SAS-VW will be compared to those from the 2016 DIII-D Metal Rings Campaign used to assess impurity leakage and transport from an open divertor, which suggested the existence of an impurity accumulation zone between the OMP and crown for the equivalent magnetic field direction.