Understanding the impact of divertor & main chamber ion fluxes on divertor closure in the DIII-D tokamak*

The Geometric Restriction Parameter (GRP) is introduced to quantify outer divertor restrictions & serve as an indicator for neutral retention in attached conditions, with lower GRP values indicating reduced retention & increased neutral leakage. Utilizing data from 12 DIII-D discharges characterized by various divertor geometries, plasma conditions, & drift orientations, Window-Frame Analysis & the OEDGE modeling tool are employed to investigate neutral dynamics in the SOL. Our analysis reveals that lower divertor restrictions increase neutral leakage. Using shots with opposing toroidal field directions, we highlight the impact of ExB drifts on neutral particle transport in L-mode. An inverse correlation between divertor closure & main chamber flux magnitude underscores the importance of divertor restrictions in H-mode. The study also emphasizes the influence of SOL opacity on main chamber & divertor fluxes. In L-mode favorable drift conditions, divertor recycling is the dominant factor for all divertor configurations with increased restrictions and neutral compression. Additionally, divertor compression estimated, influenced by varying opacity, have implications for GRP. This provides insights into divertor restrictions between shots for assessing operating conditions such as detachment in DIII-D, with potential extension to other devices in the future.