Impact of outer divertor leg closure on the low field side main chamber particle fluxes in DIII-D

A Tokamak Divertor Closure Parameter (TDCP) is considered over a range of magnetic & baffle structure of the DIII-D divertor, where higher the TDCP value, lower the closure. Higher TDCP leads to increased magnitude of flux in the main chamber wall (I_wall). Estimates of I_wall are experimentally determined via Window Frame Analysis (WFA). As TDCP increases, recycled neutrals ionize near the midplane. This along with the neutral recycling at the midplane that induces main chamber recycling (MCR) impact the I_wall value. WFA is used to calculate f_wall, the ratio of I_wall to total ion flux at divertor target, I_div. In this study, I_wall is estimated using three diagnostics, viz., D_α detectors, neutral pressure gauges & Langmuir probes, as these provide an accurate radially resolved flux results inside windowpane region, assuming flux across the outer wall is uniform. Results show lower f_wall for lower TDCP (i.e., higher closure) at divertor in both L-mode & H-mode. Comparative studies depict USN floor & USN SAS divertor has the highest closure.