Floating Potential Fluctuation Measurements with Langmuir Probes in the DIII-D Divertor During Wide Pedestal QH-Mode

Recent experiments show considerable negative floating potential (V_f) and increased fluctuation levels peaking near the strike point in the first such measurements during wide pedestal quiescent H-mode (WPQH-mode) in DIII-D. The fluctuation amplitude decay profile in the scrape-off layer (SOL) indicates that upstream pedestal turbulence, near the separatrix, is driving fluctuations in the divertor. WPQH-mode is an ELM-free operating regime with significantly improved core confinement and a pedestal limited by broadband turbulence. Previous measurements of the divertor heat flux width (λ_q) suggest that λ_q increases with pedestal density fluctuations, exceeding the Eich scaling. These results motivated V_f fluctuation measurements in the divertor during WPQH-mode. One of the DIII-D fixed Langmuir probes was used to continuously measure V_f (DC-500kHz) as the strike point was swept past the probe. The effects of V_f fluctuations on λ_q will be analyzed. The Langmuir probe V_f fluctuations will be correlated with Beam Emission Spectroscopy (BES) density fluctuation measurements in WPQH-mode experiments during the 2022 DIII-D experimental campaign.