Experimental measurements of the particle flux and sheath power transmission factor profiles in the divertor of DIII-D

Abstract

Comparisons have been made between heat flux measurements from Langmuir probes and embedded thermocouples in the divertor of DIII-D. Good agreement has been found near the outer strike point (OSP) during L-mode operation with Neutral Beam Injection (NBI) using a sheath power transmission factor (SPTF) of 7, predicted by collisionless 1-D sheath theory. Previous SPTF measurements taken from Langmuir probes and IR imagery on DIII-D demonstrated values below the theoretical limit. The Langmuir probe array has since been upgraded and an embedded thermocouple array has been utilized to measure heat flux. The SPTF has also been measured during a NBI heated H-mode shot. This shot demonstrated a SPTF greater than 7 neat the OSP, which is due to a larger scrape-off layer (SOL) current density during H-mode operation. These studies represent a significant advancement towards finding agreement between theoretical predictions of the SPTF at the divertor and experimental measurements from the divertor diagnostics.