Session 7F - DIII-D: Edge and H-Mode.
ORAL session, Thursday morning, November 14
Vail Room, Adam's Mark
We report the results of experiments conducted on DIII--D with simultaneous external D_2 gas injection (\sim 100--200 torr-\ell/s) and divertor exhaust to assess the dependence of scrape-off-layer flow on divertor retention of neon. During these experiments, direct measurements have been made of the neon concentration in the core (CER spectrscopy) and divertor (SPRED UV spectroscopy) plasmas and in the exhaust gas (modified Penning gauge). In these experiments, exhaust enrichment (ratio of neon fraction in exhaust gas to the neon fraction in the core plasma) is in the range 1--2, suggesting that significant compression of neon in the divertor plasma is difficult. Systematic scans of various parameters expected to determine divertor retention (e.g., external D_2 gas flow magnitude and location, divertor recycling, ELM frequency, gas fueling) have been carried out. Particle balance analysis suggests that wall retention is likely a major player in the overall neon particle balance in these discharges.