EFFECT OF LOW-DENSITY H-MODE OPERATION ON EDGE AND DIVERTOR PLASMA PARAMETERS

We present a study of the impact of H-mode operation at low density on divertor plasma parameters on the DIII-D tokamak. The line-average de nsity in H-mode was scanned by variation of the particle exhaust rate, using the recently installed divertor cryo-condensation pump. The max imum decrease (50%) in line-average electron density was accompanied b y a factor of 2 increase in the edge electron temperature, and 10% and 20% reductions in the measured core and divertor radiated power, resp ectively. The measured total power to the inboard divertor target incr eased by a factor of 3, with the major contribution coming from a fact or of 5 increase in the peak heat flux very close to the inner strike point. The measured increase in power at the inboard divertor target w as approximately equal to the measured decrease in core and divertor r adiation.