Multi-faceted asymmetric radiation from the edge formation in DIII-D high-confinement mode discharges with continuous gas puffing

A set of continuously gas fueled DIII-D [Plasma Physics and Controlled Fusi on Research (International Atomic Energy Agency, Vienna, 1986) p. 159] high confinement mode (H-mode) shots at three neutral beam injection powers and two values of magnetic field (q(95)) have been analyzed to investigate the evolution of plasma edge conditions leading to the formation of X-point MA RFEs (multifaceted asymmetric radiation from edge), which are followed by a n H-L transition that constitutes a practical density limit for this class of shots in DIII-D. The MARFE initiation is found to be caused by a combina tion of a sharply increasing concentration of recycling neutrals in the pla sma edge, decreasing edge inverse temperature and density gradient scale le ngths, and increasing edge density. The line-average density at which MARFE s precipitates increases with increasing injection power and with decreasin g q(95). It is not clear whether the formation of the X-point MARFE causes or merely precedes the H-L transition. (C) 1999 American Institute of Physi cs. [S1070-664X(99)03210-3].