Pedestal profiles during QH-mode operation on DIII-D

The quiescent high confinement mode (QH-mode) on DIII-D exhibits an H-mode like edge pedestal, with values of pedestal pressure and global energy confinement similar to those of the ELMing H-mode, but without ELMs. In many cases this mode is observed to reach a nearly stationary operating point, limited in duration only by hardware constraints. This mode is usually obtained in a plasma configuration that is strongly pumped with electron densities at the top of the pedestal below 0.3 of the Greenwald density. Electron temperatures at the top of the pedestal range from 1.2 to 2.2keV. Ion temperatures at the pedestal are much higher, ranging up to 5 keV. In this paper, we will present edge profiles observed in the QH-mode. A selection of these profiles are used as input to the Corsica code to calculate the edge current profile, which is dominated by the bootstrap current. We discuss the implications of these edge profiles on the stability of the QH edge against ballooning/peeling modes. We also discuss results of experiments in which we attempt to expand the range of edge parameters, especially the edge density, achievable in the QH-mode.