Creation and Sustainment of Quiescent H-mode Plasmas in DIII-D with Zero Net NBI Torque*

Recent experiments have demonstrated both creation and sustainment of wide pedestal QH-mode with zero net neutral beam injected (NBI) torque.  QH-mode is an attractive operating regime for future devices since it has excellent energy confinement time and can operate without ELMs at zero net NBI torque.  Wide pedestal QH-mode exhibits an increase in the pedestal pressure height and width and increased global energy confinement associated with a bipolar change in the edge ExB shear [1].  Previous low torque QH-mode shots utilized a startup phase with significant NBI torque which was reduced to zero later in the shot.  Since future devices will not have appreciable NBI torque, creation and sustainment of QH-mode at zero NBI torque is an important step towards using QH-mode in those devices.  These recent shots  have plasma conditions relevant for future devices:  β_N = 1.75, ITER H_98y2 = 1.25, ν*_e^PED = 0.3-0.4 and stationary conditions for at least 20 energy confinement times, limited only by hardware constraints.  Unlike the rapid transition to wide pedestal conditions seen previously [1], the wide pedestal state forms gradually over a period of roughly 100 ms in the present cases

[1] K.H. Burrell et al, Phys. Plasmas 23, 056103 (2016)