Comparison of Wide-pedestal Quescient H-mode Operation in Both Plasma Current Directions on DIII-D*

Naturally ELM-stable, reactor relevant wide pedestal QH-mode has now been achieved with both directions of plasma current (Ip) on DIII-D. Wide-pedestal QH-mode (WPQH) was discovered in one direction of Ip using counter-Ip NBI torque ramp down in standard QH-mode plasmas. WPQH has been seen with a range of NBI torque [1] including zero net NBI torque throughout the discharge [2]. Experiments reported here with opposite sign of Ip confirm that the direction of the plasma current does not matter.  Pedestal height, width, and overall confinement in both directions of Ip are equivalent. The carbon content is generally lower in WPQH plasmas using the typical Ip direction.  Experiments with a slow torque scan from counter-torque (2-3Nm) to co-torque (3-4Nm) produced the transition from QH to WPQH and then to ELMy H-mode.  Edge ExB shear in WPQH phase is lower than in the QH and ELMy H-mode phases, consistent with previous observations [1,2]. A low frequency (<100kHz) lab-frame IDD quasi-coherent mode is observed when the pedestal width significantly exceeds the EPED-KBM width.

[1] Chen Xi, et al NF 60 092006 (2020)                [2] Burrell K.H., et al NF 60 086005 (2020)