Advances in Wide-Pedestal Quiescent H-mode on DIII-D Towards ITER Conditions

Significant parameter space expansion of the wide-pedestal quiescent H-mode (QH-mode) towards ITER and reactor conditions has been achieved in DIII-D. This natural ELM-stable QH regime was first discovered when the NBI torque was ramped from strong ctr-Ip towards net-zero in balanced double null standard QH plasma. Recent experiments reveal it can operate at a large range of NBI torque fully covering the scaled ITER-equivalent NBI torque. Stationary wide-pedestal QH-mode with net-zero injected NBI torque throughout the discharge has also been demonstrated; zero torque operation greatly benefits from using NTV from 3D fields to maintain enough plasma rotation to avoid locking. Plasma shapes with wide-pedestal QH operation have been expanded to include LSN with ITER δ_avg. In the assessment of its compatibility with RF-heated zero-torque operation, confinement improvements with ECH were observed in some conditions and the plasma remains ELM-stable at the power ratio of ECH to NBI up to 3:1. Initial results of impurity transport in wide-pedestal QH will be presented. Work is continuing to lower q95 for higher fusion gain (to date, obtained with 4.7<q₉₅<7.5, transiently 3.8)