Trends in Pedestal Structure and Associated Transport Mechanisms of Quiescent and ELMing H-modes in DIII-D

Thorough profile fits spanning wide pedestal (WPQH), standard Quiescent (QH), and ELMing H-mode regimes in DIII-D demonstrate that pedestal profile structure has a regime-dependent response to NBI torque and plasma current direction, with standard QH and ELMing pedestals exhibiting radial shifts between density n_e and temperature T_e pedestal centers, as well as location of dominant E x B shear suppression. Counter-I_p torque QH and ELMing discharges exhibit inward radial shifts of n_e pedestals and electric field E_r well minima compared to their corresponding T_e pedestals, with shift magnitudes growing linearly in proportion to the torque. Conversely, co-I_p torque cases exhibit outward shifts whose magnitudes decrease (with shifts eventually reversing) with torque. These shifts correlate with different turbulent physics via n_e-T_e gradient ratios, collisionalities, and shear suppression (via ω_E×B), leading to the ability to differentiate between regimes through fluxes calculated with TRANSP [1]. Torque-dependent profile characteristics that strongly affect pedestal transport and stability will have important implications for performance and operational regime prediction in future machines.

[1] R.J. Hawryluk, "An Empirical Approach to Tokamak Transport", in Physics of Plasmas Close to Thermonuclear Conditions, ed. by B. Coppi, et al., (CEC, Brussels, 1980), Vol. 1, pp. 19-46.