Gyrokinetic simulations of high-performance wide pedestal quiescent H-mode at DIII-D

Wide pedestal quiescent H-mode at DIII-D exhibits insensitivity of the energy confinement time to the heating power (P_NBI). The lack of power degradation of the confinement is due to ion internal transport barriers (ITB) formation and the increased stored energy as P_NBI increases [Houshmandyar et al NF (2022)]. Flux-matched TGLF/TGYRO analysis predicts that the ion temperature gradient (ITG) mode is the dominant turbulence mechanism and it is stabilized by the Shafranov shift within the ITB. GENE gyrokinetic simulations of the flux-matched profiles show that within the ITB, the underlying turbulence mechanism changes from trapped electron mode -TEM- to ITG (for k_θρ_s < 1) as the heating power increased, while for k_θρ_s ~ 0.1-0.2 evidence for microtearing modes exists. As P_NBI is increased, several seemingly disparate elements undergo significant changes, prompting a working hypothesis: inward particle transport contributes to the lack of power degradation in energy confinement by stabilizing ITG modes. Key observations include: 1) large coherent turbulent structures measured by BES - commonly known as blob-void pair - have their birth-place location moved into mid-pedestal; 2) the density gradient increased within the ITB; 3) density fluctuations which originate from mid-pedestal regions propagate inward. Within the pedestal of these discharges, the preliminary results from global GENE simulations are consistent with TEM.