Stability and transport of gyrokinetic critical pedestals

A gyrokinetic threshold model for pedestal width-height scaling predic- tion is applied to multiple devices. A shaping and aspect-ratio scan is per- formed on NSTX equilibria, finding Δped = 0.92A1.04κ-1.240.38δβ$^{1.05}_{θ,ped}$ for the wide-pedestal branch with pedestal width Δped, aspect-ratio A, elon- gation κ, triangularity δ, and normalized pedestal height βθ,ped. A width- transport scaling is found to vary significantly if pedestal height is varied either with fixed density or fixed temperature, showing how fueling and heating sources affect the pedestal density and temperature profiles for the kinetic-ballooning-mode (KBM) limited profiles. For an NSTX equilib- rium, at fixed density, the wide-branch is Δped = 0.028 (qe/Γe - 1.7)1.5 ~ η$^{1.5}_e$ and at fixed temperature Δped = 0.31 (qe/Γe - 4.7)0.85 ~ η$^{0.85}_{e}$ where qe and Γe are turbulent electron heat and particle fluxes and ηe = ∇ ln Te/∇ ln ne for electron temperature Te and density ne. Pedestals close to the KBM limit are shown to have modified turbulent transport coefficients com- pared to strongly driven KBMs. The role of flow-shear is studied as a width-height scaling constraint and pedestal saturation mechanism for a standard and lithiated wide pedestal discharge. Finally, the stability, transport, and flow-shear constraints are combined and examined for a NSTX experiment.