Stability and Transport of Gyrokinetic Critical Pedestals

A gyrokinetic threshold model for pedestal width-height scaling prediction is applied to multiple devices and to a shaping and aspect-ratio scan giving ${\mathrm{\Delta }}_{\mathrm{p}\mathrm{e}\mathrm{d}}=0.92A^{1.04}{\kappa }^{-1.24}{0.38}^{\delta }{\beta }_{\theta ,\mathrm{p}\mathrm{e}\mathrm{d}}^{1.05}$ for pedestal width ${\mathrm{\Delta }}_{\mathrm{p}\mathrm{e}\mathrm{d}}$, aspect-ratio $A$, elongation $\kappa$, triangularity $\delta$, and normalized pedestal height ${\beta }_{\theta ,\mathrm{p}\mathrm{e}\mathrm{d}}$. We also find a width-transport scaling ${\mathrm{\Delta }}_{\mathrm{p}\mathrm{e}\mathrm{d}}=0.028{(q_e\mathrm{/}{\mathrm{\Gamma }}_e-1.7)}^{1.5}\sim {\eta }_e^{1.5}$ where $q_e$ and ${\mathrm{\Gamma }}_e$ are turbulent electron heat and particle fluxes and ${\eta }_e=\mathrm{\nabla }\ln T_e\mathrm{/}\mathrm{\nabla }\ln n_e$ for electron temperature $T_e$ and density $n_e$. Pedestals close to those limited by kinetic-ballooning-modes (KBMs) have modified turbulent transport properties compared 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 wide pedestal discharge.