Pedestal transport validation in NSTX and development of a general ETG pedestal transport model

Experimental validation of nonlinear gyrokinetic simulations finds that transport from electron temperature gradient (ETG) and microtearing mode (MTM) turbulence, in addition to neoclassical transport, can account for total power flow in NSTX wide-pedestal H-modes. Gyrokinetic analysis (CGYRO) predicts that a variety of NSTX H-modes, from narrow ELMy to wide ELM-free cases, are within 10% of kinetic ballooning mode (KBM) stability thresholds across the entire pedestal. This indicates KBM remains a viable candidate for constraining the maximum pressure gradient at low aspect ratio. However, the experimentally inferred ratio of electron particle to heat diffusivity (from SOLPS) is smaller than predicted by KBM. Both MTM and ETG, expected to transport primarily electron heat flux, are also predicted unstable. Nonlinear electron-scale ETG simulations predict a range of electron heat flux (Q_e,ETG≈0-2 MW) depending on local parameters. Combined with neoclassical (NC) ion thermal transport (Q_i,NC≈1 MW, from NEO), transport from ETG + NC accounts for 50-75% of the power flow for the wide pedestal and progressively less for the narrow pedestal. Nonlinear ion-scale MTM simulations predict electron heat flux comparable to that from ETG. Together, ETG + MTM + NC accounts for the total power flow in the wide-pedestal discharge in which the largest deviations from KBM transport ratios are observed. To develop a predictive capability, we use additional simulations to develop a reduced ETG pedestal transport model that reproduces many of the dependencies with driving gradients and equilibrium parameters. The resulting model unifies the NSTX results with those from recently published DIII-D analysis.