The Effect of Micro-instabilities on Pedestal Profile Reconstruction in Spherical Tokamaks (ST)

We investigate Electron Temperature Gradient (ETG) instabilities and transport in spherical tokamaks, focusing on the pedestal region and its transition to the core. In the steep gradient region of the pedestal, ETG modes exhibit slab-like characteristics, with transport described by established expressions. At the density pedestal top, ETG transport becomes more complex. Simulations reveal that profile curvature can significantly influence transport, with discrepancies between local and global simulations quantified by the ratio of radial correlation length to profile curvature scale. We also show that parallel magnetic field fluctuations () destabilize larger electron-scale ETG modes at the pedestal top and upper pedestal region for NSTX in some parameter regimes, substantially increasing the heat flux in comparison with simulations without parallel magnetic fluctuations. We will present reduced models derived from these studies and apply them to modeling pedestal profiles in several NSTX discharges. The sensitivity of modeled profiles to the separatrix boundary conditions for density and temperature will be investigated. The role of kinetic ballooning modes (KBM) and microtearing modes (MTM) will also be described.