Pedestal Width-Height Scaling and Dependence on Plasma Shaping Parameters in Spherical Tokamaks MAST-U and NSTX

A systematic database study of the effect of plasma shaping on the pedestal width-height scaling in spherical tokamaks is presented. While H-mode can increase temperature and pressure in the plasma core, it is often characterized by deleterious edge-localized modes (ELMs), which degrade the pedestal and deposit unacceptably high heat loads on the divertor. Electron density and temperature profiles from Thomson scattering data are obtained from the third physics campaign of the upgraded Mega Ampere Spherical Tokamak (MAST-U). An automatic profile fitting algorithm is used to calculate pedestal width and height for ~70,000 time slices across ~700 shots. Using EFIT++ reconstructions of equilibria with varying elongation, triangularity, and aspect ratio, the effect of plasma shaping parameters on pedestal scaling is explored. A similar analysis will be performed for the National Spherical Torus Experiment (NSTX), leading to a comparison of the two low-aspect ratio devices. Promising regimes for generating robust pedestals are proposed for future spherical tokamak experiments.