Investigating ETG in NSTX-U Pedestal: Local and Global Simulations with Profile Curvature Correction

This study investigates the behavior of electron temperature gradient (ETG) modes in the pedestal region of the National Spherical Torus Experiment Upgrade (NSTX-U) using a comprehensive approach of local and global simulations with profile curvature correction. It is observed that global effects can stabilize ETG in the pedestal top for Mega Ampere Spherical Tokamak (MAST). The non-lithiated NSTX-U pedestal shows a similar pedestal profile, which might also demonstrate similar global effects on ETG. Local linear and nonlinear simulations are performed at radial locations from the steep gradient region to the pedestal top to gain insight into ETG dynamics and their influence on the pedestal structure. Key parameters affecting ETG growth and stability are identified through the analysis of local simulations. To account for global effects, profile curvature correction terms are incorporated into the local simulations. This allows for the capture of the impact of profile shape on ETG behavior and potential modifications in the pedestal structure. A comparison is made between local simulations with profile curvature correction and dedicated global simulations to assess the adequacy of the profile curvature correction approach in capturing global effects accurately. A combination of local and global simulations, along with local simulations including a profile curvature correction, will inform strategies for modeling the electron temperature pedestal in spherical tokamaks.