4D full-f gyrokinetic simulation of NSTX-U

We use the full-f gyrokinetic code Gkeyll to perform 4D simulations of NSTX-U discharges. Both single- and double-null scenarios from the tokamak's initial run in 2016 are investigated within four-dimensional (4D) axisymmetric geometries, in which the perpendicular transport is given by diffusion, however, parallel dynamics remains (gyro)kinetic. These 4D simulations include the X-point and allow computing steady-state profiles of the plasma, including the effects of sheaths. Further, the results can be used to initialize full-f 5D simulations, and serve as the first step towards probing edge turbulence in spherical tokamaks. A key motivation for this project is to prepare Gkeyll for validation against experimental data following NSTX-U's planned resumption of operations in 2026, and applications to design of ST-based fusion power-plants.