Numerical study of neoclassical plasma pedestal in a tokamak geometry

A massively parallel numerical guiding center code XGC was used to investigated the fundamental neoclassical properties of a steep plasma pedestal. The steepest pedestal gradients allowed by neoclassical physics were understood by analyzing the orbital relaxation of an infinitely sharp density and kinetic energy pedestal and the associated radial electric field. At a quiescent diverted edge, a steep neoclassical pedestal was formed as the particle source from the neutral penetration was balanced by the increasing convective ion loss toward the separatrix. An anomalous diffusion coefficient suppressed the steep neoclassical pedestal and the strong radial electric field.