Turbulence-induced diffusion analysis of national Spherical Torus Experiment based on the gyrocenter shift

The radial current generated by ion-neutral momentum exchange is suggested to be one of the methods for generating the radial electric field (E _r), the turbulence transport, and the low-confinement-mode (L-mode) to high-confinement-mode (H-mode) transitions at the edge of tokamak plasmas. In this analysis of the gyrocenter shift, the plasma pressure gradient, the neutral density gradient and the neutral velocity are the major driving mechanisms of the radial current and the electric field. When there is turbulence, small-scale Ẽ × B eddies induce cross-field transport. The confinement time of the National Spherical Torus Experiment is compared with the density fluctuation level to verify the turbulence-induced energy diffusion coefficient from the theory of the gyrocenter shift.