Plateau Diffusion Including Flux Surface Geometry in a Toroidal Helical System

Abstract

Neoclassical plateau diffusion coefficient in a toroidal helical system is calculated by using the magnetic coordinates. It is assumed that dominant contribution to the plateau regime comes from particles moving along the trough of the helical ripple with parallel velocity almost independent of the toroidal coordinate. It is shown that an elliptic deformation due to l=2 helical coils enhances the diffusion which is opposite to that in vertically elongated tokamaks.