Plasma flows and radial electric field in nonaxisymmetric toroidal plasmas

The ambipolarity of the plasmas in nonaxisymmetric toroidal systems is studied by considering the momentum relaxation on a flux surface. A set of two time-dependent equations for two chosen independent variables, the parallel plasma flow velocity U/sub parallel/ and the radial electric field E/sub r/, is employed to describe the momentum relaxation process. In general, these two variables are coupled through plasma viscosities. At the steady state, one of the equations produces the viscous relaxation criterion summation/sub a/ = 0, and the other gives rise to the well-known ambipolarity constraint summation/sub a/e/sub a/GAMMA/sup a//sub na/ = 0, where Pi/sub a/, e/sub a/, and GAMMA/sup a//sub na/ are the viscous tensor, electric charge, and nonambipolar particle flux, respectively, for species a, and B is the magnetic field. After U/sub parallel/ and E/sub r/ are determined, the plasma is in the ambipolar state; that is, both electrons and ions diffuse at the same rate across the flux surface