Neoclassical toroidal plasma viscosity in the superbanana regime in tokamaks

Abstract

Neoclassical toroidal plasma viscosity in the superbanana regime resulting from the symmetry breaking magnetohydrodynamic activities or error fields in tokamaks is calculated. The superbanana regime becomes important when the E × B drift frequency is comparable to or smaller than the ∇B drift frequency and when the effective collision frequency is less than the bounce frequency of the superbananas. Here, E is the radial electric field, B is the magnetic field and B = |B|. The width of the superbananas depends on the relative strength of the magnetic field perturbations to the inverse aspect ratio of tokamaks. It is independent of the particle energy and the magnitude of the equilibrium magnetic field. The viscosity and the transport fluxes are found to be proportional to the collision frequency. The toroidal flow damping rate is greatly enhanced in this regime.