On neoclassical effects in the theory of magnetic islands

Neoclassical viscosity affects the stability of magnetic islands by providing additional source of the transverve electric current contributing to the net longitudinal current in the magnetic island. One component of such neoclassical longitudinal current has a structure similar to the ion polarization current with enhanced plasma inertia and was investigated previosly. We show that in addition to the neoclassical inertia term, there is additional neoclassical current associated with variations of plasma pressure within the perturbed magnetic surfaces. Such variations can be caused by the ion polarization drift across the magnetic surface and finite heat conductivity in the parallel direction. A contribution of the neoclassical current due to plasma pressure variations is of the same order or larger than the standard ion polarization and bootstrap current terms. New terms will affect overall stability of magnetic islands and may provide a new threshold mechanism for the neoclassical tearing modes. (C) 2004 American Institute of Physics.