The physics of neoclassical magnetohydrodynamic tearing modes

Neoclassical effects alter the nonlinear evolution properties of magnetic islands in toroidal plasmas. While the perturbed bootstrap current effects tend to dominate the nonlinear evolution and mode saturation properties in tokamak plasmas, a number of additional effects complicate the picture. A novel aspect of the mode evolution properties is the appearance of a nonlinear threshold width, below which island formation is suppressed. The structure and strength of various closure relations for the ion viscosity and heat fluxes impact the size and scaling of the threshold width. The potential impact of this physics on low aspect ratio tokamaks and stellarator configurations is also discussed. (C) 1998 American Institute of Physics.