Magnetohydrodynamic modes driven by anomalous electron viscosity and their role in fast sawtooth crashes

Dispersion relations are derived for both small- and large-Δ′ modes (m≥2 and m=1 modes, respectively) driven by anomalous electron viscosity. Under the assumption that the anomalous kinematic electron viscosity is comparable to the anomalous electron thermal diffusivity, it is found that the viscous mode typically has a higher growth rate than the corresponding resistive mode. Computational results in cylindrical and toroidal geometries are compared with theory and some nonlinear results for viscous m=1 modes in both circular and D-shaped boundaries are presented and their possible role in fast sawtooth crashes is discussed.