Effects of nonvanishing ion viscosity on the linear stability of drift tearing modes in a tokamak

The inviscid drift tearing modes dispersion relation is a singular limit of the viscous theory. We show that a finite viscosity leads to dissipative coupling of branches of the drift tearing mode dispersion relation. As a consequence, linear magnetic field reconnection perturbations appear. unstable also at large drift frequency. The effects present analogies with the theory of the Orr-Sommerfeld equation for viscous fluids. Applicability to edge localized resistive modes in a tokamak is suggested.