A unified description of tearing modes in plasmas

Abstract

A unified description of tearing modes in an electron–ion plasma is presented. For this purpose, by employing the two-fluid model, which is valid beyond the magnetohydrodynamic model, new coupled mode equations for tearing modes are derived by retaining magnetic shear, the parallel electron inertia, the electron resistivity, the electron/ion neutral drag, as well as the ion Lorentz and the perpendicular ion inertial forces on the same footing. A general dispersion relation for tearing instabilities is obtained by invoking constant ψ-approximation. The newly found dispersion relation admits a rapidly growing collisional tearing instability whose growth rate is much larger (smaller) than the ion gyrofrequency (electron collision frequency). The relevance of our investigation to reconnection of magnetic field lines in laboratory and space plasmas has been discussed.