Collisionless reconnection of magnetic field lines in dusty plasmas

Abstract

Stability of a thin current sheet in an inhomogeneous dusty plasma is investigated. A new mechanism for the collisionless reconnection of the magnetic field is found. It is associated with the linear instability of a surface shear-Alfvén mode which exists at the boundary between two plasma regions with different orientations of the sheared magnetic field. This new mode is possible only in dusty plasmas in which the electron and ion densities are inhomogeneous and different from each other. The dispersion properties of the surface mode are found to be strongly dependent on the spatial profile of the current sheet. The unstable linear mode is found in the case of a current sheet with steep edges. It is identified as the bending- (or kink-) mode, whose electrostatic and vector potentials, φ and Az, are symmetric and antisymmetric functions, respectively. In such a plasma configuration, the surface tearing mode (φ-antisymmetric, Az-symmetric) cannot propagate as an eigenmode. It arises only as a forced mode through the resonant coupling with the bending mode and the local convective cell. The increment of the bending/tearing instability is estimated from the second-order contribution of the resonance.