Oblique aperiodic instability driven by cross-field current in space plasmas

Abstract

Electric currents across the magnetic field can occur in the solar atmosphere because of quasi-stationary magnetic shear, plasma non-uniformity, or MHD waves. We propose a new physical mechanism that can cause the anomalous dissipation of these currents and initiate energy release in solar plasmas. In the framework of linear kinetic theory, we show that the cross-field currents are unstable with respect to low-frequency perturbations. The instability growth rate is quite high, about 2% of the ion-cyclotron frequency when the differential electron/ion velocity is 0.2 of the ion thermal speed. We identify the unstable perturbations as degenerated ion-acoustic modes coupled with backward kinetic Alfvén modes.