Generation of large-scale magnetic-vortex structures in stratified magnetized plasma by a small-scale force

Abstract

In this study, within the framework of electron magnetohydrodynamics, taking into account thermomagnetic phenomena, we obtained a new large-scale instability of the α-effect type, which ensures the generation of large-scale vortex and magnetic fields. This instability occurs in a flat layer of temperature-stratified plasma under the influence of an external uniform magnetic field inclined relative to the layer, combined with a small-scale external force having zero helicity. The external force is presented as a source of small-scale oscillations in the speed of electrons with a low Reynolds number R≪1. The presence of a small parameter in the system allowed us to apply the method of multiscale asymptotic expansions to derive nonlinear equations for vortex and magnetic disturbances. These equations were obtained in third-order Reynolds number. Using solutions for the velocity field in zero order in Reynolds number, we determined the average helicity H=v0·rotv0¯ and its relation to the α-effect. A necessary condition for the generation of average helicity in stratified magnetized plasma is the inclined orientation of the external magnetic field and the presence of a small-scale force. A new effect related to the influence of thermal force (the Nernst effect) on large-scale instability is discussed. It is shown that an increase in the Nernst parameter leads to a decrease in the amplification factor α and thereby prevents the development of large-scale instability. With the help of numerical analysis, stationary solutions to the vortex and magnetic dynamo equations in the form of localized structures like nonlinear waves of the Beltrami were obtained.