Generation of zonal flows and large-scale magnetic fields by drift-Alfvén turbulence

Abstract

The possibility of generating zonal perturbations by drift-Alfven turbulence in a plasma with a finite pressure (1>β>me/mi) is investigated. A set of coupled equations is derived that includes the equation for the spectral function of the turbulence and the averaged equations for zonal perturbations. It is shown that, in particular cases, the equation for the spectral function possesses action invariants; i.e., it takes the form of a conservation law for some quantities that are proportional to the spectral function of turbulence. Two types of instability of the zonal perturbations are revealed. The first type of instability generates only a zonal flow. Two regimes of this instability—resonant and hydrodynamic regimes—are examined, and the corresponding instability growth rates are determined. The second type of instability takes place when the resonant interaction of drift-Alfven waves with electrons is taken into account. Because of this instability, the generation of a zonal magnetic field is inevitably accompanied by the generation of a zonal flow. It is found that the growth rate of the second type of instability is slower than that of the first type.