Effect of an electric field on the spectrum of oscillations in an inhomogeneous plasma

Abstract

The effect of an inhomogeneous electric field on the spectrum of low-frequency oscillations of a spatially inhomogeneous plasma contained by a strong magnetic field is investigated in the approximation of geometrical optics. The curvature of the lines of force of the containing magnetic field is considered by introducing an effective gravitational field. The cases of a plane and a cylindrical geometry of the inhomogeneous plasma are discussed. Based on the kinetic equation with self-consistent field, expressions are obtained for the longitudinal dielectric permeability characterizing oscillations derivable from a potential of the electromagnetic field in the plasma. Analysing of the oscillation spectra demonstrated a considerable influence of the inhomogeneous electric field on the low-frequency oscillations of the plasma for the case in which this field is comparable to or greater than the thermal field. The electric field has the strongest influence on the long-wave flute and drift oscillations. In plane geometry for an inhomogeneous plasma these oscillations are suppressed under the action of the electric field, the conditions of stabilization improving as the electric field increases. On the other hand, in cylindrical geometry, the increase of the electric field does not, generally speaking, improve the conditions for suppression of the flute oscillations of an inhomogeneous plasma. This is the result of the azimuthal rotation of the cylindrical plasma column under the action of the crossed radial electric and longitudinal magnetic fields leading to a renormalization of the effective gravitational field. In a cylindrical inhomogeneous plasma, therefore, an effective suppression of the flute instability is possible only in a thin layer near the plasma surface.