CONTRIBUTION OF THE ION-BEAM ACOUSTIC INSTABILITY TO THE GENERATION OF BROAD-BAND ELECTROSTATIC NOISE - 3-DIMENSIONAL QUASI-LINEAR APPROACH

In order to explain the generation mechanism of the high-frequency part of broadband electrostatic noise (BEN) in the plasma sheet boundary layer of the Earth's magnetotail the nonlinear dynamics of the ion-beam acoustic (IBA) instability is studied within the three-dimensional quasi-linear plasma theory for the background electron distribution function e. During the development of the IBA instability first the plateau formation on e in the velocity space is obtained in the direction quasiparallel to the ion-beam propagation, and quasiparallel wave modes with frequencies up to the order of the electron plasma frequency and even higher values are excited, which is in accordance with the experimental BEN data. As the resonance region in the three-dimensional case is much larger than that in the one-dimensional approximation the energy level of the generated waves increases essentially. In the course of time the plateau formation on fe propagates into the oblique direction. Thus the wave energy generation is displaced to oblique wave modes, and the maximum generated wave power changes to lower frequencies. © 1990.