Proton cyclotron instability in the drifting magnetoplasma

A general expression for the tensor of the dielectrical susceptibility in a n anisotropic plasma with particle drifts is derived, and the dispersion eq uation is found for waves propagating in arbitrary direction with respect t o the mean magnetic field. The dispersion equation is solved for the case o f electromagnetic ion-cyclotron waves. It is found that in the plasma of th e auroral magnetosphere strong plasma instability may occur so that the val ue of the growth rate of the waves is of the order of the wave frequency. B esides, the plasma instability is excited at less values of the wave number if the magnetospheric altitude becomes larger.