Three modes of the shear-flow-driven ion cyclotron instability

The electrostatic shear-flow-driven ion cyclotron instability of magnetic field aligned sheared plasma flow is investigated analytically. It is shown that the shear-flow-driven electrostatic ion cyclotron instability can be considered as a combination of three different instabilities determined by theirs own mechanism of excitation: ion-kinetic, ion-hydrodynamic and electron-kinetic. Each of these instabilities are dominant in different ranges of the wavelength along the magnetic field. The linearized dispersion equation is solved within the limits of long and short waves along the magnetic field where effects of electrons and ions, respectively, are dominant in the development of these instabilities. The general criterion of instability excitation, which couples the flow velocity shear and wave number across the magnetic field, is obtained.