Excitation of electromagnetic quasi-perpendicular ion cyclotron waves in collisional plasmas

The process of spontaneous excitation of electromagnetic (non-potential) and quasi-perpendicular (with respect to the external magnetic field) ion cyclotron waves by electron drift in a weakly ionized plasma is analysed. An infinite plasma placed in mutually parallel d.c. electric and magnetic fields is considered, and its dynamics is described by kinetic equations with BGK model collision integrals. The threshold electron drift necessary for the onset of the corresponding ion cyclotron instability is evaluated. It is shown that the instability sets in first for wavelengths much larger than the electron mean free path, so that the electron collisions, dominant in this range of wavelengths, play a facilitating rather than an impeding role in this process. The results are compared with those for the spontaneous excitation of electrostatic (potential) quasi-perpendicular ion cyclotron waves and, for the same set of plasma parameters, the threshold drift is found to be smaller for the electromagnetic waves.