It is shown that an exact (finite-amplitude) solution is possible for the propagation parallel to the external magnetic field of right and/or left circularly polarized waves in cold multispecies plasmas with different equilibrium drifts along the external magnetic field. The method of derivation indicates that such a plane-wave solution must be at constant amplitude. No special frequency regime is required for these finite-amplitude waves. Because of possible applications to cometary plasmas, a brief discussion is given of the Alfven or low-frequency, long-wavelength approximation.
Dielectric properties of an inhomogeneous plasma