Cyclotron Waves in a Nonneutral Plasma Column

A kinetic theory of linear electrostatic plasma waves with frequencies near the cyclotron frequency Ωcs of a given plasma species s is developed for a multispecies nonneutral plasma column with general radial density and electric field profiles. Terms in the perturbed distribution function up to O(1/Ωcs) are kept, as are the effects of finite cyclotron radius rc up to O(r 2 c ). At this order the equilibrium distribution is not Maxwellian if the plasma temperature or rotation frequency is not uniform. For rc → 0 the theory reproduces cold-fluid theory, and predicts surface cyclotron waves propagating azimuthally. For finite rc the wave equation predicts that the surface wave couples to radially and azimuthally propagating Bernstein waves, at locations where the wave frequency equals the local upper hybrid frequency. The equation also predicts a second set of Bernstein waves that do not couple to the surface wave, and therefore have no effect on the external potential. The wave equation is solved both numerically and analytically in the WKB approximation, and analytic dispersion relations for the waves are obtained. The theory predicts that both types of Bernstein wave are damped at resonances, which are locations where the Doppler-shifted wave frequency matches the local cyclotron frequency as seen in the rotating frame.