Inhomogeneity and nonlinearity effects on stop bands of Alfvenic ion cyclotron waves in multicomponent plasma

The existence of stop bands for left handed Alfvenic ion cyclotron waves propagating in the direction of magnetic field in a multicomponent plasma is studied. Three effects are discussed: finite ion temperature, inhomogeneous magnetic field and nonlinear wave amplitude. All of them affect the existence of stop bands and set critical bounds on the relevant physical parameters, particularly on the density of heavy ions. Using the model of a linearly varying, longitudinally inhomogenous magnetic field, the critical lower bound on heavy ion density is calculated as a function of longitudinal inhomogeneity, and the difference between the truly inhomogeneous and essentially homogeneous situations is discussed. Typical values for the wave vector in the resonance region are derived. The upper bound on the wave amplitude for the linear theory to be applicable is found and the condition for stop band formation in the nonlinear case is derived. The obtained results are applied to the magnetospheric environment and shown to lead to relevant modifications.