Ponderomotive impacts of ion cyclotron waves on the ions in the equatorial zone of the magnetosphere

Abstract

The ponderomotive influence of ion cyclotron waves on the field-aligned distribution and motion of ions in the equatorial zone of the magnetosphere is examined. The hydrodynamic, quasi-hydrodynamic and “test-particle” approaches are used for the study of ponderomotive wave-particle interaction. Particular attention has been given to the challenging questions encountered in applying the general theory to the magnetospheric physics. The closed system of quasi-linear equations describing the ponderomotive effects is derived. Analytical investigation of the basic equations has demonstrated the diverse manifestations of the ponderomotive impact of ion cyclotron waves on the ion population in the magnetosphere. It is found that the redistribution of ion density under the action of ponderomotive force with increase in the wave amplitude follows the pattern of phase transition of the second kind. The density distribution changes qualitatively as the point in plane of the governing parameters of system crosses a demarcation line. It has been found that the magnetic equator is an attractor for heavy ion. The period of the finite (oscillatory) motion of a heavy ion, which is trapped in the potential trough in the vicinity of magnetic equator, depends on the wave frequency, wave amplitude, together with the energy of motion. In addition, the diffusion equilibrium of ions in a multicomponent plasma is considered, and the ponderomotive separation of ions in a binary mixture is demonstrated. It is shown that the heavy ions collect near the magnetic equator provided the waves are comparatively strong. It suggests that the ponderomotive effects play a part in formation of structure and dynamics of the magnetosphere.