On the interchange stability of the Van Allen belt

The interchange stability of the Van Allen belt is studied in the electrostatic approximation. The destabilizing currents are obtained from the description of the particle motion developed by Northrup and Teller when the magnetic moment and bounce actions are invariant. The stabilizing currents are described by the three-fluid (electrons, ions, and neutral particles) zero-temperature dielectric tensor discussed by Fejer. For frequencies of the order of the azimuthal drift periods of the energetic particles in the belt, the stabilizing currents arise primarily from the ionosphere. With a reasonable choice of belt parameters, the energetic particles appear to be quite stable against interchanges for the electron densities which obtain in the ionosphere during the daytime, but are near marginal stability for nighttime ionospheric densities.