STOCHASTIC ACCELERATION OF ENERGETIC IONS IN JUPITER MAGNETOSPHERE

An equation governing the combined radial diffusion and stochastic acc eleration of super-Afvenic ions by magnetohydrodynamic waves in Jupite r's outer magnetosphere is derived. The formulation is based upon a to tal energy invariant of the adiabatic transport which applies to an is otropic distribution undergoing rapid pitch angle scattering by waves. An analytic solution to the double diffusion equation is obtained and numerical results are presented for two models of ion injection. The first model assumes S+ and O+ are injected throughout a broad region o f space through photoionization of Jupiter's magnetospheric neutral wi nd and obtain an initial energy corresponding to the local corotation energy after pickup by the planetary magnetic field. The second model assumes a monoenergetic distribution of energetic protons is implanted in the middle magnetosphere by the action of field-aligned potential drops in Jupiter's auroral ionosphere. For both light and heavy ions t he injection process creates a seed population of particles which are further accelerated nonadiabatically by the MHD waves and adiabaticall y through radial diffusion. A comparison of the theoretical results wi th a recent data analysis of Voyager low-energy charged particle measu rements is made with very good agreement thus providing a rigorous qua ntitative account of and definitive explanation for the high-energy io n component of Jupiter's magnetosphere.