Expected charge states of energetic ions in the magnetosphere

Abstract

This paper reviews major developments in our understanding of the physics of energetic heavy ions in the Earth's plasma environment during the past four years (1974–1977). Emphasis is placed on processes that influence or are influenced by the ion charge states. This has been a period of growing awareness of the important role heavy ions play in space plasmas. Large fluxes of helium ions and even heavier ions have been observed at the geostationary altitude and in the heart of the radiation belts. Such ions have also been observed on low latitude rockets and satellites, and oxygen ion precipitation exceeding that of protons has been reported. In the outer parts of the Earth's plasma envelope there is mounting evidence for significant fluxes of heavy ions: in the magnetotail, the magnetosheath and in the polar cusp regions. In the inner magnetosphere there is a limited theoretical understanding of equatorially mirroring ions, but generally only radial diffusion at one pitch angle and pitch angle diffusion at one L- shell have been studied; for ions the coupled equations are yet unsolved even for the simplest case of only one charge state (protons). Theoretical modeling of the charge state structures of geophysical heavy ion populations is in part frustrated by the lack of adequate laboratory measurements of the pertinent charge exchange cross sections. A first attempt has, however, been made to treat the charge state transformation processes in the radiation belts for equatorially mirroring atomic oxygen ions. Wave-particle interactions in the magnetosphere become much more complex in multi component and multi charge state plasmas where hybrid resonances and wave-particle interaction induced non-linear species-species coupling could be important. Heavy ion plasma physics in the Earth's magnetosphere and in the magnetospheres of other planets should be a field of fruitful study for both experimentalists and theoreticians in the years ahead.