On the chaos and stability problem in the trapping of anomalous cosmic ray heavy ions by the Earthʹs magnetosphere

Ions of nitrogen, oxygen and neon have been observed in detectable quantities in the Earthʹs inner radiation zone between L-shells of 1.2 and 2.4. Russian and American spacecraft observations of these ions pertain to low altitudes near the top of the atmosphere. Because of large loss rates during cross-field diffusion, the source of these ions cannot simply be radial transport from the outer radiation zone, but rather must be an effective local source at low L-shells. This source is now believed to be the direct entry of anomalous cosmic ray ions in low charge states and thus high geomagnetic rigidity. These ions can charge exchange with atmospheric paricles to become multiply charged and thus instantaneously trapped by the geomagnetic field. The energies of these ions are sufficiently high to violate the strict adiabaticity criterion of trapped particles, and thus their bounce motion and azimuthal drift-like transport will be at least partially non-adiabatic and may be considered chaotic in nature. The stability and chaos-like pitch angle scattering process expected for such inner radiation zone energetic heavy ions are discussed. From the theory considered, the ACR ions of energy about tens of MeV nucleon−1 could be trapped only when they have atomic mass A ⩾ 7 and arrive at the Earth from the westward direction.