High Energy Proton Model for the Inner Radiation Belt
The high energy protons of the inner radiation belt offer a unique test for theories of magnetospheric processes. These fluxes are relatively stable, being only slightly affected by magnetic activity, and the very high energy of some of the protons restricts the mechanisms which can be invoked for their acceleration. At the lower edge of the belt the earth’s atmosphere provides a calculable loss mechanism and thereby specifies a minimum to the source strength which must exist to maintain the belt. Shortly after the discovery of the inner radiation belt it was suggested (Singer, 1958; Kellogg, 1959; Vernov et al., 1959) that these protons resulted from the decay in flight of albedo neutrons produced by cosmic ray interactions in the atmosphere. The belt was envisioned to represent the equilibrium flux resulting from this source and the losses caused by collisions of the protons with atmospheric constituents. Extensive calculations based on these assumptions were performed, and many of the features of the belt were in agreement with this theory, in particular the spectrum of high energy protons. However, as experimental data on the trapped proton flux, the albedo neutron intensity, and the atmospheric density improved, it became apparent that the theory was deficient in at least two important respects: (a) The energetic proton fluxes predicted by the theory were too small by a factor of 10 to 50, and (b) the spatial distribution of the protons was not in agreement with experiment. There was also a gross discrepancy at low energies where the cosmic ray albedo theory was hopelessly inadequate to supply the observed fluxes.
KeywordsPitch Angle Secular Variation Radial Diffusion Radiation Belt Proton Flux
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