Pitch angle diffusion by bounce resonance

Abstract

The paper aims at removing the restriction x<1 (where x is the cosine of the equatorial pitch angle) in the theory of pitch angle diffusion by bounce resonance. When the fourth order anharmonicity term is included in the expansion of the magnetic field around the equator, the parallel displacement of a particle becomes a superposition of the first and third harmonics of the fundamental frequency. The diffusion coefficient for pitch angle scattering by bounce resonance has been evaluated by taking into consideration the anharmonicity effects, and this expression can be expected to be valid for particles which mirror at higher latitudes also.