Rapid diffusion of energetic charged particles across magnetic fields

Abstract

In crossed electric and magnetic fields (E·B=0), diffusion of energetic charged particles across the magnetic field occurs through the combination of pitch angle scattering and the subsequent grad B drifting through the electric field. The estimated diffusion coefficient for this compound process in a magnetic field of fixed direction is where D(cos α) is the diffusion coefficient appropriate to pitch angle (α) diffusion of cos α, ϵI is e times the characteristic potential of the electric field cells, ϵ is energy of charged particle, tI is time spent in the pitch angle diffusion region, and tD is drift period. The diffusion coefficient appropriate to a curved magnetic field is similar but has a modification for the curvature. Conditions that must be fulfilled for radial diffusion to be faster than pitch angle diffusion are determined in both the absence and presence of an absorber (atmosphere) in a general celestial magnetic field. The conditions are specified in terms of pitch angle, electric field strength, and magnetic field distortion. These conditions may be met in the magnetosphere during magnetic storms for a wide range of particle energy up to 1 Mev and more. But the theory has wider applications.