The parallel diffusion coefficient and adiabatic focusing of cosmic-ray particles

Abstract

In this paper, the problem of focused particle transport is revisited. A description in terms of a system of stochastic differential equations, completely equivalent to the Fokker-Planck equation, is suggested. The coefficient for spatial diffusion parallel to the mean magnetic field is calculated. The case of isotropic pitch angle scattering and weak focusing is analyzed in detail. The disagreement between a recent analysis by Shalchi and other treatments of the same problem is discussed.