Anomalous and classical diffusion of cosmic rays due to nonlinear two‐dimensional structures and random magnetic fields

Abstract

Magnetic field turbulence in the heliosphere is modeled by two‐dimensional coherent vortex structures and random‐phase linear wave fields added to a background magnetic field. Energetic particle trapping and acceleration by interaction with the turbulent fields are studied numerically. The corresponding radial and field‐aligned diffusion coefficients are estimated. Different diffusion regimes (subdiffusion, superdiffusion, classical diffusion) are controlled by the following parameters: the ratio between amplitudes of the random component and the regular vortex field, ε1, and the ratio between the average particle gyroradius and the magnetic field correlation length, ε2. The anomalous diffusion regime occurs when the correlation length of magnetic field disturbances is about the same or larger than the particle gyroradius (ε2 ≤ 1). Applications of our results to cosmic ray transport are discussed.