Numerical Investigation of Perpendicular Diffusion of Charged Test Particles in Weak Magnetostatic Slab Turbulence

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Abstract
The perpendicular diffusion of charged test particles in a static representation of low-frequency, weakly turbulent magnetic fields superimposed on a steady background field is investigated with numerical simulations. The magnetic field variation is purely one-dimensional, consistent with an ensemble of field-aligned Alfvén waves in the limit of zero Alfvén speed. The diffusion coefficient κ⊥ obtained from the numerical simulations is compared with Bieber & Matthaeus's recent theory of spatial diffusion, specialized to one-dimensional field geometry, for a number of particle energies/rigidities. It is found that the recent theory provides a better fit to the numerical data for Ωτ > 2, where Ω is the particle gyrofrequency and τ is a rigidity-dependent decorrelation time, than does the well-known quasi-linear theory, or field line random walk limit. However, while the Bieber & Matthaeus theory fails to fit the simulation data for Ωτ < 1, the theory corresponding to the field line random walk limit exhibits only a 20% error here. Possible reasons for the discrepancy between the theory and simulations are discussed.