On the cosmic ray cross field diffusion in the presence of oblique MHD waves

The process of particle cross-field diffusion in the presence of finite MHD amplitude wave fields is considered using the Monte Carlo particle simulations. We derive the crossfield diffusion coefficient κ⊥ and the parallel diffusion coefficient κ‖ for the flat and the Kolmogorov wave spectra, including the waves propagating oblique to the mean magnetic field B0. We note a substantial difference in the cross-field diffusion efficiency between the considered turbulent fields. Much larger values of κ⊥ appear in the presence of fast-mode waves in comparison to the Alfvén waves and we reproduce the expected increase of κ⊥ with the growing power of waves propagating perpendicular to B0. We interpret these results in terms of the particle drifts in non-uniform magnetic fields.