On the cosmic ray cross-field diffusion for solar wind turbulence

The cross-field diffusion coefficient of charged particles in the presence of pure isotropic Alfven waves, pure isotropic magnetosonic waves and their mixture is considered using Monte Carlo particle simulations. We show that the cross-field diffusion coefficient k(perpendicular to) strongly depends on the assumed spectrum and amplitude of MHD turbulence but much less on the type of waves considered. It is demonstrated that transport perpendicular to the average magnetic field is mostly determined by compound diffusion which combines the effects of scattering off magnetic irregularities with magnetic braiding. The ratio k(perpendicular to)/k(parallel to) D-M approximate to const: is independent of rigidity over the wide range considered.