Interplanetary transport mechanisms of solar energetic particles

Numerical simulations of charged particle trajectories in a Parker field with model turbulence are used to study the transport mechanisms of solar energetic particles (SEPs): magnetic focusing, pitch-angle diffusive transport due to magnetic fluctuations, and adiabatic cooling. The results of the simulations are compared with analytical formulae for the transport effects. We find that adiabatic cooling is significant for SEPs traveling from the Sun to 1 AU. The simulation results agree much better with the anisotropic adiabatic cooling effect theory than with the isotropic one. Also, we show that the simulation results agree well with the theory of magnetic focusing with pitch-angle scattering by magnetic fluctuations. In addition, in order for quasilinear theory to be valid, the average particle's Larmor radius must be much smaller than the correlation scale of the two-dimensional component of turbulence.