Context. Spacecraft observations have motivated the need for a refineddescription of the phase-space distribution function. Of particular importanceis the pitch-angle diffusion coefficient that occurs in the Fokker-Plancktransport equation. Aims. Simulations and analytical test-particle theories arecompared to verify the diffusion description of particle transport, which doesnot allow for non-Markovian behavior. Methods. A Monte-Carlo simulation codewas used to trace the trajectories of test particles moving in turbulentmagnetic fields. From the ensemble average, the pitch-angle Fokker-Planckcoefficient is obtained via the mean square displacement. Results. It is shownthat, while excellent agreement with analytical theories can be obtained forslab turbulence, considerable deviations are found for isotropic turbulence. Inaddition, all Fokker-Planck coefficients tend to zero for high time values.
展开▼
