Time-dependent test-particle scattering perpendicular to a mean magnetic field: the four transport regimes and validity of the FLRW limit

By employing a compound transport model the problem of charged test-particle scattering perpendicular to a mean magnetic field is investigated. In comparison with previous approaches a full time-dependent description is provided. According to these new results there are at least four different transport regimes, namely, the ballistic regime, the strong diffusive regime, the FLRW limit and the subdiffusive regime. It is also shown that the FLRW limit, and therefore quasilinear theory, can only be correct for intermediate time-scales and for high energetic particles. For low energetic particles there is a strong diffusive regime with κperpendicular/κparallel ∼ 1. These results are very important for understanding solar wind observations and recent test-particle simulations