Time-Dependent Perpendicular Transport of Energetic Particles

The motion of energetic particles in magnetic turbulence across a mean magnetic field can be explored analytically. The approach discussed in this paper allows for a full time-dependent description of the transport, including compound sub-diffusion. For the first time it is shown systematically that as soon as there is transverse structure of the turbulence, diffusion is restored even if no Coulomb collisions are invoked. Compared to other non-linear theories the new approach has the advantage that a diffusion approximation is no longer part of that theory. Criteria for sub-diffusion and normal Markovian diffusion are provided as well. A comparison with test-particle simulations is also discussed.