Compound diffusion of energetic particles: a Kappa model for the parallel distribution function

One can assume that energetic particles follow magnetic field lines while they propagate through a magnetized plasma. The latter scenario is usually described by the so-called field line random walk limit. This limit, however, is only valid if parallel diffusion is suppressed. As soon as the latter effect is taken into account, perpendicular transport becomes subdiffusive. This physical scenario is usually called compound diffusion or compound subdiffusion and can be described by a Chapman-Kolmogorov equation. In the latter equation the parallel distribution function is an essential ingredient. In the present paper we replace the standard Gaussian model by a Kappa distribution to compute distribution functions and mean square displacements across the field.