Collision frequency and mean free path for plasmas described by kappa distributions

Abstract

The paper shows the surprising result of the universality of the mean-free-path formulation for plasmas described by kappa distributions. In particular, the ratio of the mean-free-path over the Debye length depends only on the Debye number - the number of particles within the Debye length scale. The derived formula appears to be identical for the cases of Maxwell-Boltzmann and kappa distributed plasmas; thus, it is not explicitly depended on kappa - the parameter that labels and governs the kappa distributions. The key aspect of these results is the specific functional dependence of the mean-free-path on the polytropic index; this is inextricably linked to the dependence of the Debye length on the polytropic index. The importance of the dependence of the mean-free-path on the polytropic index is demonstrated with applications in the solar wind plasma.