Coulomb collision rates for self-similar and kappa distributions

The Coulomb collision operator for two nonthermal particle distributions, the self-similar and kappa distributions, is investigated theoretically. Associated friction and diffusion rates are evaluated and calculated numerically as a function of velocity. It is shown that the full collision term can be cast into a relaxation-time form with an effective collision rate which differs drastically from the smooth overall diffusion rates and is very sensitive to the shape of the distribution. Numerical results for the effective rates are presented, and the relevance of the present analysis to observed distributions in space plasmas and to quasi-linear turbulence is discussed. 26 references