D. Summers Memorial University of Newfoundland, St. John's, Newfoundland, Canada
Space plasmas are generally observed to possess a particle distribution with a non-Maxwellian high-energy tail. The distribution typically has a power-law tail in energy,and can often be modelled by a generalized Lorentzian (or kappa) distribution. A kinetic equation is formulated for the electron distribution incorporating the effects of stochastic acceleration by whistler-mode waves and Coulomb collisions. The stationary solution to the equation, subject to a zero-flux boundary condition, is found to be a generalized Lorentzian distribution. The spectral index of the distribution depends strongly on the relative wave intensity R. Taking into account the minimum energy required for gyroresonance of electrons with whistlers,we calculate a range of values of R for each of a number of different space plasmas for which Lorentzian distributions can be expected to be formed. This study is one of the first to provide a theoretical justification for the formation of Lorentzian particle distributions in space plasmas.