Power-law Particle Distributions Generated by Whistler-Mode Turbulence
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.