Modeling of stochastic forces in turbulent space plasmas

Abstract

A model of a Langevin equation for electrons in turbulent, almost collisionfree magnetoactive plasmas is developed, which can form the starting point for particle simulations, especially in regions with reconnection of magnetic-field lines. The mean wave force is expressed by a friction force and a velocity derivative of the intensity of the stochastic force. The obtained expression for the Langevin force is consistent with the kinetic theory in a polarization approximation. The intensity of the stochastic force corresponds to the velocity diffusion tensor of the electrons, which is estimated for plasmas with ionacoustic turbulence using two different methods. One method is based on direct calculation of the space-time spectral density of the wave energy. The second method uses approximations of quasi-linear plasma theory. The estimates for the intensities of the stochastic forces found by the two methods differ by orders. A table of parameters of ion-acoustic waves, electron-wave collision frequencies, and intensities of stochastic-wave forces on electrons in solar flares, in the solar wind, as well as in different regions of the earth's magnetosphere is presented. Results are given for the entire ranges of available experimental data for the mean magnetic induction, mean plasma temperatures, and mean particle densities.