Chapter 11 - Electron Distributions in Space Plasmas

Abstract

Space plasmas are essentially collisionless systems out of thermal equilibrium, where enhanced populations of suprathermal particles are observed. The typical distributions are generally better described by kappa distributions than by Maxwellians, especially for electrons, which has serious consequences since their small electron mass makes them major agents for plasma energy transport. This chapter presents suprathermal electrons and their critical role in the heating and acceleration of plasmas in several important space and astrophysical contexts. They affect the generation of the ambipolar electric field and contribute to the collisionless electron heat flux. In the solar corona, such electrons make a dominant contribution to the electron heat flux and play an important role in the coronal heating energy budget. They also support large ambipolar electric fields along open magnetic flux tubes in solar/stellar coronae and in planetary ionospheres and thus contribute significantly to solar and stellar wind acceleration, outflow from planetary ionospheres, and possibly even exoplanetary atmospheric loss. For the Earth’s environment, it has been demonstrated that suprathermal electrons play a controlling role in the plasmasphere thermal structure, have a major effect on ionospheric outflows, and control the electron temperature and consequently the topside ionospheric scale height through the generation of heat flux.