Core, halo and strahl electrons in the solar wind

Electron velocity distribution functions (VDF) observed in the low speed so lar wind flow are generally characterized by 'core' and 'halo' electrons. I n the high speed solar wind, a third population of `strahl' electrons is ge nerally observed. New collisional models based on the solution of the Fokke r-Planck equation can be used to determine the importance of the different electron populations as a function of the radial distance. Typical electron velocity distribution functions observed at 1 AU from the Sun are used as boundary conditions for the high speed solar wind and for the low speed sol ar wind. Taking into account the effects of external forces and Coulomb col lisions with a background plasma, suprathermal tails are found to be presen t in the electron VDF at low altitudes in the corona when they exist at lar ge radial distances.