Self-consistent model of solar wind electrons

We model the transformation of the steady state electron velocity distribution function in the collisional transition region of the solar wind by solving the Fokker-Planck equation. Alongside the proton and electron Coulomb collisions, effects of gravitational and electric and magnetic forces are also considered. The Coulomb collision term is calculated for any background velocity distribution function using a spectral method that we have developed and applied previously [Pierrard et al., 1999]. Consistent treatment of electron self collisions is obtained using an iterative numerical method to match the velocity distribution functions of "test" and "background" electron distributions. Electron collisions with background solar wind protons are also taken into account. We find that Coulomb collisions have important effects on angular scattering of the electrons (i.e., on the pitch angle distribution) without changing their average density or mean radial temperature distribution. Finally, the importance of boundary conditions on the solution of the Fokker-Planck equation is discussed and emphasized.