A Fokker-Planck approach for the expansion of the fast solar wind: Why andhow?

We present recent observations of the plasma parameters in coronal holes at the origin of the fast solar wind and in the interplanetary medium. A mode l based on the heat conductivity law in a dilute plasma shows the coherency of the electron and proton temperature observations from coronal holes to the interplanetary medium. These new observations are severe constraints fo r any model of the expansion of the fast solar wind. We discuss why and how non-equilibrium multispecies Fokker-Planck approach must be developed and present a generalized Grad's solution.