A Fokker-Planck Approach for the Expansion of the Fast Solar Wind: Why and How?

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 model 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 for 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. This revised version was published online in July 2006 with corrections to the Cover Date.