Generation of suprathermal electron tails in the solar wind

The observed core-halo structure of the electron distribution function (hereafter e.d.f.) in the solar wind can be interpreted in two ways. In the first type of interpretation, the core adjusts adiabatically to the local solar wind conditions while the suprathermal particles result from the collisionless expansion of the coronal plasma. The second interpretation is fully local, the halo electrons resulting from the wave particle interactions, as observed in practically all low density collisionless plasmas. In this work we explore this last interpretation using numerical simulations of the Vlasov - Poisson equations. We propose that the source of the waves able to interact with the thermal electrons is to be found in the cascade from large scale, fluid fluctuations towards small, kinetic scales. In our approach we use a low frequency, random force acting on the protons to represent the effect of the fluid cascade and a high frequency, random force to excite a level of plasma waves modeling the effects of the thermal noise.