Proton-proton collisions in the turbulent solar wind: Hybrid Boltzmann-Maxwell simulations.

The mechanism of heating for hot, dilute and turbulent plasmas represents a long-standing problem in space physics, whose implications concern both near-Earth environments and astrophysical systems. Here, in order to explore the possible role of inter-particle collisions, for the first time, collisional and collisionless simulations of plasma turbulence have been compared using Eulerian Hybrid Boltzmann-Maxwell simulations, that explicitly model the proton-proton collisions through the nonlinear Dougherty operator. Although collisions do not significantly influence the statistical characteristics of the turbulence, they strongly suppress the production of non-thermal features in the proton distribution function. The latter consists in a suppression of the enstrophy/entropy cascade in the velocity space, damping the spectral transfer towards large Hermite modes. Moreover, we observe that dissipation is located within regions of strong current activity, confirming that the heating process in turbulent plasmas is spatially inhomogeneous.