Ion Collisional Effects in Slow Solar Wind: Hybrid Simulations

The solar wind is highly ionized, magnetized plasma flow ing supersonically from the Sun's corona into deep space. Though its composition varies considerably, protons (ionized hydrogen) and alpha particles (fully ionized helium) constitute the vast majority of ions. We investigate collisional evolution of the solar wind ions in the inner heliosphere. W e focus on the two m o st abundant ion species: protons and alpha particles. In particular, we will d etermine the role of the Coulomb collisions on the (slow) solar wind temperature as a function of radial distance from Sun, d etermine the role of Coulomb collisions and compare it with the effects of kinetic instabilities driven by the expansion of the solar wind, a ssess the contribution of Coulomb collisions to solar wind ion-energetics and compare their importance relative to other effects ( e. g. , heating from solar wind turbulence), e xtend/extrapolate our results below 0.3 AU towards the acceleration region in order to estimate plasma properties in this region and d etermine the importance of the Coulomb collisions in the fast solar wind. We study the self-consistent evolution of solar wind plasma in the inner heliosphere using the Hybrid Expanding Box model. We will include a mo del of plasma turbulence. We compare the results to the predictions from our analysis of transport coefficients and to in situ observations. I nstead of calculating of the theoretical predictions from collisional transport coefficients, we will investigate the evolution of the plasma system using the collisional hybrid expanding box model. In this model, expansion is realized as an external force, and Coulomb collisions are treated by the stochastic Langevin equation that is equivalent to the Fokker-Planck equation (assuming that the particle distribution functions remain close to bi-Maxwellians).