Thesis Defense |
Our second study examines the effects of Coulomb collisions in solar-wind heating. The temperature of the solar wind plasma expanding from the hot solar corona does not decrease with the distance as fast as predicted by the adiabatic expansion law. The heating of the solar-wind electrons results from the energy exchange of the fast electrons propagating from the corona along the background magnetic field (the beam or strahl) and the electrons trapped between the electric potential and magnetic mirror walls (the core). The level of the trapped population is a result of two competing processes—particle influx from the streaming population due to pitch-angle scattering and particle losses through the boundary due to energy diffusion. As scattering rates are a free parameter in our study, we can determine how the scattering rates affect the electron distributions, and in turn temperature of the solar wind electrons. Using 1D cylindrical simulations we found the electron temperature profiles scaled with the ratio $\nu{ee}/\nu{ei}$, higher the $\nu{ee}/\nu{ei}$ higher the electron temperatures. The dependency of the electron temperatures and trapped electron population on $\nu{ei}/\nu{ee}$ in the kinetic simulations implies that the Coulomb collisions have a significant effect on the electron temperature profiles as suggested by the collisional model.