Mean free path and energy loss of electrons in the solar corona and the inner heliosphere

We have studied the mean free path of electrons in the solar atmosphere in dependence on their initial velocity and their starting height above the photosphere. The net pitch angle change results from the combined effects of Coulomb scattering and the decreasing field strength of the large-scale magnetic field. We show that above a certain velocity all electrons can travel a distance of at least five AU without deflection. This treshold velocity decreases with increasing starting height. Furthermore the loss of kinetic energy due to Coulomb collisions as a function of distance from the Sun has been calculated. At small distances, up to at least 1.5 R (solar radius), the energy component parallel to the magnetic field (assumed as radial from the Sun) decreases but above 1.5 R this component increases though the total particle energy decreases. If we assume that the injected electrons also have a velocity component perpendicular to the magnetic field (pitch angle θ > 0), the radial velocity component will increase even at low coronal heights. The theoretical results are compared with observational data of solar type III radio bursts.