Energetics of solar wind electrons from Helios observations

The electron heat flux properties in the solar wind have been examined based on Helios 1 and 2 in situ observations. The data set covers the heliocentric radial range between 0.3 and 1.0 AU in the ecliptic plane only. Understanding the fundamental heat transport and energy dissipation in the expanding solar wind plasmas requires a detail analysis of electron velocity distribution functions (eVDF) and particularly their non-thermal features. Our study is based on a full three component (core-halo-strahl) analytical modelling of measured 2D eVDF and consequent analysis of derived eVDF moments. First we provide radial profiles of observed characteristics (densities, temperature, heat flux) for each of the eVDF component. These profiles are further used to analyse corresponding heating/cooling rates in the expanding solar wind, separately for the slow and fast solar wind streams.