COULOMB COLLISIONAL ANALYSIS OF SOLAR WIND IONS
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Owing to its low density and high temperature, the solar wind frequently exhibits strong departures from local thermodynamic equilibrium (LTE). Previous studies have focused on non-LTE features but were largely limited to using observations from single spacecrafts. In contrast, this research utilized contemporaneous, in-situ observations from two different spacecraft at two different distances from the Sun. Collisional analysis combines the effects of collisional relaxation and large-scale expansion, quantifying how ion relative temperature and differential flow evolve through the heliosphere. This generates a prediction for the distribution of these quantities in the solar wind at any distance from the Sun. Results suggest that ion relative temperature and differential flow through the inner heliosphere is largely governed by the effects of expansion and Coulomb collisions, and that preferential heating is largely limited to the corona.