Validation of the Heuristic Model for the Mobility of Quasi-free Electrons in Dense Helium Gas

The electron mobility in dense, cold Helium gas has mainly been studied because its behavior is the macroscopic manifestation of the electron self-localization phenomenon leading to the formation of electron bubbles. The measured mobility consists of the weighted contri- butions of quasi-free electrons and electron bubbles. A good description of the experimental outcome requires a detailed knowledge of the density dependence of the quasi- free electron mobility. As the main interest was focused on the precipitous decrease of the mobility with increasing gas density because of the localization process dominated by the rapid growth of the electron bubbles number, the low-density range, where electron bubbles are few or even absent, was not investigated with very high accuracy. As we developed a heuristic model to successfully rationalize the electron mobility in dense Argon and Neon gases, we have carried out accurate measurements of the electron mobility in order to validate such model in the temperature range 26K < T < 300K and in a density range, in which the electron bubble contribution is negligible. Here, we report the new measurements and their description by means of the heuristic model.