Validation of the Heuristic Model for the Electron Mobility in Dense Helium Gas

The investigation of the mobility $\mu$ of quasi-free electrons in dense, cold helium gas as a function of its density $N$ is made difficult by the fact that a significant fraction of electrons is localized in low mobility bubbles. The measured mobility is a weighted average of the contributions of the slow electron bubbles, whose mobility is determined by hydrodynamics, and of the fast quasi-free electrons. A precise description of the fast electron mobility is thus required. In the past we have developed a heuristic model that proved succesful at rationalizing the electron mobility in argon and neon gases. In order to validate it, we have carried out new accurate %electron mobility measurements in helium gas in the temperature range $\textbf{26} \, \text{K} < \text{\em T} < \textbf{300}\,$K at densities, in which the presence of localized states is negligible. The analysis of these new data confirms the validity of the model.