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 measurements in helium gas in the temperature range 26 K < T < 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.