Quantitative Study of 4He Real Gas Effects Using Supersonic Beams

Abstract

Abstract The experimental realization of accurately defined source conditions, combined with an undisturbed flight path of precisely known length, permits the generation of supersonic molecular beams with an extremely well characterized axial velocity distribution. This achievement can be used for a quantitative assessment of theoretical models of condensation during the jet expansion, based on high accuracy equations of state. For helium-4, which is commonly put on a level with the ideal gas, we contrast two empirical equations of state with respect to enthalpy changes. These can be validated through a comparison with experimentally determined mean terminal flow velocities. At cryogenic temperatures, strong deviations from the ideal gas behavior are observed. Most notably, even the differences between the predictions of the two fundamental equations are large enough to be distinguished by high-resolution time-of-flight measurements.