Adiabatic Melting Experiment on Helium Mixtures: Status and Prospects

Abstract

We describe the improvements made to our earlier experiment, aiming to cool saturated helium mixtures at the melting pressure to ultra-low temperatures in the microkelvin regime. Cooling is produced by dissolving pure \(^3\)He in the superfluid state to pure \(^4\)He being released from the solid phase within the mixture of isotopes at the melting pressure. The limiting factor for the performance was considered to be the inevitable coupling of the liquid mixture with the surroundings at higher temperatures, such as through the filling line and the sintered surfaces needed for the pre-cooling phase. These issues could be largely eliminated by the new design of the experiment. Results of testing the new components at low temperatures are presented and discussed.