Helium Mixtures

The sample cell and some auxiliary probes for the adiabatic melting experiment mounted on the top of the copper nuclear stage for cooling the helium mixtures.

Adiabatic Melting Experiment

Variety of physical properties of the helium isotopes at low temperatures are taken of advantage to make dilution cooling of He-3 to He-4 possible with a starting temperature below 1 mK, where the pure He-3 is already in the superfluid state. The different quantum statistics obeyed by the two isotopes make the melting pressures, superfluid transition temperatures, entropies, solubilities and so forth very much different between those two chemically identical components. All this, suitably arranged, leads to the situation, where we can manipulate the isotopes within the experimental cell kept constantly at a very low temperature to produce a cooling effect in the liquid itself. There is a great promise that temperatures far below those achievable by conventional methods become explorable and, eventually, it may become possible to enter the superfluid regime of the dilute He-3.


The schematic diagram of the experimental cell used in the adiabatic melting experiment.

Helium liquids at temperatures below 0.1 mK are essentially decoupled from any external devices, so that the measurements on the status of the experiment becomes exceedingly difficult in the regime we are about to enter. We have equipped the experimental cell with an ultra sensitive capacitive pressure transducer to indicate any anomalies in the melting pressure. Also, a couple of vibrating wire resonators within the liquid volume will be used to monitor the damping of the motion of the resonators due to the quasiparticle excitations in the surrounding medium. The onset of superfluidity kills such excitations in an exponential manner below the transition point.