Helium Mass Flow Through a Solid-Superfluid-Solid Junction

We report the results of flow experiments in which two chambers containing solid He-4 are connected by a superfluid Vycor channel. At low temperatures and pressures, mechanically squeezing the solid in one chamber produced a pressure increase in the second chamber, a measure of mass transport through our solid-superfluid-solid junction. This pressure response is very similar to the flow seen in recent experiments at the University of Massachusetts: it began around 600 mK, increased as the temperature was reduced, then decreased dramatically at a temperature, T-d, which depended on the He-3 impurity concentration. Our experiments indicate that the flow is limited by mass transfer across the solid-liquid interface near the Vycor ends, where the He-3 collects at low temperature, rather than by flow paths within the solid He-4.