Disruption of superfluid helium film flow in filling capillary

Abstract Superfluid liquid 4He consists of superfluid and normal components. The superfluid component has zero viscosity and zero entropy, therefore flows without dissipation. The normal component carries the heat and can produce a high velocity flow which leads to very high thermal conductivity. In neutron scattering and muon spectroscopy experiments with powder samples the 4He gas is often used as exchange medium to thermalise the sample. Below 2 K the inner surface of capillary, used for dosing of exchange gas into experimental can, is covered with superfluid 4He film that provides strong thermal link between parts with different temperatures. This thermal link affects performance of a dilution refrigerator that cools experimental can. In our experiment we used 0.1% mixture of 3He in 4He to disrupt superfluid helium film flow and, as a result, to reduce significantly parasitic thermal flow to the experimental can. Addition of a small amount of 3He into 4He is allowing significant improvement of thermal performance of a dilution refrigerator which is affected by high thermal conductivity of a superfluid helium film formed in a capillary used for dosing helium exchange gas into powder samples for thermalisation.