Analog of the dc Josephson effect in superfluid helium

An experiment is described in which we study the flow of helium through a 20-μ orifice which connects two helium baths. Closed capacitors are used to measure the helium level. Flow-gravitational-head difference characteristics are traced for various temperatures from 1.15 to 2.26 °K. Subcritical and supercritical flow are clearly observed, and the effect of temperature on the relation between the chemical potential and the level difference is discussed. Abrupt appearance of supercritical flow is observed. With a quartz transducer placed in front of the coupling hole, a decrease and subsequent increase of the flow velocity with quartz voltage is measured.