Study of flow of superfluid He-II very near Tλ

We report here preliminary data from an experiment studying flow of superfluid helium through a slit orifice (of sub-micron width) very close to T-lambda. Critical supercurrent (I-c) data are obtained from a step function drive to the diaphragm in a Helmholtz resonator cell. The superfluid density (rho(s)) data can be obtained from the resonant frequency of the Helmholtz oscillator, as determined by transfer function of the resonator or from the free ringing after the step function excitation. Preliminary data shows that I-c similar to rho(s)(1.27) and rho(s)(1.27) similar to t(0.73), where t is the reduced temperature. However, the magnitude of I-c is much larger than expected, indicating a possible parallel flow path. Further investigations are in progress. (C) 2000 Elsevier Science B.V. All rights reserved.