Study of flow of superfluid He-II very near T-lambda

We report here preliminary data from an experiment studying flow of superfl uid helium through a slit orifice (of sub-micron width) very close to T-lam bda. Critical supercurrent (I-c) data are obtained from a step function dri ve to the diaphragm in a Helmholtz resonator cell. The superfluid density ( rho(s)) data can be obtained from the resonant frequency of the Helmholtz o scillator, as determined by transfer function of the resonator or from the free ringing after the step function excitation. Preliminary data shows tha t 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 th an expected, indicating a possible parallel flow path. Further investigatio ns are in progress. (C) 2000 Elsevier Science B.V. All rights reserved.