THE DETERMINATION OF THE ENERGY BARRIER FOR PHASE SLIPS IN SUPERFLUIDHE-4

The velocity dependence of the energy barrier for vortex creation in m icroscopic apertures is determined. When compared to results from othe r laboratories, the energy barrier seems to be a universal function of velocity. This universality suggests that the vortex nucleation proce ss is independent of the microscopic surface structure of the aperture . In DC flow experiments, the vortices are nucleated at rates lip to 7 00 kHz. In single phase slip experiments, the rate of nucleation is on the order of 10 Hz. Each of these types of experiments gives the ener gy barrier in a different velocity regime. The energy barrier has more curvature, as a function of velocity, than can be accounted for by th e half-ring model of vortex nucleation.