Effect of a Constriction on the Vortex Density in He II Superflow
We have performed experimental studies of the influence of a constriction on the vortex density in He II superflow. The vortex density in the flow is analyzed by measuring the extra attenuation α’ = α- α 0 (α 0 is the static attenuation) of a second-sound resonant wave. The experimental apparatus is similar to that described in Ref. 1 except that the constriction and the superleak are now allowed to stand at different places; in all of our experiments the superflow, thermomechanically driven by a heater, goes from the second-sound resonator (SSR) to the constriction and thus the second sound always probes the vortex density in the part of the tube which is beyond the constriction. The apparatus maintains a constant hydrostatic pressure difference along the fountain tube (typically 15 cm He) so the temperature difference between the heater chamber and the bulk (or SSR) is constant and corresponds to this hydrostatic fountain pressure as long as there is no important dissipation along the superflow.
KeywordsCritical Velocity Superfluid Helium Resonant Wave Heater Chamber Static Attenuation
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