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Suspension of particles in the superfluid wind tunnel Chung, David Yih

Abstract

This thesis describes the investigation of hydrodynamic properties of pure superfluid flow in liquid helium II by observing the motion of suspended particles in a special experimental arrangement called 'Superfluid Wind Tunnel'. The flow properties of pure superfluid in different velocity regions have been investigated by using particles made with a suitable mixture of hydrogen and deuterium gases as indicators. Two critical velocities, Vp,c and Vs,c, corresponding to 0c and 0t of the oscillating sphere experiments (Benson and Hallett (1956)) have been found. Below Vp,c, the superfluid flow is a perfect potential flow of zero viscosity. Above Vp,c quantized vortex lines are created, therefore the pure superfluid flow breaks down. On the other hand in the vicinity of Ys,c, the starting point of fully developed turbulence, the magnitude of turbulent fluctuations has a maximum which confirms Feynman's prediction (1955) about critical velocity. A rough calculation shows that the velocities of a particle, which obtains energy from a segment of quantized vortex line, are of the same order as that of experimental values. This suggests that by this way, other than Vinen's (1961) vibrating wire experiment, the quantization of superfluid circulation in units of h/m might be verified by visual observations.

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