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A helium II rotation experiment Turkington, Ralph Robert


In this thesis a rotating helium experiment is described. A special dewar featuring a separate experimental chamber and optical windows was constructed and operated satisfactorily. A small helium bucket was rotated using a magnetic coupling to the outside driving mechanism. Observations of the free helium surface were made using monochromatic parallel light incident to the surface at an oblique angle. By observing the astigmatic images it was possible to calculate the curvature of the helium surface. Detecting the presence of angular momentum in this way we had hoped to elucidate the findings of Hall (1957) and Walmsey and Lane (1958). Their results suggest a "disappearance" or non-conservation of angular momentum at low angular velocities. The angular velocities in our experiment ranged from 1.58 to 13.7 radians per second, the lower value being limited by surface disturbances. Over this range classical behaviour of the helium surface was observed, so we conclude that the "disappearing" angular momentum phenomenon is confined to angular speeds lower than 1.58 radians per second. The effect of surface tension upon the shape of the rotating helium surface was considered at the lower angular velocities. An argument is advanced which shows that if certain scaling conditions are satisfied a helium model may be constructed. This entails choosing another liquid with suitable density and surface tension and matching, by calculation, the diameter of the container. In this way the curvature of the model is related to the helium surface curvature for both stationary and rotational states. From this we calculate the curvature-angular velocity relationship, which is shown to be in agreement with the observed helium data. It appears that there need be no lower angular velocity limitation due to surface tension in wide bucket rotating helium experiments. The rate of formation of curvature was also examined in a few instances. A review of the general properties of liquid Helium II and some of the hydrodynamical aspects are also presented.

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