Second Sound Scattering in Superfluid Helium

Citation

Rösgen, Thomas (1985) Second Sound Scattering in Superfluid Helium. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/r8ge-j070. https://resolver.caltech.edu/CaltechETD:etd-10292003-161340

Abstract

Focusing cavities are used to study the scattering of second sound in liquid helium II. The special geometries reduce wall interference effects and allow measurements in very small test volumes.

In a first experiment, a double elliptical cavity is used to focus a second sound wave onto a small wire target. A thin film bolometer measures the side scattered wave component. The agreement with a theoretical estimate is reasonable, although some problems arise from the small measurement volume and associated alignment requirements.

A second cavity is based on confocal parabolas, thus enabling the use of large planar sensors. A cylindrical heater produces again a focused second sound wave. Three sensors monitor the transmitted wave component as well as the side scatter in two different directions. The side looking sensors have very high sensitivities due to their large size and resistance. Specially developed cryogenic amplifiers are used to match them to the signal cables.

In one case, a second auxiliary heater is used to set up a strong counterflow in the focal region. The second sound wave then scatters from the induced fluid disturbances.

Attempts to observe scattering from quantized vortex lines in the rotating parabolic cavity ultimately did not succeed, although a theoretical estimate seems to indicate a basic feasibility.

Thesis Files