Measurements of Vortex Diffusivity in 2d Superfluid Helium-4

Volz, Stephen Michael

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https://hdl.handle.net/2142/77405 Copy

Description

Title

Measurements of Vortex Diffusivity in 2d Superfluid Helium-4

Author(s)

Volz, Stephen Michael

Issue Date

1987

Department of Study

Physics

Discipline

Physics

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

Physics, Condensed Matter

Language

eng

Abstract

We measure for the first time the characteristics of vortex induced superfluid flow dissipation at temperatures well below the Kosterlitz-Thouless superfluid transition temperature. Our studies are with films of coverage .25 < (sigma)(,s) < 1.9 superfluid atomic layers and with .55 < T(,KT) < 1.9(DEGREES)K. We use a third sound resonator combined with a new detection technique('17) which allows us to measure the vortex dynamics in the superfluid. Using a model developed by Gillis, et al('16,32), we fit the vortex induced dissipation to the data using as our adjustable parameters the vortex diffusivity D and the free vortex creation time (tau)(,free). We find D to be dependent on superfluid thickness and temperature (for 90 mK < T < 600 mK), but to be independent of superfluid flow velocity, frequency of the oscillating velocity field, and, with the exception of the thinnest film on Neon, of the ('4)He-substrate van der Waals strength. However we find the free vortex creation time (tau)(,free) to be a strong function of the van der Waals strength. Measurements on Ar yield (tau)(,free)('(TURN))T('-1.3) while on Ne (tau)(,free)('(TURN))T('-5.2). For the thinnest film on Ne ((sigma)(,s) = .60 layers) D is anomalously large yet temperature independent, and (tau)(,free) is immeasurably large. We postulate that surface roughness may affect the diffusivity of this thin film.

Graduation Semester

1987

Type of Resource

text

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http://hdl.handle.net/2142/77405

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