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Title:Measurements of Vortex Diffusivity in 2d Superfluid Helium-4
Author(s):Volz, Stephen Michael
Department / Program:Physics
Discipline:Physics
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:Ph.D.
Genre:Dissertation
Subject(s):Physics, Condensed Matter
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.
Issue Date:1987
Type:Text
Language:English
Description:128 p.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1987.
URI:http://hdl.handle.net/2142/77405
Other Identifier(s):(UMI)AAI8711897
Date Available in IDEALS:2015-05-13
Date Deposited:1987


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