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Volz, Stephen Michael 2015-05-13T15:41:56Z 2015-05-13T15:41:56Z 10000-01-01 1987 1987 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. Made available in DSpace on 2015-05-13T15:41:56Z (GMT). No. of bitstreams: 2 license.txt: 4848 bytes, checksum: 96035ab3f5e1c23cc7138a224ce498bd (MD5) 8711897.PDF: 3229174 bytes, checksum: b55e2e07c09aa86cbfc42c0f2ad88a46 (MD5) Previous issue date: 1987 Embargo set by: Seth Robbins for item 78616 Lift date: Forever Reason: Restricted to the U of I community idenfinitely during batch ingest of legacy ETDs Restricted to the U of I community idenfinitely during batch ingest of legacy ETDs U of I Only 128 p. Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1987. http://hdl.handle.net/2142/77405 (UMI)AAI8711897 eng Physics, Condensed Matter Measurements of Vortex Diffusivity in 2d Superfluid Helium-4 text Physics Physics University of Illinois at Urbana-Champaign Dissertation Ph.D.