{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/77405"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/77405","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"Measurements of Vortex Diffusivity in 2d Superfluid Helium-4","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.","abstract_html":"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.","abstract_has_math":false,"creators":["Volz, Stephen Michael"],"institution":"University of Illinois at Urbana-Champaign","degree_name":"Ph.D.","degree_level":"Dissertation","degree_discipline":"Physics","degree_department":null,"school":null,"contributors":[],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2015,"date_issued":"2015-05-13T15:41:56Z","date_published":"2015-05-13T15:41:56Z","updated_at":"2026-07-22T22:26:10Z","subjects":["Physics, Condensed Matter"],"languages":["eng"],"rights":[],"rights_urls":[],"identifier_entries":[{"key":"dc:identifier","label":"Identifier","values":["(UMI)AAI8711897"],"render_values":[{"text":"(UMI)AAI8711897","href":null,"code":true}]}]},"links":{"outbound_url":"http://hdl.handle.net/2142/77405","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:creator","label":"Author","values":["Volz, Stephen Michael"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2015-05-13T15:41:56Z","10000-01-01","1987"]},{"key":"dc:type","label":"Dc Type","values":["text"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Physics"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Dissertation"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Ph.D."]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["University of Illinois at Urbana-Champaign"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Physics, Condensed Matter"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["eng"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["http://hdl.handle.net/2142/77405","(UMI)AAI8711897"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["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). 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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). 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