University of Illinois Urbana-Champaign

Model for the onset of nonlinear flow dissipation in 2D superfluid helium films

Gillis, Keith Alan

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Description

Title
Model for the onset of nonlinear flow dissipation in 2D superfluid helium films
Author(s)
Gillis, Keith Alan
Issue Date
1987
Doctoral Committee Chair(s)
Mochel, J.M.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
  • nonlinear flow dissipation
  • 2D superfluid helium films
  • flow velocity
  • renormalization group calculation
Language
en
Abstract
A model for the onset of nonlinear dissipation in AC and DC flows is presented as an extension of the linear theory of Ambegaokar, Halperin, Nelson, and Siggia to include to flow velocity. The renormalization group calculation is carried out on a computer to determine the dissipation as a function of superfluid velocity. We find the onset of nonlinear dissipation is driven by two mechanisms whose relative contributions are temperature dependent. The free vortex contribution is most important at the higher temperatures whereas the bound pair contribution is dominant at low temperatures. The model is fitted to experimental measurements with two weakly coupled adjustable paramters: the vortex diffusivity and a free vortex creation time. Our model does not predict a critical velocity in the usual sense except at T=O, but we define a characteristic velocity in order to compare the theory with experiment. At T=O we find a critical velocity given by the Feynman criterion, where the frequency dependent vortex diffusion length coincides with the zero in the vortex energy. In addition, a novel experimental apparatus using a 3p. I.D. capillary to allow us to change the helium film thickness at low temperatures is described.
Type of Resource
text
Permalink
http://hdl.handle.net/2142/25223
Copyright and License Information
1987 Keith Alan Gillis

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Graduate Theses and Dissertations at Illinois