Files in this item



application/pdf1987_gillis.pdf (8MB)Restricted to U of Illinois


Title:Model for the onset of nonlinear flow dissipation in 2D superfluid helium films
Author(s):Gillis, Keith Alan
Doctoral Committee Chair(s):Mochel, J.M.
Department / Program:Physics
Subject(s):nonlinear flow dissipation
2D superfluid helium films
flow velocity
renormalization group calculation
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.
Issue Date:1987
Genre:Dissertation / Thesis
Rights Information:1987 Keith Alan Gillis
Date Available in IDEALS:2011-06-02
Identifier in Online Catalog:1269150

This item appears in the following Collection(s)

Item Statistics