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

Thesis/Dissertation · Thu Jan 01 04:00:00 EST 1987

OSTI ID:5330428

Gillis, K A

A model for the onset of nonlinear dissipation in a-c and d-c 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. 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 parameters: the vortex diffusivity and a free-vortex creation time. The model does not predict a critical velocity in the usual sense except at T = O, but a characteristic velocity is defined in order to compare the theory with experiment. At T = O, a critical velocity given by the Feynman criterion is found, where the frequency-dependent vortex diffusions length coincides with the zero in the vortex energy. In addition, a novel experimental apparatus using a 3..mu..I.D. capillary to allow change of the helium film thickness at low temperatures is described.

• Research Organization: Illinois Univ., Urbana (USA)
• OSTI ID: 5330428
• Country of Publication: United States
• Language: English

Related Subjects

640450* -- Fluid Physics-- Superfluidity
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
COMPUTER CALCULATIONS
CRITICAL VELOCITY
FLOW MODELS
MATHEMATICAL MODELS
NONLINEAR PROBLEMS
RENORMALIZATION
SUPERFLUIDITY
TEMPERATURE DEPENDENCE
VELOCITY