The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
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Numerical Calculations on Vortex Phenomena in Helium Superfluids

Juha Kopu

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Engineering Physics and Mathematics for public examination and debate in Auditorium F1 at the Helsinki University of Technology (Espoo, Finland) on the 9th of June, 2001, at 12 o'clock noon.

Overview in PDF format (ISBN 951-22-5489-1)   [304 KB]
Dissertation is also available in print (ISBN 951-22-5488-3)

Abstract

This thesis reports numerical calculations on quantized vortices in 4He and 3He superfluids. Vortices are of crucial importance in understanding many of the superfluid properties. All the calculations presented in the thesis have experimental relevance, either in understanding measured results or in predicting the outcome of planned experiments.

Superfluid 4He has been observed to exhibit incomplete wetting on certain solid substrates. The variations in the thickness of the fluid layer are explained by a model with a nonuniform distribution of pinned vortices.

Superfluid 3He under weak perturbations (due to container walls, flow and magnetic fields) is studied with the hydrostatic theory. Within this theory, the equilibrium properties of the superfluid are controlled by the distribution, i.e. the texture, of the order parameter describing the superfluid state.

In the anisotropic A phase of 3He, vorticity usually appears in doubly-quantized continuous vortices, having no singular core. They can be created by applying a flow with a velocity exceeding an experimentally measurable threshold. The critical velocity can be theoretically identified with the instability of the underlying order-parameter distribution. The flow textures and critical velocities in 3He-A are calculated for different initial configurations in both one-dimensional and two-dimensional geometries.

The full transverse NMR spectrum of 3He-B in a cylindrical container is calculated numerically. The effects of rotation, magnetic field and the number of vortices are included in the model. The results are used to determine the optimal sensitivity for observing changes in the number of vortices, the finite-size effect due to the end plates of the cylinder, and the change of absorption induced by the presence of a spin-mass vortex.

This thesis consists of an overview and of the following 6 publications:

  1. R. Luusalo, A. Husmann, J. Kopu, and P. J. Hakonen, Pseudo-contact angle due to superfluid vortices in 4He, Europhys. Lett., vol. 50 (2), pp. 222-228 (2000).
  2. J. Kopu, R. Hänninen, and E. V. Thuneberg, One-dimensional textures and critical velocity in superfluid 3He-A, Phys. Rev. B, vol. 62, pp. 12374-12380 (2000).
  3. V. M. H. Ruutu, J. Kopu, M. Krusius, Ü. Parts, B. Plaçais, E. V. Thuneberg, and W. Xu, Critical velocity of vortex nucleation in rotating superfluid 3He-A, Phys. Rev. Lett., vol. 79, pp. 5058-5061 (1997).
  4. J. Kopu and E. V. Thuneberg, Soliton-limited superflow in 3He-A between parallel plates, accepted for publication in J. Low Temp. Phys.
  5. J. Kopu, R. Schanen, R. Blaauwgeers, V. B. Eltsov, M. Krusius, J. J. Ruohio, and E. V. Thuneberg, NMR line shape of rotating 3He-B at large counterflow velocity, J. Low Temp. Phys., vol. 120, pp. 213-232 (2000).
  6. J. Kopu and M. Krusius, Spin-mass vortex in 3He-B: order-parameter texture and NMR signature, Report TKK-KYL-005 (2000), submitted to Phys. Rev. B.

Keywords: superfluid, vortices, texture, critical velocity, NMR

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© 2001 Helsinki University of Technology

Last update 2011-05-26