Approaching the zero-temperature limit in superfluid dynamics and dissipation

Jaakko Hosio

    Research output: ThesisDoctoral ThesisCollection of Articles

    Abstract

    Most collective physical systems freeze and become immobile at zero temperature. Thus, there exist few systems where hydrodynamics can be experimentally studied in the zero-temperature limit. Most notable among these are the helium superfluids which remain in liquid state down to zero temperature and may support dissipationless superflow at sufficiently low flow velocities. The measurements of this thesis present the first information on the interplay of laminar and turbulent flow at higher velocities in the zero-temperature regime and the associated dissipation in these flow states. In contrast to earlier beliefs, the results show that there exist residual dissipation mechanisms in both cases which cause damping even in the zero-temperature limit. A remarkable feature of superfluids is the quantization of flow through the creation of quantized vortex lines. These are formed at higher flow velocities, usually at some critical velocity. At higher temperatures the motion of vortices is damped by their interaction with the normal excitations, but this source of dissipation vanishes rapidly towards zero temperature. Thus, the motion of vortices should become dissipationless in the zero-temperature regime. However, as in viscous fluids, the smaller the dissipation the easier the flow is perturbed and becomes turbulent. Accordingly, vortex flow was expected to be turbulent in most experimentally achievable situations in the zero-temperature limit. In this thesis superfluid dynamics is explored in a rotating ultra-low-temperature refrigerator with nuclear magnetic resonance and with measurements of Andreev scattering of ballistic quasiparticle excitations from quantized vortex lines in a cylindrical sample of superfluid helium-3. In an axially symmetric smooth-walled container, vortex flow turned out to be laminar, but perturbations, such as breaking the axial symmetry with obstacles or by changing the surface friction, was found to lead to turbulence. To stabilize laminar flow, the minimization of surface interactions is found to be of major importance. In spite of the sub-millikelvin temperatures, which are needed for the present studies, the advantage of superfluid helium-3 over the experimentally more accessible helium-4 superfluid is the more than two orders of magnitude larger vortex core diameter which reduces decisively disturbances in the flow of the vortex ends along solid walls.
    Translated title of the contributionDynamiikka ja häviöt supranesteessä lähestyttäessä nollalämpötilarajaa
    Original languageEnglish
    QualificationDoctor's degree
    Awarding Institution
    • Aalto University
    Supervisors/Advisors
    • Kaivola, Matti, Supervising Professor
    • Eltsov, Vladimir, Thesis Advisor
    Publisher
    Print ISBNs978-952-60-4849-9
    Electronic ISBNs978-952-60-4850-5
    Publication statusPublished - 2012
    MoE publication typeG5 Doctoral dissertation (article)

    Keywords

    • hydrodynamics
    • helium-3
    • superfluid
    • quantized vortices
    • turbulent and laminar flow
    • dissipation

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