We study fundamental properties of superfluidity and the turbulent state of superfluid 4He, known as quantum turbulence (QT).
We are interested in examining the electrical activity of 4He, exciting it and detecting it by the propagation of second-sound in He II, the superfluid phase of liquid helium. Second-sound is a sound mode which arises from the relative motion of the normal (viscous, entropic) component and the superfluid (inviscid, non entropic) component of He II. The out-of-phase oscillation of the two component densities results into a temperature wave. We generate and detect second sound using the mechanical vibration of nuclepore membranes.
Electrical activity in helium is a weak but remarkable effect, considering its spherically symmetrical and electrically neutral atoms, and for this reason it may lead to new understanding of electro-physical properties of helium.
Because of quantum mechanical restrictions, rotational motion in a superfluid is only possible by the spontaneous nucleation of topological defects in the form of thin vortex lines with quantized velocity circulation. A complex tangle of interacting vortex lines is the most general configuration of QT.
Within the Joint Low Temperature Laboratory framework we are studying experimentally QT in 4He in the high and low temperature limit, with techniques including: bellows-driven turbulent flows in channels, turbulence induced by vibrating objects, visualization of turbulence by illuminated particles, determination of vortex tangle density by attenuation of second-sound.
Superfluid turbulence is a fundamental quantum property of matter, but also it bears important similarities with turbulence in classical fluids. Since the quantum vortex is a simpler, better defined object than the classical vortex, this is expected to enhance the understanding of classical turbulence too.
Research team: T. Chagovets, S.Babuin
More information at website of Superfluidity Laboratory.
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