Abstract
We report measurements of quantum turbulence generated by a vibrating grid in superfluid $^3$He-B at zero pressure in the zero temperature limit. Superfluid flow around individual vortex lines Andreev-reflects incoming thermal ballistic quasiparticle excitations, and allows non-invasive detection of quantum vortices in $^3$He-B. We have compared two Andreev reflection-based techniques traditionally used to detect quantum turbulence in the ballistic regime: quasiparticle transmission through and reflection from ballistic vortex rings and a turbulent tangle. We have shown that the two methods are in very good agreement and thus complement each other. Our measurements reveal that vortex rings and a tangle generated by a vibrating grid have a much larger spatial extent than previously realised. Furthermore, we find that a vortex tangle can either pass through an obstacle made from a mesh or diffuse around it. The measured dependence of vortex signal as a function of the distance from the vibrating grid is consistent with a power-law behaviour in contrast to turbulence generated by a vibrating wire which is described by an exponential function.
Highlights
Quantum turbulence in the zero-temperature limit shares many of the general properties of its classical counterpart but is conceptually much simpler, being a tangle of singly quantized vortex lines in an incompressible fluid that possesses no viscous dissipation [1]
We report measurements of quantum turbulence generated by a vibrating grid in superfluid 3He-B at zero pressure in the zero temperature limit
Our results show that the two methods give virtually identical fractional screening and complement each other
Summary
Quantum turbulence in the zero-temperature limit shares many of the general properties of its classical counterpart but is conceptually much simpler, being a tangle of singly quantized vortex lines in an incompressible fluid that possesses no viscous dissipation [1]. A comparison is made between an incident quasiparticle flux scattered from an oscillating object in the presence and absence of quantum vortices [5] This technique has allowed turbulence at different distances from the source of quantum vortices to be observed [14,15], as well as the statistical properties of fluctuations in the steady state and the cross-correlation between various detectors to be measured [9,10,16]. The bolometric technique has been successfully applied to quantum vortices produced inside the BBR in order to study the energy decay of turbulence [22] and propagation of a rotating vortex front [23] In this manuscript, we use both transmission and reflection techniques to probe quantum vortices in the same region of our experimental volume. Our measurements are consistent with a recent theoretical result predicting a similar amount of Andreev reflection at low temperatures using “particle” and “energy” flux, which correspond to transmission and reflection techniques, respectively [24]
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