QFS2016 Book of Abstracts

Abstracts

O3.2 The decay of counterflow turbulence in superfluid 4 He J. Gao(1,2), W. Guo(1.2), V.S. L’vov(3), A. Pomyalov(3), L. Skrbek(4), E. Varga(4), W.F. Vinen(5) 1) National High Magnetic Field Laboratory, 1800 East Paul Dirac Drive, Tallahassee, Florida 32310, USA. 2) Florida State University, Mechanical Engineering Department, Tallahassee, Florida 32310, USA. 3) Weizmann Institute of Science, Department of Chemical Physics, Rehovat 76100, Israel. 4) Charles University, Faculty of Mathematics and Physics, Ke Karlova 3, 121 16 Prague, Czech Republic. 5) University of Birmingham, School of Physics and Astronomy, Birmingham B15 2TT, UK. Experiments, based on the attenuation of second sound and on the visualization of normal-fluid flow with metastable He2 excimer molecules, are reported, showing that the form of the decay of thermal counterflow turbulence in superfluid 4 He after a heat current is switched off depends on whether in the steady state there is turbulence in the normal fluid: in the absence of such turbulence, the decays follows that expected from Vinen’s phenomenological equations; in the presence of such turbulence, the decay has the more complicated form that is usually observed. A simple theory is presented that accounts, semi-quantitatively, for this more complicated form. O3.3 Interplay between ultraquantum and quasiclassical turbulence in 4 He in the T=0 limit P. M. Walmsley, A. I. Golov School of Physics and Astronomy, University of Manchester, Manchester, M13 9PL, UK We investigated free decay of the density, L(t), of tangled quantized vortices generated by negative ions in superfluid 4 He at T 0.2 K. By varying the current of ions and duration of their injection, we could control the initial energy of large-scale flow in the superfluid. Hence, either pure ultraquantum ‘Vinen’ (uncorrelated tangles decaying as L ≈ t − 1 ) or pure quasiclassical (structured tangles decaying as L ≈ t − 3 / 2 ) turbulence could be created, as well as a mixture of the two, in which the former decay law L(t) converts into the latter after a delay. The polarization (ratio of lengths of the structured and random components) of the tangle in its ultimate state is estimated.

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