Berlin 2018 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 95: Cold Atomic Gases, Superfluids, Quantum Fluids and Solids

TT 95.6: Talk

Thursday, March 15, 2018, 16:15–16:30, HFT-FT 131

Dynamics of the density of quantized vortices in counterflow turbulence — Emil Varga and •Ladislav Skrbek — Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic

Thermal counterflow of superfluid 4He represents the most extensively studied form of quantum turbulence, initiated by pioneering experiments of Vinen, who also introduced a phenomenological model for its description based on the concept of a random tangle of quantized vortices of vortex line density L. Recently the interest in thermal counterflow has been renewed and resulted in an intense theoretical debate about what form, if any, of the so-called Vinen equation accurately captures the dynamics of L. We address this problem experimentally, in a square channel equipped by three pairs of second sound sensors. Based on large statistics of experimental data in square-wave modulated thermally induced counterflow we investigate the phase portrait of general form of the governing dynamical Vinen-like equation and conclude that for sparse tangles all proposed forms of this equation provide equally adequate description of the growth of L while for dense tangles neither of them is satisfactory and cannot account for the significant slow-down in tangle growth rate as the steady state is approached. We claim, however, that agreement with theory is recovered if geometric parameter c2 introduced in numerical studies by Schwarz is allowed to vary with vortex line density which also greatly improves the prediction of the observed decay rate.

The support of the Czech Science Foundation under project GA17-03572S is acknowledged.