QFS2016 Book of Abstracts

Abstracts

P3.36 Turbulent Transition in Superfluid 4 He Oscillatory Flows Martin James Jackson(1), David Schmoranzer(1), Ladislav Skrbek(1), Viktor Tsepelin(2), Andrew John Woods(2) and Jakub Bahyl(3) 1) Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 3, 121 16, Prague 2, Czech Republic 2) Physics Department, Lancaster University, Lancaster, LA1 4YB, United Kingdom 3) Faculty of Mathematics, Physics and Informatics, Comenius University in Bratislava, Mlynsk ´a dolina F1, 842 48, Bratislava, Slovak Republic We discuss recent investigations into the transition to turbulence in oscillatory flows of superfluid 4 He. We studied the in-line forces acting on a quartz tuning fork with a 6.5 kHz fundamental and a 40 kHz flexural resonant mode in the temperature range 10mK to 2.17 K. By extending the accessible range of velocities with respect to previous works, we have observed more than one distinct hydrodynamic critical velocity at low temperatures. We discuss the significance of these critical velocities, focusing on the behaviour of pure superfluid at very low temperatures. In the two-fluid regime, we were able to determine the vortex line density generated by the fork from the attenuation of second sound. We present results which characterize quantitatively the formation of classical and quantum turbulence and we show that both can arise separately. P3.37 Transition to turbulence in He II due to a double paddle oscillator David Schmoranzer(1), Martin James Jackson(1), Elisa Zemma(2) and Javier Luzuriaga(2) 1) Faculty of Mathematics and Physics, Charles University, Ke Karlovu 3, 121 16, Prague, Czech Republic 2) Centro Atomico Bariloche, Avda. E.Bustillo, S. C. de Bariloche, Rio Negro, Argentina We present results on the transition to turbulence in isotopically pure superfluid 4 He due to an oscillating double-paddle structure, investigated in the temperature range from 20 mK (pure superfluid) to 1100 mK (two-fluid regime). The double-paddle displays a high-Q resonance which is strongly non-linear even at very low drives in He II as well as in vacuum. Critical velocities for the onset of non-linear drag force are clearly identified and compared to other experimental results on oscillators in He II such as tuning forks or vibrating grids. The utility of the micromachined double-paddle as a new type of quantum turbulence generator/detector for very low temperatures is discussed.

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