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Two types of quantum turbulence: mechanically VS thermally driven 4 He superflow in a channel

Two types of quantum turbulence: mechanically VS thermally driven 4 He superflow in a channel. Simone Babuin , Mathias Stammeier , Miloš Rotter , Ladislav Skrbek. SUPERFLUIDITY GROUP Joint Low Temperature Laboratory. Institute of Physics, Academy of Sciences of the Czech Republic &

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Two types of quantum turbulence: mechanically VS thermally driven 4 He superflow in a channel

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  1. Two types of quantum turbulence:mechanically VS thermally driven 4He superflow in a channel Simone Babuin, Mathias Stammeier, MilošRotter,LadislavSkrbek SUPERFLUIDITY GROUP Joint Low Temperature Laboratory Institute of Physics, Academy of Sciences of the Czech Republic & Faculty of Mathematics and Physics, Charles University Prague, Czech Republic

  2. The system counterflow N S sq 7 mm Liquid Helium-4 1.3 K < T < 2.0 K @ saturated vapour pressure 115 mm [Chagovets & Skrbek, PRL 100, 215302 (2008) JLTP 153,162 (2008)] (A) Mechanical flow generation: bellows [present work] (B) Thermal flow generation: counterflow heater

  3. What we measure Peak maximum Second sound resonance flow speed = 10 cm/s A0 A w0 A0 Temperature = 1.45 K A • Scattering of second sound waves against vortex lines • Assume vortex tangle homogeneous and isotropic • Take into account scattering depends on angle B(T): mutual friction coefficient k: quantum of circulation average vortex line length per unit volume

  4. Vortex line density Mechanically driven flow (A) Comparison with thermally drive flow Open symbols: from full resonant curve Full symbols: from peak maximum A B 1.58K 1.73K 1.92K 1.49K A B

  5. Slopes A B C D (SchwarzPRB 18 (1978) 245) 0.13 X 80 mm C Tough et al. PRL 46 (1981) 658

  6. A from extrapolation Critical velocity A B C from direct measurement

  7. Summary of the main facts • B: TC&LS (2008) • pure superflow • thermally driven • 7x7 mm2 sq channel • second sound att. • C: Tough (1981) • -pure superflow • thermally driven • 0.13 mm circ channel • temp gradients • D: Schwarz theory (1978) • counterflow in frame of normal component • no boundaries • A: present work • -pure superflow • mechanically driven • 7x7 mm2 sq channel • second sound att. • A and Bdisagree in (1), (2) and (3) • A, C and D agree in (1) and (2), but disagree in (3) • B, C and D agree in (3), but disagree in (1) and (2) Functional relation between L and v Magnitude of L across whole range of v Critical velocity

  8. Extra: comparison withL from other systems

  9. Extra: temperature differences The temperature is measured inside the bellows, and the difference is before and during a bellows compression

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