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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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