565 research outputs found
Diffusion of an Inhomogeneous Vortex Tangle
The spatial diffusion of an inhomogeneous vortex tangle is studied
numerically with the vortex filament model. A localized initial tangle is
prepared by applying a counterflow, and the tangle is allowed to diffuse freely
after the counterflow is turned off. Comparison with the solution of a
generalization of the Vinen equation that takes diffusion into account leads to
a very small diffusion constant, as expected from simple theoretical
considerations. The relevance of this result to recent experiments on the
generation and decay of superfluid turbulence at very low temperatures is
discussed.Comment: 2 pages, 2 figure
The Generation of Turbulence by Oscillating Structures in Superfluid Helium at Very Low Temperatures
The paper is concerned with the interpretation of many experiments that have
been reported recently on the production of quantum turbulence by oscillating
spheres, wires and grids in both 4He and 3He-B at temperatures so low that
there is a negligible fraction of normal fluid. The experimental results are
compared with those obtained in analogous experiments with classical fluids and
with preliminary simulations of the quantum turbulence. Particular attention is
paid to observed values of drag coefficients and to the very different critical
velocities observed in 4He and 3He. It is tentatively concluded that in the
case of 4He behaviour may well be similar to that observed in the classical
analogues, with relatively small changes when the characteristic size of the
oscillating structure is not large compared with the quantized vortex spacing,
but that in the case of 3He behaviour is very different and due perhaps to very
rapid intrinsic nucleation of the quantized vortices.Comment: 13 pages, 9 figure
Derivation of the transverse force on a moving vortex in a superfluid
We describe an exact derivation of the total nondissipative transverse force
acting on a quantized vortex moving in a uniform background. The derivation is
valid for neutral boson or fermion superfluids, provided the order parameter is
a complex scalar quantity. The force is determined by the one-particle density
matrix far away from the vortex core, and is found to be the Magnus force
proportional to the superfluid density.Comment: Latex, 6 page
Quantum Turbulence in a Trapped Bose-Einstein Condensate
We study quantum turbulence in trapped Bose-Einstein condensates by
numerically solving the Gross-Pitaevskii equation. Combining rotations around
two axes, we successfully induce quantum turbulent state in which quantized
vortices are not crystallized but tangled. The obtained spectrum of the
incompressible kinetic energy is consistent with the Kolmogorov law, the most
important statistical law in turbulence.Comment: 4 pages, 4 figures, Physical Review A 76, 045603 (2007
Kolmogorov spectrum of superfluid turbulence: numerical analysis of the Gross-Pitaevskii equation with the small scale dissipation
The energy spectrum of superfluid turbulence is studied numerically by
solving the Gross-Pitaevskii equation. We introduce the dissipation term which
works only in the scale smaller than the healing length, to remove short
wavelength excitations which may hinder the cascade process of quantized
vortices in the inertial range. The obtained energy spectrum is consistent with
the Kolmogorov law.Comment: 4 pages, 4 figures and 1 table. Submitted to American Journal of
Physic
The approach to vortex reconnection
We present numerical solutions of the Gross--Pitaevskii equation
corresponding to reconnecting vortex lines. We determine the separation of
vortices as a function of time during the approach to reconnection, and study
the formation of pyramidal vortex structures. Results are compared with
analytical work and numerical studies based on the vortex filament method.Comment: 11 pages, 9 figure
Thermal dissipation in quantum turbulence
The microscopic mechanism of thermal dissipation in quantum turbulence has
been numerically studied by solving the coupled system involving the
Gross-Pitaevskii equation and the Bogoliubov-de Gennes equation. At low
temperatures, the obtained dissipation does not work at scales greater than the
vortex core size. However, as the temperature increases, dissipation works at
large scales and it affects the vortex dynamics. We successfully obtained the
mutual friction coefficients of the vortex dynamics as functions of
temperature, which can be applied to the vortex dynamics in dilute
Bose-Einstein condensates.Comment: 4 pages, 6 figures, submitted to AP
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