247 research outputs found
Turbulence in quantum fluids
This paper reviews briefly the recent important developments in the physics
of quantum turbulence (QT) in superfluid helium and atomic Bose-Einstain
condensates (BECs). After giving basics of quantum hydrodynamics, we discuss
energy spectrum, QT created by vibrating structures, visualization among topics
on superfluid helium. For atomic BECs we review three-dimensional QT,
two-component BECs, and spin turbulence in spinor BECs. The last part is
devoted to some perspectives of this issue.Comment: arXiv admin note: text overlap with arXiv:1208.0422, arXiv:0901.460
Hydrodynamic Instability and Turbulence in Quantum Fluids
Superfluid turbulence consisting of quantized vortices is called quantum
turbulence (QT). Quantum turbulence and quantized vortices were discovered in
superfluid He about 50 years ago, but innovation has occurred recently in
this field. One is in the field of superfluid helium. Statistical quantities
such as energy spectra and probability distribution function of the velocity
field have been accessible both experimentally and numerically. Visualization
technique has developed and succeeded in the direct visualization of quantized
vortices. The other innovation is in the field of atomic Bose-Einstein
condensation. The modern optical technique has enabled us to control and
visualize directly the condensate and quantized vortices. Various kinds of
hydrodynamic instability have been revealed. Even QT is realized
experimentally. This article describes such recent developments as well as the
motivation of studying QT.Comment: submitted to Proceedings of QFS201
Quantum turbulence: From superfluid helium to atomic Bose-Einstein condensates
This article reviews recent developments in quantum fluid dynamics and
quantum turbulence (QT) for superfluid helium and atomic Bose-Einstein
condensates. Quantum turbulence was discovered in superfluid He in the
1950s, but the field moved in a new direction starting around the mid 1990s.
Quantum turbulence is comprised of quantized vortices that are definite
topological defects arising from the order parameter appearing in Bose-Einstein
condensation. Hence QT is expected to yield a simpler model of turbulence than
does conventional turbulence. A general introduction to this issue and a brief
review of the basic concepts are followed by a description of vortex lattice
formation in a rotating atomic Bose-Einstein condensate, typical of quantum
fluid dynamics. Then we discuss recent developments in QT of superfluid helium
such as the energy spectra and dissipative mechanisms at low temperatures, QT
created by vibrating structures, and the visualization of QT. As an application
of these ideas, we end with a discussion of QT in atomic Bose-Einstein
condensates
Spin Turbulence in a Trapped Spin-1 Spinor Bose--Einstein Condensate
We numerically study spin turbulence in a two-dimensional trapped spin-1
spinor Bose--Einstein condensate, focusing on the energy spectrum. The spin
turbulence in the trapped system is generated by instability of the helical
structure of the spin density vector in the initial state. Our numerical
calculation finds that in the trapped system the spectrum of the spin-dependent
interaction energy in the ferromagnetic case exhibits a -7/3 power law, which
was confirmed in a uniform system by our previous study. The relation between
the -7/3 power law and the motion of the spin density vector is discussed by
investigating the orbits of dynamical variables in the spin space
Spherically symmetric formation of localized vortex tangle around a heat source in superfluid He
We study the dynamical process of the vortex tangle development under a
spherically symmetric thermal counterflow around a heat source submerged into a
bulk superfluid 4He. We reveal a peculiar vortex dynamics that is unique to
this geometry, which is greatly diverse from the vortex dynamics in a
homogeneous counterflow. Two types of heater are considered here, namely, a
spherical heater with a solid wall and a point-like heater. In both cases, a
spherical vortex tangle is formed surrounding the heater. The mechanism of
vortex tangle development in the vicinity of a solid wall is strongly governed
by Donnelly-Glaberson instability; while, far away from the heater or around a
point heater, the mechanism is governed by the dynamics of polarized vortex
loops in radial counterflow. The decay process of such localized vortex tangles
is also investigated and is compared with that of homogeneous vortex tangles
Numerical Studies of Counterflow Turbulence, Velocity Distribution of Vortices
We performed the numerical simulation of quantum turbulence produced by
thermal counterflow in superfluid {\rm He} by using the vortex filament
model. The pioneering work was made by Schwarz, which has two defects. One is
neglecting non-local terms of the Biot-Savart integral (localized induction
approximation, LIA), and the other is the unphysical mixing procedure in order
to sustain the statistically steady state of turbulence. We succeeded in making
the statistically steady state without the LIA and the mixing. This state shows
the characteristic relation between the
line-length-density and the counterflow relative velocity with the
quantitative agreement of the coefficient with some typical
observations. We compare our numerical results to the observation of experiment
by Paoletti {\it et al}, where thermal couterflow was visualized by solid
hydrogen particles.Comment: 6 pages, 12 figures, svjour3.st
Spin-superflow turbulence in spin-1 ferromagnetic spinor Bose-Einstein condensates
Spin-superflow turbulence (SST) in spin-1 ferromagnetic spinor Bose-Einstein
condensates is theoretically and numerically studied by using the spinor
Gross-Pitaevskii (GP) equations. SST is turbulence in which the disturbed spin
and superfluid velocity fields are coupled. Applying the Kolmogorov-type
dimensional scaling analysis to the hydrodynamic equations of spin and velocity
fields, we theoretically find that the -5/3 and -7/3 power laws appear in
spectra of the superflow kinetic and the spin-dependent interaction energy,
respectively. Our numerical calculation of the GP equations confirms SST with
the coexistence of disturbed spin and superfluid velocity field with two power
laws.Comment: 7 pages, 5 figure
Counterflow quantum turbulence in a square channel under the normal fluid with a Poiseuille flow
We perform a numerical analysis of superfluid turbulence produced by thermal
counterflow in He II by using the vortex filament model. Counterflow in a low
aspect ratio channel is known to show the transition from laminar flow to the
two turbulent states TI and TII. The present understanding is that the TI has
the turbulent superfluid and the laminar normal fluid but both fluids are
turbulent in the TII state. This work studies the vortex tangle in the TI
state. Solid boundary condition is applied to walls of a square channel, and
the velocity field of the normal fluid is prescribed to be a laminar Poiseuille
profile. An inhomogeneous vortex tangle, which concentrates near the solid
boundaries, is obtained as the statistically steady state. It is sustained by
its characteristic space-time oscillation. The inhomogeneity of the vortex
tangle shows the characteristic dependence on temperature, which is caused by
two competitive effects, namely the profile of the counterflow velocity and the
mutual friction.Comment: submitted to the proceedings of LT2
Onsager vortex formation in two-component Bose-Einstein condensates
We numerically study the dynamics of quantized vortices in two-dimensional
two-component Bose-Einstein condensates (BECs) trapped by a box potential. For
one-component BECs in a box potential, it is known that quantized vortices form
Onsager vortices, which are clusters of same-sign vortices. We confirm that the
vortices of the two components spatially separate from each other-even for
miscible two-component BECs-suppressing the formation of Onsager vortices. This
phenomenon is caused by the repulsive interaction between vortices belonging to
different components, hence, suggesting a new possibility for vortex phase
separation.Comment: 4 pages, 4 figure
Expansion of a Bose-Einstein Condensate with Vortices
The expansion of Bose-Einstein condensates (BECs) is numerically studied.
Usually, the aspect ratio of a condensate is inverted due to the anisotropy of
the uncertainty principle. In turbulent BECs, however, the aspect ratio remains
constant. The reason for this phenomenon is still unknown, being a challenging
topic in the study of quantum turbulence. Here, the two-dimensional
Gross-Pitaevskii equation is solved and the time development of the aspect
ratio and of the radii of the condensates are calculated in the presence of
vortices. The results indicate that vortex pairs must be added to a condensate
in order to expand it while maintaining its aspect ratio. The anisotropy due to
the vortex pairs competes with that due to the uncertainty principle so that
the aspect ratio remains constant
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