Search results for "Quantum vortex"
showing 10 items of 11 documents
Nonlocal effects in superfluid turbulence: Application to the low-density- to high-density-state transition and to vortex decay
2005
We discuss a phenomenological equation for the evolution of vortex tangle in counterflow superfluid turbulence, which takes into account the influence of the nonlocal effects, introducing into the original equation of Vinen two simple corrective terms dependent on a nonvanishing ratio between the average separation between vortex lines and the diameter of the channel. The equation allows one to describe, in relatively good agreement with experimental results, the two turbulent regimes present in counterflow superfluid turbulence and the transition between them. The decay rate of the vortex line density L, when the heat flux is suddenly turned off, is also investigated; due to the simplicity…
Effective temperature and scaling laws of polarized quantum vortex bundles
2011
Abstract An effective non-equilibrium temperature is defined for (locally) polarized and dense turbulent superfluid vortex bundles, related to the average energy of the excitations (Kelvin waves) of vortex lines. In the quadratic approximation of the excitation energy in terms of the wave amplitude A, a previously known scaling relation between amplitude and wavelength k of Kelvin waves in polarized bundles, namely A ∝ k − 1 / 2 , follows from the homogeneity of the effective temperature. This result is analogous to that of the well-known equipartition result in equilibrium systems.
Effective thermal conductivity of helium II: from Landau to Gorter–Mellink regimes
2014
The size-dependent and flux-dependent effective thermal conductivity of narrow channels filled with He II is analyzed. The classical Landau evaluation of the effective thermal conductivity of quiescent He II is extended to describe the transition to fully turbulent regime, where the heat flux is proportional to the cubic root of the temperature gradient (Gorter–Mellink regime). To do so, we use an expression for the quantum vortex line density L in terms of the heat flux considering the influence of the walls. From it, and taking into account the friction force of normal component against the vortices, we compute the effective thermal conductivity as a function of the heat flux, and we disc…
Vortex density waves and high-frequency second sound in superfluid turbulence hydrodynamics
2010
In this paper we show that a recent hydrodynamical model of superfluid turbulence describes vortex density waves and their effects on the speed of high-frequency second sound. In this frequency regime, the vortex dynamics is not purely diffusive, as for low frequencies, but exhibits ondulatory features, whose influence on the second sound is here explored.
Turbulent Superfluid Profiles and Vortex Density Waves in a Counterflow Channel
2012
In this paper we study the two-dimensional profiles of the superfluid component velocity and the quantized vortex-points density in a counterflow channel where the influence of the walls cannot be neglected. The numerical results obtained show the presence of vortex density waves in the channel, as shown in a recent paper by means of the one-fluid model.
Non-equilibrium Thermodynamical Description of Superfluid Transition in Liquid Helium
2017
In previous papers a phase field model for λ-transition in 4He was proposed, which is able to describe the influence of the heat flux on the temperature transition. The model presented here generalizes previous results taking into account of a homogeneous presence of quantized vortices below the λ-transition. As parameter that controls the transition, a dimensionless field f linked to the modulus of the condensate wave function is used. In addition to the field f , the resulting model chooses the following field variables: Density, velocity, temperature and heat flux. Nonlocal terms to describe inhomogeneities in the field variables and dissipative effects of mechanical and thermal origin…
Non-equilibrium temperature of well-developed quantum turbulence
2009
Abstract A non-equilibrium effective temperature of quantum vortex tangles is defined as the average energy of closed vortex loops. The resulting thermodynamic expressions for the entropy and the energy in terms of the temperature of the tangle are confirmed by a microscopic analysis based on a potential distribution function for the length of vortex loops. Furthermore, these expressions for the entropy and energy in terms of temperature are analogous to those of black holes: this may be of interest for establishing further connections between topological defects in superfluids and cosmology.
Classical and quantum vortex leapfrogging in two-dimensional channels
2020
The leapfrogging of coaxial vortex rings is a famous effect which has been noticed since the times of Helmholtz. Recent advances in ultra-cold atomic gases show that the effect can now be studied in quantum fluids. The strong confinement which characterizes these systems motivates the study of leapfrogging of vortices within narrow channels. Using the two-dimensional point vortex model, we show that in the constrained geometry of a two-dimensional channel the dynamics is richer than in an unbounded domain: alongsize the known regimes of standard leapfrogging and the absence of it, we identify new regimes of backward leapfrogging and periodic orbits. Moreover, by solving the Gross-Pitaevskii…
Non-equilibrium thermodynamics, heat transport and thermal waves in laminar and turbulent superfluid helium
2018
This review paper puts together some results concerning non equilibrium thermodynamics and heat transport properties of superfluid He II. A one-fluid extended model of superfluid helium, which considers heat flux as an additional independent variable, is presented, its microscopic bases are analyzed, and compared with the well known two-fluid model. In laminar situations, the fundamental fields are density, velocity, absolute temperature, and heat flux. Such a theory is able to describe the thermomechanical phenomena, the propagation of two sounds in liquid helium, and of fourth sound in superleak. It also leads in a natural way to a two-fluid model on purely macroscopical grounds and allow…
Vortex creep crossover in YBCO/PrBCO superlattices during standard magnetization relaxation measurements
2011
We investigated the relaxation of the irreversible magnetization in a series of 200?nm thick YBa2Cu3O7/PrBa2Cu3O7 [(YBCO)n/(PrBCO)m] superlattices, where the thickness m of the nonsuperconducting PrBCO layer (measured in unit cells) was kept to m = 4 (sufficient to decouple the superconducting YBCO layers), whereas the thickness n of the YBCO layer was varied between 2 and 20 unit cells. The analysis of standard zero-field-cooling dc magnetization relaxation data obtained in the low temperature T region with the applied magnetic field H oriented along the c axis reveals the occurrence of a crossover elastic (collective) vortex creep at low T?plastic vortex creep at high T, generated by the …