Superfluid Liquid Research Articles

Relativistic hydrodynamics of a superfluid liquid

Superfluid liquid moving with relativistic velocities is studied. Thermodynamical identities are derived. The variational principle enabling one to obtain nondissipative equations of hydrodynamics is constructed. An expression for the energy-momentum tensor is found. The dissipative terms in the equations of hydrodynamics are studied.

Hydrodynamic Equations of 3He-a Phase Superfluid Liquid

A generalized theory of 3He-A phase superfIuid is establisped, which can comprise the Khalatnikov-Lebedev’s theory treated as a special case. The starting point of this work is the Zilsel’s principle in which the density of the superfluid component is defined as an independent variable. It has the advantage of including naturally the “heating effect” of 3He-A superfluid liquid, whereby overcoming the difficulties encountered in Khalatnikov-Lebedev’s theory.

On a mechanism of magnetic field generation in pulsars

Consideration is given to a two-component superfluid neutron-proton Fermi liquid in the npe phase of a neutron star. Equations are obtained for the thermal Green functions and the anomalous expectation values of the two-component Fermi liquid. The Green functions are used to obtain an expression for the superconducting proton current and an equation for the magnetic field within the star. It is shown that the rotation leads to the occurrence of proton vortex filaments at the positions of neutron vortex filaments. In addition, rotation leads to the occurrence of a weak homogeneous static magnetic field.

Thermal conductivity of several fibre-reinforced composites between 2 K and 300 K

Future X-ray observatories in space, such as European Space Agency's (ESA) X-ray evolving universe spectroscopy (XEUS) mission, will require cooling to the region 10–100 mK to enable the utilisation of advanced cryogenic photon detectors in cryogenic spectrometer instruments. Such missions are envisaged to be completely cryogen-free, replacing the traditional superfluid liquid helium cryostat with a space worthy mechanically cooled system. As part of the Mullard Space Science Laboratory's (MSSL) adiabatic demagnetisation refrigerator (ADR) development programme, we have investigated the construction of a flight cryostat containing a 10 mK ADR (the MSSL double ADR (dADR)) that can be cooled by a single Astrium (formally Matra Marconi Space (MMS)) 4 K mechanical cooler. A proto-type dADR has been constructed and will be flight proven as part of a sounding rocket payload, where the dADR system will be used to cool an array of superconducting tunnel junction (STJ) detectors at the focus of an X-ray telescope.

Collective excitations of normal liquidHe4, at 3.1 K, studied by neutron inelastic scattering

Neutron inelastic scattering from normal liquid $^{4}\mathrm{He}$ at $T=3.1$ K and wave vectors in the region $0.2l~\ensuremath{\kappa}l~2.2$ ${\mathrm{\AA{}}}^{\ensuremath{-}1}$ reveals the existence of propagating collective excitations, as measured by peaks at finite energies in the dynamical structure factor $S(\ensuremath{\kappa}, \ensuremath{\omega})$. The spectra are in some respects similar to spectra of the superfluid liquid. The relation to other normal liquids, in particular to Rb and Ar, is discussed.

Superfluid plug as a control device for helium coolant

New results have been obtained on the characteristics of the superfluid plug as a nonmechanical control device for supplying cold helium vapour on demand from a container of superfluid helium. The superfluid plug is a device which has been proposed for space applications to serve as a phase separator for liquid helium in the superfluid state. Typical plugs are made of a porous material having pores of one to ten μm in diameter. The experimental arrangement is such that one side of the plug is in contact with the superfluid liquid helium while vapour at a low pressure (of order 1 to 10 torr) is maintained on the other side.The data reported here are for a plug with approximately 5 μm diameter pores. Temperatures, pressures, and flow rate were monitored during the experiment. A theoretical background and steady state data are presented on mass flow rates and pressures as a function of liquid temperature.The typical response of the flow rate to a change in heat input from a heater is an exponential rise or fall to an equilibrium flow rate which is proportional to the amount of heat input. The time constants of the exponential changes were measured for two heater control modes under study. The study has included an investigation of the important parameters effecting the dynamic response of the plug including the superfluid properties, plug material properties, plug pore size and plug permeability. Operating temperatures from 1.5 K to the lambda point were investigated and heating rates up to two watts were applied. These tests serve to demonstrate that the superfluid plug can be employed as a flow control device in a control system designed to provide coolant on demand.

Anisotropic gap distortion due to superflow and the depairing critical current in superfluid 3He-B

We have calculated the pair-breaking critical current for superfluid 3He-B at all temperatures by taking into account the anisotropic distortion of the order parameter in the presence of superflow. We find that the component of the order parameter along the flow δ∥ is strongly reduced, while δ⊥, the component perpendicular to the flow, slightly increases. The superfluid density ϱs has also been determined as a function of the superfluid velocity v s. Fermi liquid corrections are explicitly included and it is shown that these corrections lead to a drastic change in the functional dependence of δ∥, δ⊥, ϱs, etc., on v s. In contrast to this, the pair-breaking critical current is shown to be independent of the Fermi liquid corrections.

Vortex formation near proturberances on a solid surface and the structure of the Ginzburg-Pitaevski equations

It is shown that when a superfluid liquid flows around protuberances or corners on a solid boundary then areas analogous to local supersonic zones in a subsonic flux are formed, where hydrodynamical perturbations of the surfaces of discontinuity may initiate the nucleation of vortices.

Hydrodynamics of a superfluid bose liquid with allowance for dissipative processes in a model with weak interaction

Hydrodynamics of a superfluid bose liquid with allowance for dissipative processes in a model with weak interaction

Theory of the rotation of a superfluid liquid in pulsars with allowance for relativistic effects in vortices

Theory of the rotation of a superfluid liquid in pulsars with allowance for relativistic effects in vortices

Hamiltonian equations of hydrodynamics of anisotropic superfluid liquid 3HeA

On the basis of the Hamiltonian technique equations describing hydrodynamics of anisotropic superfluid liquid 3HeA are obtained. The conservation laws are formulated. Expressions for dissipative terms are found.

Erratum: Surface tension and boundary conditions for superfluid Fermi liquid. Size effect and the effect of a magnetic field on the phase diagram

Erratum: Surface tension and boundary conditions for superfluid Fermi liquid. Size effect and the effect of a magnetic field on the phase diagram

Equations of hydrodynamics and transport coefficients for a superfluid bose liquid

Equations of hydrodynamics and transport coefficients for a superfluid bose liquid

Free energy of superfluidHe3

We present a systematic scheme for calculating the free energy of superfluid Fermi liquids by an asymptotic expansion in the small parameter $\frac{{T}_{c}}{{T}_{F}}$. We use this scheme to evaluate the strong-coupling corrections to the free energy of superfluid $^{3}\mathrm{He}$. We show that the leading corrections can be expressed in terms of the normal-state quasiparticle scattering amplitude, and discuss the strong-coupling results using the $s\ensuremath{-}p$ approximation for the scattering amplitude.

Surface tension and boundary conditions for superfluid Fermi liquid. Size effect and the effect of a magnetic field on the phase diagram

The boundary conditions for the Ginzburg-Landau equations for an anisotropic superfluid Fermi liquid are obtained. The surface tension is taken into account. The observable surface tension is calculated for the simplest cases. It is shown that surface tension can lead to a profound effect on the phase diagram which is analogous to the one observed in a magnetic field. The influence of a magnetic field on the phase diagram is also calculated. (AIP)

Correlation theory of fluctuations of the surface of a transparent liquid in the field of strong optical radiation

A co-relation theory is given of fluctuations of the surface of a transparent liquid of arbitrary viscosity in the presence of strong optical radiation. It is shown that an analysis based on the well-known Onsager hypothesis gives an expression for the spectral density of fluctuations of the surface which is different from that obtained by introducing external fluctuation forces and assuming that the strength of these forces is governed by the equilibrium fluctuation-dissipation theorem. The theory is generalized to a superfluid liquid.

Maintaining the Unit of Voltage at PTB via the Josephson Effect

In Section I a report on high precision voltage comparisons between the mean EMF of the former PTB voltage standard (consisting of a group of 39 saturated Weston cells) and the Josephson reference voltage is presented. The experiments were carried out with a total uncertainty (1 σ) of 4 parts in 108. The measured rate of change of the mean EMF during a 1¾ year period was - 1.3 X 10-7 V per year. This voltage stability is sufficient to maintain the unit of voltage by this group of standard cells for several months until a new comparison with the Josephson reference voltage becomes necessary. Due to the effects of thermal EMF's in the millivolt circuit of the measuring system used at present, the Josephson reference voltage (≈ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> . mV) is only stable during a short time. In Section II a prototype cryogenic voltage standard developed at PTB is described. By immersing the main measurement components into the superfluid liquid helium bath, a long term voltage stability can be achieved. These components include the cryogenic resistive divider, consisting of a new copper alloy, and the SQUID null detector. The resistance ratio of the cryogenic resistive divider of 320:1 is determined by a ten-decade inductive voltage comparator operating at 84 Hz. The effects of power dissipation introduce only errors of second order because the currents in the calibration mode and the measurement mode are the same.

Elementary excitations in superfluid liquid helium based on the Bogoliubov-Zubarev formalism

The Bogoliubov-Zubarev (BZ) formulation of the superfluid Bose liquid in terms of density as a collective variable leads to a non-Hermitian Hamiltonian (${H}_{\mathrm{BZ}}$) for describing the elementary excitations. An appropriate mathematical framework for dealing with non-Hermitian operators is here employed for the first time to develop schemes for studying the elementary excitations of the Bose liquid. The energies of the ground and the first excited states associated with ${H}_{\mathrm{BZ}}$ in "perturbation" theory are derived. A consistent scattering theory appropriate to ${H}_{\mathrm{BZ}}$ is also given from which the two-roton scattering amplitude in the leading order of "perturbation" theory is explicitly deduced. A finite-temperature Green's-function theory is also presented. These results are shown to be equivalent to those based on the Sunakawa Hamiltonian. Results for the energy spectrum are also shown to be equivalent with those evaluated by means of a variation-perturbation procedure based on the method of correlated basis functions in the uniform limit.

"Sound" in superfluid liquids

The existence of two sounds of different natures in the superfluid liquid is one of the best known and most thoroughly investigated properties of helium. An enormous mass of experimental and theoretical material on wave processes in helium has accumulated during the years that have passed since the discovery of second sound. Interest in these problems has especially increased in the last decade, first, because of the discovery of third and fourth sound (oscillations that propagate when the normal component of the liquid is clamped), and second, because of the possibility of investigating ultrashort sound waves by neutron and photon scattering. In this article the fundamental theoretical concepts and experimental results concerning the propagation of sound waves of the several types in superfluid liquid (in He4 and He3-He4 solutions) are reviewed. Much attention is given to quantitative, as well as qualitative, comparison of the experimental results with theory. The bibliography has been made as complete as possible. The following topics are not discussed, although they touch directly upon the subject under review: the propagation of sound near the lambda point, the passage of waves across liquid-liquid and liquid-vapor interfaces, and the propagation of large-amplitude sound waves.

"Звук" в сверхтекучей жидкости

"Звук" в сверхтекучей жидкости