Scattering of first and second sound waves by quantum vorticity in superfluid helium

We study the scattering of first and second sound waves by quantum vorticity in superfluid Helium using two-fluid hydrodynamics. The vorticity of the superfluid component and the sound interact because of the nonlinear character of these equations. Explicit expressions for the scattered pressure and temperature are worked out in a first Born approximation, and care is exercised in delimiting the range of validity of the assumptions needed for this approximation to hold. An incident second sound wave will partly convert into first sound, and an incident first sound wave will partly convert into second sound. General considerations show that most incident first sound converts into second sound, but not the other way around. These considerations are validated using a vortex dipole as an explicitely worked out example.     

Proposal of holography with second sound in helium II

The possibility of holography with second sound waves in He II is investigated theoretically. The radiation pressure of the second sound deforms the liquid-gas interface and the resulting relief could serve as the hologram for the optical reconstruction. The necessary heat current densities are calculated. Inhomogeneities in He II that could be observed by second sound are: stationary heat currents, variations of concentration of the isotope He³, and possibly systems of vortex lines.     

Cylindrical standing surface waves in superfluid helium

A theoretical analysis is given of the resonant frequencies of standing surface waves produced in a cylinder filled with superfluid⁴He. In particular, it is shown that a heat transfer coefficient involved in a recently proposed empirical boundary condition can be related to the Kapitza resistance.     

Sound conversion phenomena at the free surface of liquid helium. I. Calculation of the coefficients of reflection,transmission, and transformation of sound waves incident on the liquid-vapor interface of helium

On the basis of a set of boundary conditions describing quite generally mass and energy transport processes across the free surface of helium II, the acoustic coefficients of reflection, transmission, and transformation of first sound, second sound, and the sound wave propagating in the vapor are calculated in the case of perpendicular incidence of sound waves against the liquid-vapor phase boundary. Considering rigorously the influences of the Onsager surface coefficients, the isobaric thermal expansion coefficients, and the thermal conductivities of the liquid and the vapor, we derive sets of equations from which the acoustic coefficients are determined numerically. For estimations, simple explicit formulas of the acoustic coefficients are given. It is shown that the evaporation and energy transport processes occurring at the free surface of helium II due to the incidence of sound waves may be connected with appreciable energy dissipation. The surface absorption coefficients of first, second, and gas sound waves are deduced.     

Healing and relaxation in flows of helium II. Part II. First,second, and fourth sound

In Part I of this series, a theory of helium II incorporating the effects of quantum healing and relaxation was developed. In this paper, the propagation of first, second, and fourth sound is discussed. Particular attention is paid to sound propagation in the vicinity of the point where the effects of relaxation and quantum healing become important.Supported in part by a special research grant GR/A/0556 from the Science Research Council of Great Britain, and (for RNH) by U.S. Air Force grant AFOSR 76-2880 and National Science Foundation grant ENG-76-07354.     

Effect of Kapitza resistance on standing surface waves in superfluid helium

We analyze theoretically the resonant frequencies of standing surface waves produced by second sound in⁴He. In particular, we show that an empirical heat transfer coefficient involved in a recently proposed boundary condition can be related to Kapitza resistance. We also calculate the heat flux within the helium and deduce that the height of the surface waves is strongly frequency dependent.     

Underwater light polarization and radiance fluctuations induced by surface waves

The underwater light field is an ever-changing environment. Surface waves induce variability in the radiance and the light's polarization. We examined the dependence of the polarization fluctuations associated with diffuse light (not including contribution from direct skylight) on the viewing zenith angle (30 degrees, 70 degrees, and 90 degrees), solar zenith angle (23 degrees -72 degrees), depth of 0.5-3 m, and light wavelength (380-650 nm) while observing within the azimuthal plane in the wind-wave direction. Polarization and radiance fluctuated with time. Light variability (presented by the coefficient of variation calculated over a series of fluctuations in the radiance and percent polarization, and by the standard deviation calculated over a series of fluctuations in the e-vector orientation) was highest at a viewing zenith angle of 70 degrees , depended positively on the solar zenith angle, and decreased with depth at viewing zenith angles of 30 degrees and 70 degrees . Additionally, the variability of the percent polarization was significantly higher than that of the radiance. The temporal light fluctuations offer possibilities, such as enhancing the detection of transparent and reflecting objects; however, they set constraints on the optimal underwater polarization vision by both animals and by the use of instruments.     

Possible interfacial transport induced by small amplitude waves along solid helium–vacuum interfaces

We perform the macroscopic calculations of the possible entrainment in a cylinder filled with solid helium and vacancies. The wavy transport is induced by a small-amplitude surface elastic wave propagating along the flexible interface by considering the nonlinear coupling between the interface and the rarefaction effect. The possible critical bounds obtained for zero-flux states corresponding to specific rarefaction measure and wave number might be relevant to the rather small critical velocity or disappearance of superflow of solid helium.     

Influence of quantum turbulence on the evolution of moderate plane second sound heat pulses in helium II

Recent experiments have shown the existence of a very strong temperature overshoot behind a propagating second sound shock wave close to the heated surface. The ratio of the temperature overshoot to the shock wave amplitude depends strongly on the rest time between two consecutive heat pulses. These results can be reproduced by a simple theoretical model using only the Gorter-Mellink mutual interaction force and a vortex line density (VLD) evolution equation. The evolution equation is taken to be that proposed by Vinen as extended to include spatial dependence. The drift velocity of the VLD is assumed to have a specific form, and the initial VLD is chosen as a parameter. Experimental observations and existing physical considerations led to the formulation of the used theoretical model. The quantitative agreement between the theoretical calculations and experiments is fair for an overshoot ratio below about 3. At stronger heat pulses the agreement is only qualitative. The model describes well the mechanism of development of a hot layer close to the heated surface and the evolution of the counterflow velocity and temperature field behind the second sound shock wave and indicates possible improvements of the theoretical model.     

Experimental studies on fourth sound in superfluid helium

In a superfluid liquid-helium cavity packed with a fine powder, only the supercomponent is free to move and pressure waves transmitted by the supercomponent are called fourth sound. We have observed that the resonance frequency of the powder-filled chamber may be shifted by introducing vortices. Both static and dynamic measurements were made on the resonance frequency and signal height in order to explore the effect of exceeding the critical velocity of the superfluid in the powder-filled chamber.Supported by the Robert A. Welch Foundation, Houston, Texas.     

Characterization of laser hardened steels by laser induced ultrasonic surface waves

Ultrasonic surface waves are suitable for the characterization of surface hardened materials. This is shown on laser hardened turbine blades. The martensitic microstructure within the surface layer of surface hardened steels has a lower surface wave propagation velocity than the annealed or normalized substrate material. Because the propagation velocity depends on the ratio of layer thickness to wavelengthd/, its measurement allows the determination of the hardening depth. If the surface wave frequency is high enough, the surface wave propagates mainly within the hardened layer. A correlation of the surface wave velocity to the surface hardness has been found. Because the variation of the surface velocity in hardened steels is small, a high measurement accuracy is necessary to obtain the interesting hardening parameters with sufficient certainty. Therefore, a measuring arrangement has been developed where laser pulses, guided by optical fibers to the surface hardened structure, generate simultaneously surface wave pulses at two different positions. The two ultrasonic pulses are received by a piezoelectric transducer. The surface wave velocity is obtained from the time delay between these pulses which is determined by the cross-correlation method. To evaluate simultaneously surface waves with different penetration depths from the same signal acquisition, digital filtering has been used in connection with the cross-correlation.     

Use of the bare chip Cernox™ thermometer for the detection of second sound in superfluid helium

Bare chip Cernox™ thermometers model CX-1030 from LakeShore Cryotronics Inc. have been used to detect second sound in superfluid helium. This paper presents some examples of second sound measurements and comments on the electrical and thermal time constants of these thermometers.     

Instability induced in a relativistic plasma flux by the excitation of surface waves

An analysis is made of the instability of a plasma flux caused by the excitation of a new type of cylindrical surface electromagnetic waves at the interface between the flux and a stationary plasma. It is shown that, unlike the conventional case ε₁>0 and ε₂,<0, at the interface of a relativistic plasma beam there exist growing surface waves at frequencies corresponding to positive values of the permittivities on both sides of the discontinuity. For a given geometry and plasma density the critical parameter for the excitation of these waves is the wave radius of the flux. Pis’ma Zh. Tekh. Fiz. 23, 76–79 (March 12, 1997)     

Electronic surface states on liquid helium

Beginning with a microscopically obtained density profile near the free surface of liquid helium an analysis of the electronic surface states, both inside and outside, is carried out. For the potential barrier seen by electron bubbles trapped inside the surface layer we find an upper bound of 38 K, in comparison with experimental values ranging from 25 to 30 K. For outside states we find a binding energy of 9 K and a hydrogenlike spectrum. There are no adjustable parameters in the theory.     

Elastic waves in randomly stratified medium. Numerical calculations

Summary The propagation of elastic harmonic waves through a stratified slab is investigated. It is assumed a nonzero angle of inclination of an incident wave. The equations for the amplitudes of reflected and transmitted waves obtained in reference [1] are transformed to a form more convenient for numerical calculations and generalized for more complicated laminates. an example of the elastic waves propagating through the steel-titanium laminate in aluminimm environment is studied numerically. The limiting case where the density of stratification of the slab tends to infinity is analyzed. The dependence of the effective reflection properties on the material parameters of the strata is presented.     

Electromigration in Al thin films induced by surface acoustic waves: application to imaging

The propagation of a high amplitude surface acoustic wave in an Al thin film induces a large-scale electromigration phenomenon resulting in a permanent etching of the acoustic field in the film. The etched patterns depend on the time of propagation and on the acoustic characteristics. Preliminary observations of a few grooved structures in Al films have been performed by different techniques. A first explanation of this phenomenon based on dynamical Grinfeld instabilities is proposed. By providing permanent pictures of acoustic fields emitted by transducers, this effect could be used to perform imaging of surface acoustic wave propagation.     

Analysis on direct problem of S2 surface of helium turbine impeller by calling helium properties program

为了保证EAST大型低温系统的稳定运行,其核心部件氦透平膨胀机必须满足参数设计,利用流线曲率法对低温氦透平膨胀机T3叶轮流场进行计算.通过编程计算,得出T3叶轮子午面流场,分析得到进出口的参数压力和温度达到设计的要求.同时考虑到,T3叶轮进口参数处于高压、深低温区,此时工质氦不能看作理想气体,因此调用氦物性程序,使得结果更加符合实际情况.