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Jun 1977

Volume 61, Issue S1, pp. S1-S96

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back to top Session I. Physical Acoustics III: Physical Acoustics of Superfluid Helium
Invited Papers
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Sounds of superfluid helium (A)

S. Putterman

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S19-S19 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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A review of the hydrodynamic interpretation of the various sound or collective modes which propagate in superfluid helium will be presented. These will be separated into two categories: (a) bulk geometries, (b) helium confined between walls as narrow as 10 Å. As regards the bulk, the thermal propagating waves (second sound) as well as ordinary density waves will be discussed. For the confined geometries third sound (analogous to long gravity waves with the restoring force replaced by the van der Waals attraction to the substrate) and fourth sound (another pressure wave propagated through a modified compressibility) will be discussed. Use of the propagation and attenuation of sound to measure various thermodynamic properties will be explored.
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First sound in superfluid helium (A)

H. J. Maris

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S19-S19 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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A description of those properties of superfluid helium which make it of special interest to acousticians will be given. Two areas of recent research will then be treated in detail. The first of these is the study of the scattering of sound by thermal waves in liquid helium. This work has led to a better understanding of the dispersion of the thermal waves. The second topic is the transmission of first sound across interfaces between solids and liquid helium. Despite much work, both theoretical and experimental, a full understanding of this problem has not yet been achieved. [Work supported by the NSF through the Materials Research Laboratory at Brown University and through Grant No. DMR75‐14761.]
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Some applications of second sound to the study of superfluid helium (A)

G. Ahlers

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S19-S19 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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The generation and detection of second sound in superfluid helium will be described. Measurements of the second‐sound velocity and attenuation can be applied to obtain important information about many aspects of the physics of superfluid helium. A few selected examples of these applications will be discussed.
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Third sound: a study of the superfluid‐helium film (A)

K. L. Telschow

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S19-S19 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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Liquid‐helium films of only a few atomic layers thickness exhibit a remarkable mobility as a result of the condensed superfluid state. The atoms are tightly bound to the substrate surface by the van der Waals attraction leaving almost complete freedom of motion in the lateral directions. Disturbances in the film thickness then propagate as waves called third sound. A wealth of information concerning the static and dynamic properties of the film have come from third‐sound group‐velocity measurements primarily through detecting small temperature oscillations accompanying the wave. We have learned that these waves can propagate in essentially monolayer films thus exhibiting a two‐dimensional superfluid. A very important quantum‐mechanical length describing the coherence of the condensate atoms is now known from static third‐sound velocity measurements. Experiments on the Doppler shift of flowing films have delineated the superflow phase region. Recently experiments have demonstrated the potential flow nature of the film and measured its ability to trap circulation. Subsequent measurements of the decays of these persistent currents are yielding new insights into the general stability of the superflow state.
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Application of fourth sound to study the superfluid helium‐4 and the recently discovered superfluid helium‐3 (A)

H. Kojima

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S19-S20 (1977); (2 pages)

Online Publication Date: 11 Aug 2005

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Fourth sound is propagated in a superfluid placed in the tiny pores of tightly packed fine powder. Since it is a type of usual sound (pressure‐density) propagation, fourth sound may be excited and detected by condenser transducers. In superfluid helium‐4 fourth sound has been used (1) to determine the superfluid component density by measuring the sound velocity, and (2) to study the nature of persistent currents using Doppler‐shifted fourth sound. In superfluid helium‐3 propagation of fourth sound provided conclusive evidence of superfluidity of liquid helium below 2.6 mK. Superfluid component density and some anisotropic properties of superfluid helium‐3 have been investigated using fourth sound.
Contributed Papers
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Attenuation and dispersion of first sound in pressurized liquid 4He near Tλ (A)

R. Carey, Chr. Buchal, and F. Pobell

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S20-S20 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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High precision measurements of the velocity u, the attenuation α, and dispersion D of first sound have been made along the lambda line in 4He for frequencies up to 1 MHz and for temperatures ∣T − Tλ∣ ⩽1 mK. Our data can be understood in terms of order‐parameter relaxation and order‐parameter fluctuations. We find that the time τ characterizing the relaxation process below Tλ and the time τ characterizing the fluctuations both above and below Tλ have the same temperature and pressure dependence; that is, only one time scale is important very near the phase transition. The analysis of the attenuation due to fluctuations above Tλ allows us to determine a simple scaling law for all our data, valid over four decades in ωτ, α(T > Tλ)/α(T  =  Tλ)  =  ωτ/(c + ωτ), where c ≃ 0.5. A similar relation for the dispersion at T > Tλ was also determined.
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Investigation of ultrasonic cavitation in liquid helium in the Megahertz frequency range (A)

R. F. Carey, J. A. Roeney, and C. W. Smith

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S20-S20 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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Considerable evidence, both theoretical and experimental, indicates that the lowest‐energy state of an excess electron in liquid helium consists of the electron bound in a helium‐free spherical cavity of about 1.7 nm radius. This state has become known as the electron‐bubble. Investigators have suggested that these electron‐bubbles may serve as nuclei for ultrasonic cavitation. To examine this possibility, acoustic spectra in liquid helium were studied using quartz transducers whose resonant frequencies were in the low megahertz range. These spectra were measured as a function of displacement amplitude both above and below the lambda point. In addition, these spectra were obtained in the presence and absence of a source of electron‐bubbles. Results will be compared with similar studies at lower frequencies and the role of the electron‐bubble as a nucleus for cavitation will be discussed. [This work was supported in part by the Air Force Office of Scientific Research.]
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Parametric generation of sound by resonant mode conversion in helium II (A)

Steven Garrett, Seth Putterman, and Isadore Rudnick

J. Acoust. Soc. Am. Volume 61, Issue S1, pp. S20-S20 (1977); (1 page)

Online Publication Date: 11 Aug 2005

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When nonlinear effects are included, the two fluid hydrodynamic description of superfluid helium possesses solutions which couple first and second sound. Resonant conversion of two second‐sound waves into a first sound wave is calculated. An experiment to observe this effect is currently under construction and will be described. [Work supported by ONR and NSF.]
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