Investigation of ultrasonic cavitation in liquid helium in the Megahertz frequency range

Abstract

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.]