New Measurements of the Tensile Strength of Liquid 4He
A piezoelectric hemispherical transducer was used to focus high-intensity ultrasound into a small volume of superfluid helium. The transducer was gated at its resonant frequency of 566 kHz with gate widths less than 1 ms in order to minimize the effects of transducer heating and acoustic streaming. The onset of nucleation was detected with small-angle scattering of laser light from the cavitation zone by microscopic bubbles. The laser probe also was used to confirm calculations of the pressure amplitude at the focus based on the power radiated into the liquid, the geometry of the transducer, and the nonlinear attenuation of the sound. The cavitation pressure observed was significantly greater than previously reported in the literature and in agreement with homogeneous nucleation theory.
KeywordsLiquid Helium Pressure Amplitude Focal Zone Superfluid Helium Acoustic Streaming
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