Production and Detection of Solitary Macroscopic Quantized Vortices in Helium II

Abstract

Ultrasonic cavitation was induced in liquid helium using plane and cylindrical standing-wave systems resonant at 89 and 53 kc/sec, respectively. The threshold voltage for cavitation noise was measured at different rotation rates of a shaft, with and without an attached paddle, rotating in the vicinity of the sound field. Below the $\lambda$ point the threshold was found to be lowered sharply at a critical rotation rate ${\omega }_c$. The experiments were repeated with five different shaft sizes, and ${\omega }_c$ was found to be inversely proportional to $r^2$, where $r$ is the radius of the shaft. The constant of proportionality was found to be $\frac{\hslash }{m}$, where $m$ is the mass of one helium atom. Further, smaller threshold reductions were observed at rotation rates of $2{\omega }_c$, with the largest shaft sizes. These results are consistent with the theory of quantized vortex formation and appear to indicate that such vortices play a role in the cavitation nucleation process.