Cavitation density of superfluid helium-4 around 1 K

Using an optical interferometric method, the cavitation density of bulk superfluid helium at $T=0.96\mathrm{K}$ is measured and found to be ${\rho }_{\mathrm{cav}}=0.1338\pm 0.0002\mathrm{g}{\mathrm{cm}}^{-3}$. A well-established equation of state for liquid helium at negative pressures converts this to the cavitation pressure $P_{\mathrm{cav}}=-5.1\pm 0.1\mathrm{bars}$. This cavitation pressure is consistent with a model taking into account the presence of quantized vortices, but disagrees with previously published experimental values of $P_{\mathrm{cav}}$.

Figure 1

Experimental setup. At the center of the transducer, the small star is the acoustic focus where cavitation occurs. A CCD camera monitors the focus plane through a lens. The camera image is composed of pixels distributed in lines and columns. We optimized the camera orientation so that lines are parallel to the $x$ axis.

Figure 2

Typical radial density profile for $P_{st}=0.15$ bar at the time when the density is minimum at acoustic focus. The static density corresponding to $P_{st}$ is shown by the horizontal dashed line. The error bar calculation is detailed in Sec. 5.

Figure 3

Left: Cavitation probability at $0.96\mathrm{K}$ for three different pressures $P_{st}$: circles, $0.15\mathrm{bars}$; triangles, $0.65\mathrm{bars}$; crosses, $1.26\mathrm{bars}$. The corresponding lines are fits according to Eq. (4). Right: Image of a bubble recorded by the camera $10\mu \mathrm{s}$ after its creation.

Figure 4

Experimental measurements of minimum densities ${\rho }_{\min }$ for different driving voltages $V$ at $T=0.96\mathrm{K}$ and $P_{st}=0.15\mathrm{bars}$. The dashed line represents the cavitation voltage.

Figure 5

Cavitation density as a function of static pressure at $T=0.96\mathrm{K}$. For more clarity, the different measurements are shifted from their actual $P_{st}$ values (black circles). The horizontal continuous line represents the average cavitation density and the dashed lines its uncertainty.

Figure 6

Reproduction of Ref. [6] experiment. $P_{st}$ as function of ${\rho }_{st}{V}_c$. The 3 data points (black circles) correspond to static pressures of 0.15 bars, 0.65 bars, 1.26 bars. Cavitation voltages are the ones shown in Fig. 3. The dotted line is the linear extrapolation of the data points.