Dramatic effect of superfluidity on the collapse of ${}^4\mathrm{He}$ vapor bubbles

The lifetime of cavitation bubbles produced by an acoustic wave focused in liquid helium-4 is investigated. This lifetime is found to be different by orders of magnitude depending on whether the liquid is superfluid or not. We show that if the liquid is in the superfluid state, the bubble lifetime is well explained by a purely mechanical model, corresponding to the so-called Rayleigh regime. In the normal state, the Rayleigh-Plesset regime applies, in which heat diffusion plays a crucial role and dramatically increases the bubble lifetime.

Figure 1

Experimental setup. The cavitation bubble induced by the focused acoustic wave produced by the piezoelectric transducer (PZT) is imaged by a lens $\mathcal{L}$ onto a CCD camera. $L$ is the thickness removed from the originally hemispherical transducer.

Figure 2

Determining the lifetime of cavitation bubbles: data for $T_0=0.87$ K. (a) Images of typical bubbles at different times $t$ (see text). The upper rectangular black area is the shadow of the PZT. (b) Probability of existence of a bubble at time $t$. The solid line is a fit assuming that the lifetime of the bubble is Gaussian distributed.

Figure 3

Lifetime of bubbles in liquid helium as a function of temperature. The vertical dashed line marks the superfluid transition temperature ($T_{\lambda }=2.17$ K). Above $T_{\lambda }$, we can only estimate the lower bound of the lifetime.

Figure 4

Cavitation bubbles at $T_0=2.19$ K.

Figure 5

Bubble radius as a function of time at $T_0\sim 1$ K. On all figures, black solid line is the Rayleigh solution of the Rayleigh-Plesset equation [Eq. (2)]. (a) Data points from the movie reconstruction method (see text and Fig. 1). (b) Signals collected with a fast photodiode. (c) Another photodiode measurement: after the bubble has collapsed, a second bubble is created.