Phase synchronization and collective instability in oscillating bubble clouds.

The effect of bubble interactions within a bubble cloud under ultrasonic forcing is investigated. Under certain conditions, phase synchronization is found, revealing parameter regimes where the dynamics of the bubble system are primarily determined by the interactions of the bubbles, rather than the applied ultrasonic acoustic field. Due to the Bjerknes interaction, the stability thresholds for critical pressure and size leading to unpredictable oscillations for bubble clouds are lower than the stability thresholds for single bubbles. Interestingly, numerical simulations confirm that in the regimes where bubbles exhibit chaotic oscillations, the dynamics are determined by a complicated geometric object called a low‐dimensional strange attractor which is qualitatively the same as that for the chaotic oscillations of a single bubble. Thus an averaged equation may also be low‐dimensional. The effects of synchronization on Landau damping are discussed. The effect of delays between the interactions is also inv...