A train of vapor bubbles is formed by ejection into a subcooled liquid pool. In the base flow, surface tension pinch-off drives a liquid "spear" through the center of the vapor bubble to form a vapor torus that leads to rapid condensation. Alternatively, using a directed 1.7 MHz pulsed acoustic beam early in the vapor bubble formation (and prior to pinch-off) exploits the liquid-vapor acoustic impedance mismatch to force a similar liquid "spear," forming a vapor torus and accelerating the bubble collapse.
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