A “water hammer” powers up

Sonoluminescence. In household plumbing, a water hammer can occur when a sudden slowdown of the water’s flow generates a temporary vacuum and a shock wave that together violently shake the piping. Now, Seth Putterman of UCLA and his colleagues have used a water hammer to generate sonoluminescence (SL), bursts of light from collapsing bubbles. The researchers vertically shook a 60-cm-tall, 4-cm-diameter cylindrical tube—containing a small amount of xenon gas dissolved in water—with an acceleration of 2g. During a shake cycle, bubbles formed and collapsed sporadically and produced as many as 3 × 10⁸ photons (about a hundred times more than earlier SL experiments). That emission corresponds to a peak power of almost half a watt. (C.-K. Su et al, Phys. Fluids   15 , 1457, 2003  https://doi.org/10.1063/1.1572493 .)