Pop goes the plasma: extreme conditions inside imploding bubbles | Engineering at Illinois: "High-intensity ultrasound waves traveling through liquid leave bubbles in their wake. Under the right conditions, these bubbles implode spectacularly, emitting light and reaching very high temperatures, a phenomenon called sonoluminescence. Researchers have observed imploding bubble conditions so hot that the gas inside the bubbles ionizes into plasma, but quantifying the temperature and pressure properties has been elusive.
Plasma emission from collapsing bubbles: The imploding bubbles move around after each collapse, tracing out a lit path, like a person flinging their arm around while holding a flashlight.
In a paper published in the June 27 issue of Nature Physics, University of lllinois professor Kenneth S. Suslick and former student David Flannigan, now at the California Institute of Technology, experimentally determine the plasma electron density, temperature and extent of ionization."