Wednesday, March 02, 2005

Why Sonofusion Could Work

In New Scientist today (actually, dated 5 March, but who's counting?), this piece on the actual temperature inside collapsing bubbles undergoing cavitation. The problem many physicists had with sonofusion is the widespread view that individual cavitating bubbles had temperatures around 10,000 kelvin, far too low to support nuclear fusion. By contrast, the core of the sun is much hotter -- around 10M kelvin.

But the 10k kelvin figure may be misleading. Measurements of the sun's surface show it to be 7k kelvin, much lower than the temperature at the core. According to David Flannigan and Ken Suslick at the University of Illinois at Urbana-Champaign, spectra from bubbles collapsing in a sulphuric acid solution yielded light signatures from "exotic ions" such as positively charged oxygen that can only exist at temperatures of 200,000 kelvin. "Crum believes that, like the sun, the bubbles may hide even higher temperatures. 'So maybe [bubble] fusion is technically possible,' he says." Good news.

Update, 5/5: Ken Suslick, in PhysicsWeb:

"Our results are in such a different set of experimental parameters that they can neither confirm or deny Taleyarkhan’s claims to fusion," Suslick told PhysicsWeb. "A plasma is a prerequisite but certainly not a sufficient condition for fusion."

The Illinois scientists now plan to optimise cavitation and explore the conditions generated during bubble collapse. "Is inertial confinement fusion possible in a collapsing bubble? I think the verdict is still out," says Suslick. "The underlying physics is solid - it is simply a question of whether the collapse can generate a shockwave that is sufficiently intense and remains spherical long enough."

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