sonofusion

The May 2005 edition of IEEE Spectrum (available in the reference section of the nearest engineering library) has a interesting article on sonofusion: using focused sound waves to produce nuclear fusion. The experimental apparatus uses a flask of deuterated acetone, acetone where the molecules use deuterium instead of hydrogen, at 0 deg. C. They first remove all the dissolved gasses. Then, they use a piezoelectric element to set up an extremely powerful standing sound wave in the container. The sound wave oscillates between extreme low pressure and extreme high pressure. Finally, they spray it with neutrons that are carefully timed to match the low pressure of the sound wave. The neutrons make tiny little bubbles, which immediately expand to 100,000 times their original size. Then, when the high pressure rolls around, the bubbles slam back together and some of the deuterium fuses. They know it's fusing because they can detect the neutrons it gives off (at a different time and energy than the neutrons they're feeding in), and because the level of dissolved tritium increases over time.

According to the article, they've published results in Science (8 March 2002) and Review E (March 2004). Initially, there was a lot of skepticism, but there are reports of other labs being able to reproduce the results.

This process is a ways from producing more power than you feed it, but at least one company, Impulse Devices, is trying to create a commercial version of it. Online resources are pretty scarce, but you can find some PDFs here, and there's a PDF version of a power-point presentation here.

Much of the Spectrum article talks about the difficulty of scaling the technology to the size of a nuclear power plant. What I find intriguing is its potential compactness: instead of trying to supply an entire city, could we create generators small enough to power a neighborhood, a city block, or a house?