More Bang From The Bubble?

Sonofusion may one day outshine other nuclear methods in generating energy

Ross Tessien is a big-think guy. He believes that his tiny startup, Impulse Devices Inc. in Grass Valley, Calif., will be able to pull off a staggering breakthrough that for a half-century has defied the world's best minds in physics. The 48-year-old mechanical engineer expects to build a commercial fusion-energy generator within a decade or so.

Fusion power is the holy grail of energy research. By emulating the reactions that cause the sun to shine, fusion would create cheap and virtually limitless electrical power -- and produce far less radiation than today's nuclear power plants. Government agencies in the U.S., Europe, and Asia annually spend hundreds of millions of dollars on this quest. Nevertheless, fusion power has always remained 20 years or more in the future.

So how does Tessien figure he'll be able to outshine such big-bucks programs? By harnessing a new but controversial approach, dubbed sonofusion. It works by bombarding a liquid with sound waves to create tiny bubbles. The bubbles mushroom in size and then collapse so violently that they generate a flash of light and enormous heat. This phenomenon, which has been studied for years, is known as sonoluminescence.

Sonoluminescence emerged as a serious candidate for fusion with a report in the Mar. 8, 2002, issue of the journal Science. A team led by engineers at Oak Ridge National Laboratory in Tennessee claimed it had produced bubbles hot enough to trigger fusion among atoms of deuterium, a form of hydrogen. Most physicists scornfully dismissed the report: It smacked of the "cold fusion" debacle of 1989.


Now, the same team is back with better results from more detailed experiments, using improved equipment funded by the Pentagon's Defense Advanced Research Projects Agency. The report will appear in the journal Physical Review E, but draft copies have already been circulating among physicists for months. "All the questions that people brought up about our first paper have been clarified," insists team leader Rusi P. Taleyarkhan, who last year was awarded an endowed chair at Purdue University's School of Nuclear Engineering. "Taleyarkhan's new findings seem very, very impressive," says Henry E. Bass, director of the National Center for Physical Acoustics, a federally funded lab at the University of Mississippi.

Not all physicists have been won over by the latest report, however. Seth J. Putterman, a sonoluminescence pioneer at the University of California at Los Angeles, says that some of the new data would be "pretty exciting" if it weren't for one fact: Oak Ridge physicists failed to replicate the original experiment two years ago. Until there's independent confirmation, Putterman says he'll remain a skeptic.

For the most recent round of experiments, Taleyarkhan's team used more sensitive gear and detected increased signs of fusion -- that is, more tritium, a telltale byproduct of fusion, and more neutrons, which fusion reactions emit. Moreover, the new round of experiments included "control" runs that hadn't been done for the 2002 report. In the control tests, neither tritium nor abnormal counts of neutrons were spotted. To Tessien, this adds up to "conclusive evidence of fusion."

Tessien expects to confirm Taleyarkhan's results by using much more powerful equipment, which was developed with the help of D. Felipe Gaitan, chief scientist at Impulse Devices. Most sono research is done by holding the liquid in small, 2-inch-diameter spheres or cylinders made from glass. Impulse Devices has fabricated 9.5-inch-diameter aluminum spheres with thick walls to withstand internal pressures of 1,000 atmospheres.


That improvement is significant, according to Putterman. "Since ordinary sonoluminescence delivers so much energy at pressures of only one or two atmospheres," he says, "you could hope that at 1,000 atmospheres, you'd be in fusion territory -- if the temperature also scaled up. But that's a really big 'if."'

Still, Bass of the National Center for Physical Acoustics, in Mississippi, can't wait to get his hands on Impulse Devices' equipment. "We've got to get involved," says Bass. "If sonofusion is real, it would bring a major scientific revolution."

Impulse Devices sells its equipment for $250,000. But such devices are just a stepping stone to the systems that Tessien believes will one day free the world of its dependency on oil and coal. Sonofusion spheres measuring a few feet in diameter, he predicts, will soon lift the living standards of remote Chinese and African villages. If he's right, great things would grow from small bubbles.

By Otis Port in Grass Valley, Calif.

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