To date, the main--and ghastly--use of fusion has been in hydrogen bombs. No existing technology can both control and sustain such a fusion reaction in a way that could be used to generate electricity. Nuclear physicists have been trying ever since the first hydrogen bomb exploded in 1952. So imagine their surprise when a team of engineers asserts that they have developed a new method that may produce sustained nuclear fusion. The technique is called sonofusion--sound-triggered fusion--because it supposedly works by pumping ultrasound waves and a beam of neutrons into a modified form of acetone, a common solvent that's used in fingernail polish remover, for example.
Even though the new claim is already provoking a heated debate similar to the furor that engulfed cold fusion, this time the official announcement comes with the imprimatur of Science--and more than a year of peer reviews by leading scientists. While not all of the sonofusion reviewers voted in favor of publication, the report of tabletop fusion does come from an outfit well versed in nuclear physics: Oak Ridge National Laboratory. However, the team consists mainly of engineers, not nuclear physicists, hence much of the initial skepticism. In fact, even Oak Ridge management had second thoughts and asked two of its nuclear physicists to verify the work. They failed. The sonofusion team insists that the double-check effort was flawed. Claims and counterclaims have been flying across the Internet. "These guys are almost to the point of calling each other liars," says Seth J. Putterman, a University of California at Los Angeles physicist and a reviewer for Science.
Clearly, getting published in Science doesn't guarantee acceptance. Claims of fundamental scientific breakthroughs, says William C. Moss, a reviewer and a physicist at Lawrence Livermore National Laboratory, must be held to the highest standards. Tabletop fusion would be potential Nobel prize work, he explains, "so it's easy for people to lose their objectivity." But Moss isn't writing off sonofusion altogether. "In fact, I wrote a paper a few years ago saying that it might be possible."
The Oak Ridge team that took up that challenge is led by senior scientist Rusi Pesi Taleyarkhan. It consists of two other Oak Ridge researchers, plus Richard T. Lahey Jr., an engineering professor at Rensselaer Polytechnic Institute, and Robert I. Nigmatulin of the Russian Academy of Sciences. To generate the immense heat needed to fuse nuclei, they turned to an obscure phenomenon called sonoluminescence.
Sonoluminescence uses ultrasound energy to create little bubbles in a liquid--bubbles that grow to many times their original size, then swiftly collapse and disappear with a wink of light. It all happens in a tiny fraction of a second, so determining what goes on is extraordinarily difficult. Even after studying sonoluminescence for two decades, Putterman can't say precisely how much heat is released by the imploding bubbles, but temperatures may reach as high as those in the sun.
Harnessing the sun's source of power would be the ultimate energy technology. In a world where fusion is possible, seawater could be fuel. A cubic kilometer of seawater contains as much energy as all the world's oil--in the form of deuterium, a "heavy" variant of hydrogen that has a neutron as well as a proton in its nucleus. And the oceans have millions of cubic kilometers of water.
However, five decades of painstaking fusion research have failed to tap the energy locked up in seawater. The two orthodox roads to forcing deuterium to fuse are expensive and confoundingly complex. Magnetic confinement, the leading candidate, would create an artificial sun suspended in a magnetic field, since no material can withstand temperatures of 100 million C. The other would use a football-stadium-size array of powerful lasers to zap little glassy spheres of deuterium. Both can achieve fusion, but only briefly, and they consume much more energy than they produce.
The latest hope for magnetic confinement is ITER, short for International Thermonuclear Experimental Reactor. The U.S., Canada, Europe, Japan, and Russia began designing it in the late 1980s. But when the price tag hit $10 billion, the U.S. had second thoughts and yanked its support in 1999. Since then, a redesign has trimmed the size of ITER and slashed the projected investment to $4.5 billion. Early this year, the U.S. began to think about rejoining the program. Groundbreaking for ITER is expected around 2003 or 2004.
ITER would cap a 50-year quest--but wouldn't end it. Fusioneers have always said commercialization is at least 20 years in the future, and it probably still is. ITER is just one more stepping-stone to harnessing fusion energy. And despite fusion-research budgets in the U.S. of upwards of $250 million a year, scientists say they could use even more.
So when a small group from outside the fusion Establishment claims it can produce fusion on a shoestring, researchers working on the big-bucks programs tend to worry about the future of their pet schemes. Rensselaer's Lahey hints that this might have affected the replication effort by Oak Ridge nuclear physicists Dan Shapira and Michael J. Saltmarsh. But Putterman points out that Shapira and Saltmarsh measured something not in the Taleyarkhan team's paper: correlating the detection of neutrons, which are one of the telltale signs of fusion, with when bubbles imploded; no meaningful relationship was found. Lahey retorts that Shapira and Saltmarsh didn't set up their instruments properly.
The first order of business is to end the bickering, says Lawrence A. Crum, a researcher at the University of Washington's Applied Physics Laboratory in Seattle and a reviewer. "What matters now is to confirm whether there really is fusion going on. If this really is confirmed, there'll be a bunch of companies started," he predicts, to build bubble-fusion power sources.
Lahey is cautiously optimistic that his group's design could turn into a big source of future energy. "The first step would be to increase the neutron yield by replacing the deuterium with tritium," an even heavier form of hydrogen with two neutrons. Adds Taleyarkhan: "We've already filed patents on lots of ideas for scaling up."
Even small units could find immediate markets. Applications would include sterilizing food, boosting the production of chemicals by raising the temperature of reactions, and producing the streams of neutrons needed for small, inexpensive detectors for sniffing out explosives at airports and remotely peering into cargo containers at seaports.
Actually, the entrepreneurial phase has already begun. Three years ago, engineer Ross Tessien founded Impulse Devices Inc. His Grass Valley (Calif.) startup has hired a leading sonoluminescence researcher--D. Felipe Gaitan, a protege of Crum's--and is working on simulations of sonofusion reactors up to 20 feet in diameter that would create giant bubbles. Tessian is now negotiating with Los Alamos National Laboratory to verify his computer models.
Among the original sonofusion pioneers is Roger S. Stringham, a former researcher at SRI International. He co-founded First Gate Energies in the mid-1990s, and the Woodside (Calif.) company has recently built several demonstration sonofusion devices. He will discuss his latest efforts on Mar. 22, during a final-day cold-fusion session at the American Physical Society's Annual March Meeting in Indianapolis.
Session moderator Scott R. Chubb, head of Research Systems Inc. in Arlington, Va., predicts that researchers will eventually uncover "some very exotic reactions" that explain how tabletop fusion works. For instance, he suggests the physical dynamics of sonofusion "become deeply intertwined with electromagnetism," causing deuterium to behave somewhat like electrons. "This is something you'd never expect to see in conventional fusion reactions," he adds. As more physicists get intrigued by sonofusion in coming months, he anticipates many other surprises. By Otis Port in New York