Sun in a Bottle - Charles Seife [111]
Unfortunately, the Farnsworth fusor, as well as later devices that use electric fields to confine plasmas, will probably never be able to produce more energy than it gobbles up. Clever as the fusor design is, it is not a very good bottle for a star. Its electric fields let particles escape, and the motion of electrons in the plasma radiates energy away at an alarming rate. Nevertheless, fusors have acquired something of a cult following.
Young Thiago Olson’s fusor—fundamentally the same as Farnsworth’s device—is just one of more than a dozen that have sprung up in amateurs’ basements around the country. Olson was the eighteenth amateur to achieve fusion on his own, according to a roll of honor on a Farnsworth fusor aficionado Web site that Olson regularly visited. (In fact, he wasn’t the first high schooler on the list. The fifth amateur to achieve fusion, Tanhui Li, was also a high-school student; his fusor won him a scholarship in the 2003 Intel Science Talent Search.)82 Though Olson doesn’t make any claims that his device will solve the world’s energy problems, many die-hard fusor fans are convinced, hoping against hope, that fusors will soon lead to a fusion reactor—a source of unlimited energy.
On November 9, 2006, just days before the Olson story broke, the fusion physicist Robert Bussard gave a talk at Google about his research with a modified fusor. He had been working for the navy, but after a number of years he had run out of money for the program. The scientist told his audience that if he could only get his hands on $200 million, he would be able to produce a working power plant within four to five years. Bussard was deceiving himself if mainstream scientific thought is any guide. The equations of plasma physics strongly imply that fusorlike devices are very unlikely ever to produce more energy than they consume. Nature’s inexorable energy-draining powers are too hard to overcome.
Luckily, the fusor is not the only tabletop fusion device around. Plenty of researchers are building small, cheap fusion machines. Scientists without huge budgets have gotten fusion to work with inexpensive lasers, and by even stranger means.
A major hurdle with laser fusion is that electrons tend to absorb the light beam’s energy better than the heavy nuclei they are attached to. But hot electrons are pretty much useless for inducing fusion, which requires hot, fast-moving nuclei instead. In an ingenious experiment, Todd Ditmire, a Livermore physicist, figured out how to turn this liability into an asset.
Ditmire injected microscopic droplets of deuterium into a vacuum chamber and then zapped them with a cheap infrared laser. Ordinary laser fusion scientists had long since abandoned infrared lasers because infrared light heats electrons too much. However, this effect was precisely what Ditmire was looking for. When he shot the laser at the deuterium microdroplets, the laser heated up their electrons, boiling them off in a fraction of a second. The positively charged nuclei left behind, stripped of their negatively charged electrons, began repelling their neighbors. All the nuclei immediately tried to escape from one another, and the droplets exploded with great force, spewing deuterium nuclei at high speeds in all directions. Ditmire’s laser did the exact opposite of what traditional laser fusion was trying to do: instead of compressing and confining a dollop of deuterium plasma, he was causing it to blow apart. Ditmire discovered that on occasion, though, the fragments from exploding droplets—fast-moving deuterium nuclei—collide with each other and fuse. For every laser shot, he got about 1,200 neutrons from fusion. Considering that the energy of the laser was so low, less than what’s put out by a Christmas light in a second, this was an impressive fusion yield. Even so, the energy produced by the fusion was ten million times less than the energy the laser poured in. Ditmire’s scheme might be useful for studying fusion on a very tiny scale, but