Fusion: Stepping closer to reality
Scientists now say 100 million degrees C is not too hot to handle in this powerful energy-generating process.
When two physicists gather at a restaurant with steak on the menu and fusion on the agenda, you're likely to find scribbles. Or so it must have seemed to the server who cleared Robert Goldston's table recently.Skip to next paragraph
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A colleague had missed a talk Dr. Goldston had given on new developments in fusion-energy research. So the two repaired to a local eatery for a recap. By the time the check arrived, "the napkins and half the table cloth were covered with equations," recalls Goldston, director of Princeton's Plasma Physics Laboratory.
Fusion, in other words, is generating renewed excitement among scientists in the field.
Given the challenges facing today's nuclear reactors, they have long dreamed of harnessing the same energy source that powers the sun. In theory, they could generate power more efficiently, more safely, and with less nuclear waste than today's reactors, and use a virtually limitless source of fuel - hydrogen. Fusion reactors represent a kind of holy grail for an energy-dependent world.
Now, researchers are poised to take the next big step in evaluating the technology's commercial potential. Scientists say they are more confident than ever that they can successfully build and operate a planned experimental fusion reactor. The bigger hurdle now looks political. The six-nation project - called the International Thermonuclear Experimental Reactor, or ITER - is caught in a big-money squabble over where to put the $5 billion reactor. Japan and France both want the privilege.
Scientists, meanwhile, are chafing to loose the bulldozers.
"There have been dramatic advancements in our scientific understanding" over the past five to 10 years, Goldston notes. The basic conclusion: The "fire" in the type of reactor planned for ITER may not be as finicky to control as many had previously believed.
Initial simulations had suggested that triggering and sustaining the fusion reactions might be too difficult. But "we've made enormous steps forward," says Anne Davies, director of the US Energy Department's Office of Fusion Energy Science. An International Atomic Energy Agency meeting last month in Portugal generated considerable excitement because experiments with test reactors around the world suggested ITER's reactor would work as designed.
The idea behind fusion is fairly straightforward. Today's nuclear reactors derive their energy by splitting atoms in a process called fission. Fusion works by combining them - actually the nuclei of two forms of hydrogen known as deuterium and tritium. Fusing nuclei requires more energy than splitting them, but the payoff is larger. A fusion reaction gives off three to four times as much energy as a fission reaction does.
The challenge: For fusion to occur, the surroundings must be torrid. Researchers anticipate their experimental reactor will run at 100 million degrees C - roughly six times as hot as the sun's core. At these temperatures, atoms and their electrons part company and form a roiling particle soup called a plasma. Such temperatures also give the nuclei of the atoms enough speed to fuse with other nuclei when they hit them. But because the plasma is filled with electrically charged particles, many researchers hold that the only way to keep the plasma bottled up is with magnetic fields.