Science: On the Road to Star Power

A new fusion reactor passes its first important test

Long after most workers in the lab at Princeton University had gone home for the night, scientists and engineers were still on the job, putting the finishing touches on the three-story-high, 1,500-ton behemoth of steel and wire. Finally, after hours of tinkering, they began their countdown. At exactly 3:06 a.m., the huge, cylindrical-shaped machine started operating. As powerful electrical currents surged through its magnetic coils, the gases in its circular vacuum chamber heated up to temperatures of 100,000° Celsius. The test lasted barely one-twentieth of a second, but it was enough to set off cheers and the pop of champagne corks.

The ceremony marked an important step on the long road to harnessing nuclear fusion and taming the power of the stars. The Princeton Plasma Physics Laboratory had successfully turned on the first of a new breed of experimental reactors that could point the way toward a limitless source of energy. That goal may be decades off. But, as Presidential Science Adviser George Keyworth noted last week, the machine's initial burst was "an essential milestone."

Under Einstein's famous formula E=mc2, matter can be converted into energy in two ways. In fission, the process at work in existing nuclear power plants, the nuclei of large atoms, like those of uranium or plutonium, are split, releasing the energy that binds them together. In fusion, nuclei of hydrogen, the simplest of all atoms, are squeezed together to form helium, also releasing energy. Though fusion occurs in hydrogen bombs, scientists have struggled for more than 30 years to achieve it in a slow, nonexplosive way. Unlike fission reactions, fusion produces short-lived, easily disposable radioactive debris. It also depends on a form of hydrogen, deuterium, easily obtainable from sea water.

In the U.S. and abroad, physicists are experimenting with lasers and electron guns to pound hydrogen nuclei together. But the most promising technique, and the one at work in the $314 million Princeton machine, is based on an idea suggested in the early 1950s by Soviet scientists, one of them Andrei Sakharov, the human rights activist. The scheme employs magnetic fields to hold and compress hydrogen gases inside a doughnut-shaped chamber until they reach temperatures of about 100 million° Celsius, seven times as hot as the sun's interior. Until now, the reactors, like Thermos bottles that are too small, have been unable to contain the heat long enough.