Lab Reports Nuclear Fusion ‘Milestone’

In a scientific first that researchers are terming a “significant milestone,” European physicists have produced unusually large amounts of energy in a controlled fusion reaction and sustained the reaction far longer than has previously been possible.

The feat, accomplished over the weekend, has been hailed as a major step toward an unlimited source of clean energy, but researchers cautioned that it will still be decades before commercial fusion power plants are constructed.

Fusion, the nuclear reaction that powers the sun, has been a goal of the physics community for half a century because it promises to produce unlimited amounts of energy from materials found in abundance in seawater. But fusion research has been in a shadow recently, in part because of retrenchments in funding in the United States and because of the controversy surrounding the purported discovery of “cold fusion.”

The new announcement may well put the physics community back on the fast track toward its goal of making commercial fusion feasible early in the next century.

Taken out of context, the milestones achieved by researchers at the Joint European Torus lab in Culham, England, may not seem all that impressive. When the workers fired up the reactor Saturday, they produced about 1.7 million watts of power--enough to energize 17,000 100-watt light bulbs--and managed to sustain the reaction for two seconds.

“Two seconds is a long time in fusion,” said physicist John Maple, spokesman for the project. In fact, most controlled fusion reactions that had been achieved had durations of only hundredths of seconds.

The energy output was also unprecedented, said physicist Paul-Henri Rebut, leader of the JET team. “This is the first time that a significant amount of power has been obtained from controlled nuclear fusion reactions,” he said. “It is clearly a major step forward in the development of fusion as a new source of energy.”

Nuclear fusion occurs when the nuclei of two small atoms are fused together to make a larger atom. In the process, a small amount of mass is lost and that mass is converted into huge amounts of energy, following Albert Einstein’s famous equation: E=mc 2. That reaction also occurs in the hydrogen bomb.

But it is extremely difficult to force two nuclei together because the positive charges in the nuclei repel each other very strongly.

In the sun, and other stars, that repulsion is overcome by the extremely high gravitational forces created by its huge mass. In the hydrogen bomb, the nuclei are squeezed together by the energy released by the force of an atomic explosion.

Physicists are attempting to simulate the interior of stars in the laboratory by confining the atoms in an extremely powerful magnetic field shaped like a doughnut, but known mathematically as a torus, and then injecting energy so that the atoms slam together at a speed high enough to overcome the repulsive force.

(Two years ago, a pair of Utah chemists reported that they could achieve fusion at room temperature by confining the small atoms in a metal rod under an electric field. Such a development would have eliminated the need for the expensive reactors required for conventional “hot” fusion, but most scientists have failed to confirm their “cold fusion” discovery.)

In Saturday’s JET experiment, the researchers injected 15 million watts of energy into the reactor, producing a temperature nearly 10 times as hot as the core of the sun. The fusing atoms produced the 1.7 million watts of power until the reaction petered out. The project thus failed to meet one of the key criteria physicists have established for a controlled fusion reaction--releasing as much energy as is pumped into it. But researchers hope that future refinements will allow them to meet that goal, perhaps within the decade.

The unusual power output was achieved because the researchers used a new fuel. Most fusion experiments have used deuterium as a fuel. It is a heavy form of hydrogen that has an extra neutron in its nucleus. The European researchers used tritium, which has two extra neutrons.

Tritium fusion reactions release more energy, but it is much more difficult to contain tritium than deuterium within a reactor, and harder to accelerate it to the high speeds required. In fact, there are only two test reactors in the world that are capable of doing it: the JET, which is sponsored by the governments of 14 European countries, and the Tokamak Test Fusion Reactor at Princeton University, which is funded by the U.S. government.

Physicist Dale Meade, deputy director of Princeton’s Plasma Physics Laboratory, expressed admiration and a bit of regret at the JET announcement, noting that the Princeton group had expected to complete a similar experiment this year, but was unable to do so when federal funding for the project was cut back.

“We had originally planned to initiate experiments in March of 1991 that would have produced between 10 million and 20 million watts of fusion power,” he said. “But due to funding shortages, that part of our fusion program has been delayed until July of 1993. So here’s a case where the United States had it within its grasp to do 10 times as much and to do it earlier. But we didn’t.”