European Lab Scores Fusion First : Science: Researchers use a new combination of fuels to produce the largest amount of power ever from such nuclear experiments.

A team of researchers in England has brought the world one step closer to the still-elusive goal of harnessing nuclear fusion as a source of electric power.

Over the weekend, the group recorded the largest amount of power--about 2 million watts, enough to light 20,000 hundred-watt bulbs--ever produced in a fusion reactor by using a new combination of fuels.

The reaction only lasted two seconds, but “this is the first time that a significant amount of power has been obtained from controlled nuclear fusion reactions,” said Paul-Henri Rebut, director of the Joint European Torus (JET) lab near Oxford. “It is clearly a major step forward in the development of fusion as a new source of energy.”

For nearly half a century, scientists have hoped that fusion--the process that fires the sun and warms the Earth--might one day be exploited to generate safe, cheap and dependable electric power. The process is well understood: In the solar core, the nuclei of hydrogen atoms are compressed so densely under such intense heat that they “fuse” into a heavier element, helium, releasing energy and a spray of subatomic particles.

Fusion can also be achieved on Earth--with explosive force, as in thermonuclear weapons, or in controlled bursts in a fusion reactor. Because Earthbound researchers cannot take advantage of the titanic gravity in the sun, they have to use temperatures of 100 million to 200 million degrees Celsius (about eight times hotter than the solar core) to induce hydrogen nuclei to fuse.

In the sun, even simple hydrogen atoms, consisting of one proton and one electron, can be squashed into heavier elements. In terrestrial labs, this is usually done by taking a quantity of deuterium--a “heavy” variant (or isotope) of hydrogen that has a neutron in addition to the proton in its nucleus--and blasting it with huge quantities of electricity. In the resulting heat, surrounding electrons disengage from the hydrogen, creating a “plasma” or soup of particles that is then confined in a doughnut-shaped (torus) reactor with powerful magnetic fields.

When two deuterium nuclei, each containing one proton and one neutron, fuse, they produce a helium nucleus with two protons and one neutron. The surplus neutron and a quantity of now-unneeded binding energy are released and slam into the side of the reactor chamber.

The heat generated by that energy can, in theory, be used to make steam and drive an electrical generator.

Scientists have long known that they would get much more energy if they could add to the plasma soup tritium, another isotope of hydrogen, which has two neutrons in its nucleus. Combining deuterium and tritium produces a helium nucleus with four particles, plus a surplus neutron and over five times as much energy as the deuterium-deuterium fusion.

There are only two facilities in the world that can handle a deuterium-tritium reaction--JET, which is funded by the European Community, Sweden and Switzerland, and the Tokamak Fusion Test Reactor (TFTR) at Princeton University--and both have been hard at work on the problem.

It will likely take decades, however, before reactors can be improved to the point at which they put out more energy than is required to ignite the plasma in the first place. (In order to achieve the JET reaction of 2 million watts, scientists had to whack the plasma with about about 15 million watts of power). And it may take even more decades to make the reactions “self-sustaining”--that is, capable of keeping themselves going in controlled circumstances. Maple said that a commercial fusion reactor would probably not be possible before 2040.

Even if the high-cost “tritium were free and we could use it tomorrow,” said Robert L. Park of the American Physical Society, “the capital costs of a fusion reactor would make it financially impossible to build in the near future.

“We still have no sensible way of harnessing the energy. Neutrons are one of the worst things on Earth to boil water with.”

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

“At TFTR,” he said, “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. 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.”