A TWO-SECOND burst of energy, 10 times hotter than the sun's core, has put European scientists on course for generating virtually limitless amounts of cheap, pollution-free electricity in the 21st century.What nuclear scientists at the Joint European Torus (JET) laboratory at Culham, near Oxford, England, describe as a "quantum leap" in nuclear physics occurred at supper time on Nov. 9. Alan Gibson, associate director of the 14-nation JET project, says he and fellow researchers had spent 35 years pursuing the goal of controlled nuclear fusion. "At last we have succeeded. It is a real milestone," Dr. Gibson says. The successful experiment is being compared by scientists at Culham to the work of Enrico Fermi, the Italian-born physicist who, working at the University of Chicago in 1941, achieved the first self-sustaining nuclear-fission reaction. This led to the creation of the present type of nuclear-power station. The Culham experiment, carried out inside a 3,500-ton doughnut-shaped fusion reactor and witnessed by 200 scientists, produced only 2 megawatts of power - enough to boil a few hundred kettles, as one researcher remarked. But, Gibson says, the technique used is what mattered. Unlike fission reactors, which split atoms to produce energy, the Torus reactor pushed atoms of deuterium and tritium together. Their collision generated a temperature of 200 million degrees C (350 million degrees F.). The Torus - a graphite-lined vacuum chamber the height of three London double-decker buses - was able to contain the resulting plasma (a "soup" of positively and negatively charged particles) long enough for the heat not to spill away. It is the success of the containment process that is elating scientists, some of whom have been involved in hydrogen-weapons research, which uses a comparable (but uncontained) fusion technique. The United States physicist Edward Teller once said trying to hold plasma within lines of magnetic force was like confining jelly with rubber bands. "That is what we have succeeded in doing," says Angus Swanson of the British Nuclear Energy Society. Workers on the JET project are well aware that in recent years there have been a number of anti-climaxes in chasing the dream of fusion power. Two years ago scientists at the University of Utah in the United States claimed to have achieved "cold fusion," using comparatively simple bench-top techniques. Their experiments came under attack and have since been largely discredited. There was nothing bench-top about the Culham breakthrough. The apparatus took 18 years to plan and build, and cost British pounds1 billion ($1.78 billion). Paul-Henri Rebut, head of the JET team, came to Britain from France in 1973 to launch the project. Working with a team of 450 scientists, engineers, and other staff, he set about designing a fusion chamber that in effect provided the "rubber bands." "The whole project is a team effort, and all the nationalities pulled together," Dr. Rebut says. "This is the first time that a significant amount of power has been obtained from controlled nuclear-fusion reactions. "It is clearly a major step forward in the development of fusion as a new source of energy. It confirms Europe's leading position in fusion research. We are ahead of our main rivals in the US, the Princeton Plasma Physics Laboratory." The theoretical advantages of "bottling the sun's power," as science journalists describe the fusion process, are enormous. Fusion does not run the risk of producing accidental chain reactions, as happened at Chernobyl and Three Mile Island. Unlike uranium, which is used in today's nuclear-power stations, nuclear fission fuels are cheap, safe, and plentiful, Mr. Swanson says. Deuterium and tritium are present in seawater. According to senior researchers at Culham, about one pound of fusion fuel could generate as much energy as a million gallons of oil. A fusion reactor would not produce radioactive waste. Only the fusion "bottle" and other parts of the reactor would create future environmental hazards, Rebut says. Explaining the methods used at Culham, Rebut says the crucial step forward had been the use of tritium - an isotope of hydrogen. Deuterium by itself is fairly easy to handle but is not an ideal fuel. The addition of a "puff" of radioactive tritium, however, had altered the energy balance of the plasma by throwing off neutrons at a high rate. Theoretical work at Culham, Rebut says, suggested that 10 grams of deuterium and 15 grams of radioactive tritium could meet the energy needs of one person living for 70 years. How long will it be before that stage is reached? John Maple, a spokesman for the Culham Laboratory, says it would probably be 40 to 50 years before the first commercial fusion-power station using a 50-50 mix of deuterium and tritium began operating. Scientists do not yet fully understand the behavior of the nuclear plasma generated by the fusion process, Mr. Maple says. As temperature increases, the plasma becomes more unstable and begins to degenerate in quality. There is a problem with impurities from the containment vessel entering the plasma and reducing its heat-generating capacity. Rebut says it will take some years to come to grips with these challenges. Then the task of designing, building, and paying for a working fusion reactor must be confronted. Already finance is proving a problem for the JET project. Funds have been coming from an annual British pounds75 million grant from the European Community, and until the Nov. 9 breakthrough, there were indications that Brussels might be about to order a cutback on its outlay. Rebut hopes the successful experiment will guarantee a steady flow of funds in the future. "Just now money is short," he says. IN the longer term, a much broader international effort will be required to move beyond the present research stage and launch a full quest for commercial fusion power. Steps in this direction are already being taken. Physicists in Europe, the United States, Japan, and the Soviet Union have opened contacts with each other with the aim of building what they call ITER - the International Thermonuclear Experimental Reactor. A likely site for ITER would be near San Diego, but there is certain to be enormous rivalry. Britain had to battle hard against European rivals before Culham was chosen as the site for JET. Rough forecasts suggest that ITER would cost about British pounds3 billion. If the necessary money can be mobilized in time, the reactor could begin operating in the first decade of the 21st century. The super-hot plasma in the station would be used to heat water to rotate turbines, much as happens in existing commercial fission reactors. The process would cause insignificant atmospheric pollution and would not contribute to global warming, according to leading members of the JET team. Meanwhile, Rebut and his international colleagues are already working on plans to take the JET doughnut apart and provide it with new inner walls that will prevent the hot plasma from being contaminated by impurities. This, Rebut says, is the key to being able to contain the plasma for longer periods. He and the JET team have set the target of 1996 for reaching that point.