![]() In terms of energy released, nuclear reactions pack roughly a million times more punch than chemical reactions do-and are vastly harder to get going. If that tiny fraction ignites, the energy it releases is enough to ignite the rest of the fuel. The spark isn’t massive, but it doesn’t have to be: All it has to do is ignite a small fraction of the gasoline-air mixture. A small amount of gasoline mixes with air and then ignites from a spark. Physicist Riccardo Betti, an expert on laser-driven nuclear fusion at the University of Rochester, likens the challenge of fusion ignition to burning gasoline in an engine. Yet it’s so diffuse, it easily cools off. To support fusion, it has to reach truly staggering temperatures. ![]() ![]() The trouble is, plasma is unruly: It’s electrically charged, which means it both responds to magnetic fields and generates its own as it moves. Since the late 1950s and early 1960s, fusion reactors have had the same basic goal: create as hot and dense a plasma as possible, and then confine that material for long enough that the nuclei within it reach ignition. Scientists learned decades ago how to unleash this process explosively inside hydrogen bombs, and today’s fusion reactors can make it happen in a controlled way for fleeting instants. In laboratories, coaxing hydrogen nuclei to fuse into helium requires creating and confining a “plasma”-an electrically charged gas, where electrons are no longer bound to atomic nuclei-at temperatures several times hotter than inside the sun. In the process, they release a small part of their combined mass as energy. In fusion, however, small, light atoms such as hydrogen fuse into bigger ones. Today’s nuclear power plants rely on nuclear fission, which releases energy when large, heavy atoms such as uranium break apart due to radioactive decay. Though nuclear fusion and nuclear fission both draw energy from the atom, they operate differently. “It looks like science fiction, but they did it, and it’s fantastic what they’ve done,” says Ambrogio Fasoli, a fusion physicist at the Swiss Federal Institute of Technology in Lausanne. “It’s a fundamental building block.”Įven so, after decades of trying, scientists have taken a major step toward fusion power. “I don’t want to give you the sense that we’re going to plug the NIF into the grid-that’s not how this works,” Budil added. According to Kim Budil, director of Lawrence Livermore National Laboratory, the lasers required 300 megajoules of energy to produce about 2 megajoules’ worth of beam energy. While NIF’s reaction produced more energy than the reactor used to heat up the atomic nuclei, it didn’t generate more than the reactor’s total energy use. The achievement does not mean that fusion is now a viable power source. Being able to study the conditions of ignition in detail will be “a game-changer for the entire field of thermonuclear fusion,” says Johan Frenje, an MIT plasma physicist whose laboratory contributed to NIF’s record-breaking run. In reaching scientific breakeven, NIF has shown that it can achieve “ignition”: a state of matter that can readily sustain a fusion reaction. Energy Secretary Jennifer Granholm said at a Washington, D.C. “Simply put, this is one of the most impressive scientific feats of the 21st century,” U.S. Fusion researchers have long sought to achieve net energy gain, which is called scientific breakeven. Though the conflagration ended in an instant, its significance will endure. In a tiny blaze lasting less than a billionth of a second, the fusing atomic nuclei released 3.15 megajoules of energy-about 50 percent more than had been used to heat the pellet. The pellet compressed and generated temperatures and pressures intense enough to cause the hydrogen inside it to fuse. On December 5, an array of lasers at the National Ignition Facility (NIF), part of the Lawrence Livermore National Laboratory in California, fired 2.05 megajoules of energy at a tiny cylinder holding a pellet of frozen deuterium and tritium, heavier forms of hydrogen. For the first time, a fusion reactor has produced more energy than was used to trigger the reaction. ![]() Today, researchers announced a milestone in this effort. For more than 60 years, scientists have pursued one of the toughest physics challenges ever conceived: harnessing nuclear fusion, the power source of the stars, to generate abundant clean energy here on Earth.
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