Since 2010, scientists at Lawrence Livermore National Laboratory’s National Ignition Facility (NIF) in California have sought to harness fusion, a physical process that releases energy from nuclear reactions. Nuclear fusion is the natural process that powers the Sun and other stars. Initially discovered in the 1930s, physicists have attempted to harness this process for controlled energy production ever since. Until recently, those attempts failed because more energy was required to power the reaction than was produced. However, on December 5, 2022, NIF scientists reported the first fusion reaction in a laboratory setting that produced more energy than the laser energy required to power the reaction. While there are still many hurdles to overcome, researchers are cautiously optimistic that this breakthrough could eventually lead to carbon-free fusion power plants that would aid in the fight against global climate change. In the meantime, the findings will advance NIF's research goal of helping assess the reliability and safety of the United States' nuclear weapons stockpile. See also: Energy; Global climate change; Nuclear fusion

Laser preamplifiers at the National Ignition Facility at Lawrence Livermore National Laboratory. These preamplifiers increase the energy of the laser’s light by a factor of 10 billion and shape the beam into a square to be passed into the amplifiers for further shaping and power increase. (Credit: Damien Jemison/Lawrence Livermore National Lab under CC BY-SA 3.0 license)

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Today’s nuclear power plants are powered by fission reactions, which involves breaking apart heavy atoms in radioactive decay. Nuclear fusion, on the other hand, involves the buildup of lighter atoms into heavier, larger atoms. Nuclear fusion is highly attractive as an energy source compared to fission. The nuclear fuel for fusion reactions—primarily a type of hydrogen—is available in virtually inexhaustible supply and readily extractable from seawater, and less radioactive wastes are generated in the process. Fusion also releases about four times more energy than fission. Compared to the burning of fossil fuels such as coal, oil, and gas, fusion releases four million times more energy in equivalent mass and does not generate climate-warming carbon dioxide or other greenhouse gases. See also: Atom; Fossil fuel; Greenhouse effect; Nuclear fission; Nuclear power; Radioactive waste management

To initiate nuclear fusion, atomic nuclei must be squeezed together under extreme temperatures in excess of 100 million degrees Celsius and extreme pressures 100 billion times that of Earth's atmosphere. Such conditions have been expectedly very difficult to obtain on Earth, except in brief, uncontrolled moments—for instance, during detonation of thermonuclear weapons. NIF researchers devised a way to reach these required extremes through what is known as inertial confinement fusion. Their approach involved focusing 192 amplified, high-energy x-ray lasers on a diamond housing that subsequently imploded onto a small hydrogen target. The lasers ultimately heated and compressed the target enough to trigger the fusion reaction that released more energy than was used to start the reaction—a condition known as ignition and the chief aim of NIF. Specifically, 2.05 megajoules of energy—about the amount of energy the average U.S. household consumes in 40 minutes—pumped in via laser resulted in a hydrogen fusion reaction that produced 3.15 megajoules of energy, representing an increase in energy of just over 50%. See also: Atomic nucleus; Hydrogen; Inertial confinement fusion; Laser

This long-awaited result is a small but critical step toward developing a functional fusion power plant which—if based on NIF's approach—would require overcoming major engineering challenges to scale up energy production and be commercially viable. For instance, whereas the fusion reaction at NIF produced a net gain of energy, the inertial confinement process as a whole resulted in a net energy loss due to the energy required to prepare the laser array to fire. One of the nearer-term benefits of the results, though, will be creating controlled fusion reactions for studying nuclear weapons. Since the U.S. stopped performing underground nuclear weapons tests in 1992, the nation has sought alternative ways of gathering data on nuclear explosions without detonating warheads. Overall, the ignition breakthrough, along with continuing research at NIF and the insights the facility's work will provide for other fusion researchers, have raised hopes for fusion energy and enhanced nuclear weapons stockpile stewardship. See also: Hydrogen bomb; Nuclear explosion