The World's Biggest Laser Powers Up

Now complete, the National Ignition Facility could soon create controlled fusion using lasers.

The most energetic laser system in the world, designed to produce nuclear fusion--the same reaction that powers the sun--is up and running. Within two to three years, scientists expect to be creating fusion reactions that release more energy than it takes to produce them. If they're successful, it will be the first time this has been done in a controlled way--in a lab rather than a nuclear bomb, that is--and could eventually lead to fusion power plants.

Fusion central: 192 lasers will shoot through openings in this spherical chamber, focusing near the tip of the cone projecting from the right. A worker in a service module can be seen at the left. Credit: Lawrence Livermore National Security, LLC, Lawrence Livermore National Laboratory, and the Department of Energy

The National Ignition Facility (NIF), at the U.S. Department of Energy's Lawrence Livermore National Laboratory (LLNL), comprises 192 lasers that fire simultaneously at precisely the same point in space: a sphere of fuel two millimeters in diameter. They are designed to deliver 1.8 megajoules of energy in a few billionths of a second. That's enough to compress the fuel to a speck 50 micrometers across and heat it up to three million degrees Celsius. The lasers, which were fired together for the first time last month, have so far produced pulses of 1.1 megajoules.

"Depending on how you count it, it's between 60 and 100 times more energetic than any laser system that's ever been built," says Edward Moses, the principle associate director for NIF and Photon Science at LLNL. Eventually, the fusion reactions produced by each pulse are expected to generate at least 10 times the energy delivered by the lasers, a significant net gain that could be useful for generating power.

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The $3.5 billion facility, which has been in development for 15 years, was funded primarily as a way to better understand nuclear weapons, after a ban on testing in the 1990s. NIF will produce tiny thermonuclear explosions that give scientists insight into what happens when a nuclear bomb goes off. That data can, in turn, be used to verify computer simulations that help determine whether the United States' nuclear stockpile will continue to work as the weapons age. The data could also provide insight into the processes that power the sun and other stars, and answer other scientific questions. Finally, NIF could serve as a proof-of-concept design for a fusion power plant.

To generate fusion, 192 laser beams are generated, amplified, converted from infrared to ultraviolet light, and then aimed at a small gold canister the size of a pencil eraser. Inside that canister is a sphere containing the fuel: two isotopes of hydrogen called deuterium and tritium. The lasers are positioned all around the sphere to create the temperatures and pressures needed to ignite a fusion reaction. If all goes as planned, some of the hydrogen atoms should fuse, producing helium and releasing energy. This should, in turn, cause more fusion reactions until the fuel runs out. The whole process will take just a few billionths of a second.