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National Ignition Facility surpasses long-awaited fusion milestone

13 December 2022

The shot at Lawrence Livermore National Laboratory on 5 December is the first-ever controlled fusion reaction to produce an energy gain.

Illustration of a laser shot at the National Ignition Facility.
In the indirect-drive method used at the National Ignition Facility, a UV laser is fired at a cylinder called a hohlraum rather than at the hydrogen fuel. The hohlraum then emits x rays, which compress the fuel inside. Credit: Lawrence Livermore National Laboratory

Thirteen years after completion of the $3.5 billion National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL), the goal embodied in the giant laser’s name has finally been achieved. For the first time in the nearly 70-year history of controlled fusion research, a fusion reaction has yielded more energy than it took to spark it.

According to Mark Herrmann, program director for weapons physics and design at LLNL, a laser shot performed on 5 December produced about 3.15 megajoules of fusion energy from the 2.05 MJ of laser light that reached the small cylindrical chamber known as a hohlraum, which converts the UV to x rays. Suspended inside was a diamond-coated, peppercorn-size capsule containing deuterium–tritium fuel, which the x rays imploded.

The results were officially announced by Energy secretary Jennifer Granholm, Office of Science and Technology Policy director Arati Prabhakar, and other officials on 13 December. The findings have not been peer reviewed, and Herrmann says he would have preferred they be released through a scientific journal. But the results were sure to leak out, and it was important that the advance be reported correctly, he adds.

The yield surpasses the criteria for ignition established by the National Research Council in 2007. By other measures, such as the amount of energy deposited on the fuel capsule—around 250 kilojoules—the gain, or Q, is around 10, says Michael Campbell, who led NIF construction until 1999. Yet the amount of fusion energy from the record shot amounts to just 1% of the 300 MJ from the grid that’s required to power the 192-beam NIF laser, Herrmann says. Thus, although the lab’s achievement is a significant step, inertial fusion is still a long way from becoming a viable energy source.

Ignition is a key process in nuclear weapons, says Herrmann, and will enable experiments in which materials can be exposed to highly intense fluxes of the 14 MeV neutrons that are produced in fusion reactions. That, he says, has direct application to maintaining the weapons stockpile—NIF’s primary mission.

NIF fusion yields versus time.
Over the past few years, NIF researchers have made strides in producing more energetic fusion reactions. The record-breaking 5 December shot benefited from a laser energy of 2.05 MJ, as opposed to 1.9 MJ for the shots conducted in previous years. The bar colors represent different design approaches. Credit: Mark Herrmann/LLNL

The success caps what has been a tortuous path for NIF, which was controversial even before its construction began in 1997. The project began as a lifeline to LLNL, which faced an existential threat in the post-Cold War era, says Victor Reis, former assistant secretary for defense programs at the Department of Energy and a progenitor of DOE’s science-based program to maintain the nuclear stockpile without testing. One DOE advisory commission had recommended consolidating weapons research at Los Alamos National Laboratory. “People were saying we don’t need Livermore,” Reis says. “You really needed some big science projects that [would] test the laboratories. NIF was that for Livermore.”

After delays and budget overruns, NIF opened for experiments in 2009. The facility then missed its original 2012 target for ignition. In a 2016 report, DOE’s National Nuclear Security Administration (NNSA) expressed doubt that what remains the world’s most energetic laser could ever attain its eponymous mission. The agency toned down the ignition objective, emphasizing NIF’s ongoing experiments to investigate materials’ behavior under extreme densities and pressures in support of nuclear stockpile maintenance. About 10% of NIF’s shots are reserved for unclassified research by academic researchers.

Many scientists believed that the laser’s energy was insufficient to overcome laser–plasma instabilities, which create pancake- or sausage-shaped asymmetric implosions. In response, NIF researchers have tried out numerous capsule and hohlraum configurations and materials. Campbell credits NIF’s latest achievement to advances in the last four to five years in the understanding of hohlraums and improved capsule fabrication, with contributions from other labs and the private sector.

As with the previous record shot in August 2021, the lab used nanocrystalline diamond–coated capsules for experiments. When blasted with x rays, the diamond shell blows off like a rocket, creating the implosion. The shell used in last week’s shot was about 10% thicker than those in previous attempts.

“We’ve always known we’re sensitive to defects in the capsules, but we had been blind to some of the defects in our metrology and the types of defects that were actually significant,” says Herrmann. “When we did follow-on experiments, we found there was more mixing of the capsule material into the fusion fuel, which was lowering the performance of implosions. Over the last year, we’ve put together a picture that says we have accounted for the degradations we observe.”

Another major contributor to last week’s success was the 10% increase to NIF’s original 1.9 MJ maximum laser energy. “It’s not that the laser couldn’t produce more energy,” Herrmann says, “but we didn’t want to break the laser.” In recent years, laser and optical scientists have succeeded in hardening the optics.

NIF's achievement in perspective.
Researchers at NIF achieved ignition by generating more energy in fusion reactions (green circles) than was delivered by the laser (yellow circles). But each laser shot requires about 300 MJ of energy from the grid (gray circles). Energy amounts are approximate. Credit: Andrew Grant and Greg Stasiewicz; created in Flourish

Campbell predicts the achievement will spark another frenzy of interest in fusion as an energy source. But laser fusion energy has a long list of engineering hurdles to overcome, such as finding ways to mass manufacture fusion capsules, to conduct laser shots continually, and to breed tritium.

“Ignition is a necessary but not sufficient condition for stewardship, because you’d want higher gain for stewardship, but it’s a really good start,” says Campbell, who retired last year as director of the DOE-supported Laboratory for Laser Energetics at the University of Rochester. “It shows the quality of the science and technology that NIF represents.”

Herrmann agrees that “the more the output, the more the utility for stockpile stewardship.” He thinks NIF could one day routinely produce laser pulses of 2.6–3 MJ to help initiate higher-gain reactions. “That will take many years, and we are discussing that with NNSA.”

There shouldn’t be any concerns about the size of the explosions inside NIF’s target chamber. It’s currently rated to safely accommodate yields up to 45 MJ, Herrmann says, and modest upgrades could increase that to 100 MJ.

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