Nuclear-fusion lab achieves ‘ignition’: what does it mean?

Scientists at the world’s largest nuclear-fusion facility have for the first time achieved the phenomenon known as ignition — creating a nuclear reaction that generates more energy than it consumes. Results of the breakthrough at the US National Ignition Facility (NIF), conducted on 5 December and announced today by US President Joe Biden’s administration, has excited the global fusion-research community. That research aims to harness nuclear fusion — the phenomenon that powers the Sun — to provide a source of near-limitless clean energy on Earth. Researchers caution that, despite the latest success, a long path remains to achieving that goal.

“It’s an incredible accomplishment,” says Mark Herrmann, the deputy director for fundamental weapons physics at Lawrence Livermore National Laboratory in California, which houses the fusion laboratory. The landmark experiment follows years of work by multiple teams on everything from lasers and optics to targets and computer models, Herrmann says. “That is of course what we are celebrating.”

A flagship experimental facility of the US Department of Energy’s nuclear-weapons programme that was designed to study thermonuclear explosions, NIF originally aimed to achieve ignition by 2012 and has faced criticism for delays and cost overruns. In August 2021, NIF scientists announced that they had used their high-powered laser device to achieve a record reaction that crossed a critical threshold on the path to ignition, but efforts to replicate that experiment, or shot, in the following months fell short. Ultimately, scientists scrapped efforts to replicate that shot and rethink the experimental design — an effort that paid off last week.

“There were a lot of people who didn’t think it was possible, but I and others who kept the faith feel somewhat vindicated,” says Michael Campbell, former director of the fusion laboratory at the University of Rochester in New York and an early proponent of NIF while at Lawrence Livermore lab. “I’m having a cosmo to celebrate.”

Nature looks at NIF’s latest experiment and what it means for fusion science.

What did NIF achieve?

The facility used its set of 192 lasers to deliver 2.05 megajoules of energy onto a pea-sized gold cylinder containing a frozen pellet of the hydrogen isotopes deuterium and tritium. The pulse of energy caused the capsule to collapse, creating temperatures only seen in stars and thermonuclear weapons, and the hydrogen isotopes fused into helium, releasing additional energy and creating a cascade of fusion reactions. The laboratory’s analysis suggests that the reaction released some 3.15 megajoules of energy — roughly 54% more than the energy that went into the reaction, and more than double the previous record of 1.3 megajoules.

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