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A nuclear fusion reaction has produced the brightest X-rays ever on Earth, rivalling those emitted by some stars. This could open the door for new extreme experiments, such as mimicking how the sun absorbs radiation and testing how materials that could improve future fusion reactions hold up to nuclear blasts.

The reaction itself was also hotter than the sun. “The truth of the matter is, when the fuel is burning, and ignition is occurring, and that [blast] wave is propagating out, we’re hotter than the sun,” says Ryan Lester at Los Alamos National Laboratory in New Mexico. “We are the hottest point in the local solar system.”

In 2021, researchers at the Lawrence Livermore National Laboratory’s National Ignition Facility in California achieved nuclear fusion ignition, a reaction that is energetic enough to be self-sustaining. This was a milestone on the path to developing nuclear fusion as a useful source of energy.

Now, Lester and his colleagues have added windows to the tiny cylinder within which ignition happens. This let out the brightest X-rays ever created in the lab and turned ignition into an unprecedentedly extreme physics experiment.

The researchers shot 192 very energetic laser beams into a gold cylinder about the size of a pencil eraser, which contained a carbon capsule filled with heavy versions of hydrogen atoms. The beams generated a bath of X-rays that compressed and heated the capsule so much that the hydrogen fuel started to undergo nuclear fusion, leading to ignition.

Once ignition happened, the windows evaporated and let the X-rays out, emitting tens of trillions of watts of power, on a par with the brightness of some red dwarf stars.

There are decades of computer simulations, prototyping and experimental tests behind every element of the apparatus that ultimately achieved ignition, says Lester. “This is a highly refined, highly optimised system to keep the radiation in, keep it warm [and] control capsule symmetry so that all the things line up in a perfect row and ignition can occur,” he says.

Laura Berzak Hopkins at the Princeton Plasma Physics Laboratory in New Jersey says that achieving ignition in the first place was a generational accomplishment, requiring details that researchers have worked on for decades. It is significant that ignition could not only be repeated, but repeated with a modified cylinder, she says.

To move from demonstrating ignition to using nuclear fusion as an efficient energy source, we have to learn something new about it every time it happens, says Berzak Hopkins. Lester and his colleagues have shown more ways to do so, she says.

Most studies of extremely energetic conditions, whether in nuclear fusion reactors or stars, rely on computer simulations, but the latest experiment could offer a more direct and exact alternative. One notable example would be studies of the sun’s opacity, or how some elements within it absorb radiation.

Lester says he hopes the experiment will also aid in designs for future ones, for example by providing a more detailed view of what happens when very low-density foams are added to the capsule. This is because it has been theorised that they could stabilise the reaction and make it more efficient. Such experiments could start as early as next year, he says.

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