Enlarge / Researchers at the Lawrence Livermore National Laboratory in California have used the world’s most powerful laser to fuse the nuclei of hydrogen isotope. (credit: John Jett & Jake Long/Lawrence Livermore National Laboratory/Reuters)

US government scientists have achieved net energy gain in a fusion reaction for the second time, a result that is set to fuel optimism that progress is being made toward the dream of limitless, zero-carbon power.

Physicists have since the 1950s sought to harness the fusion reaction that powers the Sun, but until December no group had been able to produce more energy from the reaction than it consumes—a condition also known as ignition.

Researchers at the federal Lawrence Livermore National Laboratory in California, who achieved ignition for the first time last year, repeated the breakthrough in an experiment on July 30 that produced a higher energy output than in December, according to three people with knowledge of the preliminary results.

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Enlarge / Where the action happens inside the National Ignition Facility. (credit: Damien Jemison/LLNL )

On Tuesday, the US Department of Energy (DOE) confirmed information that had leaked out earlier this week : its National Ignition Facility had reached a new milestone, releasing significantly more fusion energy than was supplied by the lasers that triggered the fusion. "Monday, December 5, 2022 was an important day in science," said Jill Hruby, head of the National Nuclear Security Administration. "Reaching ignition in a controlled fusion experiment is an achievement that has come after more than 60 years of global research, development, engineering, and experimentation."

In terms of specifics, the lasers of the National Ignition Facility deposited 2.05 megajoules into their target in that experiment. Measurements of the energy released afterward indicate that the resulting fusion reactions set loose 3.15 megajoules, a factor of roughly 1.5. That's the highest output-to-input ratio yet achieved in a fusion experiment.

Before we get to visions of fusion power plants dotting the landscape, however, there's the uncomfortable fact that producing the 2 megajoules of laser power that started the fusion reaction took about 300 megajoules of grid power, so the overall process is nowhere near the break-even point. So, while this was a real sign of progress in getting this form of fusion to work, we're still left with major questions about whether laser-driven fusion can be optimized enough to be useful. At least one DOE employee suggested that separating it from its nuclear-testing-focused roots may be needed to do so.

Enlarge / The high-powered Nova Laser before it creates nuclear fusion inside its target chamber at the Lawrence Livermore National Laboratory. (credit: Corbis via Getty Images )

US government scientists have made a breakthrough in the pursuit of limitless, zero-carbon power by achieving a net energy gain in a fusion reaction for the first time, according to three people with knowledge of preliminary results from a recent experiment.

Physicists have since the 1950s sought to harness the fusion reaction that powers the sun, but no group had been able to produce more energy from the reaction than it consumes — a milestone known as net energy gain or target gain, which would help prove the process could provide a reliable, abundant alternative to fossil fuels and conventional nuclear energy.

The federal Lawrence Livermore National Laboratory in California, which uses a process called inertial confinement fusion that involves bombarding a tiny pellet of hydrogen plasma with the world’s biggest laser, had achieved net energy gain in a fusion experiment in the past two weeks, the people said.

Enlarge / Where the action happens inside the National Ignition Facility. (credit: Damien Jemison/LLNL )

On Monday, a paper was released that describes some confusing results from the National Ignition Facility, which uses a lot of very energetic lasers focused on a small target to begin a fusion reaction. Over the past few years, the facility has passed some key milestones, including ignition of fusion and creating what's termed a burning plasma.

Now, researchers have analyzed the properties of the plasma as it experiences these high-energy states. And to their surprise, they found that burning plasmas appear to behave differently from those that have experienced ignition. At the moment, there's no obvious explanation for the difference.

Ignition vs. burning

In the experiments at issue here, the material being used for fusion is a mix of tritium and deuterium, two heavier isotopes of hydrogen. These combine to produce a helium atom, leaving a spare neutron that's emitted; the energy of the fusion reaction is released in the form of a gamma ray.