Net energy gain shows that technology could provide a lot of fossil fuel alternatives that don’t produce any carbon. Please use the tools for sharing that can be found by clicking the share button at the top or side of each article. The FT.com Terms and Conditions and Copyright Policy say that you can’t copy articles to give them to other people.

To buy more rights, send an email to licensing@ft.com. With the gift article service, subscribers can send up to 10 or 20 articles to other people each month. You can find out more here. According to three people who know the preliminary results of a recent experiment, US government scientists have made a big step forward in their search for unlimited, carbon-free power by getting a net energy gain from a fusion reaction for the first time.

Fusion energy  Since the 1950s, physicists have tried to harness the fusion reaction that powers the sun. However, no group had been able to get the reaction to produce more energy than it uses. This is called “net energy gain” or “target gain,” and it would show that the process could be a reliable, abundant alternative to fossil fuels and traditional nuclear energy.

People said that in the last two weeks, a fusion experiment at the federal Lawrence Livermore National Laboratory in California, which uses a process called “inertial confinement fusion” that involves hitting a tiny pellet of hydrogen plasma with the world’s biggest laser, had produced net energy gain.

Even though many scientists think fusion power plants are decades away, it’s hard to ignore the potential of the technology. Fusion reactions don’t give off carbon or long-lasting radioactive waste, and a small cup of hydrogen fuel could, in theory, power a house for hundreds of years.

The US breakthrough comes at a time when the rest of the world is struggling with high energy costs and the need to quickly stop burning fossil fuels to keep average global temperatures from rising to dangerous levels. With the help of the Inflation Reduction Act, President Joe Biden’s administration is putting almost $370 billion into new subsidies for low-carbon energy in an effort to cut emissions and win the global race for the next generation of clean technology.

People who know about the results said that the fusion reaction at the US government facility made about 2.5 megajoules of energy, which is about 120% of the 2.1 megajoules of energy in the lasers. The data is still being looked at.