The Department of Energy plans to announce Tuesday that scientists have been able for the first time to produce a fusion reaction that creates a net energy gain — a major milestone in the decades-long, multibillion-dollar quest to develop a technology that provides unlimited, cheap, clean power.

The aim of fusion research is to replicate the nuclear reaction through which energy is created on the sun. It is a “holy grail” of carbon-free power that scientists have been chasing since the 1950s. It is still at least a decade — maybe decades — away from commercial use, but the latest development is likely to be touted by the Biden administration as an affirmation of a massive investment by the government over the years.

Huge amounts of public and private funds have been funneled into the fusion race worldwide, with the aim of ultimately manufacturing fusion machinery that could bring electricity to the grid with no carbon footprint, no radioactive waste and far fewer resources than it takes to harness solar and wind power. Beyond the climate benefits, promoters say it could help bring cheap electricity to impoverished parts of the world.

“To most of us, this was only a matter of time,” said a senior fusion scientist familiar with the work of the National Ignition Facility at the Lawrence Livermore National Laboratory in California, where the discovery was made.

The development was first reported by the Financial Times on Sunday. It was confirmed by two people familiar with the research, who spoke on the condition of anonymity to avoid getting ahead of the official announcement. Energy Secretary Jennifer Granholm was slated to make the announcement Tuesday at a media event billed as the unveiling of “a major scientific breakthrough.”

The department and the lab declined to comment. A lab official said researchers there are still finalizing their analysis and will not be releasing any official findings before Tuesday.

The science of nuclear fusion relies on smashing two atoms together at incredibly high speeds and transforming the energy from that reaction into electricity that can power homes and offices without emitting carbon into the air or dumping radioactive waste into the environment.

In the decades scientists have been experimenting with fusion reactions, they had not until now been able to create one that produces more energy than it consumes. While the achievement is significant, there are still monumental engineering and scientific challenges ahead.

Creating the net energy gain required engagement of one of the largest lasers in the world, and the resources needed to recreate the reaction on the scale required to make fusion practical for energy production are immense. More importantly, engineers have yet to develop machinery capable of affordably turning that reaction into electricity that can be practically deployed to the power grid.

Building devices that are large enough to create fusion power at scale, scientists say, would require materials that are extraordinarily difficult to produce. At the same time, the reaction creates neutrons that put a tremendous amount of stress on the equipment creating it, such that it can get destroyed in the process.

And then there is the question of whether the technology could be perfected in time to make a dent in climate change.

Even so, researchers and investors in fusion technology hailed the breakthrough as an important advancement.

“There is going to be great pride that this is something that happened in the United States,” said David Edelman, who leads policy and global affairs at TAE, a large private fusion energy company. “This is a very important milestone on the road toward fusion energy.”

It comes as the Biden administration is prioritizing fusion energy research in its climate and energy agenda. The projects are among the front of the line for the tens of billions of dollars in subsidies and grants authorized through the major climate package Biden signed over the summer, called the Inflation Reduction Act.

Over the past several decades, the United States, Russia and various European nations have allocated billions in government dollars trying to master the science, believing that if they could, it would be a boon for the world.