To create what can be called a miniature star, scientists needed 192 lasers that were installed in a high-security federal government building the size of a football stadium, reports The Washington Post. The lasers were fired into a small chamber containing a pellet of hydrogen about half the size of a 4.5 mm BB.

As the beam fired, the atomic particles in the gas fused together and released more energy than was used by the lasers. The first achievement in the history of nuclear fusion took place on December 5 at the Lawrence Livermore National Laboratory facility in Northern California and was officially announced on Tuesday at a press conference in Washington. It’s a major milestone in decades of efforts to harness nuclear fusion, an energy source that has the potential to generate large amounts of clean electricity, officials said.

The announcement of the experimental success came bracketed by cautionary notes. It may be many more years before this technology can be employed for everyday use. This was a science experiment more than a demonstration of a practical technology.

However, this was the first time anyone had managed to create a net increase in energy. The experiment delivered 2.05 megajoules of energy to the lasers’ target and resulted in 3.15 megajoules of energy at the output, officials said. Basically, two in, three out.

“This is a landmark achievement,” Energy Secretary Jennifer Granholm said at department headquarters Tuesday. The department runs the Livermore lab and its National Ignition Facility, where the experiment took place. “This milestone will undoubtedly spark even more discovery. … This is what it looks like for America to lead.”

Pointing to the challenges ahead for real-world application of the technology, the results do not take into account the 300 megajoules of energy required to create the lasers in the first place.

This is not the only experiment to produce fusion, and there is now something of a race to see which method works best. For decades, the field was dominated by fusion experiments involving powerful magnets, not lasers.

“I’m not sure magnetic fusion is going to beat [laser] fusion,” said Steven Cowley, director of the Department of Energy’s Princeton Plasma Physics Laboratory, which uses magnets in its fusion experiments. “I think fusion is so important we should have at least two technologies vying for completion. One of them is going to end up the airplane, and one of them is going to end up the Hindenburg.”

The Biden administration is aggressively pushing investments in clean energy technologies such as fusion, which are still years away from practical deployment. Scientists warn that while nuclear power has the potential to provide a 24-hour supply of electricity without the pollution or radioactive risks of traditional coal, gas and nuclear power plants, it will be a long time before any of it is brought to the grid.

“Probably decades,” said Kim Budil, director of the Lawrence Livermore laboratory. “Not five decades, which is what we used to say. I think it’s moving into the foreground. And probably with concerted effort and investment, a few decades of research on the underlying technologies could put us in a position to build a power plant.”

The reaction that scientists produced at the National Ignition Facility required the firing of an immense laser system that was built only after massive cost overruns and years of delays. The development touched off a new round of debate about how far government should go in incubating multibillion-dollar long-shot technologies that may never get put to use commercially — but could change the world if they make it to market.

Producing electricity from nuclear fusion would require a reaction, which was reported Tuesday and is called “ignition,” every second throughout the day. Achieving this would be a monumental engineering feat. After all, just producing a fraction of a second of net energy gain, as happened during an experiment at the Livermore Laboratory, puts such a heavy load on expensive equipment that the process tends to break it down.

Commercial fusion energy has been a marginal pursuit for years amid disappointing results from national laboratories and constant threats that funding for fusion experiments will be cut.

“We had some rocky times,” said Rep. Zoe Lofgren, a Bay Area Democrat who fought multiple efforts to defund the National Ignition Facility. “To see they have achieved ignition is fabulous. It is a profound breakthrough that brings an enticing promise that we could produce a nonpolluting, basically limitless source of energy.”

Whether this promise will ever be fulfilled is hotly debated among scientists.

“Useful energy production from miniature fusion explosions still faces enormous engineering challenges, and we don’t know if those challenges can be overcome,” said Ian Hutchinson, a professor of nuclear science and engineering at MIT (Massachusetts Institute of Technology).

Scientists will now focus on finding more practical and affordable ways to recreate the thermonuclear reaction that powers the Sun. In the core of the Sun, the enormous pressure forces the hydrogen nuclei to gather together. They combine to create helium and other light elements, turning part of the mass into energy.

This is such an efficient way of producing energy that it has allowed the Sun to burn at a constant rate for many billions of years, long enough for life to appear and develop on our sun-warmed planet some 93 million kilometers away.

Nuclear fusion also allows hydrogen bombs to cause extremely powerful explosions. Such thermonuclear bombs are much more powerful than atomic bombs, which use nuclear fission, and in which atoms split rather than fuse.

The peaceful use of nuclear fusion has been a technological goal for decades. Experimental fusion reactors heat plasma — free electrons and atomic nuclei — to temperatures in excess of 100 million degrees Celsius, hotter than the Sun’s core.

The next step is to contain this hot plasma in a tiny space where the atomic particles can potentially undergo a fusion reaction. This can be done in a variety of ways, as reflected in the various business plans of energy startups that hope to eventually harness fusion energy into the grid.

The history of research in the field of nuclear fusion is a history of gradual achievements and periodic disappointments.

It’s been a long and expensive job, largely funded by the US government as well as other governments, and there’s still a long way to go. A standard joke in the industry is that commercially available fusion power is always 20 years (or so) away.