LIVERMORE, California - After more than 50 years of false starts, nuclear fusion is finally taking a resolute step closer to becoming the world’s newest energy source.

The United States Department of Energy on Tuesday announced that scientists at a laboratory in California managed for the first time to generate more electricity from a fusion reaction than they needed to trigger it.

The historic breakthrough raises the prospect that someday – perhaps decades from now – the global economy will be run on carbon-free electricity generated by the very process that powers the sun and stars.

“The fusion breakthrough will go down in history,” said US Secretary of Energy Jennifer Granholm during a press conference. “This is what it looks like for America to lead.” 

It is a stunning moment for a technology that has failed for nearly half a century, and it comes as leaders of the world’s 10 biggest economies and dozens of smaller countries have pledged to transition to clean energy sources.

But fusion is unlikely to help boost faltering progress towards net-zero emissions, at least not without work that most experts think will take decades of additional development. That means this historic breakthrough probably would not help displace traditional fossil fuels at a moment when the world is facing an entrenched energy supply crunch and greenhouse gas levels are still rising.

“We have to take a positive but sceptical approach,” said Mr Andrew Sowder, a senior technical executive at the independent, non-profit EPRI, formerly known as Electric Power Research Institute. “You are going to have to demonstrate you can take the energy and turn it into something useful.” 

Fusion energy is produced by melding together atoms and is the power source of stars, whose immense gravity crushes together atoms of hydrogen to form helium. With fusion, there is no long-lived radioactive waste – that is a stark contrast to the fission technology currently used at nuclear reactors to generate electricity.

Researchers at the Energy Department’s Lawrence Livermore National Laboratory used lasers to bombard hydrogen isotopes held in a superheated plasma state in order to fuse them into helium, releasing a neutron and carbon-free energy in the process.

The reaction produced about 2.5 megajoules of energy, compared with the 2.1 megajoules used to power the lasers, a net energy gain the scientists have been trying for decades to achieve.

To move this technology out of the lab, a fusion system would need to be affordable and easy to build. However, the Lawrence Livermore test uses some of the most powerful lasers ever built: They are big, costly and not readily available for mass deployment, making it difficult to convert this technical accomplishment into a successful business.

“The fact that you have net energy gain does not mean you’ll have a commercial device on the market,” said Mr Chris Gadomski, head nuclear analyst for BloombergNEF. “Yes, we have fusion, but at what cost?”

Still, the announcement should unleash funding and support for a civilian technology development programme, said Mr Stephen Dean, president of Fusion Power Associates, a non-profit public benefit corporation. BLOOMBERG