Scientists are celebrating a huge experimental breakthrough that could one day provide the world with a near-limitless source of clean energy.

For decades great minds have been trying to harness nuclear fusion which powers the sun and stars and is considered the “holy grail” of energy production.

In a major announcement, researchers working on nuclear fusion have for the first time achieved “net energy gain”, the US Energy Department said.

This happens when more energy is produced in a fusion reaction than was used to ignite it.

Fusion works by pressing hydrogen atoms into each other with such force that they combine into helium, releasing enormous amounts of energy and heat.

Proponents of fusion hope that it could one day produce nearly limitless, carbon-free energy, displacing fossil fuels and other traditional energy sources.

Unlike other nuclear reactions, it does not create radioactive waste.

But being able to power homes and businesses from fusion is still decades away.

Laser energy is converted into X-rays inside the hohlraum, which then compress a fuel capsule until it implodes. Photo: AAP

The experiment was successfully undertaken for the first time at the Lawrence Livermore National Laboratory in California.

United States Energy Secretary Jennifer Granholm announced the “major scientific breakthrough” in the decades-long quest.

The achievement will pave the way for advancements in defence and the future of clean power, Ms Granholm and other officials said on Tuesday (local time).

“This is a landmark achievement for the researchers and staff at the National Ignition Facility who have dedicated their careers to seeing fusion ignition become a reality, and this milestone will undoubtedly spark even more discovery,” Ms Granholm said at a news conference in Washington DC.

The fusion breakthrough “will go down in the history books,” she said.

White House science adviser Arati Prabhakar called it “a tremendous example of what perseverance really can achieve” and “an engineering marvel beyond belief”.

Researchers said it was a significant step.

“It’s almost like it’s a starting gun going off,” Professor Dennis Whyte, director of the Plasma Science and Fusion Center at the Massachusetts Institute of Technology, said.

“We should be pushing towards making fusion energy systems available to tackle climate change and energy security.”

‘Holy grail’ of clean energy

Net energy gain has been an elusive goal because fusion happens at such high temperatures and pressures that it is incredibly difficult to control.

Billions of dollars and decades of work have gone into fusion research that has produced exhilarating results — for fractions of a second.

Previously, researchers at the National Ignition Facility, the division of Lawrence Livermore where the success took place, used 192 lasers and temperatures multiple times hotter than the centre of the sun to create an extremely brief fusion reaction.

The lasers focus an enormous amount of heat on a small metal can.
The result is a superheated plasma environment where fusion may occur.

A technician at Lawrence Livermore National Laboratory inside the preamplifier support structure. Photo: AAP

Riccardo Betti, a professor at the University of Rochester and expert in laser fusion, said an announcement that net energy had been gained in a fusion reaction would be significant.

But he said there is a long road ahead before the result generates sustainable electricity.

He likened the breakthrough to when humans first learned that refining oil into petrol and igniting it could produce an explosion.

“You still don’t have the engine and you still don’t have the tyres,” Betti said.

“You can’t say that you have a car.”

The net energy gain achievement applied to the fusion reaction itself, not the total amount of power it took to operate the lasers and run the project.

For fusion to be viable, it will need to produce significantly more power and for longer.

Dr. Marvin Adams with a cylinder similar to one used by the Lawrence Livermore National Laboratories. Photo: AAP

Net energy gain is not a huge surprise from the California lab because of progress it had already made, according to Jeremy Chittenden, a professor at Imperial College in London specialising in plasma physics.
“That doesn’t take away from the fact that this is a significant milestone,” he said.

It takes enormous resources and effort to advance fusion research.

One approach turns hydrogen into plasma, an electrically charged gas, which is then controlled by huge magnets.

This method is being explored in France in a collaboration among 35 countries called the International Thermonuclear Experimental Reactor as well as by researchers at the Massachusetts Institute of Technology and a private company.

Last year the teams working on those projects in two continents announced significant advancements in the vital magnets needed for their work.