A major breakthrough has been announced by US scientists in the race to recreate nuclear fusion.
Physicists have pursued the technology for decades as it promises a potential source of near-limitless clean energy.
Researchers yesterday confirmed they have overcome a major barrier - producing more energy from a fusion experiment than was put in.
But we are still many years away from seeing a power plant being built, as much research has still to be carried out.
The BBC says the experiment took place at the National Ignition Facility at the Lawrence Livermore National Laboratory (LLNL) in California.
LLNL director Kim Budil said: "This is a historic achievement...over the past 60 years, thousands of people have contributed to this endeavour and it took real vision to get us here."
Holy grail
Nuclear fusion is described as the holy grail of energy production. It is the process that powers the Sun and other stars.
It works by taking pairs of light atoms and forcing them together - this "fusion" releases a lot of energy.
It is the opposite of nuclear fission, where heavy atoms are split apart. Fission is the technology currently used in nuclear power stations, but the process also produces a lot of waste that continues to give out radiation for a long time. It can be dangerous and must be stored safely.
Nuclear fusion produces far more energy, and only small amounts of short-lived radioactive waste. And importantly, the process produces no greenhouse-gas emissions and therefore does not contribute to climate change.
But one of the challenges is that forcing and keeping the elements together in fusion requires very high temperatures and pressures. Until now, no experiment has managed to produce more energy than the amount put in to make it work.
The National Ignition Facility in California is a £2.85billion experiment.
Peppercorn
It puts a tiny amount of hydrogen into a capsule the size of a peppercorn.
Then a powerful 192-beam laser is used to heat and compress the hydrogen fuel.
The laser is so strong it can heat the capsule to 100million degrees celsius - hotter than the centre of the Sun.
The capsule begins to implode on itself, forcing the hydrogen atoms to fuse and release energy.
On announcing the breakthrough, Marvin Adams, deputy administrator for defense programs at the US National Nuclear Security Administration, said that the laboratory's laser had input 2.05 megajoules (MJ) of energy to the target, which had then produced 3.15 MJ of fusion energy output.
Melanie Windridge, CEO of Fusion Energy Insights, told the BBC: "Fusion has been exciting scientists since they first figured out what was causing the Sun to shine. These results today really put us on the path to the commercialisation of the technology."
True breakthrough
Jeremy Chittenden, professor of plasma physics and co-director of the Centre for Inertial Fusion Studies at Imperial College London, called it "a true breakthrough moment".
"It proves that the long sought-after goal, the 'holy grail' of fusion, can indeed be achieved," he said.
On the question of how long before we could see fusion being used in power stations, Dr Budil, the LLNL director, said there were still significant hurdles, but that: "with concerted efforts and investment, a few decades of research on the underlying technologies could put us in a position to build a power plant".
One of the main hurdles is getting costs down and scaling up the energy output.
The experiment was only able to produce enough energy to boil about 15-20 kettles and required billions of dollars of investment.
And.,although the experiment got more energy out than the laser put in, this did not include the energy needed to make the laser work - which was far greater than the amount of energy the hydrogen produced.