Scientists have moved closer to achieving the holy grail of clean energy production, ITV News correspondent Rebecca Barry reports
In the middle of an energy crisis, the search for clean, dependable, abundant power feels particularly pressing.
Nuclear fusion - described by one scientist as "like putting the sun in a bottle" - has long been the holy grail for energy researchers.
Scientists have long understood how nuclear fusion has worked and have been trying to duplicate the process on Earth as far back as the 1930s. It could one day help shift the planet away from reliance on fossil fuels, which are contributing to the climate crisis.
And now, in the decades-long quest to harness the energy that powers the sun and stars, scientists have made a significant breakthrough.
For the first time, researchers at the Lawrence Livermore National Laboratory in California produced more energy in a fusion reaction than was used to ignite it, something called net energy gain.
Could this breakthrough be the energy game changer the world is looking for?
What is nuclear fusion?
“Nuclear fusion is the process that powers the Sun, where two atoms fuse together, liberating huge amounts of energy," Dr Aneeqa Khan, Manchester-ISIS Neutron and Muon Source Research Fellow in Nuclear Fusion at The University of Manchester explained.
How does fusion work?
Fusion works by pressing hydrogen atoms into each other with such force they combine into helium, releasing enormous amounts of energy and heat.
The reaction happens when two light nuclei merge to form a single heavier nucleus. Because the total mass of that single nucleus is less than the mass of the two original nuclei, the leftover mass is energy that is released in the process.
In the case of the sun, its intense heat - millions of degrees Celsius - and the pressure exerted by its gravity allow atoms that would otherwise repel each other to fuse.
Researchers at the Livermore lab fired a 192-beam laser - the largest laser in the world - at a small capsule filled with deuterium-tritium fuel.
Professor Jeremy Chittenden from Imperial College London explains what factors stand in the way of a nuclear fusion power station
The laser compresses heavy hydrogen, similar to conditions in the centre of the sun.
Prof Justin Wark, Professor of Physics at the University of Oxford and Director of the Oxford Centre for High Energy Density Science explained: "The lasers enter the ends of a centimetre-scale cylinder, hitting its inner walls, making them glow x-ray hot.
"These x-rays then heat a sphere at the centre that contains the nuclear fuel. The outside of the sphere vaporises and becomes a plasma, that rushes off the surface, creating an imploding ’spherical rocket’ which in a few billionths of a second reaches velocities of order 400 kilometres per second.
"The subsequent ‘crunch’ at the centre is tailored in a specific way to make a hot spark in the middle, and the density of the compressed ‘fuel’ surrounding the spark is so great that the nuclear fusion reaction takes place in about a tenth of a billionth of a second - faster than the tiny hot sphere can fly apart."
What are the benefits of fusion energy?
Proponents of fusion hope it could one day produce nearly limitless, carbon-free energy, displacing fossil fuels and other traditional energy sources.
Fusion does not release carbon dioxide into the atmosphere and unlike other nuclear reactions, it doesn't create radioactive waste.
Why is fusion energy so difficult to harness?
Net energy gain has been an elusive goal because fusion happens at such high temperatures and pressures that it is incredibly difficult to control.
Dr Khan said: "Recreating the conditions in the centre of the sun on Earth is a huge challenge.
"We need to heat up isotopes of hydrogen (deuterium and tritium) gas so they become the fourth state of matter, called plasma. In order for the atoms to fuse together on Earth, we need temperatures ten times hotter than the Sun – around 100 million Celsius, and we need a high enough density of the atoms and for a long enough time."
How significant is this scientific milestone?
Prof Gianluca Gregori, Professor of Physics at the University of Oxford who specialises in high power lasers and fusion energy, said: “For many years fusion energy has been described as the holy grail of the world's energy problems - a limitless and clean energy source that would address the ever-increasing demands free from carbon emissions."
'We're starting to see this technology become reality' says Physicist Dr Helen Czerski at University College London
Dr Khan adds: "If we can make it work it has the potential to provide a stable baseload of electricity to the grid, as well as the potential for secondary applications such as hydrogen production or heating.
"It is not ready yet and therefore it can’t help us with the climate crisis now, however, if progress continues it has the potential to be part of a green energy mix in the latter half of the century and should be part of our long term strategy, while we use other existing technologies such as fission and renewables in the near term."
But despite its significance and the excitement of many scientists, Dr Khan said fusion "is already too late to deal with the climate crisis".
What effect will this have on us?
While the Livermore lab's breakthrough is a significant step, producing energy that powers homes and businesses from fusion is still decades away.
The costs of targets remain exorbitant, and the amount of energy released by the experiment is "smaller than wall plug electricity costs".
For fusion to be viable, it will need to produce significantly more power and for longer.
But scientists have hailed what has been described as a "cosmic gamechanger", declaring it a turning point in human history and likening it to humans first learning that refining oil into gasoline and igniting it could produce an explosion.
Dr Mark Wenman, Reader in Nuclear Materials at Imperial College London, said it was a "remarkable point in human history, which in future could usher in an era of green, secure and essentially inexhaustible form of compact energy, without long-lived nuclear waste".