Scientists at the National Ignition Facility (NIF) in the US have successfully generated a net gain in energy via a nuclear fusion reaction for the first time in history – a phenomenon known as ignition.
The breakthrough comes after efforts spanning decades carried out by researchers across the globe. It represents a significant step towards a clean, reliable energy source that could one day end humanity’s dependence on fossil fuels.
“The pursuit of fusion ignition in the laboratory is one of the most significant scientific challenges ever tackled by humanity, and achieving it is a triumph of science, engineering, and most of all, people,” saidLawrence Livermore National Laboratory Director Dr Kim Budil, speakingat a press conference held by the Department of Energy’s National Laboratory on 13 December.
“Crossing this threshold is the vision that has driven 60 years of dedicated pursuit — a continual process of learning, building, expanding knowledge and capability, and then finding ways to overcome the new challenges that emerged. These are the problems that the US national laboratories were created to solve.”
Fusion reactions occur when the nuclei of light atoms are forced together by extreme pressures or temperatures. When this force is strong enough to overcome the electrostatic force that repels them, the nuclei are pulled together by the strong nuclear force - one of the forces described by the Standard Model of particle physics. This leads to them being fused together and creating a new, heavier nuclei.
In the case of the NIF, which is based in the LLNL in California, the nuclei used were two isotopes of hydrogen: deuterium, which contains one neutron and one proton; and tritium, which contains two neutrons and one proton. These combine to form helium nuclei. As the mass of the helium nuclei is slightly less than the mass of two hydrogen nuclei this extra mass is released as energy according to Einstein’s famous equation E=mc2.
The reactor achieves this by shooting nearly 200 energetic lasers into a hollow cylinder containing a small spherical capsule of fuel. It is the world's largest and most powerful system. This generates an aura of X-rays that in turn triggers an implosion that moves at more than 400km/s. This creates huge pressures and temperatures that cause frozen hydrogen isotopes placed with the capsule to fuse.
In their latest run, the researchers put around 2.05MJ of energy in and got 3.15MJ out – a net gain within the system. This represents a significant improvement on the previous record set by the NIF team in August 2021 when they got 1.3MJ out of an input of 2MJ.
However, they had to put 300MJ of energy into the lasers to provide the 2MJ to the target – a figure that is still considerably lower than what would be needed to consistently generate electricity. This means that, although the results are promising, we are still a way off from seeing the building of the first nuclear fusion power plant.
"What the NIF result shows is that inertial fusion can release more energy from fusion than goes into heating the fuel. This is a huge boost for all fusion efforts and will raise ambitions across the board," said Dr Valerie Jamieson, Fusion Cluster Technology Manager at UK Atomic Energy Authority, who was not involved in the research.
"Bear in mind that NIF is an experiment, not a power plant and its specific approach using 192 high power lasers isn’t commercially viable.
"That said, this result is really important to commercial fusion efforts that are working towards a power plant.
"There are still challenges to overcome, but we have never been closer to fusion."
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