The prospect of a green energy source based on the power of the stars has received a boost after scientists set a world record for the amount of energy created by fusing atoms together. Researchers at the Joint European Torus (JET), an experimental fusion reactor at the Culham Centre for Fusion Energy in Oxfordshire, generated 69 megajoules of energy over five seconds from a mere 0.2 milligrams of fuel in the final fusion experiment performed at the facility. The burst of energy, equivalent to 16.5kg of TNT, was described as a “fitting swansong” for the project, which has pioneered technology for future commercial fusion reactors since it began operating in 1983. It beat the previous record of 59 megajoules of heat, set by the same facility in 2022. If fusion power is shown to be viable at scale, future reactors could drive a green energy revolution. One kilogram of fusion fuel contains about 10m times more energy than a kilogram of coal, oil or gas, and fusion reactions do not release greenhouse gases. The JET facility ended its scientific work in December. It will now be decommissioned in a 17-year process that researchers will document in painstaking detail to inform the building and dismantling of fusion reactors in the decades ahead. More than 300 scientists and engineers from a consortium called EUROfusion contributed to the experiments. Prof Ian Chapman, chief executive of the UK Atomic Energy Authority, said: “JET has operated as close to powerplant conditions as is possible with today’s facilities and its legacy will be pervasive in all future power plants. It has a critical role in bringing us closer to a safe and sustainable future.” The reactor at the Culham Centre for Fusion Energy is known as a tokamak, a structure that uses powerful magnetic fields to confine plasmas, or highly ionised gases, in a doughnut shape. The gases are heated to 150m celsius, about 10 times hotter than the centre of the sun. The extreme conditions in the tokamak drive fusion reactions in which atomic nuclei bind together to form new elements, releasing enormous amounts of energy in the process. Stars are powered by the same reactions, but do not require such high temperatures as their gravity is strong enough to do some of the work. Experiments at JET have explored the feasibility of using two isotopes of hydrogen, known as deuterium and tritium, as fuel. In fusion reactions, the two combine to produce helium gas. The record-breaking pulse of energy, announced on Thursday, is encouraging for Iter, a larger fusion project being built in the south of France. That reactor aims to start burning fusion fuel in 2035 with the goal of generating more energy that is used to heat the plasma. Andrew Bowie, the minister for nuclear and networks, said: “JET’s final fusion experiment is a fitting swansong after all the groundbreaking work that has gone into the project since 1983. We are closer to fusion energy than ever before.” If the next generation of experimental fusion facilities, such as Iter, prove the technology is viable at scale, researchers plan to build a European demonstration plant that generates more power than it uses. Dr Aneeqa Khan, a research fellow in nuclear fusion at the University of Manchester, said: “These results are really exciting for the fusion community and a great end to the operations of JET which has provided the scientific community with really valuable data over its lifetime, feeding into the designs for new projects. “However, to put this in context of commercial fusion, there was still no net energy produced.” She added: “This is a great scientific result, but we are still a way off commercial fusion. We need to be training up a huge number of people with the skills to work in the field and I hope the technology will be used in the latter half of the century.”