![]() In an experiment on 21 December 2021, JET’s tokamak produced 59 megajoules of energy over a fusion ‘pulse’ of 5 seconds - more than double the 21.7 megajoules released in 1997 over around 4 seconds. (It’s quite good with the sound on, too.) Credit: UKAEA The record-breaking pulse in action inside JET’s doughnut-shaped internal vessel. Tritium was last used by a tokamak fusion experiment when JET set its previous record in 1997. That ramps up the energy output, but JET had to undergo more than two years of renovation to prepare the machine for the onslaught. Tritium is a rare and radioactive isotope of hydrogen when it fuses with the isotope deuterium, the reactions produce many more neutrons than do reactions between deuterium particles alone. To break the energy record, JET used a fuel made of equal parts tritium and deuterium - the same mixture that will power ITER, which is being built in southern France. Under heat and pressure, the isotopes fuse into helium, releasing energy as neutrons. JET and ITER use magnetic fields to confine plasma, a superheated gas of hydrogen isotopes, in the tokamak. US achieves laser-fusion record: what it means for nuclear-weapons research “I am sure I am not alone in the fusion community in wanting to extend very hearty congratulations to the JET team.” The experiments - the culmination of almost two decades of work - are important for helping scientists to predict how ITER will behave, and will guide its operating settings, says Anne White, a plasma physicist at the Massachusetts Institute of Technology in Cambridge who works on tokamaks, reactors that, like JET, have a doughnut shape. “It’s a really, really good sign and I’m excited.” Two decades’ work The same modelling now says ITER will work,” says fusion physicist Josefine Proll at Eindhoven University of Technology in the Netherlands, who works on a different kind of reactor called a stellarator. JET’s results do not change that, but they suggest that a follow-up fusion-reactor project that uses the same technology and fuel mixture - the ambitious US$22-billion ITER, scheduled to begin fusion experiments in 2025 - should eventually be able to reach this goal. But so far, no experiment has generated more energy than has been put in. ![]() If researchers can harness nuclear fusion - the process that powers the Sun - it promises to provide a near-limitless source of clean energy. The UK Atomic Energy Authority hosts JET, but its scientific programme is run by a European collaboration called EUROfusion. “These landmark results have taken us a huge step closer to conquering one of the biggest scientific and engineering challenges of them all,” said Ian Chapman, who leads the Culham Centre for Fusion Energy (CCFE), where JET is based, in a statement. Scientists at the Joint European Torus (JET) near Oxford, UK, announced on 9 February that they had generated the highest sustained energy pulse ever created by fusing together atoms, more than doubling their own record from experiments performed in 1997. Credit: Christopher Roux (CEA-IRFM)/EUROfusion (CC BY 4.0)Ī 24-year-old nuclear-fusion record has crumbled. The water evaporates into steam which turns a turbine, which in turn drives a generator to produce electricity.The Joint European Torus tokamak reactor near Oxford, UK, is a test bed for the world’s largest fusion experiment - ITER in France. ![]() The kinetic energy of the neutrons is harnessed by the nuclear reactor and used to heat water. ![]() ![]() The reactor is covered with a thick concrete shield to ensure that no radiation is able to penetrate through and escape the reactor. To stop this happening, the reactor contains control rods, usually made of boron, which absorb some of the extra neutrons so that only a single neutrons is released per fission event. It is important that the chain reaction doesn’t get out of hand, otherwise the reactor could explode. These neutrons hit other nuclei in a chain reaction. When a neutron is absorbed by a nucleus, it undergoes a fission event, breaking apart into two nuclei and two or three neutrons. Fission only works if the neutron is moving slowly enough to be absorbed by a nucleus so nuclear reactors contain something called a moderator, usually made of graphite, which reduces the speed of the neutrons, making them more likely to be absorbed by a nucleus. Fission is used in nuclear reactors to produce energy. ![]()
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