At the last minute, the largest experimental nuclear fusion reactor in the world has generated a record amount of energy. The device, which was retired at the end of last year after forty years of service, thus provides important knowledge for future fusion reactors.
It was announced on Thursday afternoon that the European fusion experiment Joint European Torus (JET) produced 69.26 megajoules of heat energy in 5.2 seconds in early October. That is comparable to the electrical energy consumption of a three-person household in two days. This means that the previous record – also set by JET in 2022 – has been broken by 10 megajoules. The reactor used only 0.21 milligrams of fuel, the weight of a fruit fly.
With these experiments, researchers try to imitate the nuclear fusion process that powers the sun by fusing atomic nuclei in a controlled manner. Because it releases a lot of energy and produces less radioactive waste than current nuclear fission reactors, nuclear fusion is a promising sustainable and safe energy source.
Valuable knowledge
Successful fusion experiments have been carried out with JET and other reactors, but so far it has not been possible to produce more energy than the total energy required to start the reaction. The experiments did provide valuable knowledge for the next generation of reactors, such as the larger experimental nuclear fusion reactor ITER that is under construction in the south of France and the European demonstration reactor DEMO that is still in the drawing board phase. The goal of ITER is to generate more heat energy than is consumed. DEMO will also supply electricity.
JET, near Oxford, England, closed at the end of December and shortly before that conducted the final experiments with fusion fuel consisting of deuterium and tritium. These two heavy variants (isotopes) of hydrogen atoms fuse at sufficiently high pressure, density and temperature to form helium atomic nuclei. At JET this happens in a doughnut-shaped room, in which the fuel is heated to 150 million degrees, ten times hotter than the sun. Powerful magnets trap this red-hot fuel plasma. JET was the only experiment able to work with the deuterium-tritium fuel mix that will be used in future fusion power plants.
During the last deuterium-tritium experiments, the researchers ensured that all parts and the heating process performed optimally, to get the most out of the machine once again. That resulted in the new merger record.
Hot reactor wall
“That record is super cool, but for us it was a side issue,” says fusion researcher Matthijs van Berkel of the Eindhoven research institute Differ and involved in the JET experiments. “More important were tests of techniques needed for future reactors, such as ITER and DEMO.”
The aim of these techniques, for example, was to prevent the reactor wall from becoming too hot and to remove and cool combustion products and other unwanted material from the plasma, so that the wall at the discharge point is not damaged. Van Berkel: “As Differ we have contributed to this, among other things, with the development of control techniques, such as computer algorithms that independently measure what happens with the plasma and what happens, for example, by opening gas valves to ensure safe and rapid cooling.”
Partly thanks to the JET results, a lot is now happening in the field of mergers, says Van Berkel. “In addition to ITER and DEMO, work is also being done in China and there are several start-ups that want to build a fusion reactor within five years that generates as much energy as it puts in. Interesting times are ahead.”
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