The largest experimental nuclear fusion reactor in the world has generated a record amount of fusion energy. The results are promising for nuclear fusion as a safe and clean energy source. that’s today announced†
The European fusion experiment Joint European Torus (JET) produced 59 megajoules of heat energy in five seconds; more than doubling the previous record of 21.7 megajoules set in 1997 – also by JET. It is comparable to the amount of electrical energy a two-person household consumes in two days. JET used 0.18 milligrams of fusion fuel for this. “You would need more than a kilogram of natural gas or almost four kilograms of lignite for the same amount of energy,” says Tony Donné, program manager of EUROfusion – the consortium that conducted the experiment.
Following the nuclear fusion process that powers the sun, researchers have been trying for decades to fuse atomic nuclei in a controlled manner in order to make use of the large amount of energy that is released. There have been successful fusion experiments, but they have never been able to produce more energy than it takes to start the reaction.
donut shaped room
The new record does not change that. Still, the results are good news for the larger experimental nuclear fusion reactor ITER under construction in the south of France. ITER – a global partnership – must generate more energy from 2035 than is needed to initiate the merger. “But ITER will not supply any electricity either,” says Donné. “That will only happen with DEMO, which is planned for 2055.”
Read a report about ITER: Building a sun on the Côte d’Azur
“JET is the machine that comes closest to ITER,” says Egbert Westerhof of the Eindhoven research institute Differ and involved in EUROfusion. Like ITER, JET is a so-called tokamak reactor, which consists of a donut-shaped chamber containing the fusion fuel. Around it are powerful magnets that trap the red-hot fuel plasma. The fuel consists of deuterium and tritium, heavy variants (isotopes) of hydrogen atoms. These fuse at sufficiently high pressure, density and temperature to form helium atomic nuclei. In JET, this happens at a temperature of 150 million degrees, ten times hotter than the sun.
That temperature is reached step by step. First by running a strong current through the plasma. And then by further heating it with radio or microwave rays and bundles of energy-rich neutral particles. ITER will also use these techniques.
It took nearly 25 years for JET to break its own energy record as the machine received a facelift. The heating capacity has been increased and the old reactor wall has been replaced with a metal wall made of tungsten and beryllium, materials that ITER will also use.
The limits of JET
After the refurbishment, it was first tested with deuterium plasma. “We wanted to understand the influence of the new wall well before we started fusion experiments,” says Donné. “After fusion experiments, the reactor is somewhat radioactive. This means that you cannot enter the machine hall for several weeks. Moreover, tritium is scarce and expensive.” Future fusion reactors will solve this by forming tritium from lithium themselves.
The record has pushed the boundaries of JET. “We had to stop after those five seconds, otherwise the magnets would overheat,” says Donné. “JET still uses copper coils from 1983 that are cooled with water. ITER will be able to handle discharges of more than fifteen minutes, thanks to superconducting coils that hardly heat up.”
“The record is nice, but it was not all about that,” says Westerhof. “We were able to test our theoretical models with the experiments.” The JET results confirm that the researchers are on the right track. The metal wall for ITER seems to be a good choice and the models that predict the plasma behavior seem to be correct. The presence of tritium even seems to provide additional stabilization to the plasma, which is good news.
“These are exciting results,” says Josefine Proll of Eindhoven University of Technology, who conducts theoretical research into stellarators, another form of fusion reactors. “In the record, the years of work and research come together nicely. The researchers show that they can get the most out of JET that it contains. That gives confidence that ITER will also succeed.”
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