After 40 years of major nuclear fusion milestones, the Joint European Torus (JET) facility finally shut down in December 2023—but not without one final record shattering achievement. On Thursday, representatives for the groundbreaking tokamak reactor confirmed its final experiment generated 69.26 megajoules of energy in only five seconds. That’s over 10 megajoules more than JET’s previous world record, and more than triple its very first 22 megajoule peak power level back in 1997.
[Related: The world’s largest experimental tokamak nuclear fusion reactor is up and running.]
Located in Oxfordshire, UK, the JET reactor facility began operations in 1983 in the hopes of edging the world closer to sustainable, economically viable fusion production. While fission emits massive amounts of energy through splitting atoms, fusion involves smashing atoms such as tritium and deuterium together at temperatures over 150 million degrees Celsius to create helium plasma, a neutron, and ridiculous amounts of energy. The sun—and every other star, by extension—are essentially gigantic celestial nuclear fusion reactors, so mimicking even a fraction of that kind of power here on Earth could revolutionize the energy industry.
The first tokamak—an acronym of “toroidal chamber with magnetic coils”—reactor came online in the USSR in 1958. Tokamaks resemble a huge, extremely high-tech tire filled with hydrogen gas fuel that is then spun at high speeds through magnetic coiling. The force of its rotations around the chamber then ionizes the atoms into helium plasma.
While multiple facilities around the world can produce nuclear fusion reactions, it remains extremely cost prohibitive. JET’s December record, for example, pulled off its all-time energy levels in only five seconds—but that 69 megajoules was still only enough to warm a few bathtubs’ worth of water.
Even the most optimistic realists estimate it could take another 20 years (at the very least) before affordable fusion energy is a viable option. Others, meanwhile, argue useful fusion reactors will never be a financially feasible solution. It currently costs hundreds of thousands of dollars to simply fire up a fusion reactor, much less sustain its processes indefinitely—which none can, since the technology isn’t available yet. On top of that, today’s climate emergency can’t wait for a solution two-or-more decades down the line. But if society ever does make fusion reactors a real and sustainable alternative, however, it will be largely owed to everything JET accomplished over its four decades of service.
Speaking with the BBC on Thursday, UK Minister for Nuclear and Networks Andrew Bowie called JET’s final experiment a “fitting swan song” for the reactor pushing the world “closer to fusion energy than ever before.”
With JET powered down for good, the world’s largest fusion reactor is now Japan’s six-story-tall JT-60SA tokamak located north of Tokyo. Although inaugurated in December 2023, if all goes as planned the JT-60SA won’t hold the title for long. Its European sibling, the International Thermonuclear Experimental Reactor (ITER) is scheduled to go online sometime in 2025—although that project has not been without its difficulties and delays.