If you’ve ever had an MRI, you’ve been inside the strongest magnet most people will ever get near. Those machines run at about 1.5 to 3 tesla, and hospitals respect them enough to screen every paperclip that enters the room. So when a fusion company outside Oxford, England, says its magnet system peaked at 13.7 tesla and held together, that number’s earned a second of your attention.

The company is Tokamak Energy, and the system is called Demo4: 44 superconducting coils arranged the way they’d wrap around a spherical tokamak, the squashed version of the classic donut-shaped fusion reactor, plus the cooling, power and control gear needed to run them as one machine. Tokamak Energy announced on September 9 that it had finished a 14-month test campaign on the whole assembly. And honestly, the 13.7 tesla wasn’t the number that got me. Demo4 spent roughly 10,000 hours energized over those 14 months, by the company’s count, including long stretches at high field.