World’s largest fusion reactor tests 330-tonne magnet built to control superhot plasma

ITER has completed a major test campaign on one of its 330-tonne superconducting magnets, successfully energizing the massive component to 34 kiloamperes (kA) before removing it from its magnet cold test facility. The D-shaped toroidal field coil, designated #17, was cooled to 4 Kelvin (minus 269 degrees Celsius) and tested at half its nominal operating current of 68 kA. The successful campaign allowed engineers to assess how the magnet deforms under electromagnetic loads and compare its behavior with structural models. The coil was transferred from the facility to a transport frame on October 30. It will now be moved into temporary storage before heading to ITER’s Assembly Hall for integration into the plasma chamber’s final sector module. The achievement provides valuable operational experience ahead of the commissioning of ITER’s integrated magnet systems. Superconducting coil passes tests The magnet cold test facility was developed to evaluate ITER’s superconducting magnets and their supporting infrastructure before installation in the tokamak. This includes cryogenics, vacuum systems, power supplies, electrical feeders and control systems. Its first testing campaign began in May 2026 with toroidal field coil #7. Engineers cooled the magnet to 4 K and energized it to 10 kA, allowing them to assess electrical resistance at its joints and evaluate the system responsible for detecting a loss of superconductivity, known as a quench. Testing of coil #17 began in August. Reaching 34 kA marked a significant increase in testing current and allowed engineers to examine the component’s structural response under stronger electromagnetic forces. “It is an important step to reach 34 kA and to confirm the coil is behaving as predicted by the models,” said Adrien Deydier, ITER’s lead mechanical engineer involved in the testing. The campaign also provided operational experience for teams preparing for integrated commissioning, he added. Next coil targets full current With coil #17 removed, the magnet cold test facility will prepare for toroidal field coil #19, which was manufactured as a spare. Its cooldown to 4 K is scheduled to begin in April 2027, followed by testing at 34 kA. The next campaign will introduce Paschen-tight connections between the in-cryostat feeder and the coil. These connections replicate those planned for the tokamak and will allow engineers to assess the magnet’s high-voltage ground insulation. The facility will subsequently be opened to install a reinforcement structure designed to prevent coil deformation when it is energized to its full operating current of 68 kA. Engineers will also conduct temperature-margin tests by deliberately heating parts of the coil to trigger a loss of superconductivity. This will help verify the magnet’s operating margins and protection systems. After testing coil #19, the facility will be reconfigured to accommodate poloidal field coil #1, a ring-shaped magnet that forms another part of ITER’s magnetic confinement system. ITER’s toroidal field magnets are essential to confining the superhot plasma inside the reactor. The project will use 18 D-shaped toroidal field coils, alongside six poloidal field coils and a central solenoid, to generate and control the magnetic fields required for fusion experiments.The cold-testing program is intended to identify potential problems before the magnets are integrated into the machine, reducing risks during commissioning and future operation.Get the latest in engineering, tech, space & science - delivered daily to your inbox.With over a decade-long career in journalism, Neetika Walter has worked with The Economic Times, ANI, and Hindustan Times, covering politics, business, technology, and the clean energy sector. Passionate about contemporary culture, books, poetry, and storytelling, she brings depth and insight to her writing. When she isn’t chasing stories, she’s likely lost in a book or enjoying the company of her dogs.