Halfway to full current

The second testing campaign has been completed at the magnet cold test facility with one of ITER's 330-tonne, D-shaped toroidal field coils demonstrating robust performance after being cooled to 4 K (minus 269 °C) and energized to 34 kA-half its nominal operating current of 68 kA.

"It is an important step to reach 34 kA and to confirm the coil is behaving as predicted by the models," says Adrien Deydier, the ITER Lead Mechanical Engineer participating in the testing. "The campaign has provided valuable operational experience for the teams ahead of integrated commissioning."

The magnet cold test facility was built to test several of ITER's superconducting magnets and the supporting infrastructure (cryogenics, vacuum, power supply, power feeders, and control-command functions) ahead of the commissioning of the magnet systems in the tokamak. The facility began operations with the first coil in May 2026 with the successful cooldown to 4 K and energization to 10 kA of toroidal field coil #7. During this first campaign, steady-state current tests were used to measure the electrical resistance of the coil's joints, while current discharge tests helped assess the quench detection system, which monitors for any loss of superconductivity.

The testing of the second coil, toroidal field coil #17, began in August 2026. The successful energization up to 34 kA allowed a better evaluation of the coil deformation under electromagnetic loads as compared to the structural model. Now that the campaign is complete, the magnet will begin its journey into the machine. After a brief sojourn in temporary storage, it will be moved into the Assembly Hall and integrated into the plasma chamber's final sector module.

As for the magnet cold test facility, it will now welcome toroidal field coil #19, built as a spare, for an intensive test program. Cooldown to 4 K is scheduled to begin in April 2027, followed by testing at 34 kA. This time, Paschen-tight connections will be made between the in-cryostat feeder and the coil; these connections, which replicate those used in the tokamak, will allow engineers to assess the high-voltage ground insulation of the coil. (Paschen's law describes how electrical insulation can break down at certain gas pressures.)

The facility will then be opened so that a reinforcement structure can be installed to prevent deformation when the coil is energized to its full operating current of 68 kA. This stage of the campaign will also include temperature margin tests, with parts of the coil deliberately heated to trigger a loss of superconductivity to verify the operational margins.

Following the testing of toroidal field coil #19, the facility will be reconfigured to test the ring-shaped poloidal field coil #1.