ITER coil #17 completes cold test at 34 kA, half operating current

ITER's toroidal field coil #17 completed a cold test at 34 kA, half its 68 kA operating current, and left the magnet cold test facility at Cadarache, France, on 30 October. The 330-tonne D-shaped magnet will go into temporary storage before integration into the final sector module of the plasma chamber.

Why the result matters

ITER is a 35-nation tokamak under construction in southern France to prove fusion's feasibility; it will generate no electricity. Its magnets must hold plasma at 150 million Celsius, about ten times the core of the Sun, away from the machine's walls. The design calls for 500 MW of fusion power from 50 MW of heating, a gain of Q=10, and targets deuterium-tritium operation in 2039.

The coil test

The magnet cold test facility cooled coil #17 to 4 Kelvin, or minus 269 Celsius, and energised it to 34 kA. Superconductors carry current without resistance only below a critical temperature, and the cooldown put the conductor into that state. The 34 kA test was more than three times the 10 kA used in the facility's first campaign, which began in May 2026 with coil #7. Testing of coil #17 began in August 2026.

The Cadarache stand tests cryogenics, vacuum systems, power supplies, electrical feeders and control systems before magnets go into the tokamak. Each test campaign takes four to six months per coil, ITER said.

What the test proves

Engineers measured how the coil deformed under electromagnetic loads and compared that with structural models. “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 gave teams operating experience ahead of integrated commissioning of the magnet system, he added.

The magnet cold test programme aims to validate high-voltage ground insulation at different temperatures, demonstrate quench detection and verify coil performance at nominal current, ITER said.

What happens next

ITER said engineers will cool coil #19, a spare, to 4 K in April 2027 and test it at 34 kA. That run will be the first to use Paschen-tight connections between the in-cryostat feeder and the coil, replicating the tokamak configuration and letting engineers test high-voltage ground insulation.

The facility will then be opened to install a reinforcement structure designed to prevent coil deformation at the full 68 kA. Engineers will also heat sections of the coil deliberately to trigger a loss of superconductivity as part of temperature-margin testing. After coil #19, the facility will be reconfigured for poloidal field coil #1. ITER's magnet system will use 18 D-shaped toroidal field coils, six poloidal field coils and a central solenoid.