ITER receives final correction coils, completing 18-unit magnet set

ITER has cleared a key magnet milestone: the last correction coils are now on site, giving the tokamak its full set of 18. That matters because these are the magnets that fine-tune the field around the plasma, helping keep it centered and stable inside one of the most demanding machines ever built.

The final deliveries closed out in stages, with two side correction coils arriving in April 2026 and two more reaching the ITER site in southern France on May 22. ITER said the coils are inspected as soon as they arrive, a step that rules out any transport damage before the hardware moves into the next stage of assembly. For a component built to superconducting tolerances, that checkpoint is more than routine paperwork, it is the gate between freight and reactor hardware.

Correction coils are the smallest of ITER’s superconducting magnets, but they carry an outsized job. The full suite weighs up to 4.5 tonnes per unit and measures as much as 8.3 metres, and the 18 coils are arranged as six bottom, six side and six top units. ITER and Chinese project materials say they are used to correct magnetic asymmetries and field errors caused by misalignment, winding deviations, joints, leads, busbars and assembly tolerances, with current through the coils creating compensating fields that restore plasma symmetry.

The Chinese Domestic Agency delivered the set after a multiyear qualification program carried out by the Institute of Plasma Physics of the Chinese Academy of Sciences in Hefei, Anhui Province, China. That long pre-production run reflected the unusual shapes and precision demands of the coils, which have to fit into a machine that already contains far larger toroidal and poloidal field systems. China also reported in April 2025 that it had completed and shipped the final correction-coil in-cryostat feeder components, underlining how the coil package and feeder package moved forward as linked parts of the same magnet effort.

The arrival of all 18 coils does not mean the work is finished. ITER still has to complete inspection, integration and installation before the magnets can contribute to reactor performance, and the broader assembly campaign is still advancing, with ITER saying in May 2026 that only one vacuum vessel sector remained to build the plasma chamber. Even so, the final correction-coil delivery closes a major hardware chapter and brings the machine closer to a fully integrated tokamak magnet system.