The US ITER has completed the final deliveries for the central solenoid magnet at the International Thermonuclear Experimental Reactor (ITER) in Cadarache, France. The latest shipments included busbars and leads for electrical connections. 

The central solenoid is 18 meters (59 feet) tall and 4.25 meters (14 feet) wide, composed of six individual modules. Each module weighs more than 122.5 tonnes (135 tons) and is wound from 6 kilometers (3.7 miles) of niobium-tin superconducting cable. 

This component belongs to a magnetic system weighing 3,000 tonnes (3,300 tons) that interacts with nine vacuum vessel sectors. ITER, which is intended to become the world’s biggest nuclear fusion reactor, targets 500 MW of power for 400 seconds with 50 MW of heating power. It is reported that an additional 300 MWe of electricity input may be required for its operation.

The 15-year manufacturing project was conducted at the General Atomics Magnet Technologies Center in Poway, California. Each module required over two years for fabrication and testing. 

On-site assembly and integration of ITER project

To manage technical risks, the project included a seventh spare module. Earlier in 2025, US ITER delivered a 60-foot-tall exoskeleton support structure designed to stabilize the magnet against the forces it generates. 

This structure surrounds the superconducting magnet at the center of the fusion machine, which also utilizes toroidal field coils, poloidal field coils, and correction coils.

Assembly is in progress at the ITER site under the direction of the ITER Organization, and five of the six modules are currently stacked in the assembly hall. The final module, which arrived in September, is scheduled to be added to the stack later in 2026. 

Once stacking is complete, a compression structure will apply downward precompression to the module stack. Technical support for this phase is provided through an agreement with the US ITER project team based at the Oak Ridge National Laboratory.

The central solenoid will remain on its platform in the Assembly Hall until the vacuum vessel sector modules have been installed. It will then be moved into the center of the tokamak pit. The magnet induces the magnetic flux change needed to initiate the plasma and maintain the plasma current during the burn time. 

Demonstrating the feasibility

Kevin Freudenberg, US ITER Interim Project Director, stated that the completion of the magnet demonstrates the capacity of the United States to design and deliver technical fusion systems.

“Congratulations to the entire team who contributed, including those here at Oak Ridge National Laboratory who led the work, and our suppliers who fabricated critical components,” Freudenberg concluded.

ITER is an international collaboration to build a tokamak fusion device to demonstrate fusion as a carbon-free energy source. While the facility requires external electricity for operation, it aims to prove the technical feasibility of fusion power. The project intends to show that a fusion reaction can be sustained to produce a net gain in energy. 

The completed central solenoid is the primary component for generating the required plasma current. As an experimental device, ITER will not generate electricity for the commercial grid.