A 135-ton superconducting magnet module, the last of six built in the United States for the ITER fusion reactor, has arrived at the project’s construction site in Saint-Paul-lez-Durance in southern France. The delivery closes out a manufacturing and logistics campaign that stretched across more than a decade, spanned two continents, and required custom transport rigs capable of hauling a single coil heavier than a Boeing 787 from a San Diego factory floor to a reactor pit in Provence.
The central solenoid is the electromagnetic spine of ITER’s tokamak, the doughnut-shaped machine designed to prove that fusing hydrogen isotopes can produce more energy than it consumes. Stacked together, the six modules will stand roughly 18 meters tall and generate the intense pulsed magnetic field needed to drive electrical current through a plasma heated to 150 million degrees Celsius, ten times hotter than the core of the sun. Without it, the plasma cannot be shaped, confined, or sustained long enough for fusion reactions to take hold.
Building and testing the magnets
General Atomics, the San Diego-based defense and energy contractor, fabricated all six modules under a procurement package managed by US ITER, the American arm of the 35-nation collaboration. Each module is wound with niobium-tin (Nb3Sn) superconducting cable, a brittle, high-performance conductor that must be cooled to roughly 4.5 Kelvin, just a few degrees above absolute zero, before it loses all electrical resistance and can carry the enormous currents the solenoid demands.
Before the first module shipped, engineers subjected it to a battery of qualification tests documented in a peer-reviewed paper published through Oak Ridge National Laboratory in Fusion Engineering and Design. The module was cooled to operating temperature, energized to 40,000 amps, and put through high-voltage and vacuum (Paschen) checks that simulate the thermal shocks and electromagnetic stresses of real tokamak pulses. It passed, confirming that the engineering margins built into the design could absorb transient current spikes without quenching the superconductor or damaging the insulation.
Those test results remain the strongest publicly available evidence that the American-built magnets meet ITER’s performance specifications. No equivalent dataset for the remaining five modules has been published in the open literature, though each module was manufactured to the same design and underwent factory acceptance procedures before shipment.
Getting 810 tons across two continents
Moving six modules, each the size of a small house and sensitive to vibration, from Southern California to a hillside in southeastern France was an engineering project in its own right. Oak Ridge National Laboratory documented the logistics in a detailed account of the US ITER transport campaign, describing how early modules traveled by road from General Atomics’ facility to the Port of Houston, then crossed the Atlantic on specialized heavy-lift vessels before navigating narrow European roads to the ITER site.
Separate from the coil modules, a parallel campaign delivered the central solenoid’s structural support components, fabricated in Pennsylvania. These steel assemblies anchor the stacked modules and absorb the massive pulsing forces generated during plasma operation, preventing even microscopic shifts that could quench the superconductor or distort the magnetic field geometry. Oak Ridge confirmed that the final structural shipment has reached ITER, meaning the full hardware package, modules and support structure alike, is now on site.
Where the project stands now
An ITER announcement distributed through EurekAlert in spring 2025 stated that the sixth module was completed at General Atomics in April of that year and that all components for the project’s pulsed magnet system, built by the United States, Russia, Europe, and China, were finished. The release described the system as the world’s largest and most powerful of its kind, a characterization that is plausible given ITER’s scale but originates from the project’s own communications rather than independent measurement.
An important distinction separates “fabrication complete” from “ready to operate.” Stacking six 135-ton modules with the sub-millimeter alignment a superconducting magnet demands, connecting thousands of electrical joints and cryogenic feed lines, and then cooling the assembly to near absolute zero while neighboring systems, including toroidal field coils, vacuum vessel sectors, and thermal shields, are still being installed is a sequence that will take years of additional work. No official ITER statement in the public record specifies when the solenoid stack will be fully assembled or when it will undergo its first integrated energization test inside the reactor.
That uncertainty sits inside a broader schedule question. In mid-2024, the ITER Council endorsed a “staged approach” that restructured the project’s path to First Plasma and pushed key milestones further into the future. The revised plan acknowledged years of delays driven by manufacturing defects in other components, pandemic disruptions, and cost growth that has pushed the project’s estimated price tag well beyond $22 billion. General Atomics has not released public data on whether the sixth module met its original budget and schedule targets, and post-delivery inspection results from ITER’s site engineers in France have not appeared in the public record.
What the solenoid delivery actually proves
For anyone tracking fusion energy’s long road from laboratory concept to power plant, the central solenoid delivery is a tangible, measurable milestone. This is not a rendering, a funding proposal, or a press conference promise. It is 810 tons of superconducting hardware physically sitting at a construction site, backed by at least one module’s worth of peer-reviewed performance data showing it works under realistic operating conditions.
At the same time, the gap between delivered components and a working fusion reactor remains vast. ITER must still assemble the solenoid stack, integrate it with dozens of other first-of-a-kind systems, and demonstrate that the whole machine can confine a burning plasma long enough to produce more fusion power than the energy pumped in. Private fusion ventures, including Commonwealth Fusion Systems and TAE Technologies, are racing toward smaller, faster machines that could reach some of those milestones on a different timeline, adding competitive pressure to a project originally conceived in the 1980s.
The verified record, as of June 2026, supports a clear but bounded conclusion: the United States has fulfilled its commitment to design, build, test, and ship the central solenoid, and the hardware is where it needs to be. Whether ITER can turn that hardware into a functioning heart for the world’s largest fusion experiment is a question the magnets alone cannot answer.
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*This article was researched with the help of AI, with human editors creating the final content.
