In the assembly hall of the ITER fusion complex in Saint-Paul-lès-Durance, France, a crane lowered the final module of the central solenoid into position in late spring 2026, completing a vertical stack of superconducting magnets that weighs roughly 1,000 metric tons and stands about 59 feet tall. The moment capped more than a decade of fabrication, testing, and transatlantic shipping, and it retired one of the single largest hardware risks in the effort to build the world’s most ambitious fusion energy experiment.
The central solenoid is the electromagnetic spine of ITER’s tokamak, the doughnut-shaped machine designed to confine a plasma heated to 150 million degrees Celsius and sustain the conditions needed for hydrogen nuclei to fuse and release energy. When energized, the solenoid will act like a massive transformer coil, inducing an electrical current of up to 15 million amperes in the plasma and helping to shape and stabilize the superheated gas. According to the ITER Organization, the peak electromagnetic force the magnet can generate is roughly 56 million newtons, a figure the organization compares to the force needed to lift a Nimitz-class aircraft carrier clear of the water.
Built in California, assembled in France
The solenoid’s six operational modules were manufactured by General Atomics at its facility in Poway, California, as part of the United States’ in-kind contribution to the international project. A seventh module was produced as a spare. Each module contains thousands of meters of niobium-tin superconducting cable wound into a steel case and designed to operate at around 4 kelvins, just a few degrees above absolute zero.
Before any module left the factory floor, it underwent a rigorous qualification campaign. A DOE technical report on the pre-shipment testing describes mechanical load simulations, electrical insulation checks, and cryogenic cooldown cycles intended to screen for defects that might surface only under operating conditions. Producing a spare seventh module reflected the program’s recognition that replacing a failed unit after installation would be extraordinarily difficult once the rest of the tokamak structure was built up around the solenoid.
Fabrication records archived by the Department of Energy’s Office of Scientific and Technical Information document the stacked configuration and the manufacturing complexity behind each module, from conductor winding to final dimensional inspection.
A lift with no margin for error
Getting each module from ground level to its correct position in the stack required a purpose-built lifting fixture engineered by Oak Ridge National Laboratory. A published ORNL mechanical study details how engineers calculated load paths, stress limits, and alignment tolerances to ensure that a module weighing well over 100 metric tons could be raised, rotated, and seated without exceeding structural margins. A failure during any single lift could have damaged a module beyond repair and set the schedule back by years, making the fixture itself a critical piece of the assembly puzzle.
Each module had to align within tight tolerances so the combined magnetic field would be symmetric and mechanical stresses would distribute as designed during operation. Oak Ridge, which served as the lead U.S. laboratory coordinating the solenoid procurement, also oversees American contributions to ITER’s diagnostics, heating systems, and other tokamak components. But the central solenoid stands apart in the portfolio because it directly underpins the machine’s ability to drive and sustain the plasma current essential for fusion experiments.
What the milestone does and does not prove
Completing the physical stack is a significant engineering achievement, but it is not the same as proving the magnet works. The pre-shipment tests confirmed that individual modules met their specifications in isolation. They did not, and could not, capture the system-level interactions that will emerge when all six modules are cooled together, energized to full current, and subjected to the combined magnetic environment of an operating tokamak.
Several technical unknowns will only be resolved during integrated commissioning. How the solenoid’s electrical joints behave at superconducting temperatures, how mechanical preload evolves after repeated magnet cycles, and how the solenoid’s fields interact with the surrounding toroidal and poloidal coils will all shape ITER’s performance envelope. Engineers will be watching for thermal contraction measurements during cooldown, joint-resistance readings across module interfaces, and current-ramp profiles that confirm the solenoid can reach its design field without a quench, the sudden loss of superconductivity that can release stored energy destructively.
The spare module, meanwhile, sits in storage as an expensive insurance policy. If the six installed modules pass commissioning and early operations without incident, it may never be used. If one fails under electromagnetic or thermal loads, the spare could save the project from a multi-year delay that would otherwise be needed to manufacture a replacement from scratch. No public documentation addresses the specific failure modes or inspection thresholds that would trigger its deployment.
Cost, schedule, and the road to first plasma
The $22 billion figure widely associated with ITER reflects construction cost estimates that have grown substantially since the project’s original baseline. The ITER Council acknowledged major schedule pressures during its 2024 review, and a revised project plan is still being finalized. The DOE and ORNL engineering documents that detail the solenoid’s fabrication do not contain an updated, integrated cost-to-complete breakdown or a schedule variance report, so it is not possible to say from public technical sources alone exactly how the completed stack shifts the path to first plasma.
What is clear is that the solenoid’s completion removes a bottleneck. With the magnet in place, assembly teams can proceed to surrounding work, including the installation of thermal shielding, correction coils, and vacuum vessel sectors, without the logistical constraint of reserving crane access and vertical clearance for solenoid lifts.
ITER remains the largest international science collaboration ever attempted, involving 35 nations and a supply chain that stretches from California to South Korea to India. The central solenoid, born in a San Diego suburb and now locked into the core of a reactor in Provence, is one tangible piece of evidence that the project’s industrial machinery can deliver hardware at the scale fusion demands. Whether that hardware performs as designed under the brutal conditions inside a tokamak is the question the next phase of work is built to answer.
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*This article was researched with the help of AI, with human editors creating the final content.
