How does a fusion reactor ignite a star-like fire without allowing it to touch the wall? The answer comes from ITER, which stands in southern France with the six modules of the central solenoid manufactured in the United States now ready for installation. As with ITER’s other magnets, the central solenoid is no mere heavy object inside a massive machine. Instead, it is the machine its elf’s pulse generator the element that drives current through the plasma to transform a simple puff of hydrogen fuel into a confined, superheated electrical gas inside a tokamak.
To appreciate the scope, consider that each of the six modules has a mass of over 122 tones, and the entire 18-meter assembly stands at the heart of the world’s largest and most integrated superconducting magnet system. Together with the toroidal, poloidal, and correction coils, the full pulsed magnet system is intended to help shape and contain plasma temperatures approaching 150 million degrees Celsius. No solid vessel could contain such heat directly. Only magnetic confinement works. This is why the central solenoid is crucial.
In a tokamak, one set of coils wraps the plasma into a torus, another controls its shape, and the central solenoid induces the plasma current that makes the configuration work. According to the U.S. Department of Energy, tokamaks depend on the combined application of toroidal and poloidal fields to create the twisted magnetic field required for confinement. ITER’s solenoid is meant to drive a plasma current of up to 15 mega-amperes, with its peak magnetic field estimated by ITER at 13 tesla making it the most powerful magnet in the machine. It is also a tale of manufacture, not just physics.
The modules were produced over the course of about 15 years at General Atomics in California with the use of niobium-tin superconducting cable that requires refrigeration down to a temperature of around 4 kelvin for zero resistance. This low-temperature demand raises the problem of structural engineering, as the design had to accommodate thermal contraction, coolant pressure, seismic loads, and extreme magnetic forces during operations. According to a 2025 analysis of the cryogenic piping of the ITER magnet systems, the ITER solenoid’s cryogenic cooling system is designed to withstand all applicable stress and fatigue conditions while maintaining the 4 K operating temperature necessary for superconductivity.
The assembly is just beginning, but progress has been steady. Five modules have already been installed, with the sixth module due to join them sometime in 2026. After stacking, the magnet assembly will be fixed in place with a support structure and recompression system that will secure the modules against the forces that ITER compares to several thousand tones. ITER will remain a research reactor, not a power station; its goal is to demonstrate whether fusion can generate 500 MW of thermal output from 50 MW of plasma heating for pulses measured in hundreds of seconds.
This difference is significant. ITER will never supply electricity to the grid, and its new schedule anticipates first plasma production in the 2033–2034 timeframe, with fueling campaigns occurring at later dates. Nevertheless, the magnet arriving at the heart of the experiment is more than a delivery milestone. It reflects a broader truth about fusion energy engineering: victory or defeat hinges upon superconductors, cryogenics, precision, and international cooperation to assemble one machine to millimeter-level accuracy.