The most recent deliveries included busbars and leads for electrical connections between the modules; earlier, all magnet modules, support structures, and tooling components had been delivered.
The central solenoid magnet consists of six individual sections, or modules, each wound from about 6 kilometres of niobium-tin superconducting cable and weighing more than 122.5 tonnes. Each module required more than two years to fabricate, followed by testing, and then shipment to France. As part of ITER’s strategy to build redundancy into mission-critical systems, a full spare module was manufactured to reduce technical and schedule risk. It will be deployed only if a problem emerges with one of the six modules already on site. The 15-year project to produce the modules was completed inside General Atomics’ Magnet Technologies Center in Poway, California.
The 18-metre-tall, 4.25-metre-wide magnet is now under assembly at the ITER site. Five of six modules are stacked, with the final module – delivered in September – to be added later this year. Assembly is the responsibility of the ITER Organization, with additional technical support provided through an agreement with the US ITER project team based at Oak Ridge National Laboratory.
Once all six modules are in place, a compression structure, tasked with applying downward precompression on the module stack, will be put in place. The completed central solenoid will then remain on its platform in the Assembly Hall until all nine vacuum vessel sector modules are installed, and then will be moved into the centre of the tokamak pit.
US ITER has also delivered the ‘exoskeleton’ support structure that will enable the central solenoid to withstand the extreme forces it will generate. The exoskeleton is comprised of more than 9000 individual parts, manufactured by eight US suppliers.
ITER’s central solenoid will generate most of the magnetic flux charge of the plasma, initiating the initial plasma current and contributing to its maintenance.
“The completion of the central solenoid magnet highlights the capability of the United States to design and deliver the world’s most complex fusion systems,” said Kevin Freudenberg, US ITER Interim Project Director. “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.”
ITER’s magnetic system consists of toroidal and poloidal magnetic field coils, correction coils, and the central solenoid. This is the largest superconducting system ever created. The fully assembled pulsed magnetic system will weigh almost 3000 tonnes.
ITER is a major international project to build a tokamak fusion device designed to prove the feasibility of fusion as a large-scale and carbon-free source of energy. The goal of ITER is to operate at 500 MW (for at least 400 seconds continuously) with 50 MW of plasma heating power input. It appears that an additional 300 MWe of electricity input may be required in operation. No electricity will be generated at ITER.
Thirty-five nations are collaborating to build ITER – the European Union is contributing almost half of the cost of its construction, while the other six members (China, India, Japan, South Korea, Russia and the USA) are contributing equally to the rest. Construction began in 2010 and the original 2018 first plasma target date was put back to 2025 by the ITER council in 2016. However, in June 2024, a revamped project plan was announced which aims for “a scientifically and technically robust initial phase of operations, including deuterium-deuterium fusion operation in 2035 followed by full magnetic energy and plasma current operation”.
