Photos: Building the World’s Largest Fusion Reactor

A massive fusion reactor, seen under construction. Two tall, metal wedge-shaped, or D-shaped modules sit on either side of a thick central pillar. The interior of each wedge bristles with mounting points for instruments and shielding.

Four massive vacuum-vessel modules sit in place around the central solenoid coil of the ITER tokamak (a type of fusion reactor) in April 2026. Each of the nine wedge-shaped modules stands 13 meters (42.65 feet) tall and weighs approximately 1,200 tons. They are designed to contain a huge volume of intensely-hot plasma inside a torus-shaped vacuum vessel, confined by powerful magnetic fields.

Several construction workers walk on a web of concrete reinforcing bars arranged in a radiating-circle pattern before a thick concrete foundation will be poured on top.

Science Photo Library / Reuters

Reinforcing bars are laid in place across the facility’s foundation, before a 1.5-meter-thick concrete foundation slab will be poured over. The building will house the tokamak of the ITER experimental fusion reactor. The acronym ITER is also a word in Latin, meaning “journey,” or “path.”

A construction worker stands among many 6-foot-tall concrete columns that are topped with steel-and-rubber plating, acting as anti-seismic pads.

Science Photo Library / Reuters

The 300,000-ton tokamak complex will rest on top of 493 anti-seismic bearings that are mounted on concrete plinths rising up from the foundation.

An aerial view of a sprawling complex of large and small buildings and electrical infrastructure

An aerial view of the 100-acre central platform of the ITER Complex, seen in early 2026 in Saint-Paul-lès-Durance, France. The largest buildings, seen at the center, are the Tokamak Complex and its assembly building. Surrounding it are more than 35 support buildings that house workshops, diagnostic centers, heating, cooling, power handling, and more. Construction continues, with a target date of 2033 for its first successful generation of plasma.

A virtual forest of rebar and supports, seen inside a complex construction site

A snapshot of construction progress on the assembly building and the Tokamak Complex, seen on April 7, 2025

A view looking upward into the interior of a complicated cylindrical structure about 10 feet around; a worker on a ladder stands inside

The first 110-ton module of the central solenoid, seen from below on December 6, 2023. When complete, the central solenoid will form an 18-meter-tall column at the heart of the tokamak, acting as an incredibly powerful superconducting magnet, driving current into the plasma. Teams from the United States fabricated the central solenoid, then shipped the modules to France. Thirty-five nations around the world are collaborating on the ITER project, building and contributing “in-kind” components and sharing the costs of construction and operation.

A room filled with complicated pipes and tubing

Science Photo Library / Reuters

Construction is underway inside the liquid nitrogen plant, part of ITER’s massive cryoplant, which will produce and circulate liquid nitrogen and liquid helium to the shielding and electromagnets of the tokamak.

A truck pulls a long trailer with a large metal cabin-like shipping container on it

The fourth and last vacuum-vessel sector from Korea is ready to leave the staging area and travel the last leg of its journey to France from the Hyundai Heavy Industries shipyard in Ulsan, South Korea, in 2024. Each of the 440-ton components was packed in metal cabin-like shipping containers for the long ocean journey.

A large and complex metal segment of a fusion reactor lies on its side in a tall building

A view of one of the vacuum-vessel sectors lying on its side inside the former Cryostat Workshop, which is now used for assembly-related activities

A large metal lid hangs from a gantry crane above a 30-meter-deep circular pit.

The cryostat base hangs above the opening of the 30-meter-deep tokamak assembly pit, before being slowly lowered to the bottom. When complete, the ITER cryostat will become the largest stainless-steel high-vacuum pressure chamber ever built, containing the vacuum vessel and its powerful magnets.

A large metal component of a fusion reactor hangs from cables in a gantry crane, while being slowly flipped.

Vacuum-vessel sector #3 has been positioned under a gantry crane for an outdoor “flip” operation that will expose its second side, in May 2026.

People stand inside a large open building beside huge rigs and machinery being assembled

.© ITER Organization

To the right, a 330-ton toroidal field coil (a powerful superconducting magnet) is being tilted up, raised from horizontal to vertical prior to its transfer into the arms of the sub-assembly tool, to the left, where it will be paired with a vacuum-vessel sector, in July 2025.

A large D-shaped component of a fusion reactor is lowered into place among many supports and other partially complete components.

A vacuum-vessel module (top) was installed in the ITER tokamak pit during an overnight operation from May 26 to 27, 2026.

A worker rappels down the side of a large component of a fusion reactor that is under construction.

A worker from the CNPE Consortium engineering group rappels down one of the massive vacuum-vessel sectors in the pit, past interior staging that has been installed to give teams access to every corner.

The interior of a complex steel chamber, part of a fusion reactor

Gilles Bader / Le Pictorium / Reuters

A view from inside the heart of the Tokamak reactor, showing mounting points for diagnostic sensors and interior blanket shielding, seen on November 17, 2025

A worker welds an object onto the interior wall of a fusion reactor component.

One by one, supports for magnetic sensors are welded to the vacuum vessel’s inner surface in February 2026. There are approximately 2,000 such supports per sector.

A gantry crane lowers a large D-shaped component of a fusion reactor into place in a circular pit beside other components.

The fifth sector module nears the end of its 12-hour journey from the tooling area, and is lowered by a gantry crane into its final landing spot in the tokamak pit in May 2026.

A large metal component of a fusion reactor lies on its side in a huge building, beneath gantry cranes.

Gao Jing / Xinhua / Getty

A vacuum-vessel sector sits on its side in a preassembly hall in Saint-Paul-lès-Durance on November 23, 2023.

A huge, rounded metal lid is suspended beneath a gantry crane, about to be placed on top of a chamber filled with complicated equipment.

This insulated 11-by-22-meter lid is lifted by a gantry crane, on its way to close the cryostat of the ITER magnet cold-test facility in April 2026. The cold-test facility will allow massive magnets to be tested at temperatures of about 4 Kelvin (a few degrees above absolute zero) before they are installed in the tokamak.

Ten workers move together to push a large component into place beneath a fusion reactor.

A team from Italy uses muscle power for the last stage of inserting a gravity support under a vacuum-vessel sector in the tokamak pit in March 2026.

Several workers stand in and around a scissor lift near components of a fusion reactor.

Workers stand on the cryostat base at the bottom of the tokamak assembly pit on December 17, 2025.

A worker stands beside a tall, massive robotic arm.

Standing 4 meters tall, with an arm that extends up to 5 meters, “Godzilla” is a platform for developing and testing the tools and technologies that will be used by robots to install components inside the completed vacuum vessel, photographed in March 2026.

Several people gesture toward and look at a scale model depicting a nuclear-fusion reactor.

CFoto / Future Publishing / Getty

At the 2026 China International Nuclear Industry Exhibition in Beijing, visitors learn about the ITER reactor while looking at a scale model of the facility, on April 22, 2026.

The interior of a partially completed torus-shaped fusion chamber, studded with small and large attachment points

A dense forest of attachments, seen on the inside of the ITER vacuum vessel. Tiny “bosses” for diagnostics are seen here amid the much larger support pads (yellow) for the blanket shield blocks.

An overview of a complex partially completed torus-shaped fusion chamber

Five of the nine vacuum-vessel modules were in place in the tokamak assembly pit as of June 2026. Once all of the modules are in place, sensors and blanket shielding will be added. The plan is to create a donut-shaped chamber that will use the largest magnets in the world, alongside blanket shielding cooled to nearly absolute zero, to contain 840 cubic meters of plasma that will be 10 times hotter than the core of the sun. The ultimate goal is to create more energy output than input, and to use that to generate electricity in future projects.

Hundreds of people gather beside a road for a group photo in front of a large facility.

Hundreds of staff members, contractors, ITER-project associates, interim personnel, and staff from Fusion for Energy and the other members’ domestic agencies gathered on the ITER platform for a group photo in September 2024.