ITER advances tokamak assembly with two-thirds of plasma chamber now in place and critical-path module on schedule

Between May and August 2025, the ITER Organization declared a “summer of substantial progress” on its international fusion project, pointing to a string of milestones. Six of nine sector modules are now installed in the tokamak pit — two-thirds of the plasma chamber in position — while three vacuum vessel sectors rest on their gravity supports and teams gear up for the welding phase. Sector module 9, expected to finish assembly by November, sits on the project’s critical path and is targeted for transfer to the pit in early December.

Six of nine sector modules now installed in the tokamak pit

The July installation of sector module 1 was more than a routine lift. It marked the sixth of nine sector modules to enter the tokamak pit, putting two-thirds of the plasma chamber officially in place. Each sector module is a substantial assembly on its own — combining a vacuum vessel sector, two toroidal field coils, thermal shields, and a range of auxiliary components — so getting six of them positioned correctly inside the pit represents a serious accumulation of precision work.

The July operation also closed a chapter on one phase of international manufacturing contributions. It marked the installation of the last vacuum vessel sector manufactured in South Korea, completing that country’s fabrication commitment to the machine’s core structure.

Five sets of rectangular port cell bellows are already in place, and the full welding project associated with the bellows is expected to span five years.

Vacuum vessel sectors advance toward welding phase

While sector modules grab attention for their scale, a quieter but equally important milestone unfolded alongside them. Three vacuum vessel sectors are now resting on their gravity supports inside the tokamak pit — including sector 5, transferred in August. That three-sector configuration proved stable enough for teams to begin welding preparations, a confirmation ITER described as essential before that phase could proceed.

Assembly teams have since turned their attention to sector 3, which carries 120 sensors designed to measure magnetic field during machine operation. Technicians are installing instrumentation on the outer shell and welding bosses on the inner shell, making sector 3 one of the most heavily instrumented vacuum vessel sectors in the entire machine. Work began immediately after bevel repairs and other preparatory activities wrapped up — the kind of tight handoff that matters on a project where delays in one area ripple across the schedule.

Sector module 9 on critical path for December pit transfer

Of all the ongoing assembly activities, sector module 9 is drawing the closest attention from project managers. Its vacuum vessel component was positioned in the subassembly tool back in June, thermal shields followed, and in August the two toroidal field coils were added — bringing the subassembly close to completion.

ITER expects the full assembly of sector module 9 to wrap up by the end of November, with transfer to the tokamak pit scheduled for early December. Machine assembly program manager Jens Reich explained the stakes: module 9 sits on the project’s critical path, and until it moves to the pit, the final sector can’t take its place in the subassembly tool. That’s a hard dependency the team can’t work around. “We’re dealing with tight sequences,” Reich said, “but at this point we are happy with the progress.”

Three-year thermal shield repair completed and bellows installation under way

One of the summer’s less visible but technically demanding achievements was the completion of a repair project running since 2021, when inspectors discovered microscopic stress-corrosion cracks in the vacuum vessel thermal shield. The repair involved removing approximately 11 kilometers of cooling pipework and grinding away 1 metric ton of silver coating to eliminate risks from chlorine residues. New piping was then welded to the thermal shield panels, and the surfaces were polished to restore their reflective properties. The project wrapped up in July, roughly three years after it began.

Separately, installation of the bellows system has started. The 93 bellows will connect the vacuum vessel to the cryostat and the cryostat to the seven-story tokamak building — flexible joints that accommodate movement and thermal expansion across the machine. Five sets of rectangular port cell bellows are already in place, and the full welding project associated with the bellows is expected to span five years.

Superconducting magnet testing expands and project timeline remains unchanged

On September 7, ITER took another step in its magnet testing program. Teams began preparations to test a 330-metric-ton toroidal field coil at 34 kA — more than three times the current achieved when the magnet cold test facility launched operations earlier in the year. Further upgrades, including additional structural reinforcement, are planned before 68 kA testing begins with toroidal field coil #19.

ITER’s broader schedule remains unchanged. The organization is targeting the start of research operations in 2034, full magnetic energy in 2036, and deuterium-tritium operation in 2039.

The summer’s collective progress spans multiple fronts at once: six sector modules installed, vacuum vessel welding preparations under way, a three-year repair completed, bellows installation started, magnet testing advancing. Each milestone feeds into the next, and ITER characterized the period as a meaningful boost toward those long-range goals.

Kelly Lippke

Kelly is an experienced writer with 15 years of experience exploring the big stories that shape our world, from tech breakthroughs and space exploration to climate, energy, and the fascinating quirks of science. She has a talent for turning complex ideas into sharp, memorable insights that stay with readers long after they’ve finished reading.