The operation looks slow and almost uneventful from the outside, yet each movement inches humanity closer to a long-promised goal: using nuclear fusion as a practical, large-scale source of low-carbon energy.
Another huge piece clicks into place at ITER
On 25 November 2025, inside the ITER site at Cadarache, crews guided an enormous metallic sector into the heart of what will be the world’s largest fusion reactor. This component, known as vacuum vessel module no. 5, now sits alongside modules 6 and 7, which were installed in April and June.
The three sectors form one third of the doughnut-shaped chamber where, in the 2030s, a superheated plasma will swirl at around 150 million degrees Celsius. That is several times hotter than the core of the Sun, held in place not by walls but by magnetic fields.
Each module installation looks like just another heavy-lift operation. In practice, it marks an incremental but crucial shift from theoretical fusion dreams to visible hardware.
ITER, short for International Thermonuclear Experimental Reactor, is an experimental tokamak machine: 30 metres tall, 30 metres across, and designed as a test bed to prove that fusion can generate far more energy than it consumes. If it works, commercial reactors could follow in subsequent decades.
How do you install a 400-tonne “slice” of a star machine?
A choreography measured in tenths of a millimetre
At first glance, the operation sounds simple: move the module from a workshop into a pit and lower it into position. In reality, this is one of the most delicate construction jobs on Earth.
First, the module passes through a giant cleaning hall where surfaces are meticulously dusted. Any stray particle can compromise vacuum quality inside the chamber years from now.
Then, powerful overhead cranes lift the structure and carry it into the assembly hall. Operators on the ground and in control rooms work together, nudging the load in three dimensions. Clearances around the module are tiny, and allowed deviations are measured in fractions of a millimetre.
The structure is not just heavy; it is dense with technology. Each vacuum vessel sector includes:
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- a thick steel shell that forms part of the chamber wall
- superconducting coils that help shape and control the plasma
- a thermal shield that limits heat transfer between hot and cold parts of the machine
- interfaces for diagnostics, heating systems and internal components
Lowering the module into the tokamak pit feels, to those involved, less like industrial work and more like exceptionally slow surgery.
Three hearts installed, six more to go
ITER’s vacuum chamber is split into nine sectors arranged in a ring, each one a slightly different piece of a vast three-dimensional puzzle. With sectors 7, 6 and now 5 in place, one arc of that ring is starting to look complete.
Three of nine modules are installed, which means a visible third of the vacuum vessel now stands in the pit. The geometry of the future reactor is no longer just an engineering drawing; it is becoming a physical object.
The remaining six modules are scheduled to be installed progressively through 2026, with a new sector lowered into the pit roughly every two to three months. After that, engineers will weld the segments together, seal the structure, and begin a long campaign of leak tests and alignment checks.
A truly global machine
Industries from four continents on a single site
ITER’s complexity does not stop at the technology. The project brings together 35 nations, including the EU countries, UK, China, India, Japan, Russia, South Korea and the United States. The latest module installation shows how industrial players from different regions mix on a single, tightly choreographed worksite.
Among the key companies involved in the current phase:
- CNPE consortium (China and France) – manages assembly of the cryostat, magnet feed systems, the central solenoid support and integration of modules into the tokamak pit.
- SIMIC S.p.A. (Italy) – responsible for the precise positioning and mechanical connection of the vacuum vessel sectors.
- Larsen & Toubro (India) – handles ultra-accurate welding of vessel “windows” and other openings.
- Westinghouse (US) – in charge of the final welds that will permanently join all nine modules into a single pressure boundary.
Every component is essentially bespoke. Manufacturing tolerances run down to microns. When something does not match exactly, teams must assess whether to adjust, rework, or redesign. That partly explains why the project schedule has slipped over the years.
Progress and delays, side by side
ITER’s first plasma was once promised for 2025. That date now looks distant. The current roadmap suggests vacuum tests near the end of the decade, around 2028–2029, followed by a first low-power hydrogen plasma around 2030.
The ambitious target is to run a stable plasma fuelled with deuterium and tritium — two heavy forms of hydrogen — sometime between 2035 and 2039. That phase would demonstrate whether a large tokamak can produce a sustained fusion reaction that gives out more energy than the machine needs to operate.
| Module | Installation date | Status |
|---|---|---|
| No. 7 | April 2025 | Installed |
| No. 6 | June 2025 | Installed |
| No. 5 | 25 November 2025 | Installed |
| Nos. 1–4, 8–9 | Planned 2026 | Awaiting installation |
Cost has climbed along with time. Estimates now put the overall bill above €22 billion, shared between the major partners. For supporters, that figure looks high but defensible when set against long-term decarbonisation needs and defence budgets of large economies.
From steel structure to burning plasma
What happens inside that vacuum chamber?
Once assembly ends and the vessel is sealed, the interior will host a highly controlled environment. Pumps will remove air, leaving an ultra-high vacuum where stray gas molecules become rare. Powerful magnets will then confine a loop of plasma — a soup of charged particles — so that it never touches the vessel walls.
External systems will heat this plasma using radiofrequency waves, neutral particle beams and resistive heating. The goal is to raise the temperature to around 150 million degrees Celsius. At that point, deuterium and tritium nuclei can overcome their mutual repulsion and fuse, releasing large amounts of energy as fast neutrons and heat.
ITER is not a power plant. Its purpose is to show that a large tokamak can ignite and sustain a fusion plasma that yields more energy than the device consumes.
Those neutrons will slam into a surrounding “blanket” lining the inside of the vessel, where they deposit heat. Future commercial reactors would capture that heat to produce steam and drive turbines, just as in conventional nuclear plants. They might also breed tritium fuel from lithium inside the blankets.
Why fusion still attracts so much attention
Fusion appeals to policymakers and engineers for several reasons. The fuel mix uses isotopes of hydrogen, which can be extracted from seawater or bred from lithium. The reaction produces no CO₂ at point of generation. Long-lived radioactive waste is far more limited than in existing fission reactors.
Risks, though, do exist. Components exposed to neutron bombardment become activated and must be handled as radioactive waste. Deuterium-tritium operation requires strict control of tritium, a radioactive gas. Complex devices like ITER can also suffer from unexpected technical failures, delays and cost overruns.
Still, if fusion devices eventually operate reliably, they could play a complementary role alongside renewables, fission reactors, storage technologies and demand management. Rather than a single “silver bullet”, many energy specialists see a broad mix of solutions as the most resilient route to stabilising the climate.
Key concepts behind ITER’s giant leap
Understanding a few fusion terms
Several pieces of jargon surround the ITER project. A short guide helps make sense of them:
- Tokamak – a doughnut-shaped magnetic confinement device invented in the Soviet Union in the 1950s, still the main design for large fusion experiments.
- Vacuum vessel – the steel chamber where the plasma sits. It keeps air out and forms a safety barrier between radioactive materials and the environment.
- Plasma – often called the fourth state of matter, a gas so hot that electrons separate from nuclei, turning atoms into charged particles.
- Deuterium–tritium (D–T) fuel – a mix of hydrogen isotopes that fuses more easily than other combinations, making it the most realistic fuel for first-generation reactors.
As module no. 5 locks into position at Cadarache, these terms start to look less abstract. The reactor is still years from operation, yet the visible progress inside the pit signals a shift: fusion energy, for decades a distant promise, now has a growing amount of actual hardware behind it.
Originally posted 2026-03-05 01:57:58.