Preparations for the critical installation of bellows within the Tokamak Building are currently in progress, marked by the successful completion of the initial welds in the port cells.

Simultaneously, a specialised installation tool is currently at sea, bound for the ITER site. This bespoke piece of equipment, known as the bellows transportation, upending and alignment trolley, is making its way to France following the successful passing of its factory acceptance tests in India.

The ITER Tokamak is a machine defined by extreme precision, where massive components must be positioned within a fraction of a millimetre. The technical specifications are incredibly meticulous to ensure every part fits perfectly within highly compact spaces.

However, despite this rigidity, the machine is also specifically designed to move. Various factors, including thermal expansion during plasma operations, the natural settling of the building, or minor seismic events, mean the vacuum vessel chamber will engage in a subtle dance, with vertical and horizontal movements expected to reach up to 2.5 centimetres.

According to Sébastien Koczorowski, ITER’s Deputy Program Manager for the ports and bellows installation project, these bellows effectively allow the machine to "breathe." They provide the necessary flexibility for the entire structure to adapt to mechanical loads and movements ranging from a few millimetres to several centimetres. By acting as a flexible interface, they accommodate the motion of the vessel relative to other systems and the surrounding concrete walls.

The project utilises two distinct shapes of bellows: rectangular and circular. The rectangular port cell bellows serve to connect the upper and lower cylinders of the cryostat to the Tokamak Building, helping to compensate for structural shifts and seismic activity.

Meanwhile, the rectangular port duct bellows create an interface between the vacuum vessel chamber and the inner wall of the cryostat, accommodating the thermal expansion and mechanical loads that occur during machine operation.

Each of these rectangular units is a significant piece of engineering, measuring approximately 4 x 4 x 1 metres and weighing as much as four tonnes. In contrast, circular bellows are situated at the entry points for the heating and diagnostic neutral beam lines. Much like their rectangular counterparts, these circular versions manage movements between the cryostat and the building, as well as between the cryostat and the vacuum vessel.

In total, the ITER Tokamak will feature 85 rectangular bellows and 8 circular bellows, all of which are manufactured in China. Currently, nearly 20 of these units have already been received and are being held in storage on-site. The installation process is being overseen by a dedicated team including ITER engineer Elena Rodilla, Rajkumar Suwalka from Larsen & Toubro, ITER Machine Assembly Program Manager Jens Reich, and Sébastien Koczorowski.

The Indian firm Larsen & Toubro was awarded the installation contract in 2024. Having previously delivered the ITER cryostat, the company possesses a valuable familiarity with the machine's interfaces. Two major milestones have recently been achieved in this partnership.

The custom-designed, remote-controlled trolley tool has passed its factory acceptance and mockup tests in Hazira, India. Developed with support from Tata Consultancy Services and input from ITER designer Karsten Friedel, the tool is designed to navigate the tight galleries and port cells of the building using interchangeable interfaces to adapt to different component shapes.

This installation tool is expected to arrive at the Port of Marseille Fos in early May. Nirbhay Naik, the deputy technical responsible officer for the project, noted that the success of the mock-up tests ensures the installation can remain on schedule or perhaps even progress faster than originally planned.

While the tool travels, work on-site has continued; on Tuesday 31 March, the first embedded plate corner joints were welded on the B1 level of the Tokamak pit.

The completion of these corner joints clears the way for full installation work to commence in late May or early June. The first phase of this process will focus on the lower bellows at the B1 level and is expected to take roughly one year. The remaining bellows will be installed once all sector modules are in the pit and vacuum vessel welding has begun, with a target start date for this second phase set for 2028.

Notably, all bellows at the equatorial (L1) and upper (L2) levels will be installed with a specific vertical offset and horizontal pretension. This engineering strategy ensures that as the vacuum vessel expands during operation, the bellows will align horizontally with the port cells and reach their intended normal state.

ITER