[5:31 pm] Nuclear fusion: the heart of itter takes shape, a key step in the site is imminent

The ITER construction site, the experimental nuclear fusion reactor under construction in the south of France, has just taken a real step forward with the reception of a huge support structure that will soon house one of the most important parts of the machine.

The operation of tokamaks like ITER relies largely on the creation of a plasma, the electrically charged substrate heated to a temperature of over 100 million degrees where fusion reactions take place. To make it emerge, a tremendous amount of energy must first be applied to a mixture of tritium and deuterium gas. The challenge then becomes to keep this plasma at a good distance from the reactor walls, but also and above all to stabilize it, otherwise the reaction cannot cross the famous "ignition threshold" that allows it to self-sustain.

The central solenoid, the backbone of the reactor

To achieve this, engineers rely on gigantic superconducting coils weighing several hundred tons, which generate an extremely intense magnetic field. Most of these magnets are positioned around the chamber, with one exception: the gigantic central solenoid positioned in the middle of the "donut," which will become the most powerful superconducting magnet on the planet.

The latter will be responsible for a mission of the utmost importance: creating a current in the plasma. This flow of charged particles is absolutely crucial. It actively participates in the rise in temperature, and it also plays a decisive role in stabilizing the reaction. It is therefore one of the most important parts of the reactor.

But installing this engineering marvel is anything but straightforward. It is in fact composed of six modules, each weighing 121 tons, and the whole thing must be positioned with a margin of error of a few millimeters! To ensure that it plays its role perfectly, it is therefore necessary to start by building a gigantic support structure, a sort of high-tech scaffolding of several thousand parts that must withstand gigantic stresses without moving an inch. A colossal engineering challenge.

"The primary role of the structure is to hold the six central solenoid modules in position with strict tolerances, on the order of a millimeter," explains Kevin Freudenberg, technical director of ITER engineering in the United States. "The real challenge then arises during operation. At key moments, the vertical force exerted on the stack of modules can reach 60 meganewtons, more than double the force generated by a rocket at takeoff.»

A key construction step

Eight American companies specializing in structural engineering and high-precision manufacturing worked hand in hand for almost ten years to design and build this colossal structure. This key step is finally complete: in a press release, the ITER consortium announced that the last elements of this gigantic cage have finally been delivered to the Cadarache construction site.

This is a very important milestone in the history of the reactor. Indeed, it means that the assembly of the central solenoid will soon be completed. The first four modules are now in place, and the final two are expected to be stacked by the end of the year, once the final newly received frame elements have been assembled and rigorously tested.

But that doesn't mean the engineers and workers are finally done—far from it. The next big step will be integrating this metal monster into the tokamak's structure. This will involve connecting the solenoid to the other peripheral superconducting magnets, and then ensuring that everything is perfectly aligned so that the first plasmas are as stable as possible. Then the remaining structural components and instruments that will confine the plasma will need to be installed, starting with the vacuum chamber itself.

Some of the most exciting stages of construction are now beginning to emerge, and it will be fascinating to follow the progress of this unique engineering effort. Hopefully, the next steps will now follow regularly, in a context where project leaders were recently forced to postpone the date of first plasma.

Nuclear fusion: in turmoil, the ITER project changes its roadmap