Building a new Sun: The world’s largest science experiment continues to take shape


From a small hill above Vinon-sur-Verdon in southern France, you can see two suns. Right before sunset, the effect is even more startling. One of the two suns has been blazing for the past 4.5 billion years and is slowly setting. The other is being built by thousands of human hands, and is very slowly rising. As the Sun sets, its rays cast a magical glow over a huge construction site, where the world’s biggest fusion reactor is being built.

The ITER (International Thermonuclear Experimental Reactor) project, a joint venture by 35 countries, is one of the world’s most important scientific projects. The aim of the project is to prove nuclear fusion – a process constantly taking place inside our Sun and other stars – can be utilised on Earth, to produce electric energy on an industrial scale. ITER hopes it will be the first fusion device to sustain fusion power over a long period of time. If successful, it could well signal a direction away from using fossil fuels for good.

Since 1973, global energy usage has doubled. By the end of this century it might actually triple. 70 per cent of all carbon dioxide emissions into the atmosphere are created through our energy consumption. 80 per cent of all the energy we consume is still derived from fossil fuels. Therefore, replacing these harmful emissions will help hugely with reducing pollution worldwide, and help slow climate change.

The EU has officially pledged to start producing more than half of electric energy from renewable sources by 2030. By 2050, the hope is that the EU will be a fully carbon-neutral society. To achieve this, it is important to find alternative sources of energy, and many believe that nuclear fusion could be the answer to the world’s long-term energy needs.

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But before that happens, there is still a long way to go. ITER is not expected to be conducting plasma experiments until 2025, with the facilities not being fully complete and operational until 2035.

We take a look at how this state-of-the-art facility is taking shape.

Text by Bostjan Videmsek

The world’s biggest magnets

In theory, ITER will produce fusion energy 10 times hotter than the sun. The heat is contained by two layers of magnetic coils made of niobium-tin and niobium-titanium. These are the only ITER components manufactured on-site. With diameters between 17 and 24m, they are too large to be built and transported to the site. Photographed in Saint-Paul-lès-Durance, France, 7 October 2020. Photo by Matjaz Krivic

Looking into the tokamak pit

A view from above shows the scale of the tokamak chamber before the installation of the vacuum vessels. A tokamak is an experimental machine designed to harness the energy of fusion. Inside a tokamak, the energy produced through the fusion of atoms is absorbed as heat in the walls of the vessel. Just like a conventional power plant, a fusion power plant will use this heat to produce steam and then electricity by way of turbines and generators. Photo by Matjaz Krivic

The view from inside

Inside of the tokamak pit, three tower-like alignment tools have been installed for the fitting of the lower parts of the thermal shield. Photo by Matjaz Krivic ©Matjaz Krivic

Vacuum cleaner

A worker stands inside one of the vacuum vessels during construction, in October 2020. Photo by Matjaz Krivic

These 20m structures are ITER’s sector sub-assembly tools (SSAT) for pre-assembling a vacuum vessel, complete with thermal shields. The word ‘tokamak’ is a Russian acronym for ‘toroidal chamber with magnetic coils’, a concept developed in 1957 by the Soviet physicist Igor Golovin. Photographed at Saint-Paul-lès-Durance, France, 6 October 2020. Photo by Matjaz Krivic

Another view of the tokamak pit

Construction work inside the tokamak pit continues, in this image taken in October 2020. Photo by Matjaz Krivic

Piece by piece

One of the huge vacuum vessels is pictured here before installation, in October 2020. Photo by Matjaz Krivic

More images from Science Focus:

Keeping cool

The extensive cryogenic power needed to cool the ITER magnets, thermal shield and cryopumps will be delivered from a single location on the ITER site, shown here under construction. Photographed at Saint-Paul-lès-Durance, France, 6 October 2020. Photo by Matjaz Krivic

House assembly

ITER’s assembly hall, next to the main tokamak building, is pictured during construction in Saint-Paul-lès-Durance, France. Photo by Matjaz Krivic

Powering up #1

The 400kV electrical switchyard on the ITER site. The yard features reactors, capacitors, resistors and sensors that aim to smooth the flow of AC current to power the ITER tokamak. The plant will need large amounts of power during plasma operation. Photo by Matjaz Krivic

Powering up #2

Another view of ITER’s reactive power compensation and harmonic filtering system, designed to reduce ‘harmonic distortions’ in the AC current that ITER receives from the grid. Photo by ITER

Slow and steady wins the race

An aerial view of the construction site of ITER and the surrounding complex at Saint-Paul-lès-Durance, France. Construction at the site began in August 2010, and is not expected to be completed until at least 2025. Photo by Matjaz Krivic

The assembly hall

Assembly Hall at ITER

The view of all the different work zones in the assembly hall. The sheer scale of the construction can be seen in this image, taken on 23 November 2020. Photo by ITER

Vacuum vessel part 1

First coil put in place

This image, taken on 9 September 2022, shows the first part of the vacuum vessel section being placed and secured into position. Photo by ITER

A shining performance

The shinier a thermal shield’s silver coating, the better its thermal radiation performance. In this image taken on 9 September 2022, a segment of the vacuum vessel is hand-polished before being moved into position on the vacuum vessel sub-assembly tool. Photo by ITER

Danger! High voltage

Aerial view of the high voltage building

The structure of the High Voltage Supply Building is emerging in this image, taken on the 12 September 2022, with three ‘branches’ heading towards the tokamak building, and showing the trajectory that the transmission lines will follow. Photo by ITER

Giant jigsaw

Vacuum vessel moved into place at ITER

Vacuum vessel section number 8, built in South Korea, is shown as it is transferred into the assembly hall on 12 September 2022. This vessel section is the third section to be delivered to the ITER complex. Six more sections will soon be delivered in order to complete the vessel. Photo by ITER

Down in the pit

Bottom of the tokamak pit

In this image we can see underneath the tokamak pit, where sensitive equipment is covered to prevent the ingress of dust and dirt. Looking up, we can see the vacuum vessel after it has been installed. Photographed on 21 September 2022. Photo by ITER

Looking at the next stages

How the vacuum chamber will look

This image, generated from ITER CAD data, shows how platforms will be installed inside of the vacuum chamber for the teams carrying out in-vessel assembly work. Photo by Brigantium and Bentley Systems/ITER

Bottom-up assembly

Tokamak pit from above

In the heart of the tokamak building, this 30m-deep pit is the location of the ITER machine assembly. Photographed on 17 October 2022. Photo by ITER



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