Tucked away in the hills of Cadarache, Southern France, 33 nations are working together to create ITER – the International Thermonuclear Experimental Reactor – which, upon completion, will be the largest magnetic fusion device in the world.
Set to replicate the process that powers our Sun and stars here on Earth, the project is aiming to investigate and demonstrate the viability of controlling a nuclear fusion reaction at scale to produce masses of clean, renewable energy.
Nuclear fusion is a reaction in which two or more light atomic nuclei – namely, at ITER, two hydrogen isotopes, deuterium (D) and tritium (T) – collide and fuse to form heavier helium atoms, releasing a tremendous amount of energy in the process.
In the core of the Sun and the stars, of course, gravitational forces create the necessary conditions for fusion, but on Earth, achieving a similar environment is no easy feat.
Replicating this reaction in a lab requires extremely high temperature – a staggering 150 million °C – the right amount of plasma particle density to encourage the needed collision of atoms, and sufficient containment time.
Achieved through magnetic confinement in a tokamak device, powerful magnetic fields are used to confine and heat the plasma that is converted from the gas produced, in a ring-shaped container called a torus. In the fusion device, as in a star, plasmas provide the environment in which light elements can fuse and yield energy.
The initial aspirational idea for an international fusion research project was first proposed by US President Ronald Raegan and the Soviet Union’s General Secretary Mikhail Gorbachev at the Geneva Summit in 1985, which ultimately paved the way for the project today.
The official ITER Agreement was signed in 2006 by China, the EU, India, Japan, South Korea, Russia, and the US, with the formal ITER Organisation created a year later. Construction began on the site in 2010, with the initial machine assembly beginning a decade later.
Spanning 42 hectares (420,000 square metres) and comprised of almost 50 facilities, the site, though it sits on French soil, is jointly owned by each contributing country, highlighting the collaborative nature of the project.
Current rising geopolitical tensions aside, ITER prides itself on being entirely apolitical, to ultimately protect its joint research and overall mission. No country can be kicked off the project, and those that decide to leave are still tied in financially until completion. The UK is the only contributing country so far to have lost access to ITER as a result of Brexit, with the country now pursuing its own nuclear research.
“We are doing this all together in order to create something that nobody could do alone,” said Alain Bécoulet, Deputy Director General and Chief Scientist at ITER. “The ITER Agreement is supported by an international treaty, which is very different from CERN, for example. We refrain from politics inside here, which I think is the right thing to do. We are very proud of the example we’re setting, that science can be one of the areas for diplomacy.
“Our quality of life depends on energy, and yet energy is one of the greatest challenges we face. We need cleaner, more efficient and more reliable energy than any other source. To make that a reality, we are creating a sun here on planet Earth.”
THE TOKOMAK
Though not the first large-scale nuclear fusion project, ITER is certainly aiming to be the biggest.
Its tokomak – an acronym derived from the Russian ‘toroidal chamber with magnetic coils’ – will hold five times the plasma volume of the largest machine in operation today.
ITER’s machine, which is part-way through construction, will weigh 23,000 tons at completion, and is set to generate 500 MW of fusion energy output power – at least ten times more energy than is required to heat the plasma in the first place.
As with conventional power plants, the Tokomak generates actual power through steam. Inside the tokamak, the fusion plasma that is created by the reaction is confined by extremely strong magnetic fields.
The energy produced through the fusion of atoms in the plasma is absorbed as heat in the walls of the vessel, with the heat set to be used to produce steam to turn turbines and generators. To account for the experiment’s scale, the ITER magnet system will be the largest and most integrated system ever built.
Ten thousand tonnes of magnets, with a combined stored magnetic energy of 51 Gigajoules (GJ), will produce the magnetic fields intended to confine, shape and control the plasma. Manufactured from niobium-titanium, the magnets become superconducting when cooled with supercritical helium, in the range of -269 °C, or 4 Kelvin.
Further, a ginormous vacuum vessel will contain the ITER experiments, providing a high-vacuum environment for the plasma and acting as the primary confinement barrier for radioactivity. Cooling water constantly circulating through the vessel's double steel walls will remove the heat generated during the operation.
In a tokomak machine in particular, it becomes easier to confine the nuclear plasma, and thus generate more energy from the reaction, as the volume of the vacuum chamber becomes larger. This vacuum vessel – with a interior volume of 1,400 m³, an outer diameter of 19.4 metres, and a weight of approximately 5,200 tonnes – is set to provide a ‘unique experimental arena’ for fusion physicists, ITER said, thanks to its sheer size.
Surrounding every piece of the tokomak is the cryostat, a vacuum-tight vessel that minimises heat transfer and allows the superconducting magnets to operate at the extremely low temperatures needed. It also supports the tokomak’s weight and overall structure, and provides safe access for a number of components and diagnostic technology.
Standing 30 metres tall and as many wide, the internal diameter of the cryostat – 28 metres – is determined by the largest components it surrounds, the two largest electromagnet poloidal field coils surrounding the tokomak plasma. Made of stainless steel, the cryostat weights 3,850 tonnes. Its base section, weighing in at 1,250 tonnes, will be the single largest load of the entire assembly.
Unsurprisingly, the ITER cryostat will be the largest stainless steel high-vacuum pressure chamber ever built.
PRECISION IS KEY
The machine assembly began in 2020, with ITER on course to complete construction and begin its research operation by 2033. At every stage, thus far and going forward, Hexagon’s metrology technology is paramount to the project’s success.
Made up of over a million components and constantly moving and shifting during construction, the tokomak needs to be continually monitored. Hexagon supplies ITER with a whole suite of large volume metrology technology – from temperature sensors and laser trackers, to coordinate measuring machines (CMMs) and metrology software – to ensure complete precision and quality needed for such an ambitious build.
As with any major project, ITER has faced a number of challenges since ideation: rising costs, delays due to the Covid-19 pandemic, and changing safety concerns as the construction moves forward, for instance.
Defects found in components like the vacuum vessel have required in-depth examinations and corrective quality checks, while stress corrosion cracking has also occurred in the thermal shields. Incredibly complex manufacturing processes, tight tolerances, finding the right materials and eventually integrating each component to create a functional whole all pose as potential barriers to completion.
“This is a key experimental step between today’s fusion research machine and tomorrow’s fusion power plant. The challenge is to build ITER as well as we possibly can,” Beatrice Alix, Metrology and Reverse Engineering Coordinator at ITER, explained.
“In the Metrology and Reverse Engineering department, we’re in charge of the damage of risk, so anything that can happen in terms of dimensions during the machine installation, operation and also during the maintenance. Metrology is everywhere throughout the assembly.”
ITER has a number of Hexagon 3D laser tracking systems stationed around the site, equipped with automatic target localisation, and real-time probing and scanning systems. Across the build, almost 400 reflector sensors feedback to these systems, providing automatic tracking data.
The accuracy of the network of target points has been measured within a global uncertainty range of 0.2 to 0.4 mm, allowing for sub-millimetre installation accuracy.
“As all of our components are coming from our member states, it would be impossible to construct ITER without extremely precise metrology. Hexagon is our preferred supplier for the equipment, with the great support and vast amount of capability they supply,” Alix added.
“The use of the Hexagon instruments is combined with the Hexagon software. We acquire real measurements of the built components, then do a virtual fitting to compare with the CAD files in a kind of hybrid model. This data is then combined with the supplier data into one reference, which helps us to identify any deviations, repairs, clashes, collision rates, to potentially not being able to assemble as designed. It saves both cost and time, so it is key to the success of the project.”
INNOVATION IN GOVERNANCE
Europe is responsible for the largest proportion of ITER’s construction costs – around 45 per cent – with the rest shared by the remaining countries, at around 9 per cent each. But this project seems to evade monetary focus. Instead, nine-tenths of member contributions are delivered to ITER in the form of components, complete systems or scientific buildings.
“ITER has chosen to develop a tokomak, but of course, there are other technologies and research projects for fusion. ITER is not alone, and we are not enemies in this,” explained Sabina Griffith, ITER’s Communication Officer since 2006, when the project first started.
“We have thousands of people working here, from across three continents, speaking approximately 40 languages. We have paved the way for a fusion industry, but the industry will not wait another ten years until the next machine is being built. We have to keep these people in the industry, keep the young people trained and the knowledge containment alive, and this is where we look to private industry. It’s a joint effort.
“We have also paved the way for the nuclear licensing of fusion that has never been done before, because so far, the experiments and reactors were more or less laboratory experiments. ITER is addressing all of the commercial aspects of fusion – we have a big cooling plant, a power plant, a cryoplant, for example. Everything we are doing here is first of its kind and industrial size. It’s innovation on a massive scale.”
Aiming to bridge the gap between today’s smaller-scale experiments and the fusion power plants of the future, ITER is pushing the limits of every aspect of fusion energy, with an ultimate goal of achieving a sustained fusion reaction that can produce significantly more energy than is needed to initiate it.
Currently focused on finalising its research plan, ensuring system integration and preparing for the start of its operation, ITER is aiming for the ‘first plasma’ in 2034, with full operation now projected for 2039.
Though no actual electricity will be generated, and the reactor will eventually be decommissioned after an estimated 20-year operational campaign, the work ITER is doing will undoubtedly pave the way for the future of energy as we know it.
First thought of as an unachievable feat just a century ago, ITER is proving that fusion energy is possible – but that it can only be achieved through peaceful and international collaboration, for the collective future of the world’s energy as a whole.
