In the serene hills of southern France, a colossal machine is taking shape—one that could redefine the future of energy and mark a turning point in human technological achievement. The International Thermonuclear Experimental Reactor, better known as ITER, has entered its most delicate and decisive phase: the assembly of its core, a vacuum vessel designed to contain plasma hotter than the sun. This moment represents not just a milestone in engineering, but a testament to global cooperation and the relentless pursuit of clean, limitless energy.
A Star on Earth: The Promise of Fusion
Humanity’s Boldest Scientific Endeavor: ITER Enters Its Most Critical Phase
Fusion energy has long been hailed as the “holy grail” of power generation. Unlike nuclear fission, which splits atoms and produces long-lived radioactive waste, fusion merges light atomic nuclei—typically isotopes of hydrogen—into heavier ones, releasing immense energy in the process. It’s the same reaction that powers the sun and stars, and if harnessed on Earth, it could provide virtually unlimited, carbon-free energy with minimal environmental impact.
ITER’s mission is to demonstrate the feasibility of fusion at a scale never before attempted. The goal is to achieve a fusion power amplification factor (Q) of 10, meaning the reactor will produce 500 megawatts of fusion power from just 50 megawatts of input heating. While ITER itself will not generate electricity for the grid, it is the critical proof-of-concept that will pave the way for future fusion power plants.
Engineering the Impossible
At the heart of ITER lies the tokamak—a doughnut-shaped chamber where plasma will be confined using powerful magnetic fields. The vacuum vessel, a 19-meter-wide double-walled steel structure, is being assembled from nine massive sectors, each weighing approximately 440 tonnes. These components have been shipped from Europe and South Korea and must be welded together with millimetric precision. The final structure will weigh over 5,200 tonnes, rivaling the size of naval warships.
The engineering challenges are staggering. The vessel must withstand temperatures exceeding 150 million degrees Celsius, magnetic forces stronger than those found in MRI machines, and thermal expansion that could distort the metal. If the plasma touches the chamber walls, the reaction fails. There is no room for error.
To tackle this monumental task, the American nuclear company Westinghouse has been awarded a $180 million contract to lead the assembly, working alongside European partners Ansaldo Nucleare and Walter Tosto. These teams are not just building a machine—they are constructing a star.
A Global Effort Without Precedent
ITER is not a national project; it is a global endeavor involving 35 countries, including the United States, China, Russia, Japan, South Korea, India, and all EU member states. Each nation contributes components, expertise, and technology. The site at Cadarache has become a planetary-scale jigsaw puzzle, where pieces from across the globe are integrated with astonishing precision.
Europe is providing five of the vacuum vessel sectors, South Korea four. The United States has shipped superconducting magnets over 18 meters long, while Japan is supplying critical sections of the central solenoid. This unprecedented collaboration has led some to call ITER a “nuclear United Nations,” where science replaces politics as the common language.
Originally slated to achieve its first plasma in 2018, ITER has faced delays due to redesigns, funding debates, and the sheer complexity of the undertaking. According to the latest schedule, the reactor will begin its deuterium-deuterium phase in 2035, reach full magnetic energy and plasma current in 2036, and commence deuterium-tritium operations in 2039.
Beyond ITER lies DEMO, the planned successor that will generate electricity for the grid. DEMO is already in early planning stages across Europe and Asia, and its success depends entirely on ITER’s ability to prove that fusion can work at scale.
A Future Powered by Stars
The stakes could not be higher. As the world grapples with climate change, energy insecurity, and the limitations of fossil fuels, fusion offers a beacon of hope. It promises energy that is clean, safe, and abundant—enough to power civilization for millions of years using fuel derived from seawater.
ITER is more than a machine. It is a symbol of what humanity can achieve when it dares to dream big and work together. As engineers weld together the heart of this artificial star, they are not just building a reactor—they are shaping the future of energy, and perhaps, the destiny of our species.