The World's Largest Nuclear Fusion Project Is A Step Closer To Recreating The Sun's Power Here On Earth

Ever since nuclear fusion was first discovered in the 1930s, scientists have imagined ways to harness its energy. The earliest designs for nuclear fusion reactors began in earnest in the 1950s, with the proposal of the "tokamak," a machine that employs magnetic fields to contain the plasma at the core of a fusion reaction. Since then, nations have poured enormous resources into developing functioning fusion reactors, and the world is now closer than ever to realizing the dream of producing power in the same way that the sun does. A new milestone was reached on September 7, 2025, when a massive fusion experiment in southern France began the assembly of the machine's most critical component: the vacuum chamber.

The ITER tokamak is expected to be the world's largest ever nuclear fusion experiment when assembly is completed (projected for 2033). But piecing together the main core of such a colossal machine is no small feat. In total, nine sectors, mostly made of high-grade steel, must be welded together, with each weighing roughly 485 tons. The sectors were built and shipped from plants in South Korea and Europe, while the United States company Westinghouse, normally involved in nuclear fission projects, is tasked with assembling them at the ITER's main site in Saint-Paul-lès-Durance, France.

The project is the result of a vast international collaboration. It's estimated that 33 nations in total are involved in the project. Yet, while the ITER experiment may be the largest ever once finished, it's not the first. A few dozen tokamak machines exist across the world, and each seeks to study the practical methods of containing fusion reactions to generate clean energy. Recently, China made headlines when its EAST tokamak reactor successfully contained a fusion-inducing plasma for over 1,000 seconds. Once built, the ITER reactor is expected to leave such records in the dust.

Tokamak reactors have always been experimental rather than functional. Before they can start generating electricity from fusion, scientists first need to tackle the challenges involved in creating and containing the extremely high temperatures of fusion-inducing plasma. After all, we're talking about the power of the sun, so there's a lot of advanced engineering to consider.

The ITER project is also experimental, but the scale and scope of its tokamak reactor are unprecedented. According to the project's website, the completed ITER tokamak will be able to contain "five times the plasma volume of the largest machine operating today." The reason for its greater capacity is largely thanks to the massive size of the vacuum chamber, making the recent commencement of its assembly all the more monumental. The machine's one million components will have a combined weight of over 25,000 tons, and the entire facility and its equipment will have a greater mass than the Empire State Building.

Most importantly, the fusion power output is expected to be orders of magnitude greater than the current world records. The machine will use 50 MW to heat the plasma to 150 million degrees Celsius. Once hot enough, nuclear fusion will kick off and generate an expected 500 MW of fusion power. In other words, the power return will be ten-fold. Currently, no tokamak reactor has ever generated a greater output than input, so ITER's expected ten-fold power gain will likely mark the start of a new age in energy generation. Indeed, we've come a long way since the wood furnaces of the Industrial Revolution.