From developing welding procedures for first-of-a-kind components to devising strategies for welding in the tokamak’s confined spaces, ITER’s welding engineers are helping to define the techniques and standards that may shape fusion projects for decades to come. Welding is fundamental at ITER. Everything on the tokamak is metallic and every major system relies on welding—from joining cooling pipes or attaching diagnostic sensors, to joining the nine vacuum vessel sectors into a single plasma chamber. Yet while the basics of the welding methods used at ITER are the same as those found in fission projects and across heavy industry, there are challenges that are unique to fusion and to ITER.“Because of the size of the tokamak, the complexity of the instrumentation, and the space constraints, we are solving problems that nobody has encountered before,” says Frédéric Lobinger, an ITER welding engineer in the Machine Assembly Program who focuses on port cells, diagnostics, and other tokamak systems. “Accessibility, shrinkage, installation sequencing, repair strategies, quality requirements, and integration of diagnostics are all areas where ITER is creating new knowledge.”Welding at ITER can be measured in both small and big ways. Welds range from the miniscule (0.1 mm-thick welds to attach temperature sensors on the central solenoid magnet) to the mammoth (105 mm-thick closure welds on the toroidal field coils). In between, there are so many welds of all sizes that the cumulative volume is colossal: 10 tonnes of weld metal will be deposited on the plasma chamber, while a further 40 tonnes will be deposited in the port cells. ITER welding engineer Frédéric Lobinger demonstrates the “pull test” that is used to qualify welding procedures. The objective is to verify that the weld remains attached to the base material. One of the welding challenges at ITER is that the project involves first-of-a-kind components and new instrumentation configurations. While the fission sector has had 60 years of experience building reactors and optimizing designs to facilitate welding, there have only been a handful of tokamaks built and none have been as big as ITER.“The standards we use are based on proven industrial experience, but ITER's designs are often unlike anything that has been built before,” says Hoyoung Kim, a welding engineer at ITER who supports assembly activities for systems such as cooling water and cryogenic networks, thermal shields, magnet feeders, and the central solenoid. “The welding process itself is not fundamentally different. The difference is that in the fission industry, decades of experience have led to standardized designs that are practical to manufacture and weld. Fusion systems are newer and many of the component designs have not yet been fully optimized for welding. Future fusion projects will benefit from the experience gained here.”Another of the welding challenges ITER faces is “shrinkage.” When metal is welded, it heats up. As the weld cools, both the deposited metal and the surrounding material contract. In stainless steel this shrinkage can be significant, and it becomes more pronounced as thickness increases.While devices such as JET faced shrinkage challenges, the dimensions and thicknesses involved were smaller so the experience cannot be perfectly extrapolated to ITER. Work is ongoing to model the welding shrinkage of the ITER vacuum vessel because of the importance shrinkage will have on final dimensions, alignment, and assembly tolerances. A Top Welding, Top ITER competition was held to showcase welding expertise at the project. From left to right: ITER’s Jin Sung-Wook who served as a judge, ITER welding engineer Hoyoung Kim who helped establish the competition rules, and Tanya Meyer from Equans-MECANUC, one of the participating firms. Compared to existing fusion projects or fission reactors, instrumentation is also a consideration for welding engineers at ITER. The ITER tokamak contains an enormous number of diagnostics, sensors, cables, studs, and supports because the machine is designed as an experimental device and scientists want to measure and understand virtually everything that happens inside the plasma. This means ITER has far more instrumentation to weld into place than any eventual commercial fusion power plant, which would be optimized for operation. But perhaps the most daunting challenge welders face is space constraints. When components are manufactured in factories or welds are performed on-site in ITER’s support buildings or sector sub-assembly tools, there is room to work. Inside the tokamak, space is becoming increasingly constrained and some welding locations are difficult to access. ITER has developed virtual reality simulations of the tokamak configuration that will help engineers create new welding strategies adapted to the environment.“Now that five sector modules have been installed in the tokamak pit, everyone can see how limited the available space is becoming,” says Frédéric Lobinger. “The machine is large, but once dozens of workers, tools, pipes, diagnostics, and support structures occupy the same area, access is an issue. Accessibility will be one of the defining challenges of welding.”As these diverse welding issues are solved over the coming years, the techniques will be rigorously documented to help define future fusion standards. The Top Welding, Top ITER competition brought welders from across the project together to test their skills in a series of welding categories. Here, first-place welders celebrate their victory on stage with head judge Robert Pearce (left), Head of Construction Project Sergio Orlandi (second from right), and Machine Assembly Program Manager Jens Reich. Top Welding, Top ITERTo celebrate the art of welding and recognize its critical role in tokamak assembly, the ITER Organization hosted the Top Welding, Top ITER competition from 8 to 17 June. Organized by the CNPE Consortium, the competition featured welders from seven companies representing four countries showcasing their skills in a range of categories from fastest pipe welding to best manual tungsten inert gas (TIG) welding in confined spaces.“ITER is only successful when we are welding in a successful manner,” said Machine Assembly Program Manager Jens Reich, who oversaw ITER’s participation in the competition. “The welding competition recognized the diverse welding expertise at the project and provided an opportunity for welders to exchange knowledge and techniques. This combination of productive collaboration and positive competition reflects the spirit of ITER.”Welders from CNPE-CNI23 won first prizes in the TIG welding categories while a welder from Equans-Mecanuc won the fastest piping award and welders from SIMIC, Equans-Mecanuc, and Larsen & Toubro won the best volumetric welding awards.

Earlier this month, the Princeton Plasma Physics Laboratory celebrated a key milestone in the National Spherical Torus Experiment-Upgrade (NSTX-U) Recovery Project: the arrival of the central magnet bundle from Bilbao, Spain. The bundle includes two components, both assembled by Elytt Energy. A pillar-shaped, toroidal field coil serves to create most of the magnetic fields that stabilize and confine the plasma. An ohmic heating coil wraps around it—much like thread on a bobbin—to drive a current and provide heating. This bundle will be the last major component installed before NSTX-U begins machine commissioning, followed by the start of experiments in 2027.NSTX-U is a spherical tokamak—a more compact fusion device than traditional tokamaks like ITER. Its shape better resembles a cored apple than a donut, a design that offers both technical and financial advantages. Namely, spherical tokamaks can achieve higher plasma pressures at a given magnetic field, and with lower construction costs. Data from NSTX-U will help ITER optimize conditions for a self-sustaining burning plasma and investigate whether the spherical design could be viable at reactor-scale.This device succeeds the former NSTX, which operated from 1999 to 2012. Although the earlier machine advanced plasma physics research, it did not run at fusion-relevant conditions. PPPL upgraded the device to double the toroidal field strength, plasma current, and auxiliary heating power, while quintupling the pulse durations. NSTX-U launched in 2016, but the failure of an inner poloidal field coil prematurely ended the campaign.Over the past ten years, PPPL has worked to restore the device, and the central magnet bundle is critical to that effort. “The magnet bundle is at the heart of the project—literally and figuratively,” said NSTX-U Project Director Dave Micheletti in an interview from 2024. NSTX-U nears completion and awaits the installation of the central magnet bundle. (Image credit: Michael Livingston, PPPL Communications Department) Next, engineers will lower a carbon-studded shield around the bundle to protect it from the plasma’s heat. Technicians will install the magnet in the centre of NSTX-U, hook up the power sources, and finalize any outstanding systems. That includes attaching the cooling system’s hoses, affixing the last heat-protectant tiles inside the vacuum vessel, and preparing the bakeout system to remove all residual contaminant particles. The team can then proceed with commissioning, or the final verification of machine components before experimentation. Soon, a new generation of plasma physicists, engineers, and technicians will have access to this fusion research device. “I welcome all fusioneers everywhere to this amazing research opportunity and encourage them to use this facility to help advance humanity’s understanding of plasma and fusion energy,” said Jonathan Menard, PPPL’s deputy director for research. “What a thrilling moment—for PPPL, the nation and the world.” See the full report from PPPL: Delivery of magnet bundle signals a new age of fusion research.

Sector #9 is the latest vacuum vessel sector to be lowered into sector sub-assembly tooling. On Friday 19 June, vacuum vessel sector #9 was lowered by overhead crane into the V-shaped embrace of a sector sub-assembly tool. Approximately six months from now, it will re-emerge as sector module #9—one of the nine segments of ITER's torus-shaped vacuum vessel.The 22-metre-tall vacuum vessel sub-assembly tools have been designed to support the sectors while thermal shield panels and two 310-tonne toroidal field coils are positioned and aligned to millimetre-level assembly tolerances. Precision hydraulics drive the tool's lateral wings; as the wings approach the suspended vacuum vessel sector, actuators on the rotating platforms allow the components to be positioned with the highest accuracy and adjusted to six degrees of freedom*. Sector #9 is the seventh to enter the vacuum vessel assembly line since September 2024. Five completed sector modules are in the tokamak pit and a sixth will be transferred from sub-assembly tooling in July.*Six degrees of freedom refers to adjustability along X, Y and Z axes (up and down, side to side, forward and backward) as well as in rotational directions relative to the axes (swivel, tilt, pivot).

The Consulate General of India in Marseille was host to the International Day of Yoga at ITER. Dozens of people gathered early on Monday morning, 22 June, for an early session of yoga outside of ITER Headquarters. The event was hosted for the second year in a row by the Consulate General of India in Marseille.Over the past decade, the International Day of Yoga has become a worldwide movement, uniting millions in the practice of yoga to enhance physical and mental wellbeing. The theme for the 2026 celebration was “Yoga for Healthy Ageing.” Approximately 500 people have joined a yoga and pilates group at ITER, with classes offered several times a week on site at the fitness centre inaugurated last year.The Consulate General of India sponsored the 2026 event at ITER with yoga mats, T-shirts and a healthy breakfast. Starting the day with 30 minutes of mindfulness.