ITER begins installing 230 flux loops inside its vacuum vessel

The ITER Organization announced on 9 November 2026 that flux-loop installation had begun inside the vacuum vessel of ITER, under construction in southern France. Work started on 5 November as part of the in-vessel assembly project. Slender copper-coated cables are being unspooled and secured along the vessel’s inner walls.

The plan calls for 230 loops comprising two kilometres of cable. Approximately 50% will be installed in the first phase, with the remaining 50% installed after the vacuum vessel sectors have been welded together. The announcement marks the start of installation, not completion of all 230 loops.

Flux loops are diagnostic instruments used to study plasma conditions. A change in the magnetic flux passing through a loop of conducting wire induces a voltage. Measuring that signal, together with data from other sensors, allows the plasma’s shape and position to be reconstructed. Rather than relying only on direct observation, the system uses changes in magnetic flux to understand plasma conditions.

Assembly of the large vacuum vessel is progressing alongside installation of the instruments that will measure the plasma inside it. The two-stage plan illustrates how diagnostic installation must be coordinated with vessel welding.

For ITER’s research goals and the wider construction programme, see FI’s introduction to ITER.