Mitsubishi Heavy Industries Ltd (MHI) has completed manufacture of the final toroidal field (TF) coil ordered by Japan's National Institutes for Quantum & Radiological Science & Technology (QST) for the International Thermonuclear Experimental Reactor (ITER) under construction at Cadarache in France. Japan is responsible for the manufacture of nine of 19 TF coils for ITER, with MHI producing five coils.

These are massive superconducting coils, 16.5 metres high and 9 metres wide weighing 300 tonnes each, and requiring a manufacturing accuracy of within 0.01%. MHI completed the world's first TF coil in January 2020. The four completed coils already completed by MHI have been shipped from the port of Kobe to southern France, and are now being installed at the construction site. The unit is schedule for shipment shortly.

In addition to the TF coils, MHI is also working on other core components, including the divertor and equatorial EC launcher. The divertor is used to remove impurities in the core plasma, as well as to inhibit high heat load and particle loading. The equatorial EC launcher injects high-frequency electromagnetic waves to heat the plasma.

ITER's 18 D-shaped superconducting TF coils will encompass the vacuum vessel container and generate a powerful magnetic field (maximum of 12 tesla) to confine high-temperature, high-density plasma within the vessel. The ITER Project requires a total of 19 TF coils (including one spare). Nine (including the spare) are being made in Japan and 10 in Europe. The inboard coil structures for all 19 TF coils will be manufactured at MHI's Futami Plant. Mitsubishi Electric Corporation is manufacturing the niobium-tin (Nb3Sn) superconducting winding packs for the five TF coils (including the spare) built in Japan. The outboard coil structures are being manufactured in South Korea, with final assembly at the Futami Plant.

QST began R&D for the TF coil manufacturing technology in 2005, and MHI began their manufacture in 2012. Working together, QST and MHI developed high-precision technology for winding niobium-tin conductors, as well as durable structural materials made from a special stainless steel capable of withstanding cryogenic temperatures. To determine manufacturing methods to suppress deformations caused by welding, parameter tests were conducted. The welds were verified using both miniature and full-scale specimens. This provided the basis for developing fundamental technologies suited to the material's properties, including advanced welding procedures and machining techniques.

Image courtesy of Mitsubishi Heavy Industries