Mitsubishi Heavy Industries Ltd (MHI) said on 24 May it had completed manufacture of four toroidal field (TF) coils (of a total of five, including one spare) ordered by the National Institutes for Quantum and Radiological Science and Technology (QST) for the International Thermonuclear Experimental Reactor (Iter) under construction in Saint-Paul-lès-Durance in southern France. The completed TF coils will be shipped to southern France from Kobe, and installed on site by the Iter Organisation. The reactor is scheduled to achieve first plasma in 2025.

MHI completed the world’s first TF coil for Iter in January 2020, holding a ceremony at its Futami Plant to mark the achievement. This first coil, and the second unit completed in March 2020, are currently in the process of being installed in the reactor. The third coil, completed in November 2020, has arrived at the site and testing has been completed.

The TF coils that are the core components of Iter require high precision manufacturing to secure the plasma with a high degree of accuracy, and sufficient thickness to withstand the strong magnetic field of tens of thousands of tons. In addition to handling the final assembly process for five of the total 19 TF coils in Iter, MHI manufactured the structure and winding used in the TF coils, achieving a level of precision within 0.01%. The superconducting coils are 16.5 metres high and 9 metres wide, with a gross weight of 300 tonnes.

In addition to the completion of the four TF coils, MHI is also working on manufacturing other core components, including the divertor and equatorial EC launcher. The divertor is adevice to remove impurities in the core plasma, as well as inhibit high heat load and particle loading. The equatorial EC launcher injects high-frequency electromagnetic waves to heat the plasma. MHI plans to complete manufacture of the remaining TF coil (spare coil) of the five in 2022.

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