Japan has completed its first 360-tonne D-shaped toroidal field coil for the Iter international fusion project under construction in France.

The coil, which is largest superconducting coil ever built, was manufactured by The Fusion Energy Directorate of the National Institutes for Quantum and Radiological Science and Technology (QST) and Mitsubishi Heavy Industries, Ltd. (MHI).

A formal ceremony took place at MHI's Futami Plant in Hyogo Prefecture, Japan, on 30 January to mark the completion of the coil.

It is one of 18 D-shaped toroidal field magnets that will be placed around the Iter vacuum vessel to produce a magnetic field whose primary function is to confine the plasma particles.

The toroidal field coils, measuring 9x17m, are designed to produce a magnetic field of up to 11.8T and store 41GJ of energy.

Because the precision of coil geometry is critical to creating the magnetic field for plasma confinement, particular attention has to be paid to dimensional control throughout the fabrication process.

Manufacturing Iter's 18 TF coils

Japan is providing eight TF coils, with Europe manufacturing nine plus one spare.

QST commenced R&D for the TF coil manufacturing technology in 2005, and MHI started manufacture in 2012.
Plans call for five TF coils to be made at the Futami Plant. They will be shipped from Kobe Port to southern France by 2022, in the run-up to the start of ITER operations in 2025.

Mitsubishi Electric Corporation is producing the Nb3Sn superconducting winding packs for five TF coils (including the recently completed coil), with the outer coil structures being manufactured in Korea.

The inner coil structures for all 19 TF coils will be manufactured at MHI's Futami Plant, where the first Japanese coil was made.

MHI said the newly completed TF coil is the first main structural component for ITER's magnet system, and its completion is a "major milestone forward for the reactor's construction".

Factory acceptance tests were completed on the first Japanese TF coil on 19 January 2020, with electrical tests, dimensional inspection, visual inspection and pressure drop measurements confirming that the coil meets all technical specifications, according to Iter Organization.

The component will now be packed for international shipment. It is scheduled to leave the port of Kobe, Japan in early March for an eight-week sea voyage to France.

Photo: The TF coil was assembled at MHI's Futami Plant in Japan (Credit: MHI)