Industrial milestone
Japan completes the first D-shaped coil of the ITER Tokamak
3 Feb 2020
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ITER Japan
In a ceremony on 30 January, a major industrial achievement was celebrated in Japan—the completion of the first 360-tonne D-shaped toroidal field coil for the ITER Tokamak. This first-of-a-kind magnet will leave the port of Kobe in early March for an eight-week sea voyage to France.
Celebrating a major technical and human achievement in Japan on 30 January. During his congratulatory speech, ITER Director-General Bernard Bigot described the industrial component as one of the most complex first-of-a-kind components of the ITER machine.
"I am deeply honoured to be here with you to celebrate the completion of this first-of-a-kind component," said ITER Director-General Bernard Bigot during the event held at Mitsubishi Heavy Industries' Futami plant in Hyogo Prefecture, Japan. "As you know [this coil has been] years in design, procurement, production and testing. Congratulations to all who contributed to this major technical and human achievement!"
Eighteen "D"-shaped toroidal field magnets placed around the ITER vacuum vessel will produce a magnetic field whose primary function is to confine the plasma particles. The toroidal field coils are designed to produce a maximum magnetic field of 11.8 tesla and store 41 gigajoules of energy. Weighing 360 tonnes each, and measuring 9 x 17 m, they are among the largest components of the ITER machine.
The technical specifications of the coils were transferred by the ITER Organization to the procuring Domestic Agencies through Procurement Arrangements in 2008. Since then, ITER Japan (nine toroidal field coils plus all coil cases) and Europe's Fusion for Energy (ten toroidal field coils) have selected industrial suppliers, completed design and manufacturing qualification activities for each fabrication step, and launched series production. What begins at the factories will be continued at ITER as—by pair—the toroidal field coils are interlinked with one vacuum vessel sector and vacuum vessel thermal shielding before taking their place in the Tokamak assembly pit. All toroidal field coils are expected at ITER by 2022.
Because the precision of coil geometry is critical to creating the magnetic field required for plasma confinement, any non-conformity of fabrication tolerances or assembly misalignments can result in errors in magnetic configuration. As a result, particular attention has been paid to dimensional control throughout the fabrication process—from the manufacturing of the core winding pack and case structures, to the insertion of the winding pack inside of the case, and finally closure welding and final machining.
Factory acceptance tests were completed on the magnet on 19 January 2020 with the participation of ITER Organization observers. Electrical tests, dimensional inspection, visual inspection and pressure drop measurements confirmed that the coil meets all technical specifications. The component will now be packed for international shipment.
Celebrating an achievement that was more than 10 years in the making. The exceptional size and weight of this first toroidal field coil—17 metres in length and 800 tonnes once packed—means that there are only 13 boats in the world capable of transporting the component to France.
Japan's National Institutes for Quantum and Radiological Science and Technology (the procuring agency, QST) joined with Mitsubishi Heavy Industries, Ltd. and representatives of the ITER Organization to celebrate the completion of ITER's first toroidal field coil. Among the attendees were QST President Toshio Hirano; MHI President and CEO Seiji Izumisawa and Senior Vice President Akihiko Kato; ITER Organization Director-General Bernard Bigot; Parliamentary Vice-Minister of Education, Culture, Sports, Science and Technology Shuhei Aoyama; and members of the Japanese Diet.
During the first insertion operation last year, laser trackers were used to adjust the winding pack inside of the steel case to within less than 1 mm of target accuracy, maintaining the coil's identified current centre line within nominal geometric tolerances. [More at https://www.iter.org/newsline/-/3263]
Case closure welding
To prevent welding deformation during coil case closure from disturbing the position of the winding pack and its current centre line—especially over the 70 metres of weld length required to seal the case shut—contractors supported the winding pack inside of the case with custom shims and monitored out-of-plane welding deformation by precision laser tracker in real time, allowing the welding sequences to be adjusted as the work progressed. The required tolerances of bevels at the welding grooves were respected across the board at less than 1 mm.
The penultimate activity—filling the gap between the winding pack and the toroidal field coil case with resin in order to link the components mechanically—was carried out over three days in August 2019. ITER Japan contractors created inlets at several locations around the huge coil to ensure that the resin—whose viscosity increases with time—had the chance to permeate the slim 4 mm gap along the full length of the magnet coil while it was fresh and less viscous.
To respect the tight tolerances demanded at critical interfaces—as tight as +/-0.2 mm at some points—extra material was left on these surfaces and final machined to compensate the closure welding deformation and avoid out-of-tolerance issues that could imperil proper Tokamak assembly and magnetic field quality.
Acceptance tests
Factory acceptance tests on the first toroidal field coil produced in Japan were carried out at Mitsubishi Heavy Industry's Futami plant on 19 January 2020. Electrical tests, dimensional inspection, visual inspection and pressure drop measurements confirmed that the coil meets all technical specifications.