ITER magnet assembly begins
On April 26, as the ITER Organization announced that magnet assembly had begun with the April 21 placement of the divertor coil in the bottom of the machine, the organization also published an Image of the Week that bears an unmistakable—and unintentional—resemblance to the Olympic rings. The pre-compression rings were being prepped for installation in the ITER Assembly Hall when the serendipitous arrangement was captured by Bruno Levesy, a project manager at ITER.
The ITER Organization has held its own ITER games in the nearby village of Vinon-sur-Verdon since 2011, most recently in 2019, when the event attracted more than 650 participants.
The divertor coil was lifted 25 meters above the Assembly Hall floor. Photo: ITER
Heavy metal: The 10-meter diameter, 330-metric ton ITER divertor coil, dubbed PF6, is thick and heavy because it has more conductor layers than any other poloidal field coil and more conductor turns per layer. The lifting, handling, and installation of PF6 was an eight-hour operation that required a complex rigging system capable of rotating the coil and positioning it to within 4 millimeters of tolerance.
The divertor coil is designed to create a null field point that allows for the removal of helium ash from the plasma, according to ITER.
“In order to have zero magnetic field at the divertor null field point, the bottom magnet needs to generate a field equivalent in intensity to the one created by the plasma current—but with an opposite polarity,” explained Nello Dolgetta, of the ITER Magnet Section. “And this is the reason why, despite its relatively small diameter, PF6 is so heavy. Since the magnetic field is defined by the intensity of the electric current times the number of conductor turns, we have 30 to 50 percent more coil turns in PF6 than in the other poloidal field coils.”
PF6 was lowered onto temporary supports, where it will remain during the installation of nine vacuum vessel sector subassemblies. Photo: ITER
PF6 was manufactured in China by the Institute of Plasma Physics of the Chinese Academy of Sciences and took seven years to complete. Finished in September 2019, the coil was shipped in March 2020 by barge on the Yangtze River to Shanghai, where it was loaded for ocean transport to the French port of Fos-sur-Mer, arriving in June.
PF6 will remain on temporary supports for a few years, pending the installation and welding of nine vacuum vessel subassemblies, according to ITER. A hydraulic system in the temporary supports will then slightly lift the coil to anchor it to the toroidal field coil superstructure. A similar sequence of events awaits the next poloidal field coil, which is to be installed inside the machine pit this summer.
