459th (and last) turn

At the Institute of Plasma Physics of the Chinese Academy of Sciences (ASIPP), in Hefei, teams have been at work since February 2016 on the fabrication of ITER's bottommost ring-shaped coil. From the successful completion of qualification windings through the serial production of the nine double-layered "pancakes" that make up the core of the magnet, it has been a long and technically challenging journey.

Poloidal field coil #6 (PF6) is being fabricated in China under an agreement signed between ASIPP and the procuring party, the European Domestic Agency. The magnet is due for delivery on site in mid-2019.

The winding of each double pancake involves the integration of two superconducting cable lengths into a spiralled, circular assembly of rigorously controlled dimensions. Each turn of superconductor is electrically insulated from the adjacent turn with layers of Kapton and fibreglass tapes, and inlets are created for the flow of liquid helium.

If you multiply the number of conductor layers (18, or nine double pancakes) by the number of spirals in each layer (25.5), that's 459 turns around the winding table.

Late June, ASIPP and the European Domestic Agency celebrated the completion of the ninth of nine double pancakes. The next step in the process—the impregnation of each double pancake with resin—should be completed at the end of this month, paving the way for the stacking of the different layers into the final coil assembly. After a final round of ground insulation and impregnation the completed coil will be shipped to the ITER site in France, where European contractors are winding poloidal field coils 2, 3, 4, and 5 and where a cold testing facility has been installed for the final testing of the coils at low temperature.

Please see the report on the European Domestic Agency website.