Europe is responsible for the manufacturing of 10 out of the 18 Toroidal Field (TF) coils of the ITER machine. The gigantic “D” shaped superconducting magnets will create a magnetic cage where the super-hot plasma will be confined. Their main challenge will be to keep the 150 million ˚C plasma burning without touching the walls of the reactor’s vessel. The double pancake is a large D-shaped disk that is 13m long, 9m wide and 0.1m thick. It is composed of a stainless steel plate, known as the radial plate, with grooves machined on both sides and where a 450m long insulated superconductor is located and impregnated.
A major part of the works linked to the TF coils manufacturing unfolds in the ASG facilities, located in La Spezia, Italy. It is where key processes such as winding, heat treatment, insertion of the superconductor inside the radial plate and laser welding of the radial plates-produced by SIMIC and CNIM-take place. Recently, an important milestone was celebrated in Europe: the first-ever double pancake prototype passed successfully a series of technically demanding tests. It’s a reassuring result for Alessandro Bonito-Oliva, F4E’s Project Manager for Magnets, and his team as well as all the suppliers involved, who have been working relentlessly for this achievement. The technology they have opted for and the method of work have proved them right. It is also important to mention the importance of the role played by the ITER International Organization TF coil Central Team and the respective team of the Japanese Domestic Agency. The excellent collaboration between the three teams, offering a dynamic exchange of technical reviews, expertise and information, have also played an important role towards the successful completion of this milestone.
So what did the tests entail? In order to check the capability of the prototype to withstand the cryogenic temperatures of ITER, the double pancake was first cooled down to liquid nitrogen temperature, which is approximately -196 ˚C, and then, it was brought back to room temperature. Afterwards, the prototype went through a series of tests to check its response to High Voltage above 2KV in air, and was also tested in Paschen conditions, considered as the most demanding electrical conditions due to the fact that even a tiny insulation defect would cause failure. Last, but not least, the prototype went through a leak test. All hurdles were passed without any problems. It’s also worth highlighting the impressive dimensional tolerances achieved which indicated only a minute deformation of less than 1mm in the prototype, in spite the 900m long laser welding applied to the radial plate.
“This is an important technological step towards the manufacturing of one of the biggest and most complex superconducting coils ever produced. It is the result of the partnership established between F4E and ASG Superconductors, Iberdrola Ingeneria, Elytt Energy, CNIM and SIMIC” explains Alessandro Bonito-Oliva. The TF coils production series is moving at a galloping pace. 12 radial plates have already been produced by CNIM and SIMIC, 25 double pancakes have been wound, 15 of them have already been heat treated, of which 11 have been transferred inside a radial plate.