Division of accelerators, cryogenics and magnetism

  The W7-X machine is a low-shear stellarator of the Wendelstein line being assembled in Greifswald, Germany. The magnet system of W7-X consists of 70 superconducting coils integrated with a central support structure and intercoil elements, busbars, current leads and power supplies. The magnets are sub-divided into 50 non-planar coils, which establish the basic magnetic confinement configuration, and 20 planar coils. They are manufactured with a superconducting NbTi cable co-extruded in an Aluminium jacket. After insulation and vacuum pressure impregnation, the windings are embedded in cast stainless steel casings, which are then finish-machined and equipped with cooling systems. All coils are tested in cryogenic conditions in a dedicated facility at CEA Saclay. This presentation will give an overview of the manufacture, testing and assembly of the W7-X magnets and highlight the main technical and project management challenges. The main lessons learned in the large scale production of superconducting cables, windings and structures will be presented. The critical items to be considered in the design, manufacture and testing of similar systems for future large fusion devices, such as ITER, will be highlighted.