Purpose and design of trim coils for the Wendelstein 7-X stellarator experiment

The stellarator fusion experiment Wendelstein 7-X (W7-X) is currently under construction at the Max-Planck-Institut für Plasmaphysik in Greifswald, Germany. The main magnetic field will be provided by a superconducting magnet system which generates a fivefold toroidal periodic magnetic field. However, not avoidable tolerances can result in small deviations of the magnetic field disturbing the toroidal periodicity. In order to have a tool to influence this field errors additional five normal conducting trim coils were designed to allow a fine tuning of the main magnetic field during plasma operation. The detailed design of the coils and the manufacturing will run within a collaboration program between the Princeton Plasma Physics Laboratory, Oak Ridge National Laboratory, Los Alamos National Laboratory and the Wendelstein 7-X project funded by the U.S. Department of Energy.