Wendelstein 7-X–Commissioning of the Superconducting Magnet System

The Wendelstein 7-X stellarator (W7-X), one of the largest stellarator fusion experiments, is presently being taken into operation at the Max Planck Institute for Plasma Physics in Greifswald. The main objective of the experiment is to prove the reactor relevance of the optimized stellarator concept. The W7-X experiment has a superconducting magnet system with 50 nonplanar and 20 planar coils grouped in five equal modules, which are electrically connected in 7 circuits with 10 coils of each type. The connections between the coils are made by superconducting the bus bars using the same NbTi Cable-in-Conduit Conductor as used for the superconducting coils. Particularly developed high-temperature superconducting current leads feed the current into the cryostat by bridging the temperature gradient from room temperature down to the 4-K level. Seven power supplies provide individual currents in the seven circuits. The quench detection system permanently checks the superconducting system regarding the occurrence of a quench. In case of a quench, the magnet safety system has to be activated, and a set of switches lead the current into the dump resistors. The commissioning of the magnet system was successfully performed until July 2015 with tests of the complete magnet system functionality needed for plasma operation at a magnetic field of 2.5 T.