Commissioning of the Wendelstein 7-X in Vessel Control Coils

Abstract

The magnet system of the stellarator fusion device Wendelstein 7-X (W7-X) is composed of three different groups of coil systems. The main magnetic field is created by a superconducting magnet system that is accompanied by two sets of normal conducting coil groups, the trim coils positioned outside of the cryostat and the control coils (CCs) inside the plasma vessel. The CC system consists of ten 3-D shaped coils, power supplies, cooling systems, high current feeds, and an autonomous remote control system. The coils are situated behind the baffle plates of the ten divertor units. The magnetic field created by the CC system allows for the correction of error fields to influence the islands at the plasma boundary and for the sweeping of the separatrix, e.g., the point of the largest power position across the divertor. At the end of 2015, the installation of the CC system was completed and the integral commissioning took place in parallel with the ongoing completion of W7-X. For the first time, the CCs and their power supply were operated in conjunction with all auxiliary systems like the power distribution system, the high current feeds, the interspace vacuum system, the cooling system, and the safety control system. This article describes the results obtained and experiences gained during the integral commissioning of the CC system, including the baking process in preparation for the first experimental campaign of W7-X.