The Wendelstein 7-X trim coil system commissioning and first operational results

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 Control Coils inside the plasma vessel and the Trim Coils (TC) positioned outside of the cryostat. The TC system consists of five coils, power supplies, cooling systems, high current connections and superordinated control systems for autonomous remote control. There are four coils (type A) of equal shape; the fifth coil (type B) has a slightly different shape due to space restrictions at the assembly position. Five individual power supply units whose design is based on four-quadrant current converters using Insulated-Gate-Bipolar-Transistors power the TC with individual currents and ramp rates. This allows the correction of error fields and also increases the experimental flexibility by providing a means to balance the divertor heat loads among the five field periods. The TC with its instrumentation and the power supplies including the switchgear to be connected to the coils have been designed and build in collaboration between IPP, Germany and PPPL, USA, funded by the Department of Energy. The design and integration of all auxiliary systems like the grid station, cooling for coils and powers supplies, control system and the associated cabling and piping has been developed, manufactured and accomplished in 2014. This paper describes the results obtained during the integral commissioning of the TC system, the operational experiences during the first experimental campaign of W7-X and its impact on the physics program. (C) 2017 The Authors. Published by Elsevier B.V.