Design and Prototype of the High Voltage In-Service-Tests on the Superconducting Magnet System of Wendelstein 7-X
The stresses induced during the energizing and de-energizing process of the Wendelstein 7-X super conducting magnet system could cause cracks in the embedding of the winding packages and consequently a ground fault that would not be detected during normal operation as the operating voltage of the magnet is system is too low. With a ground fault present during a fast discharge, the middle point grounding needed to half the voltage could be rendered useless and one coil group could be stressed with the full voltage of up to 4 kV which would endanger the high voltage integrity of the whole superconducting magnet system. To prevent such undesirable occasions, the insulation of the superconducting magnet system shall be monitored by a high voltage In-Service-Test. With the In-Service-Test, a voltage of 2.5 kV can be applied during the operation of the magnets especially after significant changes in the coil current. The measured leak current can then be used to determine any changes in the quality of the insulation. In a first step, the feasibility of such a system has been evaluated with a simulation model of one coil group with Simplorer. The next step was to find a design which can be implemented in the given magnet power supply system and to build and test a prototype for final confirmation of the concept.
First Operational Phase of the Superconducting Magnet System of Wendelstein 7-X
Abstract The Wendelstein 7-X stellarator (W7-X), one of the largest stellarator fusion experiments, has accomplished successfully the first operational phase at the Max Planck Institute for Plasma Physics in Greifswald, Germany. To confine 30 m 3 plasma the W7-X machine has a superconducting magnet system with 50 non-planar and 20 planar coils. The magnet commissioning was successfully performed until mid of 2015 with tests of the complete magnet system functionality required for plasma operation, at a magnetic field of 2.5 T. The first operational phase started mid of December 2015 with He plasmas heated by the ECRH (Electron Cyclotron Resonance Heating) system followed by H 2 plasmas in February 2016. The magnet system operation was accompanied by an online monitoring of the mechanical sensors installed on the superconducting coils and their support structure to detect any deviations from the predicted behavior.
Strategy of Structural Analysis of W7-X Magnet System
The Wendelstein 7-X (W7-X) stellarator project goal is to demonstrate that the stellarator is a viable option for a fusion power-plant. The W7-X is in advanced construction phase and has entered the assembly phase in Greifswald, Germany. The W7-X "pentagonal" basic magnet system is highly sensitive to the parameter variations; therefore the strategy of the structural analysis with the ultimate goal to create a tree of numerical models, which has to reliably predict stellarator structural behaviour, is in development and implementation phases. This paper gives an overview of the strategy and focuses on challenging boundary conditions and the most interesting results of the analyses