title: ac Modeling and impedance spectrum tests of the superconducting magnetic field coils for the Wendelstein 7-X fusion experiment.
abstract: The impedance spectrum test was employed for detection of short circuits within Wendelstein 7-X (W7-X) superconducting magnetic field coils. This test is based on measuring the complex impedance over several decades of frequency. The results are compared to predictions of appropriate electrical equivalent circuits of coils in different production states or during cold test. When the equivalent circuit is not too complicated the impedance can be represented by an analytic function. A more detailed analysis is performed with a network simulation code. The overall agreement of measured and calculated or simulated spectra is good. Two types of short circuits which appeared are presented and analyzed. The detection limit of the method is discussed. It is concluded that combined high-voltage ac and low-voltage impedance spectrum tests are ideal means to rule out short circuits in the W7-X coils.
authors.affiliation: Max-Planck-Institute for Plasma Physics, EURATOM-Association, Wendelsteinstrasse 1, D-17489 Greifswald, Germany. hartmut.edmler@hmi.de
authors.forename: Hartmut
authors.initials: H
authors.lastname: Ehmler
authors.forename: Matthias
authors.initials: M
authors.lastname: Köppen
mesh_terms: D003198:Computer Simulation; D004553:Electric Conductivity; D055590:Electromagnetic Phenomena / Q000295:instrumentation* / Q000379:methods; D004867:Equipment Design; D019544:Equipment Failure Analysis; D008962:Models, Theoretical; D009681:Nuclear Fusion; D015203:Reproducibility of Results; D012106:Research / Q000295:instrumentation*; D012107:Research Design; D012680:Sensitivity and Specificity; D013057:Spectrum Analysis / Q000379:methods*; D014159:Transducers