Enabling impedance measurements of energised superconducting circuits through differential probing

Impedance measurements are essential for validating the electrical integrity of superconducting magnets. However, traditional measurements are conducted on de-energised circuits, restricting the ability to perform continuous validation. To enable measurements on energised systems, several challenges must be addressed. Key of which, the presence of the power converter alters the impedance of the system, and these effects need to be isolated to enable accurate impedance measurements. Additionally, the stimulus signal used for measurement must be designed to prevent degradation of the operational performance of any peripheral equipment, such as the power converter. In this study, a method utilising multiple voltage sources to inject differential stimuli is proposed, allowing the decoupling of impedances within the circuit's elements from the power converter. This approach enables the measurement of each segment's isolated impedance. The method is demonstrated on an energised superconducting quadrupole magnet and serves as a proof of principle. Further theoretical and practical validation is required to assess its performance under realistic operating conditions and its integration within a full installation.