Evaluating the Electro-Magnetic Effects of Electrical Short-Circuits in a Nb-Ti Accelerator Magnet

Abstract

Electrical short-circuits in the coil winding pack of a superconducting magnet can severely impact the magnet's performance and safety during operation. Hence, finding ways to detect and assess these non-conformities is essential. Measurements of the complex impedance as a function of the frequency are a promising method to investigate such non-conformities more closely. The complex impedance of one HL-LHC recombination dipole magnet was recently measured at the CERN magnet test facility. Moreover, to mimic an inter-turn short in the coils, resistances at warm were connected externally to the voltage taps and the complex impedance of the magnet was measured. The acquired measurements are used to validate a developed lumped-element network model, reproducing the electromagnetic behaviour of the HL-LHC recombination dipole magnet in the frequency domain. The simulation results are compared to the measurements without artificial short circuits and are in good agreement up to a frequency of 10 kHz. The simulated effects of short circuits across a few turns in the frequency domain are compared to the measurements performed on the magnet. Since good agreement between measurements and simulations was obtained, these models can be used to predict the electromagnetic effects of any inter-turn short in the HL-LHC recombination dipole magnet or similar types of accelerator magnets.