Quench Localization in the High Order Corrector Magnets using the Harmonic Field Method

INFN LASA, within the CERN-INFN research collaboration for the Hi-Luminosity LHC upgrade project, has been entrusted for the series production qualification of the High Order Corrector magnets. The magnets, designed with a superferric configuration, are tested at 4.2 K in a stacked layout to evaluate the training performance and to characterize the magnetic field. This paper presents an in-depth analysis of different quench events of the High Order Corrector magnets. In this analysis, the reconstruction of the quenched coil position has been performed by measuring the residual magnetic field after the magnet has been discharged. The method used for the quench localization considers the effects of the superconductor coil magnetization, which is canceled by the transition to the normal resistive state only in the quenched coil, on the residual magnetic field. Experimental results of real events during the magnet series tests are presented and analyzed. The model previously developed for the field quality calculation has been extended to consider different quenched coils in the same event. The results are here compared and discussed. From the comparison between the model and the experimental data, the position of the quenched coil/coils has been directly retrieved for all the magnet orders and cross-checked with the acquired voltages from the magnet. The simplicity of this method and its effectiveness make it a promising way to further improve the diagnostic system of the superconducting magnets with a superferric design similar to the High Order Corrector magnets.