Impedance-frequency characterization of a HL-LHC Nb3Sn MQXFS model magnet during full power operation at nominal current

Impedance measurements have long been used to study superconducting magnets in their non-energized state, providing valuable insights into their electromagnetic behaviour. However, studies involving powering have primarily been conducted at low currents, due to initial safety constraints. This paper presents a comprehensive set of impedance measurements on the powered MQXFS superconducting magnet, marking the first time such measurements have been performed at its nominal operating current of 16 kA.<br/>The magnet was characterized using two distinct measurement configurations: high-frequency (1 kHz-40 kHz) and low-frequency (10 Hz-1 kHz). Measurements were conducted across all powering phases (ramp-up, steady state, and ramp-down) at two cryogenic temperatures, 1.9 K and 4.5 K. Clear impedance variations as a function of current were observed at 1.9K, with the most notable result being an impedance shift towards the impedance measured at 4.5 K while approaching the nominal operating current.<br/>These findings represent a significant step in developing impedance-based diagnostics for superconducting magnets, demonstrating their potential for characterizing magnet behaviour under operating conditions.