Franco Mangiarotti

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 the impact of the power converter impedance on the measurement. This paper presents a comprehensive set of impedance measurements on the powered MQXFS7 superconducting magnet, marking the first time such measurements have been performed up to its nominal operating current of I=16.23kA. The magnet's impedance was characterized using two distinct measurement configurations: low-frequency (f=10Hz-1KHz) and high-frequency (f=1kHz-45KHz). Measurements were conducted across all powering phases (ramp-up, steady state, and ramp-down) at two cryogenic temperatures T=1.9K and 4.5K. Impedance variations as a function of current were observed at T=1.9K, with the most notable result being an impedance shift towards the impedance measured at T=4.5K as the nominal operating current was approached. We hypothesize that this may be due to the presence of superconducting (Ti–6Al–4V) magnet poles. Being able to measure the impedance of superconducting magnets in a powered state represent a significant improvement in the understanding of impedance-based diagnostics for superconducting magnets, demonstrating their potential for characterizing magnet behaviour under operating conditions.

During the Long Shutdown 3 of the LHC, scheduled to start in 2026, the interaction regions will be upgraded to increase the integrated luminosity by about one order of magnitude. Among the components to be replaced are the MBRD (Main Bending Recombination Dipole, also known as D2), which are double-aperture magnets providing aligned magnetic fields to steer the two beams into the ATLAS and CMS experiments and subsequently recombine them onto their nominal trajectories. To meet the demanding requirements of the High-Luminosity LHC, a new magnet design was developed by INFN-Genova, featuring a larger aperture, a higher operating field, and innovative solutions to mitigate the strong electromagnetic cross-talk between the apertures while ensuring mechanical integrity against the large repulsive Lorentz forces. The development program included the construction of a 1.6-m model, a full-length prototype, and six series magnets, of which four will be installed in the LHC and two kept as spares. Series production is ongoing at ASG Superconductors, and the first magnet has been successfully cold-tested at CERN. This contribution reports on the main challenges faced during series production and discusses the first test results.

One of the goals of the High Field Magnet (HFM) Program at CERN is to explore High-Temperature Superconducting (HTS) magnet technology for accelerator applications that go beyond the limits of low-temperature superconductors such as Nb₃Sn. This offers a pathway for the development of higher energy and more sustainable particle accelerators operating at temperatures above 1.9 K or even 4.5 K. As a stepping-stone to achieve these goals, CERN has launched the development of model coils in racetrack geometry that can be scaled up for use in common coil-type magnets. The model coils were used to validate winding tooling, a newly developed cable insulation application method, instrumentation placement, conductor performance, and other key design choices with a short iteration cycle that allows for rapid development. We detail the coil electromagnetic design, and several lessons learned during the progression from single-layer to double-layer coils with an internal layer jump that allows for a modular magnet design approach. Additionally, the results from liquid nitrogen tests and preliminary findings from liquid helium testing are discussed.

The SHiP experiment, to be located at CERN in the ECN3 North Area cavern, aims at detecting feebly interacting particles, potentially shedding light on neutrino mass and dark matter. A key component of the detector is the Hidden Sector Spectrometer, potentially the first large-scale, energy-efficient experimental magnet relying on superconducting MgB$_{2}$ cables. This technology, initially developed for the High Luminosity upgrade of the Large Hadron Collider (HL-LHC) at CERN, has been adapted for electromagnets, cooled by gaseous helium (GHe) at about 20 K. We present the current status of the proof-of-principle demonstrator, which features a coil from MgB$_{2}$ cable wound onto an aluminum former and mounted inside a low-carbon steel yoke. The demonstrator has been successfully tested in GHe at 20 K. In the next development, the demonstrator will be upgraded to test indirect cooling of the MgB$_{2}$ cables, while the yoke will remain at ambient temperature. This work represents a validation step toward the design of the spectrometer magnet for SHiP, with a focus on achieving good homogeneity at a magnetic integrated field of 0.65 T.m over a large aperture of 4 m × 6 m. The conceptual design of the magnet is outlined, along with the production challenges.

At the heart of the High-Luminosity Project (HL-LHC) to upgrade the CERN Large Hadron Collider (LHC), new Nb$_{\text{3}}$Sn superconducting quadrupole magnets will be installed on each side of the ATLAS and CMS experiments. Half of these magnets are built by CERN and are called MQXFB. A total of 12 MQXFB magnets are being constructed for installation: two to be installed in the Inner Triplet (IT) String facility, for systems qualification; four to be installed in the LHC near ATLAS; four to be installed in the LHC near CMS, and two spare magnets. In the last two years, the first seven MQXFB magnets have been tested and qualified up to nominal current in nominal operating conditions. In this paper we present the tests and analyze the magnets’ performance, with emphasis on qualification, non-conformity detection, and reliability evaluation.

The Fusillo project at CERN aims to design and build a demonstrator magnet with multi-harmonic corrected fields in a 90°, curved, Canted-Cosine-Theta magnet. Two subscale magnets are built with 30° bending, about 1/30 of the demonstrator conductor length, and increased current to reach coil stresses equivalent to those of the demonstrator. These magnets enable qualification of the technology developments, fabrication methods, winding and assembly procedures, magnetic and quench protection design and measurement setups. The second Fusillo subscale magnet had dedicated instrumentation, including temperature sensors, a heater on the aluminium formers, and a set of sensing coils positioned in the curved bore. The magnet voltage and current were also measured. A specific powering sequence was applied to the magnet, including forced energy extractions. The eddy currents and heat propagation in the formers and the windings are simulated in three dimensions. A cooperative simulation approach was used, which involves tools developed at CERN as part of the STEAM framework: FiQuS, a finite element-based tool, and LEDET, a finite difference-based tool. The measurement results are compared with simulations, and the key aspects of the magnet transient behaviour are discussed. The simulation model inputs are refined using the measurement results, and the methodology for doing this is presented.

The magnet development (MagDev) laboratory at the Paul Scherrer Institute (PSI) has designed the subscale stress-managed common-coils (subSMCC1) 2-in-1 dipole magnet as part of the CHART (Swiss Accelerator Research and Technology) contribution to the CERN HFM (High-Field Magnet) programme. This R&D vehicle is part of the CHART/MagDev high-field roadmap. The nature of the subscale magnet allows it to be manufactured and tested quickly, so lessons learned from it will be applied to the high-field stress-managed common-coils demonstrator that is currently under development. The magnet has a straight section of 150 mm, two clear bore apertures of 22 mm, and an inter-beam spacing of 120 mm. In the first version, the magnet structure consists mainly of inner and outer pads surrounding the straight sections of the coil, and inner and outer pads at the coil ends, with no iron yoke or shell. Axial pre-load is provided by six rods connected to the end pads. All structural components, including the split-former pieces, are made from the same stainless-steel alloy. The first magnet, with four stress-managed Nb₃Sn common-coils, was manufactured and tested. This contribution presents the detailed manufacturing process as well as test results, training behavior and mechanical measurements.

The inner triplet (or low-β) quadrupole magnets are among the components to be upgraded in LHC interaction regions for the HL-LHC project. The new quadrupole magnets, called MQXF, are based on Nb₃Sn superconducting magnet technology, with a conductor peak field of 11.3 T. CERN is in charge of the fabrication of the MQXFB variant, the longest Nb₃Sn accelerator magnets designed and manufactured up to now, with a magnetic length of 7.2 m. Two magnets, MQXFBP3 and MQXFB02, reached the HL-LHC project requirements. However, they still exhibited a limitation at 4.5 K with a phenomenology similar to the one observed on the first two prototypes. After improvements on the cold mass (longitudinal welding) and magnet assembly (elimination of overstress on the conductor during loading) procedures, a series of modifications were implemented in MQXFB03 at the level of the coil fabrication to address and/or reduce weaknesses in the coils. The magnet was tested and was the first to achieve performance requirements at both 1.9 K and 4.5 K, with no signs of conductor limitation at 4.5 K. MQXFB is now in the series production phase, with around 2/3 of the coils completed and half of the magnets assembled. We provide in this paper an overview of the MQXFB program, with a summary of the main recent achievements and an overall status of the fabrication.