Mariano Pentella

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.

The Magnet Development (MagDev) laboratory at the Paul Scherrer Institute (PSI) has designed and successfully manufactured the first subscale stress-managed common coil magnet. The magnet was tested at CERN and reached 98% of its short sample current at 4.5 K. Following the high-field magnet roadmap of the Swiss Accelerator Research and Technology initiative (CHART), a new magnet was assembled after replacing two of the four Nb₃Sn coils and manufacturing and integrating four copper-based coils, which are part of the Energy Shift with Coupling (ESC) quench protection method. The ESC system uses normal-conducting auxiliary coils that are strongly magnetically coupled with the magnet’s Nb₃Sn coils for protection. When a quench is detected, a current is discharged through the auxiliary coils, leading to a rapid transfer of the magnet’s energy from the Nb₃Sn coils to the copper-based coils. This process results in transient losses and quick transition to the normal state of the Nb₃Sn conductor, which facilitates quick energy extraction. This work presents the manufacturing of the copper-based coils, magnet assembly, and test results of the subscale SMCC2.

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.

Canted Cosine Theta (CCT) magnet is an interesting design for compact accelerators or gantry systems for hadron-therapy. It offers great flexibility in generating complex field harmonics in straight and curved configurations while remaining compact. The Fusillo project based at CERN aims to design, build, and test a Nb-Ti curved CCT dipole demonstrator generating 3 T at 4.5 K in a large aperture of 236 mm, bent over 90$^{\circ }$ with a small bending radius of 1 m, and multi-harmonic field features to correct for the curvature. In this paper, we describe the fabrication process, the winding and the assembly of a Fusillo demonstrator that at present is being cold tested in liquid helium.

The FCC-ee booster dipoles are low-field iron-dominated cycled H-type magnets. They consist of an 11-meter-long laminated steel yoke with anodized aluminium busbars instead of coils. The magnet is required to operate at fields down to 6.5 mT for 20Ge V injection. At such low field levels parasitic effects become significant, for example, the Earth’s magnetic field, yoke hysteresis, and stray fields from cables. This poses a unique set of design challenges that are answered in this paper. The hysteretic effect is modelled, and the cross-section of the magnet is optimised to obtain the required field quality across the full cycle from 6.5 mT to 59 mT. The predictive power of the hysteresis model is validated by the test of a similar magnet from CERN stock. Finally, magnetic measurements from a short prototype magnet are reported. The test results confirm that the proposed magnet meets the design requirements, demonstrating the feasibility of dipoles for 20Ge V booster injection energy.

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 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.

GaToroid is a novel idea of a steady-state, toroidal magnet that directs multiple charged particle beams for hadron or electron therapy without rotating parts or magnet ramping. GaToroid has the potential of conformal radiotherapy with a configuration that can be simpler and lighter than conventional rotating gantries, also offering FLASH capability well beyond what is presently possible. A crucial feature of the magnet is the field profile, which is optimized to maximize acceptance (large field area) and beam transmission (good field homogeneity). We have built and tested a 1:3 scale Nb-Ti demonstrator of the proton GaToroid to verify performance, field profile and quench protection. Here we describe the specific features of the demonstrator cable, coil and magnet, and report the main test results. The magnet reached critical current with no training, the field profile is within 1% of the expected values, and quench detection and protection are well understood, thus proving that this magnet technology is ripe for a full-size system demonstration.

In the framework of the HL-LHC project, CERN has the responsibility to develop, qualify and assemble three different types of cold masses, namely Q2 (final focus quadrupole in the triplet), CP (corrector package) and D2 (separation dipole). In this paper, we describe the various designs, which incorporate several novel features. For example, for the cold masses containing an MQXFB quadrupole – based on a bladder-and-key structure with aluminium cylinders – we proposed and qualified a longitudinal welding process that takes into account the developed length of the loaded magnet (measured with a laser tracker), the geometry of the stainless steel half shells of the liquid helium vessel, and the welding shrinkage, so to match the requirements of mechanical uncoupling in the transversal plane, while introducing a sound fixed point in the longitudinal direction. In the case of the D2 cold mass, we introduced an orbital welded joint between two half units, with on one side the main recombination dipole, and on the other the dipole correctors, which comes with specific challenges for the relative alignment. Then, in the CP design we integrated a large number (nine) of high order correctors, together with a nested dipole corrector. We report as well on the special test cold mass developed to allow fast track cold testing of the MQXFB magnet in a standalone horizontal configuration, which was not in the initial baseline of the project. Besides detailing the various designs, the paper provides feedback from the manufacturing experience of the first units.