Abstract This paper presents the cold test results of the Fusillo technology demonstrator, a Curved Canted Cosine Theta (CCCT) Nb–Ti dipole developed at CERN for compact particle accelerator or hadron-therapy applications. The magnet is designed to generate a 3 T central field at 288 A at 4.5 K in a 236 mm diameter aperture, with a bending angle of 90 ∘ and a bending radius of 1 m, and incorporates multi-harmonic field correction features to compensate for errors induced by the winding’s curvature. Following fabrication, winding, and assembly, the demonstrator was tested in liquid helium to validate its performance. In this paper, the training behaviour, the quench detection and protection, as well as the validation of the magnetic field quality and the effectiveness of the integrated harmonic corrections are discussed. The measured results show good agreement with design expectations, confirming the feasibility of the CCCT dipole with a large aperture and advanced field shaping, and supporting the applicability of the Fusillo magnet to compact particle accelerators or medical systems.

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.

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 MgB2 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 MgB2 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 MgB2 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 4m x 6m. 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(degrees) 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 inner triplet (or low-beta) 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.

The Fusillo project at CERN aims to design and build a demonstrator magnet with multi-harmonic corrected fields in a 90 degrees, curved, Canted-Cosine-Theta magnet. Two subscale magnets are built with 30 degrees 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.

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.

Due to its flexibility in generating advanced field harmonic corrections and potential for low cost compared to traditional designs, the Canted Cosine Theta (CCT) configuration is particularly interesting for compact particle accelerators and gantries for medical applications. This paper presents the design of a curved demonstrator named Fusillo, a Canted Cosine Theta Nb-Ti dipole magnet that is being developed at CERN, featuring a large aperture of 236 mm, a small bending radius of 1 m, a bending angle of 90 $^{\circ }$ , and multi-harmonic field correction, with a 3.61 T conductor peak field. We detail the magnetic coil design, incorporating high-order magnetic field correction of the errors produced by the heavily curved coil, peak field reduction at the coil ends, the development of a new rope type cable, and the mechanical design and the development of the former that supports the coil and provides the curved shape. We also present the first results of a subscale model used to qualify the coil's former manufacturing process, the rope cable, the coil winding optimization, and the coil impregnation system.

The electron cooler operating at the Antiproton Decelerator (AD) at CERN is at the end of its life cycle. The electron cooler, operated for over 40 years, has been used to decelerate anti-proton beams having an energy of about 5.3 MeV. A new electron cooler is being designed and expected to be commissioned during the Long Shutdown 3 (LS3) in 2026. The initial magnet system design consists of an array of pancake solenoid coils as well as an expansion solenoid. The mechanical alignment of the pancake coils must comply with challenging requirements, where the coils need to have 0.1 mrad angle positioning accuracy and B-z/B-r<5x10(-4) in terms of field quality. In this article, a new measurement method for the determination of a solenoid coil angle is presented, which allows for faster identification of the pancake-coil angles. The method was experimentally validated on an existing transducer, and the results were used for the design of a new measurement system capable of meeting the requirements.

Magnetic measurements of superconducting magnets at room temperature are performed for quality control and alignment, aiming to position the cold mass accurately, namely the assembly of one or more magnets in its cryo-vessel. The main challenge in performing these measurements is related to the sensitivity of the transducer, as the field values achievable in the magnet bore are in the 1 mT range. The single stretched-wire method is a proven technique for measuring DC-powered normal-conducting and superconducting accelerator magnets. It is vastly used to locate the magnetic axis in quadrupole magnets and higher-order magnets for their alignment and positioning in the accelerator. However, it fails to provide accurate measurements when used to measure superconducting magnets at room temperature because the typical magnet current levels are three orders of magnitude lower than the nominal level used in operation, leading to field values scaling by the same order of magnitude. The problem of the alignment of superconducting quadrupole magnets at room temperature has already been addressed in the literature by adopting alternating current (AC) magnet powering to enhance measurement sensitivity. This paper presents a comprehensive overview of the single stretched-wire method with AC magnet powering, showcasing the different performance compared with the DC powering technique. To further validate the method, a case study of a superconducting quadrupole magnet is presented, and the results are compared against those from a rotating coil scanner.

The Outer Tracker of the Compact Muon Solenoid (CMS), one of the large experiments at the CERN Large Hadron Collider, will consist of about 13,200 modules, each built up of two silicon sensors. The modules and support structures include thousands of parts that contribute to positioning and cooling the sensors during operation at −30 °C. These parts should be low mass while featuring high thermal conductivity, stiffness and strength. Their thermal expansion coefficient should match that of silicon to avoid deformations during cooling cycles. Due to their unique thermal and mechanical properties, aluminium-carbon fibre (Al/Cf) Metal Matrix Composites are the material of choice to produce such light and stable thermal management components for High Energy Physics detectors. For the CMS Outer Tracker, about 500,000 cm3 of Al/Cf raw material will be required to be produced through a reliable process to guarantee consistent properties throughout parts manufacturing. Two Al/Cf production routes are currently considered: liquid casting by gas-pressure infiltration and a powder metallurgy process based on continuous semi-liquid phase sintering. The dimensional stability of the resulting material is of paramount importance. Irreversible change of shape may be induced by moisture adsorption and the onset of galvanic corrosion at the discontinuous interfaces between Cf and Al. This paper presents the results of an extensive investigation through Computed Microtomography, direct microscopical investigations, analysis of the interfaces and metrology measurements aimed at comparing and interpreting the response to different environments of the respective products. The results obtained confirm the suitability of the two investigated Al/Cf MMCs for application to components of the CMS Outer Tracker, requiring tight geometrical control and microstructural stability over time. However, for PM parts sintered through the semi-liquid phase process, a multilayered protective noble metal coating is necessary the make them impervious to moisture, allowing dimensional stability to be guaranteed and the onset of corrosion phenomena to be avoided, while the product obtained by gas-pressure infiltration has shown less sensitive even to extreme temperature-humidity cycles and may be used uncoated.

We present results from exploratory studies, supported by the Physics Beyond Colliders (PBC) Study Group, of the suitability of a CERN site and its infrastructure for hosting a vertical atom interferometer (AI) with a baseline of about 100 m. We first review the scientific motivations for such an experiment to search for ultralight dark matter and measure gravitational waves, and then outline the general technical requirements for such an atom interferometer, using the AION-100 project as an example. We present a possible CERN site in the PX46 access shaft to the Large Hadron Collider (LHC), including the motivations for this choice and a description of its infrastructure. We then assess its compliance with the technical requirements of such an experiment and what upgrades may be needed. We analyse issues related to the proximity of the LHC machine and its ancillary hardware and present a preliminary safety analysis and the required mitigation measures and infrastructure modifications. In conclusion, we identify primary cost drivers and describe constraints on the experimental installation and operation schedules arising from LHC operation. We find no technical obstacles: the CERN site is a very promising location for an AI experiment with a vertical baseline of about 100 m.

Rotating-coil measurement systems are widely used to measure the multipolar fields of particle accelerator magnets. This paper presents a rotating-coil measurement system that aims at providing a complete data set for the characterization of quadrupole magnets with small bore diameters (26 mm). The PCB magnetometer design represents a challenging goal for this type of transducer. It is characterized by an aspect ratio 30% higher than the state of the art, imposed by the reduced dimension of the external radius of the rotating shaft and the necessity of covering the entire magnet effective length (500 mm or higher). The system design required a novel design for the mechanical asset, also considering the innovation represented by the commercial carbon fiber tube, housing the PCB magnetometer. Moreover, the measurement system is based primarily on standard and commercially available components, with simplified control and post-processing software applications. The system and its components are cross-calibrated using a stretched-wire system and another rotating-coil system. The measurement precision is established in a measurement campaign performed on a quadrupole magnet characterized by an inner bore diameter of 45 mm.

FASER, the ForwArd Search ExpeRiment, is designed to search for new, yet undiscovered, light and weakly-interacting particles and study the interactions of high-energy neutrinos. Three dipoles, one 1.5 m-long and the other two 1.0 m-long each, installed upstream of the ATLAS experiment at CERN, are required to achieve sufficient separation of pairs of oppositely charged, high-energy Standard Model particles originating from decays of new physics particles. The dipoles have an aperture of 200 mm in diameter and a required magnetic field at the centre ≥ 0.55 T. Due to tight space constraints, a design based on permanent magnet technology was proposed. This paper describes the design, manufacturing, assembly and magnetic measurement of these large Halbach array dipoles.

Sensing coils are inductive sensors commonly used to measure magnetic fields, such as those generated by electromagnets used in many kinds of industrial and scientific applications. Inductive sensors rely on integrating the output voltage at the coil's terminals in order to obtain flux linkage, which may suffer from the magnification of low-frequency noise resulting in a drifting integrated signal. This article presents a method for the cancellation of integrator drift. The method is based on a first-order linear Kalman filter combining the data from the coil and a second sensor. Two case studies are presented. In the first one, the second sensor is a Hall probe, which senses the magnetic field directly. In a second case study, the magnet's excitation current was used instead to provide a first-order approximation of the field. Experimental tests show that both approaches can reduce the measured field drift by three orders of magnitude. The Hall probe option guarantees, in addition, one order of magnitude better absolute accuracy than by using the excitation current.

The luminosity of a particle collider is an extremely crucial performance parameter describing its capability of producing interactions in the collision point. However, imperfections in a collider can lead to luminosity loss. Among different imperfections, an important one is stray magnetic fields. For the Compact Linear Collider (CLIC), a collider being considered as one of the main options in Europe after the Large Hadron Collider, simulations showed an unprecedented sensitivity of the machine to fields on the order of 0.1 nT. Hence, such tight constraints require special design considerations to prevent performance loss. Different shielding techniques are available in the literature, typically relying on an active shielding strategy and capable of reducing the magnetic field amplitudes down to the nano-Tesla level. However, measuring fields with such amplitudes is challenging by using state-of-the-art commercially available sensors and therefore, a passive shielding strategy, consisting in enveloping sections of the beamline with a magnetic shield, is a more attractive option. For CLIC, Mumetal (R), a Ni-Fe alloy with advertised relative permeability above 100,000, was chosen. In this paper, the DC and AC magnetic characterization of two samples of Mumetal (R), one annealed in its final form and the other one non-annealed is presented, showcasing how the annealing results in a boost of the magnetic permeability of more than order of magnitude. As a case study, the shielding performance of a 1-mm thin layer of Mumetal (R) enveloping CLIC's beamline is estimated.

Accelerators magnets must have minimal magnetic field imperfections for reducing particle-beam instabilities. In the case of coils made of high-temperature superconducting (HTS) tapes, the field imperfections from persistent currents need to be carefully evaluated. In this paper we study the use of superconducting screens based on HTS tapes for reducing the magnetic field imperfections in accelerator magnets. The screens exploit the magnetization by persistent currents to cancel out the magnetic field error. The screens are aligned with the main field components, such that only the undesired field components are compensated. The screens are passive, self-regulating, and do not require any external source of energy. Measurements in liquid nitrogen at 77 Kelvin show for dipole-field configurations a significant reduction of the magnetic-field error up to a factor of four. The residual error is explained via numerical simulations, accounting for the geometrical imperfections in the HTS screens, thus achieving satisfactory agreement with experimental results. Simulations show that if screens are increased in width and thickness, and operated at 4.5 Kelvin, field errors may be eliminated almost entirely for the typical excitation cycles of accelerator magnets.

In this article, a static-sample magnetometer is presented to measure the relative permeability of weakly magnetic materials. The method consists of scanning the magnetic field inside a dipole magnet by using an NMR teslameter to measure the perturbation of a test specimen on the externally applied field. Then, an inverse problem is used to compute the specimen's relative permeability. As a case study, the measurement of three different materials with different shapes and dimensions is carried out. The method was validated by measuring the same material by vibrating sample magnetometry as proposed by the standard ASTM A342/A342M-14. The expanded measurement uncertainty of the relative permeability, evaluated by Monte Carlo simulations, is about 10(-4) for all the cases, with a level of confidence of 95%.

At the European Organization for the Nuclear Research (CERN), several efforts were combined for a preliminary design of a new accelerator, the Future Circular Collider (FCC), a 100-TeV double-ring hadron collider to be installed in a 100-km tunnel. As potential intermediate step, a high-luminosity lepton collider called FCC-ee is foreseen with more than 9,000 magnets. This paper provides an insight into the magnetic properties of the steels, potentially considered for the new dipole magnets, with nominal field of only 56 mT. The influence of the properties of these steels on the magnet transfer function has been assessed analytically using an equivalent reluctance network to model the first 1-m long dipole prototypes. The analytical results were validated experimentally. The proposed approach can be a useful tool for traceability and quality control during the series production.