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.

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.

An induction-coil magnetometer has been produced at CERN to determine the location of an incipient quench in the HL-LHC Nb3Sn inner-triplet quadrupoles. The instrument, known as a quench-antenna, allows the measurement of the position and propagation of quenches with a reduced number of acquisition channels. This is possible because four layers of nested coils are designed to be sensitive only to the normal and skew sextupole and octupole components. Moreover, the magnetometer allows the study of fast magnetic transients due to flux jumps observed during the ramping of Nb3Sn superconducting accelerator magnets. This paper presents the observation and characterization of flux jumps during powering ramps similar to machine operations. Spatial and temporal distributions of flux jumps are derived from the induced voltages in the quenchantenna as a function of the transport current. Modeling flux jumps as traveling magnetic moments allows the reconstruction of the effect in terms of position and magnitude and, thus, an estimation of the impact on the magnetic field quality.

With the assembly and test results of four Nb3Sn short-model quadrupoles (MQXFS) for the High Luminosity Upgrade of the CERN Large Hadron Collider (LHC), an optimum pre-load level was established for the construction of the full-length, series magnets. Successive MQXFS magnets were used as testbeds for potential changes (including pre-load fine tuning) to be implemented in the series, and to better understand the stress dependence of Nb3Sn magnet performance. In this paper we report the findings of the short model MQXFS7, where we investigated the effect of higher azimuthal pre-load on the performance of this magnet assembled with coils wound from Nb3Sn Restacked-Rod-Process (RRP) conductors, which are the baseline for MQXF magnets, and Powder-In-Tube (PIT) conductors, which were initially considered as a potential candidate but subsequently set aside. Starting at the baseline level of 110 MPa azimuthal preload at 1.9 K (corresponding to a full preload at nominal current, which is 77% of the short sample limit at 1.9 K), we increased the pre-load in steps of 20 MPa up to 190 MPa. The magnet was able to operate above 90% of the short sample limit indicating a large range of possible preloads. Indications of performance degradation at 90-95% of the short sample limit were found in the PIT conductor at 170 and 190 MPa. The test included a significant set of observables, such as the ramp rate dependency on the quench current, and V-I measurements to see growing resistance in segments of the coil.

A quench protection study was performed on the Fusillo Demonstrator Curved Canted Cosine Theta (CCCT) dipole magnet developed at CERN. This magnet features an aperture of 236 mm and a bending radius and angle of 1 m and 90 degrees, respectively. It has an inductance of 9.14 H, a peak winding field of 3.6 T and multi-harmonic aperture field correction. Ten turns of a rope cable made of Nb-Ti strands are placed in each channel of aluminium formers, which are surrounded by an aluminium shell. The aluminium structures not only support mechanical forces but also affect the quench behavior of the magnet. A discharge of the stored energy over an external resistor results in significant eddy current heating of the aluminium structures, which quickly brings a large part of the superconducting winding to the resistive state. A three-dimensional (3D) simulation of the eddy currents and heat propagation in the formers with heat propagation in the magnet windings was performed. It uses a cooperative simulation approach involving two software tools developed at CERN as part of the STEAM framework: a finite-element-based tool called FiQuS and a finite-difference-based tool called LEDET. FiQuS calculates the eddy currents and the temperature distribution of the formers, whereas LEDET calculates the current, voltage, and temperature of the windings. This approach enables a 3D quench simulation with great geometrical detail while maintaining reasonable computational cost. Energy extraction with a fixed resistor is studied, and key parameters of the discharge are calculated. The voltage of the magnet remains below the target specification of 1.5 kV, and the adiabatic hot spot temperature of the windings reaches 185 K. It is shown that the magnet differential inductance and winding resistance dominate the protection transient. The simulations provide great insights into the transient behaviour of the magnet, including the metal structures' temperature and the eddy currents' temporal and spatial distribution.

The 5.2-m-long, 11 T double-aperture Nb3Sn Dipole Magnet was designed to replace some of the standard, 15-m-long 8.3 T Nb–Ti main dipole magnets in the Large Hadron Collider. After the production and test of several of 2-m-long models, the test of full-length 11 T series magnets revealed signs of performance degradation in the coil ends after a sequence of electromagnetic and thermal cycles. The possible sources for performance degradation were categorized into two groups: issues internal to the coils and issues with the coil support structure, in particular in the magnet ends. To address the constraints external to the coil, two mitigation measures were proposed: (1) reducing peak stresses in the coil ends and (2) improving the coil end support and axial loading. To validate the mitigation measures, a double-aperture model magnet, MBHDP301, was designed, manufactured, and power tested. The magnet was manufactured with four available coils, three of which had been assembled and tested in previous magnets. Two new features were implemented in both apertures to reduce the peak stresses in the coil ends (mitigation measure 1). The first involved a change in material of the removable pole from titanium to austenitic stainless steel, while the second introduced a gradual reduction of prestress applied in the ends of the coil straight section. For one of the two apertures, in addition, an end cage system was installed to improve coil end support and axial loading (mitigation measure 2). The two apertures in the magnet can be independently powered, facilitating comparison studies. This paper describes the manufacturing, mechanical measurements analysis and cold powering test campaign results of the MBHDP301 model magnet. The lessons learned from this work can be useful and directly applicable to future cosθ high field dipole magnets.

A promising way to realize controlled nuclear fusion involves the use of magnetic fields to control and confine the hot plasma configuration. This approach requires superconductor magnets operating above 15 T for the next generation of fusion devices. Due to their high in-field transport current capacity, rare-Earth barium copper oxide (REBCO) coated conductors are promising materials for manufacturing of cable-in-conduit conductors (CICCs) for fusion. However, the high-aspect-ratio geometry makes it difficult to find a multi-tape CICC configuration that fulfills the high engineering current density requirements while retaining enough flexibility for winding large-scale magnets. Moreover, the multilayer structure and inherent brittleness make the REBCO tapes susceptible to degradation during CICC manufacturing and operation. For more than a decade, the development of a reliable REBCO-based CICC that can sustain the huge combined mechanical, thermal, and Lorentz loads without degradation has been ongoing, albeit with limited progress. In this paper, we report on a prototype REBCO CICC that can withstand an applied cyclic Lorentz load of at least 830 kN m-1, corresponding to a transport current of 80 kA at 10.85 T and 4.5 K. To our knowledge, this is the highest load achieved to date. The CICC uses 288 tapes wound into six strengthened sub-cables, making it capable of having a current sharing temperature, Tcs, of around 39 and 20 K when operated under 10.85 T with a current of 40 and 80 kA, respectively. Scaled to a 20-T peak field and 46.5-kA transport current, this provides a temperature margin of over 10 K with respect to an operating temperature of 4.5 K. In addition, no perceptible transport current performance degradation was observed after cyclic Lorentz loading, cyclic warm-up/cool-down (WUCD), and quench campaigns. The proposed REBCO CICC is a milestone in the development of high-temperature superconductors for large-scale and high-field magnet applications. (c) 2025 THE AUTHORS. Published by Elsevier LTD on behalf of Chinese Academy of Engineering and Higher Education Press Limited Company. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

The superconducting system of the High Luminosity LHC project (HL LHC) at CERN comprises a total of 38 new cold masses, prototypes and spares included, all requiring cryostats for magnet operation at 1.9 K. These cryostats shall ensure optimal thermal performance, as well as magnet alignment stability over the machine lifetime. Specific cold mass dimensions and a multitude of interfaces related to cryogenics, power supply and instrumentation resulted in 19 cryostat assembly types. Having so many design variants relative to the number of units to be built is a challenge in terms of cost, resources, and schedule management. Our answer was the development of a modular concept maximising component sharing between cryostat types, which also allows for a common assembly infrastructure. To date, manufacturing of cryostat components is nearly finished, and a pre-series comprising the first cryostat assemblies for each cold mass type has been built up to the stage of readiness for cold testing. This paper presents our experience and lessons learnt from component manufacturing and first assemblies, how we set up an assembly hall with purpose-built tooling, and insights on logistics and resources. We also explain our plans to ensure timely delivery of the cryostat assemblies, without compromises to the high reliability level expected for equipment that will become part of the 27 km long particle collider.

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 future of particle accelerators is strongly linked to the development of high-field magnets. The European Organization for Nuclear Research (CERN) is currently developing Nb3Sn-based magnets for the high-luminosity upgrade of the large hadron collider (HL-LHC), to fully exploit its potential and surpass the intrinsic performance limitations of Nb-Ti-based magnets. The fabrication of Nb3Sn magnets is a challenging process as it requires managing the brittle and strain sensitive conductor after the reaction heat treatment to generate the superconducting phase. Accelerator magnet coils are usually manufactured following the wind-react-and-impregnate fabrication process. This reduces the difficulty of working with brittle compounds but adds uncertainties associated with volume change during phase transition and thermal expansion/contraction differentials during the temperature ramps of the heat treatment and cooldown to cryogenic temperatures. To investigate the root causes of performance limitation or degradation observed on HL-LHC magnet prototypes, several Nb3Sn-based coils have been examined. The present paper illustrates an innovative methodology of investigations of the root causes at several fabrication stages and after cooldown and powering. The approach is based on a sequence of mesoscale observations of whole coil sections by an innovative high-energy linac x-ray computed tomography, followed by materialographic assessment of internal events, geometrical distortions and potential flaws using light microscopy. Additionally, scanning electron microscopy and focused ion beam were used to analyze damage at localized positions. This comprehensive approach provides an in-depth view of the examined coils by characterizing atypical features and imperfections in both the strands and the glass fiber/resin of the insulation system, univocally associating the limiting quenches experienced by the coils to identified physical events.

Advanced Series on Directions in High Energy PhysicsThe High Luminosity Large Hadron Collider, pp. 371-389 (2024) Open AccessChapter 16: 11T Dipole and New Connection Cryostats for CollimatorsBernardo Bordini, Luca Bottura, Arnaud Devred, Lucio Fiscarelli, Mikko Karppinen, Gijs de Rijk, Lucio Rossi, Frédéric Savary, Daniel Schörling, and Gerard WilleringBernardo BordiniCERN, Geneva 23, CH-1211, Switzerland, Luca BotturaCERN, Geneva 23, CH-1211, Switzerland, Arnaud DevredCERN, Geneva 23, CH-1211, Switzerland, Lucio FiscarelliCERN, Geneva 23, CH-1211, Switzerland, Mikko KarppinenCERN, Geneva 23, CH-1211, Switzerland, Gijs de RijkCERN, Geneva 23, CH-1211, Switzerland, Lucio RossiCERN, Geneva 23, CH-1211, Switzerland, Frédéric SavaryCERN, Geneva 23, CH-1211, Switzerland, Daniel SchörlingCERN, Geneva 23, CH-1211, Switzerland, and Gerard WilleringCERN, Geneva 23, CH-1211, Switzerlandhttps://doi.org/10.1142/9789811278952_0016Cited by:0 (Source: Crossref) PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail Abstract: This chapter describes the design of, and parameters for, the 11 T dipole [11] developed at FNAL and the European Organization for Nuclear Research (CERN) for the High Luminosity Large Hadron Collider (HL-LHC) project. FiguresReferencesRelatedDetails Recommended The High Luminosity Large Hadron ColliderMetrics History Information© Oliver S Brüning and Lucio RossiThis is an open access article published by World Scientific Publishing Company. It is distributed under the terms of the Creative Commons Attribution 4.0 (CC BY) License.PDF download

In order to meet the target operating parameters of the toroidal field coils (TFCs) for the next-generation Chinese compact burning plasma tokamak, high critical current density (J(c)) Nb3Sn strand will be applied to the high-field winding-package of the TFC. To improve the transverse stiffness of the cable in withstanding the huge Lorentz force and avoiding conductor performance degradation, the short-twist-pitch and copper-wound-strand cable patterns were taken into consideration. In the processes of cabling and compaction of the conductor, the tight cable configurations lead to severe local plastic deformation (LPD) within the strands. The strands in the conductor are subjected to strain caused by thermal contraction and Lorentz force during conductor cooling down and operation. So far it is unknown, whether the LPD could impact the critical current (I-c) versus uniaxial applied strain behavior of high-J(c) Nb3Sn strand. Aiming to investigate the effect of LPD on the I-c of strands under uniaxial strain, three types of high J(c) Nb3Sn strand with different indentation depths were tested on a U-shaped bending spring. The axial strain ranges from -0.9% to +0.4% at 14 T and 4.2 K. The three types of strands showed more strain sensitivity and lower tensile irreversible strain limit with increasing LPD, while even irreversible degradation of the I-c could be observed in the compressive strain region. The sample preparation, test process, test results and analysis are reported.

The cold powering test of the first two MQXFB prototype quadrupoles, the Nb 3 Sn inner triplet magnets to be installed in the HL-LHC, has found performance limitations. This prompted putting on hold the coil fabrication, to review in depth the full manufacturing process, while in parallel performing destructive inspections on selected coils. In particular, the post-mortem analysis of the limiting coil in MQXFBP1 identified a recurrent defect on top of the inner layer pole turn in the 2D cross-section, in correspondence to the titanium pole-to-pole transitions in the longitudinal direction. The next two magnets, MQXFBP3 and MQXFB02, reached the required performance for operation in the machine at 1.9 K. However, they still showed a limitation at 4.5 K, with a phenomenology similar to the one observed on MQXFBP1 and MQXFBP2. The review of the coil manufacturing process pointed to some improvement axes, which are being treated in a systematic manner. With the aim of addressing the potential root causes, the coil production gradually restarted, with transition coils, where additional measurements were carried out and selected changes in the procedure implemented. This article presents the challenges of fabricating 7.2-m-long accelerator quality Nb 3 Sn coils, together with the solutions specifically adopted for MQXFB, which could be instrumental also for future projects.

The design and production of Nb3Sn-based dipole and quadrupole magnets is critical for the realization of the High-Luminosity Large Hadron Collider (HL-LHC) at the European Organization for Nuclear Research (CERN). Nb3Sn superconducting coils are aimed at enhancing the bending and focusing strengths of accelerator magnets for HL-LHC and beyond. Due to the brittle nature of Nb3Sn, the coil fabrication steps are very challenging and require very careful QA/QC. Flaws in the Nb3Sn filaments may lead to quenches, and eventually, performance limitation below nominal during magnet testing. A novel inspection method, including advanced non-destructive and destructive techniques, was developed to explore the root-causes of quenches occurring in performance-limiting coils. The most relevant results obtained for MQXF coils through this innovative inspection method are presented. This approach allows for precise assessment of the physical events associated with the quenches experienced by magnet coils, mainly occurring in the form of damaged strands with transversely broken sub-elements. Coil-slice preparation, micro-optical observations of transverse and longitudinal cross-sections, and a deep etching technique of copper will be illustrated in the present work, with a focus on the results achieved for a CERN coil from a non-conforming quadrupole magnet prototype, and two coils fabricated in the US, in the framework of the Accelerator Upgrade Project (AUP) collaboration, from two different non-conforming quadrupole magnets, respectively. The results obtained through the proposed inspection method will be illustrated.

The use of pressurized bladders for stress control of superconducting magnets was firstly proposed at Lawrence Berkeley National Laboratory in the early 2000s. Since then, the so-called ‘bladders and keys’ procedure has become one of the reference techniques for the assembly of high-field accelerator magnets and demonstrators. Exploiting the advantages of this method is today of critical importance for Nb 3 Sn-based accelerator magnets, whose production requires the preservation of tight stress targets in the superconducting coils to limit the effects of the strain sensitivity and brittleness of the conductor. The present manuscript reports on the results of an experimental campaign focused on the optimization of the ‘bladders and keys’ assembly process in the MQXFB quadrupoles. These 7.2 m long magnets shall be among the first Nb 3 Sn cryomagnets to be installed in a particle accelerator as a part of the High Luminosity upgrade of the LHC. One of the main practical implications of the bladders technique, especially important when applied to long magnets like MQXFB, is that to insert the loading keys, the opening of a certain clearance in the support structure is required. The procedure used so far for MQXF magnets involved an overstress in the coils during bladder inflation. The work presented here shows that such an overshoot can be eliminated thanks to additional bladders properly positioned in the structure. This optimized method was validated in a short model magnet and in a full-length mechanical model, becoming the new baseline for the series production at CERN Furthermore, the results are supported by numerical predictions using finite element models.