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In the framework of the HL-LHC project, the present LHC low-β superconducting quadrupoles will be substituted with higher performance Nb3Sn magnets (MQXF) with 11.4 T coil peak field. MQXF coils are impregnated with epoxy resin to reduce risk of stress concentration on the brittle conductor. The magnet quench protection is provided by CLIQ and quench heaters to ensure a redundant system. Quench heaters are impregnated with the coils in order to have suitable thermal contact with them, and to prevent the hot spot temperature from exceeding 350K during normal operation in case of a quench. Quench heaters are insulated from the coil by S-2 Glass and polyimide. The test of the first MQXF prototype (4 m long) MQXFAP1 was stopped by a coil-to-ground short circuit triggered by a heater-to-coil short. This issue triggered a root analysis of the causes of this short. Here we prove that the use of a non-conforming cloth in coil impregnation, further weakened by non-conforming high voltage test, has triggered the shorts. Moreover, we present an analysis of the heater-to-coil insulation strength, showing the role of blistering phenomena and how they are triggered by a combination of magnet powering and heater firing.

International audience; In the framework of the HL-LHC project, a NbTi double aperture quadrupole magnet MQYY is being developed as an option to replace the LHC magnet MQY. This 90 mm double aperture cos-2θ quadrupole has an operating gradient of 120 T/m at 1.9 K. To demonstrate the validity of the design, a single aperture short model of 1.2 m called MQYYM has been developed. Designed by CEA and manufactured in collaboration with CERN, the MQYYM magnet is being prepared for cold test at CEA in a dedicated cryogenic station with LHe bath at 1 bar 4.2 K and 23 mbar 1.9 K. First, this paper will summarize the initial and as-built magnet designs based on the assembly at CERN. Second, updated mechanical measurements of collaring and axial pre-loading will be presented. Finally warm magnetic measurements performed at CERN during the assembly and at CEA during test preparation will be detailed.

In the family of the High-Luminosity LHC high order correctors, the skew quadrupole was the most critical magnet as three assemblies with different solutions were needed to meet the design specifications. This paper summarizes the prototyping phase of the magnet, discussing the observed nonconformities, the subsequent root cause analyses, and the adopted solutions. A first-hand experience showed us the importance of adopting rigorous quality assurance methods for the electrical insulation, aimed at the early defect detection, and implementing a consistent measurement-to-simulations chain for the optimization of the coils mechanical support. The improvements discussed in the paper are integrated into the final magnet design for the series production of six skew quadrupole correctors.

The recombination dipoles D2 (MBRD) for the luminosity upgrade of the Large Hadron Collider (LHC) are double aperture magnets to be placed on each side of ATLAS and CMS experiments, generating 4.5 T along a magnetic length of 7.78 m and a bore diameter of 105 mm. Its development plan foresees the construction of a short model 1.6 m long, followed by a prototype and by the series of 6 magnets. The magnet design was carried out at INFN Genova in a collaboration framework with CERN and the construction is ongoing in the industry (ASG Superconductors, Italy). The short model activities have just been accomplished after a successful power test performed at CERN, while the prototype is in its construction phase. In this contribution, the main features of the D2 magnet will be described, underlining the improvements implemented in the prototype with respect to the short model design. Then, the main results of the power test will be presented, focusing on training performance, protection scheme effectiveness and magnetic measurements.

For the High Luminosity Upgrade project (HL-LHC) of the CERN Large Hadron Collider (LHC), lower $\beta$ * quadrupole magnets based on advanced Nb $_\text{3}$ Sn conductors will be installed on each side of the ATLAS and CMS interaction points. To quantify the endurance and technological limits of these magnets, beyond their maximum operational conditions, two short length model magnets have been extensively tested at the CERN SM18 test facility. Both magnets were subjected to eight thermal cycles. One of them was trained beyond its ultimate current (17.89 kA, corresponding to 143 T/m field gradient and 12.2 T peak field), reaching a maximum of 19.57 kA at 1.9 K (corresponding to 155 T/m, 13.4 T peak field and 95.4% of the short sample limit) in a 150 mm diameter bore. This magnet currently has the record highest field gradient of this quadrupole magnet class. The second short model had zero re-training quenches up to nominal (16.47 kA) and ultimate current at 1.9 K during the thermal cycles; more than 1000 current cycles to nominal current; and provoked quenches to simulate the most severe failure scenarios of the protection system. After all these tests, both magnets continue to perform beyond requirements for operating current and temperature. In this paper, the tests performed on the two magnets are discussed.

The second prototype of the MCBXFB nested orbit corrector for the upgrade of the LHC has been manufactured at CIEMAT and assembled at CERN, in the framework of the HL-LHC project. This paper describes the changes introduced with respect to the first prototype in order to test some design improvements intended for the series magnets. The preload of the coils has been carefully studied, aiming to improve the performance in combined operation. A power test campaign has been carried out for this second prototype at CERN. Both dipoles reached ultimate current without any quench when individually powered. However, the results in combined operation did not improve those of the first prototype. Further analysis and studies are ongoing.

For the HL-LHC project, a 90 mm double aperture NbTi quadrupole magnet is being developed as an option to replace the 70 mm aperture LHC quadrupole MQY. This cos2θ magnet has an operating gradient of 120 T/m at 1.9 K and a magnetic length of 3.67 m. A single aperture short model magnet with a magnetic length of 1.2 m has been designed at CEA and is being manufactured in collaboration with CERN. The magnet support structure is relying on self-supporting collars. We present here the mechanical analysis along with the assembly of the short model magnet from coil fabrication and mechanical characterization to collaring and yoking.

In the context of CERN's high-luminosity upgrade project (HL-LHC) for the Large Hadron Collider (LHC), a new double aperture beam orbit corrector magnets will be installed near the recombination dipole (D2). These 2.2 m long NbTi dipoles are built with the canted cosine theta (CCT) technique. The two independently powered apertures are oriented such that their field vectors are perpendicular to each other and to the direction of the beams. A full-length double aperture prototype was built and tested at CERN in the SM18 test facility. Here we present the results of powering tests at 1.9 and 4.5 K: training of each aperture, magnetic field quality and cross-talk effects, quench detection system effectiveness, quench protection performance and quench-back with several energy extraction systems.

INFN is developing at LASA laboratory (Milano, Italy) the prototypes of five high order corrector magnets, from skew quadrupole to dodecapole, which will equip the high-luminosity interaction regions of the High Luminosity-LHC (HL-LHC). These magnets are based on a superferric design, which allows a relatively simple, modular and easy to construct magnet. This activity takes place within the framework of a collaboration agreement between CERN and INFN. Four prototypes, from sextupole to dodecapole, have been built and tested starting in 2016. We present here the last prototype of the high order correctors, to be installed in LHC, the skew quadrupole: magnetic and mechanical design are discussed together with quench protection. We report also on the overall experience gained during construction aiming toward the series production. The power test of the quadrupole, including the training, the qualification and the quench behavior in operational conditions are also described.

High Energy Research Organization (KEK) has developed three short-scale model magnets of the beam separation dipole, MBXF, which is to be installed for the High Luminosity Large Hadron Collider, HL-LHC, in CERN. We will soon undertake production of a prototype of MBXF and its magnetic design has to be finalized before the fabrication. We established a strategy for designing the new coil cross section by taking into account different error sources for its field quality. In this paper, focused on b 3 , we describe how the final b 3 integral, which should be within 2.9 units according to the acceptance criteria, is achievable.

Nb-Ti based large-aperture beam separation dipoles (MBXFs) will be installed on both sides of two interaction points, ATLAS and CMS, for the high-luminosity LHC upgrade. The most important requirements for MBXF is a coil aperture of 150 mm and the field integral of 35 T⋅m. Nominal dipole field is 5.6 T at 12 kA and 1.9 K. KEK is in charge of developing MBXF within a framework of CERN-KEK collaboration. This study reports training performance of three 2-m long model magnets (MBXFS1–3) assembled under different mechanical support conditions. Azimuthal pre-stress both in the straight section and at coil end, and axial pre-load were controlled to counteract Lorentz force. In MBXFS2 and 3, wet-winding was also applied but solely to the coil end. Quench start locations for the model magnets are compared to validate the effectiveness of each support method.

The first prototype of the short orbit corrector for the upgrade of the LHC has been fabricated at CIEMAT, in collaboration with CERN, in the framework of the HL-LHC project. It consists of two nested dipoles, with an aperture of 150 mm and physical length of 1.5 m. A first power test was performed without the outer dipole coils, which were replaced by a support structure to align the iron yoke with the collared inner dipole. This test was aimed to validate the coil fabrication techniques, which are innovative for a NbTi Rutherford cable. In the power test of the full assembled magnet, individual training of both dipoles was fine to ultimate current. However, the magnet was not able to reach nominal torque in combined operation. Several power tests and re-assemblies were necessary to be able to power both dipoles till nominal current. This paper describes the test results and analysis of the measurements. The magnet is heavily instrumented with voltage taps, collars with strain gauges and bullet gauges at the axial pushers.

In collaboration with CERN, High Energy Accelerator Research Organization (KEK) has designed and developed short-scale model magnets of the beam separation dipole, MBXF, which will be installed for the High Luminosity Large Hadron Collider, HL-LHC. A new quench protection heater for MBXF was designed and tested during the cold test of the short-scale models. Combining data taken since the test of the 1st model magnet, we confirmed the maximum hotspot temperatures are well below 300 K in the case of the low field (1 T) and high field (5 T) quenches, respectively. In addition, a simulation model was developed and tuned with the obtained data for the full-scale prototype magnet. The hotspot temperature after quench initiation was then computed with the new heater circuit and found to be below 300 K even for the case of failure in firing the heater.

Author(s): Mangiarotti, F; Bajas, H; Ambrosio, G; Bajko, M; Bordini, B; Bourcey, N; Duda, M; Desbiolles, V; Feuvrier, J; Fleiter, J; Bermudez, SI; Chiuchiolo, A; Devred, A; Ferracin, P; Fiscarelli, L; Mentink, M; Nobrega, A; Pepitone, K; Ravaioli, E; Schmalzle, J; Todesco, E; Perez, JC; Vallone, G; Willering, G; Yu, M | Abstract: For the high luminosity upgrade of the CERN large hadron collider, lower β∗ quadrupole magnets based on advanced Nb3Sn conductors will be installed on each side of the ATLAS and compact muon solenoid (CMS) experiment insertion zones. As part of the technological developments needed to achieve the required field gradient of 132.6 T/m within a 150-mm aperture, short length model magnets, named MQXFS, are tested both at the CERN SM18 and Fermilab test facilities. The model magnets rely on two types of Nb3Sn conductors (restack rod process (RRP) and powder-in-tube (PIT)) and on an innovative bladders and keys design to provide mechanical support against the Lorentz forces. In 2016 and 2017, the powering tests of the first two models MQXFS3 (RRP) and MQXFS5 (PIT) proved that nominal performance (16.5 kA) could be reached with excellent memory of the quench current after thermal cycle. However both magnets showed a slow training behavior with clear observations of voltage disturbances before the quench. Besides, only MQXFS5 could reach ultimate current (17.9 kA) whereas erratic behavior was observed on MQXFS3 due to conductor local degradation at the head of one of the coils. In 2018, this limiting coil was changed and the applied azimuthal prestress increased. While ultimate current could then be reached, no stable current could be maintained due to identified defect on the outer layer of the new coil. Finally the outcome of the test of the new model MQXFS4, featuring the final RRP conductors that will be used for the series production and variation on the inner layer quench heater designs are here reported in details.

In the frame of the high-luminosity upgrade project for the large hadron collider, new twin aperture beam orbit corrector magnets will be installed near the recombination dipole (D2). These magnets are 2.2 m long canted cosine theta NbTi dipoles, with two independently powered apertures oriented such that their field vectors are perpendicular to each other and to the direction of the beams. A 0.5 m model magnet in single and double aperture configuration and a full-length double aperture prototype were built and tested at CERN. In this paper, the performance of these magnets at 1.9 K in terms of training behavior, quench detection and protection, and other tests is discussed. In addition, the thermal response of the magnet to a hypothetical beam discharge is simulated and analyzed.

A new recombination dipole D2 for the luminosity upgrade of the Large Hadron Collider at CERN (LHC) is under development since 2016 at INFN in a collaboration framework with CERN. These twin aperture magnets will be installed on both sides of LHC main multipurpose experiments, ATLAS and CMS, interaction points. The target integral magnetic field in an aperture of 105 mm is 35 T m, obtained with a magnetic field of 4.5 T and a magnetic length of 7.78 m. The coils in both apertures are asymmetric for canceling the unwanted multipoles caused by the magnetic field cross-talk. The asymmetric design and the demanding requirements on the field quality made preferable an independent collaring, which allows for a more accurate assembly: the mechanical stability is ensured by a novel approach of coil integration in an Al-alloy mechanical structure. After a design phase, the construction of a short model has been planned followed by the construction of a full-length prototype. This contribution is focused on the aspects of the short model assembly and the implications on the prototype design in terms of mechanical tolerances, manufacturing processes, and materials involved in the construction.

The high-luminosity upgrade of the large hadron collider (HL-LHC) requires new high-field and large-aperture quadrupole magnets for the low-beta inner triplets (MQXF). The US Hilumi-LHC Accelerator Upgrade (HL-LHC AUP) and CERN are jointly developing a 150 mm aperture Nb3Sn magnet. Due to the large beam size and orbit displacement in the final focusing triplet, MQXF has challenging field quality targets at collision energy. Magnetic measurements have been performed both at ambient and cryogenic temperatures in the four short models built and tested. This paper presents the magnetic analysis, comparing field measurements with the expectations and the field quality requirements. The analysis is focused on the geometrical harmonics and iron saturation effect, including three dimensional effects and transfer function repeatability. Persistent currents and dynamic effects are also discussed. The high-luminosity upgrade of the Large Hadron Collider (HL-LHC) requires new high-field and large-aperture quadrupole magnets for the low-beta inner triplets (MQXF). The U.S. HiLumi-LHC Accelerator Upgrade and CERN are jointly developing a 150-mm aperture Nb3Sn magnet. Due to the large beam size and orbit displacement in the final focusing triplet, MQXF has challenging field quality targets at collision energy. Magnetic measurements have been performed both at ambient and cryogenic temperatures in the four short models that were built and tested. This paper presents the magnetic analysis, comparing field measurements with the expectations and the field quality requirements. The analysis is focused on the geometrical harmonics and iron saturation effect, including three-dimensional effects and transfer function repeatability. Persistent currents and dynamic effects are also discussed.

The High Luminosity LHC (HL-LHC) is a program to upgrade the performance of the collider in order to achieve, in the ATLAS and CMS collision regions, instantaneous luminosities a factor of five larger than the actual nominal value. To obtain this result, all the magnets in the collision region will have to be substituted, together with other important devices. In the framework of this program, the Italian National Institute for Nuclear Physics (INFN-LASA laboratory) is entrusted to develop five corrector magnets (skew quadrupole, sextupole, octupole, decapole, and dodecapole), which in the magnet chain will have to correct the magnetic imperfections of the main magnets in the regions (low-beta quadrupoles Q1/Q3 and dipole D1/D2). These corrector magnets have been designed with relatively simple, robust, and easy to construct concepts, using superferric configuration. The first prototypes, a sextupole, an octupole, and a decapole, have been tested in 2016 and 2017. We present here the prototype of dodecapole. We report magnetic and mechanical designs and the experience during construction. The qualification, the cold test, and the quench behavior in operational conditions are also described.

Large aperture beam separation dipoles (D1 magnet) must be developed for the interaction regions in the high-luminosity large hadron collider (HL-LHC). The most important specifications of this magnet are a coil aperture of 150 mm and field integral of 35 Tm, which will be realized by Nb-Ti superconducting magnets operated at 12 kA at 1.9 K. High Energy Accelerator Research Organization (KEK) is developing 2-m-long model magnets for D1. The first model magnet was re-assembled after increasing the coil pre-stress (MBXFS1b); subsequently, it showed good training performance, achieving maximum quench current, which was higher than the ultimate current. However, mechanical support of the coils was still insufficient in MBXFS1b. Especially at coil end, some coil end blocks deformed toward the coil bore due to Lorentz force. In the second model magnet (MBXFS2), the change of iron yoke cross section was requested so that the position of heat exchanger holes penetrating iron yoke is in agreement with those of the final focusing Nb 3 Sn quadrupole magnets. Because this has a large impact on field quality, magnetic design including the magnet's cross section and coil end shape was updated. Some countermeasures were also taken to enhance mechanical support of the coil such as wet-winding with radiation-resistant resin at coil end and increase in coil pre-stress. This paper reports design update, fabrication, and training performance of MBXFS2 with new iron cross section.

MCBXF magnets are nested orbit correctors, needed for the upgrade of the large hadron collider (LHC), in the framework of the high luminosity (HL) LHC project. There are two versions with different physical lengths, 1.5 and 2.5 m, which share the same cross section to decrease fabrication costs. These magnets have a large aperture of 150 mm and due to the high radiation dose, a mechanical clamping is necessary to hold the large torque between both dipoles. Centro de Investigaciones Energeticas, Medioambientales y Tecnologicas CIEMAT is developing the short MCBXFB prototype in collaboration with CERN. This paper describes the engineering design of the magnet, which is based on previous magnetic and mechanical calculations. The axial pre-stress on the coil ends is analyzed in detail. Some innovative techniques have been developed for the coil fabrication because of the high number of turns and large aperture.

We report the test results of the second short model magnet of the beam separation dipole for the High Luminosity Large Hadron Collider. The test shows that the second model has a good training performance and is capable of operating at the ultimate current that corresponds to 108% of the nominal one. Magnetic field measurements reveal that b 3 is around 18 units, which is 15 units higher than the calculations. This can be explained in part by geometrical coil deformation caused during the construction process.

In the framework of the high-luminosity upgrade of the Large Hadron Collider, the U.S. LARP collaboration and CERN are jointly developing a 150 mm aperture Nb3Sn quadrupole for the LHC interaction regions. Due to the large stored energy density and the low copper stabilizer section, the quench protection of these magnets is particularly challenging, relying on a combination of quench heaters attached to the coil surface and coupling loss induced quench (CLIQ) units electrically connected to the coils. This paper summarizes the performance of the quench heater strips in different configurations relevant to machine operation. The analysis is focused on the inner layer quench heaters, where several heater strips failed during powering tests. Failure modes are discussed in order to address the technology issues and provide guidance for future tests.

The National Institute for Nuclear Physics (INFN) is developing at the Laboratory of Accelerators and Applied Superconductivity (LASA) laboratory (Milano, Italy) the prototypes of five corrector magnets, from skew quadrupole to dodecapole, which will equip the high-luminosity interaction regions of the High Luminosity Large Hadron Collider (HL-LHC). These magnets are based on a superferric design, which allows a relatively simple, compact, and easy to construct magnet. This activity takes place within the framework of a collaboration agreement between European Organization for Nuclear Research (CERN) and INFN. The first prototypes, a sextupole and an octupole, have been tested in 2016 and 2017, respectively. We present here the results of the cold tests of the decapole that has been assembled and tested in the second half of 2017, including the training performed at 4.2 K and the qualification at 2.17 K. We report also on the overall experience gained during construction and tests and the improvements toward the series production. Other important results concern quench studies.

The high-luminosity Large Hadron Collider (HL-LHC) project aims at allowing to increase the collisions in the LHC by a factor of ten in the decade 2025-2035. One essential element is the superconducting magnet around the interaction region points, where the large aperture magnets will be installed to allow to further reduce the beam size in the interaction point. The core of this upgrade is the Nb3Sn triplet, made up of 150-mm aperture quadrupoles in the range of 7-8 m. The project is being shared between the European Organization for Nuclear Research and the US Accelerator Upgrade Program, based on the same design, and on the two strand technologies. The project is ending the short model phase, and entering the prototype construction. We will report on the main results of the short model program, including the quench performance and field quality. A second important element is the 11 T dipole that replaces a standard dipole making space for additional collimators. The magnet is also ending the model development and entering the prototype phase. A critical point in the design of this magnet is the large current density, allowing increase of the field from 8 to 11 T with the same coil cross section as in the LHC dipoles. This is also the first two-in-one Nb3Sn magnet developed so far. We will report the main results on the test and the critical aspects.

INFN is developing at LASA Laboratory (Milano, Italy) the prototypes of five corrector magnets, from skew quadrupole to dodecapole, which will equip the high-luminosity interaction regions (IRs) of the High Luminosity-LHC (HL-LHC). These magnets are based on a superferric design, to allow a relatively simple, modular, and easy to construct magnet. This program takes place within the framework of a collaboration agreement between CERN and INFN. In this paper, we present an overview of the activity, from the design, to the construction and test at the operation condition.

In the framework of the high-luminosity upgrade of the large hadron collider, the U.S. LARP collaboration and CERN are jointly developing a 150-mm aperture Nb3Sn quadrupole for the Large Hadron Collider (LHC) interaction regions. Due to the large beam size and orbit displacement in the final focusing triplet, MQXF has challenging targets for field quality at nominal operation conditions. Three short model magnets have been tested and around 30 coils have been built, allowing a first analysis of the reproducibility of the coil size and turns positioning. The impact of the coil shimming on field quality is evaluated, with special emphasis on the warm magnetic measurements and the correlation to field measurements at cold and nominal field. The variability of the field harmonics along the magnet axis is studied by means of a Monte-Carlo analysis and the effects of the corrective actions implemented to suppress the low-order unallowed multipoles are discussed.

A large aperture beam separation dipole (D1 magnet) is required to generate a field integral of 35 Tm at 12 kA and 1.9 K for the high luminosity upgrade of the large hadron collider (HL-LHC). High-energy accelerator Research Organization (KEK) fabricated the first 2 m model (MBXFS1) and a magnet test was performed in 2015–2016. Although the quench current reached the nominal operating current, training performance was not satisfactory. The measured azimuthal coil pre-stress was completely released below the nominal current, and this was suggested to be the main reason for the insufficient training performance. After the magnet test, MBXFS1 was disassembled and reassembled as MBXFS1b after increasing the coil pre-stress. In this paper, we report the reassembly of the magnet and test results focusing on the training performance.

The large hadron collider (LHC) at CERN has been operating and generating physics experimental data since September 2008, and following its first long shut down, it has entered a second, 4-year-long physics run. It is to date the largest superconducting installation ever built, counting over 9000 magnets along its 27-km long circumference. A significant operational experience has been accumulated, including the occurrence and consequences of electrical faults at the level of the superconducting magnets, as well as their protection and instrumentation circuits. The purpose of this paper is to provide a first overview of the most common electrical faults and their frequency of occurrence in the first years of operation, and to perform a statistical analysis that can provide reference values for future productions of similar dimensions and nature.

During 2016, one-quarter of the LHC main dipoles have has been powered above the 7.7 T operational field, to reach a field of 8.1 T. These tests were done to confirm the extrapolation of the training behavior based on a Gaussian tail of the quench distribution. In this paper, it is shown that a modified Gaussian distribution can be used to better model the quench distributions. We then present the data above 6.5 TeV, showing that they are compatible with the previous expectations. We present the data of retraining of sector 12, which was warmed up in 2016 to replace a magnet, and training of individual magnets that went through several thermal cycles: there is an indication that training campaigns during successive warm-ups and cool-downs could become shorter. We finally show that a significant correlation is found between the training of the installed magnet and individual test after a thermal cycle (second cool-down). On the other hand, no correlation is found with individual test under virgin conditions (first cool-down).

The beam separation dipole magnet (D1), which is being operated in the large hadron collider (LHC), has to be replaced in accordance with upgrade to the high-luminosity LHC. The new D1 will be equipped with several circuits of heaters by which most of the stored energy is dissipated in the whole of the magnet during its quench, thereby avoiding localization of hot spots. Prior to construction of the production magnet, the 2-m mechanical short model is fabricated, and performance of this quench protection heater is evaluated through a series of the cold tests. As a result, we confirm that the maximum hot spot temperature obtained in the measurement reaches the practical limit of 300 K, and determine to design a new heater circuit. In this paper, we report the heater studies together with the prospect for future design of the quench protection heater.

The large hadron collider (LHC) upgrade, called high-luminosity LHC is planned for the next decade. A wide range of magnets and new technologies are currently under development. One of these systems will be a set of twin aperture beam orbit correctors positioned on the approaches to the ATLAS and CMS experiments. This twin aperture magnet system comprising 16 magnets, approximately 2 m long, with large 105-mm clear aperture coils. Each aperture will independently deliver 5-T⋅m integral field, between apertures the field vectors are rotated by 90° from each other, and individually powered. This paper presents the sequence of component developments to produce a cost-effective canted cosine theta model magnet. We describe the challenges encountered during the manufacture of the coil formers with their helical canted coil winding process which places a number of insulated wires into the 2-mm-wide 5-mm-deep slot. We describe the: pressurized impregnation process, multiple jointing to connect inner and outer sets of wires within the confines of the coil assembly, and magnet assembly into support structure and yoke. Finally, we present the quench performance and initial test results of this novel coil configuration.

The high luminosity upgrade will enhance the discovery potential of the LHC in the next decade. Among other magnets and technologies currently under development, the MCBXF orbit correctors will be required to this end. In order to save space, they consist in two perpendicularly and coaxially arranged dipole coils under a large torque. Coils cannot be glued due to the high radiation dose expected, and mechanical clamping is mandatory. With the goal of turning the conceptual design into a tangible reality, this paper depicts the final magnetic design, with special attention to 3-D electromagnetic calculations and the different operation scenarios. It also includes more accurate mechanical FE models results, achieved by measuring the Young's modulus of impregnated cable stacks. Besides assembly spring-back, cool-down, and energization, simulations have been also carried out for the pressing process of both dipoles, analysing stress distribution, and displacements. Finally, a short mechanical model has been designed, fabricated, and tested. Its main purpose is to assess the feasibility of the proposed clamping structure, the reliability of the FE mechanical models and the design of an important part of the tooling required for the magnet fabrication.

A dedicated D1 beam separation dipole is currently being developed at KEK for the large hadron collider luminosity upgrade (HL-LHC). Four 150-mm aperture, 5.6-T magnetic field, and 6.7-m-long Nb–Ti magnets will replace resistive D1 dipoles. The development includes fabrication and testing of 2.2-m model magnets. The dipole has a single-layer coil and thin spacers between coil and iron, giving a nonnegligible impact of saturation on field quality at nominal field. The magnetic design of the straight section coil cross section is based on two-dimensional (2-D) optimization and a separate optimization concerns the coil ends. However, magnetic measurements of the short model showed a large difference (tens of units) between the sextupole harmonic in the straight part and the 2-D calculation. This difference is correctly modeled only by a 3-D analysis: 3-D calculations show that the magnetic field quality in the straight part is influenced by the coil ends, even for the 6.7-m-long magnets. The effect is even more remarkable in the short model. We investigate similar 3-D effects for other magnets, namely the 11-T dipole for HL-LHC. We also consider the case of the 4.5-T recombination magnets for HL-LHC (D2), where the larger space between coil and iron makes this effect less important, but still visible. We conclude the paper by outlining the different classes of accelerator magnets, where this coupling between 3-D effects and iron saturation can be relevant.

© 2002-2011 IEEE. The European Organization for Nuclear Research (CERN) and U.S. LHC Accelerator Research Program (LARP) are jointly developing Nb-3Sn quadrupole magnets to be installed in the LHC for its upgrade to higher luminosity. These magnets' quench protection system will include a combination of quench heaters attached to the coil surfaces and coupling-loss-induced quench (CLIQ) units electrically connected to the magnets. Different protection elements have been characterized separately and simultaneously by implementing them on two 1.2-m-long model quadrupole magnets, tested at Fermi National Acceleration Laboratory and CERN, and one 4-m-long mirror magnet tested at Brookhaven Nation Laboratory. After analyzing the test data, their performances have been positively evaluated. Furthermore, the electrothermal transients occurring after a quench have been simulated with the LEDET software and the results are compared to experimental results. The preferred quench protection system configuration relies both on heaters and CLIQ. This solution is based on electrically robust components, achieves an effective reduction of the coils hot spot temperature after a quench, and offers increased redundancy against component failures.

The high-luminosity upgrade of the large hadron collider (HL-LHC) requires new high-field and large-aperture quadrupole magnets for the low-beta inner triplets (MQXF). CERN and LARP are currently collaborating to develop a 150-mm-aperture quadrupole based on Nb $_3$ Sn superconducting cables for the coils, and an aluminum shell with the bladder-key technology for the support structure. This paper presents the test setup for magnetic measurements, both at ambient and cryogenic temperatures, and the instrumentation being used for the first two short-models of MQXF built and tested at CERN. Finally, the measurement results, in terms of field quality, effects of persistent currents, and iron saturation are reported and discussed.

A beam separation dipole magnet for the high luminosity large hadron collider upgrade is developed. The development of the 2-m-long model magnet (MBXFS1) was initiated so as to evaluate the design and performance of the beam separation dipole magnet. In the first cold test in 2016, the quench performance was not satisfactory because the coil prestress at the pole was completely released during excitation. After reassembly to improve the quench performance, the excitation test of the modified model magnet (MBXFS1b) was performed at 1.9 K in 2017 at KEK. Due to the large coil aperture and limited outer diameter of the iron yoke, the control of iron saturation effects on the field quality has been a design issue. Regarding the magnetic performance, field saturation effects on the transfer function and the multipole field variation along the excitation, and coil end effects to the straight section need to be evaluated by the field measurement. In this paper, field measurement results will be presented and the comparison with the three-dimensional field calculation will be discussed.

In the framework of the High-Luminosity Large Hadron Collider, the installation of a new generation of quadrupole magnets is foreseen on each side of ATLAS and CMS experiments. The new magnets are based on Nb3Sn technology and shall be able to reach an ultimate current of 17.9 kA with a peak field of 12.3 T in the coil. In 2016 and 2017, the first two short models, called MQXFS3 and MQXFS5, have been tested at 4.2 and 1.9 K in the two new test benches at the European Organization for Nuclear Research. This paper presents the result of the quench performance of the two models; the first magnet reached nominal but failed to reach ultimate, showing detraining in one coil. MQXFS5 reached ultimate performance without any detraining phenomena, validating the PIT conductor used for the first time in this magnet program.

Author(s): Bermudez, SI; Ambrosio, G; Chlachidze, G; Ferracin, P; Holik, E; Di Marco, J; Todesco, E; Sabbi, GL; Vallone, G; Wang, X | Abstract: As part of the Large Hadron Collider Luminosity upgrade (HiLumi-LHC) program, the US LARP collaboration and CERN are working together to design and build 150-mm aperture Nb3Sn quadrupoles for the LHC interaction regions. A first series of 1.5-m-long coils were fabricated, assembled, and tested in the first short model. This paper presents the magnetic analysis, comparing magnetic field measurements with the expectations and the field quality requirements. The analysis is focused on the geometrical harmonics, iron saturation effect, and cold-warm correlation. Three-dimensional effects such as the variability of the field harmonics along the magnet axis and the contribution of the coil ends are also discussed. Moreover, we present the influence of the conductor magnetization and the dynamic effects.

In 2015, the 1232 Nb-Ti dipole magnets in the Large Hadron Collider (LHC) have been commissioned to 7.8 T operational field, with 172 quenches. More than 80% of these quenches occurred in the magnets of one of the three cold mass assemblers (3000 series), confirming what was already observed in 2008. In this paper, the recent analysis carried out on the quench performance of the Large Hadron Collider dipole magnets is reported, including the individual reception tests and the 2008 and 2015 commissioning campaigns, to better understand the above-mentioned anomaly and give an outlook for future operation and possible increase of the operational field. The lower part of the quench probability spectrum is compatible with Gaussian distributions; therefore, the training curve can be fit through error functions. An essential ingredient in this analysis is the estimate of the error to be associated with the training data due to sampling of rare events, allowing to test different hypothesis. Using this approach, an estimate of the number of quenches required to reach 8.3 T (corresponding to the 7 TeV nominal energy) is given, and we propose to have two LHC sectors trained toward this target before the next warm up of the LHC.

The large hadron collider (LHC) upgrade, called high luminosity LHC (HL-LHC) is planned for the next decade. A wide range of magnets and new technologies are currently under development. One of these systems will be a set of twin-aperture beam orbit correctors positioned on the approaches to the ATLAS and CMS experiments. This twin-aperture magnet system comprising 16 magnets, approximately 2 m long, with large 105 mm clear aperture coils. Each aperture will independently deliver 5 T·m integral field, between apertures the field vectors are rotated by 90° from each other, individually powered, crosstalk between apertures is controlled to give good field quality independent of aperture powering status. This paper presents the sequence of magnet optimisations performed that determine optimal coil geometry for the canted cosine theta coil design, to achieve good field quality between the individually powered large apertures, quench optimization, integration of the magnet with the adjacent magnetic objects, and radiation hard robust design. Finally the design focuses on low system cost with minimal tooling.

The upgrade of the large hadron collider to achieve higher luminosity requires the installation of twenty-four 150 mm aperture, 12 T, Nb 3 Sn quadrupole magnets close to the two interaction regions at ATLAS and CMS. The protection of these high-field magnets after a quench is particularly challenging due to the high stored energy density, which calls for a fast, effective, and reliable protection system. Three design options for the quench protection system of the inner triplet circuit are analyzed, including quench heaters attached to the coil's outer and inner layer, Coupling-Loss Induced Quench (CLIQ), and combinations of those. The discharge of the magnet circuit and the electromagnetic and thermal transients occurring in the coils are simulated by means of the TALES and LEDET programs. The sensitivity to strand parameters and the effects of several failure cases on the coil's hot-spot temperature and peak voltages to ground are assessed. A protection system based only on quench heaters attached to the outer layer can barely maintain the hot-spot temperature below the target limit and cannot guarantee the coil protection under failure scenarios. On the contrary, systems including either inner quench heaters or CLIQ are adequate to protect the coil under all realistic operation and failure scenarios. In particular, the option including outer quench heaters and CLIQ achieves lowest hot-spot temperatures, and highest redundancy and robustness.

The large aperture superconducting beam separation dipole (D1) must be developed as part of the high luminosity upgrade of the Large Hadron Collider (HL-LHC) at CERN. The most important specifications of the D1 are a coil aperture of 150 mm and field integral of 35 T·m at 12.0 kA and 1.9 K. The technical challenges of this magnet include predicting the changes in the size of the coils during fabrication, achieving a high radiation resistance, and management of the iron saturation. KEK is in charge of developing the D1. After conducting a series of design studies, a design consisting of a single-layer coil based on Nb-Ti technology with a collared yoke structure was selected. The fabrication of the first 2 m model of the D1 started at KEK in 2015. Newly developed radiation resistant glass-fiber-reinforced-plastics were utilized as coil parts in the accelerator magnets for the first time. The 2 m model was subjected to two cycles of cold test in the vertical cryostat at KEK. In this paper, we report on the fabrication of the 2 m model. We also present and discuss the quench test results from the perspective of the coil prestress.

INFN is developing at LASA lab (INFN Milano, Italy) the prototypes of five corrector magnets, from skew quadrupole to dodecapole, which will equip the high-luminosity interaction regions of the High Luminosity-LHC. These magnets are based on a superferric design, which allows a relatively simple, modular, and easy to construct magnet. This activity takes place within the framework of a collaboration agreement between CERN and INFN. The first prototype, a sextupole, has been assembled in early 2016. We present here the results of the cold test, including the training performed at 4.2 K and the qualification at 2.2 K. We report also on the overall experience gained during its construction and test. An important aspect is represented by the analysis of the manufacturing tolerances of the mechanical pieces and the alignment accuracy achieved. These results will serve as a basis for the design of the next magnets, the octupole, and the decapole. Other important results concern the cold performance of the coil-to-coil electrical joints (especially critical in a magnet with a large number of coils), dynamic inductance measurements and quench studies.