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 High-Luminosity upgrade of the Large Hadron Collider (HL-LHC) is underway at CERN. The upgrade will rely, among other magnets, on the inner triplet quadrupoles (MQXF). The coils of these magnets are wound from Nb3Sn Rutherford cables experiencing magnetic fields of up to 12 T. High performance and precise control of cable dimensions (within a few mu m) are of primary importance for these accelerator magnets. The paper reviews the main characteristics of these cables and addresses the critical points of the design with respect to their use in HL-LHC. Then the status of the production of the superconducting cables is reported, with particular emphasis on the QA/QC procedures and data. Those procedures are performed to ensure that the series production cables conform to the tight technical requirements. Non-conformities identified during cable production are also presented and discussed.

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

The accelerator magnets for the high luminosity upgrade of the large Hadron collider use Nb3Sn conductor to achieve the required in-field performance. To sustain the Lorentz forces during operation, a pre-compression is applied to the coils during the fabrication of the magnet. This can lead to an irreversible degradation of the Nb3Sn conductor due to its mechanical sensitivity. In this study, the impact of the pre-compression applied to the conductor at room temperature is investigated using a reacted double-stack specimen made of two Nb3Sn Rutherford cables. The cables have a keystone angle and are stack with a non-inverted configuration, without compensating the angle. The rectangular specimen is submitted to increasing transverse compressive stresses at room temperature applied perpendicularly to its width. The non-inverted configuration and the rectangular shape of the total specimen can thus lead to stress concentration. The pressure applied covers the range from 130 MPa to 190 MPa with a 10 MPa step increase. After each cumulated stress level, transport current measurements are performed in liquid helium and in background fields of up to 9.6 T in the FReSCa test station at CERN Metallographic analyses of several samples are made at selected stress levels. Monotonic and cumulated stresses are applied and the impact of mechanical cycling is analyzed. Procedures are specifically developed to minimize surface damage during samples' preparation. The observations are compared with the electrical measurements in order to correlate the irreversible effect of the transverse pressure with the A15 damage state in the cross section. The transport current measurements of the double-stack specimen show degradation of critical current and n-value starting at respectively 170 MPa and 160 MPa cumulated loadings. However, cracks in the A15 phase are already observed in a metallographic sample subjected to 140 MPa.

The Superconducting Ion Gantry (SIG) project aims to design, construct, and test a curved superconducting dipole demonstrator magnet for an ion gantry (up to a rigidity of 6.6 Tm). The main demonstrator magnet parameters are a dipolar field of 4 T generated into a toroidal aperture with an 80 mm diameter, 1.65 m curvature radius, and 30(degrees)angular sector. The project is inserted in the framework of the EuroSIG collaboration among CNAO, CERN, INFN, and MedAustron. Within this collaboration, the main goal of SIG is to perform a feasibility study of winding and assembling cos-$\theta$ coils with a small curvature radius. In addition, a parallel program at CERN is dedicated to the study of the indirect cooling problem through the construction of a straight thermal demonstrator magnet sharing the SIG cross-section. The basic idea behind these programs is to check whether the vast experience of the community on superconducting accelerator magnets design can lead to a breakthrough in the gantry magnets domain. This article shows the main elements of the conceptual design of the SIG magnet and reports on the first winding trial performed at the LASA laboratory, in Milan, with a copper dummy cable. Moreover, possible solutions for the winding, curing, and impregnation of highly curved cos$\theta$ coils are discussed.

In the production of Rutherford cables, Nb3Sn strands are subjected to severe deformation; and to evaluate this degradation prior to cabling, uniaxial rolling with a thickness reduction of similar to 15% has often been used. The effects of this deformation on superconducting performance differ significantly between wire designs. In this article, wire deformation behavior is investigated by image analysis of electron micrographs, and the resulting degradation of critical current and residual resistance ratio is quantified, for several designs of internal tin (RRP and distributed tin) and powder-in-tube wire in use or under study at CERN for the HL-LHC upgrade and High Field Magnets program. The suitability of uniaxial rolling as a predictor of cabling degradation is assessed and recommendations are made for improved testing procedures.

This contribution describes the experimental program already undergoing and to be completed on the High Luminosity Large Hadron Collider (HL-LHC) Inner Triplet (IT) String, an important intermediate milestone of the HL-LHC project at CERN. First, it describes the magnet circuits of the HL-LHC IT String. Afterwards, the different systems installed to perform the experimental program are detailed. The proposed tests are defined for the validation of the cryogenic system, the full remote alignment system, the powering system, and the protection schemes of all magnets working in unison. This strategy will allow for a verification of the integrated powering system before the final installation and commissioning in the HL-LHC's underground areas.

In the framework of the High Field Magnets (HFM) program, CERN is developing and qualifying Nb 3 Sn Rutherford cables to support magnet development towards the requirements of a future energy-frontier collider, using both state-of-the-art commercial wires and experimental wires under development with industrial partners. The trend towards higher current density and larger diameter wires imposes challenges for magneto-thermal stability. In this study, rolling trials and Rutherford cabling have been performed at CERN for two designs of a 1 mm diameter distributed tin Nb 3 Sn wire produced by KAT, and for 1 mm and 1.1 mm diameter RRP® Nb 3 Sn wires procured from Bruker OST, and the self-field stability and cabling degradation have been analyzed. The 1 mm RRP® wire shows significant degradation in Ic and stability on cabling. Although the latter is not expected to impact the performance of research magnets, the potential of heat treatment optimization to improve stability has also been quantified. The distributed tin wire shows substantially poorer stability, but promising indications of low cabling degradation. The influence of wire design characteristics on cabling behavior and stability have been assessed, and the implications for future wire optimization towards high field accelerator magnet applications have been discussed.

As part of the High Field Magnet technology development carried out at CERN, demonstrators are under construction to explore the full potential of Nb3Sn. The Racetrack Model Magnet (RMM) is one of them, building upon the successful Enhanced Racetrack Model Coil (eRMC) eRMC1a magnet which reached 16.5 T peak field or 16.3 T bore field at 1.9 K. The RMM1a,b magnet is composed of the same two previously tested eRMC racetrack-type coils and an additional middle RMM coil. This central racetrack-type coil features a closed cavity with a diameter of 50 mm and a total length of 526 mm. The coil pack is assembled in the same shell-based support structure as eRMC1a, using bladders and keys to allow for a precise control of the preload with minimal spring back and conductor overstress. The magnet was preloaded with a conservative approach limiting the equivalent peak stress in the coil blocks below 150 MPa. It was then successfully tested up to 16.7 T peak field or 16.5 T bore field at 1.9 K. This paper describes the assembly of the RMM1a,b magnet, relying on Finite Element Analysis (FEA) and mechanical instrumentation, as well as the powering test results at 4.2 K and 1.9 K.

About one hundred magnets of six different types shall be installed in the High Luminosity LHC (HL-LHC) in the years 2026--2028 at CERN. The magnets design, construction and test are based on CERN collaborations with institutes and industrial partners in USA, Spain, Italy, Japan and China. Three types of correctors are based on Nb–Ti technology and feature conductor peak fields in the 2 to 4 T range: for all of them the protoype phase has been successfully completed. The production is well advanced for the superferric correctors, and is starting for the canted cos theta correctors and for the nested correctors. The separation and recombination Nb–Ti dipoles D1 and D2, with a 4.5-6 T bore field range, are both in the prototype phase after the completion of the short model program. The most challenging magnet, the Nb3Sn quadrupole with conductor peak field above 11 T, is in the prototype phase at CERN and halfway through the production phase in the USA. In this paper we will give, for each type of magnet, an overview of the main achievements obtained so far and we will outline the technical points still needing validation from the prototype program.

High-current Superconducting Links are being developed at CERN for the powering of the superconducting magnets of the LHC High Luminosity upgrade (HL-LHC). The Superconducting Links consist of an assembly of magnesium-diboride (MgB2) cables powering different magnet circuits. They have a total DC current capability of up to about |120| kA at 25 K. The MgB2 cables are connected at one side, at 4.2 K, to the Nb-Ti bus bars of the superconducting magnets and at the other side, to round high temperature superconducting (HTS) rare-earth-barium-copper-oxide (REBCO) cables operated, in helium gas, up to 60 K. We have developed, constructed, and commissioned an automated cabling machine for producing long lengths of round, multi-layer, electrically insulated REBCO cables. The machine allows precise adjustment of the cable geometry and control of the cabling parameters. It controls in high speed, with field programmable gate array (FPGA) and Linux real-time (RT) based controllers, the tension applied to the REBCO tapes, to the polyimide insulating tapes, and to the copper core of the cable. It records all cabling and process parameters in addition to the mechanical tensions and it provides the reporting needed for the quality control procedures that are integral to the fabrication of components of the HL-LHC. In this manuscript we report on the development, design and construction of the machine from the concept to the mechanical realization, including control and data acquisition systems. We also report on the commissioning on the machine via the production of round REBCO cables.

High current MgB2 based transmission lines (called Superconducting Links) have been developed at CERN in the framework of the High-Luminosity upgrade of the Large Hadron Collider (HL-LHC). A Superconducting Link is composed of 80–140 m long MgB2 superconducting cables incorporated in a flexible cryostat. The cables, which are actively cooled by forced flow of 5 K to 17 K gaseous helium, will be used for the cold powering of the superconducting magnets of HL-LHC. Three demonstrators were built and tested at CERN, over the past two years, to assess the performance of SC Links operated in conditions similar to those in the HL-LHC machine. Investigations included cryogenic and electrical tests in nominal, transient and accidental conditions. The electro-magnetic cross talk among cables was measured with nominal ramp rates in the circuits as well as with provoked fast current discharges. In this paper the tests performed on the demonstrators are reported and discussed.

In a dipole or in a quadrupole accelerator magnet, the displacement of the coil turns induced by the electromagnetic forces can cause quenches limiting the magnet performance. For this reason, an azimuthal preload is applied to avoid azimuthal movements of the coil up to the required operational current. However, several tests showed that accelerator magnets can operate with a partial preload, i.e. that coil unloading during the ramp does not prevent reaching higher currents. This issue is particularly relevant for Nb3Sn magnets, where the loads applied to the Nb3Sn filaments can reach the degradation limits of critical current. In order to investigate the impact of coil preload on the quench performance, the MQXFS6 short model quadrupole for the High Luminosity Upgrade was tested under an azimuthal preload at 80% of the short sample current, reaching 93% of short sample current at 1.9 K. The preload was then released to 60%, still showing ability to operate in the range of 80-85% of short sample current as required by HL-LHC project. With this lower preload, the ability of going above 90% of short sample was lost, and a significant training appeared above 85%. When the preload was restored to the original 80% value, the magnet reached with few quenches 95% of short sample (13.4 T peak field). Magnetic measurements confirm the larger movement of the coil in the case with lower preload, and agree with finite element simulations.

The High Luminosity Large Hadron Collider (HL-LHC) is the new flagship project of CERN. First endorsed in 2013 and approved in 2016, HL-LHC is an upgrade of the accelerator aiming to increase by a factor of ten the statistics of the LHC collisions at the horizon of 2035–2040. HL-LHC relies on cutting edge technologies: among them, large aperture superconducting magnets will replace the present hardware to allow a smaller beam size in two interaction points (IPs). The project involves the construction of about 150 magnets of six different types: the quadrupole triplet, two main dipoles and three orbit correctors. The triplet, manufactured at CERN and in the USA, will consist of 30 magnets based on Nb 3 Sn technology, with an operational peak field of 11.4 T. These will be the first quadrupole Nb 3 Sn magnets installed in a particle accelerator. The other five types of magnets, all relying on Nb–Ti technology, present non-trivial challenges in the design and construction; they will be manufactured as part of in-kind contribution under the responsibility of institutes in Japan, China, Spain, and Italy. The project is now in the phase of transition between qualification through short models and prototypes and the beginning of the series construction. In this paper we review the magnet requirements, the reasons for selecting the design, the technological challenges with respect to previous projects, and we summarize the steps that have been taken to validate the baseline.

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). With a nominal operating gradient of 132.2 T/m in a 150 mm aperture and a conductor peak field of 11.3 T, the new quadrupole magnets are based on Nb3Sn superconducting technology. After a series of short models constructed in close collaboration by LARP (LHC Accelerator Research Program) and CERN, the development program is entering in the series production phase with CERN on one side and the US Accelerator Upgrade Project (US-AUP) on the other side assembling and testing full-length magnets. This paper describes the status of the development activities at CERN, in particular on the cold powering test of the first MQFXB prototype and on the construction of the second full scale prototype. Critical operations such as reaction heat treatment, coil impregnation and magnet assembly are discussed. Finally, the plan towards the series production is described.

The hadron collider proposed by the Future Circular Collider (FCC) study would require high-field superconducting magnets capable of producing a dipole field of around 16 T in a 50 mm aperture. To develop a suitable conductor for these magnets, CERN is coordinating a conductor development programme aiming to obtain Nb3Sn wire with a non-copper critical current density of 1500 A mm−2 at 16 T and 4.2 K, in lengths suitable for manufacturing 14 m long magnets, and able to withstand cabling without significant degradation. Here we report the superconducting characterisation and quantitative microscopy of recently-developed Nb3Sn wires with novel layouts and compositions, and evaluate their suitability for Rutherford cabling based on cabling trials and rolling studies. An analysis of the influence of wire layout, materials and mechanical characteristics on cabling performance is presented, to support recommendations for future wire designs.

The Superconducting Link (SC-Link) being developed at CERN in the context of the LHC High-Luminosity upgrade (HL-LHC) will supply the current to superconducting magnets of the HL-LHC Inner Triplets and Matching Sections. The SC-Link consists of MgB2 high-current cables, and it includes high temperature superconducting REBCO cables making the electrical transition between the MgB2 and the current leads. Electrical protection of superconducting devices made of REBCO against unexpected quenches is challenging especially when operation is at high current density. Adequate electrical protection of REBCO cables is crucial to insure good performance of the circuit over the lifetime of the machine; protection relies on the detailed knowledge of the quench propagation velocity. In this paper we reviewed the electromagnetic properties of REBCO tapes procured for prototype work. We measured the splice resistance (R-S) of the REBCO conductors and found a significant variation among the different batches of conductor. The normal zone propagation velocity (NZPV) was reported to be affected by the interfacial resistance which is governing the splice resistance: increasing the interfacial resistance enhances the NZPV. In order to determinate the influence of the internal resistance on the quench behaviour of the tapes, we investigated the normal zone propagation velocity of the epoxy-impregnated tapes at 77 K in self-field and 4.2 K in field up to 7 T in the FRESCA test station. We found that despite the R-S variation observed (up to factor 4), the tapes show similar NZPV at both temperatures. In addition we observed a significant field dependence of the NZPV of the tapes at 4.2 K. The results are compared to numerical simulation and discussed.

Presents corrections to author information for the above named paper.

Among the components to be upgraded in LHC interaction regions for the HiLumi-LHC projects are the inner triplet (or low-β) quadrupole magnets, denoted as Q1, Q2a, Q2b, and Q3. The new quadrupole magnets, called MQXF, are based on Nb3Sn superconducting magnet technology and operate at a gradient of 132.6 T/m, with a conductor peak field of 11.4 T. Q1 and Q3 are composed of magnets (called MQXFA) fabricated by the U.S. Accelerator Upgrade Project (AUP), with a magnetic length of 4.2 m. Q2a and Q2b consist of magnets (called MQXFB) fabricated by CERN, with a magnetic length of 7.15 m. After a series of short models, constructed in close collaboration by the US and CERN, the development program is now entering in the prototyping phase, with CERN on one side and BNL, FNAL, and LBNL on the other side assembling and testing their first long magnets We provide in this paper a description of the status of the MQXF program, with a summary of the short model test results, including quench performance, and mechanics, and an update on the fabrication, assembly, and test of the long prototypes.