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As a part of a collaborative effort with CERN on the long road to FCC-hh, CEA is developing a 1.4 m-long single aperture short dipole demonstrator. This Nb3Sn block dipole, named F2D2, is foreseen to produce 15.5 T with a 14% margin at 1.9 K, and will use a shell-based support structure. In order to be compact, this magnet relies on the use of different cable grades in each coil. Among the milestones in this project, a single-layer graded racetrack dipole will be constructed in order to demonstrate grading in a simplified geometry while preserving key features of F2D2. This magnet, named Research Racetrack Dipole Demonstrator (R2D2), will permit the mastering of the fabrication methods foreseen for F2D2 and to confirm the behavior of Nb3Sn cables representative of FCC. It should also validate some key technological aspects: compactness, operation at high-current (up to 16 kA), intermediate magnetic field (in the range of 11-12 T), and quench protection at very high energy/unit length (up to 650 kJ/m, corresponding to 168 MJ/m3).

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.

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.

F2D2, the FCC Flared-ends Dipole Demonstrator, is a 15 T single-aperture short model being developed within a collaboration between CEA Paris-Saclay and CERN. The design phase is ongoing at CEA; the magnet will be fabricated at CEA and then tested at CERN. The 2D magnetic and mechanical designs have been optimized previously and allowed defining the operating points and the required structural components. This paper reports on the preliminary design phase, focused on 3D mechanical optimizations of coils and structure. F2D2 will be the first Nb3Sn block-coil magnet using two cable grades. The cables will be spliced outside of the magnet, which represents one of the most complex design feature, and requires a special focus on the magnet ends. To do so, the design of the magnet has been performed using a CAD (Computer Aided Design) and both magnetic and mechanical 3D FEM (Finite-Elements Models). The CAD defines precisely the complex coil-ends shape that allows positioning the layer jumps and routing the cable exits. The FEM are used to optimize the longitudinal pre-load system in order to contain the large Lorentz forces during operation. The magnet is pre-loaded transversally with bladders and keys and with an external Al shell; and longitudinally with Al tie-rods and end-plates. The pre-load levels are computed to operate the magnet under sufficient compression, while minimizing the stress in the coil and avoid degradation.

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 Nb3Sn technology, with an operational peak field of 11.4 T. These will be the first quadrupole Nb3Sn 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.

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.

International audience; In the framework of the Hi-Lumi LHC Project, CERN and U.S. LARP are jointly developing MQXF, a 150-mm aperture high-field Nb3Sn quadrupole for the upgrade of the inner triplet of the low-beta interaction regions. The magnet is supported by a shell-based structure, providing the preload by means of bladder-key technology and differential thermal contraction of the various components. Two short models have been produced using the same cross section currently considered for the final magnet. The structures were preliminarily tested replacing the superconducting coils with blocks of aluminum. This procedure allows for model validation and calibration, and also to set performance goals for the real magnet. Strain gauges were used to monitor the behavior of the structure during assembly, cool down and also excitation in the case of the magnets. The various structures differ for the shell partitioning strategies adopted and for the presence of thick or thin laminations. This paper presents the results obtained and discusses the mechanical performance of all the short models produced up to now.

© 2015 IEEE. In preparation for the high-luminosity upgrade of the Large Hadron Collider (LHC), the LHC Accelerator Research Program (LARP) in collaboration with CERN is pursuing the development of MQXF: a 150-mm-aperture high-field Nb3Sn quadrupole magnet. The development phase starts with the fabrication and test of several short models (1.2-m magnetic length) and will continue with the development of several long prototypes. All of them are mechanically supported using a shell-based support structure, which has been extensively demonstrated on several RD models within LARP. The first short model MQXFS-AT has been assembled at LBNL with coils fabricated by LARP and CERN. In this paper, we summarize the assembly process and show how it relies strongly on experience acquired during the LARP 120-mm-aperture HQ magnet series. We present comparison between strain gauges data and finite-element model analysis. Finally, we present the implication of the MQXFS-AT experience on the design of the long prototype support structure.

The U.S. LHC Accelerator Research Program (LARP) has started the fabrication of 3.7-m long Nb$_3$Sn quadrupole models. The Long Quadrupoles (LQ) are ldquoProof-of-Principlerdquo magnets which are to demonstrate that Nb$_3$Sn technology is mature for use in high energy particle accelerators. Their design is based on the LARP Technological Quadrupole (TQ) models, developed at FNAL and LBNL, which have design gradients higher than 200 T/m and an aperture of 90 mm. The plans for the LQ R&D; and a design update are presented and discussed in this paper. The challenges of fabricating long accelerator-quality Nb$_3$Sn coils are presented together with the solutions adopted for the LQ coils (based on the TQ experience). During the fabrication and inspection of practice coils some problems were found and corrected. The fabrication at BNL and FNAL of the set of coils for the first Long Quadrupole is in progress.

The quench protection of the several meter long, large aperture high-field Nb3Sn quadrupoles that the LARP collaboration is developing for the LHC interaction region upgrade, requires efficient protection heaters to quickly generate large resistive segments across the windings. To support the protection design, experiments in the recently tested LARP R&D magnets are aimed to characterize the coil response to different protection schemes. In particular, the delay to quench and the final hotspot temperatures are evaluated after firing the heaters at different powering regimes and coverage. Also, the contribution of external energy extraction is investigated. Based on the performed studies and computer simulations, it seems that if the same protection efficiency per unit length that is measured in a 1 m long model magnet can be scaled to a 3.6 m long magnet, and the heater coverage can be improved, about 1 MJ/m of stored energy can be absorbed in the magnet after a quench. However, significant technology dev...