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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.

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.

The production of superconducting magnets for particle accelerators involves high-precision assemblies and tight tolerances, in order to achieve the requirements for their appropriate performance. It is therefore essential to have a strict control and traceability over the geometry of each component of the system, and also to be able to compensate possible inherent deviations coming from the production process. The objective of this paper is to present the experience from systematic geometrical measurements performed during the ongoing production of model magnets for the high luminosity–Large Hadron Collider upgrade. First, the methodology for the data acquisition and its ulterior analysis is described. Then, the results obtained in terms of coil geometry are explained with the goal of identifying the principal factors causing systematic and unexpected dimensional deviations. Finally, the integrated effect of assembly operations, cool down, and powering of the magnet is investigated looking at measurements before and after cold tests.

The future circular collider or FCC is a study aimed at exploring the possibility to reach 100 TeV total collision energy that would require 16 T dipoles. Upon the conclusion of the high luminosity upgrade, the US LHC accelerator upgrade project in collaboration with CERN will have an extensive Nb3Sn magnet fabrication experience. This experience includes robust Nb3Sn conductor and insulation scheming, 2-layer cos 2θ coil fabrication, and bladder-and-key structure and assembly. By making improvements and modification to existing technology, the feasibility of a two-layer 16 T dipole is investigated. Preliminary designs indicate that fields up to 16.6 T are feasible with conductor grading while satisfying the HE-LHC and FCC specifications. Key challenges include accommodating high-aspect ratio conductor, narrow wedge design, Nb3Sn conductor grading, and especially quench protection of a 16 T device.

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.

Author(s): Wang, X; Ambrosio, G; Chlachidze, G; DiMarco, J; Ghosh, AK; Holik, EF; Prestemon, SO; Sabbi, G; Stoynev, SE | Abstract: The U.S. large hadron collider (LHC) Accelerator Research Program, in close collaboration with The European Organization for Nuclear Research (CERN), has developed three generations of high-gradient quadrupole (HQ) Nb3Sn model magnets, to support the development of the 150 mm aperture Nb3Sn quadrupole magnets for the high-luminosity LHC. The latest generation, HQ03, featured coils with better uniformity of coil dimensions and properties than the earlier generations. The HQ03 magnet was tested at fermi national accelerator laboratory (FNAL), including the field quality study. The profiles of low-order harmonics along the magnet aperture observed at 15 kA, 1.9 K can be traced back to the assembled coil pack before the magnet assembly. Based on the measured harmonics in the magnet center region, the coil block positioning tolerance was analyzed and compared with earlier HQ01 and HQ02 magnets to correlate with coil and magnet fabrication. To study the capability of correcting the low-order nonallowed field errors, magnetic shims were installed in HQ03. The expected shim contribution agreed well with the calculation. For the persistent-current effect, the measured a4 can be related to 4% higher in the strand magnetization of one coil with respect to the other three coils. Finally, we compare the field errors due to the interstrand coupling currents between HQ03 and HQ02.

Author(s): Holik, EF; Ambrosio, G; Carbonara, A; Dietderich, DR; Dimarco, J; Pong, I; Sabbi, GL; Santini, C; Schmalzle, J; Wang, X | Abstract: The U.S. LHC Accelerator Research Program (LARP) quadrupole HQ02 was designed and fully tested as part of the low-beta quad development for Hi-Lumi LHC. HQ02's design is well documented with full fabrication accounting along with full field analysis at low and high current. With this history, HQ02 is an excellent test bed for developing a methodology for measuring turn locations from magnet cross sections and comparing with CAD models and measured field. All four coils of HQ02 were cut in identical locations along the magnetic length corresponding to magnetic field measurement and coil metrology. A real-time camera and coordinate measuring equipment was used to plot turn corners. Measurements include systematic and random displacements of winding blocks and individual turns along the magnetic length. The range of cable shifts and the field harmonic range along the length are in agreement, although correlating turn locations and measured harmonics in each cross section is challenging.

The High Luminosity (HiLumi) Large Hadron Collider (LHC) project has, as the main objective, to increase the LHC peak luminosity by a factor five and the integrated luminosity by a factor ten. This goal will be achieved mainly with a new interaction region layout, which will allow a stronger focusing of the colliding beams. The target will be to reduce the beam size in the interaction points by a factor of two, which requires doubling the aperture of the low-β (or inner triplet) quadrupole magnets. The use of Nb3Sn superconducting material and, as a result, the possibility of operating at magnetic field levels in the windings higher than 11 T will limit the increase in length of these quadrupoles, called MQXF, to acceptable levels. After the initial design phase, where the key parameters were chosen and the magnet's conceptual design finalized, the MQXF project, a joint effort between the U.S. LHC Accelerator Research Program and the Conseil Europeen pour la Recherche Nucleaire (CERN), has now entered the construction and test phase of the short models. Concurrently, the preparation for the development of the full-length prototypes has been initiated. This paper will provide an overview of the project status, describing and reporting on the performance of the superconducting material, the lessons learnt during the fabrication of superconducting coils and support structure, and the fine tuning of the magnet design in view of the start of the prototyping phase.

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 a 150 mm aperture Nb$_{3}$Sn quadrupole for the LHC interaction regions. A first series of 1.5 m long coils were fabricated and assembled in a first short model. A detailed visual inspection of the coils was carried out to investigate cable dimensional changes during heat treatment and the position of the windings in the coil straight section and in the end region. The analyses allow identifying a set of design changes which, combined with a fine tune of the cable geometry and a field quality optimization, were implemented in a new, second-generation, coil design. In this paper we review the main characteristics of the first generation coils, describe the modification in coil lay-out, and discuss their impact on parts design and magnet analysis. As part of the Large Hadron Collider (LHC) Luminosity upgrade program, the U.S.-LHC Accelerator Research Program collaboration and CERN are working together to design and build a 150-mm aperture Nb_3Sn quadrupole for the LHC interaction regions. A first series of 1.5-m-long coils was fabricated and assembled in a first short model. A detailed visual inspection of the coils was carried out to investigate cable dimensional changes during heat treatment and the position of the windings in the coil straight section and in the end region. The analyses allow identifying a set of design changes which, combined with a fine tune of the cable geometry and a field quality optimization, were implemented in a new second-generation coil design. In this paper, we review the main characteristics of the first generation coils, describe the modification in coil layout and discuss their impact on parts design and magnet analysis.

The U.S. LHC Accelerator Research Program (LARP) and CERN combined their efforts in developing Nb3Sn magnets for the high-luminosity LHC upgrade. The ultimate goal of this collaboration is to fabricate large aperture Nb 3Sn quadrupoles for the LHC interaction regions. These magnets will replace the present 70-mm-aperture NbTi quadrupole triplets for expected increase of the LHC peak luminosity up to 5 × 1034 cm –2s–1 or more. Over the past decade, LARP successfully fabricated and tested short and long models of 90 and 120-mm-aperture Nb3Sn quadrupoles. Recently, the first short model of 150-mm-diameter quadrupole MQXFS was built with coils fabricated both by LARP and CERN. The magnet performance was tested at Fermilab's vertical magnet test facility. This paper reports the test results, including the quench training at 1.9 K, ramp rate and temperature dependence, as well as protection heater studies.

Author(s): DiMarco, J; Ambrosio, G; Chlachidze, G; Ferracin, P; Holik, E; Sabbi, G; Stoynev, S; Strauss, T; Sylvester, C; Tartaglia, M; Todesco, E; Velev, G; Wang, X | Abstract: The U.S. LHC Accelerator Research Program (LARP) and CERN are developing high-gradient Nb3Sn magnets for the high luminosity LHC interaction regions. Magnetic measurements of the first 1.5-m long, 150-mm aperture model quadrupole, MQXFS1, were performed during magnet assembly at LBNL, as well as during cryogenic testing at Fermilab's Vertical Magnet Test Facility. This paper reports on the results of these magnetic characterization measurements, as well as on the performance of new probes developed for the tests.

The US LHC Accelerator Research Program is constructing prototype interaction region quadrupoles as part of the US in-kind contribution to the Hi-Lumi LHC project. The low-beta MQXFA Q1/Q3 coils have a 4-m length and a 150 mm bore. The design is first validated on short, one meter models (MQXFS) developed as part of the longstanding Nb$_{3}$Sn quadrupole R&D; by LARP in collaboration with CERN. In parallel, facilities and tooling are being developed and refined at BNL, LBNL, and FNAL to enable long coil production, assembly, and cold testing. Long length scale-up is based on the experience from the LARP 90 mm aperture (TQ-LQ) and 120 mm aperture (HQ and Long HQ) programs. A 4-m long MQXF practice coil was fabricated, water jet cut and analyzed to verify procedures, parts, and tooling. In parallel, the first complete prototype coil (QXFP01a) was fabricated and assembled in a long magnetic mirror, MQXFPM1, to provide early feedback on coil design and fabrication following the successful experience of previous LARP mirror tests.

In high field magnet applications, Nb$_{3}$Sn coils undergo a heat treatment step after winding. During this stage, coils radially expand and longitudinally contract due to the Nb$_{3}$Sn phase change. In order to prevent residual strain from altering superconducting performances, the tooling must provide the adequate space for these dimensional changes. The aim of this paper is to understand the behavior of cable dimensions during heat treatment and to provide estimates of the space to be accommodated in the tooling for coil expansion and contraction. This paper summarizes measurements of dimensional changes on strands, single Rutherford cables, cable stacks, and coils performed between 2013 and 2015. These samples and coils have been performed within a collaboration between CERN and the U.S. LHC Accelerator Research Program to develop Nb$_{3}$Sn quadrupole magnets for the HiLumi LHC. The results are also compared with other high field magnet projects. In high field magnet applications, Nb_3Sn coils undergo a heat treatment step after winding. During this stage, coils radially expand and longitudinally contract due to the Nb_3Sn phase change. In order to prevent residual strain from altering superconducting performances, the tooling must provide the adequate space for these dimensional changes. The aim of this paper is to understand the behavior of cable dimensions during heat treatment and to provide estimates of the space to be accommodated in the tooling for coil expansion and contraction. This paper summarizes measurements of dimensional changes on strands, single Rutherford cables, cable stacks, and coils performed between 2013 and 2015. These samples and coils have been performed within a collaboration between CERN and the U.S. LHC Accelerator Research Program to develop Nb_3Sn quadrupole magnets for the HiLumi LHC. The results are also compared with other high field magnet projects.

The U.S. LHC Accelerator Research Program (LARP) and CERN are combining efforts for the HiLumi-LHC upgrade to design and fabricate 150-mm-aperture, interaction region quadrupoles with a nominal gradient of 130 T/m using Nb3Sn. To successfully produce the necessary long MQXF triplets, the HiLumi-LHC collaboration is systematically reducing risk and design modification by heavily relying upon the experience gained from the successful 120-mm-aperture LARP HQ program. First generation MQXF short (MQXFS) coils were predominately a scaling up of the HQ quadrupole design allowing comparable cable expansion during Nb3Sn formation heat treatment and increased insulation fraction for electrical robustness. A total of 13 first generation MQXFS coils were fabricated between LARP and CERN. Systematic differences in coil size, coil alignment symmetry, and coil length contraction during heat treatment are observed and likely due to slight variances in tooling and insulation/cable systems. Analysis of coil cross sections indicate that field-shaping wedges and adjacent coil turns are systematically displaced from the nominal location and the cable is expanding less than nominally designed. Lastly, a second generation MQXF coil design seeks to correct the expansion and displacement discrepancies by increasing insulation and adding adjustable shims at the coil pole and midplanes to correct allowed magneticmore » field harmonics.« less