Herve Prin

During the Long Shutdown 3 of the LHC, scheduled to start in 2026, the interaction regions will be upgraded to increase the integrated luminosity by about one order of magnitude. Among the components to be replaced are the MBRD (Main Bending Recombination Dipole, also known as D2), which are double-aperture magnets providing aligned magnetic fields to steer the two beams into the ATLAS and CMS experiments and subsequently recombine them onto their nominal trajectories. To meet the demanding requirements of the High-Luminosity LHC, a new magnet design was developed by INFN-Genova, featuring a larger aperture, a higher operating field, and innovative solutions to mitigate the strong electromagnetic cross-talk between the apertures while ensuring mechanical integrity against the large repulsive Lorentz forces. The development program included the construction of a 1.6-m model, a full-length prototype, and six series magnets, of which four will be installed in the LHC and two kept as spares. Series production is ongoing at ASG Superconductors, and the first magnet has been successfully cold-tested at CERN. This contribution reports on the main challenges faced during series production and discusses the first test results.

At the heart of the High-Luminosity Project (HL-LHC) to upgrade the CERN Large Hadron Collider (LHC), new Nb$_{\text{3}}$Sn superconducting quadrupole magnets will be installed on each side of the ATLAS and CMS experiments. Half of these magnets are built by CERN and are called MQXFB. A total of 12 MQXFB magnets are being constructed for installation: two to be installed in the Inner Triplet (IT) String facility, for systems qualification; four to be installed in the LHC near ATLAS; four to be installed in the LHC near CMS, and two spare magnets. In the last two years, the first seven MQXFB magnets have been tested and qualified up to nominal current in nominal operating conditions. In this paper we present the tests and analyze the magnets’ performance, with emphasis on qualification, non-conformity detection, and reliability evaluation.

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

New high field and large-aperture quadrupole magnets for the low-beta inner triplets (Q1, Q2, Q3) have been built and tested as part of the high-luminosity upgrade of the Large Hadron Collider (HL-LHC). These new quadrupole magnets are based on Nb3Sn superconducting technology. The US Accelerator Upgrade Project (US-AUP) is producing the Q1 and Q3 Cryo-Assemblies: a pair of ∼ 5 m long magnet structures installed in a stainless-steel helium vessel (Cold Mass) and surrounded by cryostat shields, piping, and a vacuum vessel. This paper gives an overview of the design, production, and the results of the horizontal test of the first pre-series Q1/Q3 Cryo-Assembly.

In the framework of the HL-LHC project, CERN has the responsibility to develop, qualify and assemble three different types of cold masses, namely Q2 (final focus quadrupole in the triplet), CP (corrector package) and D2 (separation dipole). In this paper, we describe the various designs, which incorporate several novel features. For example, for the cold masses containing an MQXFB quadrupole – based on a bladder-and-key structure with aluminium cylinders – we proposed and qualified a longitudinal welding process that takes into account the developed length of the loaded magnet (measured with a laser tracker), the geometry of the stainless steel half shells of the liquid helium vessel, and the welding shrinkage, so to match the requirements of mechanical uncoupling in the transversal plane, while introducing a sound fixed point in the longitudinal direction. In the case of the D2 cold mass, we introduced an orbital welded joint between two half units, with on one side the main recombination dipole, and on the other the dipole correctors, which comes with specific challenges for the relative alignment. Then, in the CP design we integrated a large number (nine) of high order correctors, together with a nested dipole corrector. We report as well on the special test cold mass developed to allow fast track cold testing of the MQXFB magnet in a standalone horizontal configuration, which was not in the initial baseline of the project. Besides detailing the various designs, the paper provides feedback from the manufacturing experience of the first units.

As a Japanese contribution to the High-Luminosity Large Hadron Collider (HL-LHC) upgrade, KEK is in charge of developing the beam separation dipole cold masses. The full-scale prototype magnet (MBXFP1) was constructed in Hitachi and powering test at cold was conducted at KEK. After the test, the magnet was returned to Hitachi for the final assembly of the cold mass. The pressure vessel design of the cold mass was carried out by KEK in accordance with ASME code. A new design of bus leads was proposed to satisfy the requirement of flexibility as well as mechanical support and electrical insulation. Welding of the extremity pipes was challenging due to tight position tolerance. This article reports the structure, pressure vessel design, and assembly of the LMBXF prototype cold mass (LMBXFP1) including bus work, instrumentation, and welding works with geometrical measurements.

The High Luminosity Large Hadron Collider (HL-LHC) is a major upgrade to the existing Large Hadron Collider (LHC) at CERN, aimed at increasing the integrated luminosity of the collider by a factor of ten [1]. A key component of the HL-LHC are the superconducting Nb3Sn quadrupole magnets, known as MQXF, whose purpose is to focus the particle beam [3]. In order to ensure the proper operation and structural reliability of the MQXF quadrupoles, it is essential to qualify the welds of their cold mass, used as a He container of the magnets. This paper describes the process of qualification of the welds involved in the closure of the cold mass, including the testing and inspection methods used to evaluate their strength and soundness. The results of the qualification process are used to ensure that the MQXF quadrupoles cold masses can withstand the high-stress operating conditions of the HL-LHC and operate as expected at cryogenic temperature. The qualification process has been used to implement a novel approach for quality control of the production parts using Phased Array Ultrasonic Testing (PAUT). This advanced testing method uses phased array ultrasonic probes to scan the welds and generate a detail 3D image of their internal structure. This allows for a more accurate and efficient inspection of the welds, compared to traditional ultrasonic testing methods. Overall, the welding qualification process for the cold mass of the MQXF quadrupoles is a crucial step in ensuring the safe and reliable operation of the HL-LHC.

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.

This article describes the design and development of a translating-coil magnetometer for the room-temperature magnetic measurements of the superferric, high-order corrector magnets for the high-luminosity upgrade of the Large Hadron Collider at CERN (HL-LHC). The measurement system consists of a set of induction coils, tangentially positioned on a measurement head. The translation of the measurement head yields an induced voltage proportional to the longitudinal field profiles of the magnets. In this way, it is possible to locate the longitudinal center and calculate the magnetic length. The measurements provide feedback to the assembly and fabrication processes. The metrological characterization of the induction-coil configurations is presented, and the measurement results are discussed in view of the target requirements of the HL-LHC project.