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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 prototype phase has been successfully completed. The production is well advanced for the superferric correctors, and is starting for the canted cosine 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.

Under the U.S. High Luminosity LHC Accelerator Upgrade Project (HL-LHC AUP), the 150 mm bore, high-field Nb3Sn low-β MQXFA quadrupole magnets are being fabricated, assembled and tested, in the context of the CERN Hi-Luminosity LHC (HL-LHC) upgrade. These magnets have 4.2 m magnetic length and 4.56 m long iron yoke. To date, eight MQXFA magnets have been tested. One of the magnets additionally underwent a successful endurance test with 40 triggered quenches, and two magnets did not perform as expected. This work summarizes for the first time the available strain gauge data from eight identical Nb3Sn MQXFA tested magnets, focusing on the endurance test, and on a possible cause of underperformance of the two magnets that did not pass the vertical test. We applied methods to prevent this from happening in future MQXFA magnets, which shown to be effective for last two tested magnets. Under the U.S. High Luminosity LHC Accelerator Upgrade Project (HL-LHC AUP), the 150 mm bore, high-field Nb3Sn low-{̱e̱ṯa̱}̱ MQXFA quadrupole magnets are being fabricated, assembled and tested, in the context of the CERN Hi-Luminosity LHC (HL-LHC) upgrade. These magnets have 4.2 m magnetic length and 4.56 m long iron yoke. To date, eight MQXFA magnets have been tested. One of the magnets additionally underwent a successful endurance test with 40 triggered quenches, and two magnets did not perform as expected. This work summarizes for the first time the available strain gauge data from eight identical Nb3Sn MQXFA tested magnets, focusing on the endurance test, and on a possible cause of underperformance of the two magnets that did not pass the vertical test. We applied methods to prevent this from happening in future MQXFA magnets, which shown to be effective for last two tested magnets.

Fermi National Accelerator Laboratory (FNAL) and Lawrence Berkeley National Laboratory (LBNL) are building a new High Field Vertical Magnet Test Facility (HFVMTF) for testing superconducting cables in high magnetic field. The background magnetic field of 15 T in the HFVMTF will be produced by a magnet provided by LBNL. The HFVMTF is jointly funded by the US DOE Offices of Science, High Energy Physics (HEP), and Fusion Energy Sciences (FES), and will serve as a superconducting cable test facility in high magnetic fields and a wide range of temperatures for HEP and FES communities. This facility will also be used to test high-field superconducting magnet models and demonstrators, including hybrid magnets, produced by the US Magnet Development Program (MDP). The paper describes the status of the facility, including construction, cryostat designs, top and lambda plates, and systems for powering, and quench protection and monitoring.

In 2008, Michigan State University was selected to establish the Facility for Rare Isotope Beams (FRIB). Construction of the FRIB accelerator was completed in January 2022. Phased accelerator commissioning with heavy ion beams started in 2017 with the normal-conducting ion source and radio-frequency quadrupole. In April 2021, the full FRIB driver linear accelerator (linac) was commissioned, with heavy ion beams accelerated to energies above 200 MeV/nucleon by 324 superconducting radiofrequency (SRF) resonators operating at 2 K and 4 K with liquid-helium cooling. In preparation for high-power operation, a liquid lithium charge stripper was commissioned with heavy ion beams up to uranium-238, followed by the simultaneous acceleration of multiple-charge-state heavy ion beams to energies above 200 MeV/nucleon. In December 2021, selenium-84 was produced with the FRIB target using a krypton-86 primary beam, demonstrating FRIB’s capability for scientific discovery.

Distributed temperature sensing is the preferred approach for detecting and localizing normal zones in the high-field magnets of particle accelerators and fusion energy systems based on high-temperature superconductors. Optical fibers show promise in realizing this approach but suffer from known drawbacks, such as fiber fragility and cross-sensitivity to strain. Guided acoustic wave-based thermometry is a viable alternative to fiber optics; however, its application is currently limited by the leaky nature of wave propagation in acoustic waveguides. We propose the novel concept of a cladded acoustic waveguide in which, due to the elimination of the adhesion between the core and cladding, propagation of longitudinal acoustic excitations is sustained over long distances without leaking wave energy to the environment. These acoustic fibers can be structurally integrated into superconducting magnets and enable the distributed detection of local heating via thermally driven variations in the sound velocity. We present the practical design of acoustic fibers and the results of the experimental detection and localization of heat sources using our technique under ambient and cryogenic conditions. The prospects of using this technique for superconducting magnet quench diagnostics are discussed.

European Strategy Update | Laboratory Directors Group Editor: Nicolas Mounet The 2020 update of the European Strategy for Particle Physics emphasised the importance of an intensified and well-coordinated programme of accelerator R&D, supporting the design and delivery of future particle accelerators in a timely, affordable and sustainable way. This report sets out a roadmap for European accelerator R&D for the next five to ten years, covering five topical areas identified in the Strategy update. The R&D objectives include: improvement of the performance and cost-performance of magnet and radio frequency acceleration systems; investigations of the potential of laser/plasma acceleration and energy-recovery linac techniques; and development of new concepts for muon beams and muon colliders. The goal of the roadmap is to document the collective view of the field on the next steps for the R&D programme, and to provide the evidence base to support subsequent decisions on prioritisation, resourcing and implementation.

The Muon Ionization Cooling Experiment (MICE) will perform a detailed study of ionization cooling to evaluate the feasibility of the technique. To carry out this program, MICE requires an efficient particle-identification (PID) system to identify muons. The Electron-Muon Ranger (EMR) is a fully-active tracking-calorimeter that forms part of the PID system and tags muons that traverse the cooling channel without decaying. The detector is capable of identifying electrons with an efficiency of 98.6%, providing a purity for the MICE beam that exceeds 99.8%. The EMR also proved to be a powerful tool for the reconstruction of muon momenta in the range 100-280 MeV/$c$., 22 pages, 19 figures

A superconducting dipole, designed for use as a sweeper magnet for nuclear physics experiments, is being constructed by the NHMFL for operation at the NSCL. The magnet operates at a peak mid-plane field of 3.8 T in a 140 mm gap. A multi-particle beam enters the magnet from the upstream side. The neutrons continue straight through to a neutron detector. The charged particles are swept 43 degrees on a one meter radius into a mass spectrometer. Extensive model-based computer analysis (MBA) have been applied for optimizing the coils and the stainless steel bobbin with regard to its shape while keeping the strain and the fraction of actual to critical current within reasonable limits. The structural FEM analysis had to address a variety of complex physical phenomena (composites with orthotropic material properties, cool down, surface-to-surface contacts, etc.) and the loads due to operation (Lorentz forces) had to be obtained from a parallel/coupled magnetic field analysis. One of the challenges magnet designers face in optimizing magnet systems is that the detail required to obtain reasonable accuracy is not well known. This paper presents results of the structural design optimization for the sweeper project and evaluates the adequacy of alternative modeling approaches. Also the final magnetic design of the system is summarized and progress toward fabrication is presented.

The muon collider is a new idea for lepton colliders. The ultimate energy of an electron ring is limited by synchrotron radiation. Muons, which have a rest mass that is 200 times that of an electron can be stores at much higher energies before synchrotron radiation limits ring performance. The problem with muons is their short life time (2.1 /spl mu/s at rest). In order to operate a muon storage ring large numbers of muons must be collected, cooled and accelerated before they decay to an electron and two neutrinos. As we see it now, high field superconducting solenoids are an integral part of a muon collider muon production and cooling systems. This report will describe the design parameters for superconducting and hybrid solenoids that are used for pion production and collection, RF phase rotations of the pions as they decay into muons and the muon cooling (reduction of the muon emittance) before acceleration.

The problem of optimizing the design of magnet systems to simultaneously satisfy a set of constraint equations for field, geometry, protection, and stability while minimizing the total system cost is considered. A mathematical description of the problem is given, along with details concerning possible constraint algorithms and cost functions. Rules for the optimal selection of magnet technology (potted, ventilated, and cable-in-conduit coils) are presented. The resulting sets of equations can be solved by different numerical methods; the final choice is based on considerations of functional form as well as computational speed and accuracy. Depending on the choice of constraint equations, the resulting problem may or may not be smooth, and may or may not admit multiple minima. The choice of minimization algorithm can be tailored to the situation at hand to yield optimal performance. We present results pertaining to an alternating-field solenoid system being considered by the MuCool collaboration. The system design requires consideration of field profile, magnet stability, magnet structure, and protection, as well as total cost. A key application of the optimization code is the analysis of cost trade-off with respect to the imposed constraints, and examples are given in the alternating-solenoid case.

The Muon-Electron Conversion experiment, to be built at Brookhaven National Laboratory, requires a complex set of solenoids to generate the required field profile. Field magnitude, gradient and oscillations must all be controlled along the /spl sim/27 meter curved beamline to allow for optimal capture of /spl pi/ and /spl mu/ particles, the sign and momentum selection of appropriate /spl mu/ particles, and their transport to the detector region. The solenoid system is designed to yield the required field profile in an efficient and cost-effective manner. A critical concern is the removal of field gradient reversals along the beamline. The system is decomposed into a large number of simple solenoids of equal current density, whose dimensions vary so as to obtain the required field contribution. Analysis of the field influence of cosmic ray shielding is provided, along with the field footprint of the entire system. Structural aspects are discussed, in particular relating to magnetic forces and cryostat requirements.

The design of multi-coil resistive magnets can be greatly improved by optimizing the numerous variables involved. We have developed a code that optimizes the design for maximum field. Maximum magnetic field at the center (the objective function) is sought under numerous geometric and mechanical constraints. We apply the penalty method to reduce the constrained problem to a sequence of unconstrained optimizations. The objective function and the majority of the constraints are nonlinear. The BFGS quasi-Newton method is used at the core of the optimization procedure. We give the mathematical problem formulation and describe the code implementation. The method is shown to be easily modified to account for new constraints. Examples of code results and typical nonlinear behavior of the function being minimized are shown.

An upgrade of the Advanced Light Source (ALS) to enable top‐off operation has been completed during the last four years. The final work centered around radiation safety aspects, culminating in a systematic proof that top‐off operation is equally safe as decaying beam operation. Commissioning and transition to full user operations happened in late 2008 and early 2009. Top‐off operation at the ALS provides a very large increase in time‐averaged brightness (by about a factor of 10) as well as improvements in beam stability. The following sections provide an overview of the radiation safety rationale, commissioning results, as well as experience in user operations.

Superconducting undulator (SCU) technology has the potential to significantly enhance the performance of synchrotron radiation sources for storage ring and FEL applications. Since 2002, our team at Lawrence Berkeley National Laboratory has been performing R&D on superconducting undulators, including the fabrication of three Nb3Sn prototypes. We have demonstrated experimentally the possibility to provide the prototype with trim coils that could be used for phase error correction. The research effort that we report here demonstrates the possibility to add degrees of freedom to the field correction provided by these coils in a cryogenic environment. By means of bridge of superconducting switches, we can modify the current direction through a trim coil. Here we describe the design of the experimental bridge we fabricated, the results we obtained and finally the generalized concept one could plan to apply to correct the phase errors with trim coils connected to a network of superconducting bridges.

The concepts and technical challenges related to developing a fourth generation electron cyclotron resonance (ECR) ion source with a rf frequency greater than 40 GHz and magnetic confinement fields greater than twice B(ECR) will be explored in this article. Based on the semiempirical frequency scaling of ECR plasma density with the square of operating frequency, there should be significant gains in performance over current third generation ECR ion sources, which operate at rf frequencies between 20 and 30 GHz. While the third generation ECR ion sources use NbTi superconducting solenoid and sextupole coils, the new sources will need to use different superconducting materials, such as Nb(3)Sn, to reach the required magnetic confinement, which scales linearly with rf frequency. Additional technical challenges include increased bremsstrahlung production, which may increase faster than the plasma density, bremsstrahlung heating of the cold mass, and the availability of high power continuous wave microwave sources at these frequencies. With each generation of ECR ion sources, there are new challenges to be mastered, but the potential for higher performance and reduced cost of the associated accelerator continues to make this a promising avenue for development.

Heat load on beamline optics is a serious obstacle for devices designed to generate pure linearly polarized photons in third generation synchrotron radiation facilities. For permanent magnet undulators, this problem can be overcome by implementing a figure-eight design configuration. As yet there has been no good method to tackle this problem for electromagnetic elliptical undulators. Here, a novel design and operational mode is suggested, which can generate pure linearly polarized photons with very low on-axis heat load. Additionally, the minimum photon energy capability of linearly polarized photons can be significantly extended by this method.

This report describes some solenoid design work done for the cooling experiment for the muon collider collaboration. This report describes an analysis section of superconducting solenoids that have a center line induction of 3.0 T. The section is bent in the shape of an S. Each bend in the S bends the muon beam one radian (57.3 degrees). The warm bore diameter of the solenoid bent solenoid is 300 to 320 mm. The radius of the bend at the solenoid center line is 1000 mm. This report shows the results of three dimensional field calculations and presents a solenoid design that will include four TPC detectors that are 240 mm in diameter and 550 mm long as well as a 1300 mm long section of 1300 MHz RF cavities. The TPC sections need a solenoid warm bore diameter of about 300 320 mm while RF cavities require a warm bore diameter of 440 mm. The superconducting solenoid design must take into account the varying warm bore diameter requirements for the magnet string yet meet the stringent solenoidal field uniformity requirements within the active volume of the four TPCs.

The cooling channel for a neutrino factory consists of a series of alternating field solenoidal cells. The first section of the bunching cooling channel consists of 41 cells that are 2.75-m long. The second section of the cooling channel consists of 44 cells that are 1.65-m long. Each cell consists of a single large solenoid with an average diameter of 1.5 m and a pair of flux reversal solenoids that have an average diameter of 0.7 to 0.9 meters. The magnetic induction on axis reaches a peak value of about 5 T at the end of the second section of the cooling channel. The peak on axis field gradients in flux reversal section approaches 33 T/m. This report describes the two types of superconducting solenoid magnet sections for the muon-cooling channel of the proposed neutrino factory.

The proposed neutrino factory will produce a defined beam of neutrinos from the decay of muons in a storage ring [1,2,3]. The storage ring will be oriented so that the neutrinos can be detected at one or more detectors several thousand kilometers from the storage ring. This report presents an overview of the proposed neutrino factory and its subsystems that use cryogenics. Superconducting magnets will be used in the following ways in the neutrino factory; 1) the outsert solenoid for the 20 T pion capture system, 2) the decay channel where pions decay to muons, 3) the muon phase rotation system, 4) the muon cooling system, 5) focusing during the first stage of muon acceleration, 6) bending and focusing magnets in the re-circulating linac accelerator and 7) bending and focusing magnets in the muon storage ring where the neutrino beams are generated. Low temperature superconducting RF cavities will be used to accelerate the muons from about 200 MeV to 20 GeV. The muon cooling system uses liquid hydrogen abso...

It is pointed out that the optimum current density distribution for stress-limited, high-field, high-power magnets can be approached by magnets built up of many thin coils, to maximize their efficiency ('tesla per watt'). By optimizing the radial thickness and height of each subcoil, magnets consisting of only 8 Bitter coils can closely approximate the optimum. For instance with 24 MW such a magnet of inner and outer radii of 28 mm and 420 mm, respectively, could generate over 30 T. The authors therefore propose a new method of magnet construction, the Poly-Bitter magnet. >

Author(s): Caspi, S; Ferracin, P; Prestemon, S | Abstract: CHATS-AS workshop has been organized to discuss applied superconductivity at the Lawrence Berkeley National Laboratory (LBNL), Berkeley, USA, on September 5-7, 2006. The workshop provided an ongoing opportunity to discuss and advance the science of simulations and modeling specifically applied to superconducting magnets. CHATS-AS 2006 has contributed to the development and refinement of models used to study the stability of superconductors, simulate quench propagation, and perform structural analysis of superconducting magnets. A number of presentations provided significant advances in measuring and modeling current sharing and contact resistances between superconducting strands in CHATS-AS workshops. The workshop included both LTS and HTS applications, extending the LTS experience in modeling superconducting devices to the realm of HTS applications.