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HD3 is the latest magnet of a series of block-type Nb3Sn dipole model magnets developed by the Superconducting Magnet Program at Lawrence Berkeley National Laboratory. The magnet is 1 m long with a clear aperture of 43 mm. As a model magnet designed with accelerator-quality features, each coil has flared ends to provide a clear bore for a beam tube. The magnet design was also optimized to minimize the geometric and saturation field errors. In 2013, HD3b reached a peak dipole field of 13.4 T at 4.4 K. As part of the magnet test, we measured field quality using rotating coils with lengths of 26 and 130 mm developed by Fermi National Accelerator Laboratory. Here, we report and analyze the measured static and dynamic field errors. We discuss the insight provided by the field quality study of HD3, which can be useful for the development of high-field block-type dipole magnets for next-generation circular colliders.

The superconducting ECR source magnet for the Facility for Rare Isotope Beams at Michigan State University was designed and built by the Superconducting Magnet Group at Lawrence Berkeley National Laboratory (LBNL). The 28-GHz NbTi ion source magnet features a sextupole-in-solenoids configuration, which is comparable to the VENUS ECR magnet operated at LBNL. A shell-based support structure using bladders and keys has been incorporated into the design to allow for adjustments of the preload and reversibility of the magnet assembly process. The magnet has been assembled and successfully tested to operational currents at LBNL. This paper describes the basic design of the magnet and the passive quench protection system. The test results are also presented, including the quench behavior of the magnet, the training performance, and the magnetic measurement results.

The superconducting electron cyclotron resonance (ECR) source magnet for the facility for rare isotope beams at Michigan State University was designed and built by the Superconducting Magnet Group at Lawrence Berkeley National Laboratory (LBNL) in 2017. The 28 GHz NbTi ion source magnet features a sextupole-in-solenoids configuration which is comparable to the VENUS ECR magnet operated at LBNL. However, the mechanical design of this magnet utilizes a shell-based support structure which allows fine adjustments to the sextupole preload and reversibility of the magnet assembly process. The magnet has been assembled and tested to operational currents at LBNL. This paper describes the mechanical analyses performed to estimate the sextupole's and solenoids' preloads. We will report on the 3-D finite element analysis during room temperature assembly, cool-down, and magnet excitation, and then describe the magnet preload operations. Finally, we will describe the performance of the support structure during the quench training.

A future circular collider (FCC) with a center-of-mass energy of 100 TeV and a circumference of around 100 km, or an energy upgrade of the LHC (HE-LHC) to 27 TeV require bending magnets providing 16 T in a 50-mm aperture. Several development programs for these magnets, based on Nb3Sn technology, are being pursued in Europe and in the U.S. In these programs, cos-theta, block-type, common-coil, and canted-cos-theta magnets are explored; first model magnets are under manufacture; limits on conductor stress levels are studied; and a conductor with enhanced characteristics is developed. This paper summarizes and discusses the status, plans, and preliminary results of these programs.

The development of Nb3Sn quadrupole magnets for the High-Luminosity LHC upgrade is a joint venture between the US LHC Accelerator Research Program (LARP)∗ and CERN with the goal of fabricating large aperture quadrupoles for the LHC interaction regions (IR). The inner triplet (low-β) NbTi quadrupoles in the IR will be replaced by the stronger Nb3Sn magnets boosting the LHC program of having 10-fold increase in integrated luminosity after the foreseen upgrades. Previously, LARP conducted successful tests of short and long models with up to 120 mm aperture. The first short 150 mm aperture quadrupole model MQXFS1 was assembled with coils fabricated by both CERN and LARP. The magnet demonstrated a strong performance at Fermilab's vertical magnet test facility reaching the LHC operating limits. This paper reports the latest results from MQXFS1 tests with changed prestress levels. The overall magnet performance, including quench training and memory, ramp rate, and temperature dependence, is also summarized.

The LHC accelerator research program (LARP), in collaboration with CERN and under the scope of the high luminosity upgrade of the Large Hadron Collider, is in the prototyping stage in the development of a 150 mm aperture high-field Nb3Sn quadrupole magnet called MQXF. This magnet is mechanically supported using a shell-based support structure, which has been extensively demonstrated on several R&D models within LARP, as well as in the more recent short (1.2 m magnetic length) MQXF model program. The MQXFA magnets are each 4.2 m magnetic length, and the first mechanical long model, MQXFA1M (using aluminum surrogate coils), and MQXFAP1 prototype magnet (the first prototype with Nb3Sn coils) have been assembled at the LBNL. In this paper, we summarize the tooling and the assembly processes, and discuss the mechanical performance of these first two assemblies, comparing strain gauge data with finite element model analysis, as well as the near-term plans for the long MQXF magnet program.

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.

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.

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.

The Large Hadron Collider Luminosity upgrade (HiLumi) program requires new low-β triplet quadrupole magnets, called MQXF, in the interaction region to increase the LHC peak and integrated luminosity. The MQXF magnets, designed and fabricated in collaboration between CERN and the U.S. LARP, will all have the same cross section. The MQXF long model, referred as MQXFA, is a quadrupole using the Nb3Sn superconducting technology with 150 mm aperture and a 4.2 m magnetic length and is the first long prototype of the final MQXF design. The MQXFA magnet is based on the previous LARP HQ and MQXFS designs. In this paper, we present the baseline design of the MQXFA structure with detailed three-dimensional (3-D) numerical analysis. A detailed tolerance analysis of the baseline case has been performed by using a 3-D finite element model, which allows fast computation of structures modeled with actual tolerances. Tolerance sensitivity of each component is discussed to verify the actual tolerances to be achieved by vendors. Tolerance stack-up analysis is presented in the end of this paper.

Within the scope of the High-Luminosity LHC project, the collaboration between CERN and U.S. LARP is developing new low-$\beta$ quadrupoles using the Nb3Sn superconducting technology for the upgrade of the LHC interaction regions. The magnet support structure of the first short model was designed, and two units were fabricated and tested at CERN and at LBNL. The structure provides the preload to the collar-coil subassembly by an arrangement of outer aluminum shells pretensioned with water-pressurized bladders. For the mechanical qualification of the structure and the assembly procedure, superconducting coils were replaced with solid aluminum 'dummy coils,' and the structure was preloaded at room temperature and then cooled-down to 77 K. The mechanical behavior of the magnet structure was monitored with the use of strain gauges installed on the aluminum shells, the dummy coils, and the axial preload system. This paper reports on the outcome of the assembly and the cooldown tests with dummy coils, which were performed at CERN and at LBNL, and presents the strain gauge measurements compared with the 3-D finite-element model predictions.

Protection heaters are essential elements of a quench protection scheme for high-field accelerator magnets. Various heater designs fabricated by LARP and CERN have been already tested in the LARP high-field quadrupole HQ and presently being built into the coils of the high-field quadrupole MQXF. In order to compare the heat flow characteristics and thermal diffusion timescales of different heater designs, we powered heaters of two different geometries in ambient conditions and imaged the resulting thermal distributions using a high-sensitivity thermal video camera. We observed a peculiar spatial periodicity in the temperature distribution maps potentially linked to the structure of the underlying cable. Two-dimensional numerical simulation of heat diffusion and spatial heat distribution have been conducted, and the results of simulation and experiment have been compared. Imaging revealed hot spots due to a current concentration around high curvature points of heater strip of varying cross sections and visualized thermal effects of various interlayer structural defects. Thermal imaging can become a future quality control tool for the MQXF coil heaters.

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 Europeén pour la Recherche Nucleaíre (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.

In high field magnet applications, Nb3Sn coils undergo a heat treatment step after winding. During this stage, coils radially expand and longitudinally contract due to the Nb3Sn 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 Nb3Sn 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) has been developing Nb3Sn quadrupoles of increasing performance for the high-luminosity upgrade of the large hadron collider. The 120-mm aperture high-field quadrupole (HQ) models are the last step in the RD phase supporting the development of the new IR Quadrupoles (MQXF). Three series of HQ coils were fabricated and assembled in a shell-based support structure, progressively optimizing the design and fabrication process. The final set of coils consistently applied the optimized design solutions and was assembled in the HQ03a model. This paper reports a summary of the HQ03a test results, including training, mechanical performance, field quality, and quench studies.

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 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 Europeén pour la Recherche Nucleaíre (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.

Within the scope of the High-Luminosity LHC project, the collaboration between CERN and U.S. LARP is developing new low-$\beta$ quadrupoles using the Nb3Sn superconducting technology for the upgrade of the LHC interaction regions. The magnet support structure of the first short model was designed, and two units were fabricated and tested at CERN and at LBNL. The structure provides the preload to the collar-coil subassembly by an arrangement of outer aluminum shells pretensioned with water-pressurized bladders. For the mechanical qualification of the structure and the assembly procedure, superconducting coils were replaced with solid aluminum 'dummy coils,' and the structure was preloaded at room temperature and then cooled-down to 77 K. The mechanical behavior of the magnet structure was monitored with the use of strain gauges installed on the aluminum shells, the dummy coils, and the axial preload system. This paper reports on the outcome of the assembly and the cooldown tests with dummy coils, which were performed at CERN and at LBNL, and presents the strain gauge measurements compared with the 3-D finite-element model predictions.

A multilayer high field dipole magnet has been designed for future particle accelerators. The magnet has eight layers of a Nb3Sn outsert coil and four layers of a Bi-2212 insert coil (see Figs. 1 and 2). The layers are graded, delivering a short-sample field of 17.7 T in a 40-mm bore. The coil layers are of a canted cosine-theta design - with ribs and spars that guide and support the coil windings, shape the field, intercept Lorentz forces, and minimize conductor prestress. We present a general overview of the concept and report on the magnetic and mechanical design including an initial cost estimate and construction plan.

The ECR source magnet of the FRIB facility has been designed by the Superconducting Magnet Program at the Lawrence Berkeley National Laboratory (LBNL). The magnetic parameters are close to the VENUS magnet (sextupole-in-solenoids) operated at LBNL. The mechanical assembly concept, however, is different and uses a shell-based support structure. The main advantage of this structure is the ability to finely tune the sextupole prestress both azimuthally (by way of bladder and key technology, and axially by means of end plates. This method of structural pre-loading applies the desired compression on the sextupole coils while maintaining acceptable peak stresses. Also, bladder and key technology is a reversible assembly process allowing fast and easy coil replacement, when necessary. This paper also describes the mechanical analysis required to estimate the sextupole and solenoids preloads. The stress distribution in the windings and structural components are presented during assembly, cool-down, and magnet excitation.

Persistent magnetization currents are induced in superconducting filaments during the current ramping in magnets. The resulting perturbation to the design magnetic field leads to field quality degradation, particularly at low field, where the effect is stronger relative to the main field. The effects observed in NbTi accelerator magnets were reproduced well with the critical-state model. However, this approach becomes less accurate for the calculation of the persistent-current effects observed in Nb3Sn accelerator magnets. Here, a finite-element method based on the measured strand magnetization is validated using three state-of-the-art Nb3Sn accelerator magnets featuring different subelement diameters, conductor critical currents, magnet designs, and test temperatures. The temperature dependence of the persistent-current effects is reproduced. Based on the validated model, the impact of conductor design on the persistent-current effects is discussed. The strengths, limitations, and possible improvements of the approach are also discussed.

The Superconducting Magnet Program at the Lawrence Berkeley National Laboratory (LBNL) is completing the design of a 28 GHz NbTi ion source magnet for the Facility for Rare Isotope Beams (FRIB). The design parameters are based on the parameters of the ECR ion source VENUS in operation at LBNL since 2002 featuring a sextupole-in-solenoids configuration. Whereas most of the magnet components (such as conductor, magnetic design, protection scheme) remain very similar to the VENUS magnet components, the support structure of the FRIB ion source uses a different concept. A shell-based support structure using bladders and keys is implemented in the design allowing fine tuning of the sextupole preload and reversibility of the magnet assembly process. As part of the design work, conductor insulation scheme, coil fabrication processes and assembly procedures are also explored to optimize performance. We present the main features of the design emphasizing the integrated design approach used at LBNL to achieve this result.

A two-layer Canted-Cosine-Theta (CCT) superconducting dipole magnet was built and tested. The magnet's unique mandrel design uses machined channels and spars to guide the windings, intercept Lorentz forces, and circumvent tangential stress accumulation. The CCT magnet design provides a "near-perfect" current density distribution and requires minimal coil prestress. The CCT magnet design, with these inherent features, makes it a desirable option for a high field accelerator magnet. A two layer dipole (CCT1) using NbTi cable and a 50.8-mm clear bore was built and tested generating a 2.4 T dipole field. We report on the winding experience, measured field quality and quench history.

The US LARP collaboration has been pursuing the development of Nb3Sn technology for the interaction region low-beta quadrupole magnets for the future LHC luminosity upgrade. A key component for safe operation of these high-field magnets is the quench protection system. Due to the high stored energy density and the low stabilizer fraction in the conductor, quench propagation in the windings needs to be accelerated to limit the hot spot temperature and coil internal voltages during a quench. For this purpose, quench protection heaters are used to introduce multiple quenches across the windings. Heater delay, i.e. the time delay between heater activation and normal zone initiation under the heater, is a critical design parameter. We present an analysis of the heater delays characteristics for Nb3Sn coil windings based on our recently developed Code for Heater Delay Analysis (CoHDA), and compare with experimental results for various operational currents and temperatures in the LARP HQ and LQ magnets. We demonstrate applicability of our simulation model for heater design optimization of the LHC type low-beta quadrupole coils.

Large-aperture, high-field, Nb3Sn quadrupoles are being developed by the U.S. LHC accelerator research program (LARP) for the High luminosity upgrade of the Large Hadron Collider (HiLumi-LHC). The first 1 m long, 120 mm aperture prototype, HQ01, was assembled with various sets of coils and tested at LBNL and CERN. Based on these results, several design modifications have been introduced to improve the performance for HQ02, the latest model. From the field quality perspective, the most relevant improvements are a cored cable for reduction of eddy current effects, and more uniform coil components and fabrication processes. This paper reports on the magnetic measurements of HQ02 during recent testing at the Vertical Magnet Test Facility at Fermilab. Results of baseline measurements performed with a new multilayer circuit board probe are compared with the earlier magnet. An analysis of probe and measurement system performance is also presented.

Canted-Cosine-Theta (CCT) magnet is an accelerator magnet that superposes fields of nested and tilted solenoids that are oppositely canted. The current distribution of any canted layer generates a pure harmonic field as well as a solenoid field that can be cancelled with a similar but oppositely canted layer. The concept places windings within mandrel's ribs and spars that simultaneously intercept and guide Lorentz forces of each turn to prevent stress accumulation. With respect to other designs, the need for pre-stress in this concept is reduced by an order of magnitude making it highly compatible with the use of strain sensitive superconductors such as Nb3Sn or HTS. Intercepting large Lorentz forces is of particular interest in magnets with large bores and high field accelerator magnets like the one foreseen in the future high energy upgrade of the LHC. This paper describes the CCT concept and reports on the construction of CCT1 a "proof of principle" dipole.

The Canted-Cosine-Theta (CCT) magnet design offer significant reductions in conductor stress by using mandrels t prevent the accumulation of operating Lorentz forces. Each mandre consists of a cylindrical spar with ribs guiding the conductor These ribs intercept the turn-To-Turn accumulation of forces b transferring them to the spar. Design studies of a layered CC coil pack coupled to a shell-based structure are shown. The us of a 3-D periodic symmetry region to reduce the problem size fo finite element modeling is detailed along with a discussion of axia boundary conditions. ANSYS calculation results for a two laye NbTi dipole being constructed at LBNL (CCT1) are presented ANSYS calculations show the Lorentz force induced stress i CCT1 at the single turn level, demonstrating interception an suggesting investigation of CCT design with minimal structur external to the coil pack.

This paper presents a recently developed Code for Heater Delay Analysis (CoHDA), which is a tool for modeling protection heater induced quenches in superconducting Nb3S high-field accelerator magnets. The CoHDA thermal model numerically computes the heat diffusion from the heater to the coil and estimates the time delay to quench initiation by comparing the coil temperature with its critical surface. The model takes into account heater geometry, power, and various insulation layers and coil properties. Computational heater delays are compared with experimental data from the U.S. Large Hadron Collider Accelerator Research Program Nb3S High-Gradient Quadrupole magnet with good agreement. Based on the results, CoHDA provides a useful tool for quench protection design in impregnated magnets. Copyright © 2014 IEEE.

The US LARP collaboration has been pursuing the development of Nb3Sn technology for the interaction region low-beta quadrupole magnets for the future LHC luminosity upgrade. A key component for safe operation of these high-field magnets is the quench protection system. Due to the high stored energy density and the low stabilizer fraction in the conductor, quench propagation in the windings needs to be accelerated to limit the hot spot temperature and coil internal voltages during a quench. For this purpose, quench protection heaters are used to introduce multiple quenches across the windings. Heater delay, i.e. the time delay between heater activation and normal zone initiation under the heater, is a critical design parameter. We present an analysis of the heater delays characteristics for Nb3Sn coil windings based on our recently developed Code for Heater Delay Analysis (CoHDA), and compare with experimental results for various operational currents and temperatures in the LARP HQ and LQ magnets. We demonstrate applicability of our simulation model for heater design optimization of the LHC type low-beta quadrupole coils.

We report test results for the one meter long dipol HD3b, a block-Type accelerator quality Nb3Sn magnet built a LBNL with operational bore fields in the range of 13-15 T. Th magnet is an upgrade of the previously reported HD2 and HD3 versions, with several modifications implemented to improve conducto positioning, reduce cable "hard-way" bending radius, an strengthen electrical insulation between cables and coil parts The magnet exhibited long training behavior, but showed a goo "memory" of the trained state upon thermal cycling. Ramp-rat dependence of the quench current, field quality performance characteristics and protection heater studies were conducted. Quenc propagation velocity and quench locations were determined base on the voltage signals; quench localization was further improve using inductive quench antenna and acoustic emission sensors Short-And long-Term acoustic precursors to quenching wer observed.

Large-aperture, high-field, Nb3Sn quadrupoles are being developed by the U.S. LHC accelerator research program (LARP) for the High luminosity upgrade of the Large Hadron Collider (HiLumi-LHC). The first 1 m long, 120 mm aperture prototype, HQ01, was assembled with various sets of coils and tested at LBNL and CERN. Based on these results, several design modifications have been introduced to improve the performance for HQ02, the latest model. From the field quality perspective, the most relevant improvements are a cored cable for reduction of eddy current effects, and more uniform coil components and fabrication processes. This paper reports on the magnetic measurements of HQ02 during recent testing at the Vertical Magnet Test Facility at Fermilab. Results of baseline measurements performed with a new multilayer circuit board probe are compared with the earlier magnet. An analysis of probe and measurement system performance is also presented.

The U.S. LHC Accelerator Research Program has been developing Nb3Sn quadrupole magnets of progressively increasing performance and complexity for the High-Luminosity LHC project. The magnets are wound with Rutherford cables following the wind-and-react process. The resulting inter-strand coupling can generate strong field distortions during current ramp. The latest series of 120 mm aperture magnets (HQ) are designed and built for high field quality, offering an opportunity for detailed studies of these effects. Magnetic measurements of first-generation HQ magnets showed strong ramp-rate dependence. A stainless-steel core was introduced for the second generation of magnet coils to control the inter-strand coupling currents and the resulting dynamic multipoles. We report the observed dynamic effects and compare with calculations taking into account the coil geometry and cross-contact resistance in the Rutherford cable. In particular, the dependence of field quality on width and position of the stainless steel core is discussed. © 2002-2013 IEEE.

The Superconducting Magnet Group, at Lawrence Berkeley National Laboratory (LBNL), has been developing a canted cosine-theta (CCT) superconducting dipole coil as well as the coil's supporting magnet structure. This contribution reports on the progress in the development of the coil's winding mandrel and its fabrication options. A comprehensive study of the coil's Lorentz forces was performed to validate the winding mandrel's "stress interception" attributes. The design of the external structure and the application of the "Bladder & Key" technology is also discussed. Additionally, the application of these studies to a curved ion-therapy CCT dipole magnet is reported.

This paper presents a recently developed Code for Heater Delay Analysis (CoHDA), which is a tool for modeling protection heater induced quenches in superconducting Nb3S high-field accelerator magnets. The CoHDA thermal model numerically computes the heat diffusion from the heater to the coil and estimates the time delay to quench initiation by comparing the coil temperature with its critical surface. The model takes into account heater geometry, power, and various insulation layers and coil properties. Computational heater delays are compared with experimental data from the U.S. Large Hadron Collider Accelerator Research Program Nb3S High-Gradient Quadrupole magnet with good agreement. Based on the results, CoHDA provides a useful tool for quench protection design in impregnated magnets. Copyright © 2014 IEEE.

We report test results for the one meter long dipol HD3b, a block-Type accelerator quality Nb3Sn magnet built a LBNL with operational bore fields in the range of 13-15 T. Th magnet is an upgrade of the previously reported HD2 and HD3 versions, with several modifications implemented to improve conducto positioning, reduce cable "hard-way" bending radius, an strengthen electrical insulation between cables and coil parts The magnet exhibited long training behavior, but showed a goo "memory" of the trained state upon thermal cycling. Ramp-rat dependence of the quench current, field quality performance characteristics and protection heater studies were conducted. Quenc propagation velocity and quench locations were determined base on the voltage signals; quench localization was further improve using inductive quench antenna and acoustic emission sensors Short-And long-Term acoustic precursors to quenching wer observed.

The U.S. LHC Accelerator Research Program has been developing Nb3Sn quadrupole magnets of progressively increasing performance and complexity for the High-Luminosity LHC project. The magnets are wound with Rutherford cables following the wind-and-react process. The resulting inter-strand coupling can generate strong field distortions during current ramp. The latest series of 120 mm aperture magnets (HQ) are designed and built for high field quality, offering an opportunity for detailed studies of these effects. Magnetic measurements of first-generation HQ magnets showed strong ramp-rate dependence. A stainless-steel core was introduced for the second generation of magnet coils to control the inter-strand coupling currents and the resulting dynamic multipoles. We report the observed dynamic effects and compare with calculations taking into account the coil geometry and cross-contact resistance in the Rutherford cable. In particular, the dependence of field quality on width and position of the stainless steel core is discussed. © 2002-2013 IEEE.

As part of the development of very high field dipole magnets for particle accelerators, the Superconducting Magnet Program at Lawrence Berkeley National Laboratory is developing block-type dipole magnets. One of the main challenges of this geometry is to provide support to the coil in the aperture while maintaining an adequate clear bore. Through finite element method analysis, strain-gauge measurements, and test results, this paper reviews the design of HD3, a 1-m-long, 43-mm-bore Nb3Sn dipole magnet, presents the findings in terms of strain gauges monitoring, and summarizes their implications. © 2002-2011 IEEE.

As part of the development of very high field dipole magnets for particle accelerators, the Superconducting Magnet Program at Lawrence Berkeley National Laboratory is developing block-type dipole magnets. One of the main challenges of this geometry is to provide support to the coil in the aperture while maintaining an adequate clear bore. Through finite element method analysis, strain-gauge measurements, and test results, this paper reviews the design of HD3, a 1-m-long, 43-mm-bore Nb3Sn dipole magnet, presents the findings in terms of strain gauges monitoring, and summarizes their implications. © 2002-2011 IEEE.

For the last several years, the Lawrence Berkeley National Laboratory has been engaged in the development of Nb3Sn block-type accelerator quality dipoles with operational bore fields in the range of 13-15 T. The magnet design features two coil modules wound around a titanium-alloy pole with a clear aperture of 43 mm. The latest model, HD3, incorporates several new features to overcome the limitations observed in previous tests. Among the key objectives are improved conductor positioning at critical transitions between straight section and end regions, and a more robust fabrication process. To date, several coils have been fabricated and we describe their performance with respect to these design and process changes. Additionally, we present our experience in design and fabrication of a new generation of magnet coils that introduce a two-piece pole design that allows for cable growth during reaction. These experiences are intended to form the basis for scale-up to longer lengths and larger aperture magnets. © 2002-2011 IEEE.

For the last several years, the Lawrence Berkeley National Laboratory has been engaged in the development of Nb3Sn block-type accelerator quality dipoles with operational bore fields in the range of 13-15 T. The magnet design features two coil modules wound around a titanium-alloy pole with a clear aperture of 43 mm. The latest model, HD3, incorporates several new features to overcome the limitations observed in previous tests. Among the key objectives are improved conductor positioning at critical transitions between straight section and end regions, and a more robust fabrication process. To date, several coils have been fabricated and we describe their performance with respect to these design and process changes. Additionally, we present our experience in design and fabrication of a new generation of magnet coils that introduce a two-piece pole design that allows for cable growth during reaction. These experiences are intended to form the basis for scale-up to longer lengths and larger aperture magnets. © 2002-2011 IEEE.

With the first test of LQS03, the long quadrupole (LQ) R&D by LARP (the US LHC Accelerator Research Program, a collaboration of BNL, FNAL, LBNL, and SLAC) is approaching conclusion. LQS03 is the third 3.7-m-long quadrupole, with 90 mm aperture, using a full new set of Nb3Sn coils. The LQS03 coils were made using 108/127 RRP strand (with 108 Nb3Sn subelements) produced by Oxford Superconducting Technology, whereas both previous models used 54/61 RRP strand (with 54 larger Nb3Sn subelements). In this paper, LQS03 test results are presented and discussed. The test results are also compared with the performances of the previous models. Observations are made for the future use of Nb3Sn in accelerator magnets. © 2002-2011 IEEE.

With the first test of LQS03, the long quadrupole (LQ) R&D by LARP (the US LHC Accelerator Research Program, a collaboration of BNL, FNAL, LBNL, and SLAC) is approaching conclusion. LQS03 is the third 3.7-m-long quadrupole, with 90 mm aperture, using a full new set of Nb3Sn coils. The LQS03 coils were made using 108/127 RRP strand (with 108 Nb3Sn subelements) produced by Oxford Superconducting Technology, whereas both previous models used 54/61 RRP strand (with 54 larger Nb3Sn subelements). In this paper, LQS03 test results are presented and discussed. The test results are also compared with the performances of the previous models. Observations are made for the future use of Nb3Sn in accelerator magnets. © 2002-2011 IEEE.

After the successful test of the first long Nb 3Sn quadrupole (LQS01) the US LHC Accelerator Research Program (LARP, a collaboration of BNL, FNAL, LBNL and SLAC) is assessing training memory, reproducibility, and other accelerator quality features of long Nb 3Sn quadrupole magnets. LQS01b (a reassembly of LQS01 with more uniform and higher pre-stress) was subjected to a full thermal cycle and reached the previous plateau of 222 T/m at 4.5 K in two quenches. A new set of four coils, made of the same type of conductor used in LQS01 (RRP 54/61 by Oxford Superconducting Technology), was assembled in the LQS01 structure and tested at 4.5 K and lower temperatures. The new magnet (LQS02) reached the target gradient (200 T/m) only at 2.6 K and lower temperatures, at intermediate ramp rates. The preliminary test analysis, here reported, showed a higher instability in the limiting coil than in the other coils of LQS01 and LQS02. © 2011 IEEE.

After the successful test of the first long Nb 3Sn quadrupole (LQS01) the US LHC Accelerator Research Program (LARP, a collaboration of BNL, FNAL, LBNL and SLAC) is assessing training memory, reproducibility, and other accelerator quality features of long Nb 3Sn quadrupole magnets. LQS01b (a reassembly of LQS01 with more uniform and higher pre-stress) was subjected to a full thermal cycle and reached the previous plateau of 222 T/m at 4.5 K in two quenches. A new set of four coils, made of the same type of conductor used in LQS01 (RRP 54/61 by Oxford Superconducting Technology), was assembled in the LQS01 structure and tested at 4.5 K and lower temperatures. The new magnet (LQS02) reached the target gradient (200 T/m) only at 2.6 K and lower temperatures, at intermediate ramp rates. The preliminary test analysis, here reported, showed a higher instability in the limiting coil than in the other coils of LQS01 and LQS02. © 2011 IEEE.

The test of the first LARP (LHC Accelerator Research Program) Long Quadrupole is a significant milestone toward the development of Nb3Sn quadrupoles for LHC (Large Hadron Collider) Luminosity Upgrades. These 3.7-m long magnets, scaled from the 1-m long Technological Quadrupoles, are used to develop our capabilities to fabricate and assemble Nb3Sn coils and structures with lengths comparable to accelerator magnet dimensions. The long quadruples have a target gradient of 200 T/m in a 90-mm aperture. Pre-stress and support are provided by an Al-shell-based structure pre-loaded using bladders and keys. The coils were fabricated at BNL and FNAL, the hell-based structure was designed and assembled at LBNL, the test is performed at FNAL. In this paper we present the final steps of the development of the first model (LQS01), several upgrades to the test facility, the test results of witness cables, and the short sample limit © 2006 IEEE.