11-T Dipole Research Articles

Transient Heat Transfer in Superfluid Helium Cooled Nb<inline-formula> <tex-math notation="LaTeX">$_3$</tex-math> </inline-formula>Sn Superconducting Coil Samples

An experimental setup is operational at the Central Cryogenics Laboratory of the European Organization for Nuclear Research to measure the cooling mechanisms of superfluid 4 He (He II) from prepared Rutherford-type superconducting cable stacks to a stagnant He II bath. For novel magnets designed for the so-called high-luminosity large hadron collider upgrade, a segment of a fully impregnated Nb 3 Sn 11T dipole magnet was measured. A dataset on the thermal behavior is presented, with homogeneous heat inputs of up to approximately 4.8 mW cm -3 corresponding to an average steady-state temperature of 3.1 K for the inner layer and 4.0 K for the outer layer when cooled via a 1.9 K He II bath. We discuss the steady state as well as transient behavior observed.

Advanced Nb3Sn Conductors Tested in Racetrack Coil Configuration for the 11T Dipole Project

Within the 11T dipole magnet conductor development for the high-luminosity LHC upgrade, two types of Nb3 Sn cable based on the powder-in-tube (PIT) and the Rod and Restack processes (RRP) are tested in racetrack configuration in the short model coil (SMC) magnets. In 2016 and 2017, the performances of three different coils wound with 40-strand cables, one made of OST RRP 132/169 and two of PIT 120 strands have been measured using the SMC structure. This paper reports on the main design parameters of the SMC-11T-3 (RRP), and the SMC-11T-4 and SMC-11T-5 (PIT) magnets including details on the instrumentation, applied preload, maximum expected performances, residual resistivity ratio, splice resistances, and inductances. For SMC-11T-3, eight consecutive runs have been performed varying the azimuthal prestress from 150 to 200 MPa with the aim to study the impact of the transverse pressure on the magnet stability and degradation. Only two runs were done for SMC-11T-4 and SMC-11T-5. For the three magnets, the training behavior at both 4.2 and 1.9 K is analyzed in terms of training rate, quench location, maximum quench current and its dependence to the helium bath temperature, the level of transverse prestress, and current ramp rate. The main outcome of the tests on the coil performance is given as conclusion.

Field Quality of MBH 11-T Dipoles for HL-LHC and Impact on Beam Dynamic Aperture

For the high-luminosity upgrade of the Large Hadron Collider (HL-LHC), the development of the 11-T Nb $_3$ Sn dipole (MBH) is progressing. At present, one double-aperture and five single-aperture short-model magnets have been built and tested. Magnetic measurements have been performed both at ambient and cryogenic temperatures. In addition, a double-aperture short model and the first full-length collared-coil assemblies have been produced and measured at ambient temperature. In this paper, the measurement results collected so far are presented and discussed. The geometrical field multipoles, the iron saturation effects, as well as the effects of persistent currents are summarized. Experimental data are compared with the magnetic calculations using the CERN field computation program ROXIE and discussed in view of the construction of the final magnets. In addition, based on the measured field errors, beam dynamics simulations have been carried out by taking into consideration different scenarios with and without MBH magnets installed in the accelerator.

Influence of 3-D Effects on Field Quality in the Straight Part of Accelerator Magnets for the High-Luminosity Large Hadron Collider

A dedicated D1 beam separation dipole is currently being developed at KEK for the large hadron collider luminosity upgrade (HL-LHC). Four 150-mm aperture, 5.6-T magnetic field, and 6.7-m-long Nb–Ti magnets will replace resistive D1 dipoles. The development includes fabrication and testing of 2.2-m model magnets. The dipole has a single-layer coil and thin spacers between coil and iron, giving a nonnegligible impact of saturation on field quality at nominal field. The magnetic design of the straight section coil cross section is based on two-dimensional (2-D) optimization and a separate optimization concerns the coil ends. However, magnetic measurements of the short model showed a large difference (tens of units) between the sextupole harmonic in the straight part and the 2-D calculation. This difference is correctly modeled only by a 3-D analysis: 3-D calculations show that the magnetic field quality in the straight part is influenced by the coil ends, even for the 6.7-m-long magnets. The effect is even more remarkable in the short model. We investigate similar 3-D effects for other magnets, namely the 11-T dipole for HL-LHC. We also consider the case of the 4.5-T recombination magnets for HL-LHC (D2), where the larger space between coil and iron makes this effect less important, but still visible. We conclude the paper by outlining the different classes of accelerator magnets, where this coupling between 3-D effects and iron saturation can be relevant.

Design and Construction of the Full-Length Prototype of the 11-T Dipole Magnet for the High Luminosity LHC Project at CERN

The luminosity upgrade of the Large Hadron Collider (LHC) at CERN requires the installation of additional collimators in the dispersion suppressor regions of the accelerator. The upgrade foresees the installation of one additional collimator on either side of interaction point 7 (IP7) at the location of the existing main dipoles (MBs) that will be replaced by shorter and more powerful dipoles, and of one additional collimator on either side of IP2 at the location of existing empty cryostats. This paper describes the design and the construction status of the full-length prototype of the 11-T dipole magnet, which is needed for IP7. This magnet features a two-in-one structure, like the LHC MB, impregnated coils made of Nb3Sn conductor, an inner bore of 60 mm, and a magnetic length of about 5.3 m. Two 11-T magnets are needed to replace a 15-m long MB. A by-pass cryostat placed in between the two magnets allows creating a room temperature space for the additional collimators. The magnet is designed to provide the same integrated field as the MB at nominal field. However, due to the difference in transfer function at lower field, a correction by means of a trim current has been considered. A full-length prototype is currently under construction at CERN with the goal of developing the manufacturing and inspection procedures prior to launch the series production. For this, new tooling has been developed and optimized during the fabrication of fully representative practice coils. This paper describes the design of the magnet, the main manufacturing steps, and corresponding quality indicators, which will be used to monitor the series production. Finally, the production and installation schedule will be presented.

Progress on the Development of the Nb3Sn 11T Dipole for the High Luminosity Upgrade of LHC

The high-luminosity large hadron collider (LHC) project at CERN entered into the production phase in October 2015 after the completion of the design study phase. In the meantime, the development of the 11 T dipole needed for the upgrade of the collimation system of the machine made significant progress with very good performance of the first two-in-one magnet model of 2-m length made at CERN. The 11 T dipole, which is more powerful than the current main dipoles of LHC, can be made shorter with an equivalent integrated field. This will allow creating space for the installation of additional collimators in specific locations of the dispersion suppressor regions. Following tests carried out during heavy ions runs of LHC in the end of 2015, and a more recent review of the project budget, the installation plan for the 11 T dipole was revised. Consequently, one 11 T dipole full assembly containing two 11 T dipoles of 5.5-m length will be installed on either side of interaction point 7. These two units shall be installed during the long shutdown 2 in years 2019-2020. After a brief reminder on the design features of the magnet, this paper describes the current status of the development activities, in particular the short model programme and the construction of the first full scale prototype at CERN. Critical operations such as the reaction treatment and the coil impregnation are discussed, the quench performance tests results of the two-in-one model are reviewed and finally, the plan toward the production for the long shut down 2 is described.

Integration of the 11-T Nb3Sn Dipoles and Collimators in the LHC

The Large Hadron Collider (LHC) collimation system upgrade plan comprises new collimators in the dispersion suppressors. The length required for each collimator along the LHC lattice is obtained by replacing an LHC main dipole and its cryostat with two shorter but stronger 11-T Nb 3 Sn magnets keeping the equivalent integrated field of the dipole removed. This requires a modification of the continuous cryostat, in order to create room-temperature beam vacuum sectors for the integration of the new collimators. In this paper, we present a new cryostat designed to allow the installation of a collimator between the 11-T magnets, while ensuring the continuity of the cryogenics, vacuum, and magnet powering systems of the LHC continuous cryostat. Challenging constraints, in terms of fabrication, alignment, and space, led to the development of a cryostat composed of three independent modules. Two of the modules house the 11-T dipole cold masses, which are cooled in the same 1.9-K pressurized superfluid helium bath of the main dipoles. These make use of the same design features of the LHC magnet cryostats, in order to contain construction and assembly costs and benefit from well-established procedures. A third module, which is placed between the two magnets, is equipped with cold to warm transitions on the beam lines and creates the space for the collimator between the vacuum vessel of the two 11-T magnet cryostats. The main functionalities, requirements, and implemented design solutions for this new cryostat are presented and discussed, in the context of the challenging integration in the LHC continuous cryostat and its tunnel.

The 11 T Dipole for HL-LHC: Status and Plan

The upgrade of the Large Hadron Collider (LHC) collimation system includes additional collimators in the LHC lattice. The longitudinal space for these collimators will be created by replacing some of the LHC main dipoles with shorter but stronger dipoles compatible with the LHC lattice and main systems. The project plan comprises the construction of two cryoassemblies containing each of the two 11-T dipoles of 5.5-m length for possible installation on either side of interaction point 2 of LHC in the years 2018–2019 for ion operation, and the installation of two cryoassemblies on either side of interaction point 7 of LHC in the years 2023–2024 for proton operation. The development program conducted in conjunction between the Fermilab and CERN magnet groups is progressing well. The development activities carried out on the side of Fermilab were concluded in the middle of 2015 with the fabrication and test of a 1-m-long two-in-one model and those on the CERN side are ramping up with the construction of 2-m-long models and the preparation of the tooling for the fabrication of the first full-length prototype. The engineering design of the cryomagnet is well advanced, including the definition of the various interfaces, e.g., with the collimator, powering, protection, and vacuum systems. Several practice coils of 5.5-m length have been already fabricated. This paper describes the overall progress of the project, the final design of the cryomagnet, and the performance of the most recent models. The overall plan toward the fabrication of the series magnets for the two phases of the upgrade of the LHC collimation system is also presented.

Quench Protection Studies of the 11-T Nb3Sn Dipole for the LHC Upgrade

The planned upgrade of the LHC collimation system foresees additional collimators to be installed in the dispersion suppressor areas. Fermilab and CERN are developing an 11-T Nb3Sn dipole to replace some 8.33-T 15-m-long Nb-Ti LHC main dipoles providing longitudinal space for the collimators. In case of a quench, the large stored energy and the low copper stabilizer fraction make the protection of the 11-T Nb3Sn dipoles challenging. This paper presents the results of quench protection analysis, including quench protection heater design and efficiency, quench propagation, and coil heating. The numerical results are compared with the experimental data from the 2-m-long Nb3Sn dipole models. The validated model is used to predict the current decay and hot spot temperature under operating conditions in the LHC, and the presently foreseen magnet protection scheme is discussed.

Persistent-Current Magnetization Effects in High-Field Superconducting Accelerator Magnets

Magnetic field changes in superconducting filaments are shielded by the so-called persistent currents. These currents produce field errors, which are particularly important at low energy level, where the effect is stronger compared to the field generated by the transport current. For the next generation of particle accelerators, magnetic fields higher than 10 T are needed, requiring the use of Nb3Sn as superconductor. Due to the larger filament size (typically ten times larger than in the Nb–Ti Large Hadron Collider dipoles) and higher current density, strand magnetization effects shall be carefully studied. This paper presents an analysis on the expected field errors due to persistent currents in a 16-T dipole magnet. We briefly discuss the method and compare with experimental results on the 11-T Nb3Sn dipole for the Hi-Luminosity upgrade. The model is then used to predict the persistent-current effects for different coil layouts and strand characteristics in a 16-T dipole.

Magnetic and structural design of a 15 T Nb3Sn accelerator dipole model

Hadron Colliders (HC) are the most powerful discovery tools in modern high energy physics. A 100 TeV scale HC with a nominal operation field of at least 15 T is being considered for the post-LHC era. The choice of a 15 T nominal field requires using the Nb3Sn technology. Practical demonstration of this field level in an accelerator-quality magnet and substantial reduction of the magnet costs are the key conditions for realization of such a machine. FNAL has started the development of a 15 T Nb3Sn dipole demonstrator for a 100 TeV scale HC. The magnet design is based on 4-layer shell type coils, graded between the inner and outer layers to maximize the performance. The experience gained during the 11-T dipole R&D campaign is applied to different aspects of the magnet design. This paper describes the magnetic and structural designs and parameters of the 15 T Nb3Sn dipole and the steps towards the demonstration model.

Nb3Sn High Field Magnets for the High Luminosity LHC Upgrade Project

The high luminosity upgrade of the Large Hadron Collider at CERN requires a new generation of high field superconducting magnets. High field large aperture quadrupoles (MQXF) are needed for the low-beta triplets close to the ATLAS and CMS detectors, and high field two-in-one dipoles (11-T dipoles) are needed to make room for additional collimation. The MQXF quadrupoles, with a field gradient of 140 T/m in 150 mm aperture, have a peak coil field of 12.1 T at nominal current. The 11-T dipoles, with an aperture of 60 mm, have a peak coil field of 11.6 T at nominal current. Both magnets require Nb 3 Sn conductor and are the first applications of this superconductor to actual accelerator magnets. Collaboration between the US LARP (LHC Accelerator Research Program) and CERN is developing the MQXF magnets, whereas the 11-T dipole magnets are being developed by CERN and Fermilab. This paper reviews the status of Nb 3 Sn technology for accelerator magnets, discusses its main challenges, and discusses how the MQXF and 11-T designs are addressing them.

11-T Twin-Aperture <inline-formula> <tex-math notation="TeX">$\hbox{Nb}_{3}\hbox{Sn}$</tex-math></inline-formula> Dipole Development for LHC Upgrades

FNAL and CERN are developing a twin-aperture 11-T <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">$\hbox{Nb}_{3}\hbox{Sn} $</tex-math></inline-formula> dipole suitable for installation in the LHC. This paper describes the design and parameters of the 11-T dipole developed at FNAL for the LHC upgrades in both single-aperture and twin-aperture configurations, and presents details of the constructed dipole models. Results of studies of magnet quench performance, quench protection, and magnetic measurements performed using short 1-m-long coils in the dipole mirror and single-aperture configurations are reported and discussed.

Performance of the Short Model Coils Wound With the CERN 11-T Nb&lt;sub&gt;3&lt;/sub&gt;Sn Conductor

The short model coil (SMC) dipole magnet has been designed and constructed in the framework of the European project EuCARD as a test bed for Nb 3 Sn magnet R&D in terms of coil fabrication technology and testing of Rutherford-type cables. Two pairs of racetrack coils were successfully tested in 2012, obtaining 12.5 T in the winding at 1.9 K, thus demonstrating SMC as a valid magnet design for conductor tests. These successful results prompted a new test campaign of SMC using the cable of the 11-T dipole project. The size of this cable is such that only one double pancake can be accommodated in the mechanical structure. During the latest tests using the 11-T cable, a new record field of 13.5 T was achieved, confirming the excellent capability of SMC to qualify a conductor, providing precise information of the stability and general cable performance, and to test insulation techniques, instrumentation systems, and coil fabrication processes. This paper describes the challenges of this new assembly, indicating novelties in the fabrication technology and reports on the measurements and the performance of SMC using CERN's 11-T-dipole-type conductor.

Characterization of $\hbox{Nb}_{3}\hbox{Sn}$ Rutherford Cables for the LHC 11-T Dipole Magnet

The so-called CERN-LHC DS upgrade relies on the use of 11-T dipole magnets. For these magnets, 40 strands Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn type Rutherford cables based on 0.7-mm wires are being developed. Recently, four samples of the cables were characterized in the CERN FRESCA cable test station. The critical current and the premature quench current due to magneto-thermal instability were measured at 1.9 and 4.3 K in a background magnetic field between 0 and 9.6 T (the peak magnetic field on the conductor, including the self-field of the cable, ranges from ~ 2 T to ~ 12 T). Two cable samples were based on Powder-In-Tube (PIT) wire and two on Restacked-Rod-Process (RRP) wire. The PIT samples were identical and without a core in the cable while one of the RRP samples features a 25- μm-thick stainless steel core. All cables samples tested have a width and a thickness of about 14.7 and 1.25 mm, respectively. Cables and sample holders were manufactured at CERN. In this paper, we report and discuss the cable test results and compare them to the performance of witness strands, heat treated and measured on ITER-VAMAS type sample holders.