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The EuCARD high temperature superconductor (HTS) insert is a dipole magnet generating a self-field of 5.4 T and designed to operate at 18 T within the FRESCA2 test facility; it has just been successfully tested in stand-alone configuration up to 4.5 T (see M. Durante et al.). To operate in such a large field, its winding is made of a 12 mm HTS REBCO insulated conductor; each conductor is composed of four tapes in parallel to achieve a large current of 2.8 kA. The drawbacks of using parallel HTS tapes are numerous: first, they are very sensitive to orthogonal field inducing screening currents loops within the tapes. Second, the use of tapes in parallel imposes to transpose the conductor to avoid current loops between tapes, induced from the parallel field. The screening currents in return generate a magnetic field (screening current induced field), opposed to the main one and consequently lowering it and degrading the homogeneity. We have developed a finite difference code in order to simulate the induced currents within a conductor made of parallel tapes; we have calculated the screening current induced field and showed that the order of magnitude is non negligible compared to the main field. These computations have been benchmarked against measurement of the magnetic field performed during the stand-alone configuration tests.

Based on a close collaboration between CEA and CNRS, a new hybrid magnet is being built at LNCMI-Grenoble. By combining a resistive insert, which is made of Bitter and polyhelix coils, with a large bore superconducting outsert, an overall continuous magnetic field of at least 43 T will be produced in a 34-mm warm bore aperture. The superconducting coil relies on the novel development of a Nb-Ti/Cu Rutherford cable-on-conduit conductor cooled down to 1.8 K by a bath of superfluid helium at atmospheric pressure and will produce a nominal magnetic field of 8.5 T in a 1.1-m cold bore diameter. After thorough reviews of the hybrid magnet design, which have anticipated possible upgrades of the maximum magnetic field produced, the project has entered in its production phase. The status and the next steps of the project will be reviewed highlighting the remaining technical challenges.

Current technical superconductors, such as Nb3Sn, are limited to fields around 20 T by their intrinsic material properties. Generating significantly stronger magnetic fields can only be done by using resistive magnets, or by combining superconducting and resistive magnets (hybrid magnets), at the expense of large power consumption and operating cost. A CEA–CNRS French collaboration is currently developing a new hybrid magnet, which combines a resistive insert composed of Bitter and polyhelix coils and a new large-bore superconductor outsert to produce an overall continuous magnetic field of more than 42 T in a 34-mm warm aperture. Based on the novel development of a NbTi/Rutherford cable on conduit (RCOCC) cooled down to 1.8 K by means of the bath of superfluid helium at atmospheric pressure, the superconducting coil aims to produce a continuous magnetic field of 8.5 T in a 1.1-m cold bore diameter. This paper summarizes the results of the mechanical behavior study of the cold mass cooled from room to operating temperature and Lorentz forces at operating temperature. Computations have been performed in 2-D axisymmetry and 3-D, to take into account the axisymmetric discontinuous distribution of the tie rods.

High-temperature superconductors (HTSs) are a strong candidate for high field magnets. As their properties are extraordinary, especially under high-fields and very low temperatures, there are many ongoing projects around the world. The NOUGAT project aims at building a 10-T insert operating inside a 20-T resistive background. Its objectives are not to reach a higher field than the already existing resistive magnets, but rather to overcome the main issues of using HTS above 20 T and pave the way toward full superconductive magnets at lower cost. REBCO coated conductor tape was preferred for the NOUGAT insert even if its implementation is still challenging. Both insulated and metal insulated (MI) coils have been considered for the NOUGAT project. Due to their self-protection behavior, MI windings have been selected for building the insert, but we are still investigating insulated coils for future applications. We built a fully-instrumented insulated single pancake wound with a 6-mm-wide tape. Voltage taps are set up on each turn to monitor the quench propagation in vapor helium up to 60 K under high magnetic field up to 19 T. This study aims at developing our understanding of the windings quench behavior and testing various quench detection procedures for future large-scale insulated applications. The present paper underlines the main results.

Our project is to build a high-temperature superconductor (HTS) insert generating 10 T in its center and expected to work inside a 20 T background field. In the first step, the background field is provided by a resistive magnet to avoid major coupling issues. Nevertheless, the final goal is to have the insert operating inside an LTS magnet to yield a 30 T-class all-superconducting magnet. The insert is designed as a stack of pancakes and double pancakes wound with REBCO tapes. Preliminary tests are performed on a deposited polyimide insulated coil, although design has started with metallic-insulation coils. This paper presents results obtained on a double pancake insulated HTS coil that was tested inside both a resistive coil at LNCMI and a superconducting magnet at Tohoku University. The electrical and mechanical behaviors of the sample coil are discussed, and margins are estimated taking into account the field distribution on each point of the coil. Results are encouraging as the coil passes 370 A (82.9% lc) self-field and 260 A (68.6% lc) under 8 T. Moreover, the coil is still working even after the outer magnet quench.

The key objective of the High Field Magnet work package of the European Project EuCARD is to design and fabricate the Nb3Sn dipole magnet FRESCA2. It has an aperture of 100 mm and a target bore field of 13 T. The design features four 1.5 m long double-layer coils wound with a 21 mm wide cable. The project has now entered its experimental phase in view of the magnet fabrication. We present the experimental test campaign conducted on cable samples in order to understand and to control better the cable behavior and geometry. One full scale double-layer coil using copper cable with the final dimensions and insulation scheme has been wound and heat treated in order to check the fabrication process. This has given useful feedback on the fabrication procedure and on the expected magnet dimensions, as well as on the tooling itself.

International audience; EuCARD-2 is a project partly supported by FP7-European Commission aiming at exploring accelerator magnet technology for 20 T dipole operating field. The EuCARD-2 collaboration is liaising with similar programs for high field magnets in the USA and Japan. EuCARD-2 focuses, through the work-package 10 “Future magnets,” on the development of a 10 kA-class superconducting, high current density cable suitable for accelerator magnets, for a 5 T stand-alone dipole of 40 mm bore and about 1 m length. After standalone testing, the magnet will possibly be inserted in a large bore background dipole, to be tested at a peak field up to 18 T. This paper starts by reporting on a few of the highlight simulations that demonstrate the progress made in predicting: dynamic current distribution and influence on field quality, complex quench propagation between tapes, and minimum quench energy in the multitape cable. The multiphysics output importantly helps predicting quench signals and guides the development of the novel early detection systems. Knowing current position within individual tapes of each cable we present stress distribution throughout the coils. We report on the development of the mechanical component and assembly processes selected for Feather-M2 the 5 T EuCARD2 magnet. We describe the CERN variable temperature flowing helium cold gas test system. We describe the parallel integration of the FPGA early quench detection system, using pickup coils and temperature sensors, alongside the standard CERN magnet quench detection system using voltage taps. Finally we report on the first cold tests of the REBCO 10 kA class Roebel subscale coil named Feather-M0.

As a first step to develop HTS insert technology, we plan to build a 10-T REBCO solenoid that will be tested at the French National High Magnetic Field Laboratory of Grenoble in France (LNCMI) at 4.2 K, in the aperture of a 20-T resistive magnet. Two winding approaches are being considered for the HTS insert, i.e., the no-insulation (NI) and metallic insulation (MI) winding technics. Both methods allow turn-to-turn bypassing current but differ in their turn-to-turn resistance value by three orders of magnitude. In this paper, we provide a comparative study between the two winding options using numerical simulations applied to a preliminary design of the insert, which features a cold bore diameter of 50 mm and is made of 15 double-pancake coils wound from a 6-mm REBCO tape.

In the framework of the French-German consortium Iseult/INUMAC, focused on very-high-magnetic-field molecular imaging, the development of an 11.7 T whole body MRI magnet has been launched in 2006. This magnet is mainly composed of one wet and cryostable main coil and two fully impregnated coils that shield the magnetic field in order to meet the security requirements on the fringe field. To protect the magnet in case of quench, the stored magnetic energy (338.5 MJ) is dissipated in an external resistor and inside the two shielding coils windings. It is thus an important issue to master the normal zone propagation kinetics in those coils. This paper presents the 3d finite-element computations carried out to treat that problem and the more significant obtained results.

The R3B-Glad superconducting Magnet is a large acceptance dipole, dedicated to the analysis of Reactions with Relativistic Radioactive ions Beams. It takes part in the FAIR Project at GSI. As the superconducting NbTi Rutherford cable was under production, detailed studies of the mechanical structure (with both simulation and experiment on a half-scale mock-up) led to revise the magnet design and to abandon the grading of the coils in three stages. Due to the large magnetic forces (up to 400 tons/m), the maximum shear stress level of 20 MPa was impossible to meet in the coils. The main reasons consist in the orthotropic thermo-mechanical behavior of the coils together with the large differential thermal shrinkage between the Cu stabilized coils and their Al alloy casings. Indeed after several studies of different mechanical designs, we decided to simplify the magnet in order to cope with these difficulties. One innovative point is that the coils are not blocked at room temperature, but only at 4.5 K. This paper presents the magnetic calculations of this active shielded magnet, and shows how the new design features meet the specifications. Currently, the 22 tons magnet cold mass, i.e. the 6 coils and their integration in the casings, is ordered and under construction. Meanwhile, the design of the magnet cryostat has evolved into a shape of elliptical cylinder with a lateral satellite. The total weight is expected to be around 50 tons.

The CMS experiment (Compact Muon Solenoid) is a general-purpose detector designed to run at the highest luminosity at the CERN Large Hadron Collider (LHC). Its distinctive features include a 4 T superconducting magnet with 6 m diameter by 12.5 m long free bore, enclosed inside a 10000 ton return yoke. The magnetic field is achieved by a 4-layer superconducting solenoid made of a reinforced Rutherford type superconductor with a hybrid configuration and wound inside an external aluminum cylinder. The coil is indirectly cooled at an operating temperature of 4.5 K by a thermosiphon, and it is designed to run at a nominal current of 20 kA. The corresponding maximum stored magnetic energy reaches 2.6 GJ with an E/M ratio of 12 kJ/kg. The quench protection is achieved by discharging the magnet in an external resistor in fast mode, with a peak voltage in the coil kept at 600 V and a voltage to ground of plusmn300 V during the discharge. The coil design takes benefit of the quench back effect to limit the temperature gradients inside the winding pack in case of quench. The design and the characteristics of the quench protection system are described. The computational results of the quench protection for several operating currents are presented. The behavior of the magnet in case of faulty conditions on the protection system is analyzed

In the frame of the W7X stellarator project, a cooperation agreement between the Max-Planck-Institut fur Plasmaphysik and CEA has been set-up in order to perform the acceptance tests of all the 70 superconducting coils that compose the W7X magnet system. The main purpose of these tests is to demonstrate that each coil can work at nominal operating conditions, with enough margin to ensure the coil safety during the stellerator operations. For that purpose, CEA has built a new test facility at Saclay. This paper presents a general overview of the test facility. It is mainly composed of two large cryostats (useful space of 5 m diameter and 4.2 in height), a cryogenic source to produce supercritical helium at 4.5 K and 6 bar with a power rating of 200 W, and an electrical power supply of 25 kA. Each cryostat can contain two coils. It is then possible to cool down two coils at the same time, and to warm up two others. But only one coil can be energized at the same time. As the assembly of the facility is now nearly completed, the first cryogenic tests with the prototype coil (DEMO) have started. The first conclusions of these tests and the facility performances will also be discussed in this paper.

The normal zone propagation velocity is an important feature in the design of a superconducting magnet. In the particular case of the ATLAS-Barrel toroid coil protection, it is all the more important as the fast discharge is essentially realized through the toroid windings by exciting quench heaters. The time constant of that fast discharge, and consequently the final magnet temperature, are therefore determined by the heaters activation time constant and the quench propagation kinetics. Taking into account the particular Race-track shape of the ATLAS-Barrel coil, the transverse quench propagation dominates the duration of the fast discharge. In this paper, we present, at first, the experimental measurements of the transverse normal zone propagation velocities made at CERN in 2002 on the B0 model-coil up to a maximal 24 kA operating current. Then, we present a code developed in our laboratory, based upon CAST3M finite-element code, which allows the computation, among others, of the transverse normal zone propagation velocities. We finally compare computation and experimental results and obtain a very satisfactory agreement in a large (15-24kA) operating current range.

The CMS experiment (Compact Muon Solenoid) is a general-purpose proton-proton detector designed to run at the highest luminosity at the LHC. Distinctive features of the CMS detector include a high-magnetic-field solenoid (4T) coupled with a multilayer muon system, a fully active scintillating-crystal electromagnetic calorimeter, a tile hadronic calorimeter, and a powerful inner tracking system. The two 20 kA current leads for the CMS electrical circuit have been designed, manufactured and tested by CEA Saclay. Their design, with reliability as prime goal, is based on the use of a pure-copper braid, having an RRR of 130, placed inside a conduit and cooled by evaporating helium gas. Their length is of 3.3 m to cross the return yoke and their conductive cross-section has been fixed at 1800 mm/sup 2/, slightly above the optimal section. An important specification is the behavior in case of lack of coolant: the current leads are able to hold the maximal current during 5 minutes followed by a fast discharge, time constant of 190 s, without any damage. They are fully instrumented with sensors and diagnostics (temperature, voltage and helium flow) for safety and control. In case of discharge, they are submitted to a high voltage and then must ensure an insulation of 3 kV. The tests will include insulation, mechanical and electrical tests (at nominal current, with and without coolant).

The key objective of the superconducting high field magnet work package of the European Project EuCARD, and specifically of the high field model task, is to design and fabricate the Nb3Sn dipole magnet FRESCA2. With an aperture of 100 mm and a target bore field of 13 T, the magnet is aimed at upgrading the FRESCA cable test facility at CERN. The design features four 1.5-m-long double-layer coils wound with a 21-mm-wide cable. The windings are contained in a support structure based on a 65-mm-thick aluminum shell pretensioned with bladders. In order to qualify the assembly and loading procedure and to validate the finite element stress computations, the structure will be assembled around aluminum blocks, which replace the superconducting coils, and instrumented with strain gauges. In this paper, we report on the status of the assembly and we update on the progress on design and fabrication of tooling and coils.

To produce a continuous magnetic field of at least 8.5 T in a 1.1 m cold bore diameter, the superconducting outsert of the Grenoble Hybrid magnet is based on the novel development of a Nb-Ti/Cu Rutherford Cable On Conduit Conductor (RCOCC) cooled to 1.8 K by a bath of superfluid helium pressurized at atmospheric pressure. The main results of the conductor studies and development are presented after a brief introduction to the specificity of hybrid magnets, namely the electromagnetic couplings between resistive and superconducting coils. Results obtained with short samples of conductor are reviewed including the measurements of the elastic limit, AC losses, stability and critical current. The final specification of the RCOCC is presented highlighting the proposed method for the industrialization of the insertion process of the Rutherford cable on the hollow Cu-Ag stabilizer as well as its validation phase on short samples.

The R3B-Glad magnet is part of a large acceptance spectrometer devoted to the physics of exotic nuclei, under construction at CEA Saclay (France) for the future FAIR facility at GSI (Darmstadt, Germany). The R3B-Glad project is in its final phase where the magnet cold mass is achieved and will be tested at 4.6 K and nominal current in the fall of 2011. We present the results of the R&D tests programs that were implemented to answer some issues raised after the technical design review. First, this superconducting dipole will be cooled down by indirect cooling, and its 22 tons cold mass maintained at 4.6 K by means of a two-phase helium thermosiphon loop. An experimental model set-up has been specifically built to demonstrate the cooling efficiency despite the presence of large quasi-horizontal sections in the circuit. Then the superconducting Rutherford cable joints, required between the 26 coil double pancakes, were designed and tested to minimize their electrical resistance. Finally a reduced scale mock-up of a coil in its casing, with a general design similar to the final magnet, was tested at low temperature to validate the indirect cooling and the mechanical blocking system of the coil in its casing by differential thermal shrinkage. This test was performed at a higher current (8800 A) than the nominal one (3600 A) to reach the same value of temperature margin before quenching, together with similar high level of magnetic forces on the coil (100 to 200 t/m in final magnet).