The key objective of the High Field Magnet work package of the European Project EuCARD is to design and fabricate the Nb 3 Sn 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.
The Short Model Coil (SMC) assembly has been designed, as test bench for short racetrack coils wound with cable. The mechanical structure comprises an iron yoke surrounded by a 20 mm thick aluminum ...alloy shell, and includes four loading pads that transmit the required pre-compression from the outer shell into the two coils. The outer shell is pre-tensioned with mechanical keys that are inserted with the help of pressurized bladders and two 30 mm diameter aluminum alloy rods provide the axial loading to the coil ends. The outer shell, the axial rods, and the coils are instrumented with strain gauges, which allow precise monitoring of the loading conditions during the assembly and at cryogenic temperature during the magnet test. Two SMC assemblies have been completed and cold tested in the frame of a European collaboration between CEA (FR), CERN and STFC (UK) and with the technical support from LBNL (US). This paper describes the main features of the SMC assembly, the experience from the dummy assemblies, the fabrication of the coils, and discusses the test results of the cold tests showing a peak field of 12.5 T at 1.9 K after training.
In the framework of future LHC upgrades using Nb 3 Sn magnets, supported in part by the US LHC Accelerator Research Program (LARP) and the European EuCARD program, CERN is intensifying its research ...on Nb 3 Sn Rutherford cables. In the FRESCA cable test facility at CERN, two new Nb 3 Sn cable samples were investigated concerning their quench and critical current as well as stability performance. The two samples are based on RRP type strands with comparable layout. They have 27 strands with 0.7 mm diameter while the strands have 54 or 108 superconducting sub-elements. The cables are 10 mm wide and have a transposition pitch of about 75 mm. The cables are used in magnets built for LARP. Their performance is measured as a function of magnetic field up to 10 T with ramp rates of 10 to 1000 A/s and temperature of 1.9 and 4.3 K. A hall probe array is present to study the current distribution. Point heaters are used to study cable stability and current redistribution.
The Next European Dipole (NED) Joint Research Activity was launched on 1 January 2004 to promote the development of high-performance Nb3Sn conductors in collaboration with European industry (aiming ...at a non-copper critical current density of 1500 A mm-2 at 4.2 K and 15 T) and to assess the suitability of Nb3Sn technology to the next generation of accelerator magnets (aiming at an aperture of 88 mm and a conductor peak field of ~15 T). It is part of the Coordinated Accelerator Research in Europe (CARE) project, which involves eight collaborators, and is half-funded by the European Union. After briefly recalling the Activity organization, we report the main progress achieved over the last year, which includes: the manufacturing of a double-bath He II cryostat for heat transfer measurements through Nb3Sn conductor insulation, detailed quench computations for various NED-like magnet configurations, the award of two industrial subcontracts for Nb3Sn conductor development, the first results of a cross-calibration programme of test facilities for Nb3Sn wire characterization, detailed investigations of the mechanical properties of heavily cold-drawn Cu/Nb/Sn composite wires, and the preliminary assessment of a new insulation system based on polyimide-sized glass fibre tapes. Last, we briefly review the efforts of an ongoing Working Group on magnet design and optimization.
In the framework of the EuCARD program, CERN is participating in the development of a 13 T 100-mm-aperture dipole magnet to upgrade the superconducting cable test facility FRESCA at CERN. The ...conductor candidates for building this magnet are two 1-mm Nb 3 Sn strands: the Powder In Tube (PIT) produced by Bruker-EAS and the 132/169 RRP by Oxford Superconducting Technology (OST). Recently the PIT strand has been extensively characterized by CERN in collaboration with the University of Geneva (UniGe). The critical current dependence on the magnetic field and on the axial strain has been measured at different temperatures. Furthermore, the strand magnetization has been measured at different temperature using a vibrating sample magnetometer. Finally the magneto-thermal stability of this strand was studied by measuring the quench current between 0 T and 12 T at 1.9 K and 4.3 K. The experimental results are compared with an optimized scaling law for the critical current of Nb 3 Sn strands. In this paper the results obtained for the PIT strand are summarized and discussed.
Amperostatic coulometry was applied for the thickness measurement of Sn-Ag hot dip coatings, which comprise an extended Sn-Cu interdiffusion layer. Complementary measurements, notably weight loss, ...X-ray photoelectron spectroscopy, energydispersive X-ray spectroscopy, X-ray fluorescence (XRF), and dynamic secondary ion mass spectroscopy were performed in order to obtain a better interpretation of the coulometry results. Based on the experimental results presented in this article, the three potential changes observed during coulometry measurements are ascribed to (i) the entire dissolution of pure Sn, (ii) the formation of a CuCl salt layer, and (iii) the surface passivation. The measurement of the pure Sn mass is well reproducible despite strong coating thickness variations detected by XRF. Several experimental problems, in particular, a coating undercutting, hamper the determination of the Sn mass in the intermetallic Sn-Cu layer.
The Sn concentration gradients across the A15 phase have been studied by Energy Dispersive X-ray Spectroscopy (EDS) measurements. High spatial resolution EDS measurements in the Transmission Electron ...Microscope reveal a comparatively strong Sn concentration gradient from the periphery towards the centre of individual (Nb-Ta)3Sn grains.
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