H. Nakajima1, T. Hemmi1, M. Iguchi1, T. Nabara1, K. Matsui1, Y. Chida1, H. Kajitani1, K. Takano1, T. Isono1, N. Koizumi1, Y. Nunoya1, K. Hamada1, K. Okuno1, A. Foussat2, R. Gallix2, A. Devred 2, P. Libeyre 2, N. Mitchell 2, A Bonito Oliva 3, B. Bellesia 3, E. Boter 3, M. Cornelis 3, J. Cornella 3, R. Harrison 3, L. Poncet 3, T. Boutboul 3, H. Rajainmaki 3, P. Valente 3, C. Sborchia 3, M. Losasso3, I Rodin4, V. S. Vysotsky5, K. Chan6, N. Martovetsky 6, S. H. Park7, H. Li8, Y. Wu9, J. Wei9

Full text: Starting March 2007, over 60 ITER cable-in-conduit conductors (CICC) have been tested in the SULTAN test facility in Villigen, Switzerland, including TF, CS, PF and busbars samples. The conductors are supplied by the ITER Domestic Agencies (DAs) and assembled into SULTAN samples at CRPP. The test reproduces the actual operating conditions in the ITER coils, except for the hoop load and the CS maximum field. Depending on the stage of the procurement, the SULTAN samples are categorized into Design Verification, Supplier Qualification, Process Qualification and Series Production. The number of remaining samples to be tested during the ITER construction phase is about 40. For the NbTi CICC, the results confirm the prediction from the strand data, which are made taking the peak field over the conductor cross section as operating field. At low current density, where the n-index of the transition is measurable, the NbTi CICC and the NbTi strand have the same n-index. All the NbTi samples passed the supplier qualification phase. For the Nb{sub 3}Sn CICC, the performance prediction is hindered by the irreversible degradation caused by filament damage occurring during cyclic loading. At the first run of the test campaign, the performance of all the Nb{sub 3}Sn samples largely meets the target. Contrary to the NbTi CICC case, the n-index of the transition is substantially lower than in the strands. The performance loss upon load cycles and thermal cycles has a broad range. All the TF conductor samples passed the supplier qualification phase. For the CS conductors, the supplier qualification phase will be finalized in 2012. (author)

Magnetization measurements are relevant tests for the characterization of superconductors. Practically they are the only measurements that allow estimating the critical current density at low fields of low temperature superconductors, the effective filament size and the hysteresis losses. For this purpose CERN, in collaboration with the University of Geneva, has carried out magnetization measurements on five types of Nb3Sn wires: three bronze route strands used in the ITER project; one Powder In Tube (PIT) and one Internal Tin (IT) wires used for developing next generation accelerator magnets. The field dependent magnetization has been determined using three setups: a Vibrating Sample Magnetometer (VSM), a Superconducting Quantum Interference Device (SQUID) and a special system used for the production control of LHC strands. Samples of different lengths have been tested to check the different coupling between the filaments. Unexpectedly, it was found that the magnetization of the tested bronze wires was strongly dependent on the sample length. In this paper, the results, which were obtained for different type of strands and sample lengths, are reported and compared.

Japan Atomic Energy Agency is procuring the Nb3Sn superconductors for Toroidal Field (TF) Coils as part of the ITER project. Because the required tonnage of Nb3Sn strand is quite large compared to past experience and the required superconducting performance is higher than that of the model coils fabricated and tested during the ITER-EDA period, quality control techniques are very important for the successful manufacture of the strand. Approximately 40 tons of Nb3Sn strand have been successfully completed under a severe quality control regiment and all strand meets ITER specifications. Sophisticated control techniques also are required during the jacketing process, in order to fabricate conductors with a precise outer diameter and without any defects in the welds. Inspection of the inner surface of welds using lasers is an example of the rigorous quality control techniques developed. A full-length (760 m) Cu dummy conductor has been fabricated successfully, and the suitability of all jacketing technology was confirmed during this fabrication. Specifications for manufacturing procedures which satisfy ITER requirements were established, enabling the start of fabrication of Nb3Sn conductors for the TF coils in March 2010.

The Next European Dipole (NED) activity is aimed at the development of a large-aperture, high-field superconducting magnet relying on high-performances Nb3Sn conductors. Part of the NED program is devoted to the mechanical study of a new generation of Nb3Sn wires and to predict and describe their behavior under the severe loading conditions of the cabling process. The deformation resulting from the cabling process was simulated through mechanical analyses by Finite Elements (FE). The ensuing results of FE analyses are presented, allowing the wire behavior under simple uni-axial loads to be described. They are compared to cross section micrographs of deformed wires.

We report an experimental study aiming to demonstrate the not negligible role of unreacted Nb on the magnetic instabilities in superconducting Nb3Sn multifilamentary wires, observable through partial flux jumps at magnetic field values below 0.5 T. The analysed wires were recently developed for use as dipoles required in future high-energy proton accelerators and are based on powder-in-tube technology. We studied both unreacted (only involving Nb filaments) and reacted wires, finding flux jump instabilities in both cases when performing magnetic measurements. The results can be interpreted on the basis of the critical state model and are coherent with the intrinsic stability criterion. (Some figures in this article are in colour only in the electronic version) In recent years we have observed renewed interest in Nb3Sn superconductors. In spite of the progress with high-Tc superconductors optimized for applications (e.g. YBCOcoated conductors) and of very promising developments of magnesium diboride wires, large projects involving highfield superconducting magnets are still looking for conductors based on Nb3Sn. The ITER project, aiming to develop a Tokamak fusion reactor, envisages a cable in a conduit Nb3Sn conductor for toroidal and poloidal coils and for the central solenoid. American and European teams are developing highfield-gradient quadrupole and high-field dipole magnets (15 T) for the interaction regions of the Large Hadron Collider at CERN, based on a multistrand conductor, made of Nb3Sn multifilamentary wires [1, 2]. The basic feature making Nb3Sn so appealing is its ability to carry very high current density in practical wires, typically 2400 A mm−2 at a temperature of 4.5 K and applied magnetic field of 12 T. Unfortunately, recent developments in high-field accelerator magnets showed the Achilles’ heel of wires carrying high current density [3, 4]. It is a well-known problem since the early developments of superconducting wires in the 1960s: a local temperature increase, due to a disturbance, causes a sudden magnetic flux penetration into the superconductor, generating a further heat dissipation [5, 6]. This avalanche process can be controlled (no transition to normal state occurs) if the wire is thin enough according to the formula b < √ 3γ Cp(Tc(B) − Top) μ0 J 2 c (B, Top) , (1) where b is the wire diameter, γ is the mass density, Cp is the specific heat, Tc is the critical temperature at a given magnetic field B, Top is the operating temperature and Jc is the critical current density at the operating temperature. On the basis of this simple formula (the adiabatic stability criterion) the need to develop multifilamentary wires was understood with 0953-2048/07/060034+04$30.00 © 2007 IOP Publishing Ltd Printed in the UK

The room temperature elastic and plastic properties under uniaxial tensile loading of the different phases of an un-reacted, internal-tin process, Nb3Sn wire have been determined by tensile tests of whole wires and of extracted Ta, Nb and Nb alloy filaments, as well as by indentation hardness measurements in metallographic wire cross sections Contribution to the ICFA HB2006, KEK (Japan) Work supported by the European Community-Research Infrastructure Activity under the FP6 “Structuring the European Research Area” programme (CARE, contract number RII3-CT2003-506395) 1 ICMC’06 abstract 136 Tensile properties of the individual phases in un-reacted multifilament Nb3Sn wires C. Scheuerlein 1 , A. Devred 1,2 , B. Fedelich 3 , M. Finn 3 , M. Griepentrog 3 , P. El-Kallassi 1 , F. Lecouturier 4 , L. Oberli 1 , B. Rehmer 3 , S. Sgobba 1 , L. Thilly 5 , V. Vidal 4 1 European Organization for Nuclear Research (CERN), 1211 Genève 23, Switzerland 2 CEA/Saclay, DSM/DAPNIA/SACM, 91191 Gif-sur-Yvette CEDEX, France 3 Bundesanstalt für Materialforschung und –prüfung (BAM), 12200 Berlin, Germany 4 LNCMP, CNRS-UPS-INSA, 143 avenue de Rangueil, 31400 Toulouse, France 5 LMP, Université de Poitiers, SP2MI, 86962 Futuroscope, France The room temperature elastic and plastic properties under uniaxial tensile loading of the different phases of an un-reacted, internal-tin process, Nb3Sn wire have been determined by tensile tests of whole wires and of extracted Ta, Nb and Nb alloy filaments, as well as by indentation hardness measurements in metallographic wire cross sections.