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Torre A.,Cryomagnetism Group | Ciazynski D.,Cryomagnetism Group | Durville D.,Ecole Centrale Paris | Bajas H.,CERN | Nijhuis A.,University of Twente
IEEE Transactions on Applied Superconductivity | Year: 2013

Nb3Sn is now commonly used in the design of high-field large-scale magnets. However, it is a brittle material, the superconducting properties of which degrade under mechanical strain. Both ITER TF and CS magnets make use of Nb3Sn strands in cable-in-conduit conductors. Experiments have been carried out in the TARSIS facility at University of Twente aiming at measuring the strand critical current as a function of periodically applied strain/stress. Until recently, these experiments have given good indications of the strand behavior, but they had not been fully understood because of the lack of an accurate description of the local strain along the tested strand. Furthermore, they cannot be extrapolated directly to a real cable-in-conduit conductor because they do not simulate the differential thermal contraction, which puts the strand under longitudinal compression. Using the mechanical code MULTIFIL developed at Ecole Centrale de Paris, associated with the electrical code CARMEN developed at CEA/IRFM, this paper aims at understanding the mechanisms of the critical current reduction during a TARSIS experiment by coupling the local strain map of the strand to the complex current paths between Nb3Sn filaments. Comparison with experimental results and with analytic limiting cases are presented and discussed. © 2002-2011 IEEE. Source

Torre A.,Cryomagnetism Group | Bajas H.,CERN | Ciazynski D.,Cryomagnetism Group
IEEE Transactions on Applied Superconductivity | Year: 2014

Following the test of the first Central Solenoid (CS) conductor short samples for the International Thermonuclear Experimental Reactor (ITER) in the SULTAN facility, Iter Organization (IO) decided to manufacture and test two alternate samples using four different cable designs. These samples, while using the same Nb3Sn strand, were meant to assess the influence of various cable design parameters on the conductor performance and behavior under mechanical cycling. In particular, the second of these samples, CSIO2, aimed at comparing designs with modified cabling twist pitches sequences. This sample has been tested, and the two legs exhibited very different behaviors. To help understand what could lead to such a difference, these two cables were mechanically modeled using the MULTIFIL code, and the resulting strain map was used as an input into the CEA electrical code CARMEN. This article presents the main data extracted from the mechanical simulation and its use into the electrical modeling of individual strands inside the CICC. © 2002-2011 IEEE. Source

Torre A.,Cryomagnetism Group | Duchateau J.-L.,Cryomagnetism Group | Turck B.,Cryomagnetism Group | Zani L.,Cryomagnetism Group
IEEE Transactions on Applied Superconductivity | Year: 2012

During a plasma disruption a complex map of magnetic field variation is generated along the JT-60SA TF conductor. The current variations associated with a symmetric plasma disruption are modeled in JT-60SA, on the basis of a circuit approach. The main components of the circuit model are: the poloidal field coils, the plasma represented by circular filaments, the vacuum vessel, and the stabilizing plates. The disruption induces currents in all elements of the circuit model which produce a variation of the field map. At the location of the TF coil, this field change can be assessed and used for ac losses and stability calculations on the TF conductor. An analysis of the map will allow estimating the field change time constants and investigating which points the JT-60SA TF conductor experience the most severe field variations. Based on a recent multi-constant AC losses model for the JT-60SA TF conductor, an analytical model of stability is presented to describe the temperature increase in the cable after a plasma disruption, taking into account the heat transfer to helium during the power losses deposition. A discussion will be introduced about a possible influence of the synchronous parallel field variations, which may saturate the strand filaments and increase the heat losses dissipation. © 2011 IEEE. Source

Torre A.,Cryomagnetism Group | Ciazynski D.,Cryomagnetism Group | Gros G.,Cryomagnetism Group | Cloez H.,Cryomagnetism Group | And 2 more authors.
IEEE Transactions on Applied Superconductivity | Year: 2015

Cable-in-conduit conductors made of Nb3Sn strands, as envisaged in high-field magnets for fusion applications (e.g., the International Thermonuclear Experimental Reactor (ITER) project) , have been shown to be prone to degradation of their current transport capability when subject to high electromagnetic forces (coming from the combination of a high current and a high magnetic field), particularly under cyclic loading. Although some optimization of the cable layout can be envisaged to mitigate this effect, the knowledge of the electrical properties of Nb3Sn strands under periodic bending (simulating in-cable operating conditions) is generally considered a needed characteristic for magnet designers and users. The French Alternative Energies and Alternative Energies and Atomic Energy Commission (CEA)/Institute for Magnetic Fusion Research (IRFM) has developed a new Versailles Project on Advanced Materials and Standards (VAMAS)-like mandrel in order to test under relevant field and temperature conditions high-field superconducting strands subject to periodic bending provided by the strand deformation under its own Lorentz force. The advantage of this setup is its similarity with the setup used in critical current measurements on a VAMAS mandrel, which makes its implementation in existing facilities quite easy and rather cheap, as well as possible direct comparisons with unbent samples on a classical VAMAS mandrel. This paper presents the design layouts and carefully depicts the assembly of the different tested samples. The first test results obtained on Nb3Sn strands are given and discussed. © 2002-2011 IEEE. Source

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