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Coupling losses induced in cable-in-conduit conductors (CICC) when subject to a time-varying magnetic field are a major issue commonly encountered in large fusion tokamaks (e.g., JT-60SA, ITER, DEMO). The knowledge of these losses is crucial to determine the stability of CICC but is yet difficult to achieve analytically (thus in a short computation time) given the specific and complex architecture of these conductors although numerical solutions such as THELMA and JACKPOT already exist. In an attempt to ease the resolution of this problem, we have previously presented a theoretical generic study of a group of elements twisted together (representing a cabling stage of a CICC) and derived the analytical expression of its coupling losses. We have now extended this study to a two cabling stage conductor by establishing an analytical model to calculate its coupling losses as function of its effective features. In a second part, we compare our results to these of THELMA and JACKPOT on geometries representing ITER CS and JT-60SA TF conductors. Finally, we have set up a specific algorithm to reconstruct strand trajectories from X-ray images and have extracted the effective geometrical parameters of a JT-60SA TF conductor. Our next objective is then to extract its effective electrical parameters from interstrand resistivity measurements to be able to compare the coupling losses predicted by our analytical model with those measured within the SULTAN facility.

International audience; Lorsqu'un composite supraconducteur est dans un environnement à champ magnétique variable, des courants dits de couplage sont induits. Ceux-ci, en traversant les parties résistives du composite, génèrent une puissance thermique locale. Le but de la présente contribution est de présenter un modèle permettant de calculer analytiquement et de manière précise le terme source de l'équation de la chaleur associé à cet échauffement à tout instant et en tout point de l'espace. Le modèle est ensuite appliqué à un brin réel et les résultats des simulations sont présentés et commentés.

International audience; 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.