Design of a 30 T Superconducting Magnet Using a Coated Conductor Insert

Toshiba Corp., Yokohama, Japan
IEEE Transactions on Applied Superconductivity (Impact Factor: 1.24). 07/2009; 19(3):1617 - 1620. DOI: 10.1109/TASC.2009.2018271
Source: IEEE Xplore


A program to develop a 30 T superconducting magnet based on novel concepts is now in progress at the High Field Laboratory for Superconducting Materials (HFLSM) at Tohoku University and the Tsukuba Magnet Laboratory (TML) at the National Institute for Materials Science. A 30 T superconducting magnet comprising a high-temperature superconducting (HTS) insert and a low-temperature superconducting (LTS) outsert was conceptually designed. For the high-field HTS insert, a YBCO coated conductor tape was adopted because of its high critical current density in high fields and its high mechanical strength. A relatively high tolerance limit of hoop stress in the insert coil can be assumed in the coil design according to its mechanical properties. The critical current density of the YBCO tape was analytically predicted as a function of temperature and magnetic field. To withstand a large electromagnetic force, the LTS outsert was composed of CuNb/Nb3Sn and NbTi coils. The CuNb/Nb3Sn coil was designed using high-strength cable consisting of internally reinforced Nb3Sn strands with a CuNb reinforcing stabilizer subjected to repeated bending treatment. The results of this design study show the potential for a compact high-field magnet employing an insert coil formed of YBCO coated conductor.

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    • "Several authors developed methods to predict the critical current of coils but none applied these methods to ReBCO coils at relatively low magnetic fields or compared the predictions with experiments. Some works simply predict the critical current as the intersection between the load line and the field dependence of the tape critical current at either parallel or perpendicular applied field [12] [13] [14] [15]. Although this method is quick, it is prone to errors because the lowest critical current is usually at an intermediate angle [16] [17]. "
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    ABSTRACT: Many applications of ReBCO-coated conductors operate at low magnetic fields in the superconductor (below 200 mT). In order to predict the critical current and AC loss in these applications, it is necessary to know the anisotropy and field dependence of the critical current density at low magnetic fields. In this paper, we obtain a formula for the critical current density in a coated conductor as a function of the local magnetic field and its orientation. Afterwards, we apply this formula to predict the critical current of a pancake coil that we constructed. We extract the critical current density of the tape from measurements of the in-field critical current at several orientations. Numerical simulations correct the effect of the self-field in the measurements and successfully predict the critical current in the pancake coil. We found that a simple elliptical model is not enough to describe the anisotropy of the critical current density. In conclusion, the analytical fit that we present is useful to predict the critical current of actual coils. Therefore, it may also be useful for other structures made of coated conductor, like power-transmission cables, Roebel cables and resistive fault current limiters.
    Full-text · Article · Mar 2011 · Superconductor Science and Technology
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    ABSTRACT: In a high temperature superconducting magnet consisting of pancake windings, the perpendicular magnetic field considerably reduces the value of the critical current of the outer pancake windings due to anisotropy. An air gap was inserted between each pancake winding in this paper to reduce the decrement of the critical current in each pancake winding. In a low temperature superconducting magnet, the central magnetic field decreases when there is an air gap between the pancake windings. On the other hand, the central magnetic field of a HTS magnet increases when an air gap is provided. The properties of the HTS insert/outsert magnet having an air gap between the pancake windings are examined in this paper. YBCO wire and BSCCO wire were used in the insert and the outsert magnets, respectively. An E - J relation and the evolution strategy were adopted to calculate the optimum critical currents of both magnets. The calculation results showed that there was an optimum air gap which maximized the central magnetic field. The optimum air gap was dependent on the specifications of the HTS magnet.
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    ABSTRACT: Mechanical property of GdBa<sub>2</sub>Cu<sub>3</sub>O<sub>y</sub> (GdBCO) coated conductor was investigated at 4.2 K in a magnetic field by two ways, which are the tensile test and the hoop stress test. The tensile stress/strain dependence of critical current ( I <sub>c</sub>) of a 2 mm width conductor was explored at 4.2 K, 18 T. The result provided that I <sub>c</sub> -reversible strain limit existed in between 0.43% and 0.46%, corresponding to 907 MPa and 960 MPa in stress, and the elastic constant was 203 GPa. The hoop stress test has been performed at 4.2 K, 11 T. A test coil was fabricated by winding a 5 mm width conductor on a 270 mm diameter GFRP bobbin by 1.5 turns. The maximum value of applied hoop stress, which was deduced from a product of magnetic field, current density and coil radius, was 1322 MPa. Five strain gauges glued on the conductor surface showed almost the same values, which were in a range of 0.64% to 0.67%, indicating the uniform longitudinal deformation. Furthermore, the hoop stress-strain characteristics were linear, suggesting an elastic deformation. The deduced elastic constants were in a range of 196-204 GPa. It was confirmed that the GdBCO coated conductor performance was deteriorated irreversibly by 1322 MPa hoop stress, whereas not by 1302 MPa hoop stress.
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