Finite-element analysis of the strain distribution due to bending in a REBCO coated conductor for canted cosine theta dipole magnet applications Permalink https://escholarship.org/uc/item/760535cn Journal IEEE Transactions on Applied Superconductivity, 29 (5) Abstract-High-current cables using REBCO tapes can be used to develop high-field dipole magnets. However, the strain accumulated during cable fabrication and coil winding may reduce the critical current of the conductor. Therefore, it is important to properly consider the strain when designing high-field magnets. In this work, we used structural finite element analysis to predict the strain experienced by a REBCO tape during bending in configurations relevant to the fabrication of high field accelerator magnets, in particular, the mechanical strain generated during cable fabrication and winding in a canted-cosθ (CCT) dipole configuration.We considered two different cable options: (A) flat tape that lay in the mandrel channel and (B) a REBCO tape helically wound around a circular copper core, the typical configuration of the conductor in round core cable (CORC®). Strain accumulated during tape winding is studied for different core diameters and winding tilt angles. FEA longitudinal strain results were compared with the simulations for configuration A, where higher strain was observed experimentally. Configuration B was verified indirectly by comparing experimentally measured Ic with the one predicted (based on the longitudinal strain) as function of the bending diameter. Good agreement was found up to a bending diameter of 30 mm. The presented results will help to understand the impact of bending on REBCO tapes and CORC ® wires to develop high-field magnets. Index Terms-High-temperature superconductors, yttrium barium copper oxide, superconducting cables, superconducting magnets This is the author's version of an article that has been published in this journal. Changes were made to this version by the publisher prior to publication.The final version of record is available at http://dx.
High Temperature Superconducting (HTS) tapes such as Rare Earth Barium Copper Oxide (REBCO) are an attractive option for high field magnets operated in cryogenic fluids. However, quench events can occur in which the conductor locally loses its superconducting properties. It is critical to rapidly detect and respond to such an event. Conventional quench detection methods using voltage taps are difficult in HTS devices, since the normal zone propagation velocities are 2–3 orders of magnitude lower in HTS compared to low temperature superconductors (Iwasa, Cryogenics, 2003). We propose an alternative in which a linear array of MEMS microphones is distributed down the central cooling channel of a cable in-conduit conductor. The array can detect the acoustic signature caused by a quench event which propagates in the cooling fluid. The proposed method differs from Acoustic Emission (AE) detection, which uses sensors mounted on the magnet surface to detect structural vibration (Tsukamoto, Appl. Phys. Lett., 1981). In order to implement the system, MEMS microphones and preamplifiers must operate in cryogenic fluids. We report on characterization of commercial MEMS microphones in cryogenic gaseous helium between 0.5 and 1.5 bar down to 20 K, and in liquid nitrogen at 1 bar and 77 K.
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