It is necessary to develop AC superconducting cables with large current capacity for applications to AC power apparatuses. Since the critical current of single AC wires could not be large, such single wires (strands) are twisted and bundled to make cables with large current capacity. In multiply-twisted cables, the magnetic field component that is parallel to a strand axis is produced as well as the transverse one. In this paper, the influence of such components of the magnetic field on the AC quench current degradation is investigated. The internal magnetic field are calculated in various type of cables and a winding. The AC quench current is measured in the bias magnetic field with longitudinal and transverse components simulating the internal magnetic field in the multiply-twisted cables. The influence of such magnetic field on thermo-magnetic instabilities is evaluated.
The paper presents results obtained in the study of the current -voltage characteristics, critical and quenching currents a s well as of the AC transport current and magnetization losses in four series of fine filament NbTi composites prepared by Showa Electric Wire & Cable Co., Japan. Complementary measurements have been made also on a commercially available t y p e T AC superconducting wire produced by G E C Alsthom Company, France.The samples differ in filament diameter, matrix thickness between filaments and in the number and structure of filament bundles in the composite. I n two series of samples b a r r i e r type artificial pinning centers have been introduced to increase J, and decrease the normalized magnetization losses. The conclusions concerning the optimization of multifilamentary composites and cables for AC use a t low working magnetic field are briefly reviewed.
We have fabricated a 3-axes magnetometer that can reduce the residual magnetic field below 50 µG for each direction. Josephson critical current I c between a noncentrosymmetric superconductor (CePt 3 Si or LaPt 3 Si) and Al has been investigated inside it to avoid the magnetic-flux trapping during the superconducting transition and found to show a magnetic field H dependence similar to the previous one obtained using one-axis magnetometer; asymmetric patterns with respect to H = 0 are commonly observed for CePt 3 Si and LaPt 3 Si. This suggests that the residual-field components perpendicular to H applied for I c (H) measurements does not basically affect the I c (H) patterns.
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