Evaluation of Trapped Magnetic Field Properties in Superconducting MgB2_2 Bulk Magnets of Various Shapes by Finite Element Method

The trapped magnetic field properties of superconducting MgB2 bulk magnets with various shapes such as a triangular, a quadrangular, a hexangular bulk were calculated by the Finite Elements Method (FEM). The effect for the combination of several numbers of bulks was also investigated for several kinds of shapes to obtain large area of bulk surface in spite of one large bulk. In this calculation, the simple magnetization process replaced by the field-cool magnetization was used to obtain the equivalent distribution of the magnetic field, and the thermal equation in FEM was omitted. The trapped magnetic field for the triangular bulk by FEM was compared with the experimental result. It was found that the calculated results agreed well with the experimental result. The maximum trapped magnetic field was obtained in the cylindrical shape among several kinds of shapes. The trapped magnetic field was increased by the combination of multi-bulks. It was confirmed that the trapped magnetic field of the multi-bulks was larger than that of the single bulk. The trapped magnetic field increases with increasing the number of the bulks.28th International Symposium on Superconductivity(ISS 2015), November 16-18, 2015, Tokyo, Japa

Estimation of AC loss in cylindrical superconductor with ripple current

The loss energy density (AC loss) in cylindrical superconductor with ripple current based on Irie-Yamafuji model in which the magnetic fiel dependence of critical current density is taken into account is theoretically calculated for design of DC transmission cable system. It is confirme that the AC loss does not changed for the cases with and without DC current when the critical current does not depend on magnetic fiel which is corresponding to Bean-London model. On the contrary, it is found that there is current region where the AC loss becomes smaller than that for the case without DC current. The AC loss of ripple current is seems to be enough small in layered structure of DC transmission cable made by thin tape superconductor.Proceedings of the 24th International Symposium on Superconductivity (ISS 2011), October 24-26, 2011, Tokyo, Japa

Parametric analysis of flux creep-flow model by using genetic algorithm

The pinning parameters for numerical calculation based on the flux creep-flow model are determined by using genetic algorithm (GA), which has been applied to many practical determination for parameters. Several estimation functions which describe the distance between the experimental and calculated results by GA were proposed, and the difference between the results were calculated. It is found that the pinning parameters of the flux creep-flow model are successfully deduced by GA. The difference between the calculated and experimental results and the calculation time are found to be largely depended on the estimation functions.Proceedings of the 24th International Symposium on Superconductivity (ISS 2011), October 24-26, 2011, Tokyo, Japa

Current-carrying capacity of single layer cable using superconducting Bi-2223 tapes in a parallel magnetic field

It was theoretically shown by the authors that the current-carrying capacity of superconducting dc power cable can be enhanced by choosing a force-free configuration under a parallel magnetic field produced by the current flowing back in the outer shielding conductor. This was experimentally checked for a single layer cable using Bi-2223 tapes in an applied parallel magnetic field. It was found that the current-carrying capacity took on a peak value under the force-free condition for the total magnetic field, including the self-field. This shows that the proposed structure is suitable for practical dc power transmission. The possibility of the innovative dc superconducting power cable with multi-layers with higher current-carrying capacity is discussed

AC loss of ripple current in superconducting DC power transmission cable

As a method of largely reducing the transmission loss in the electric power grid, superconducting direct current (DC) power transmission cable has been investigated. Using superconducting DC power transmission cables, large amounts of current and energy can be transferred compared to conventional copper cables. In this case, an alternating current (AC) is converted to DC and superposed AC which is known as ripple current, and the energy loss by the ripple current is generated. Therefore it is desired to estimate the energy loss density for the case of DC current and superposed AC current for a design of DC transmission cable system. In this study, the hysteresis loss for DC current of 2 kA rectified from 60 Hz alternating current is calculated using the Bean model, and coupling loss was also estimated. The diameter of the cable was 40 mm. The ripple currents generated by multi-pulse rectifiers, 6-pulse, 12-pulse, and 24-pulse were considered. It is found that the total AC loss including the hysteresis loss and the coupling loss is considerably smaller than the supposed heat loss of 0.5 W/m which is obtained with a newly developed cable.26th International Symposium on Superconductivity (ISS 2013), November 18-20, 2013, Tokyo, Japa

Evaluation of Magnetic Cutting and Polishing with Superconducting Bulks

In this paper, magnetic levitation tool with superconducting bulks is introduced as a new hollow machining technology. Magnetic levitation tool is the machine that magnet levitates above superconducting bulks and driving force of rotating magnet shaves the object. This tool is expected to use for a grinding machine and machining device because of hollow machining and micromachining by strong fixing. For using magnetic levitation tool, the attractive force, the repulsive force and rotating torque are important for grinding machine, machining outer surface and both, respectively. These forces are calculated by FEM, and compared with experimental results. The experimental results are agreed well with calculated results. However, the attractive force is one order smaller than that required in chemical mechanical polishing

Critical Current Properties in Longitudinal Magnetic Field of YBCO Superconductor with APC

The critical current density (Jc) properties of the Artificial Pinning Center (APC) introduced YBa2Cu3O7 (YBCO) films in the longitudinal magnetic field were measured. Y2O3 or Y2BaCuO5 (Y211) was introduced as APCs to YBCO, and YBCO films with APC were fabricated on SrTiO3 single crystal substrate. The sizes of Y2O3 and Y211 were 5—10 nm and 10—20 nm, respectively. As a result, Jc enhancement in the longitudinal magnetic field was observed in Y2O3 introduced YBCO films. However, it was not observed in Y211 introduced YBCO films. Therefore, it was considered that Jc properties in the longitudinal magnetic field were affected by introducing of small size APC, and it was necessary that APC does not disturb the current pathway in the superconductor.28th International Symposium on Superconductivity, ISS 2015, November 16-18, 2015, Tokyo, Japa

Evaluation of trapped magnetic field properties in superconducting MgB2 bulk magnets by finite element method

The trapped magnetic field properties in superconducting MgB2 bulk magnets with various kinds of shape such as a disk, a ring and a pair of disks were calculated by the finite element method (FEM). For simplicity, field cool magnetization was replaced by a simple magnetization process at constant temperature to obtain equivalent distribution of magnetic field, and the thermal equation in FEM was omitted. It was confirmed that the result of FEM agreed well with the result by analytical method in infinite long cylinder. We compared the trapped magnetic field property between FEM result and experimental result in reference in order to research the simple evaluation method of the trapped magnetic field of MgB2 bulk magnet. It was found that the result of FEM agreed with the experimental result and it can explain the distribution of trapped magnetic field of superconducting MgB2 bulk magnet. From these results, it was found that it was possible to be calculated in various kinds of shape with using simple evaluation by FEM. Therefore, the optimization of the maximum trapped magnetic field in superconducting MgB2 bulk magnet can be discussed.Proceedings of the 27th International Symposium on Superconductivity (ISS 2014) November 25-27, 2014, Tokyo, Japa

Calculation of critical current in DC HTS cable using longitudinal magnetic field effect

Proceedings of the 25th International Symposium on Superconductivity (ISS 2012) Advances in Superconductivity XXV , December 3-5, 2012, TOWER HALL FUNABORI, Tokyo, JapanIt is known from experimental data that the critical current of superconducting wires in a longitudinal magnetic field is higher than that in a transverse magnetic field. This property was proposed to apply to DC superconducting cables in our previous paper. Here, we propose a new calculation method of the current-carrying capacity for a new DC superconducting cable. An iteration method is used to calculate the magnetic field and critical current density in each layer and the current-carrying capacity of the cable. This enables us to calculate these quantities even for the cable with a different structure from the force-free one. When the critical current density increases with a longitudinal magnetic field, the optimal structure is found to be close to that of the force free cable. The optimal structure is obtained also when the critical current density decreases slightly with the longitudinal magnetic field. The reason for the enhanced current-carrying capacity even for such a case is a sufficiently larger critical current density in the longitudinal magnetic field than that in the transverse magnetic field