Kaoru Nemoto

Case Study of High-Tc Superconducting Bulk Magnets for Maglev

We investigated the applicability of a high-Tc superconducting bulk magnet to the Maglev system. For this purpose, each pole will be composed of numerous high-Tc superconductors, because their size at present is not sufficiently large. In this study, we investigated the design, weight, trapped magnetic field and other characteristics of the system required for the bulk magnet in which bulk superconductors are arranged in array per one pole, and determined it in comparison with the conventional race-track superconducting magnet of the Maglev system. We present an image of the bulk magnet for the Maglev system when 250mm square bulk superconductors with a 200mm square hole and 100mm in total thickness are arranged in four columns and two rows per one pole.

Magnetic Shielding of High-Tc Superconducting Plates

Magnetic shielding properties were measured at 77 K in YBaCuO superconducting plates prepared by melt processes. Melt processed YBaCuO has a high Jc value, hence the material is promising for the application to magnetic shielding in a relatively high magnetic field. The shielding plate with 1 mm in thickness reduces an external magnetic field of 7.1 mT to a minimum value of less than 0.1 mT. A plate which consists of small samples in a tile shape is considered to be realistic to design a large shielding plate, and a laminated plate can enhance the shielding properties. The touching part in one layer does not extend from the bottom to the top of the shielding plate in three layers. The laminated plate in three layers reduces an applied magnetic field of 14.4 mT to an average value of about 8 mT.

Switching performance of Nb3Sn persistent current switch

We designed a persistent current switch consisting of Nb3Sn superconducting wire for Superconducting Magneto-Hydro-Dynamic Propulsion Ship (MHDS). Nb3Sn has Tc higher than NbTi, which is commonly used for the conventional persistent current switch, and thus is expected to show a higher stability against the disturbance. We therefore performed numerical simulations for the heat transfer in a 10kA-class Nb3Sn persistent current switch by using a finite element method. The results of switching performance will be presented based on the computer simulation for temperature distribution during the heating and cooling cycle. We also present the estimated time for the transition from the superconducting to normal state (off-state) and vice versa (on-state).

Magnetic Shielding by Oxide Superconducting Plates

Since High-Tc superconductors such as Y-system and Bi-system show perfect diamagnetism at above 90 K, it is expected that a magnetic field will be shielded by superconductors cooled with liquid nitrogen. In this study, magnetic shielding effect of superconducting YBaCuO disks prepared by melt processes was measured at 77K. The results indicate that disk samples with ~16 mm in diameter and ~ 1 mm in thickness can reduce an external magnetic field in intermediate field range, but that the magnetic flux comes in through grainboundaries and cracks of the sample.

Switching reaction of Nb3Sn persistent current switch with a high current capacity

We designed a persistent current switch (PCS) consisting of Nb 3 Sn superconducting wire for superconducting magneto-hydrodynamic propulsion ship. Nb 3 Sn has T c higher than NbTi, which is commonly used for the conventional PCS, and thus Nb 3 Sn is expected to show a higher stability against disturbance. We performed numerical simulations for the heat transfer in a 3-kA-class Nb 3 Sn PCS by using a finite element method. We then constructed a 3 kA-6 Ω Nb 3 Sn PCS and measured its switching performance. The results obtained in 3-kA PCS are utilized for the simulation of 10-kA-class switching performance including numerical simulations for the heat transfer. The results of switching performance will be presented based on the computer simulation for temperature distribution during the heating and cooling cycles. We also present the estimated time for the transition from the superconducting to normal state (off-state) and vice versa (on-state).

Preliminary study of superconducting transformers for electric rolling stocks

The development of a thousand-meter class flexible wire has been achieved in silver sheathed Bi(Pb)SrCaCuO based superconducting wires, which show a high Jc at relatively low temperatures up to 77 K. A high-Tc superconducting power transformer has been demonstrated recently, and it is expected as one of the superconducting wire applications. Reducing the weight of rolling stocks is a very important issue in railways. Therefore, we discuss the possibility of a promising superconducting power transformer for electric rolling stocks in conventional railways.