Yoh Nagasaki

This study investigated the axial compressive stress dependence of the critical current of Rare Earth Barium-Copper-Oxide (REBCO) double-pancake coils. We measured the critical currents of REBCO coils cooled by liquid nitrogen while various axial compressive stresses from 0 MPa to 130 MPa were applied. After each stress was applied, the critical currents of the coils were also measured without the stress application to examine if the REBCO coils were irreversibly deteriorated. The experimental r

This study designed a high-temperature superconducting (HTS) coil using yttrium barium copper oxide (YBCO)-coated conductors, in order to obtain an adequate magnetic moment for a magnetic sail spacecraft. For the optimal design of the HTS coil system for use in space, we analyzed the current transport, thermal characteristics, and applied stresses of YBCO coils, on the basis of a magnetic field and thermal analysis, and the so-called percolation depinning model. After developing an analysis meth

We modelled the screening currents (Is) induced in high-temperature superconducting (HTS) coils to develop a method for the characterization and design of HTS magnets for space applications. The analysis made use of so-called percolation depinning and flux creep models to describe the current density versus the electric field in HTS tapes. We compared the model results with the experimental data obtained from a Bi-2223/Ag double pancake coil. The experimental residual magnetization due to the Is

This study established a system configuration and operation control method of a Superconducting Magnetic Energy Storage (SMES) system that can achieve high fluctuation compensation in an electric and hydrogen hybrid energy storage system for large-scale renewable energy generation, aiming to expand the introduction of renewable energy. We first investigated the system configuration and operation control method effective for improving the fluctuation compensation performance of the SMES. As a res

This paper reports thermal diffusivities of Bi-system and Y-system tape conductors. First, we measure temperature traces of the bundled conductors for the heater disturbance at conduction cooling conditions. Obtained results are modeled and analyzed using one-dimensional as well as two-dimensional heat balance equations. We show that the analysis results can successfully reproduce the experimental results for a wide temperature range from 20 to 77 K. On the basis of such results, we also clarify

This study investigated experimentally and analytically the power transmission characteristics of High Temperature Superconducting (HTS) coils at commercial power supply frequency (50 Hz) to realize highly efficient power transmission in wireless power transfer systems for railway vehicles. We proposed a solenoidal coil with a thin magnetic core as an HTS coil structure suitable for lower frequencies and investigated its effectiveness by finite element analysis. The analysis results showed that

This article investigated a suitable excitation method for a conduction-cooled REBCO coil to reduce the temporal attenuation of the screening current induced field (screening field) for magnetic resonance imaging. We investigated the effect of the preexcitation of the coil and high temperature magnetization method on the screening field attenuation by measuring the variation rate of the magnetic field at the side surface of a conduction-cooled rare-earth barium copper oxide double pancake coil.

This paper discusses the demonstration of a stable levitation (SL) system for a magnetic levitation type seismic isolation device using a high-temperature superconducting (HTS) bulk. The SL system utilizes a restoring force between an HTS bulk and permanent magnet (PM) to maintain the stable levitation of a base-isolation object. We first measured the restoring force between the HTS bulk and PM, and then demonstrated the performance of the SL system using a magnetic levitation type seismic isola

This study investigated the transport ac loss in a high-temperature superconducting (HTS) coil under ac ripple currents with dc offsets for space applications of the HTS coil. We developed an analysis method to evaluate the effective ac loss in the HTS coil on the basis of the percolation depinning model. Our analysis clarified that larger dc offsets greatly increase the effective ac loss even under a smaller ac current. In addition, we investigated the effect of the ac loss with the ripple curr