Hiroshi Takaichi

Experimental evaluation of the total shielding current in a bulk high-Tc superconductor [YBaCuO]

Total shielding currents of a melt processed bulk high-Tc superconductor (HTS) are evaluated from the measured voltage of a Rogowski coil when a permanent magnet is moved towards the HTS. The total shielding current and the levitation force between the magnet and the HTS show rapid growth and decay depending on the speed of the magnet. The dynamic levitation force and the magnetic relaxation are discussed from the experimental results.

Artificial Satellite Attitude Motion Simulator Supported by Superconducting Magnetic Bearing

Attitude motion of an artificial satellite was simulated generally by an air-bearing table, flight tables and/or computer simulations. The hardware simulation is necessary to evaluate the system stability influenced by the sensors and actuators nonlinearity. The attitude motion simulator supported by superconducting magnetic bearings was prepared and the attitude motion experiment was performed using a fixed flywheel or a gimbaled flywheel as a control actuator. As a result of these experiments, the superconducting magnetic bearings attitude motion simulator was proved to be a useful facility to evaluate the satellite’s attitude dynamic behaviors.

The Fabrication of YBa2Cu3O7-δ Thick Films on Yttria Stabilized Zirconia Seeded by RBa2Cu3O7-δ (R=Gd, Sm and Nd)

Thick films of YBa2Cu3O7-δ (YBCO) have been fabricated on yittria stabilized zirconia (YSZ) by using the screen printing method. In order to substantially increase Jc, it is clear that a method has to be found by which the number of weak links such as second phases and high angle grain boundaries can be reduced. In this paper, we report a promising method employing a seed crystal of RBa2Cu3O7-δ (R= Gd, Sm and Nd) by which large area of YBCO crystal can be fabricated in the thick film.

Effect of Temperature Gradient on the Growth of MPMG Processed YBCO

Recent studies have shown that large bulk YBCO superconductors with high Jc values can be fabricated, and various applications using such bulk YBCO samples are now under consideration. For most applications, we need to have a sample in which large currents can flow in a large area. In order to achieve this, the control of crystal growth is critical, since YBCO superconductors are very anisotropic in their crystal structures and superconducting properties. Recently, we have found that crystal orientation of YBCO can be controlled by applying different temperature gradients in two directions perpendicularly to each other.

Visualized Measurement of Flux Density Distribution on the Surface of YBCO

A new method was developed in order to characterize the magnetic properties of superconducting bulk materials without destroying them. The magnetic flux on the surface of MPMG-processed YBCO bulk materials under the field of -500 to 500Oe was measured by a Hall probe and its distribution was visualized into two dimensional graphics. From the measured flux density, the shielding current distribution was estimated. The pattern of flux distribution was in good agreement with the grain morphology. The relationship between the magnetic flux distribution and the grain size was qualitatively explained by Bean’s critical state model.