Possible explanation for trapped field enhancement on REBaCuO bulk by modified multi-pulse technique with stepwise cooling (MMPSC)

The time evolutions of the local fields B_L(t) have been measured on the surface of the superconducting bulk disk magnetized by a two-stage pulse-field magnetizing technique, called a modified multi-pulse technique combined with stepwise cooling (MMPSC), and the magnetic flux movement and the flux trapping have been investigated. The optimum concaved (“M-shaped”) trapped field profile, which is a necessary condition at the first stage to enhance the final trapped field B_T, makes a larger magnetic gradient (dB/dx) at the bulk periphery in the ascending stage of the applied magnetic pulse at the second stage due to the large viscous force F_v. The magnetic fluxes, which stay at the bulk periphery, start to flow to the center of the bulk, after the applied pulse field reaches a maximum, at which the flux velocity v is nearly zero and then F_v decrease. As a result, a large number of the magnetic fluxes are trapped at the bulk center. The effect of the “M-shaped” profile at the first stage in MMPSC on the enhancement of B_T is discussed.     

A superconducting stepping motor with pulsed-field magnetization for a pump

Pulsed-field magnetization is applied to a superconducting stepping motor to improve its rotor dynamics. The superconducting motor is composed of a superconducting rotor, a stator with eight electromagnets, a computer and a pulsed-power supply. Pulsed-field is applied to the superconducting rotor before the rotation. Moreover, the superconducting stepping motor is then applied to a pump that can function at extremely low temperatures. Pulsed-field magnetization is also applied to the pump motor in order to improve the performance of the pump. The static and dynamic characteristics of the motor and the pump are discussed.     

Single pulsed field magnetization for a Gd–Ba–Cu–O high-temperature superconductor large bulk with a diameter of 140 mm

For practical machine application of high-temperature superconductor (HTS) bulk magnet, a pulsed field magnetization (PFM) using small-sized magnetization coils is quite essential. HTS bulk with a diameter of 60 mm has been magnetized successfully and has made the tested axial-type motor to be stable operation by using a couple of vortex-type armature coils. In the present study we report the pulsed magnetization of HTS bulk with a diameter of 140 mm. The crystallization of such large bulk tends to be inhomogeneous around the periphery. For the sample of GdBa₂Cu₃O_y−δ with 140 mm in diameter and 20 mm thickness, new split-type magnetizing coils of 100 and 140 mm in diameter were employed. When the PFM was performed with the coils of 100 mm in diameter, magnetic fluxes penetrate near the center rather than periphery. On the other hand, when we used the coils of 140 mm in diameter, magnetic flux penetrates the whole body, and magnetic flux tends to be immobile in the area. Thus, the PFM with the coils of 100 mm in diameter is effective to magnetization for near the center of HTS bulk. They are also effective to obtain a conical shape trapped flux density distribution. The PFM with the coils of 140 mm in diameter is effective to enhance the total magnetic flux.