Research on Magnetization and Demagnetization of Bulk HTS using Increasing and Decreasing Oscillatory Pulse Magnetic Field

在这项研究中，我们提出了一个增加和减少振荡磁场的块状高温超导体（HTS）的现场磁化作为一个紧凑的方法。采用的方法是：（a）采用小型同步发电机作为交流可变电压源，（B）利用LC谐振电路的瞬态特性，（c）采用半导体电路组成的任意波形发生器。实验结果表明：（1）在交变磁场作用下，外加逐渐减小的直流磁场，可以获得约2倍的磁化强度。(2)在高温超导体上施加一个逐渐减小的交流磁场，原始磁化场约为700高斯，有效地退磁到低于10-20高斯的水平，这是原始磁化场的约1/700。(3)实验证明，在LC串联谐振电路上施加一个恒定的谐振频率电压，可以获得逐渐增大的振荡电流。(4)利用IGBT逆变电路，我们在实验室制作了任意波形发生器。使用该发生器，取得了良好的磁化效果。(5)采用交直流混合磁场，可以获得较高的磁化效率，最大磁化强度为700高斯左右，这与实际应用中的磁场强度相对较低。然而，AC/DC组合磁场的基本优点被证明。并且，该技术可以很容易地推广到5-10 T的较高磁场区域。

In this research, we proposed the use of an increasing and decreasing oscillatory magnetic field for the on-site magnetization of bulk high temperature superconductor (HTS) as a compact method. The adopted method is; (a)using a small synchronous generator as a variable AC voltage source, (b)utilizing the transient characteristics of a LC resonant circuit, (c)using arbitral wave-shape generator composed of semiconductor circuits. The obtained results are summarized as follows:(1) Using AC oscillatory magnetic field followed by gradually decreasing DC magnetic field, about 2 times higher magnetization was obtained.(2) Applying a gradually decreasing AC magnetic field on a bulk HTS, the originally magnetized field of about 700 Gauss was efficiently demagnetized to the level of lower than 10-20 Gauss, which is about 1/700 of the original magnetization field.(3) It was confirmed that the gradually increasing oscillatory current can be obtained by applying a constant magnitude resonant frequency voltage on a LC series resonant circuit.(4) Using an IGBT-based inverter circuit we manufactured in our laboratory the arbitral wave-shape generator. Using this generator, good magnetization results were obtained.(5) Using a combined magnetic field composed of AC and DC ones, higher efficiency magnetization was obtained.In this experiment, the maximum obtained field is about 700 Gauss, which is relatively low for the actual application. However, the fundamental merit of AC/DC combined magnetic field is demonstrated. And, this technology can be easily extended to the higher magnetic field region of 5-10 T.