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

在本研究中，我们提出了一种采用增减振荡磁场的方法来进行块状高温超导体（HTS）的现场磁化。所采用的方法为；(a)使用小型同步发电机作为可变交流电压源，(b)利用LC谐振电路的瞬态特性，(c)使用由半导体电路组成的任意波形发生器。所得结果总结如下：(1)采用交流振荡磁场后逐渐减小的直流磁场，可获得约2倍高的磁化强度。(2)在块状高温超导体上施加逐渐减小的交流磁场，可将原700高斯左右的磁场有效地退磁至10-20高斯以下，约为原磁场的1/700。(3)在LC串联谐振电路上施加等幅谐振频率电压，可以得到逐渐增大的振荡电流。(4)利用基于igbt的逆变电路，在实验室自制了任意波形发生器。使用该发生器，获得了良好的磁化效果。(5)采用交直流复合磁场，可获得更高的磁化效率。在本实验中，获得的最大场约为700高斯，这对于实际应用来说是相对较低的。然而，交/直流组合磁场的基本优点得到了证明。并且，该技术可以很容易地扩展到5-10 T的高磁场区域。

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.