高温超导磁体临界电流影响因素的研究

临界电流值是描述Bi2223高温超导带材性能的一个基本参数,在一定的温度条件下,Bi2223高温超导带材的临界电流是带材所在位置磁场大小和磁场方向的函数,其短样的临界电流值可以通过四引线法测量,单根超导带材的自场很小,磁场对临界电流的影响可以忽略.高温超导磁体的临界电流被定义成引发该磁体失超的最小电流,高温超导磁体的自场比单根超导带材的自场要大得多,磁体各个位置的磁场大小和方向各不相同,很难用理论的方法准确计算磁体的临界电流.对于高温超导磁体而言,除了磁场的影响因素以外,绕制磁体所用的超导带材自身的均匀性也是影响其临界电流的一个重要因素.本文对这两个因素进行探讨,并着重讨论高温超导带材自身的均匀性对临界电流大小的影响,本文的结论可以为高温超导磁体的设计、磁体绕制时带材的选择、磁体运行时安全工作电流的确定提供帮助.

STUDY ON THE FACTORS DETERMINING THE CRITICAL CURRENT OF HTS MAGNETS

The critical current I_ c is an important parameter to characterize the Bi-2223 tape. The critical current is the function of the magnitude and the direction to the tape of magnetic field at a certain temperature. It can be measured by using the electric field criterion. The critical current of HTS magnet is defined as the current at which the quench occurs. Due to the difference of magnetic field in different position of an HTS magnet, the calculation of the critical current for a magnet is complex. The inhomogeneous performance of carrying current along the tape can also result in the difference in critical current between the calculated result and the tested one. This paper studies on the factors determining the critical current of an HTS magnet. The local defect in the coil and the inhomogeneous distribution of the magnetic field along the magnet are considered. The conclusions would be helpful to design the HTS magnet and determine a safe operation current.