High-performance conductors and coils used for superconducting power machines cooled by liquid nitrogen

为了实现液氮冷却的超导电机，对超导导体及其缠绕的线圈提出了更高的要求。本研究的目的如下：(1)开发新的测量长大超导导体在各种外加磁场和传输电流条件下的电磁性能的系统，该系统基于我们最初的适合于短而直的带材样品的‘Pointing矢量法’，(2)澄清缠绕成线圈的大导体中的Bi2223带材的电磁性能，以及(3)作为高性能线圈的绕组的最合适的超导体的设计。完整的设备1可以测量单层螺线管线圈的内外表面的坡印廷矢量，这些线圈用长的Bi2223带子或导体缠绕。利用该装置，在液氮温度下，实验研究了该样品线圈在外加横向磁场和输运电流同时扫描下的损耗特性。另一方面，设备2也建成了，在该设备中，在液氦冷却的NbTi分裂磁体内放置了一对大电流的直大样品导体，样品的温度可以改变为4.2K、66K或77K。使用该装置2，与大磁滞损耗相比，大电流容量的Bi2212卢瑟福电缆产生的股间耦合损耗不那么严重。该电缆的耦合时间常数约为10毫秒。这一结果来自于对Bi2212铸坯表面进行热处理前的冶金处理。

In order to realize superconducting power machines cooled by liquid nitrogen, superconducting conductors and coils wound with them are required to have high performance. The purposes of this study are as follows :(1)Development of new systems to measure electromagnetic properties of long and large superconducting conductors under various conditions of external magnetic fields and transport currents, which is based on our original 'Poynting vector method' adequate for short, straight tape samples, (2)Clarification of electromagnetic properties of Bi-2223 tapes in large conductors wound into coils, and (3)The most suitable design of superconductors as the winding of high performance coils.The feature of this study is constructions of two original equipments of measuring the above mentioned properties. Completed Equipment 1 can be measured Poynting vectors at both inner and outer surfaces of single layered, solenoidal coils wound with long Bi-2223 tapes or concuctors. By using this Equipment 1, the loss properties of this sample coil under the simultaneous sweep of external transverse magnetic fields and transport currents are clarified experimentally at liquid nitrogen temperature. On the other hand, Equipment 2 is also completed ; in this equipment a pair of straight large sample conductors with high current capacities is set inside NbTi split magnets cooled in liquid helium and the temperature of the sample can be changed as 4.2K, 66K or 77K. By using this Equipment 2, inter-strand coupling losses produced in Bi-2212 Rutherford cables with large current capacities are not so serious compared with large hysteresis losses. The coupling time constant of this cable is about 10msec. This result comes from metallurgical treatments of Bi-2212 strand surfaces before heat treatment.