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

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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.