Fundamental study for the establishment of the design principle of conduction-cooled oxide superconducting magnets

本文以传导冷却代替传统的液氦浴冷来冷却氧化物超导磁体，研究了氧化物超导磁体的稳定性和保护方法。为了摆脱传统的基于液氦冷却特性的稳定性理论和超导磁体的保护条件（如储能回收条件）的低Tc超导磁体设计原则，我们旨在建立一种新的20K以上传导冷却氧化物超导磁体的设计原则，包括具有大电流容量的氧化物超导体的制造方法。首先，我们观察了1T低温冷却器冷却的氧化物超导线圈的电磁和热特性。结果表明，线圈的热失控取决于局部之间的热平衡，由于磁通流动损失的热量产生和冷却，由于内部的热传导的绕组，而不是之间的平衡的线圈的总热量产生和制冷机的冷却能力。接下来，我们的氧化物超导导线的热产生的温度依赖性，由于交流损耗和磁通量的损失与大的各向异性和绕组内的热导率的数值表达式。我们还开发了一个数值模拟程序的行为的传导冷却线圈，并有可能讨论的依赖于温度和运输电流的线圈的热失控。结果表明，我们的传导冷却氧化物超导磁体的设计原则，澄清了传统的浴冷却超导磁体和传导冷却氧化物超导磁体的区别。

Paying attention to the conduction cooling to cool oxide superconducting magnets in place of the conventional bath-cooling with liquid helium, we studied the stability and the protection method of oxide superconducting magnets. In order to get rid of the design principle for the conventional low-Tc superconducting magnets, which consists of the stability theory based on the cooling characteristics of liquid helium and the protective condition of superconducting magnets, e.g. the recovery-condition of stored energy, we aimed at constructing the new design principle of conduction-cooled oxide superconducting magnets operated at over 20K, including the fabrication method of oxide superconductors with a large current capacity. First we observed the electromagnetic and thermal properties of a 1T cryocooler-cooled oxide superconducting coil. It was shown that the thermal runaway of the coil depended on the local thermal balance between the heat generation due to the flux-flow loss and the cooling due to thermal conduction inside the winding, not on the balance between the total heat generation of the coil and the cooling capacity of the cryocooler. Next we made numerical expressions of the temperature dependencies of the heat generation of oxide superconducting wires due to ac loss and flux-flow loss with large anisotropy and the thermal conductivity inside the winding. We also developed a numerical simulation program of the behavior of the conduction-cooled coil and made it possible to discuss the dependences of the thermal runaway of the coil on temperature and transport current. As a result, we showed the design principle of conduction-cooled oxide superconducting magnets clarifying the difference between the conventional bath-cooled superconducting magnets and conduction-cooled oxide superconducting magnets.