Development of advanced magnetically-levitated high-temperature superconducting coils with YBCO coated conductors

高温超导线圈的磁悬浮使用最先进的YBCO涂层导体检查。三个线圈（直径：90-140 mm），并通过在外部磁场下使用液氮诱导持续电流（场冷却法）进行测试。这些线圈，尽管他们的小尺寸，已成为世界上第一个磁悬浮YBCO线圈。持续电流的衰减时间常数被发现是足够长的（2-7小时），由于应用复杂的连接结构之间的煎饼的线圈。当外加磁场以特殊方式施加时，发现持续电流在初始激励后甚至有所增加。这一现象可以用超导层中局部感应的屏蔽电流与通过线圈绕组的传输电流之间的磁耦合来解释。通过使用稳定的持续电流，磁悬浮实验进行了反馈控制和无反馈控制。在一定条件下观察到了自稳磁悬浮现象，并用超导悬浮线圈中磁通量守恒的原理进行了解释。这些结果被认为是有价值的设计升级的高场版本目前的Mini-RT设备的内部等离子体约束。此外，还进行了将YBCO高温超导体用于聚变机的可行性研究。结果表明，用于螺旋机，如大型螺旋装置，磁场校正线圈，可以提供高温超导线圈。他们应该是更有效的比目前的铜线圈，并将很快可与不久的将来的技术。

Magnetic levitations of high-temperature superconducting coils were examined using state-of-the-art YBCO coated conductors. Three coils (diameter: 90-140 mm) were fabricated and tested by inducing persistent currents using liquid nitrogen under external magnetic field (field-cooling method). These coils, despite their small sizes, have become the world first magnetically-levitated YBCO coils. The decay time constant of persistent currents were found to be long enough (2-7 hours) owing to the application of sophisticated joint structures between pancakes of the coils. When the external magnetic field was applied in a special way, it was found that the persistent current even increased after the initial excitation. This phenomenon can be explained by the magnetic coupling between the locally induced shielding currents in the superconducting layers and the transport current through the coil windings. By using stable persistent currents, magnetic levitation experiments were carried out with and without feedback controls. Self-stabilized magnetic levitations were observed with specified conditions, which could be explained by conservation of magnetic flux in the superconducting floating coils. These results are supposed to be valuable for designing the upgraded high-field version of the present Mini-RT device for internal plasma confinement. Furthermore, feasibility studies for applying YBCO high-temperature superconductors for fusion machines have been carried out. It is shown that field correction coils used for helical machines, such as the Large Helical Device, can be provided by high-temperature superconducting coils. They are supposed to be much more efficient than the present copper coils and will soon be available with the near future technology.