Study of High Stable Magnetic Field by Superconducting Transformer

2004年，尝试用500A级超导变压器感应直流输运电流。然而，由于超导变压器的设计是为了获得大电流，因此很难长时间保持直流电流。在2005年，一种新的超导变压器被设计和制造，以便长时间保持直流电流，即使电流的大小很小。通过在次级绕组中插入的低阻并联电阻处的电压来测量次级绕组中感应的传输电流。采用PID控制方法对超导变压器第一绕组电流进行控制。结果，控制时间延长到1秒左右。控制精度在正负0.4%以内。该值远低于核磁共振和核磁共振所要求的1 ppm。2006年，尝试利用前人研究中获得的知识来提高电流的准确性。为了获得稳定的电流，必须正确测量二次绕组的感应电流。因此，通过孔传感器和拾取线圈来测量二次绕组中感应的磁场。第一绕组的电流由第二绕组的测量电流控制。结果表明，该方法优于孔传感器方法，建立了更精确的控制方法。综上所述，计算并确定了超导变压器次级绕组中感应电流的直流模式。提出并实现了获得稳定磁场和电流的方法。认为这些方法可应用于多种超导器件。例如，目前的知识将应用于核磁共振和核磁共振设备，以获得高稳定性的磁场。

In 2004, DC transport current was tried to be induced by 500A class superconducting transformer. However, since the superconducting transformer was design to obtain high current, it was difficult to hold DC current for long time. In 2005, a new superconducting transformer was designed and fabricated in order to hold DC current for long time even though the magnitude of the current was small. The transport current induce in secondary winding was measured by the voltage at the low resistive shunt resistor inserted in the secondary winding. The current at the first winding of the superconducting transformer was controlled by PID method. For the result, the controlled time was extended to about 1 second. The control accuracy was within plus minus 0.4%. This value is far from 1 ppm which is required by NMR and MRI.In 2006, the accurate of current was tried to be improved by the knowledge obtained in previous studies. It is necessary to correctly measure the current induced in the secondary winding in order to obtain the stable current. Therefore, the magnetic field induced in the secondary windings was measured by a hole sensor and a pickup coil. The current of the first windings was controlled by the measured current of the secondary windings. As the result, the pickup method was better than the hole sensor method, and the more accurate control was established.In summary, the DC mode of the current induced in the secondary winding of the superconducting transformer is performed and confirmed. The methods to obtain stabilized magnetic field and current were proposed and performed. It is considered that these methods will be applied to many kinds of superconducting apparatuses. For example, the present knowledge will be applied to NMR and MRI facilities to obtain high stability magnetic field.