Low-leakage thermal contact high-temperature superconducting magnet excitation power supply based on pulse current

Abstract The DC external power supply excitation method is widely used in the excitation of high-temperature superconducting (HTS) magnets due to its clear topological structure and strong robustness. However, the contradiction between the heat transfer power and the Joule heat power on the current lead leads to the inevitable cooling burden of the contact excitation method. In this paper, we propose a contact charging scheme that uses a periodic pulse current with a duty cycle (pulse current charging, PCC) instead of DC as excitation and cooperates with a self-regulating persistent current switch. Compared with traditional thermal control power supplies, the effective current on the current lead can be adjusted by the amplitude and duty cycle of the pulse current without being constrained by the load current. Even in the face of high current loads, the lead leakage heat can be reduced to below the watt level. The system efficiency, output and loss including lead leakage heat were analyzed. The results show that the system efficiency has a maximum point with respect to the pulse current peak value. Compared with the triangular wave excitation, the square wave excitation can reach the efficiency peak at a lower current peak value. Under the same conditions, the square wave excitation with high duty cycle has high output but large heat leakage, which is suitable for rapid excitation, while the triangular wave with low duty cycle has very small heat leakage, which is suitable for long-term connection and magnetic stabilization. At the same time, we propose a simple capacitor discharge circuit to implement the PCC method, which can achieve millivolt output at a voltage of more than ten volts using millifarad capacitors, and the total heat loss of the system is less than 2 W. An experimental prototype was built, and a 0.4 H on-board HTS suspension coil was excited and stabilized by adjusting the capacitor voltage, which is flexible and predictable. Due to the absence of iron cores which may be affected by the magnet itself, the PCC method features a simple design and enhanced robustness. We believe that the PCC method can provide a portable, reliable and straightforward alternative for lightweight magnets such as on-board HTS suspension magnets under complex working conditions such as mechanical vibration, tight footprint requirement.