Study on the Excitation of a Bi-2223 Small Superconducting Coil by a Pulse-Type Magnetic Flux Pump

This paper presents further research on the pulse-type magnetic flux pump (MFP). The pulse-type MFP is used to excite a Bi-2223 double-pancake superconducting coil cooled by a cryocooler. The inductance of the coil is 76 μH. The cryogenic structure of the MFP is optimized by adding a cold frame outside. The MFP is powered by a dc voltage source. The excitation effects on the Bi-2223 coil are investigated by changing the input voltage. The pumping current curves have been obtained with various input voltage from 2.0 to 5.5 V. The fitting calculations show that the saturated current in Bi-2223 high-temperature superconductor (HTS) coil is 200 A when the input voltage is 5 V. The joint resistance is also numerically analyzed, and it is 0.18 μΩ. By measuring the current ripple of the Bi-2223 HTS coil, it is found that the excitation current fluctuation is ±4 A when the input voltage is 5 V. Consequently, it is expected that the pulse-type MFP could compensate the decaying current caused by the low n-index and joint resistance and enable the HTS magnet operating in persistent current mode. Further optimization on the structure and pumping process is still needed to improve the excitation properties of the pulse-type MFP.