Intermittent operation of flux pump to maintain persistent current mode in high-temperature superconducting magnets

Abstract

The high-temperature superconducting (HTS) travelling-wave flux pump is a groundbreaking power source designed for wirelessly supply power to HTS magnets. The physical origin of its DC voltage is the macroscopic magnetic coupling effect. It can entirely replace traditional contact-type power supplies and their current leads which add thermal load. Currently, when HTS travelling-wave flux pumps sustain the Persistent Current Mode (PCM) in HTS magnets, it is unavoidable to have AC losses within the HTS magnets. These losses increase the demand on the cooling system and compromise the precision of the controlled current. This paper achieves the intermittent operation of the flux pump by simultaneously switching on-off the AC travelling magnetic wave and DC bias magnetic field of the linear-motor type flux pump through closed-loop feedback control. This control method stabilizes the flux pump’s output current within a specific range, thereby maintaining the PCM in the HTS magnet. The benefit of this control strategy is enhanced current control precision and reduced system operational energy consumption. In the experiments conducted in this study, for an HTS magnet with an inductance of 1.31 mH operating at a temperature of 77 K, maintaining the load current at 77 %I_c (i.e. 60 A), the reduction in the current ripple factor is to 3.3 ‰, a 34 % improvement over the 5 ‰ ripple factor when only the DC bias magnetic field was controlled for feedback. Additionally, the flux pump’s operation duty cycle is 12.5 %, representing an 89 % decrease in energy consumption compared to the previous setup where only the DC bias coil was controlled.