The Underlying Mechanism of Faster Current Attenuation of HTS Magnet in Persistent Current Mode Subject to the Traveling Magnetic Fields

Abstract

High-temperature superconducting (HTS) magnet, due to its greater performance of magnetic field at higher temperature (20-40 K), better thermal stability, smaller volume and weight under the same requirements, and lower refrigeration costs, has attracted growing attention in the ultra-high-speed maglev system, high field magnet, and some other applications. Considering the practical requirements, closed-loop method is generally adopted in HTS magnet to maintain the persistent operation and to output the stable magnetic fields. But the accelerated current attenuation occurs when the HTS magnet is subjected to traveling magnetic fields, which is not conducive to the long-term operation. Therefore, this paper aims to investigate the essence of current attenuation of HTS magnet in persistent current mode under traveling magnetic fields and to further suppress this adverse behavior. In this study, to calculate the current distribution and dynamic resistance, a two-dimensional (2-D) finite element model (FEM) was established and verified by comparing with the experimental results. It can be seen from the simulation results that the dissipative losses caused by dynamic resistance present a non-negligible effect on the current attenuation of the magnet. And the mechanism of faster current attenuation was well explained by the variation of the dynamic resistance under the traveling magnetic fields.

Study on current discrepancy and redistribution of HTS non-insulation closed-loop coils during charging/discharging and subsequent transient process toward steady-state operation

“…Since their introduction by Hahn et al [1], HTS non-insulation (NI) coils have been widely used in many applications, such as in nuclear magnetic resonance (NMR) [2,3] and electrodynamic suspension (EDS) systems [4][5][6], owing to the high current-carrying density in steady-state operation. In addition, NI coils present a good self-protection capability, as the operational current can flow in the azimuthal and radial directions through the loop and turn-to-turn contact approaches, respectively, thus bypassing the hot-quenching point [7][8][9].…”