A Study on Charge-Discharge Characteristics of No-Insulation GdBCO Magnets Energized via a Flux Injector

This paper presents the charging/discharging characteristics of two types of GdBCO double pancake (DP) magnets, one wound without turn-to-turn insulation (NI magnet) and another wound with Kapton tape (INS magnet), energized via a lab-made flux injector. A permanent magnet mounted on a rotor, which was driven by a separate ac motor, was used to provide a magnetic flux linking into the GdBCO DP magnets through a GdBCO sheet that was connected to each end of the magnet to achieve a closed loop. When the GdBCO sheet was exposed to a time-varying magnetic field, the magnetic fields of the NI and INS magnets started to increase and voltage fluctuations occurred because the time-varying magnetic field interacted with an electric circuit, inducing an electromotive force. This result confirmed that the flux injector could provide effective flux injection, leading to an induced current in the closed loop. During the discharging process, the magnetic fields originally induced during the charging process decayed as a function of time due to the existence of the resistive joints, and finally, the fields reached zero, indicating that the magnets were discharged completely. Moreover, the NI magnet exhibited a lower field decay rate compared to the INS magnet owing to the characteristic resistance, which is a typical electromagnetic behavior of an RL parallel circuit. Overall, the test results demonstrated the feasibility of employing the flux injector to energize the NI magnet, which is electrically and mechanically independent of the power supply.