Magnetic Field Decay of the HTS Persistent-Current Mode Coil in Alternating Magnetic Field at 77 K

The superconducting linear synchronous motor is one of the main applications of the high-temperature superconducting (HTS) magnet made out of coated conductors. The high operation current density and temperature of HTS magnet can lower the requirement of the cryocooler system. Moreover, if the superconducting rotor magnet is designed to work in persistent-current mode, the heat load of the magnet system can be further reduced because there is no joule heat and heat leakage on the current leads. However, in real working conditions, the rotor magnet is exposed to an alternating magnetic field (AMF) caused by the vibration and harmonic magnetic field from the stator magnet. This AMF may accelerate the decay process of the magnetic field in rotor magnet. In this paper, the magnetic field decay property of the HTS coil in AMF is experimentally discussed. In order to eliminate the impact caused by the joint resistance, a kind of joint-less stack coil that can operate in real persistent-current mode is fabricated and tested in an AMF generated by an electromagnet. The tests were conducted with different AMF amplitudes and frequencies, as well as different initial magnetic field in HTS coil.