  Due to the properties of high temperature superconducting (HTS) materials,
current attenuation is inevitable during the closed-loop operation of HTS
magnets. When a contact DC power supply is used to supplement this attenuation,
it inevitably creates a huge thermal burden on the cryogenic system. The flux
pump is a revolutionary new power source that can charge closed-loop HTS magnet
wirelessly. However, for HTS magnets with a large inductance, such as particle
accelerator magnets and magnetic confinement magnet in Tokamak devices, the
flux pump cannot fast adjust the DC current of the magnet, due to its small DC
output voltage. Here, we present a method to fast regulate the current in a
closed-loop HTS magnet using a contact DC power supply and persistent current
switch (PCS). After current regulation, the HTS magnet is operated in the
persistent current mode (PCM) with a flux pump. By applying the "four-quadrant"
control theory of the flux pump allows, the current in HTS magnet is controlled
with high stability. This study provide a power strategy for the fast current
regulation and maintenance of persistent current in the HTS magnet, enabling
the industrial applications of flux pumps for HTS magnets with large
inductance.

Applied Physics