HTS Persistent Current Switch Controlled by AC Magnetic Field

High-temperature superconducting (HTS) magnets operating in persistent current mode can achieve better field stability as well as reduce loss compared with being powered by an external current source. Persistent current switch (PCS) is essential for HTS magnets to operate in persistent current mode. In this paper, we proposed, fabricated, and tested an ac-field-controlled HTS PCS. In the PCS, we used the dynamic resistance of a type-II superconductor as the source of switching-off resistance. An ac magnetic field was applied perpendicular to the surface of a piece of YBCO tape, thus forming the PCS. The performance of the PCS was tested by charging a small superconducting coil under an ac field of different magnitudes and frequencies. The switching-off resistance of the PCS in the experiment is less than 0.2 mΩ, which may be promising for various usages in HTS magnets.