Design and Implementation of a Mechanical Semipersistent Switch for HTS Magnets

Persistent-mode operation of superconducting magnets requires a persistent switch, usually a heater, to close their superconducting circuits. Here, we describe a mechanical copper switch that utilizes pressure to vary resistance. This switch is designed to provide a low-resistance short between two high-temperature superconducting (HTS) charging electrodes in an all-HTS pancake-coil magnet. The switch is able to achieve a contact resistance as low as 460 nΩ by pressing gold-coated copper surfaces together at 3.0 kN. At 77 K, with an HTS pancake coil charged to 0.45 T, the magnetic field decayed slowly with the switch closed. The decay fits to a 3.6-µΩ resistance, most of which arises from unrelated insufficient connections within the HTS magnet itself. The design shows the potential of building a persistent-mode superconducting magnet with a mechanical switch, where, as an example, a 30-T magnet with an inductance of 5.9 H has a field drift of −6 ppm/h.