Development of Persistent Current Switch made with MgB₂ Wire

Abstract

This paper reports on the fabrication and testing of a persistent current switch (PCS) using MgB₂ wire. We fabricated round 60 m-long MgB₂ mono-core wires covered with a CuNi-stabilized sheath. The MgB₂ wires were fabricated using an in-situ PIT process. To measure the resistance of the joints, a small closed-loop-circuit 1-turn coil with some joints was fabricated by winding and jointing between MgB₂ and NbTi wires. The resistance of the joints was estimated to be less than 1.0×10_-13 Ω from magnetic relaxation between 0 to 8000 s. The PCS was fabricated using MgB₂ wire, and the closed-loop circuit in persistent-current mode operation consists of the MgB₂ PCS and a NbTi coil. For the operation current of 600 A, the closed-loop circuit trapped a magnetic field for about 20,000 s without any detectable decay.