Stabilizing Current Performance of Persistent Current Switches.

Abstract

This paper shows two methods to stabilize the current performance characteristic of a persistent current switch which we intend to install in a superconducting magnet for a magnetically levitated vehicle. The switch consists of a superconductive wire made of NbTi and Cu-30%Ni matrix, a winding form core made of E-glass fiber reinforced epoxy resin, an electric heater, and a thermal insulator. This type of a persistent current switch tends to be unstable in current performance at on-state. The instability is what you call training-effect or degradation. One of the methods to suppress the instability is to adopt low thermal contraction materials for the core, and the other method is to twist double superconductive wires in which a current goes on one wire and returns on the other wire. We made small samples using the stabilizing methods, and examined their current performances. We found them better performing than those using the conventional technology. Then, we made a persistent current switch of which operating current was 600A at on-state and electrical resistance was 50 ohms at off-state.