Impact of the Complex Interface Between Bi2Sr2CaCu2Ox Filaments and Ag Matrix on the Quench Behavior of Composite Round Wires

Abstract

Bi2Sr2CaCu2Ox/Ag/Ag alloy (Bi2212) multifilamentary composite round wire is one of the candidates for fabricating superconducting magnets to generate magnetic fields greater than 20 T. After heat treatment, the microstructures of Bi2212 filaments are complex; notably, the interface between filaments and Ag matrix is meandered and many bridge connections (BCs) develop between filaments. How these microstructural features affect the electric, thermal, and mechanical properties is unknown but likely important. Building on a fractal-based theoretical frame, we investigated the impact of these features on the quench behavior of composite round wires. Our finite element models allow predicting temperature development and voltage growth during a quench in a wire with or without these features. It was found that though the influence of the meandering Ag/filament interface on the quench behavior is minimal, the BCs in the local region have a very remarkable impact. The current-carrying of the BCs is, generally, much lower than that in Bi2212 filaments, but during the quench process, the BCs can fully share the current. During this time a much higher temperature gradient is found at the BCs compared to other places, which further leads to the extremely inhomogeneous distribution of the thermal stress, and consequently, to a great extent, results in thermal and/or mechanical failure that initiated from the local region where the BCs exist.