Multi-stable static states of Bi-based superconducting composites and current instabilities at various operating temperatures

Static thermal and electric states before current instability in the current-carrying conductor like Bi-based superconducting composite are theoretically studied under the assumption that the critical current density of a superconductor and matrix resistivity are the non-linear functions of the temperature at fixed applied magnetic field. The simulation was made for the conduction-cooling conditions at different operating temperatures. The proposed analysis was based on the investigation of the non-isothermal voltage-current characteristics of composite superconductors. It is shown that they may have many-valued stable and unstable branches appearing in accordance with the non-trivial variation of the differential resistivity with increasing temperature. These states, first of all, are due to the temperature change of ∂J_c/∂T and are accompanied with the jump-like current-sharing mechanism. The parameters of the current instability onset as a function of operating temperature are numerically derived accounting for the additional stable branches of the voltage-current characteristics. In particular, it is revealed the existence of the static states when Bi-based composite superconductors may have a stable current distribution in the temperature range increasing up to the critical temperature of a superconductor without redistribution of all transport current into the matrix. The peculiarities of these phenomena are discussed.