Size effect in the formation and failure of stable current states in composites based on high-temperature superconductors

The influence of the transverse size of a composite wire based on a high-temperature superconductor on the dynamics of its thermoelectrodynamic properties at constant-rate current input has been studied. The physical mechanism behind the formation of stable regimes, which are characterized by the nonuniform distribution of the electric field and transport current over the cross-sectional area of the composite, has been determined. It has been shown that the critical current density of the superconducting composites determined from their current–voltage characteristic have lower and upper boundaries of electric voltages, which outline the allowable measurement range. It has been found that, when the input current completely penetrates into the composite, conditions for its stability are governed by the size effect. The essence of this effect is that conditions for current state stability in superconducting composites with the same cross-sectional area but various cross size differ. The conditions for the absence of unstable states in the composite the cross section of which is partially filled with the transport current have been formulated.