Study of serviceability of superconducting wires at 50-Hz frequency

A stationary equation for thermal conductivity is solved for a multifilamentary superconducting wire in the AC external magnetic field with an in-phase varying transport current of the amplitude j _m≪j_c on the assumption of a uniform current distribution between the filaments. Taking into account the temperature distribution over the wire cross section and the current-voltage characteristic exponential smearing over the temperature T₀ and current j₀ the condition for determining the wire serviceability in the dynamic regime, T(0)-T_b⩽T₀(j _c-j_m) j₀, is suggested. T(0) is the wire core temperature, T_b is the bath temperature, and j_c is the current critical density. It has been confirmed experimentally on microsolenoids operating at 50 Hz that the main characteristic of the wire serviceability in the dynamic regime is a magnetic field amplitude which can be estimated from the proposed relation for any given frequency, provided that j_m≪j_c. The calculated and experimentally observed serviceability ranges of investigated Nb-Ti, Nb ₃Sn wires, and in situ SC agree with accuracy no worse than 30%