Long-term stability of Bi(2223) and Dy(123) superconducting tapes in the direct current circuit

Abstract

The stability of critical parameters T c and I c of commercial high-temperature superconducting wires upon long-term passage of transport current (about 0.7 I c ) in liquid nitrogen (77 K) is studied. Voltage-current characteristics U ( I ), as well as the critical current and critical temperature, are investigated for the case of Bi(2223) hermetic multifilament wires and Dy(123) superconducting tapes covered by a thin Ag layer. In the former case, a considerable decrease in the critical current (by ~30%) and swelling of the wires after passage of the current for 323 h are observed. The same is true for a reference sample, which does not experience the action of current and stays in liquid nitrogen for 700 h. The decrease in the critical current in the Bi(2223) sam- ple is likely to be associated with penetration of a liquid coolant into the composite conductor: evaporating and expanding as a result of heating, it severely deforms the material. The Dy(123) sample grown epitaxially dem- onstrates high stability of the critical current after it has experienced the action of current for 400 h and been kept in liquid nitrogen for 1000 h.