OPTIMISATION OF JOINTS BETWEEN SUPERCONDUCTING Bi2Sr2CaCu2O8+ AND Ag CURRENT LEADS

Electric contacts, for high current applications, between Bi2Sr2CaCu2O8+ super-conductor and thick Ag tapes were in-situ processed during partial melting and texturing of the superconductor. At currents, I, below the critical current, IC, a constant joint resistance, RC, appears. Prolonged high-temperature annealing of current elements that produces samples of higher texture and higher IC showed a correspondingly lower RC hence lower power dissipation, due to lower contact resistivity (C 55 10−9 Ωcm2 at 77 K). Increasing the silver thickness further decreases power dissipation at joint. Current transfer occurs on a 1 mm scale in this regime. At higher currents (I> IC), non-ohmic behaviour is observed. At very high currents (I 10 IC) the flux flow resistance of the superconducting ele-ment becomes comparable to the resistance of the Ag part in the joint, resulting in current sharing, approaching a rather uniform current distribution over the whole contact. This eventually reduces power dissipation in the contact to a value below that of the superconductor itself, reducing the possibility of element failure at the contact