Critical current density (Jc) and mechanical characteristics of a Bi-2223 bulk current lead for cryocooler-cooled superconducting magnets

A Bi-2223 cylindrical bulk current lead for use in cryocooler-cooled superconducting magnets has been fabricated using a conventional sintering process. The reliability of the Bi-2223 current lead has been evaluated through detailed studies of the superconducting properties and mechanical characteristics. The critical current density (Jc) was measured as a function of magnetic field less than 3 T at temperatures of 30–90 K. High Jc values greater than 670 A/cm2 were achieved at 4 K (1.2 T) and 45 K (0.6 T), corresponding to the cold and warm end conditions of the current lead in the magnet, respectively. The cantilever bending (29–47 MPa) and tensile (17–19 MPa) fracture strengths for a Bi-2223 bulk current lead of practical size were measured at room temperature. The critical current (Ic) and contact joint resistance (Rc) measured between the Bi-2223 bulk and Ag electrode plasma-sprayed at one end of the bulk showed no damage when a bending stress of 32 MPa was applied to the cylindrical bulk. This result was achievable even after thermal cycling (50 cycles) from room temperature through to 77 K.