Optimization of the copper addition to the core ofin situCu-sheathed MgB2wires

Recent results on powder-in-tube in situ Cu-sheathed MgB2 wires have shown that copper powder additions to the core can accelerate the formation of MgB2, increasing its volume fraction and greatly decreasing the amount of Mg–Cu intermetallic phases present in the core after heat treatment. The amount of added copper and heat treatment conditions strongly affect the critical current of the wire and require optimization. To identify the optimum parameters, eight wires with starting core compositions of Mg+2B+xCu with x = 0, 0.01, 0.03, 0.05, 0.07, 0.09, 0.12 and 0.15 were prepared with two heating ramp rates and their properties were investigated by SEM, XRD and Jc and n-value measurements. The highest Jc was found to be for x = 0.09, whereas x = 0.03 resulted in the highest n-value. The results are relatively independent of the heating ramp rate used for heat treatment.