Study of HTS Bulk Current Lead With Metal Alloy Impregnation Under Vacuum

The high-temperature superconductor (HTS) bulk current lead (BCL) is a crucial device for a large number of current applications such as the propulsion motor with HTS winding. The coexistence of low thermal conductivity and superconductivity enables us to shrink the dimension of the power system. To use the BCL effectively, we have to optimize the temperature gradient across the BCL along its length. For this purpose, it is essential to obtain a better physical contact between the bulk HTS surface and Cu terminal leads. There are, however, many pores at the surface of the bulk which cause difficulties for joining. In order to solve this problem, we focused on an impregnation technique which has been known to improve strength and thermal characteristics of the bulk HTS itself by using epoxy. We succeeded to fill in the pores of the bulk HTS surface with a metal alloy impregnation. Following this method, we made the BCL of Gd-Ba-Cu-O by ourselves. By adopting a suitable cooling with a GM cryocooler, the resistance of the BCL was 0.8 muOmega across the BCL under a current flow of 300 A, considering one end was at 40 K and the other one was at 70 K. The properties of the present BCL are satisfactory for connecting a coil in large current power systems such as superconducting motors.