Joint Characteristics of YBCO Coated Conductor by Removing a Metallic Stabilizer

This paper presents the development status of joint method between the superconducting YBCO coated conductors (YBCO CC). In general, the YBCO-CC tape consists of an upper stabilizer, substrate, buffer, YBCO and a bottom stabilizer. It is suggested that the stabilizer between the two YBCO-CC tapes need to be removed, in order to improve the characteristics of the joints. The removing process was conducted by using heat and partial etching. The resistance and critical current of the joints were measured from the curve. The optical micrographs were analyzed for microstructures between the joint areas. After several times of over current test, the critical currents of the various types of joint samples were examined for applying to the high temperature superconducting magnet system.

I. Introduction

Recently, the researches on superconducting power apparatuses such as superconducting fault current limiter (SFCL) and power cable using high temperature superconductor (HTS) have increased and it is expected that those power apparatuses will be put to practical uses. In the center of this research, YBCO coated conductor (YBCO CC) plays an important part. YBCO CC has the characteristics of high index value (n value), low dependence of critical current on external magnetic filed and low AC transport current loss. With these advantages, the researches on superconducting apparatuses using YBCO CC are in progress. In order to apply HTS tapes—including YBCO CC—to superconducting apparatuses, it is necessary to make joints between the HTS tape and normal conductors or between HTS tapes [1]. In superconducting joint, there is no resistance causing losses but because of soldering, things like indium/bismuth have resistances causing losses in a realistic joint [2]. These joint resistances are one of the main reasons why efficiency of superconducting apparatuses is dropping. For example, many parallel connections of superconducting wires will be needed for flowing large current in a transmission level SFCL. More parallel connections cause more joint resistances during a normal operation and this could be one of the reasons why efficiency of SFCL is dropping. Therefore, more experimental researches are needed to obtain better joint characteristics.