In-depth resistance analysis of REBCO tape joints with indium insert and solders. (June 2020) - Hayasaka, R
Abstract: Joints between REBCO (rare-earth barium copper oxide) tapes with low joint resistance are crucial for many superconducting applications. Joining REBCO tapes with indium insert (In-joint) is a promising joining method to fabricate low resistive joints at low temperatures (20–120°C). This study investigated the joining conditions of In-joints such as pickling, surface roughness, joining time, and temperature. The joint resistivity (product of joint resistance and joint area) was successfully reduced to 22–30 nΩcm 2 at 77 K in self-field. The constitutive factors of the joint resistivity were analysed separately along with the crosssectional observations. In this study, the interface resistivity of the REBCO tape was measured as 8.5 nΩcm 2 for one REBCO tape by the previously proposed method. The resistivity of the joining interface Cu/In was calculated as <3 nΩcm 2 by subtracting the other resistivities from the entire joint resistivity. This result reveals the lower limit of the joint resistivity: the sum of the resistivity (nΩcm 2 ) of indium (measurable by thickness), the resistivity of Cu/In (<3nΩcm 2 ), and the interface resistivity of the REBCO tape (measurable beforehand). Furthermore, we demonstrated a lower and less varied joint resistivity of In-joints than those of the soldered joints.