Investigation of Stabilizer Material Properties Used With REBCO Coated Conductor Tapes for the Application in a 20-kA High-Temperature Superconductor Current Lead

In almost all fusion and accelerator experiments presently in operation or under construction, current leads (CLs), which feed the magnets, use high-temperature superconducting (HTS) materials to reduce the total cooling power consumption of the He refrigerator. These CLs carry currents in the range of 10-68 kA. The Karlsruhe Institute of Technology successfully designed, built, and tested the 70-kA demonstrator CL for the ITER magnets, which was subsequently followed by the 18.2-kA HTS CLs for the Wendelstein 7-X stellarator and the 20-kA and 26-kA HTS CLs for the JT-60SA tokamak. All these CLs use the first-generation HTS material BSCCO. The HTS part of the CL is now the focus of a new development aiming at a substitution of BSCCO by the next-generation HTS material REBCO. To limit the heat load to the cryostat, the stabilizer material of the REBCO coated tapes requires a low thermal conductivity. In addition, stabilizers with a sufficiently high electrical conductivity are mandatory in order to protect the CL in case of a quench of the REBCO tapes. A part of this new development is therefore a detailed material property investigation of REBCO coated conductor single tapes with a low thermal conductivity, in order to define a suitable conductor for a 20-kA CL and to create a database for the subsequent technical optimization process. This paper summarizes the measurement results of the thermal conductivity, electric resistivity, and specific heat capacity for REBCO single tapes with a low heat leakage. The results are analyzed with regard to earlier investigations of the BSCCO tapes used in the Wendelstein CLs serving as a reference for a future REBCO CL.