Investigation of stabilizer material properties used with REBCO coated conductor tapes for the application in a 20 kA High Temperature Superconductor Current Lead

Abstract

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 RE BCO. To limit the heat load to the cryostat, the stabilizer material of the RE BCO 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 RE BCO tapes. A part of this new development is therefore a detailed material property investigation of RE BCO 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 RE BCO 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 RE BCO CL.