Evaluation of shear strength in soldered and mechanical lap joints of high-temperature superconducting tapes intended for a remountable magnet

This study describes the electro-mechanical response under tensile and shear stresses of the mechanical and soldered lap-joint methods proposed for joining Rare-Earth Barium Copper Oxide (REBCO) high-temperature superconducting (HTS) coated conductors (CCs) in designs of a "remountable" (demountable) HTS magnet and joint-winding of an HTS magnet intended for the helical fusion reactor FFHR-d1. Proper joint of REBCO CCs for the HTS magnets not only requires sufficiently low joint resistance to avoid quench phenomena, but also involves mechanical stability against large electromagnetic forces. Results obtained from tensile test to apply shear stress namely tensile shear tests performed on mechanically jointed REBCO CCs showed that the linear proportionality between shear strength and contact conductivity of the joint is conserved for larger joint section area. An attempt to describe the failure mechanism of mechanical lap-joint revealed that a bending moment is originated at the joint section. Furthermore, results from tensile shear test on soldered joint between REBCO CCs with copper stabilizer showed failure of the REBCO CCs with small axial loads while joint remained intact.