Development and evaluation of a novel solid-state joint for long-scale fabrication of REBCO stacked strands

Abstract

Rare Earth Barium Copper Oxide (REBCO) tapes still presents considerable challenges, which restricts the development of long-scale conductors for high-field applications in fusion reactors. The integration of joints into the conductors is a promising solution. However, conventional joining techniques exhibit inherent limitations regarding electrical properties, thermal resistance, and economic efficiency. This study proposes a novel ultrasonic-assisted diffusion (UAD) method to facilitate solid-state bonding between copper-stabilized REBCO tapes within a markedly short duration. By employing a silver interlayer, the joint resistivity (R_sj) is reduced by one-third compared to solder joints, achieving a minimum value of 0.88 pΩ·m². Microscopic analysis reveals that the robust diffusion interfaces and intact tape structure are critical factors contributing to the superior electrical properties. The experimental results demonstrate that the introduction of UAD joints in stacked strands does not compromise the electrical or mechanical properties of the strands. Therefore, this simple joining method offers a straightforward and cost-effective approach for the development of long-scale HTS stacked cables utilizing commercial REBCO tapes.