Modified Interconductor Contact Resistivity in Coated Conductor Stacks and Roebel Cables

Interconductor contact resistivity (ICR) is a key property in determining the stability and current sharing of coated conductor cables. Most coated conductor cables have relatively high contact resistivity and low current sharing as fabricated because of surface roughness and an oxide layer that forms on the Cu-stabilizer. Here we work to quantify the differences in using three methods to modify ICR: sample diffusion bonding, deposition surface modification, and thin conformable inserts. At first a stack of two coated conductors was used to simulate a cable. This stack was put under transverse pressure and exposed to moderate temperatures to promote diffusion bonding via the removal of the unstable Cu-oxide layer (<; 200 °C). Such a method would normally be applied after (e.g., magnet) winding. In a second approach, the samples stack surfaces were modified with a Cr, Ag, Ni, and Ni-P/PTFE nanocomposite layer. In a third approach, a conformable “smart material” was inserted into the stack. ICR measurements were performed on stacks before and after diffusion bonding, for stacks with deposited surface layers, and for stacks with a smart material insert. In addition, Roebel cables were prepared with deposited layers on the individual strands and atmospherically controlled diffusion bonding, and ICR was compared between the as-received and modified Roebel cables as well as coated conductor stacks.