Current Transfer Length and Interfacial Resistance Between Superconductors and Metals in Commercial REBCO Tapes and Cables

High-temperature superconductors (HTSs) are used in a growing number of applications. Technical HTSs usually consist of superconducting and metallic parts. HTS conductors are characterized by their critical current density and critical temperature defined by the superconducting layer, but other quantities such as the current transfer length (CTL) and the interfacial resistance between the superconducting part and surrounding metals are also important characteristics. Since the CTL and the interfacial resistance cannot be measured directly, a method is known to evaluate these parameters indirectly from the characterization of the spatial variation of the surface voltage of the metallic surrounding that is in direct contact with the superconducting material. In this article, we present the details of the experimental method developed to determine the CTL and the interfacial resistance of commercial second-generation HTS conductors of any type of architecture. We apply this method to quantify the interfacial resistance of ten HTS tapes from six major tape manufacturers. Also, since the architecture of a commercial HTS tape is usually more complicated than an "idealized" superposition of two flat layers (i.e., a metallic layer and a superconducting layer), recourse to three-dimensional numerical modeling has been required in order to understand in details the current transfer mechanisms taking place within the tape. We also show that the method can be applied directly to more complicated structures encountered in HTS cables, namely to determine the barrier resistance between a metallic structure in contact with a superconducting tape, providing important information required in numerical modeling when designing superconducting devices.