Current Transfer Length and Interface Resistance of KC4 RE BCO Tapes

In recent years, high temperature superconductors (HTS) have been developed intensively for different applications. REBCO HTS tapes used for these applications are hybrid materials where the superconductor is thin layer within a multilayered Coated Conductor (CC) structure, and usually it is coated by metals, e.g. by silver, copper, or stainless steel. The interface resistance between the superconducting layer and the surrounding layers is an important characteristic of an HTS tape, along with current density and critical temperature, as it strongly influences the current transfer length (CTL) and the Normal Zone Propagation (NPZ) velocity. There exists a well-known method for the evaluation of the interface resistance between the HTS layer and the surrounding metal layer [1, 2], or metal contact embedded in HTS material [3]. The interface resistance often differs by orders of magnitude in commercially available HTS tapes [4]. The values of the interface resistance and CTL together with critical current can be affected by conditions of storage and application environment. Often the tapes are stored in atmospheric conditions with certain humidity before Ag depositing step. Nowadays, with growing interest to hydrogen applications, HTS tapes are often considered for usage in hydrogen environment. However, it is unclear how the hydrogen atmosphere or humidity are influencing tape´s performance. For the tapes produced by KC4, the KIT-CERN REBCO laboratory, the influence of air humidity on non-stabilized tapes and H2 exposure on silver stabilized tapes was investigated.