Characterization of the Critical Current Capabilities of Commercial REBCO Coated Conductors for an HTS Cable-in-Conduit Conductor

In 2013, the Superconductivity Laboratory at ENEA (the Italian National Agency for New Technologies, Energy, and Economica Developments) started a project aimed at using second generation (2G) High-Temperature Superconductors (HTS) tapes for the manufacture of a cable-in-conduit conductor. The considered layouts are based on a number of HTS tapes, which are arranged as five layered structures of twisted tapes wound on a helically slotted core with an external round jacket, and the conductor is designed to target 20 kA at operating conditions (T = 5 K, B = 15 T; or T = 77 K, self-field). With the commercialization of 2G HTS tapes, several options are now available on the market that can meet the ENEA cable specifications. Thus, for a sound design of the ENEA cable, a measurement campaign was launched aiming to determine the critical current, i.e., I_c, of commercial tapes as a function of an external applied field (up to 12 T) at different temperatures (in the 5-77 K range). Transport measurements were performed at 77 K in the high-field region, whereas the low-field and low-temperature critical currents have been determined from magnetization loops measured with a vibrating sample magnetometer system. Within a COMSOL Multiphysics environment, a 2-D finite-element method (FEM) magnetostatic model has been developed, in which a uniform I_c distribution is assumed in the HTS stacks. Both the experimental and FEM results are discussed in terms of cable performance, showing that current commercial tapes can already meet the ENEA cable specifications at T = 5 K, B = 15 T.