Optimization of REBCO Tapes through Division and Striation for Use in Superconducting Cables with Low AC Losses.

This study aimed to enhance the performance of Ag-stabilized high-temperature superconducting (HTS) tapes with a focus on reducing magnetization losses. Two approaches were employed: dividing the tapes into narrower widths and introducing striation at the level of the superconducting layer. The process of laser ablation proved to be an effective method for implementing these modifications. The quality of the cut edges and grooves was assessed using scanning electron microscopy. To evaluate the electrical properties, measurements were conducted on the critical current and magnetization loss in samples at different stages: in their initial state, after cutting, and after the striation process. Of the two modifications, the striation process more effectively reduced the AC losses in the HTS tapes, approximately by one order of magnitude. The retention of critical current remained high after cutting, but varied with the number of created filaments after the striation process. Subsequently, a short cable was wound from the cut and striated HTS tape. This cable demonstrated a remarkable sixfold reduction in AC losses compared to the initial HTS tape.

Thermal Cycling of (RE)BCO-Based Superconducting Tapes Joined by Lead-Free Solders.

We prepared overlap soldered joints of high-temperature superconducting tapes, using various materials and preparation conditions. In order to select the joints with optimal performance, we correlated their electrical properties (derived from current-voltage curves) with the microstructure of the respective joint cross-section by scanning electron microscopy. With the first group of joints, we focused on the effect of used materials on joint resistivity and critical current, and we found that the dominant role was played by the quality of the internal interfaces of the superconducting tape. Initial joint resistivities ranged in the first group from 41 to 341 nΩ·cm2. The second group of joints underwent a series of thermal cyclings, upon which the initial resistivity range of 35-49 nΩ·cm2 broadened to 25-128 nΩ·cm2. After the total of 135 thermal cycles, three out of four joints showed no signs of significant degradation. Within the limit of 100 thermal cycles, reliable soldered joints can be thus prepared, with normalized resistivity not exceeding 1.4 and with normalized critical current above the value of 0.85.