PROCESSING AND ELECTROMAGNETIC PROPERTIES OF LOW AC LOSS, MULTIFILAMENTARY RARE EARTH-BARIUM-COPPER-OXIDE SUPERCONDUCTOR TAPES

Extensive AC losses are a major impediment for the use of second generation (2G) high temperature superconducting (HTS) rare earth-Ba-Cu-O (REBCO) coated conductors (CC) in AC applications. Filamentization has been shown to be a viable method to reduce magnetization AC losses. Different techniques have been developed including the removal of the thick copper stabilizer layer. Non-uniform ablation, re-deposition of the removed metal, excessive degradation of the critical current, and limited throughput are some of the drawbacks associated with these techniques. In this dissertation, striation methods were developed to address these issues. For the first time, a thick copper stabilizer layer has been selectively-electroplated onto the superconducting filaments. By oxidizing the striated grooves, the striations remain copper-free due to the formation of a resistive oxide layer in between the filaments. The influence of stabilizer thickness on fully-filamentized CCs has also been investigated. The results showed no significant loss contribution from increasing the stabilizer thickness up to 30 µm in fully-filamentized tapes. This thickness should be sufficient for most of the targeted AC applications of coated conductors. Filament widths as small as 180 µm have been fabricated successfully for the first time without compromising the beneficial effect of striations on the AC losses. The loss measurements were performed in a frequency range of 40 to 500 Hz at 77K and compared with theoretical models. The experimental data agrees well with these models above the penetration fields. The adhesion strength of the conductors has also been enhanced approximately three-fold due to the reduced number of defects after modification of the composition of the REBCO film. The techniques developed in this dissertation could potentially be transferred to large-scale manufacturing of stabilized, low loss, multifilament coated conductors.