Correlation Between Superconducting Properties, Processing and Microstructure in Bi-2212 Round Wires

Being the only high-<i>T_c</i> superconductor available in multifilamentary round wires with multiple architectures, Bi-2212 is a very promising conductor for the realization of high-field applications, like accelerator, NMR, and research magnets. In fact, solenoid magnets, racetracks made with Rutherford cable, and canted-cosine-theta coils have been already demonstrated. Despite their relatively simple wire fabrication by the powder-in-tube technique, Bi-2212 wires require a tightly controlled overpressure heat treatment with a multi-parameter schedule to achieve high <i>J_c</i>. Changes in the wire design, wire diameter, powder quality, and processing conditions can lead to strong variations in both the microstructure and the superconducting performance. Particularly noticeable are the variations in filament bridging, previously observed for instance by J. Jiang <i>et al</i>. [1] and by T.A. Oloye <i>et al</i>. [2], which inevitably affects <i>J_c</i> as well as the AC losses. In this presentation, we will focus on how, using conventional magnetic characterizations, we can gain valuable insights to estimate for instance the variation of the effective filament diameter, the level of bridging and inter/intragrain properties in wires that underwent different processing. These results will be correlated to transport properties and microstructures in order to obtain a deeper understanding on the cause of performance variation.<br/>[1] J. Jiang <i>et al.</i> IEEE trans. Appl. Supercond. 31(5), 6400206 (2021).<br/>[2] T.A. Oloye <i>et al</i>., in preparation.<br/>Acknowledgement<br/>This work was supported by the U.S. DOE Office of High Energy Physics under Grant DE-SC0010421, by the NHMFL NSF under Award DMR-1644779, and by the State of Florida, and is performed under the purview of the U.S. Magnet Development Program (MDP).