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High field magnets are integral to the success of various significant scientific and technological endeavors such as materials characterization, high energy physics, and plasma fusion generators. Superconductors are integral to building high field magnets, and since their discovery Nb-Ti and Nb3Sn, both low temperature superconductors (LTS), have matured into commercially available, practical magnet conductors. Major advantages of these materials are that they can be made as isotropic multi-filamentary round wires (RW) where the superconducting filaments are bonded to a high-conductivity normal metal which provides electromagnetic and mechanical stability, as these qualities are ideal for building superconducting magnet coils. As LTS magnets are limited by Nb₃Sn's irreversibility field μ₀H[subscript irr](4.2K) of ~24 T, high temperature superconductors (HTSs) promise a solution to this limitation due to their high μ₀H[subscript irr](4.2K)(4.2K) > 100\ T. However, since the discovery of HTS in 1986, constructing practical high field HTS magnets has proven difficult due to the limitations of the fundamental physics at play and the challenges of materials engineering. Three cuprate superconductors, YBa₂Cu₃O₇₋ᵪ (YBCO), Bi₂Sr₂CaCu₂O₈₊ᵪ (Bi-2212) and its closely related sibling (Bi,Pb)₂Sr₂Ca₂Cu₃Oᵪ are the most mature and promising candidates for practical high field HTS magnet superconductors. Of these three, Bi-2212 is the only high J[subscript c] (~6500 A/mm² at 15 T, 4.2 K), high field HTS available as a macroscopically isotropic multi-filamentary round wire. In addition to being LTS like in their macroscopic properties, Bi-2212 round wires do not seem to suffer from the limitation of weakly connected grain boundaries that the other cuprates have to compensate for. Understanding the nature of the grain boundaries that contribute significantly to transport supercurrent in Bi-2212 round wires is therefore a scientifically interesting problem. Moreover, understanding and quantifying the connectivity of the Bi-2212 RW current path is integral to improving its critical current density J[subscript c], which would enable even higher fields. The magnetization behavior of a superconducting wire, which is related to the dissipative losses associated with changing magnetic fields, should also be well understood and optimized. This thesis details experiments characterizing the oxygen doping dependence of the transport supercurrent path connectivity in state-of-the art Bi-2212 round wires, as well as the connectivity of their induced current path introduced by magnetization and the associated hysteretic losses.
Bi-2212, Connectivity, Grain boundaries, High Temperature Superconductors, Hysteretic loss, Superconductivity
Date of Defense
June 29, 2021.
A Dissertation submitted to the Department of Physics in partial fulfillment of the requirements for the degree of Doctor of Philosophy.
Includes bibliographical references.
David C. Larbalestier, Professor Co-Directing Dissertation; Irinel Chiorescu, Professor Co-Directing Dissertation; Eric E. Hellstrom, University Representative; Nicholas Bonesteel, Committee Member; David C. Collins, Committee Member; Fumitake Kametani, Committee Member.
Florida State University
Oz, Y. (2021). Investigation of the Transport and Magnetization Properties of High Jc Bi-2212 Round Wires. Retrieved from https://purl.lib.fsu.edu/diginole/2021_Summer_Oz_fsu_0071E_16714