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Mechanical and Electrical Characterization of Critical Current Density in Round and Rectangular Reinforced Bi₂Sr₂CaCu2O₈₊ₓ Wires for High Field Magnet Applications

In recent years there has been a large push for magnet technologies extending into the 20 to 30 T range. High field solenoids can be made
using resistive materials like Cu, however the resistive losses associated with Cu electromagnets is large (~ 20 MW for 31 T Cu solenoid).
Superconductors, when cooled below a critical temperature, conduct electricity without resistive losses, significantly reducing the energy
needed to maintain a magnetic field. For this reason, superconductors are used extensively in magnet technology. For the last 50 years,
technologies have been dominated by the low temperature superconductors (LTS): Nb3Sn and Nb-Ti, which are metallic, isotropic,
multi-filamentary, twisted, round wire. Despite their wide use, LTS conductors are limited by their irreversibility fields to below ~ 24 T (@
4.2 K). If higher fields are to be reached, other materials must be used. The cuprate high temperature superconductors (HTS) have
irreversibility fields 3 to 4 times larger than those of LTS conductors, making them a promising technology in the pursuit of superconducting
magnets in exceeding 24 T. Limitations exist for the cuprate conductors, namely their electrical anisotropy, requiring the material be textured
if large current densities are to be maintained. HTS conductors like YBCO and Bi-2223 achieve this texture by fabrication as anisotropic flat
tapes. However, Bi-2212 is special in that it is the only HTS material capable of achieving texture in a round wire form with a metallic matrix
used in the more common LTS technologies. Furthermore, Bi-2212 is multi-filamentary and can be twisted, while also being macroscopically
isotropic with respect to magnetic field. For these reasons, Bi-2212 stands alone as the only HTS with the ability to use the most common
cabling technologies originally developed for LTS conductors. The limitation of Bi-2212 is its brittle ceramic filaments, which must be well
protected from significant amounts of strain, especially since 2014, when Bi-2212 experienced a large jump in critical current density upon
using overpressure heat treatment (OPHT). We report here on ways of reinforcing Bi-2212 on the strand and coil levels. We show through
experiment and modeling that, with a combination of reinforcing methods, Bi-2212 has the potential to reach high magnetic fields especially when
used as insert coils. In preparation for use at high fields, we also present here high field measurements up to 31 T, and address the cause of
large variation seen in the JC for Bi-2212 wires produced over the last decade. We attribute these large differences to variations in the
connectivity between grains, altering the effective cross-section of the conductor. Lastly, we introduce a fit for determining the high field
behavior (up to 31 T) of Bi-2212 wires from low field data (< 15 T) that is more easily attainable in common laboratories which do not have
immediate access to fields in excess of 20 T. / A Dissertation submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements
for the degree of Doctor of Philosophy. / Fall Semester 2018. / November 16, 2018. / Includes bibliographical references. / David C. Larbalestier, Professor Directing Dissertation; Simon Foo, University Representative; William
Oates, Committee Member; Sastry Pamidi, Committee Member; Seungyong Hahn, Committee Member.
ContributorsBrown, Michael DeForest (author), Larbalestier, D. (professor directing dissertation), Foo, Simon Y. (university representative), Oates, William (committee member), Pamidi, Sastry V. (committee member), Hahn, Seung Yong (committee member), Florida State University (degree granting institution), FAMU-FSU College of Engineering (degree granting college), Department of Mechanical Engineering (degree granting departmentdgg)
PublisherFlorida State University
Source SetsFlorida State University
LanguageEnglish, English
Detected LanguageEnglish
TypeText, text, doctoral thesis
Format1 online resource (124 pages), computer, application/pdf

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