Browsing by Author "Liang, Yongxuan"

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    Fabrication and Characterization of Superconducting Core Fibers with Fused Silica Cladding
    Liang, Yongxuan (Virginia Tech, 2014-01-29)
    Since the discovery of superconductivity, its fantastic properties have fascinated the scientific community. The discovery of high critical temperature (Tc) superconducting compositions further inspires the wide applications of superconductors with relatively inexpensive liquid nitrogen cooling. Recently, the integration of superconductivity and optical waveguides has put forward the potential for ultrasensitive, ultra-fast and ultralow noise light detectors. However, simple and cost effective superconductor designs and fabrication processes are still required to enable wide implementation. The objective of this research was to study the fabrication of the superconductor core fibers with a fused silica cladding via the melt-draw approach, as well as develop appropriate characterization techniques to describe the fibers produced. In addition, a further objective was to determine the cooling efficiency of ordered holes around a superconductor core and construction of a one dimensional (1-D) single-phase steady state model to predict the heat transfer during cryogenic liquid transfer inside glass tube. In this thesis, both Pb and YBCO superconductor core fibers with fused silica cladding have been demonstrated. The fibers were fabricated via the melt-draw technique and maintained overall diameters ranging from 200-900 μm and core diameters of 100-800 μm. Surface morphology, chemical composition, interface effect, and superconductivity were further investigated. Surface morphology analysis confirmed that the Pb and YBCO core fibers possessed good circularity and clean interfaces between the core and cladding. Both the Pb and YBCO cores were relatively dense after the melt-draw process. The melt-draw process avoided contamination during fabrication as indicated by the composition analysis. Limited PbO was examined on the Pb core surface but further action will be required to detect the source of oxygen. The YBCO core maintained a stoichiometric ratio comparable to the superconducting phase even after the melt forming process. The elemental mapping showed that limited cross-diffusion occurred between the Pb core and fused silica cladding. Conversely significantly more elemental cross interaction between the core and cladding was noted for the YBCO core fiber. Superconductivity of the Pb core was verified by a custom designed four-probe technique in liquid helium. The YBCO core was also confirmed to be superconductive after heat treatment with O₂ present. The feasibility of efficient cooling by the holey glass tubes was confirmed. A 1-D single-phase steady state model was constructed to evaluate the heat transfer mechanism. The experimental results are in reasonable agreement to the theoretical calculation.
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    High-Temperature Superconducting Fiber
    Homa, Daniel S.; Liang, Yongxuan; Pickrell, Gary R. (Springer, 2014-01-29)
    In this study, we demonstrated superconductivity in a fiber with an yttrium barium copper oxide core and fused silica cladding. The fibers were fabricated via a modified melt-draw technique and post-process annealing treatment in excess oxygen. The fibers maintained overall diameters ranging from 100–900 microns and core diameters of 50–700 microns. Superconductivity of this fiber design was validated via the traditional four-point probe test method in a bath of liquid nitrogen at temperatures on the order of 93 K. The high-temperature superconducting fiber provides a glimpse of its cross cutting potential in fields of electromagnetism, healthcare, optics, and energy and lends credence to the promise for superconductivity.