Studies of nonlinear electrodynamics of high-temperature superconductors

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Nonlinear electrodynamics of high-{Tc} superconductors are studied both theoretically and experimentally. For powdered samples, a novel model is presented in which the metallographically observed superconducting grains in the powder are modeled as superconducting current loops of various areas with weak links. Surprising harmonic generation behavior in an arc field, H{sub 1} cos({omega}t), is predicted by the model; the power at high harmonics show sharp dips almost periodic in a superposing dc magnetic field, revealing flux quantization in the prototype loops in the model. Such oscillation of the harmonic power in dc magnetic field P{sub nf}(H{sub dc}), is indeed experimentally observed ... continued below

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Pages: (263 p)

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Lam, Quan-Chiu H. August 1, 1991.

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Nonlinear electrodynamics of high-{Tc} superconductors are studied both theoretically and experimentally. For powdered samples, a novel model is presented in which the metallographically observed superconducting grains in the powder are modeled as superconducting current loops of various areas with weak links. Surprising harmonic generation behavior in an arc field, H{sub 1} cos({omega}t), is predicted by the model; the power at high harmonics show sharp dips almost periodic in a superposing dc magnetic field, revealing flux quantization in the prototype loops in the model. Such oscillation of the harmonic power in dc magnetic field P{sub nf}(H{sub dc}), is indeed experimentally observed in powdered YBa{sub 2}Cu{sub 3}O{sub 7}. Other experimental aspects also agree with model predictions. For bulk sintered cylindrical samples, a generalized critical state model is presented. In this model, the nonlinear electrodynamics are due to flux-pinning, somewhat similar to low-temperature type-II superconductors, but with a more generalized critical current densities' dependence on magnetic field -- J{sub c}(H){approximately}H{sub local}{sup -{beta}}, with {beta} being an adjustable parameter. Experiments in ac and dc magnetic fields on a sintered cylindrical rod of YBa{sub 2}Cu{sub 3}O{sub 7} yield unambiguous evidence of independent inter- and intragranular contributions to the complex harmonic permeability {tilde {mu}}{sub n} = {mu}{prime}{sub n} -i{mu}{double prime}{sub n}. Temperature- dependence measurements reveal that, while the intragranular supercurrents disappear at {Tc}{ge}91.2 K, the intergranular supercurrents disappear at T{ge}86.6 K. This result is, to our knowledge, the first clear measurement of the phase-locking temperature of the 3-D matrix formed by YBa{sub 2}Cu{sub 3}O{sub 7} grains, which are in electrical contact with one another through weak links.

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Pages: (263 p)

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OSTI; NTIS; GPO Dep.

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  • Other Information: Thesis (Ph.D.)

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  • Other: DE92000814
  • Report No.: LBL-31143
  • Grant Number: AC03-76SF00098
  • DOI: 10.2172/5994150 | External Link
  • Office of Scientific & Technical Information Report Number: 5994150
  • Archival Resource Key: ark:/67531/metadc1099439

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  • August 1, 1991

Added to The UNT Digital Library

  • Feb. 18, 2018, 3:59 p.m.

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  • April 25, 2018, 7:09 p.m.

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Lam, Quan-Chiu H. Studies of nonlinear electrodynamics of high-temperature superconductors, report, August 1, 1991; [Berkeley,] California. (digital.library.unt.edu/ark:/67531/metadc1099439/: accessed June 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.