Self-field measurements and current distribution in ceramic superconductors

Niculescu, H.; Sáenz, Alejandro; Khankhasayev, M.; Gielisse, P. J.

doi:10.1016/0921-4534(96)00172-4

Cited by 10 publications

(6 citation statements)

References 19 publications

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“…We will come back now to the second basic method for determining j(x, y) from the measured B z (x, y) by inversion of equation ( 27) (Grant et al 1994, Niculescu et al 1996, Brandt 1995b, Wijngaarden et al 1996, Johansen et al 1996, Pashitskii et al 1997, Jooss et al 1998a. Despite the restrictions discussed before, this second basic method represents a modelindependent determination of the current density distribution.…”

Section: Determination Of Supercurrentsmentioning

confidence: 99%

Magneto-optical studies of current distributions in high-T_csuperconductors

et al. 2002

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In the past few years magneto-optical flux imaging (MOI) has come to take an increasing role in the investigation and understanding of critical current densities in high-T c superconductors (HTS). This has been related to the significant progress in quantitative high-resolution magnetooptical imaging of flux distributions together with the model-independent determination of the corresponding current distributions. We review in this article the magneto-optical imaging technique and experiments on thin films, single crystals, polycrystalline bulk ceramics, tapes and melt-textured HTS materials and analyse systematically the properties determining the spatial distribution and the magnitude of the supercurrents. First of all, the current distribution is determined by the sample geometry. Due to the boundary conditions at the sample borders, the current distribution in samples of arbitrary shape splits up into domains of nearly uniform parallel current flow which are separated by current domain boundaries, where the current streamlines are sharply bent. Qualitatively, the current pattern is described by the Bean model; however, changes due to a spatially dependent electric field distribution which is induced by flux creep or flux flow have to be taken into account. For small magnetic fields, the Meissner phase coexists with pinned vortex phases and the geometry-dependent Meissner screening currents contribute to the observed current patterns. The influence of additional factors on the current domain patterns are systematically analysed: local magnetic field dependence of j c (B), current anisotropy, inhomogeneities and local transport properties of grain boundaries. We then continue to an overview of the current distribution and current-limiting factors of materials, relevant to technical applications like melt-textured samples, coated conductors and tapes. Finally, a selection of magneto-optical experiments which give direct insight into vortex pinning and depinning mechanisms are reviewed.

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Section: Determination Of Supercurrentsmentioning

confidence: 99%

Magneto-optical studies of current distributions in high-T_csuperconductors

et al. 2002

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“…The magnetic field distributions ascribed to shielding currents or trapping currents, induced by applied or trapped magnetic fields perpendicular to a sample surface, have been recently investigated for polycrystalline superconductor films and/or tapes by scanning Hall sensor magnetometry [3][4][5][6] or by a magneto-optical method [7][8][9][10]. The homogeneity and the current distribution in the superconductor core have been investigated for Ag-sheathed Bi2223 tapes [3,5,9] using the magnetic profiles due to shielding and/or trapping currents.…”

Section: Introductionmentioning

confidence: 99%

“…The self-fields and current distribution under dc transport currents have been investigated for Ag-sheathed Bi2223 tapes [6,7]. Some approaches have also been made to solve the so-called 'inverse problem' from the magnetic profile to the current distribution [4,10].…”

Section: Introductionmentioning

confidence: 99%

Magnetic field distributions in a remanent state of screen-printed tapes with different superconductor geometries

Oota

Kawano

Fujikawa

et al. 1998

Supercond. Sci. Technol.

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Three kinds of screen-printed tapes with a single rectangular, square and circular superconductor core have been fabricated, and the trapped magnetic field distributions after removal of external field perpendicular to a tape surface have been investigated using scanning Hall sensor magnetometry with an active area of . Numerical calculations carried out by modelling current loops explain well the measured magnetic profile for the rectangular tape and the analyses yield a critical current density of that nearly agrees with the value of at 77 K in the self-field found from transport measurements. This establishes a basis for the validity of the calculation procedure for the magnetic profiles and opens a new way to characterize the sample and to determine the value in place of transport measurements. The same calculations give a nice agreement with the experimental profiles for the square and circular tapes, where the conventional dc four-probe method does not work, and the analyses determine the value to be for the former and for the latter in place of the transport data.

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“…The calculation of two-dimensional (2D) current distributions from the magnetic field generated by them has been successfully performed with various algorithms [1][2][3][4][5][6][7]. All these algorithms are based on the assumption that the current flows in infinitely thin layers [1,3,6] or that the current is uniform [5,7] (or averaged [2]) over the sample thickness.…”

Section: Introductionmentioning

confidence: 99%

“…In most cases, only the z-component of the magnetic field (orthogonal to the sample surface) is measured on a 2D grid. From this discrete field distribution the two components (x, y) of the current are calculated on a similar grid within the sample by matrix inversion [3][4][5] or by fast Fourier transformation [1,6,7]. It is straightforward to extend these algorithms to thick superconductors, if the current can be assumed to be constant over the sample thickness [8,9].…”

Section: Introductionmentioning

confidence: 99%

The significance of solutions of the inverse Biot–Savart problem in thick superconductors

Eisterer¹

2004

Supercond. Sci. Technol.

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The evaluation of current distributions in thick superconductors from field profiles near the sample surface is investigated theoretically. A simple model of a cylindrical sample, in which only circular currents are flowing, reduces the inversion to a linear least squares problem, which is analyzed by singular value decomposition. Without additional assumptions about the current distribution (e.g. constant current over the sample thickness), the condition of the problem is very bad, leading to unrealistic results. However, any additional assumption strongly influences the solution and thus renders the solutions again questionable. These difficulties are unfortunately inherent to the inverse Biot-Savart problem in thick superconductors and cannot be avoided by any models or algorithms.

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Self-field measurements and current distribution in ceramic superconductors

Cited by 10 publications

References 19 publications

Magneto-optical studies of current distributions in high-T_csuperconductors

Magneto-optical studies of current distributions in high-T_csuperconductors

Magnetic field distributions in a remanent state of screen-printed tapes with different superconductor geometries

The significance of solutions of the inverse Biot–Savart problem in thick superconductors

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Self-field measurements and current distribution in ceramic superconductors

Cited by 10 publications

References 19 publications

Magneto-optical studies of current distributions in high-Tcsuperconductors

Magneto-optical studies of current distributions in high-Tcsuperconductors

Magnetic field distributions in a remanent state of screen-printed tapes with different superconductor geometries

The significance of solutions of the inverse Biot–Savart problem in thick superconductors

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Magneto-optical studies of current distributions in high-T_csuperconductors

Magneto-optical studies of current distributions in high-T_csuperconductors