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Journal ArticleDOI

Magnetic shielding using high-temperature superconductors

01 Feb 1994-Bulletin of Materials Science (Springer India)-Vol. 17, Iss: 1, pp 87-93

TL;DR: In this paper, the critical penetration field (CPF) was defined as the value of the applied magnetic field at which a detectable field was observed inside the cylinder, varied from cylinder to cylinder and also with the ageing of the cylinders in the case of YBCO shields.

AbstractMagnetic shields of various high-temperature superconductors, YBa2Cu3O7−x (YBCO), YBa2Cu3O7−x-Ag composites (random inclusions as well as non-random coatings) and Bi2Sr2Ca2Cu3Ox (BSCCO) were prepared by uniaxial as well as isostatic compression with various dimensions. The shielding properties were measured at 77 K for dc and ac magnetic fields in the range of frequencies from 100 Hz to 10 kHz. The critical penetration field (CPF), defined as the value of the applied magnetic field at which a detectable field was observed inside the cylinder, varied from cylinder to cylinder and also with the ageing of the cylinders in the case of YBCO shields. The highest value of CPF was 16 G at 77 K for YBCO shield prepared by isostatic compression. Even though the stability of BSCCO shields with respect to ageing is good, the CPF values are very low compared to those for YBCO. Detailed studies were performed in the case of YBCO shields. The CPF decreased as a function of time over a period of 90 days. The CPF decreased as the frequency of the applied field was increased. The wave form of the field inside the pot for a sinusoidal applied field was highly distorted and showed the presence of higher harmonics with appreciable amplitude. The wave form was Fourier-analysed to yield the field inside the shield along with the harmonics. The shields with Ag addition seem to give better performance at high fields.

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Citations
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Journal ArticleDOI
TL;DR: In this article, the magnetic shielding and harmonic generation in a sintered Y1Ba2Cu3O7-x tube, subjected to an incident AC magnetic field, has been studied.
Abstract: Magnetic shielding and harmonic generation in a sintered Y1Ba2Cu3O7-x tube, subjected to an incident AC magnetic field, has been studied. This study has shown that the onset of superconductivity in the specimen introduces a magnetic shielding of about 25 dB. Odd harmonics are generated during the propagation of the AC magnetic field. Flux trapping occurs in the specimen for frequencies less than 10 kHz. This trapped flux behaves as a superimposed DC magnetic field and results in a low shielding effectiveness and generation of even harmonics in the transmitted waveform.

8 citations

Journal ArticleDOI
TL;DR: In this paper, a measurement of magnetic fields with Hall-and SQUID-sensors was done with the help of a specially constructed measuring apparatus with Hall and SQUID sensors.
Abstract: Shielding elements were made of bulk material or thick films. The bulk route is determined by large-scale processing. After an axial or isostatic pressing of the fine-grained powder composed of BSCCO, Y-123 and Nd-123, the material was sintered/textured and annealed in special programs. Then the characterization of the materials and a measurement of magnetic fields was done with the help of a specially constructed measuring apparatus with Hall- and SQUID-sensors. The objective of the thick film route was to get large, coated superconducting work pieces of YBCO and BSCCO (plates or cylinders) with current density of >1000 kA/cm 2 (and/or a shielding effect of >1 mT). Thick films were made by plasma spraying and paste technology. Substrates used were ZrO 2 , MgO, SrTiO 3 , BaZrO 3 and others. In some cases the work pieces were treated with laser radiation. After laser and thermal treatment the surface was more dense, the cracks were cured and the current density was increased by more than two times.

7 citations


References
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01 Jan 1988
TL;DR: In the years following the discovery of superconductivity in doped lanthanum copper oxide in late 1986, there has been a large multinational effort in the study of what are now called high Tc superconductors as discussed by the authors.
Abstract: In the years following the discovery of superconductivity in doped lanthanum copper oxide in late 1986 there has been a large, multinational effort in the study of what are now called high Tc superconductors. As a result of this work at least ten discrete phases of superconducting oxides have been identified. The authors felt it would be useful to have a symposium whose focus was to identify and discuss the common structural features of these oxide superconductors. These proceedings hopefully represent a state of the art view of the correlations between crystal chemistry and superconductivity in metal oxide systems.

395 citations

Journal ArticleDOI

163 citations

Journal ArticleDOI
TL;DR: In this article, the authors measured the magnetic field H' at the center of a hollow of sintered Y-Ba-Cu-O superconductor as a function of applied field H, temperature, tube length, and tube wall thickness.
Abstract: The authors have measured the magnetic field H' at the center of a hollow of sintered Y-Ba-Cu-O superconductor as a function of applied field H, temperature, tube length, and tube wall thickness. The maximum field that can be shielded H/sub sh/ agrees with the value calculated from the critical state model using the measured critical-current density J/sub c/. The maximum trapped field H/sub tr/ in the tube, on decreasing H to zero, exceeds H/sub sh/ by as much as a factor of two, and large enhancements in J/sub c/ are observed in the decreasing field. These phenomena are identified with intragranular flux pinning present only after H has exceeded H/sub c1/ of the grains. Finite tube length does not affect the H/sub tr//H/sub sh/ ratio appreciably. H/sub sh/ depends approximately on the square root of the wall thickness. >

67 citations

Journal ArticleDOI
TL;DR: In this paper, high-Tc superconducting tubes have been developed for magnetic shielding of SQUIDs at 77 K. The characteristics of such tubes show that adequate shielding exists for magnetic fields up to a critical field determined by the current density of the tube.
Abstract: High‐Tc superconducting tubes have been developed for magnetic shielding of SQUIDs at 77 K. The characteristics of such tubes show that adequate shielding exists for magnetic fields up to a critical field determined by the current density of the tube. Relaxation phenomena with two different time dependencies are observed when the external magnetic field enters the tubes.

32 citations

Journal ArticleDOI
TL;DR: In this article, the magnetic shielding has been investigated by measuring magnetic coupling between primary and secondary coils separated by a high-Tc superconductor, which can explain the existence of superconductivity related surface current, which flows out from front to rear surface to couple with the secondary coil.
Abstract: The magnetic shielding has been investigated by measuring magnetic coupling between primary and secondary coils separated by a high-Tc superconductor. The magnetic coupling between primary and secondary coils could not be zero below Tc. This can be explained by the existence of superconductivity related surface current, which flows out from front to rear surface to couple with the secondary coil.

28 citations