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.

Magnetic shielding and harmonic generation in high-Tc superconducting tubes

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.

Superconducting materials for electronic applications

We report a complete procedure to achieve multilayer YBa2Cu3O7−δ (YBCO) thick films by electrophoretic deposition on silver tubes using a suspension of YBCO powder in butanol. With the aim to optimize the magnetic shielding performances of the coatings, we have carried out an extensive investigation of the influence of the deposition parameters, the multilayer deposition sequence and the intermediate/final heat treatments on the coating microstructure. Using the optimized conditions, a 24-layer YBCO coating has been successfully prepared on an 80 mm long Ag tube: the melt growth processed multilayered YBCO thick film thus obtained can shield an applied magnetic field of 1.9 mT at 77 K, the highest value per thickness unit reported so far in the literature for these materials.

https://iopscience.iop.org/article/10.1088/0953-2048/28/1/015007/pdf

Magnetic shielding performances of YBa2Cu3O7−δ-coated silver tubes obtained by electrophoretic deposition

Effect of nano-inclusions of RE-211 (RE= Y, Nd, Sm, Gd) on critical current density in high Tc YBa2Cu3O7-x (123)

In the upcoming generation, bulk high temperature superconductors (HTS) will play a crucial and a promising role in numerous industrial applications ranging from Maglev trains to magnetic resonance imaging, etc. Especially, the bulk HTS as permanent magnets are suitable due to the fact that they can trap magnetic fields being several orders of magnitude higher than those of the best hard ferromagnets. The bulk HTS LREBa2Cu3O7-δ (LREBCO or LRE-123, LRE: Y, Gd, etc.,) materials could obtain very powerful compact superconducting super-magnets, which can be operated at the cheaper liquid nitrogen temperature or below due to higher critical temperatures (i.e., ~90 K). As a result, the new advanced technology can be utilized in a more attractive manner for a variety of technological and medical applications which have the capacity to revolutionize the field. An understanding of the magnetic field dependence of the critical current density (J c(H)) is important to develop better adapted materials. To achieve this goal, a variety of Jc (H) behaviours of bulk LREBCO samples were modelled regarding thermally activated flux motion. In essence, the Jc (H) curves follows a certain criterion where an exponential model is applied. However, to fit the complete Jc (H) curve of the LRE-123 samples an unique model is necessary to explain the behavior at low and high fields. The modelling of the various superconducting materials could be understood in terms of the pinning mechanisms.

Simulation of Field Dependence of Critical Current Densities of Bulk High Tc Superconducting Materials regarding Thermally Activated Flux Motion

Melt grown samples of Y1.2Ba1.8Cu2.4O
 x
 have been prepared and studied for their current carrying capacity. The composition was chosen to include Y2BaCuO5 (211) particles in the YBa2Cu3O
 x
 (123) phase. The critical current density (J
 c) of these samples was studied as a function of magnetic field using magnetization technique. The micrographic investigation shows well aligned grains in this material. The magnetic hysteresis measurements were done using a MPMS SQUID magnetometer up to the fields of 5.5 T. TheJ
 c was estimated from the remanent magnetization using Bean model. Isothermal magnetization hysteresis loops at low fields reveal the presence of only one kind of hysteresis loops (corresponding to intragrain magnetizations). This is a valid proof that the weak links are greatly eliminated in these samples prepared by MG process. TheJ
 c behaviour as a function of magnetic field has two components, a rapidly decaying exponential function of field and the other component that predominates at higher fields. This could be explained if we assume that the sample contains two phases of superconductors, one having a lowH
 c2 becoming normal at fairly medium fields of the order of a few kilogauss will act as pinning centres for the other phase having higherH
 c2 and hence higherJ
 c at high fields.

Critical current density of a sample of melt grown y 1-2 Ba 1-8 Cu 2-4 O x

Magnetic 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.

/pdf/magnetic-shielding-using-high-temperature-superconductors-1qtzsj9uvn.pdf

T Rajasekaran

Papers

Critical current density of a sample of melt grown y 1-2 Ba 1-8 Cu 2-4 O x

Magnetic shielding using high-temperature superconductors

Magnetic shielding studies using cylinders of YBa2Cu3O7−x prepared by isostatic compression