Improvement of Critical Current Density and Flux Trapping in Bulk High-Tc Superconductors

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Power processing unit for hall-effect thrusters on "Meteor-M №3 spacecraf"

The development results of power processing unit (PPU-M) for hall-effect thrusters on "Meteor-M №3" spacecraft are considered. The structure, weight, dimensions and main technical characteristics of the system in the paper are presented. The work peculiarity of the system is unstable input voltage of both power bus and control bus that increases the ripple voltages and currents at the input and the output and causes the additional requirements to the circuit design. A comparative analysis of the system characteristics and European analogs was carried out, and then a conclusion on the basis of available data that the characteristics of the system are not inferior to European analogs was mad

Thermoelectric properties of Ca0.9Yb0.1MnO3-x prepared by spark plasma sintering in air atmosphere

In this paper we report the densification of Ca0.9Yb0.1MnO3-x ceramics by spark plasma sintering (SPS) in different atmospheres and using different tools. The thermoelectric properties of these ceramics are reported and compared to those of ceramics obtained by conventional sintering. This study clearly demonstrated the possibility for processing oxide materials by SPS under air atmosphere and overcomes the problem of reduction due to the low oxygen partial pressure (graphitic environment, dynamic vacuum or neutral atmosphere) commonly encountered

Effect of Microstructural Refinement on Electrical Properties of BST-Based Ceramics Prepared by Spark Plasma Sintering and Spark Plasma Texturing

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Non-hyperbolic ergodic measures and horseshoes in partially hyperbolic homoclinic classes

We study a rich family of robustly non-hyperbolic transitive diffeomorphisms and we show that each ergodic measure is approached by hyperbolic sets in weak$*$-topology and in entropy. For hyperbolic ergodic measures, it is a classical result of A. Katok. The novelty here is to deal with non-hyperbolic ergodic measures.Comment: 25 pages and 1 figur

Thermoelectric properties of ZnO ceramics densified through spark plasma sintering

Thermoelectric properties of pure ZnO ceramics were investigated in this study. ZnO powders were sintered using spark plasma sintering by varying temperature (600–900 °C) and atmosphere (air and vacuum), thereafter, the ceramics were annealed in air at 600 °C. Relative densities >98% were determined for all the samples with grain sizes of the same order of magnitude, hence, thermal conductivity of ~45 W/mK was determined at room temperature. As-sintered ceramics prepared from synthetic powder (CSP) had higher carrier concentration than ceramics prepared from commercial powder (CCP) by 2.3x1017 cm−3. Thus, resistivity and Seebeck Coefficient of 0.08 Ω cm and 475 μV/K were determined, respectively, at room temperature for CSP sintered at 900 °C. There was no significant change on the performance of the ZnO ceramics when the sintering atmosphere and temperature were altered. Annealing did not improve the thermoelectric properties of ZnO ceramics. Maximum ZT of 8x10−3 was obtained for CSP sintered at 900 °C

Measurement of the magnetic field inside the holes of a drilled bulk high-Tc superconductor

We use macroscopic holes drilled in a bulk YBCO superconductor to probe its magnetic properties in the volume of the sample. The sample is subjected to an AC magnetic flux with a density ranging from 30mT to 130mT and the flux in the superconductor is probed by miniature coils inserted in the holes. In a given hole, three different penetration regimes can be observed: (i) the shielded regime, where no magnetic flux threads the hole; (ii) the gradual penetration regime, where the waveform of the magnetic field has a clipped sine shape whose fundamental component scales with the applied field; and (iii) the flux concentration regime, where the waveform of the magnetic field is nearly a sine wave, with an amplitude exceeding that of the applied field by up to a factor of two. The distribution of the penetration regimes in the holes is compared with that of the magnetic flux density at the top and bottom surfaces of the sample, and is interpreted with the help of optical polarized light micrographs of these surfaces. We show that the measurement of the magnetic field inside the holes can be used as a local characterization of the bulk magnetic properties of the sample

The role of a-axis grains in the transition to the normal state of YBa2Cu3O7−δ films and of 2G-coated conductors when induced by high electrical current densities

The influence of surface defects, in particular of a-axis grains, on the transition to the normal state induced by high current densities in YBa2Cu3O7−δ (YBCO) thin films and in a commercial 2G-coated conductor is investigated. For that purpose, the surface of the samples is observed by scanning electron microscopy and isothermal current-voltage curves are measured at different temperatures with pulsed currents up to the quenching value I*. The results show that the ratio of I* to the critical current is large if a-axis grains are not visible at the surface of the YBCO films, while it is much lower if the surface includes a-axis grains as this is the case for the coated conductor. The connection between the transition onset and the vortex dynamics, as well as the role of the a-axis grains in this process are discussed. The relation between the I* values obtained from thermal calculations and those resulting from vortex dynamics considerations is also discussed, as well as the possible consequences suggested by this work for the different applications of the coated conductors