Anisotropic AC Behavior of Multifilamentary Bi-2223/Ag Tapes

In this communication, we report on the anisotropy of the superconducting properties of multifilamentary Bi-based tapes experimentally investigated by AC magnetic susceptibility measurements. The susceptibility $\chi= \chi' - j \chi''$ was measured using a commercial system and a couple of orthogonal pick-up coils. The $\chi''$ vs. temperature curves were shown to exhibit two peaks. The smaller of the peaks, occurring near T = 72K, was only visible for particular field directions and within a given frequency window. Such results point out the role played by the phase difference between the applied magnetic field and the internal magnetic field seen by the filaments.Comment: 4 pages (2 columns); 4 figure

Magnetization of 2-G Coils and Artificial Bulks

The use of (Re)BCO is limited by the problems of magnetization/demagnetization. (Re)BCO is available in many forms, but two of the most interesting for high magnetic field applications are 2-G tape and bulks (either or as grown or manufactured artificially using 2-G tapes). The minimum joint resistance that can be achieved between YBCO tapes is on the order of 100 nΩ, but this is still too large to operate coils in persistent mode. Bulks have potential to act as very high field magnets, but in order to do this, they need to be magnetized. This paper describes flux pumping methods, which can be used to charge either coils or bulks.This is the accepted manuscript. The final published version is available from IEEE at http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=6845330. © 2014 IEEE

AC Magnetic Measurements on Superconductors: Design of a Device for Magneto-Thermal Measurements

This work describes the design and realisation of an apparatus to measure simultaneously the AC magnetic properties and the temperature distribution on the top surface of bulk superconducting samples (up to 32 mm in diameter) in cryogenic conditions (temperature range 78-120 K). First we describe the experimental set-up used for simultaneous thermal and magnetic characterization of the sample. Next we describe the practical considerations required for generating the large AC magnetic fields, possibly in the presence of DC fields. In the third section we present a custom-made high speed data acquisition system for replacing the laboratory devices (DC voltmeter and AC lock-in amplifiers) when both temperature and magnetic data need to be recorded at high a sampling rate. The performances and limitations of the system are discussed.Peer reviewe

Development of a microcontroller-based phase resolved partial discharge measurement system with application to the monitoring of flash sintering discharge patterns

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Use of 2G coated conductors for efficient shielding of DC magnetic fields

This paper reports the results of an experimental investigation of the performance of two types of magnetic screens assembled from YBa2Cu3O7-d (YBCO) coated conductors. Since effective screening of the axial DC magnetic field requires the unimpeded flow of an azimuthal persistent current, we demonstrate a configuration of a screening shell made out of standard YBCO coated conductor capable to accomplish that. The screen allows the persistent current to flow in the predominantly azimuthal direction at a temperature of 77 K. The persistent screen, incorporating a single layer of superconducting film, can attenuate an external magnetic field of up to 5 mT by more than an order of magnitude. For comparison purposes, another type of screen which incorporates low critical temperature quasi-persistent joints was also built. The shielding technique we describe here appears to be especially promising for the realization of large scale high-Tc superconducting screens.Comment: 8 pages, 3 figure

Investigation of demagnetization in HTS stacked tapes implemented in electric machines as a result of crossed magnetic field

This paper investigates the practical effectiveness of employing superconducting stacked tapes to superconducting electric machinery. The use of superconducting bulks in various practical applications has been addressed extensively in the literature. However, in practice, dramatic decrease in magnetization would occur on superconducting bulks due to the crossed field effect. In our study, we employed the superconducting stacked tapes in a synchronous superconducting motor, which was designed and fabricated in our laboratory, aiming to lessen demagnetization due to crossed field effect in comparison with superconducting bulks. Applying the transverse AC field, the effects of frequency, amplitude, and number of cycles of the transverse magnetic field are discussed. Furthermore, a stack of 16 layers of superconducting tapes is modelled and the consequences of applying the crossed magnetic field on the sample are evaluated. The confrontation between experiments and simulation allows us to thoroughly understand the crossed field effects on stacked tapes. At the end, a preventive treatment, based on the shielding characteristic of superconductor and materials with high permeability, i.e. -metal and metalic glass, is suggested. On the other hand, the shielding feature of aforementioned materials will hinder the penetration of magnetic field and, consequently, reduction of the demagnetization will be attained.This is the accepted manuscript. The final version is available from IEEE at https://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=6965587&sortType%3Dasc_p_Sequence%26filter%3DAND%28p_Publication_Number%3A77%29%26pageNumber%3D16

Magneto-transport study of nb-doped Bi/Pb2223 superconductor

The magneto-transport properties of Bi1.5Pb0.4Nb0.1Sr2Ca2Cu3O10-x polycrystalline, superconducting ceramic are reported. The material was found to be chemically homogeneous and partially textured. The mixed state properties were investigated by measuring the electrical resistivity, longitudinal and transverse (Nernst effect) thermoelectric power, and thermal conductivity. The magnetization and AC susceptibility measurements were also performed. The variation of these characteristics for magnetic fields up to 5 T are discussed and compared to those of the zero field case. The transport entropy and thermal Hall angle are extracted and quantitatively compared to previously reported data of closely related systems. (C) 2003 Elsevier Science B.V. All rights reserved

Shielding efficiency and E(J) characteristics measured on large melt cast Bi-2212 hollow cylinders in axial magnetic fields

We show that tubes of melt cast Bi-2212 used as current leads for LTS magnets can also act as efficient magnetic shields. The magnetic screening properties under an axial DC magnetic field are characterized at several temperatures below the liquid nitrogen temperature (77 K). Two main shielding properties are studied and compared with those of Bi-2223, a material that has been considered in the past for bulk magnetic shields. The first property is related to the maximum magnetic flux density that can be screened, Blim; it is defined as the applied magnetic flux density below which the field attenuation measured at the centre of the shield exceeds 1000. For a cylinder of Bi-2212 with a wall thickness of 5 mm and a large ratio of length over radius, Blim is evaluated to 1 T at T = 10 K. This value largely exceeds the Blim value measured at the same temperature on similar tubes of Bi-2223. The second shielding property that is characterized is the dependence of Blim with respect to variations of the sweep rate of the applied field, dBapp/dt. This dependence is interpreted in terms of the power law E = Ec(J/Jc)^n and allows us to determine the exponent n of this E(J) characteristics for Bi-2212. The characterization of the magnetic field relaxation involves very small values of the electric field. This gives us the opportunity to experimentally determine the E(J) law in an unexplored region of small electric fields. Combining these results with transport and AC shielding measurements, we construct a piecewise E(J) law that spans over 8 orders of magnitude of the electric field.Comment: 16 pages, 7 figure