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See detailMagnetic shielding with YBCO coated conductors: influence of the geometry on its performances
Wera, Laurent ULg; Fagnard, Jean-François ULg; Levin, G. A. et al

in IEEE Transactions on Applied Superconductivity (2012), 23(3),

A superconducting magnetic shield can be built as a stack of several sections of milled 2G coated conductors. Each section consists of a closed loop where persistent currents can flow and provide a strong ... [more ▼]

A superconducting magnetic shield can be built as a stack of several sections of milled 2G coated conductors. Each section consists of a closed loop where persistent currents can flow and provide a strong attenuation of external dc magnetic fields. The purpose of the present work is to study experimentally several geometries of such magnetic shields made out of YBa2Cu3O7 (YBCO) coated conductors from SuperPower. Our aim is to investigate in detail the influence of the aspect ratio and the number of layers of the assembly on the magnetic shielding properties. In order to do so, the magnetic shield is subjected to an axial quasi-static (“dc”) magnetic field ramped slowly at a fixed sweep rate. A Hall probe is used to measure the local magnetic induction inside the assembly as a function of the appliedmagnetic induction. Results show that the shielding factor, SF, (defined as the ratio between the appliedmagnetic induction and the magnetic induction measured inside the shield) is improved for increasing aspect ratios of the global coated conductor assembly and that the threshold magnetic induction (defined for SF = 10) increases with the number of layers. Using a double layer of 18 sections at T = 77 K, dc magnetic fields up to 56 mT can be shielded by a factor larger than 10. Finally, the effect of an air gap of constant width between coated conductor sections is also characterized.(C) 2012 IEEE [less ▲]

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See detailOptimization of thermal material in a flux pump system with high temperature superconductor
Hsu, C. H.; Yan, Y; Hadeler, O. et al

in IEEE Transactions on Applied Superconductivity (2012), 22(3), 7800404

Superconductors are known for the ability to trap magnetic field. A thermally actuated magnetization (TAM) flux pump is a system that utilizes the thermal material to generate multiple small magnetic ... [more ▼]

Superconductors are known for the ability to trap magnetic field. A thermally actuated magnetization (TAM) flux pump is a system that utilizes the thermal material to generate multiple small magnetic pulses resulting in a high magnetization accumulated in the superconductor. Ferrites are a good thermal material candidate for the future TAM flux pumps because the relative permeability of ferrite changes significantly with temperature, particularly around the Curie temperature. Several soft ferrites have been specially synthesized to reduce the cost and improve the efficiency of the TAM flux pump. Various ferrite compositions have been tested under a temperature variation ranging from 77K to 300K. The experimental results of the synthesized soft ferrites-Cu0.3Zn0.7Ti0.04Fe1.96O4, including the Curie temperature, magnetic relative permeability and the volume magnetization (emu/cm3), are presented in this paper. The results are compared with original thermal material, gadolinium, used in the TAM flux pump system.-Cu0.3Zn0.7Ti0.04Fe1.96O4 holds superior characteristics and is believed to be a suitable material for next generation TAM flux pump. © 2011 IEEE. [less ▲]

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See detailElectrical and Magnetic Characterization of BSCCO and YBCO HTS Tapes for Fault Current Limiter Application
Lamas, Jerika S; Baldan, Carlos A; Shigue, Carlos Y et al

in IEEE Transactions on Applied Superconductivity (2011), 21(3), 3398-3402

Several high temperature superconductor (HTS) tapes have been developed since the late eighties. Due to the new techniques applied for their production, HTS tapes are becoming feasible and practical for ... [more ▼]

Several high temperature superconductor (HTS) tapes have been developed since the late eighties. Due to the new techniques applied for their production, HTS tapes are becoming feasible and practical for many applications. In this work, we present the test results of five commercial HTS tapes from the BSCCO and YBCO families (short samples of 200 mm). We have measured and analyzed their intrinsic and extrinsic properties and compared their behaviors for fault current limiter (FCL) applications. Electrical measurements were performed to determine the critical current and the n value through the V-I relationship under DC and AC magnetic fields. The resistance per unit length was determined as a function of temperature. The magnetic characteristics were analyzed through susceptibility curves as a function of temperature. As transport current generates a magnetic field surrounding the HTS material, the magnetic measurements indicate the magnetic field supported by the tapes under a peak current 1.5 times higher than the critical current, I(c). By pulsed current tests the recovery time and the energy/volume during a current fault were also analyzed. These results are in agreement with the data found in the literature giving the most appropriate performance conductor for a FCL device (I(peak) = 4 kA) to be used in a 220 V-60 Hz grid. [less ▲]

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See detailNumerical Study of the Shielding properties of Macroscopic Hybrid Ferromagnetic/Superconductor Hollow Cylinders
Lousberg, Grégory ULg; Fagnard, Jean-François ULg; Ausloos, Marcel ULg et al

in IEEE Transactions on Applied Superconductivity (2010), 20(1), 33

We study the magnetic shielding properties of hybrid ferromagnetic/superconductor (F/S) structures consisting of two coaxial cylinders, with one of each material.We use an axisymmetric finite-element ... [more ▼]

We study the magnetic shielding properties of hybrid ferromagnetic/superconductor (F/S) structures consisting of two coaxial cylinders, with one of each material.We use an axisymmetric finite-element model in which the electrical properties of the superconducting tube are modeled by a nonlinear E-J power law with a magnetic-field-dependent critical current density whereas the magnetic properties of the ferromagnetic material take saturation into account. We study and compare the penetration of a uniform axial magnetic field in two cases: 1) a ferromagnetic tube placed inside a larger superconducting tube (Ferro-In configuration) and 2) a ferromagnetic tube placed outside the superconducting one (Ferro-Out configuration). In both cases, we assess how the ferromagnetic tube improves the shielding properties of the sole superconducting tube. The influence of the geometrical parameters of the ferromagnetic tube is also studied: It is shown that, upon an optimal choice of the geometrical parameters, the range of magnetic fields that are efficiently shielded by the hightemperature superconductor tube alone can be increased by a factor of up to 7 (2) in a Ferro-Out (Ferro-In) configuration. The optimal configuration uses a 1020 carbon steel with a thickness of 2 mm and a height that is half that of the superconducting cylinder (80 mm). [less ▲]

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See detailDC and AC Shielding Properties of Bulk High-Tc Superconducting Tubes
Fagnard, Jean-François ULg; Denis, Samuel; Lousberg, Grégory ULg et al

in IEEE Transactions on Applied Superconductivity (2009), 19(3), 2905-2908

We have studied numerically and experimentally the magnetic flux penetration in high-Tc superconducting tube subjected to a uniform magnetic field parallel to its long axis. This study is carried in view ... [more ▼]

We have studied numerically and experimentally the magnetic flux penetration in high-Tc superconducting tube subjected to a uniform magnetic field parallel to its long axis. This study is carried in view of designing low-frequency magnetic shields by exploiting the diamagnetic properties of high-Tc superconducting ceramics. We have measured the field attenuation for applied magnetic fields in the frequency range 5 mHz-0.1 Hz by Hall probe measurements and at audio frequencies using a sensing coil. A simple 1D analysis using the Kim critical state model was found to be able to reproduce the experimental data satisfactorily. We have also determined the phase shift between the internal and the applied field both experimentally and numerically. Finally, we have studied the sweep rate dependence of the magnetic shielding properties, using data recorded either at several constant sweep rates dB/dt or at several AC fields of various amplitudes and frequencies. Both methods agree with each other and lead to a n -value of the E ~ J n law equal to ~ 40 at 77 K. [less ▲]

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See detailThe Numerical Modeling and Measurement of Demagnetization Effect in Bulk YBCO Superconductors Subjected to Transverse Field
Hong, Z.; Vanderbemden, Philippe ULg; Pei, R. et al

in IEEE Transactions on Applied Superconductivity (2008), 18(2), 1561-1564

In this paper, the crossed field demagnetization effect of the bulk type-II superconducting materials in a variety of external magnetic field condition has been investigated both numerically and ... [more ▼]

In this paper, the crossed field demagnetization effect of the bulk type-II superconducting materials in a variety of external magnetic field condition has been investigated both numerically and experimentally. A melt-textured YBCO bulk sample was magnetized along the axial direction and after that a transverse field perpendicular to the central axis applied. The collapse of the original trapped field was measured using a Quantum Design Physical Property Measurement System. A numerical solver based on critical state model is proposed to simulate the measured results. (C) 2008 IEEE. [less ▲]

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See detailMeasurements of thermal effects in a bulk YBCO single domain superconductor submitted to a variable magnetic field
Laurent, Philippe ULg; Vanderbemden, Philippe ULg; Meslin, S. et al

in IEEE Transactions on Applied Superconductivity (2007), 17(2, Part 3), 3036-3039

When YBCO single domains are subjected to a variable magnetic field, the motion of vortices may give rise to a significant temperature increase and a degradation of the superconducting properties. We have ... [more ▼]

When YBCO single domains are subjected to a variable magnetic field, the motion of vortices may give rise to a significant temperature increase and a degradation of the superconducting properties. We have experimentally investigated such effects in bulk melt-processed YBCO single domains. Several temperature sensors, a pick-up coil and two Hall probes were placed against the surface of a monolithic bulk YBCO pellet. Data were simultaneously recorded during the application of ac magnetic fields of various amplitudes, either with or without a pre-existing dc trapped flux. The measurement results agree well with to those obtained by numerical modeling. It was also found that a superimposed dc magnetic moment reduces the temperature increase caused by the ac magnetic field. (C) 2003 IEEE. [less ▲]

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See detailAnisotropic AC behavior of multifilamentary Bi-2223/Ag tapes
Fagnard, Jean-François ULg; Vanderbemden, Philippe ULg; Cloots, Rudi ULg et al

in IEEE Transactions on Applied Superconductivity (2003), 13(2, Part 3), 2976-2979

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 ... [more ▼]

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 X = X' - jX" was measured using a commercial system and a couple of orthogonal pick-up coils. The X'' vs. temperature curves were shown to exhibit two peaks. The smaller of the peaks, occurring near T = 72 K, 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. (C) 2003 IEEE. [less ▲]

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See detailBehavior of bulk melt-textured YBCO single domains subjected to crossed magnetic fields
Vanderbemden, Philippe ULg; Dorbolo, Stéphane ULg; Hari-Babu, N. et al

in IEEE Transactions on Applied Superconductivity (2003), 13(2, Part 3), 3746-3749

We have experimentally investigated the crossed magnetic field effects on bulk melt-processed YBCO single domains. The samples were first permanently magnetized along their c-axis and then subjected to ... [more ▼]

We have experimentally investigated the crossed magnetic field effects on bulk melt-processed YBCO single domains. The samples were first permanently magnetized along their c-axis and then subjected to several cycles of a transverse magnetic field parallel to the ab planes. The magnetic properties along the c and ab directions were simultaneously measured using a couple of orthogonal pick-up coils as well as a Hall probe placed against the sample surface. The effects of both sweep amplitude and polarity were investigated. Field sweeps of alternate polarities are shown to affect the decay of the c-axis magnetization much more strongly than field sweeps of unique polarity do. However, the c-axis magnetization does not show any saturation even after a large number of field sweeps. Next, a micro-Hall probe scanning system was used to measure the distribution of magnetic induction over the top surface of the single domain subjected to the same combination of magnetic fields. The results are shown to be consistent with those determined with the sensing coils and bring out the role played by geometric effects. (C) 2003 IEEE. [less ▲]

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See detailIntragranular and intergranular superconducting properties of bulk melt-textured YBCO
Vanderbemden, Philippe ULg; Cloots, Rudi ULg; Ausloos, Marcel ULg et al

in IEEE Transactions on Applied Superconductivity (1999), 9(2), 2308-2311

We have investigated the superconducting properties of bulk melt-processed YBCO using different experimental techniques. First, single domain materials (i.e. containing no grain boundaries) have been ... [more ▼]

We have investigated the superconducting properties of bulk melt-processed YBCO using different experimental techniques. First, single domain materials (i.e. containing no grain boundaries) have been studied. Electrical resistivity, current-voltage characteristics, M-H loops, and A,C. susceptibility. have been measured for different field and current directions. The intragranular properties are characteristic of high-quality melt-processed YBCO material,,vith a critical current density J(c)(T=77K, B=1T//c) > 10(4) A/cm(2). The anisotropy ratio J(c)(ab)/ J(c)(c) is found to be close to 3. Both magnetic and transport measurements show that defects in the microstructure do not significantly impede the current flow inside the single domain. These results were compared to those measured on samples containing one "natural" single grain boundary which sometimes appears during the grain growth process. The intergranular properties show a much stronger current and magnetic field dependence than that measured within the grain and these differences are discussed. [less ▲]

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See detailTransport properties of bulk-bicrystal grain boundaries in artificially joined large-grain YBCO
Bradley, A. D.; Doyle, R. A.; Charalambous, D. et al

in IEEE Transactions on Applied Superconductivity (1999), 9(2), 2038-2041

A technique for joining large-grain YBCO has been used to produce bulk-bicrystal grain boundaries of different orientations. The behaviour of boundaries nominally of 0 degrees[100], 0 degrees[001] and ... [more ▼]

A technique for joining large-grain YBCO has been used to produce bulk-bicrystal grain boundaries of different orientations. The behaviour of boundaries nominally of 0 degrees[100], 0 degrees[001] and asymmetric 15 degrees[100]-tilt misorientation have been investigated using low frequency transport measurements in fields up to 7T. The boundaries exhibit a metallic normal state and a superconducting transition which broadens with increasing field having an irreversibility line which closely matches that of the adjoining grains. This same qualitative behaviour is seen in all the samples measured for field applied parallel and perpendicular to the c-axis and up to the highest current densities employed (20 Acm(-2)). Variation between the different samples due to microstructural differences are discussed. We interpret these results as strong suggestive evidence that this joining technique can be used to produce strongly-coupled large-grains for bulk-scale engineering applications. [less ▲]

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