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See detailMagnetic shielding properties of a superconducting hollow cylinder: Influence of a vertical or a horizontal slit
Fagnard, Jean-François ULiege; Dirickx, Michel; Elschner, Stephan et al

Poster (2011, September)

The magnetic shielding properties under both axial and transverse DC magnetic fields are measured at the liquid nitrogen temperature (77 K) on Bi-2212 hollow cylinders obtained by Melt Cast Process. The ... [more ▼]

The magnetic shielding properties under both axial and transverse DC magnetic fields are measured at the liquid nitrogen temperature (77 K) on Bi-2212 hollow cylinders obtained by Melt Cast Process. The characterized samples are cut by a slit along either a vertical (parallel to the cylinder axis) or a horizontal (perpendicular to the cylinder axis) plane. The sample with the vertical slit is subjected to a transverse magnetic field whose the direction is varied between 0° and 90° with respect to the normal of the slit plane. The measurements show that there is no influence of the presence of the slit on the magnetic shielding properties for a transverse magnetic field applied perpendicular to the slit plane but a strong reduction of the magnetic shielding efficiency when the angle between the applied transverse magnetic field and the normal to the slit plane exceeds 15°. Numerical modelling using the Finite Elements Method on short-length hollow cylinder allows us to understand how the superconducting currents flow in a slit cylinder depending on the magnetic field orientation. A second sample is cut horizontally by a median plane and is characterized in axial magnetic field configuration. Measurements are carried out along the axis of the cylinder for several slit thicknesses. [less ▲]

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See detailScreening of axial DC magnetic fields by using superconducting loops of second generation coated conductors without joints
Fagnard, Jean-François ULiege; Dirickx, Michel; Vanderheyden, Benoît ULiege et al

Poster (2010, August)

The performances of second generation (2G) YBCO coated conductors for screening DC magnetic fields at 77 K are investigated experimentally. An uninterrupted superconducting path is achieved by splitting ... [more ▼]

The performances of second generation (2G) YBCO coated conductors for screening DC magnetic fields at 77 K are investigated experimentally. An uninterrupted superconducting path is achieved by splitting two sections of a slit 2G tape in order to obtain a loop without joint. Several loops are stacked together to obtain a coil acting as a magnetic screen. Persistent currents in this coil are shown to shield efficiently magnetic fields that are applied at very low sweep rates (500 @T/s). The shielding properties are characterized by measuring the shielding factor of the screen, i.e. the ratio between the magnetic field with and without screen. In a coil made of a single layer of coated conductors, the shielding factor at the center of the coil is shown to exceed 10 for an applied DC magnetic flux density of 5 mT. The uniformity of the shielding factor along the axis of the screen is also investigated; results show the magnetic field is attenuated by a factor larger than 3 near the open ends. Both the maximum field amplitude that can be shielded and the shielding factor of the coil can be enhanced by increasing the number of concentric coils. The key advantages of this shielding technique are (i) the moderate weight compared to magnetic screens made of bulk materials and (ii) the possibility of shielding larger volumes by using longer sections of YBCO coated conductors. [less ▲]

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See detailStudy of the magnetic shielding ability in relation with the non linear E(J) relationship of melt cast Bi-2212 tubes under DC axial magnetic fields
Fagnard, Jean-François ULiege; Dirickx, Michel; Elschner, Stephan et al

Poster (2010, July)

In this work, we aim at describing as widely as possible the shielding properties and the E(J) relationship of Bi-2212 tubes from non-destructive measurements on a whole cylinder. First, the threshold ... [more ▼]

In this work, we aim at describing as widely as possible the shielding properties and the E(J) relationship of Bi-2212 tubes from non-destructive measurements on a whole cylinder. First, the threshold magnetic induction below which the shielding occurs, Blim, is measured in a large temperature range between 10 K and 77 K. The temperature dependence of Blim is compared to that of similar superconducting hollow cylinders made of Bi-2223 previously studied in [Fagnard J-F et al. Supercond. Sci. Technol. 22 (2009) 105002] and shows that the magnetic shielding capabilities of Bi-2212 below T = 60 K can exceed those of Bi-2223. In particular, the threshold value of shielded magnetic field is higher than 800 mT below T = 20 K with a 5 mm thick cylinder. Next, the sweep rate dependence of Blim is determined and analysed under several simple assumptions relating Blim to the shielding currents, J, and the sweep rate of the applied magnetic field to the electric field, E, to give information about the non-linear E(J) relationship. Then, the relaxation of the shielding currents is studied at several temperatures and the results are used to confirm the values of the power law exponent of the E(J) relationship determined by sweep creep experiments. Finally, transport and AC-shielding measurements are carried out and exploited, together with the magnetic relaxation and the sweep creep measurements, to build a piecewise E(J) graph that extends over several decades. [less ▲]

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See detailStudy of the magnetic shielding ability in relation with the non linear E(J) relationship of melt cast Bi-2212 tubes under DC axial magnetic fields.
Fagnard, Jean-François ULiege; Elschner, Stephan; Bock, Joachim et al

Conference (2010, July)

In this work, we aim at describing as widely as possible the shielding properties and the E(J) relationship of Bi-2212 tubes from non-destructive measurements on a whole cylinder. First, the threshold ... [more ▼]

In this work, we aim at describing as widely as possible the shielding properties and the E(J) relationship of Bi-2212 tubes from non-destructive measurements on a whole cylinder. First, the threshold magnetic induction below which the shielding occurs, Blim, is measured in a large temperature range between 10 K and 77 K. The temperature dependence of Blim is compared to that of similar superconducting hollow cylinders made of Bi-2223 previously studied in [Fagnard J-F et al. Supercond. Sci. Technol. 22 (2009) 105002] and shows that the magnetic shielding capabilities of Bi-2212 below T = 60 K can exceed those of Bi-2223. In particular, the threshold value of shielded magnetic field is higher than 800 mT below T = 20 K with a 5 mm thick cylinder. Next, the sweep rate dependence of Blim is determined and analysed under several simple assumptions relating Blim to the shielding currents, J, and the sweep rate of the applied magnetic field to the electric field, E, to give information about the non-linear E(J) relationship. Then, the relaxation of the shielding currents is studied at several temperatures and the results are used to confirm the values of the power law exponent of the E(J) relationship determined by sweep creep experiments. Finally, transport and AC-shielding measurements are carried out and exploited, together with the magnetic relaxation and the sweep creep measurements, to build a piecewise E(J) graph that extends over several decades. [less ▲]

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See detailUse of second generation coated conductors for efficient shielding of DC magnetic fields
Fagnard, Jean-Francois ULiege; Dirickx, Michel; Levin, G. A. et al

in Journal of Applied Physics (2010), 108

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 ... [more ▼]

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. [less ▲]

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See detailShielding efficiency and E(J) characteristics measured on large melt cast Bi-2212 hollow cylinders in axial magnetic fields
Fagnard, Jean-François ULiege; Elschner, Steffen; Bock, Joachim et al

in Superconductor Science and Technology (2010), 23

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 ... [more ▼]

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. [less ▲]

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See detailMagnetic shielding properties of high- Tc superconducting hollow cylinders: model combining experimental data for axial and transverse magnetic field configurations
Fagnard, Jean-François ULiege; Dirickx, Michel; Ausloos, Marcel ULiege et al

in Superconductor Science and Technology (2009), 22(10), 10500210

Magnetic shielding efficiency was measured on high- Tc superconducting hollow cylinders subjected to either an axial or a transverse magnetic field in a large range of field sweep rates, dBapp/dt. The ... [more ▼]

Magnetic shielding efficiency was measured on high- Tc superconducting hollow cylinders subjected to either an axial or a transverse magnetic field in a large range of field sweep rates, dBapp/dt. The behaviour of the superconductor was modelled in order to reproduce the main features of the field penetration curves by using a minimum number of free parameters suitable for both magnetic field orientations. The field penetration measurements were carried out on Pb-doped Bi-2223 tubes at 77 K by applying linearly increasing magnetic fields with a constant sweep rate ranging between 10 uT s[?]1 and 10 mT s[?]1 for both directions of the applied magnetic field. The experimental curves of the internal field versus the applied field, Bin(Bapp), show that, at a given sweep rate, the magnetic field for which the penetration occurs, Blim, is lower for the transverse configuration than for the axial configuration. A power law dependence with large exponent, n', is found between Blim and dBapp/dt. The values of n' are nearly the same for both configurations. We show that the main features of the curves Bin(Bapp) can be reproduced using a simple 2D model, based on the method of Brandt, involving a E(J) power law with an n-exponent and a field-dependent critical current density, Jc(B), (following the Kim model: Jc = Jc0(1+B/B1)[?]1). In particular, a linear relationship between the measured n'-exponents and the n-exponent of the E(J) power law is suggested by taking into account the field dependence of the critical current density. Differences between the axial and the transverse shielding properties can be simply attributed to demagnetizing fields. [less ▲]

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See detailTemperature dependence of HTS magnetic shielding properties: Measurements on Pb-doped Bi-2223 hollow cylinders submitted to axial magnetic fields
Fagnard, Jean-François ULiege; Dirickx, Michel; Ausloos, Marcel ULiege et al

Poster (2009, September)

Measurements of the magnetic shielding properties of Pb-doped Bi-2223 hollow cylinders submitted to an axial magnetic field have been carried out at several temperatures in the range 10 K - 95 K. The ... [more ▼]

Measurements of the magnetic shielding properties of Pb-doped Bi-2223 hollow cylinders submitted to an axial magnetic field have been carried out at several temperatures in the range 10 K - 95 K. The amplitude of the internal magnetic field was probed using a high sensitivity 3-axis Hall sensor. We have studied the dependence of the shielding factor (the ratio of the applied magnetic field over the internal magnetic field) with respect to the sweep rate of the applied field at several temperatures. The experimental results were compared to a 2-D modelling based on Brandt’s algorithm [1, 2] involving a non-linear E(J) relationship and a field-dependent critical current density Jc(B). We compared the penetration of the magnetic field into an open cylinders and a cylinder closed at one end. The spatial distribution of the shielding factor along the axis of both tubes has been measured. Results show that the shielding efficiency is reduced in the vicinity of the cylinder ends. [1] Brandt, E., Phys. Rev. B, 1998, 58, 6506-6522 [2] Denis, S. et al., Supercond. Sci. Technol., 2007, 20, 418-427 [less ▲]

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See detailDC and AC Shielding Properties of Bulk High-Tc Superconducting Tubes
Fagnard, Jean-François ULiege; Denis, Samuel; Lousberg, Grégory ULiege 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 detailInfluence of thermal treatment on YBa2Cu3O7-x thick films prepared by electrophoretic deposition on Ni and Ag substrates
Dusoulier, Laurent; Denis, Samuel; Dirickx, Michel et al

in Materials Research Society Symposium Proceedings (2007), 1001E

We have studied the sintering parameters of YBa2Cu3O7-x (YBCO) coatings produced by electrophoretic deposition (EPD) on Ag and Ni substrates. The maximal sintering temperature is ~ 930°C due to partial ... [more ▼]

We have studied the sintering parameters of YBa2Cu3O7-x (YBCO) coatings produced by electrophoretic deposition (EPD) on Ag and Ni substrates. The maximal sintering temperature is ~ 930°C due to partial melting and chemical contamination for Ag and Ni substrates respectively. Increasing the sintering duration does not improve significantly the densification. When Ar sintering atmosphere is used, the coating density is strongly increased on Ag substrates while adhesion is poor on Ni substrates. The Ar-sintered YBCO coating deposited on planar Ag substrate displays a significant magnetic shielding effect for low frequency applied magnetic induction. [less ▲]

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See detailCharacterisation of the magnetic shielding properties of YBaCuO thick films prepared by electrophoretic deposition on silver substrates
Denis, Samuel; Grenci, G.; Dusoulier, Laurent et al

in Journal of Physics: Conference Series (2006), 43

This communication reports experimental results on the superconducting properties of YBaCuO thick films prepared by electrophoretic deposition on silver substrates. The magnetic shielding properties of ... [more ▼]

This communication reports experimental results on the superconducting properties of YBaCuO thick films prepared by electrophoretic deposition on silver substrates. The magnetic shielding properties of the coatings were characterised by various methods. First, the electrical resistance and the transport critical current density, Jc, were determined. Our coatings exhibit a superconducting transition at a temperature of 90 K. Next, shielding characterisations were carried out at 77 K for samples having either a slab or a cylindrical geometry. In both cases, the frequency of the applied magnetic field was 103 Hz; the field behind the shielding wall was measured by a pick-up coil connected to a lock-in amplifier. In the case of cylindrical samples and for an applied induction lower than 1 G, the field inside the shielding enclosure is reduced by a factor greater than 106 (i.e. 120 dB) with respect to the applied field. [less ▲]

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See detailYBa2Cu3O(7-delta) thick films on Ag prepared by the electrophoretic deposition technique
Dusoulier, Laurent; Denis, Samuel; Fagnard, Jean-François ULiege et al

in Journal of Physics: Conference Series (2006), 43

YBa2Cu3O7-δ thick films have been deposited onto Ag substrates by the Electrophoretic Deposition (EPD) technique. Different microstructures and electrical behaviours were observed depending on the ... [more ▼]

YBa2Cu3O7-δ thick films have been deposited onto Ag substrates by the Electrophoretic Deposition (EPD) technique. Different microstructures and electrical behaviours were observed depending on the starting powder. Coatings prepared from commercial powder displayed significant porosity and the superconducting transition width was found to be magnetic-field dependent. Films produced from home-made coprecipitated powder are denser but contain some secondary phases. No dependence of the resistive transition as a function of magnetic field (H ≤ 20 Oe) was observed in that case. [less ▲]

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See detailInversion of the Biot-Savart Law: an approach based on discrete sine and cosine transforms
Dirickx, Michel; Denis, Samuel ULiege; Vanderheyden, Benoît ULiege et al

in Johansen, T. H.; Shantsev, D. V. (Eds.) Magneto-Optical Imaging, Proceedings of the NATO Advanced Research Workshop, held in Øystese, Norway, 28-30 August 2003 (2004)

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