High temperature superconductors for low frequency magnetic shielding
TL;DR: In this article, the authors report the results of magnetic shielding measurements on pure YBa/sub 2/Cu/sub 3/O/sub 7- delta /, silver-doped YBa, packed powder, laser ablated thin film, and copper.
Abstract: The authors report the results of magnetic shielding measurements on pure YBa/sub 2/Cu/sub 3/O/sub 7- delta /, silver-doped YBa/sub 2/Cu/sub 3/O/sub 7- delta / packed powder, laser ablated thin film, and copper. The shielding factors of bulk ceramics were much higher than those of other materials and were not a function of frequency in the range from 10 Hz to 3000 Hz. Simply packed superconducting powder did not show any shielding. While polycrystalline ceramics were effective as shields, the thickness of the ceramic played a crucial role in shielding. The breakthrough field increased with thickness. The influence of DC fields on the shielding behavior depended on the magnitude of the fields. >
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TL;DR: The development and the experimental validation of a cryogenic magnetic shielding system for transition edge sensor based space detector arrays is described, with the system's measured on-axis shielding factor well exceeding the requirement of the envisaged missions.
Abstract: The paper describes the development and the experimental validation of a cryogenic magnetic shielding system for transition edge sensor based space detector arrays. The system consists of an outer mu-metal shield and an inner superconducting niobium shield. First, a basic comparison is made between thin-walled mu-metal and superconducting shields, giving an off-axis expression for the field inside a cup-shaped superconductor as a function of the transverse external field. Starting from these preliminary analytical considerations, the design of an adequate and realistic shielding configuration for future space flight applications (either X-IFU [D. Barret et al., e-print arXiv:1308.6784 [astro-ph.IM] (2013)] or SAFARI [B. Jackson et al., IEEE Trans. Terahertz Sci. Technol. 2, 12 (2012)]) is described in more detail. The numerical design and verification tools (static and dynamic finite element method (FEM) models) are discussed together with their required input, i.e., the magnetic-field dependent permeability data. Next, the actual manufacturing of the shields is described, including a method to create a superconducting joint between the two superconducting shield elements that avoid flux penetration through the seam. The final part of the paper presents the experimental verification of the model predictions and the validation of the shield's performance. The shields were cooled through the superconducting transition temperature of niobium in zero applied magnetic field (<10 nT) or in a DC field with magnitude ∼100 μT, applied either along the system's symmetry axis or perpendicular to it. After cool-down, DC trapped flux profiles were measured along the shield axis with a flux-gate magnetometer and the attenuation of externally applied AC fields (100 μT, 0.1 Hz, both axial and transverse) was verified along this axis with superconducting quantum interference device magnetometers. The system's measured on-axis shielding factor is greater than 106, well exceeding the requirement of the envisaged missions. Following field-cooling in an axial field of 85 μT, the residual internal DC field normal to the detector plane is less than 1 μT. The trapped field patterns are compared to the predictions of the dynamic FEM model, which describes them well in the region where the internal field exceeds 6 μT.
25 citations
TL;DR: In this paper, the authors measured the induced current in a high-temperature Bi 2 Sr 2 CaCu 2 O x superconductor tube that was excited by an external coil driven by an AC sinusoidal voltage source.
8 citations
TL;DR: In this article, a comprehensive study of high-T c superconducting (HTS) shields from pure Y 1 Ba 2 Cu 3 O 7−x, Y 1Ba 2 Cu 7− x + Ag + Sn and Bi 2− x Pb x Sr 2 Ca 2 Cu3 O y is made.
4 citations
TL;DR: Magnetic shielding from alternating magnetic field by a NbTi/Nb/Cu superconducting multilayer composite cylinder was investigated at liquid-helium temperatures in this paper, where the magnetic shielding efficiency of this cylinder, defined as the ratio of the magnetic field strength with and without the cylinder, was found to be of the order of 10−4.
Abstract: Magnetic shielding from alternating magnetic field by a NbTi/Nb/Cu superconducting multilayer composite cylinder was investigated at liquid‐helium temperatures. The specimen employed in this study was a slender seamless cylinder about 15 mm in diameter and having an aspect ratio of 6. The frequency of the alternating magnetic field was in the range of 40–500 Hz, and the maximum amplitude was 1000 G rms at 40 and 50 Hz owing to the capacity of the ac generator. The magnetic shielding efficiency of this cylinder, defined as the ratio of the magnetic field strength with and without the cylinder, was found to be of the order of 10−4. It was also found that the magnetic shielding effect depends upon the frequency investigated in this study. These shielding effects were mainly due to the shielding current originating from the superconductivity, which turned out to give superior shielding effect than that of a Cu cylinder.
3 citations
TL;DR: In this article, the magnetic shielding characteristics of a complex structure with multiple high-Tc superconductors coaxially superposed and ferrite powder padding, and its effect on the critical current increase of a HTS current lead are presented.
Abstract: This paper presents the magnetic shielding characteristics of a complex structure with multiple high-Tc superconductors (HTS) coaxially superposed and ferrite powder padding, and its effect on the critical current increase of a HTS current lead. A model HTS current lead is inserted into the complex structure and cooled by LN2. The magnetic flux density in the innermost HTS pipe with and without the ferrite powder, and the critical current of the current lead were measured and the various complex structures were evaluated. >
3 citations
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TL;DR: The ac susceptibility of sintered sintering pellets is measured as a function of temperature and ac magnetic field amplitude and frequency to find the value for an intergrain decoupling field, above which flux creep presumably becomes flux flow at the grain boundaries.
Abstract: We measured the ac susceptibility of sintered ${\mathrm{Y}}_{1}$${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ pellets as a function of temperature and ac magnetic field amplitude and frequency. The imaginary part of the susceptibility \ensuremath{\chi}'' exhibits two peaks. A narrow peak is located at the critical temperature of the grains. A broad peak at lower temperature is attributed to hysteresis losses at the grain boundaries. There is a small shift in this coupling peak to higher temperature as the frequency increases from 10 to 1000 Hz. We explain the shift in terms of Anderson flux creep on a time scale of milliseconds. The shift depends on the amplitude of the measuring field. The activation energy for flux creep ranges from 11.9\ifmmode\pm\else\textpm\fi{}1.0 eV in the zero-field limit [0.8 A ${\mathrm{m}}^{\mathrm{r}}$-r1(0.01 Oe)] to 1.2\ifmmode\pm\else\textpm\fi{}0.3 eV at 800 A ${m}^{\ensuremath{-}}$1(10 Oe). We extrapolate our data to find the value for an intergrain decoupling field of 1--2 kA m-1 (13--25 Oe), above which flux creep presumably becomes flux flow at the grain boundaries.
199 citations
TL;DR: In this paper, the magnetic shielding effect of Ba2YCu3O7-δ, Cu and Fe-Ni plates was examined as a function of the frequency of applied ac magnetic field using magnetic heads.
Abstract: The magnetic shielding effect of Ba2YCu3O7-δ, Cu and Fe-Ni plates was examined as a function of the frequency of applied ac magnetic field using magnetic heads. The effect of Ba2YCu3O7-δ plates was superior to that of Cu and Fe-Ni plates in the low-frequency ( 10 kHz) region, the effect of Ba2YCu3O7-δ plates was almost the same or slightly inferior to that of Cu plates. The shielding effect of Ba2YCu3O7-δ plates was strongly affected by the micro cracks and porosity of the samples. The magnetic shielding effect of Ba2YCu3O7-δ plates decreased rapidly with applied dc magnetic field, while the effect of Cu and Fe-Ni plates did not change with the application of dc magnetic field.
32 citations
TL;DR: In this paper, two models are proposed to discuss the leakage of the magnetic field in the superconducting cylinder under experimental results of the shielding properties, and the authors show that the leakage can occur even though the cylinder had a length/diameter ratio large enough to expect that the shielding factor exceeded 10-8.
Abstract: The shielding factor of a BSCCO 2212 phase HTc superconducting cylinder had a maximum of 10-6, even though the cylinder had a length/diameter ratio large enough to expect that the shielding factor exceeded 10-8. Two models are proposed to discuss the leakage of the magnetic field in the superconducting cylinder under experimental results of the shielding properties.
28 citations
TL;DR: In this article, a YBa2Cu3O7 ceramic is placed coaxially on either side of a slab of superconductor of thickness 0.05-1 mm, and the voltage in the secondary coil is measured as a function of excitation current and frequency in the primary, and of the temperature and the steady magnetic field provided by an external solenoid.
Abstract: Coils are placed coaxially on either side of a slab of superconductor of thickness 0.05-1 mm. The coil diameters are less than the lateral dimentions of the slab. The voltage in the secondary coil is measured as a function of excitation current and frequency in the primary, and of the temperature and the steady magnetic field provided by an external solenoid. A YBa2Cu3O7 ceramic cooled in zero field screens almost completely, but the greater part of this screening is suppressed by low magnetic fields. The remaining part is shown to be due to isolated superconducting grains. When intergrain superconductivity is partly suppressed the condition is reasonably well described by the Bean critical-state model. Hysteresis of the screening coefficient reflects the known hysteresis of the transport critical current.
27 citations
TL;DR: A brief review of the recent progress of superconductor electronics is presented in this article, with special emphasis on the "intrinsic" development of the field, including rapid progress of the low-Tc Josephson junction technology and recent invention of several important devices.
Abstract: A brief review of the recent progress of superconductor electronics is presented. Special emphasis is made on the 'intrinsic' development of the field, including rapid progress of the low-Tc Josephson junction technology and recent invention of several important devices. In the near future, these developments promise the advent of several outstanding electronic devices which would be of practical value, despite the need for helium cooling. Against this background, introduction of the high-Tc superconductors in the foreseeable future will probably be restricted to the few simplest electronic devices and components.
24 citations