共查询到20条相似文献,搜索用时 31 毫秒
1.
A. Patel R. Pałka B. A. Glowacki G. Giunchi A. Figini Albisetti Y. Shi D. A. Cardwell S. C. Hopkins 《Journal of Superconductivity and Novel Magnetism》2013,26(4):923-929
This paper reports the experimental verification and improved concept of the previously reported fully superconducting magnetic bearing using bulks on both the rotor and the stator in a cylindrical geometry. Experimental measurements on pulsed magnetisation and levitation force between a magnetised 25.5 mm diameter YBCO bulk inside an MgB2 hollow cylinder are reported proving the concept of a bulk–bulk bearing. The maximum force achieved after field cooling of the MgB2 bulk in the field of a 1.68 T magnetised YBCO bulk was 501 N. The improved concept relies on additional ring shaped permanent magnets placed on the bottom of the MgB2 cylinder. These rings create additional axial force in the bearing system. Permanent magnet rings can boost the force for the existing bearing design by enhancing the field trapped in the MgB2 tube and providing a ‘cushion’ of magnetic field for the bottom YBCO bulk by exploiting zero field cooling. In particular the enhancement of the force is largely due to the favourable distortion of the trapped field in the MgB2 cylinder and is much greater than the direct repulsive force between a magnetised YBCO bulk and permanent magnet only. Various permanent magnet configurations are evaluated by modelling of levitation force using the perfectly trapped flux model. The high force densities of bulk–bulk bearings allow them to support large loads useful for application such as flywheel energy storage. 相似文献
2.
Bulk superconductors have great potential for various engineering applications, especially in a high-temperature superconducting (HTS) maglev vehicle system. In the vehicle system, the stable levitation can be achieved without any complex control system owed to the pinning effect of the bulks. However, the HTS bulks in the vehicle system were always exposed to the time-varying external magnetic field, which was generated by the inhomogeneous surface magnetic field of the NdFeB guideway. In our previous work, we studied the guidance force decay characteristics of the YBCO bulk over the NdFdB guideway used in the HTS maglev vehicle system by an experiment in which the AC external magnetic field generated by an electromagnet was used to simulate the time-varying external magnetic field caused by the inhomogeneity of the guideway, and calculated the guidance force decay as a function of time based on an analytic model. In this paper, we investigated the influence of thermal conductivity on the guidance force decay of HTS bulk exposed to AC field perturbation in the maglev vehicle system and tried to adopt a method to suppress the decay. From the results, it was found that the guidance force decay rate was higher for the bulk with the lower thermal conductivity. So, we could reduce the guidance force decay of the HTS bulk exposed to the AC external magnetic field perturbation in the maglev vehicle system by improving the thermal conductance of the bulks. 相似文献
3.
Superconducting maglev vehicle is one of the most promising applications of HTS bulks. In such a system, the HTS bulks are always exposed to AC external magnetic field, which is generated by the inhomogeneous surface magnetic field of the NdFeB guideway. In our previous work, we studied the guidance force decay of the YBCO bulk over the NdFdB guideway used in the High-temperature superconducting maglev vehicle system with the application of the AC external magnetic field, and calculated the guidance force decay as a function of time based on an analytic model. In this paper, we investigated the influence of the critical current density on the guidance force decay of HTS bulk exposed to AC field perturbation in the maglev vehicle system and try to adopt a method to suppress the decay. From the results, it was found that the guidance force decay rate was higher for the bulk with lower critical current density. Therefore, we could suppress the guidance force decay of HTS bulk exposed to AC external magnetic field perturbation in the maglev vehicle system by improving critical current density of the bulk. 相似文献
4.
Longcai Zhang 《Journal of Superconductivity and Novel Magnetism》2010,23(2):205-208
Bulk superconductors have great potential for various engineering applications, especially in superconducting maglev vehicle
systems using high-temperature superconducting bulks. In such a system, the HTS bulks were always exposed to AC external magnetic
field, which was generated by the inhomogeneous surface magnetic field of the NdFeB guideway. In our previous work, it was
observed that the guidance force of the YBCO bulk over the NdFdB guideway used in the high-temperature superconducting maglev
vehicle system was decayed by the application of the AC external magnetic field. In this paper, we investigate the influence
of the work height on the guidance force decay of HTS bulk exposed to an AC field perturbation in the maglev vehicle system
and try to adopt a method to suppress the decay. From the experimental results, it was found that the decay rate of the guidance
force was smaller at higher work height in the case of the same field-cooled height. So we could suppress the guidance force
decay of HTS bulk exposed to AC external magnetic field perturbation in the maglev vehicle system by increasing the work height
of the bulk. 相似文献
5.
Hiroki Kutsuma Makoto Hattori Kenji Kiuchi Satoru Mima Taketo Nagasaki Shugo Oguri Junya Suzuki Osamu Tajima 《Journal of Low Temperature Physics》2018,193(3-4):203-208
Superconducting detectors, such as microwave kinetic inductance detectors (MKIDs), are sensitive to the effects of ambient magnetic fields. There are two effects magnetic fields have on the response of MKIDs; the trapping of magnetic fields inside the superconducting materials degrades the resonator quality, and the time variation of the magnetic fields results in a baseline fluctuation. In the case of radio astronomy, this means the detector must be protected from the geomagnetic field. Here, we construct a test system to evaluate the effects described. We also evaluate the impact of the magnetic shield. We find that a shielding power of 47 dB is necessary in the case of application with a noise equivalent power of \(2.4 \times 10^{-16}\,\text {W}/\sqrt{\text {Hz}}\). We also confirm that the measured shielding power obtained using permalloy films is consistent with simulations based on the finite element method to an accuracy of 1 dB. We have designed magnetic shields for the GroundBIRD CMB telescope using these results. We achieve a sufficient shielding power of 55 dB. 相似文献
6.
Minxian Liu Yiyun Lu Suyu Wang Guangtong Ma 《Journal of Superconductivity and Novel Magnetism》2011,24(5):1559-1562
The levitation force of the YBCO bulk over an NdFeB guideway used in the high-temperature superconducting (HTS) maglev vehicle
system is oscillated by the application of the AC external magnetic field. In our previous work, we interpreted that the oscillation
is due to the shielding current fluctuation caused by fluctuant external magnetic field. In this paper, based on the Bean
model, an analytical model is adopted to evaluate the levitation force. Comparing with the experimental results, the calculated
results show good matching. The model can reveal the oscillation characteristics of the levitation force of HTS bulk which
is being exposed to AC external magnetic field. Therefore, the levitation force oscillation of the HTS bulk in the maglev
vehicle system can be evaluated by this numerical method. 相似文献
7.
Y-Ba-Cu-O(YBCO)单畴块材通常是由统一分布的YBa2Cu3O7-δ(Y123)和Y2BaCuO5(Y211)前驱坯体制备的。然而研究表明熔融生长的超导块材中Y211相粒子的浓度随着远离籽晶显著增大, 造成Y211相粒子的积聚以及限制单畴块材的超导性能。本文通过顶部籽晶熔融织构法(TSMTG)利用分层式前驱坯体制备了φ23 mm×9 mm的YBCO单畴块材, 并在生长形貌、微结构以及磁通俘获性能方面与常规方法制备的同尺寸YBCO单畴块材做了对比研究。研究结果显示, 使用分层式前驱坯体制备的YBCO单畴块材生长得更充分, Y211相粒子的平均粒径更小、分布更均匀, 并且在磁通俘获性能上有了显著的提高, 同时具备高对称性的磁通分布和强磁通俘获能力, 在77 K环境下最大磁通俘获场高达0.91 T。该结果对进一步提高YBCO超导块材的性能具有很好的参考价值。 相似文献
8.
Ali Öztürk Mustafa Doğan İbrahim Düzgün Selahattin Çelebi 《Journal of Superconductivity and Novel Magnetism》2016,29(7):1787-1791
The effect of dysprosium (Dy) doping on yttrium barium copper oxide (YBCO) prepared by conventional solid-state reaction method has been investigated by means of XRD, AC susceptibility, and DC magnetization measurements. AC susceptibility measurements for sintered YBCO pellets have been performed as a function of temperatures at constant frequency and AC field amplitude in the absence of a DC bias field. DC magnetization measurements were done at 5, 20, and 77 K upon zero field cooling (ZFC) process. The magnetization measurements showed a paramagnetic behavior existing at high magnetic fields. The magnetic field dependence of critical current density of the samples has been estimated from DC magnetization data. The partial Dy substitution for Y on YBCO superconductors improves the bulk critical current density at high magnetic fields and at high-temperature regions (higher than 20 K). 相似文献
9.
M. Wang W. M. Yang M. Z. Wang X. J. Wang 《Journal of Superconductivity and Novel Magnetism》2013,26(11):3221-3224
The top-seeded infiltration and growth process (TSIG) is a very effective method for the preparation of YBa2Cu3O7?x (YBCO) bulk superconductors. In this paper, single-domain YBCO bulk superconductors with different ratio of nanoscale Y2Ba4CuBiO y (YBi2411) inclusions have been fabricated by TSIG process. The growth morphology, microstructure and levitation force of the YBCO bulks have been investigated. The amount of nanoscale YBi2411 added to Y2BaCuO5 (Y211) is in the range from 0.5 wt.% to 5 wt.%. It is found that the optimum proportion is obtained in the sample with 3.0 wt.% YBi2411 addition. The results are very helpful for the fabrication of high-quality single-domain YBCO bulk superconductors. 相似文献
10.
Two measurement systems were used to investigate the low frequency magnetic shielding behavior of pure YBa2Cu3O7−δ, silver doped YBa2Cu3O7−δ, a packed powder, a laser ablated thin film and copper. It was found that factors which influence low frequency magnetic shielding include material composition, microstructure and properties, external a.c. and d.c. fields and sample dimensions. Among the experimental materials, only bulk ceramics showed good shielding factors which were constant with frequency in the range 10–3000 Hz. A macroscopic shielding current was necessary for a good shield. The thickness of the ceramic played a crucial role in shielding. Flux breakthrough occurred when the external field exceeded a certain value. The breakthrough field increased with sample thickness. The influence of d.c. fields on the shielding behaviour depended on the history and magnitudes of the fields. Magnetic shielding hysteresis was observed and its potential application is discussed. 相似文献
11.
The superconducting maglev vehicle is one of the most promising applications of HTS bulks. In such a system, the nonuniformity of the magnetic field along the movement direction above the NdFeB guideway is inevitable due to the assembly error and inhomogeneity of the material property of the NdFeB magnet. So it is required to study the characteristics of levitation force of the bulks affected by the non-uniform applied magnetic fields along the moving direction. In this paper, we will study the characteristics of the levitation force relaxation between the HTS bulk and the NdFeB guideway by an experiment in which AC external magnetic field generated by an electromagnet is used to simulate the time-varying external magnetic field caused by the inhomogeneity of the guideway. From the experimental results, it has found that the levitation force is decreasing with the application of the AC external magnetic field, and the decay increasing with the amplitude of the applied magnetic field and is almost independent of the frequency. 相似文献
12.
A thermally switched magnetic shield which can both shield against and trap magnetic fields is described. The shield, consisting of a Nb---Ti sheet, can trap stably fields of up to 0.3T, and shield against fields of up to 0.35 ± 0.05T, when the in superconducting state It provides large attenuation of alternating magnetic fields in the presence of a steady trapped field. It is shown to significantly reduce the eddy current damping of the mechanical vibration of a superconducting sample in a magnetic field, by shielding nearby normal metal surfaces. A specific application to magnetic levitation of gravitational radiation antennae is discussed. 相似文献
13.
The increase of the shielding factor due to shaking was measured in a scale model for a magnetically shielded room. The increase was found to be 7 dB for a single-layer square cylinder biased by the Earth's magnetic field. The shielding factor of a large-volume three-layer Mumetal®room was estimated to increase by a factor of 30, thus confirming the feasibility of shaking in magnetic shields. The shaking parameters, amplitude, and frequency are not critical according to the experiments. Winding the shaking coils along the edges of the cubic shield leads to minimum disturbances inside the cube, and the winding can also be applied to demagnetize the shield by an alternating field of 25 A/m, 50 Hz. The relative incremental permeability of Mumetal was studied as a function of the shaking and biasing fields. The permeability was found to increase considerably by shaking and by decreasing the biasing field. With zero biasing and with shaking field of Hs = 5 A/m root mean square (rms), 50 Hz, the permeability reached its maximum value of 89 000, which is sevenfold the value without shaking. 相似文献
14.
Yiyun Lu Jiasu Wang Suyu Wang Jun Zheng 《Journal of Superconductivity and Novel Magnetism》2008,21(8):467-472
This paper presents a 3D-modeling numerical method using finite element method (FEM) to simulate the electromagnetic behavior
of high-temperature superconductors (HTSC). The models are formulated by the magnetic field vector method (H-method). The
resolving code was written by FROTRAN language. The electromagnetic properties of HTSC are described though Kim critical-state
model. The magnetic fields and current distribution in the bulk HTSC in the applied non-uniform external magnetic fields generated
by the permanent magnetic guideway (PMG) are obtained using the proposed method. The magnetic levitation forces by the interaction
between the bulk HTSC and the PMG are calculated. In order to validate the method, measurement of the vertical force between
a bulk YBaCuO(YBCO) and a PMG is obtained. The measurement and simulation results show good matching. This method could be
used in the HTSC magnetic levitation transportation system optimization design.
相似文献
15.
V Ganesan R Srinivasan S Aswathy K D Chandrasekaran B Srinivas U V Varada Raju G V Subba Rao R Gopalan T Rajasekaran 《Bulletin of Materials Science》1994,17(1):87-93
Magnetic shields of various high-temperature superconductors, YBa2Cu3O7−x
(YBCO), YBa2Cu3O7−x
-Ag composites (random inclusions as well as non-random coatings) and Bi2Sr2Ca2Cu3O
x
(BSCCO) were prepared by uniaxial as well as isostatic compression with various dimensions. The shielding properties were
measured at 77 K for dc and ac magnetic fields in the range of frequencies from 100 Hz to 10 kHz. The critical penetration
field (CPF), defined as the value of the applied magnetic field at which a detectable field was observed inside the cylinder,
varied from cylinder to cylinder and also with the ageing of the cylinders in the case of YBCO shields. The highest value
of CPF was 16 G at 77 K for YBCO shield prepared by isostatic compression. Even though the stability of BSCCO shields with
respect to ageing is good, the CPF values are very low compared to those for YBCO. Detailed studies were performed in the
case of YBCO shields. The CPF decreased as a function of time over a period of 90 days. The CPF decreased as the frequency
of the applied field was increased. The wave form of the field inside the pot for a sinusoidal applied field was highly distorted
and showed the presence of higher harmonics with appreciable amplitude. The wave form was Fourier-analysed to yield the field
inside the shield along with the harmonics. The shields with Ag addition seem to give better performance at high fields. 相似文献
16.
V. Baturin V. BurkertD.S. Carman L. ElouadrhyriD. Grilli D. KashyE. Pasyuk L. QuettierB. Wieland 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2012,664(1):11-21
The Central Time-of-Flight detector for the Jefferson Laboratory 12-GeV upgrade is being designed with linear-focused photomultiplier tubes that require a robust magnetic shield against the CLAS12 main 5-T solenoid fringe fields of 100 mT (1 kG). Theoretical consideration of a ferromagnetic cylinder in an axial field has demonstrated that its shielding capability decreases with increasing length. This observation has been confirmed with finite element analysis using POISSON model software. Several shields composed of coaxial ferromagnetic cylinders have been studied. All difficulties caused by saturation effects were overcome with a novel dynamical shield, which utilizes a demagnetizing solenoid between the shielding cylinders. Basic dynamical shields for ordinary linear-focused 2-in. photomultiplier tubes were designed and tested both with models and experimental prototypes at different external field and demagnetizing current values. Our shield design reduces the 1 kG external axial field by a factor of 5000. 相似文献
17.
Magnetic shielding studies have been carried out to investigate the usefulness of high-T c YBCO ceramics for EMS applications. The starting materials were single-phase YBCO powder. The cylinders were prepared by uniaxial compresssion and isostatic compression, with and without Ag additive. The shielding fieldH *, defined as the value of the applied field at which a detectable field will be seen inside the superconducting shield, was 12 G for the shield prepared by uniaxial compression and around 17 G for shields prepared by isostatic compression. Measurements were done in both ac and dc fields. The field inside the shield for the sinusoidal ac applied field is highly distorted, showing the presence of three higher harmonics. The penetrated waveform was Fourier-analyzed to yield the rms value ofB in. When the normalized value ofB was plotted against the normalized value ofH with respect toH *, all the points corresponding to different shields fall on the same curve. 相似文献
18.
Magnetic shielding studies have been carried out to investigate the usefulness of high-T
c YBCO ceramics for EMS applications. The starting materials were single-phase YBCO powder. The cylinders were prepared by uniaxial compresssion and isostatic compression, with and without Ag additive. The shielding fieldH
*, defined as the value of the applied field at which a detectable field will be seen inside the superconducting shield, was 12 G for the shield prepared by uniaxial compression and around 17 G for shields prepared by isostatic compression. Measurements were done in both ac and dc fields. The field inside the shield for the sinusoidal ac applied field is highly distorted, showing the presence of three higher harmonics. The penetrated waveform was Fourier-analyzed to yield the rms value ofB
in. When the normalized value ofB was plotted against the normalized value ofH with respect toH
*, all the points corresponding to different shields fall on the same curve. 相似文献
19.
20.
Laura Gozzelino Bruno Minetti Roberto Gerbaldo Gianluca Ghigo Francesco Laviano Giuseppina Lopardo Carmen Plapcianu Angelo Agostino Stefano Cagliero Marco Truccato Luca Zilberti Enrica Mezzetti 《Journal of Superconductivity and Novel Magnetism》2011,24(1-2):307-312
Magnetic shielding properties of MgB2 bulk samples synthesized by the SPS (Spark?CPlasma?CSintering) technique were characterized in low applied magnetic fields at temperatures ranging from 20 to 37 K. The used growth technique allows one to produce this compound in different shapes and sizes required for shielding applications. In this framework, shielding magnetic-induction field profiles generated by MgB2-based shield components, shaped as planar thick disks, were measured by means of a suitable Hall probe in-plane array. The magnetic field distribution at different vertical distances above the sample was also obtained by a micrometric motion of the probe ensemble. Magnetic field profiles were then analyzed in the framework of the critical state model and the critical current density, J c , was evaluated. The J c magnitude indicates that the material under test is a good candidate for passive magnetic shield manufacturing up to temperatures close to the transition one. 相似文献