共查询到20条相似文献,搜索用时 15 毫秒
1.
Deviation from a homogeneous distribution of the vortex line lattice and magnetic field induced by transport current near Hc2 in the cylindrical sample of type II superconductor in the mixed state without pinning is determined. The dependence of the critical current density on the position in the sample is calculated. 相似文献
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K. Funaki K. Kajikawa H. Shiraishi M. Iwakuma S. Miyake T. Kumano T. Hasegawa 《Physica C: Superconductivity and its Applications》1998,310(1-4):132-136
We measured cyclic losses in a superconducting wire, carrying alternating transport current, simultaneously exposed to an alternating transverse magnetic field. Samples of Bi-2223 Ag-sheathed tapes have configuration of a double-layer non-inductive coil, which itself is a pickup coil to measure the AC losses. Potential taps were attached to both terminals of the sample coil. The external field was applied along the axis of the sample coil. In this procedure, we can estimate an averaged Poynting's vector on a cylindrical surface between the two layers by means of signals from a pair of the potential taps and from pickup coils for the external magnetic field and the transport current. We can also measure a magnetization and an extended transport-current components of AC losses in addition to a total cyclic loss for a combined alternating external field and transport current. Obtained results are compared with numerical predictions of the critical state model taking into account the magnetic field dependence of critical current density. 相似文献
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N.A. Bogolyubov 《Physics letters. A》2008,372(47):7073-7076
The temperature and size dependences of the critical currents in bismuth-based high-temperature superconducting ceramic samples consisting of randomly oriented grains have been studied in zero magnetic field. It is shown that the critical current is a function of the sample cross-sectional area only. At constant sample cross-sectional area the value of the critical current is independent of any variation of a sample cross-sectional shape. At the same time the distributions of the critical current density and induced magnetic field in ceramics are functions of the sample cross-sectional shape. These values very in accordance with a change of the sample cross-sectional shape (at constant cross-sectional area i.e. at constant value of the critical current). The field and current distributions in the rectangular sample are reported. 相似文献
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The temperature and size dependence of the transport critical current in Y-123 and Bi-2223 + Bi-2212 HTSC ceramic sample has been studied. It is shown that the critical current may be presented as power function of cross section area, the critical current density is homogeneous function of coordinates and a number of properties of the critical current density are reported. 相似文献
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A.J.C. Lanfredi S. Sergeenkov F.M. Araujo-Moreira 《Physica C: Superconductivity and its Applications》2006,450(1-2):40-44
The results of Hall probe magnetic measurements in the vicinity of a DyBCO tape carrying transport or magnetization currents at 77 K were used in the inverse calculation to obtain the current distribution across the tape width. Two different methods of the inverse problem calculation were used and the results compared. The transport current applied in the absence of the external magnetic field was stepwise increased and the determined current distribution was compared with that predicted by Brandt and Indenbom. The predicted convex shape of the current distribution in the central tape section was proved. Contrary to the prediction, we have observed a drop of the current at the tape edges. This result supports the conclusions of the loss measurements in YBCO tapes [O. Tsukamoto, Supercond. Sci. Technol. 18 (5) (2005) 596]. We also mapped the magnetic field in the vicinity of the tape carrying induced magnetization currents in the absence of the transport current and determined the corresponding current distribution. Superposition of the self magnetic field and a homogeneous external magnetic field (36 mT) flattens the magnetization current distribution evidently. 相似文献
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J. J. Rabbers B. ten Haken H. H. J. ten Kate 《Physica C: Superconductivity and its Applications》1998,310(1-4):101-105
BSCCO/Ag tape superconductors are developed for electrical power applications at liquid nitrogen temperatures. In these applications, e.g., superconducting transformers and power cables, an AC transport current and an AC magnetic field are present at the same time. A set-up to measure the influence of external AC magnetic field on the transport current loss, i.e., the voltage drop across a sample supplied with an AC transport current, has been developed. The magnetic field can be applied both parallel and perpendicular to the broad side of the tape conductor. An increase of the transport current loss due to the external AC magnetic field is observed. When a DC external magnetic field is applied the increase of the self-field loss can be described well by the decrease of the critical current due to the magnetic field. In the case of an AC external magnetic field this is only a minor effect. For magnetic field amplitudes higher than a certain threshold value the transport current loss is described reasonably well by the self-field loss and a dynamic resistance contribution calculated from the DC voltage–current relation in AC magnetic field. 相似文献
9.
GAO Jin-Hua SUN Qing-Feng XIE Xin-Cheng 《理论物理通讯》2009,51(3):555-560
We study the magnetic field effects on the spin-polarized transport of the quantum dot (QD) spin valve in the sequential tunneling regime. A set of generalized master equation is derived. Based on that, we discuss the collinear and noncollinear magnetic field effects, respectively. In the collinear magnetic field case,we find that the Zeeman splitting can induce a negative differential conductance (NDC), which is quite different from the one found in previous studies. It has a critical polarization in the parallel arrangement and will disappear in the antiparallelconfiguration. In the noncollinear magnetic field case, the current shows two plateaus and their angular dependence is analyzed. Although sometimes the two current plateaus have similar angular dependence, their mechanisms are different. Our formalism is also suitable for calculating the transport in magnetic molecules, in which the spin splitting is induced not by a magnetic field but by the intrinsic magnetization. 相似文献
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Equations that simulate the magnetic induction and current density distributions in half-space in view of the power I-V characteristic are derived. The magnetization front velocity is determined for a given mean rate of external magnetic field variation at the boundary of the sample. An integral condition for the electrical resistance (nonlinearly depending on the magnetic field) under which the magnetic flux penetrates into the sample with a finite rate is found. An analytical solution that simulates the power variation of the magnetic field at the boundary is given. The Bean generalized model describing the current density distribution near the critical current is considered. It is shown that solutions like shock waves may arise beyond the applicability domain of the Bean model. 相似文献
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C.A.C. Passos M.T.D. Orlando J.L. Passamai Jr. E.V.L. de Mello 《Physica B: Condensed Matter》2009,404(19):3123-3126
A model to describe the critical current density behavior of high-Tc polycrystalline superconductors is proposed for all magnetic field values. The main features of the model are as follows: the transport critical current density is controlled by the weak-link network at grain boundaries. The size distribution of weak links is well represented by a Gamma-type distribution. Finally, the tunneling critical current between grains follows a Fraunhofer diffraction pattern or a modified pattern if the applied magnetic field is lower or higher than the first critical field Hc1. 相似文献
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A. N. Lykov A. Yu. Tsvetkov G. F. Zharkov 《Journal of Experimental and Theoretical Physics》2005,101(2):341-349
Numerical methods are used to analyze the Ginzburg-Landau equations for a superconducting plate carrying transport current in a magnetic field. Critical current is calculated as a function of the applied magnetic field strength for superconducting plates with different thicknesses. The relations between the field dependence of critical current and the distributions of order parameter, magnetic field, and supercurrent in a plate are analyzed. The field-dependent critical currents computed for plates are used to determine the critical current as a function of the applied magnetic field strength and local magnetic field and current distributions for multilayers in parallel magnetic fields. The constituent superconducting layers are assumed to interact only via magnetic field. A simple method is proposed for analyzing the critical states of multilayers in magnetic fields of arbitrary strength, based on elementary transformations of the critical current-density distribution over individual layers in zero applied magnetic field. The method can be used to analyze experimental results. 相似文献
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R. Gerbaldo G. Ghigo G. Giunchi L. Gozzelino F. Laviano E. Mezzetti 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):297-300
We present results from an extended magneto-optical (MO) analysis of two samples cut from high-density pellets of MgB2. The first sample was studied in order to show that no matter how large the sample is and despite the bulk granularity, the
material enters into a critical state in a crystal-like fashion. The second sample was chosen for the quantitative analysis.
A numerical approach based on an inverted 2D Biot-Savart model was used to calculate the current paths across the homogeneous
polycrystalline bulk, as well as in the vicinity and across some morphological defects. Local current densities in the homogeneous
part were estimated as a function of the applied magnetic field at different temperatures, in three regimes: below full penetration,
at full penetration and above full penetration, respectively. A hypothesis of interpretation of the apparent absence of magnetic
granularity inside the polycrystalline microstructure is presented. It is related to a critical state likely reached by a
network of strongly coupled Josephson junctions.
Received 31 May 2001 and Received in final form 5 December 2001 相似文献
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Guchang Han Yugui Wang Hanmin Han Zhihe Wang Shunxi Wang Weifan Yuan Qiaolin Huang Zhiming Liu Jinlin Chen 《Applied Physics A: Materials Science & Processing》1993,57(4):363-366
The transport critical current properties of Bi(2223) silver-clamped thick films are studied by the measurement of its dependence on magnetic field and temperature close to T
c. It is found that the transport critical current follows a power law J
c(1–T/T
c)3/2 for the sample with J
c>2.0×104 A/cm2 (77K, zero field) and that J
c(H) is basically reversible for increasing and decreasing magnetic field. After the transport current exceeds the critical current, the voltage-current (V-I) characteristics show a flux-creep-like behaviour until they smoothly join the flux-flow state. From the measurement of V-I curves, the pinning property of the sample may be estimated using the flux-creep mode. The flux-flow resistance is found to have a nonlinear magnetic field dependence. 相似文献
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S. Yu. Gavrilkin A. N. Lykov A. Yu. Tsvetkov P. I. Bezotosnyi 《Bulletin of the Lebedev Physics Institute》2018,45(2):51-55
The effect of boundary conditions in the Ginzburg–Landau theory on the critical state of superconducting layered structures is studied. The method is based on the numerical solution of the Ginzburg–Landau nonlinear equations describing the behavior of a superconducting plate carrying a transport current in a magnetic field, provided the absence of vortices in it. The use of the general boundary condition for the Ginzburg–Landau system of equations leads to a change in the order parameter over the thickness of thin superconducting plates. The calculated dependences of the critical current of plates on the magnetic field applied in parallel to layers are used to determine the critical current of multilayered structures. It is assumed that the mutual influence of superconducting layers occurs only through the magnetic field induced by them. 相似文献
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在多晶系统的MgB2超导体中存在晶粒间较小的整体电流和晶粒内大的局域电流.用改变升温速率的方法制备了不同晶粒大小和晶粒连接性的MgB2样品,并对它们的晶粒大小进行了统计.采用一种测量超导临界电流密度的Campbell法,分别测量和计算得到了它们的整体电流和局域电流密度.研究表明:长时间的烧结造成晶粒变大,材料有较大的整体临界电流密度,而短时间烧结的样品则相反;同时发现晶粒细化只提高了样品的局域临界电流密度,而且样品内部缺陷、杂质及晶界等因素是影响MgB2超导体整体电流传输的主要因素. 相似文献
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A. Chaibi N. Ferrer-Anglada J. A. Gorri L. Fajari M. C. Anglada 《Applied magnetic resonance》1997,12(4):575-579
Polypyrroles electrochemically obtained at the same conditions and different density currents have been studied by ESR. We analyze the angular dependence of the ESR linewidths when rotating the sample in the magnetic field, and correlate it with the degree of ordering in the sample. Electrical conductivity is higher for samples obtained at high density current, for which no ordering is observed. This suggests that amorphicity contributes positively to transport in polypyrroles. 相似文献
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临界电流密度Jc是影响高温超导体在强电领域应用的一个重要参数,在实际应用中,特别在外加磁场下,临界电流密度与超导材料的磁通钉扎性质密切相关.因此,磁通钉扎一直是高温超导体研究中的一个重要领域.由于高温超导体磁通钉扎力密度Fp的标度律存在,本文根据D.Dew-Hughes总结的钉扎力函数,主要存在两种主要作用类型(正常相和△K).我们将D.Dew-HugBes给出的钉扎力密度Fp标度函数改进为一个简化的具有物理意义的函数表达式.结合文献中已有的实验数据,我们对YBcO进行了计算机模拟,确定了它的磁通钉扎类型,模拟的研究结果与实际情况比较吻合. 相似文献