Influence of Critical Current Density Distribution on Transport AC Losses in Superconducting Wire in a DC Magnetic Field

In typical application-like conditions, the inhomogeneous distribution and anisotropy of critical current density must be considered simultaneously in transport AC loss calculation. In this paper, we derive the analytical formulas of transport AC losses for high-temperature superconductors (HTSs) with linear and quadratic distribution of critical current density under applied DC magnetic field. The influence of the inhomogeneous distribution and anisotropy of critical current density has been analyzed. The results show that the impact of the distribution form on transport AC loss is more obvious under applied DC magnetic field. And the influence of applied DC magnetic field will increase as the distribution form becomes steeper.     

Thickness-Dependent Current Density and Flux Distribution in Thin Current-Carrying Superconducting Films Exposed to a Magnetic Field

With the rapid development of high-temperature superconductors, it is of great significance to get the precise current density and flux distribution within thin high-temperature superconducting films subjected to a transport current and an applied magnetic field. The transport current distribution and flux density in thin high-temperature superconducting films are calculated by a numerical method based on the Kim model and exponential model in this paper. The influences of transport current, applied magnetic field, width, and thickness of a superconducting film on the current distribution are discussed. The results reveal that the thickness has a significant effect on the critical current density of superconducting films.     

Angular Dependence of Transport AC Losses in Superconducting Wire with Position-Dependent Critical Current Density in a DC Magnetic Field

Transport AC losses play a very important role in high temperature superconductors (HTSs), which usually carry AC transport current under applied magnetic field in typical application-like conditions. In this paper, we propose the analytical formula for transport AC losses in HTS wire by considering critical current density of both inhomogeneous and anisotropic field dependent. The angular dependence of critical current density is described by effective mass theory, and the HTS wire has inhomogeneous distribution cross-section of critical current density. We calculate the angular dependence of normalized AC losses under different DC applied magnetic fields. The numerical results of this formula agree well with the experiment data and are better than the results of Norris formula. This analytical formula can explain the deviation of experimental transport current losses from the Norris formula and apply to calculate transport AC losses in realistic practical condition.     

Ion separation with respect to charge in a beam transported via a flat gap

The transport of a beam of variously charged ions via a flat equipotential vacuum gap is theoretically described. The values of the critical beam current density are determined. The current density and the average ion charge in a beam past the gap are expressed as functions of the injected beam parameters (current density, average charge, and initial energy). Regimes featuring the effective separation of singly and doubly charged ions are found.     

Numerical investigation of transient current density distributions for multi-ion electrolytes at a rotating disk electrode

A versatile model for the simulation of transient multiion transport and reaction processes is applied to investigate current density distributions over a rotating disk electrode for linear voltammetric sweep experiments. The model accounts for ion transport by convection, diffusion, and migration, in combination with Butler-Volmer type electrode reactions. For several process conditions (reversible and irreversible reactions, excess or lack of supporting electrolyte), the current density distribution over the disk surface is examined and the transient current response is compared to results from the more commonly used one-dimensional axial approach. The impact of migrational effects on the nonuniform local process conditions over the disk surface is illustrated, and the resulting effect on the current peak height, width, and position is investigated. A mathematical correlation for the current peak height as a function of the reacting ion transference number is established.     

Analysis of Current and Magnetic Distributions in REBCO Superconducting Coated Conductors in Self- and External Fields

The influence of a self-field on the critical current density J _c for a REBCO superconducting tape is presented in this paper. The distributions of the current density and magnetic field are analyzed in the tape under three kinds of conditions, i.e., applying an external magnetic field only, applying a transport current only, and applying a transport current together with an external magnetic field. In the analysis, the two-dimensional Poisson equation for the vector potential is employed. For the convenience of calculation, that the dependence of critical current versus the perpendicular and parallel fields tested from experiment is substituted for the traditional Kim-type or Bean model. The results show that the distributions of the current density and magnetic field in the REBCO tape change for the different frequencies and amplitudes of the transport current I _a and applied magnetic field B _a.     

提高MgB2超导体临界电流密度的研究进展

临界电流是超导体载流能力大小的重要表征,论述了制备工艺、元素掺杂和物理场对MgB2超导体临界电流密度的影响.使用非晶态高纯硼粉制备致密的MgB2试样有利于样品临界电流密度的提高,添加SiC或者Ti也能起到提高临界电流密度的作用,质子照射使MgB2试样在高磁场条件下的临界电流密度增加,强磁场下烧结则有利于提高MgB2样品临界的传输电流密度.     

Anisotropy of the critical current density in superconducting niobium-titanium wires

The critical current density in wires of an Nb-64 at % Ti alloy was determined in axial and circular directions by various methods. Owing to the cell structure due to cold deformation an anisotropy in the critical current density (j_{c, axially} <j_c, circularly) is present in the wires There is no major difference between magnetization currents and transport currents. Therefore it should be possible in principle to obtain the high critical current densities determined from circular magnetization currents by suitable defect structure with axial transport currents too.     

Charge transport of alkanethiol self-assembled monolayers in micro-via hole devices

In this paper we fabricated 13440 microscale via hole structure devices using different length of alkanethiol self-assembled monolayers and characterized their electronic transport properties. Statistically averaged transport parameters such as current density, transport barrier height, effective electron mass, and transport decay coefficient were obtained from the great number of these devices. The yield of working microdevices was found as 1.5%. Temperature variable current-voltage characteristics for alkanethiol micro-via hole devices showed typical tunneling behavior when properly fabricated.     

Transport ac loss of a superconducting cylinder with field dependent critical current density

The transport ac loss per cycle per unit length of a hard superconducting cylinder is calculated from the critical state model assuming a Kim-type and an exponential field dependent critical current density. Without such dependence, the results are consistent with Norris’ equations for an ellipse bar, in which the critical current density is assumed not to depend on the flux density. Based on Norris’ equations, the expressions of the loss are derived for a finite length cylinder. It is shown that the field dependence decreases and increases the loss at low and high ac currents, respectively, and the effects of the parameter p on the loss are related to the magnetization process. Compared to Norris’ prediction, the results for the Kim and exponential model show the same trend with respect to the external transport current.     

The self-field effect in twisted superconducting composites

Since twisting of composites does not cause a transposition with respect to the self-field of the transport current, they behave like a bulk superconductor with averaged critical current density, when the transport current is changed. Consequently, the electric field is given by the history of the transport current changes. Using a simplified model (J_c = const) the expressions for the electric fields and losses for the first and immediately following second increase of the transport current are derived. Experimental results are also presented which clearly show higher electric field during the first run than during the following, which agrees with theoretical predictions. Quite a good quantitative agreement between theory and experiment was obtained up to about 80% of the critical transport current. The influence of the copper matrix is also discussed.     

以SA为空穴传输层的双层结构电致发光

合在了高荧光量子效率的荧光谱化合物ＦＹ和空穴传输材料的ＳＡ，制备了ＳＡ为空穴传输层，ＦＹ为发光层的双层结构电致发光器件，得到了在１２Ｖ正向电压下的绿色发光，峰值波长为５２５ｎｍ，器件的电流密度为９１ｍＡ／ｃｍ＾２，发光亮度为８０ｃｄｍ＾２。     

Vortex dynamics at the initial stage of resistive transition in superconductors with fractal cluster structure

The effect of fractal normal-phase clusters on vortex dynamics in a percolative superconductor is considered. The superconductor contains percolative superconducting cluster carrying a transport current and clusters of a normal phase, acting as pinning centers. A prototype of such a structure is YBCO film, containing clusters of columnar defects, as well as the BSCCO/Ag sheathed tape, which is of practical interest for wire fabrication. Transition of the superconductor into a resistive state corresponds to the percolation transition from a pinned vortex state to a resistive state when the vortices are free to move. The dependencies of the free vortex density on the fractal dimension of the cluster boundary as well as the resistance on the transport current are obtained. It is revealed that a mixed state of the vortex glass type is realized in the superconducting system involved. The current-voltage characteristics of superconductors containing fractal clusters are obtained and their features are studied.     

Thermionic emission from the 2DEG assisted by image-charge-induced barrier lowering in AlInN/AlN/GaN heterostructures

The effect of image charges on current transport mechanisms investigated at the nanoscale in Al(1-x)In(x)N/GaN heterostructures was studied. Current-voltage (I-V) measurements were performed locally using a conductive AFM-tip as a nanoprobe and the conduction mechanism was modeled to explain the observed behavior. This model suggests that current transport is controlled by thermionic emission (TE) of the two-dimensional electron gas (2DEG) across the potential barrier at the heterointerface, where the image charges generated by the 2DEG induce a barrier lowering at the Al(1-x)In(x)N/GaN interface, enhancing electron transport. This barrier lowering depends on the 2DEG characteristics, such as 2DEG density n(2D), first subband energy E? and the average distance x? of the 2DEG from the interface. By fitting the experimental I-V curves with the present model the 2DEG density was evaluated. The obtained results were in very good agreement with the Hall measurements.     

Evaluation of the electrical conductivity via the time-dependent integral boltzmann equation

Following the integral method developed in neutron transport theory, the exact time-dependent density distribution and current density describing electron motion under the influence of a conservative force are obtained. From the expression for the current density, the validity of Ohm's law for various scattering interaction models can be verified.     

Kim Model of Transport ac Loss with Position Dependent Critical Current Density in a Superconducting Cylinder

In this article, the dependence of the transport ac loss on field and position is investigated for a hard superconducting cylinder, which is consisted of two concentric shells with different critical current density. The Kim model is considered for the critical state in which the critical current density is assumed to depend on the flux density. Based on Norris’ equations, the analytic expression of the loss with field and position dependence is derived for the cylindrical specimen having a composite geometry. The results obtained show that the field and position dependent critical current density have obvious effects on the loss, which may explain why Norris’ predictions and the theoretical results have small differences.     

The Influence of BaZrO3 on the Magnetic Response of (Bi,Pb) : 2223 High-Temperature Superconductors

DC magnetization and AC complex susceptibility measurements on (Bi,Pb) : 2223 high-temperature superconductors impurified with various amounts of BaZrO₃ are presented. The results are discussed in the frame of the critical state model, and the values of the inter- and intragranular critical current density as well as of the field for full penetration are estimated. The values of the intergranular critical current density are consistent with those obtained from transport measurements. The intragranular critical current density and the field for full penetration have similar values from both DC magnetization and AC susceptibility measurements. It was shown that, in the (Bi,Pb) : 2223 system, BaZrO₃ impurification changes only the properties of the intergrain matrix, while the superconducting properties of the grains are not modified.     

Li‐Metal Symmetrical Cell Studies Using Ionic Organic Plastic Crystal Electrolyte

A low current density preconditioning process, which produces an improved lithium transport mechanism is created by the action of charge flow through a plastic crystal electrolyte (figure). A reduction in cell polarisation at high applied current density is demonstrated which approaches the rates required for these electrolytes to be used in practical devices.     

The stress tensor for the mixed state of type II superconductors without volume pinning

The stress tensor is calculated for an ideal type II superconductor in the mixed state. The present stress tensor differs from Josephson's expression insofar as it takes into account the structural changes in the vortex system caused by transport current. The corresponding volume force is not only the Lorentz forcej × B; there are additional terms arising from the gradient of the number density of vortices and from the tension of the vortex lines. It turns out, in particular, that in some geometries a persistent transport current can exist and not be parallel to the magnetic inductionB. The general expressions are applied to the cases of a slab in longitudinal and transverse external magnetic fields.     

Spatial distribution of the local resistive transition and the critical current density in YBCO coated conductors using Low-temperature Scanning Laser Microscopy

Low-temperature Scanning Laser Microscopy (LTSLM) was carried out to reveal the spatial distribution of the local resistive transition temperature and the local current density in commercial YBCO coated conductors near the superconducting transition. The result of the sample with an array of holes of various sizes shows that the signal δV is proportional to the current density. The distribution of the critical temperature of the sample with two parallel bridges is quite homogeneous and the transport current flows mainly along the outer edge of the sample. Using LTSLM we directly image the current path in YBCO coated conductors of different patterns.