Current-carrying Properties Research Articles

Possible effects of the ion redistribution in the dynamo region caused by sequential sporadic E layers

The inspection of ionospheric sounding data and ground-based geomagnetic data, recorded at Grocka observatories (44°38′N, 20°46′E, I=61°), from 1978–1982, shows that there is correspondence between periods of the sporadic E day-time cycles of activity and the periods of the Sq(H) variation. This is an indication that the sporadic E formation and the Sq(H) variation are controlled by the action of the same wind modes. The coincidences were found between events of extremely dense sporadic E, (fbEs ⩾ 10 MHz), and small size disturbances of H-component values. A possible explanation of these coincidences could be that the current-carrying properties of sequential sporadic E contribute to the changes of the conductivity height profiles and so affect the current flow in the dynamo region.

Anisotropy in magnetic properties of high-Tc materials

A brief review is given on recent results concerning equilibrium flux-line lattices, the field distribution within a cell of vortex lattices, the transverse magnetization and the anisotropy related torque. Current carrying properties of boundaries between misaligned anisotropic superconductors are discussed.

Andreev reflections and critical currents in high Tc superconductors

The relevance of the intrinsic Josephson junctions, predicted by magnetization measurements, to the current flow in the metallic oxide superconductors is discussed. We establish a criterion for identifying the character of a Josephson junction, which indicates that the intergrain and the intragrain junctions are of the metallic kind, or weak links, non-tunneling metal-metal contacts. The limiting role played by the intragrain and intergrain junctions (on the current-carrying properties) is analysed and it is concluded that while the former do not determine the critical value of the current in single crystals and grains, the latter represents a strong limitation on the transport currents in the high T c superconductors.

SUPERCONDUCTING CURRENT CARRYING PROPERTIES OF YbxY1-x Ba2Cu3O7-y

The microstructure, superconductivity, and the superconducting current-carrying properties of YbxY1-xBa2Cu3O7-y are investigated systematically. We find that, when the content of Yb increases, Tc changes slightly, but the critical current density decreases with the grain size obviously. The results suggest that just decreasing the grain size can not increase the critical current density of such granuler superconductors in which the couplings among grains are weak.

Effect of anisotropy of current-carrying properties on transport current distribution in twisted superconducting wires

The author presents a problem for the solution of finding the AC transport current flowing in a wire with spiral anisotropy of superconducting properties. In the limiting instances, solutions describe the distribution of current and electromagnetic field in mono- and multifilamentary wires. The analysis shows that twisting affects the current redistribution more appreciably in wires with a low filament transverse-current-carrying ability. The work also discussed the effects on heat release, losses, and weakly expressed anisotropy.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

On the surface magnetization in superconducting NaHg 4

The surface magnetization has been obtained indirectly in superconducting NaHg 4, by measuring the Ginzburg-Landau parameter K and the thermodynamic critical field H c , at 2.50 K. Within the Abrikosov approximation, the current-carrying properties of the superconducting sheath have an associated magnetization per unit volume, which can be expressed as a function of k. We have determined this magnetization for cylindrical samples of radius R and size parameters R λ between 2.5 and 20. The dependence of the magnetization on the normalized magnetic field penetration depth gd λ has been established except for the region near the lower critical field.

A random fuse model for breaking processes

We introduce and study a simple idealized model to describe breaking processes by analysing the current-carrying properties of a random network consisting of insulators and fuses. By increasing the value of the external voltage applied across the network, a sequence of fuses will « burn out » and change irreversible into insultating bonds. This process terminates when a conducting path no longer exists in the network. We monitor several basic quantities during this breaking process, such as the conductivity of the network and the value of the voltage needed to break the hottest fuse. Two new exponents describing the behaviour of these quantities near the percolation threshold are reported.

On the current-carrying properties of mid-latitude type sporadic E-layers

The current-carrying properties of mid-latitude type sporadic E-layers are investigated in some simple cases involving the presence of either a neutral wind or an electric field. It is shown that, in the northern hemisphere, the layer current is directed towards magnetic south provided the height profile of the neutral wind is a left-handed screw with a sufficiently small pitch. If the pitch is high or the screw is right-handed, the current flows northwards. A northward current is also expected in layers created by electric fields alone. It is further pointed out that the current driven by a neutral wind is carried merely by ions, while that due to an electric field is carried by electrons. Finally, the conducting properties of the layers are investigated in terms of a 2 × 2 conductivity tensor.

Current carrying properties of double layers and low frequency auroral fluctuations

Numerical simulations showed recurring interruption and recovery of electron and ion currents through double layers. The time period τ of the recurring phenomena is governed by the ion dynamics; for ions with a drift Vi entering the simulation plasma such that Vi≲Vti, the ion thermal speed, τ is governed by the ion transit time from the location of ion injection to the location of the double layer. On the other hand, when Vi&gt;Vti ion‐acoustic modes also appear in the electron‐ and ion‐current fluctuations. The electron current fluctuations are governed by the ion current through the Langmuir criterion. It is suggested that some low frequency auroral fluctuations could possibly be explained by current fluctuations through double layers.

Nb3Sn diffusion layers. An experimental study of their superconducting properties as related to the Zr content and cold-work amount of the Nb base ribbons

In the present work the results of a systematic experimental analysis on current-carrying properties of superconducting Nb3Sn diffusion layers are presented. The influence of the Zr content (up to a maximum of 7%) and of cold-work of Nb base ribbons on the critical current (at 64 kG) is discussed. It is shown that, while the presence of zirconium leads to a higher critical current density, at the same time it affects the diffusion coefficients, so that the thickness of diffusion layer is decreased. Results concerning pinning mechanism are also presented and discussed.

Current-carrying properties of superconducting lead—bismuth alloys

Current-carrying properties of superconducting lead—bismuth alloys