Showing papers on "Electric current published in 1998"

Interaction of the Jovian magnetosphere with Europa: Constraints on the neutral atmosphere

Abstract: A three-dimensional plasma model was developed to understand the sources and sinks that maintain Europa's neutral atmosphere and to study the interaction of the Jovian magnetosphere with this atmosphere and the formation of an ionosphere. The model includes self-consistently the feedback of the plasma action on the atmosphere through mass balance. Suprathermal torus ions with a contribution from thermal ions sputter O 2 from the water ice surface, and thermal torus ions remove the O 2 atmosphere by sputtering. For an oxygen column density of 5 × 10 18 m -2 the calculated intensities of the oxygen lines OI 130.4 nm and 135.6 nm produced by electron impact dissociation agree with observations by the Hubble Space Telescope [Hall et al., 1995]. Mass balance is also consistent with this column density, with a net atmospheric mass loss of 50 kg s -1 . For a given neutral atmosphere and magnetospheric conditions, the electrodynamic model computes self-consistently plasma density, plasma velocity, electron temperature of the thermal and the suprathermal population, electric current and electric field in the vicinity of Europa, with the assumption of a constant homogeneous Jovian magnetic field. Europa's ionosphere is created by electron impact ionization where the coupling of the ionosphere with the energy reservoir of the plasma torus by electron heat conduction supplies the energy to maintain ionization. The calculated distribution of electron densities with a maximum value of nearly 10 4 cm -3 is in general agreement with densities derived by Kliore et al. [1997] from the Galileo spacecraft radio occultations. The Alfvenic current system closed by the ionospheric Hall and Pedersen conductivities carries a total current of 7 × 10 5 A in each Alfven wing.

Probe-Induced Particle Circulation in a Plasma Crystal

Abstract: A biased probe placed in an argon plasma near the sheath edge has been found to alter significantly the structure and properties of a plasma crystal, inducing particle circulation around a stable crystalline island. The origin of the island and the circulation are attributed to the formation of a nonuniform electric field in the crystal region by the probe. Variation in the space-charge flux due to the ion wake associated with the probe is also considered important, as it may alter the grain charge and the transfer of momentum to the dust particles.

Electronic and electromagnetic properties of nanotubes

Abstract: A nanotube is phenomenologically modeled as a chain of atoms wrapped helically on a right circular cylinder. The semiclassical Hamiltonian of an electron is derived, using the Wannier approach for the Schr\"odinger equation, when the nanotube is exposed to both constant (dc) and high-frequency (ac) electromagnetic fields. The Boltzmann kinetic equation is then solved in the framework of momentum-independent relaxation time approximation. An analytical expression for electric current in a nanotube is derived. The interaction of nonlinearity and chirality is analyzed, chiefly as the dependence of a current chiral angle on the amplitude of the ac electric field. The derived expressions for the electronic transport also help in stating anisotropic impedance boundary conditions on the nanotube surface. Surface wave propagation in a carbon nanotube (CN) is examined. The idea of using CN's as nanowaveguides in the infrared frequency range is established. Convective instability is shown to occur under special conditions in a CN exposed to an axial dc electric field.

High-electric-field poling of nonlinear optical polymers

Abstract: We have investigated electrical conduction phenomena during high-electric-field poling of a standard covalently functionalized DR-1 side-chain polymer. We performed electric current and second-harmonic measurements simultaneously to derive the effective internal field strength. Various metals and transparent indium tin oxide were used as electrodes. Current densities appeared to be interface (electrode) limited, with little dependence on the work function of the metal for the top electrode (Bardeen barrier at the electrode–dielectric interface), whereas for the bottom electrode–dielectric interface a dependence on the work function of the metal was observed. The field dependence of the current density was found to be Schottky charge emission for medium field strengths (EPOL≤100 V/μm), whereas it was dominated by Fowler–Nordheim tunneling at higher poling fields. In the presence of an additional inorganic barrier layer, significant suppression of tunneling was observed, which led to a reduced probability of singular breakdown events and shifted the limit of avalanche breakdown to higher internal effective poling field strengths.

The auroral current circuit and field‐aligned currents observed by FAST

Abstract: , FAST observes signatures of small-scale downward-going current at the edges of the inverted-V regions where the primary (auroral) electrons are found. In the winter pre-midnight auroral zone these downward currents are carried by upward flowing low- and medium-energy (up to several keV) electron beams. FAST instrumentation shows agreement between the current densities inferred from both the electron distributions and gradients in the magnetic field. FAST data taken near apogee (∼4000-km altitude) commonly show downward current magnetic field deflections consistent with the observed upward flux of ∼10 9 electrons cm -2 s -1 , or current densities of several μA m -2 . The electron, field-aligned current and electric field signatures indicate the downward currents may be associated with black aurora and auroral ionospheric cavities. The field-aligned voltage-current relationship in the downward current region is nonlinear.

Electric current generation associated with the deformation rate of a solid: Preseismic and coseismic signals

Abstract: We present a model for the generation of electric current in rocks under stress, involving the strain rate, (e) which is influenced by the motion of charge bearing dislocations. The relationship between current density and strain rate is demonstrated. On the basis of laboratory data, we estimate the deformation rate necessary to generate an electric signal observable at distances far enough from the source, as to qualify it as an electric earthquake precursor. Using this mechanism and the geometrical characteristics of such a type of source we simulate the propagation of the electric signal and its ‘received’ characteristics as a function of the source-receiver separation. We conclude that the expected signal waveforms at long distances from such a kind of source are similar to a class of signals (bay like waveforms), independently observed prior to earthquakes by several investigators.

Electric currents through ion tracks in silicon devices

Abstract: A modified form of Ohm's law, describing electric currents through ion tracks, is presented as a tool for future theoretical modeling efforts related to charge collection from ion tracks in silicon devices. The equation is rigorously derived from the drift/diffusion equations and accounts for all currents (electron and hole, drift, and diffusion). While only one quantitative result is given, a fairly complete description of charge collection from ion tracks in silicon diodes is qualitatively discussed.

Current‐voltage relationship in the downward auroral current region

Abstract: In the auroral zone of the earth currents flow along magnetic field lines. In the downward current region currents are mainly carried by upflowing electrons from the ionosphere. Because of the low plasma density along auroral field lines, substantial currents in the range of microamps per square meter require substantial potential drops parallel to the magnetic field in the range of a few hundred to a few thousand volts. The current-voltage relation along such magnetic field lines can be determined for simple profiles of the background ion density by invoking the condition of charge neutrality. For typical parameters, the current density is found to be a few times larger in the downward current region compared to currents in the upward current region for similar potential drops. Thus potential drops up to a few thousand volts and the consequent acceleration of ionospheric electrons up to keV energies, such as has been observed by the FAST satellite, are a necessary consequence of the observed current densities in the downward auroral current region.

Cathode arc vapor deposition method and apparatus

Abstract: The present invention relates to an apparatus and method for enhancement of the stream of plasma particles created by the process of cathode arc vapor deposition. The apparatus is designed to control through trapping the plasma particles generated from a sacrificial cathode plasma source and focus the plasma particle stream to collide with and deposit upon the substrate to be coated. The apparatus includes a magnetic field generator for generating a magnetic field of a distinctive cusp shape. The anode is insulated from the chamber to strengthen and sharpen the electric field potential created in the chamber. This stronger, sharper electric field potential is contoured to create an electron trap having an aperture through which the plasma ions are directed at the substrate to be coated. The specific configuration described directs the plasma particles efficiently in that the plasma deposition rate is higher per unit of magnetic field strength than can be obtained with other commercial designs. In addition, a smoother, more stable arc discharge per unit of applied electric current to the system is possible. The distinctive electric field potential created by the instant invention results in a more enhanced stream of vaporized source material, which improves the quality and corrosion resistance of the product coatings. A more stable cathode arc discharge is also possible.

An improved near- to far-zone transformation for the finite-difference time-domain method

Abstract: Near- to far-zone transformation for the finite-difference time-domain (FDTD) method can be performed by integration of the equivalent electric and magnetic currents originating from scattered electric and magnetic fields on a surface enclosing the object. Normally, when calculating the surface integrals, either the electric or magnetic fields are averaged since the electric and magnetic fields are spatially shifted in the FDTD grid. It is shown that this interpolation is unnecessary and also less accurate than if an integration is performed on two different surfaces. It is also shown that the accuracy of the far-zone transformation can be further improved if the phase is compensated with respect to a second-order dispersion corrected wavenumber. For validation, scattering results for an empty volume, a circular disk, and a sphere are compared with analytical solutions.

Internal voltage generator with reduced power consumption

Abstract: A first periodic pulse is rectified to generate an internal voltage by a charge pump circuit. A level detector is provided for detecting whether or not the internal voltage reaches a desired level. The charge pump circuit is controlled by a controller in accordance with the detection signal so that the internal voltage may take the desired level. A switch element switched by a second periodic pulse is provided in the current path of the level detector. A leakage current path for allowing a lower electric current than the electric current to flow through the former current path is provided between the output terminal of the charge pump circuit and a predetermined power supply terminal.

LRC-circuit analog of current-carrying magnetic loop: diagnostics of electric parameters

Abstract: The equation for an equivalent LRC-circuit of current-carrying magnetic loop is obtained. It is suggested that the electric current, driven by the converging flows in the photo- sphere, flows trough the coronal part of a loop from one footpoint to another, and closes deep in the photosphere where plasma beta 1. In a self-consistent approach both the capacitance and the resistance of a LRC-circuit depend on the electric cur- rent along the loop. This opens new possibilities for the diag- nostics of electric currents in coronal loops, by using data on high-quality modulation of microwave emission during flares. Spectral analysis of the Mets¨ ahovi millimeter wave solar data for 16 solar flares have revealed modulation periods 0.7-17 s which give currents I 610 10 -1.410 12 A. For two of the events we could compare the total energy of the electric cur- rent stored in the magnetic loop with the energy released in the flare. Only 5% of the total energy of the electric circuit was released in both flares, suggesting a very low influence of these flares on the magnetic loop structure. In the studied events there was a tendency to decrease the energy release with the increase of the current. This tendency is interpreted in terms of plasma beta, which is getting smaller as the current grows. Therefore the plasma instabilities responsible for the flare process manifestate themselves weakly with the increase of the current.

Electrochemical machining using modulated reverse electric fields

Abstract: Electrochemical machining of metals and alloys is accomplished by using a pulsed electric current incorporating modulated reverse electric current. Reverse (cathodic) pulses are interposed between forward (anodic) pulses. The process is useful for electrochemical shaping of metals, electrochemically polishing metal surfaces, and electrochemical deburring of metal articles. The process is especially useful for electrochemical processing of metals and alloys that readily form passive surface layers.

Modelling of the toroidal asymmetry of poloidal halo currents in conducting structures

Abstract: During plasma disruptions, substantial toroidal and poloidal eddy currents are generated in the vacuum vessel and other plasma facing conducting structures. Eddy currents that conduct charge through paths which close through the plasma periphery are called halo currents, and these can be of substantial magnitude. Of particular concern for tokamak design and operation is the observed toroidal asymmetry of the halo current distribution: such an asymmetric distribution leads to problematic non-uniform forces on the conducting structures. The premise is adopted that the source of toroidal asymmetry is the plasma deformation resulting from the non-linear external kink instability that develops during the current quench phase of a disruption. A simple model is presented of the kinked plasma that allows an analytic calculation of the dependence of the toroidal peaking factor (TPF) on the ratio of the halo current to the total toroidal plasma current, Ih/Ip. Expressions for the TPF as a function of Ih/Ip are derived for m/n = 2/1 and m/n = 1/1 helical instabilities. The expressions depend on a single parameter, which measures the amplitude of the saturated state of the kink instability. A comparison with disruption data from experiments shows good agreement. Numerical experiments that simulate non-linear external kinks provide guidance on the values expected for the saturated amplitude. It is proposed that a simple plasma halo model is adequate for assessing the engineering impact of asymmetric halo currents, since the force distribution on the conducting structures depends mainly on the `resistive distribution' of the eddy currents. A brief description is given of an electromagnetics code that calculates the time development of eddy currents in conducting structures, and the code is applied to two halo current disruption scenarios. These are used to emphasize the importance of having an accurate eddy current calculation to correctly estimate the engineering impact of tokamak disruptions.

Method of detecting abnormal electric current in vehicle apparatus for detecting abnormal electric current in vehicle and power supply apparatus for vehicle

Abstract: A method of detecting an abnormal electric current in a vehicle to detect passage of an abnormal electric current through an electric wire for establishing the connection between a load to which electric power is supplied and a power source, the method of detecting an abnormal electric current in a vehicle comprising the steps of: (a) detecting values of electric currents which pass through the electric wire at predetermined sampling intervals; (b) counting the number of times in a unit detection period that a sampled electric current having a value larger than a predetermined value is detected and determining passage of an abnormal electric current through the electric wire when the number of counts is larger than a first number of times; and (c) counting the number of times that a sampled electric current having a value larger than the predetermined value is detected in a unit detection period after the unit detection period in terms of time in a case where the number of counts is smaller than the first number of times and except for zero and determining passage of an abnormal electric current through the electric wire when the number of counts is larger than a second number of times

Electromagnetic excitation of a thin wire: a traveling-wave approach

Abstract: An approximate representation for the current along a perfectly conducting straight thin wire is presented. The current is approximated in terms of pulsed waves that travel along the wire with the velocity of the exterior medium. At the ends of the wire, these pulses are partially reflected, with a constant reflection coefficient and delay time. Subsequently, the traveling-wave representation for the current is used to derive an approximate expression for the electric field outside the wire that is caused by this current. For voltage excitation, this expression contains only closed-form contributions. For plane-wave excitation, the expression contains a single integral over the initial pulse that must be computed numerically. Although the expression obtained is essentially a far-field approximation, it turns out to be valid from distances of the order of a single wire length. Results for a representative choice of wire dimensions and pulse lengths are presented and discussed.

Electrolyte Transistors: Ionic Reaction−Diffusion Systems with Amplifying Properties

Abstract: The problem of constructing chemoelectric amplifying devices based on acid−base reactions is discussed It is shown that the construction of a direct analogue of the semiconductor transistor (that is, when the p- and n-doped semiconductors are replaced by ion exchange membranes in the H+ and OH- forms, respectively) is technically not feasible The new amplifying device reported here is based exclusively on mobile ions migrating in a hydrogel arrangement that contains no fixed charges The polarization curve of an acid−base interface in this medium has a diode characteristic When two of such “electrolyte diodes” are connected appropriately, a transistor action can be observed: the electric current flowing in one (reverse biased) diode is affected not only by the voltage applied there but also by the current flowing through the other (forward biased) diode The common emitter current gain of an acid−base−acid transistor studied here was between 4 and 5 The active mode characteristics of this device can

Method and device for measuring the difference in magnetic field strength with magnetoresistive sensors

Abstract: A method and device for measuring electric currents in n conductors (n≧2), the measurement of the currents being carried out with (n−1) magnetoresistive sensors. Reliable excess current and/or fault current protection is obtained.

The AI/Ni interfacial reactions under the influence of electric current

Abstract: Electromigration has been observed and quite extensively investigated in the compositionally homogeneous conducting lines in the integrated circuit devices; however, the effect of electric current upon the interfacial reactions has not been discussed. This study investigated the effect of electric current upon the chemically driven interfacial reactions in the Al/Ni system. Al/Ni reaction couples annealed at 400°C with and without the passing of electric current were examined. Two intensities of electric currents, 5×102 A/cm2 and 103 A/cm2, were used in this study. Same intermetallics, Al3Ni and Al3Ni2, were formed at the interfaces; however, the thickness of the reaction layer in the reaction couples with the passing of electric current was much larger than those without electric current. This novel phenomenon has never been reported in the literature, and the understanding of its mechanism needs further investigation.

Winding in transformer or inductor.

Abstract: A power transformer or inductor is disclosed. The winding (31) of the transformer/inductor is made of a flexible conductor (38) having electric field containing means forcing the electric field due to the electric current in the winding (31) to be contained within the insulating layer of the flexible conductor (38). The thickness of the insulating layer of the flexible conductor (38) is adopted in such a way to make the electric stress (33) constant throughout the length of the winding. The cross section area of the insulating layer of the flexible conductor (38) is thus optimized, providing for a transformer/inductor design with a high space factor.

Development of Ag-sheathed Bi2223 superconducting wires and their applications

Abstract: Silver-sheathed multifilamentary BiPbSrCaCuO 2223 superconducting wires with long length and high Jc of over 10 4 A/cm 2 (77.3K, OT) were developed by using the powder-in-tube method. A scaling law, which can be adopted in a wide temperature and magnetic field range, was found. Using this scaling law, we can estimate Jc at any temperature and magnetic field by using the wire performance at 77K without external field. Low AC loss wires and high strength wires were also developed for future applications. High electrical resistivity of the matrix and the use of twisted filaments are effective for reducing the AC losses. Good stress and strain tolerant characteristics were obtained for silver alloy sheathed wires. As a result of the progress in wire technology, we were able to fabricate many application prototypes. In high amperage conductor applications, current leads, bus bars and cable conductors were developed. In magnet applications, pancake magnets cooled by a GM refrigerator and solid nitrogen, as well as a layer wound magnet for high magnetic field NMR application at 4.2K, were developed.

Semiconductor light emitter with current block region formed over the semiconductor layer and electrode connection portion for connecting the pad electrode to the translucent electrode

Abstract: A semiconductor light emitter characterized by including a semiconductor layer for providing an electric current block region and an electric current injection region on a surface thereof, an electric current block layer formed on the semiconductor layer for defining the electric current block region, a pad electrode formed on the electric current block layer, and a light-transmissive electrode formed on the semiconductor layer for defining the electric current injection region, wherein the pad electrode has an electrode connection portion for connection with the light-transmissive electrode. Such a semiconductor light emitter can prevent failure in electric current introduction into the light emitter owing to disconnection of the light-transmissive electrode and increase of the resistance of the light-transmissive electrode. It is possible to produce light emitters with good behavior in a good yield.

Effect of electric current pulses on grain size in castings

Abstract: The effect of electric current pulses (ECP) on grain size in castings is considered. The relationship between grain size and electric current density is revealed. Numerical calculation shows that an electric current density with a magnitude of 10(3) A/cm(2) is needed to reduce the grain size by one order of magnitude for some pure metals, such as Ni, Sn, Pb, Cu, and Fe. The effects of Joule heating, skin, and pinch force are proved to be of lesser importance. The theory gives a good explanation for the experimental results reported by Conrad and co-workers.

Magnetic Field Line Reconnection in Weakly Ionized Plasmas

Abstract: We present the results of theoretical studies of the magnetic field line reconnection in weakly ionized plasmas. We investigate the propagation of small amplitude magnetohydrodynamic (MHD) waves near critical lines of the magnetic field and show the occurrence of the pile-up of electric current. This magnetic collapse is described by self-similar solutions that demonstrate the formation of singular structures in the vicinity of the magnetic field separatrix surfaces. We obtain the growth rate of the tearing mode instability of the current sheet and present a solution of the Taylor problem for a slab of a weakly ionized plasma. We have found the reconnection rate and the dimensionless parameters that describe the relative role of nonlinearity and dissipation effects near critical points. We present results of the MHD computer simulation of two-loop coalescence that show the dependence of reconnection on the value of ion-neutral drift.

Electron-correlation effects in transport through a double-quantum-dot molecule

Abstract: The effects of the electron correlation on the electronic structure and transport in a pair of vertically coupled quantum dots are studied as functions of the number of electrons and the distance between the two dots by using a numerical diagonalization method. The electron correlation drastically affects the spin structure of the ground states when the number of electrons and the distance between the dots are sufficiently large. The electronic states with the large (small) spin momentum are stable when the number of electrons is an odd (even) integer. A physical picture of this characteristic behavior can be understood by an analogy to that of the electronic states in the Hubbard model near half filling. The Coulomb oscillation can be seen in the conductance of the electric current through the double-quantum dots. When the distance between the dots is large, the amplitudes of several conductance peaks are suppressed by the electron correlation.