Showing papers on "Electric current published in 1995"

Hybrid Monte Carlo‐fluid model of a direct current glow discharge

Abstract: A self‐consistent hybrid Monte Carlo‐fluid model for a direct current glow discharge is presented. The Monte Carlo part simulates the fast electrons while the fluid part describes the ions and slow electrons. Typical results of the model include collision rates of the fast electrons, energy distributions of these electrons, fluxes and densities of the different plasma species, the electric field and the potential distribution, all as a function of position from the cathode. The influence of the negative glow on the calculations in the cathode dark space is studied. Moreover the influence of three‐dimensional scattering instead of forward scattering and the incorporation of side wall effects is investigated. Calculations are carried out for a range of voltages and pressures in order to study their influence on the calculated quantities. Comparison was made between total electrical currents calculated in the model and experimentally measured ones to check the validity of the model.

An analysis of the transport losses measured on HTSC single-phase conductor prototypes

Abstract: An analysis was made of published results of transport losses measured on state of the art HTSC single-phase conductor prototypes. Fitting the data to simple existing models was attempted and the agreement is reasonably acceptable for cable design purposes. The measured and estimated losses agree within a factor of two, in a range of peak transport current between 0.3 and 1.0 of the conductor DC critical current. The model used in this current range is one that considers the conductor as a solid SC tube in its own (purely tangential) self-field. The eddy losses are estimated as in a standard procedure for non-magnetic helical multilayer reinforcements and armours, and turn out to be negligible for this geometry. Losses higher than predicted are measured on two or more layer conductors in the low-current range, being typically for a peak transport current below 0.3 of the DC transport current of the conductor. In order to explain this, it is suggested that there might be a dephasing in the AC threshold voltages of the tapes, due to the variation of the in-field critical currents of the tapes across the conductor layers. Problems that are common to this type of measurement are discussed too. The simple model is not directly applicable to the more practical case of a non-coaxial trefoil configuration, because in this case a transverse field is also present, produced on each of the three conductors by the two others. Therefore, the losses need to be measured and modelled also on the trefoil configuration, to obtain reliable data in this practical case too.

Elevated ion charge states in vacuum arc plasmas in a magnetic field

Abstract: We report on measurements of the charge state distributions of ions formed in a vacuum arc plasma in a magnetic field. A vacuum arc ion source was used for plasma formation and ion beam extraction, and the charge state spectra were investigated using both magnetic and time‐of‐flight charge state diagnostics. We find that the charge states of all of the metal species investigated are significantly increased by a magnetic field of up to 6 kG. New high ion charge states are created, and the mean of the charge state distribution is increased by about 30% at 3.75 kG and 50% at 6 kG. The results are important fundamentally as well as being of relevance to vacuum arc ion source applications such as ion implantation and accelerator injection.

High field related thin oxide wearout and breakdown

Abstract: The high voltage wearout and breakdown of thin silicon oxides has been described in terms of traps generated inside of the oxide and at the interfaces by a high field emission process. The trap generation was accompanied by the motion of atoms which resulted in permanent traps fixed in space. Breakdown occurred when the local density of traps exceeded a critical density. The charge state of these traps could easily be changed by application of low voltages after the high voltage stresses. The energy levels of the traps varied depending on the probability of trap generation. This model has been applied to analyze the thickness, field, polarity, time, and temperature dependences of oxide wearout and breakdown observed in oxides thinner than 22 mn. It was concluded that the wearout process in oxides thinner than 22 nm was determined by the electric fields applied to the oxides and not by the passage of currents through the oxides. >

Mechanisms of interface trap-induced drain leakage current in off-state n-MOSFET's

Abstract: An interface trap-assisted tunneling and thermionic emission model has been developed to study an increased drain leakage current in off-state n-MOSFET's after hot carrier stress. In the model, a complete band-trap-band leakage path is formed at the Si/SiO/sub 2/ interface by hole emission from interface traps to a valence band and electron emission from interface traps to a conduction band. Both hole and electron emissions are carried out via quantum tunneling or thermal excitation. In this experiment, a 0.5 /spl mu/m n-MOSFET was subjected to a dc voltage stress to generate interface traps. The drain leakage current was characterized to compare with the model. Our study reveals that the interface trap-assisted two-step tunneling, hole tunneling followed by electron tunneling, holds responsibility for the leakage current at a large drain-to-gate bias (V/sub dg/). The lateral field plays a major role in the two-step tunneling process. The additional drain leakage current due to band-trap-band tunneling is adequately described by an analytical expression /spl Delta/I/sub d/=Aexp(B/sub it//F). The value of B/sub it/ about 13 mV/cm was obtained in a stressed MOSFET, which is significantly lower than in the GIDL current attributed to direct band-to-band tunneling. As V/sub dg/ decreases, a thermionic-field emission mechanism, hole thermionic emission and electron tunneling, becomes a primary leakage path. At a sufficiently low V/sub dg/, our model reduces to the Shockley-Read-Hall theory and thermal generation of electron-hole pairs through traps is dominant. >

On the conductivity model for the electrorheological effect

Abstract: A model is presented for the electric current and attractive force between two slightly conducting spherical particles in a nonpolar liquid. The model includes the nonlinear conductivity of the liquid but does not require that the zone between the particles be divided into two distinct regions, nor is there a need to assume an equipotential condition at the particle surface. Further, the model gives the pertinent properties as a function of the separation of the particles. Numerical values are presented for the properties as a function of the conductivity ratio of the particles to the host oil (silicone oil), the electric field, and the separation of the particles. It is shown that good accord exists between the predicted yield stress and that measured on a suspension of zeolite particles in silicone oil. Some accord also occurs for the current density. Illustrated is the importance of the electrical conductivity parameter Ec of the host oil on ER response. Empirical equations for the shear modulus and st...

Electrical characteristics of argon radio frequency glow discharges in an asymmetric cell

Abstract: Measurements of the current and voltage at both electrodes of a parallel-plate, capacitively coupled RF discharge cell (the Gaseous Electronics Conference Reference Cell) were combined with measurements of the voltage on a wire inserted into the glow region between the electrodes, for argon discharges at pressures of 13-133 Pa and peak-to-peak applied voltages /spl les/400 V Together, these measurements determined the RF voltage, current, impedance, and power of each sheath of the plasma Simple power laws were found to describe changes in sheath impedances observed as voltage and pressure were varied An equivalent circuit model for the electrical behavior of the discharge was obtained The equivalent circuit model can be used to relate the electrical data to plasma properties such as electron densities, ion currents, and sheath widths The results differ from models previously proposed for asymmetric RF discharges, and the implications of this disagreement are discussed

Three‐dimensionai temperature and current distribution in a battery module

Abstract: A method for treating three-dimensional current and temperature distributions in large-scale battery modules is described. Simulations are presented for a module consisting of cells formed with a lithium metal anode, a polymer electrolyte, and a vanadium oxide cathode. The calculations illustrate the nonlinear dependence of power output on system temperature, which for the investigated lithium-polymer battery module is determined primarily by the influence of temperature on the electrochemical reaction rates and ionic conductivity. An appendix is devoted to the estimation of physicochemical parameters, some of which are not available from the current literature, but are nonetheless important model inputs.

Ionic Transport in Electrochemical Cells Including Electrical Double-Layer Effects. A Network Thermodynamics Approach

Abstract: The network thermodynamics approach has been used to obtain the numerical solutions of the NemstPlanck and Poisson equations governing the ionic transport in electrochemical cells, including electrical doublelayer (EDL) effects. By using the electric circuit simulation program PSPICE, a model has been proposed, which permits easily the numerical solutions of those equations describing the behavior of the system under steady-state and equilibrium conditions, as well as the transient and frequency responses to electrical perturbations. Two physical problems are studied, namely, (i) the formation of the equilibrium EDL and (ii) the transient and frequency responses of the system to electric potential perturbations. Impedance-frequency responses and the time evolution of the surface charge density on the electrodes and the electric current density are given. Also, the ionic concentration, the electric potential and the electric field profiles across the cell were obtained as a function of time. The method is quite general and extremely efficient and permits dealing with multiion systems, whatever the boundary and experimental conditions may be.

Reduction, analysis, and properties of electric current systems in solar active regions

Abstract: The specific attraction and, in large part, the significance of solar vector magnetograms lie in the fact that they give the most important data on the electric currents and the nonpotentiality of active regions. Using the vector magnetograms from the Marshall Space Flight Center (MSFC), we employ a unique technique in the area of data analysis for resolving the 180 degree ambiguity in order to calculate the spatial structure of the vertical electric current density. The 180 degree ambiguity is resolved by applying concepts from the nonlinear multivariable optimization theory. The technique is shown to be of particular importance in very nonpotential active regions. The characterization of the vertical electric current density for a set of vector magnetograms using this method then gives the spatial scale, locations, and magnitude of these current systems. The method, which employs an intermediate parametric function which covers the magnetogram and which defines the local "preferred" direction, minimizes a specific functional of the observed transverse magnetic field. The specific functional that is successful is the integral of the square of the vertical current density. We find that the vertical electric current densities have common characteristics for the extended bipolar beta gamma delta-regions studied. The largest current systems have j(sub z)'s which maximizes around 30 mA per square meter and have a linear decreasing distribution to a diameter of 30 Mm.

Study of tunneling current oscillation dependence on SiO2 thickness and Si roughness at the Si/SiO2 interface

Abstract: The tunneling current through tin (∼50 A) silicon dioxide films is observed to have a small oscillatory component at high electric fields Three main results involving the oscillatory component of the tunneling current are reported First, a new and improved analysis for obtaining the oscillatory component from the current measurements is described Then, using this analysis, the dependence of the oscillatory component on oxide thickness and SiO2/Si interface roughness is studied The thickness study shows that the oscillation amplitude decreases exponentially as the distance traveled by the electron in the conduction band of SiO2 increases This decrease is attributed to the scattering effects and the mean free path of the electron in SiO2 is estimated to be 6 A, in agreement with previous reports The roughness study is performed on thermally oxidized purposely roughened Si surfaces, and the roughness is characterized by the atomic force microscopy The oscillations in the tunneling currents show no dep

Initial velocity effect on space‐charge‐limited currents

Abstract: The characteristics of a monopolar space‐charge region under the effect of charge injection with a uniform initial velocity are studied Poisson’s equation has been solved as a Dirichlet boundary‐value problem, other than by conventional serial integrations, to yield exact analytical expressions for the potential, field, charge density, and current The structure of the space‐charge region is characterized by a potential well and an effective diode gap, and can be explained in terms of the initial kinetic energy of the charge The Child–Langmuir limit, when calculated by using the effective diode gap, is a firm limit

Effect of Halo Current and Its Toroidal Asymmetry During Disruptions in JT-60U

Abstract: A poloidal halo current due to a vertical displacement event (VDE) is observed in experimentally simulated VDE discharges and density limit disruptions in the JT-60U tokamak. In the case of a clockwise I{sub p} and B{sub T} discharge, the halo current flows into the vacuum vessel from the inside separatrix and goes back to the plasma from the outside separatrix. A maximum halo current is produced by a change in the poloidal flux generated by plasma current decay. A toroidal asymmetry factor of 2.5 is estimated from the requirements of the fracture of the carbon-fiber composite tiles. The toroidal asymmetry is caused by the poloidal field (PF) that is produced by the toroidal field (TF) ripple, the deformation of the vacuum vessel, the setting error between the vacuum vessel and the TF and PF coils, the low-n mode during current quench, etc. To consider this asymmetry, in JT-60U, one must estimate the total halo current as nearly 26% of the plasma current just before a current quench. 25 refs., 10 figs.

Solid-state gas sensors

Abstract: Solid state gas sensors are provided, the use of which permits quantitative measurement of gaseous contaminants or change of composition of a gas or atmosphere being monitored. The gas sensor comprises at least a base, a first electrode, a second electrode. The first electrode has a finely tapered end to strengthen the electric field intensity in the gap between the first and the second electrodes. The sensing is based on ionization potential difference between the molecules of the contaminating gas and of the atmosphere. When a high voltage is applied to the electrodes, it creates a strong electric field between the electrodes, especially a very strong electric field around the tapered end of the first electrode. When the potential is sufficiently high, the gas in the vicinity of the tapered end of the first electrode will be ionized. The ions and electrons generated by the ionization create an electric current flows between the two electrodes and across the gap. The changes of this electric current with gas contamination or changes in the gas composition are used as sensing signals. Unlike other gas sensors, there is no chemical reaction, absorption or adsorption involved in this sensing process. The gas sensors of this invention may be manufactured by lithographic micromachining techniques at very low cost, and they can be easily integrated with controller and signal processing circuits to upgrade to smart microsensors. Further, in an alternative embodiment, a micro-actuator to control the gap between the two electrodes is integrated with the sensors. In another alternative embodiment, a third electrode may be mounted so as to control the intensity of the electric field.

Numerical simulation of streamer–cathode interaction

Abstract: A self‐consistent fluid model has been used to analyze streamer arrival at the cathode and its transformation to the stationary cathode fall in a positive point–to–plane corona discharge in N2 at 26.7 kPa. The model is based on a description of the electron and the ion kinetics by one‐dimensional continuity equations coupled with Poisson’s equation. The ions and electrons are assumed to be limited to a cylindrical channel with fixed radius and the field is computed using the method of disks. The computed current induced by the streamer–cathode interaction with a small cathode probe is compared with that measured experimentally. The cathode probe signal consists of an initial sharp current spike due to the displacement current followed, some 20 ns later, by a lower current hump due to the ion arrival at the cathode. The current signal is relatively insensitive to changes in the secondary electron emission coefficients. The results obtained indicate that the intense ionization and associated light flash experimentally observed near the cathode at the streamer arrival are not, as generally accepted, due to an intense electron emission but due to a sudden increase in the multiplication factor and a release of electrostatic energy accumulated in the streamer channel–cathode system.

The complete electromagnetic field of a three‐phase transmission line over the earth and its interaction with the human body

Abstract: The electromagnetic field at all points near a high‐voltage transmission line is determined in analytical form. Account is taken of the presence of the earth below the three‐wire, three‐phase power line. The electric and magnetic fields, the total axial current, and the current and power densities in the interior of a human body are determined when the body is standing on the ground under or near the line, is in an elevated basket under the line, or is reclining in bed near the height of the line. The fields are very weak and the current and power densities so small that thermal effects are ignorable, but not necessarily possible effects on nerve action, the functioning of cells, or on certain secretions.

Some observations of the effect of magnetic field and arc current on the vacuum arc ion charge state distribution

Abstract: The charge state distribution of ions produced in a vacuum arc plasma has been investigated for cathode materials Ti, Sn, and Pt as a function of arc current and magnetic field strength in which the arc is located. A vacuum arc ion source was used in combination with a time‐of‐flight charge state diagnostic. It was found that the arc impedance and the ion charge states increase substantially with magnetic field strength. While there was effectively no variation of charge state distribution with arc current for the case of zero applied field, there was a significant increase in the charge states with arc current when the applied magnetic field was 1 kG.

Effects of bias field and driving current on the equivalent circuit response of magnetoimpedance in amorphous wires

Abstract: Magnetoimpedance in as-cast, non-magnetostrictive CoFeBSi amorphous ferromagnetic wires, submitted to AC electric current, irms in the 0.1-20 mA range and frequencies between 100 Hz and 100 kHz, is analysed in terms of equivalent circuits. The effects of the bias longitudinal field, Hdc, up to 3600 A m-1 are also investigated. It is shown that the equivalent circuit representing the wire frequency behaviour can be approximated by a series RsLs arrangement, in series with a parallel LpRp arm. Ls and Lp inductor elements are associated with the rotational and domain wall contributions to circumferential permeability, respectively. Rp is related to wall damping and Rs accounts for all the resistances in the circuit (the wire itself, contacts and so on). The circumferential permeability associated with domain wall movements exhibits a maximum for irms=5 mA (that is, a circumferential field Hrmsphi =12 A m-1), similar to the classical behaviour of wall permeability. The increase in bias field has the effect of strongly decreasing the Lp value; for Hdc=3600 A m-1, the series circuit along accounts for the frequency response of the wire. The association of the circuit elements with basic magnetization processes is discussed. Results are interpreted in terms of the influence of both fields (DC bias, Hdcr,and AC circumferential, Hrmsphi fields) on the inner-core-outer-shell magnetic structure of the wire.

Comparison of experimental target currents with analytical model results for plasma immersion ion implantation

Abstract: An analytical model of the voltage and current characteristics of a remote plasma is presented. The model simulates, the ion, electron and secondary electron currents induced before, during and after a high voltage negative pulse is applied to a target immersed in a plasma. The model also includes analytical relations that describe the sheath expansion and collapse due to negative high voltage pulses. The sheath collapse is found to be important for high repetition rate pulses. Good correlation is shown between the model and experiment for a wide variety of voltage pulses and plasma conditions. >

On the conductivity model for the electrorheological response of dielectric particles with a conducting film

Abstract: An analytical approach is given for the electric current and attractive force between spherical dielectric particles surrounded by a conducting film and situated in a nonpolar liquid. Good agreement occurs between the calculated values and those measured on humidified glass beads in silicone oil. Also, the model predicts a decrease from a quadratic electric field dependence of the force as the field strength is increased, in accord with the results for many electrorheological fluids. The effects of certain parameters which govern the conductivity of the host liquid and of the particles are considered.

Composite structured piezomagnetometer

Abstract: A piezomagnetometer uses a magnetoelectric composite structure, formed by alternating layers of piezoelectric and magnetostrictive material, to convert a fluctuating magnetic field directly to electric current. Strain in the magnetostrictive layers, coming from an ambient magnetic field, stresses piezoelectric layers and drives a polarization current proportional to amplitude of the ambient field. Electrically, the composite is a current source connected in parallel with a capacitor. Its simple and direct operation and solid state sensor enables constructing a small, rugged, inexpensive magnetometer that operates at an ambient temperature with high sensitivity at low power. Multiple piezomagnetometers can be incorporated into a practical detection system capable of operating at ambient temperatures and meeting the limitations presented in civilian and military operations.

Experimental study of the acoustoelectric effects in GaAs-AlGaAs heterostructures

Abstract: We present the results of a detailed experimental study of the electric current and voltage induced in the 2DEG of a GaAs-AlGaAs heterostructure by a surface acoustic wave (SAW). New results are obtained for these acoustoelectric effects at zero and low (<0.1 T) magnetic fields. At zero magnetic field the acoustoelectric current (voltage) was found to show a non-monotonic temperature dependence with a maximum at 40-50 K. Measurements on high-mobility 2DEGs where the electron mean free path is comparable with the SAW wavelength reveal geometric resonances of the cyclotron orbit with the SAW wavelength. With increasing magnetic field the acoustoelectric effects increase significantly and display rich oscillatory structure. We compare our data for the high-magnetic-field regime with that published in the literature.

A closed‐form inversion‐type polysilicon thin‐film transistor dc/ac model considering the kink effect

Abstract: This paper reports a closed‐form inversion‐type polysilicon thin‐film transistor dc/ac model considering kink effect for circuit simulation. Using a quasi‐two‐dimensional approach and an impact ionization model, the kink effect has been explained in terms of dc/ac models as verified by the experimental data. Based on the analytical model, a smaller grain leads to a higher avalanche multiplication factor as a result of a larger average trapped charge density.

Electromagnetic field intensity calculating device

Abstract: An electromagnetic field intensity calculating device calculates according to a moment method the intensities of the electric field and the magnetic field radiated by an electric circuit device having metal portions and dielectric portions The electromagnetic field intensity calculating device comprises an input unit for inputting the precise structure of the electric circuit device including the structure of the metal portions and the structure of the dielectric portions; a deriving unit for deriving simultaneous equations based on the structure of the electric circuit device input to the input unit, a calculating unit for calculating the electric current flowing through the metal portions and the equivalent electric current and the equivalent magnetic current flowing through the dielectric portions by solving the simultaneous equations; and a computation unit for calculating the intensity of the electric field and the magnetic field radiated by the electric circuit device based on calculation results obtained by the calculating unit

Effects of Hall currents and Coriolis force on Hartmann flow under general wall conditions

Abstract: The influence of Hall currents and rotation on a generalized Hartmann flow and heat transfer is investigated. The channel is rotating with a constant angular velocity around an axis perpendicular to the walls in a uniform transverse magnetic field. The walls may have the same thickness, electrical and thermal conductivity as well as Hall parameter or different ones. The flow may be driven either by a pressure gradient or by motion of one of the walls. Exact solutions are derived for the velocity, magnetic field, viscous stress, current density, temperature distribution, yield components, electric current components, mean temperature as well as Nusselt numbers. Representative numerical results are presented in diagrams and effects of different parameters are discussed.

Vibration immunity for optical-fiber current measurement

Abstract: Optical-fiber measurement of electric current can be rendered immune from the effects of environmental vibration by utilizing the nonreciprocity of the Faraday effect in an arrangement which propagates light simultaneously in the two directions around a fiber loop enclosing an electric current. The system is compared with a back-reflection arrangement. Temperature variations are also suppressed. >

Persistent Currents in Finite-Width Mesoscopic Rings. The Role of the Interchannel Coupling and of the Electron-Electron Interaction

Abstract: The persistent currents of few interacting electrons with spin in mesoscopic rings arc calculated in the ballistic regime. The energy bands of the finite-width multi-channel ring are calculated with the transfer-matrix method including the interchannel coupling induced by the impurity scattering, and the electron electron interaction. It is shown that in the case of a narrow-width ring the electron-electron interaction and the confining potential build a rotating Wigner crystal of the few electrons, where the relative angular motions are harmonic oscillations if the impurity potential is weak. As long as this picture remains valid, the persistent current is not influenced by the electron-electron interaction. It is shown that the width of the mesoscopic ring is the critical parameter for the influence of the electron-electron interaction on the persistent current. With increasing width of the mesoscopic ring, the electron-electron interaction decreases the amplitude of the persistent current at low temperatures and increases it at higher temperatures. Further, for a finite width of the mesoscopic ring the interchannel coupling becomes important, which results in the occurrence of higher harmonics in the persistent current.

Novel p-JFET embedded in silicon radiation detectors that avoids preamplifier feedback resistor

Abstract: The paper describes the design and the performance of an original p-channel JFET embedded in the collecting anode of a silicon radiation detector. The choice of a p-channel transistor, whose gate-to-channel junction is forward biased by the leakage current from the detector, avoids the preamplifier feedback resistor and performs a continuous dc reset of the collected charge. The reported design, fully compatible with the detector fabrication, makes the operation of the detector extremely simple, ensures the best charge collection capability and leads to improved charge resolution. The first detector produced with this type of transistor has a resolution of 27 electrons rms in the measurement of the collected charge at room temperature for a pixel active area of about 0.1 mm/sup 2/, and of 22 electrons rms at T=210 K. >