Showing papers on "Electric potential published in 1975"

Image approximation to the reaction field

Abstract: The reaction field for a charge at an arbitrary position in a spherical cavity in a medium of dielectric constant e may be expressed in terms of the electrical potential of a certain image charge. For e τ 1 the potential of the reaction field in the cavity is quite accurately the same as the electrical potential of the image charge. These observations form the basis of a rather economical and accurate way to calculate the reaction field's contribution to the interaction potential of particles with electric moments within a cavity within a dielectric. The results promise to be useful in the study of models for polar fluids and solutions by the Monte Carlo and Molecular Dynamics methods.

Lunar electric fields, surface potential and associated plasma sheaths

Abstract: A review is given of studies of the electric-field environment of the moon. Surface electric potentials are reported for the dayside and terminator regions, electron and ion densities in the plasma sheath adjacent to each surface-potential regime are evaluated, and the corresponding Debye lengths are estimated. The electric fields, which are approximated by the surface potential over the Debye length, are shown to be at least three orders of magnitude higher than the pervasive solar-wind electric field and to be confined to within a few tens of meters of the lunar surface.

Electric‐field‐enhanced conductivity in solids

Abstract: The Onsager theory of dissociation, based upon the solution of Brownian equations of motion of charge carriers interacting through a Coulomb potential in an applied electric field, is shown to account for the electric‐field‐enhanced conductivity in solids. In contradistinction to often quoted one‐dimensional macroscopic Poole‐Frenkel theory and its varied three‐dimensional modifications, the Onsager theory is microscopic in nature and thus provides a quantitative description of the observed field enhancement of the conductivity.

Test charge potentials in turbulent plasmas

Abstract: The potential of stationary test charge in a uniform quiescent Maxwellian plasma decreases exponentially at distances larger than the Debye length. The possibility that the potential may decrease in a significantly different manner in a turbulent plasma was investigated. The far field potential in a weakly turbulent magnetized plasma was derived, in order to calculate collision frequencies. The effects of turbulence on the scattering of laser light by plasmas is also discussed.

Electro-optical effects in liquid crystals

Abstract: This review gives information on the electric and optical properties of liquid crystals (LC), and discusses in detail various electro-optical effects in nematic, cholesteric, and smectic LC. Dielectric deformations of LC in electric fields, electrodynamic instabilities, the electromechanical effect, etc., are treated. Special attention is paid to explaining the physical reasons for the change in the optical properties of thin LC films when acted on by an electric potential. The practical applications of LC in electro-optical devices are briefly reviewed.

Charge Deposition, Photoconduction, and Replacement Current in Irradiated Multilayer Structures

Abstract: The electronic effects on an irradiated one dimensional dielectric-metal slab structure have been modeled. The effects considered include: radiation driven currents, charge deposition, applied electric fields, deposited charge fields, field driven conductivity currents and radiation induced photoconductivity. The time and spatial dependence of the electric current density, charge density and electric field are determined. The time dependence of the replacement current flowing between metal slabs is calculated. Results are given for x-rays of energies from 30 to 1250 keV. Interesting results predict electric fields > 106 V/cm, time varying replacement currents which even reverse sign, and multipole electric fields in one dimension. Experimental measurements produce time dependent replacement currents under 60Co irradiation.

Effects of Space Charge and Reactive Wall Impedance on Bunched Beams

Abstract: Space charge and reactive wall impedance create longitudinal forces inside the bunch which change the incoherent phase oscillation frequency, the bunch length and the size of the RF-bucket. These effects have been investigated with bunched beams in the ISR. By measuring the shift of the quadrupole mode phase oscillation frequency, the strength of the self-forces was determined. The inductive wall is dominant and its impedance (divided by the mode number) was measured to be |Z|/n z 26 Ohms. An increase of bunch length with current was measured. It can be explained by the inductive impedance up to a certain current; beyond that an excessive, unexplained bunch lengthening occurs. The reduction of the bucket size affects the stacking process. By correcting for it, an increased density of the stacked beam was achieved. Ez = -e az [4 g0 dz (1)

A Stochastic Electrical Model of an Infinite Cloud: Charge Generation and Precipitation Development

Abstract: A stochastic numerical cloud model is used to investigate simultaneously growth of precipitation, the formation of electrical charges on the particles, and the development of the ambient electric field utilizing the polarization charging mechanism. The results indicate a close coupling between precipitation growth and electrification. Precipitation is reduced when the electric field reaches magnitudes of kilovolts per centimeter. The distributions of charge on the particles show charges of a realistic magnitude. Simple restraints on the coalescence efficiency based on electric charge show that, indeed particle charges can have a profound effect on rain development through coalescence. The overall results qualitatively agree with the results from the continuous collection model of Ziv and Levin, i.e., the partial levitation of the particles due to electrical forces and the termination of electric field growth can occur at electric field strengths large enough for lightning.

The dipole mapping method

Abstract: In the bipole-dipole mapping method, a current field is set up by the use of a bipole current source The current field is then studied by making measurements of electric field intensity with dipole receivers at many locations around the bipole source The values for electric field intensity may be used to compute apparent resistivities if we assume that the earth is uniform or to compute apparent conductance if we assume that the earth resembles a conducting sheet Maps of apparent resistivity values or apparent conductance values may be interpreted by comparing them with similar maps computed analytically for various simplified earth models The bipole-dipole mapping method is useful mainly in locating areas where ground resistivity varies rapidly in the horizontal direction It has found application mainly in exploration for geothermal reservoirs but also has been used for mining exploration and engineering studies, and an example of each is described

The potential and electric field at the metallurgical boundary of an abrupt p-n semiconductor junction

Abstract: Analytical equations are presented that rigorously establish the electrostatic potential and electric field at the metallurgical transition point of an abrupt p-n semiconductor junction. From these equations, the classical depletion-layer approximation is shown to be rigorously correct only when (N A = N D ), although this solution remains adequate for engineering purposes if 1.0 ≤ N A / N D ≤ 10.0, approximately. It is also shown that mechanisms of operation take place within an asymmetrical abrupt junction (N A ≥ N D ) that cannot be deduced from the depletion-layer aproximation. For example, the asymmetrical junction is shown to contain an electrostatic potential and an electric field at its metallurgical transition point that are essentially constant throughout a wide range of reverse biasing voltage. These characteristics imply that the total electrostatic charge within its p-type and n-type space charge layers remain essentially constant, and that its p-type space-charge layer is of constant width, despite the application of a reverse biasing voltage. These heretofore unreported mechanisms of operation arise from a layer of mobile charge carriers residing at the low-doped side of the metallurgical transition between n-type and p-type semiconductor material.

On pair production in intense electromagnetic fields occurring in astrophysical situations

Abstract: We show that the pair production rate in a strong magnetic field is substantially altered when an electric field is also included. We illustrate and emphasize this significant alteration by considering a few special cases. In the vicinity of the polar cap of a rotating magnetized neutron star it is currently though thatboth steady electric and magnetic fields must be present. The results presented here then indicate that some considerable degree of caution must be exercised in applying pair production rates calculated under the assumption of zero electric field to the problems of pulsar emission and the generation and maintence of pulsar magnetospheres. In general such rates are very different from the rate computed allowing for the existence of an electric field.

The Electric Field

Abstract: This chapter is concerned with time-independent electric fields arising from fixed or static charges and hence the term electrostatic field is often used. The starting point is usually from the experimental investigations carried out in 1785 by Cavendish and Coulomb, who likened the electrostatic field associated with the charge on a body to the gravitational field associated with the mass of a body.

Space-charge limits in unneutralized relativistic electron beams

Abstract: Limiting currents in annular unneutralized relativistic electron beams are calculated and compared with experiment. The limiting factor for short beams is found to be the space-charge depression of the potential due to the unneutralized beam; in longer beams self-magnetic and electric fields impose a power limit. Typical beam impedances are found to be of the order of 15 Ω with a 350 keV beam. The role of shear in the axial velocity of the beam is discussed.

Critical energy for adiabatic r.f. plugging

Abstract: Necessary and sufficient conditions are obtained for the description of particle motion by a quasi-potential in an inhomogeneous static magnetic field and an r.f. electric field. This analysis leads to a new concept of critical energy, the height of the adiabatic barrier, which is proportional to , E0 being the strength of the r.f. field in the plasma. The theoretical results are confirmed by numerical calculations. Although this concept holds in a general magnetic field, analysis is restricted to the cusped magnetic field.

The time-dependent potential in a spherical cell using matched asymptotic expansions

Abstract: A derivation is given of the equation and boundary condition for determining the electric potential in a cell. The potential is calculated for all time, everywhere inside a spherical cell and in the external bathing medium for the case of a point source of current inside the cell turned on abruptly at t= 0. The problem is solved by the singular perturbation technique of matching a short-time (inner) and a long time (outer) asymptotic expansion. The model for the cell consists of a sphere of radius a with an internal medium of conductivity σi, surrounded by a membrane of thickness δ, conductivity σm and surface capacity C m bathed in an external medium of conductivity σ0, The solution is discussed for the physiologically interesting case of ɛ=σma/σi δ ≪1, when the effective internal resistance is small compared to the effective membrane resistance. In the most important physiological case, for times much longer than C m a/σi, simple analytic expressions are obtained for the inside potential, the outside potential and the transmembrane potential. The leading term in the expansion, the isopotential cell interior, is obtained for arbitrary finite-cell shape.

Electrostatics of two conducting spheres in contact

Abstract: Two electrostatistic boundary-value problems for two perfectly conducting contiguous spheres of equal radius are solved in terms of tangent-sphere coordinates: i) charged spheres in the absence of an applied electric field, and ii) grounded spheres in a uniform electric field. Explicit expressions for the potential, surface charge distribution and resultant force acting on the spheres are presented.

Theory of Valley-Splitting in Surface Quantum States of Silicon MOSFETS*

Abstract: The experimentally observed removal of valley degeneracy along the (100)-axis in the surface quantum states of Silicon MOSFETS is explained as an effect due to the electric field and spin-orbit interaction. A combination of crystal momentum representation and effective mass theory is used from which results that within the one-band approximation a magnetic field normal to the Si surface and the electric gate field act upon the electrons independently from each other.

The lunar terminator ionosphere.

Abstract: The extended ionosphere is seen by the Suprathermal Ion Detector Experiments (SIDE) near the terminator. An analysis of the energy and mass spectra of these ions accelerated by the interplanetary electric field indicates the following: (1) the principal ion species are in the mass per unit charge ranges consistent with neon and argon, (20-28 and 40-44 amu/q); (2) the lunar atmosphere in these mass ranges is distributed exponentially; (3) the terminator region surface number density for Ne-20 is of the order of 10 to the 5th/cu cm; (4) the terminator region lunar surface potential is negative from about 10 to 100 volts; and (5) this potential has a screening length of the order of a kilometer.

Cone resonance excited by an alternating point charge in a warm magnetoplasma

Abstract: Using the quasi‐static approximation, the potential created by an alternating point charge in a warm magnetoplasma is studied theoretically. The excitation frequency is assumed to be less than both the plasma frequency and the electron gyrofrequency. An approximate expression for the dispersion relation enables us to obtain an analytical result for the potential, which remains finite on the resonance cone, while an interference structure appears either inside or outside the cone, depending on the excitation frequency.