Showing papers on "Electric field published in 1973"

Equilibrium structure of radiation belt electrons

Abstract: The detailed quiet time structure of energetic electrons in the earth's radiation belts is explained on the basis of a balance between pitch angle scattering loss and inward radial diffusion from an average outer zone source. Losses are attributed to a combination of classical Coulomb scattering at low L and whistler mode turbulent pitch angle diffusion throughout the outer plasmasphere. Radial diffusion is driven by substorm associated fluctuations of the magnetospheric convection electric field.

A semiempirical model of large‐scale magnetospheric electric fields

Abstract: Semiempirical analytic formulas for large-scale electric magnetospheric fields are developed that are valid within the inner magnetosphere as well as within the ionosphere. These electric fields drive ionospheric electric currents. Moreover, field-aligned electric currents must exist in order to maintain the magnetospheric electric field configuration. The model calculations are compared and are shown to be consistent with the shape of the plasmapause, the equivalent electric current systems of DP 1 and DP 2, the available electric field observations at ionospheric altitudes, and the observations of field-aligned electric currents.

Electron and hole ionization rates in epitaxial silicon at high electric fields

Abstract: Ionization rates for electrons and holes are extracted from photomultiplication measurements on silicon p+n mesa diodes for electric fields of 2·0 × 105−7·7 × 105 V/cm at temperatures of 22, 50, 100 and 150°C. These results are particularly pertinent to the analysis of high-frequency (∼ 100 GHz) silicon IMPATT diodes. The rates obtained here are in reasonable agreement with previously published data of van Overstraeten and DeMan, although slightly larger in magnitude. Calculated curves of breakdown voltage vs background doping level are presented using the room temperature ionization rates. Also a comparison is made to previously reported rates. The new rates provide a closer agreement between predicted and measured breakdown voltages for breakdown voltages less than 70 V.

Self‐consistent calculation of the motion of a sheet of ions in the magnetosphere

Abstract: Time-dependent magnetospheric electric fields have been computed, including the effects of Birkeland currents from the inner edge of a sheet of ions that moves under the influence of the computed electric fields. Ionospheric currents are also taken self-consistently into account with the use of a time-independent model of ionospheric conductivity that includes day-night asymmetry and auroral enhancements but neglects electric fields parallel to the magnetic field. Ion precipitation and neutral winds are also neglected. The behavior and effects of the ion sheet are studied in a series of model calculations, with the following results. (1) In agreement with the conclusions of E. T. Karlson, L. P. Block, V. M. Vasyliunas, and D. W. Swift, Birkeland currents from the Alfven layer (inner edge of the ion sheet) are found to reduce the electric field earthward of the Alfven layer to a small value by the time a steady state is reached; however, different parts of the electric field earthward of the Alfven layer are eliminated at different rates; one component of the nightside field relaxes to near its low asymptotic value in a few minutes, whereas the dayside field takes hours to relax. (2) If the ion sheet is brought in from the tail by a large cross-tail electric field that stays large, the inner edge of the sheet generally touches the magnetopause boundary layer; however, a decrease in the cross-tail field can cause the Alfven layer to contract and form a complete ring. (3) For the parameters used, a cross-tail potential of 134 kv will bring a sheet of ring current protons in to about L = 4; the results of the model calculations support the idea that convection electric fields bring low-energy ions in from the tail to form the storm time ring current; the minimum geocentric distance to which convection fields can bring the ions is found to be roughly proportional to (ημ/Φ0σρ)1/3, where η is the number of ions per unit magnetic flux, μ is the ion magnetic moment, Φ0 is the cross-tail potential, and σρ is an average height-integrated Pedersen conductivity on the dayside. (4) The nightside Alfven layer naturally produces a dividing line near local midnight, such that particles arriving west of the line drift to the west, whereas those arriving east of the line drift east; this characteristic is often observed in motions of barium clouds and auroral arcs.

Observed relationships between electric fields and auroral particle precipitation

Abstract: Simultaneous electric field and plasma observations with the low-altitude polar-orbiting satellite Injun 5 have provided a comprehensive survey of convection electric fields and their association with magnetospheric plasma phenomena. The most prominent features of the convection electric fields are reversals located at high magnetic latitudes, with generally antisunward convection poleward and sunward convection equatorward of the electric field reversal location. The electric field reversal is interpreted as the boundary between open and closed magnetic field lines. During local day the electric field reversal is observed to coincide with the equatorward boundary of the polar cusp. The plasma flow in the dayside polar cusp region is dominantly E-W, away from the stagnation point, the convection velocities typically being about 1 km/sec. At local evening, 'inverted V' electron precipitation bands are observed near or at the position of the electric field reversal. In the local late-evening sector the electric field reversal becomes less distinct, and often no single well-defined electric field reversal can be identified. In all cases the inverted V electron precipitation events are closely associated with large, typically greater than 30 mV/m, irregular electric field fluctuations with time scales of a few seconds or less.

A study of the electric field in an open magnetospheric model

Abstract: The qualitative properties of an open magnetosphere and its electric field are examined and compared to a simple model of a dipole in a constant field and to actual observations. Many of these properties are found to depend on the separatrix, a curve connecting neutral points and separating different field-line regimes. In the simple model, the electric field in the central polar cap tends to point from dawn to dusk for a wide choice of external fields. Near the boundary of the polar cap electric equipotentials curve and become crescent-shaped, which may explain the correlation of polar magnetic variations with the azimuthal component of the interplanetary magnetic field, reported by Svalgaard. Modifications expected to occur in the actual magnetosphere are also investigated: in particular, it appears that bending of equipotentials may be reduced by cross-field flow during the merging of field lines and that open field lines connected to the polar caps emerge from a long and narrow slot extending along the tail.

A method for analyzing waves in structures consisting of metal strips on dispersive media

Abstract: A method for analysis of wave propagation on structures consisting of periodic metal strips is presented. The method is an extension of earlier theories based on Legendre polynomial expansions of the electric field. The extension allows analysis of strips on any material or layers of materials, provided the electromagnetic properties can be expressed in terms of a wavenumber-dependent permittivity. Layers of dielectrics, piezoelectrics, semiconductors, and metals are typical of the materials of practical interest in connection with surface wave acoustics. Strip configurations such as interdigital transducers, multistrip directional couplers and reflectors, and strip coupled amplifiers can be analyzed by the present approach. Prescriptions for calculating the amplitudes of the space harmonics of the electric field strength are given. Closed-form expressions for strip current and voltage are developed.

Effect of Spatial Dispersion on the Properties of a Semi-Infinite Dielectric

Abstract: In this paper, we explore the properties of a model of a semi-infinite nonlocal dielectric to assess the effect of spatial dispersion on the reflectivity of the material and on the properties of surface polaritons. For the model, the nonlocal form of Maxwell's equations may be solved exactly. The additional boundary conditions follow from Maxwell's equations, and it is not necessary to introduce microscopic considerations to complete the theory. We exhibit closed expressions for the reflectivity of the material, for the case where the electric field is parallel to the plane of incidence, and for the case where it is perpendicular to the plane of incidence. At non-normal incidence, when the electric field vector is parallel to the plane of incidence, structure which owes its origin to spatial-dispersion effects appears in the reflectivity. We show that in the presence of spatial dispersion, the surface polaritons acquire a finite lifetime even in the case where the dielectric is lossless; i.e., in the presence of spatial dispersion the surface polaritons become virtual surface waves. In the quasistatic limit, we obtain an analytic expression for the dependence of the real and imaginary part of the surface-polariton frequency on wave vector in the long-wavelength limit. We then present the theory of frustrated internal reflection of radiation from a prism and crystal configuration similar to that employed in several recent experiments. In a final section, we present the results of some numerical calculations of the reflectivity of the crystal, and the width and position of the dip observed in the frustrated-internal-reflection method, for parameters characteristic of the fundamental exciton line in ZnSe.

Static distortions of a cholesteric planar structure induced by magnetic or ac electric fields

Abstract: We discuss the threshold conditions for the nucleation of a static Helfrich distortion of a planar cholesteric structure under a magnetic field or an ac electric field applied parallel to the helical axis. In opposition to the case of nematics, the magnetic threshold in cholesterics is definitely lower than the threshold field for a transition of the Freedericks type. Under ac electric fields, the behavior of the threshold field with frequency is very similar to the one observed in nematics and depends mainly on the sign of the molecular dielectric anisotropy ea. For ea > 0, the threshold field is practically independent of frequency. For ea < 0, the threshold field diverges for a critical frequency proportional to the charge relaxation frequency. All these theoretical derivations seem to be in good agreement with recent experimental results.

Tightly Bound Electrons in a Uniform Electric Field

Abstract: The energy spectrum of tightly bound electrons in a uniform electric field is studied for finite systems. It forms the Stark ladder for almost all states except those near the band edges (these can be understood as surface states) and in the case of extremely low fields such that the potential drop across the entire sample is of the order of the bandwidth. This fact is independent of the boundary conditions. A two-band tight-binding model is solved, taking into account the interband coupling, and it is found that the spectrum is that of two interspaced Stark ladders. The experimental situation is briefly reviewed and the limitations and feasibility of observing Stark ladders in solids is discussed.

Penetration of thundercloud electric fields into the ionosphere and magnetosphere: 1. Middle and subauroral latitudes

Abstract: The mapping of thundercloud electric fields at middle and subauroral latitudes is investigated analytically as a three-dimensional boundary value problem. The electrical conductivity is represented by several piecewise exponential functions of altitude, and the anisotropy of the medium is taken into account above 70-km altitude. The geomagnetic field lines are assumed to be straight and vertical below 150-km altitude. Electric field strength at great heights depends sensitively on conductivity and thundercloud models used in the calculations. Sample calculations using representative nighttime profiles show that ‘giant’ thunderclouds can produce transverse electric fields of tens of microvolts per meter in the equatorial plane of the midlatitude magnetosphere. In the daytime, corresponding electric fields are about an order of magnitude less. These results suggest that giant thunderclouds may be an important source of localized electric fields that can form field-aligned electron density irregularities in the ionosphere and the magnetosphere.

On the Theory of Hopping Transport in Disordered Semiconductors

Abstract: The electron hopping in presence of both an electric field and a temperature gradient is considered. Expressions for the transport coefficients are obtained, and the temperature dependence of the hopping thermopower is discussed for different temperature regions.

Decay of poloidal rotation in a tokamak plasma

Abstract: Radial electric fields may be built up in a tokamak by several mechanisms such as nonambipolar particle transport or loss, or the inhomogeneous deposition of electric charge which occurs as a result of the injection of fast neutral atoms. The initial effect of the radial fields is to produce a poloidal rotation of the plasma. Such rotation, however, subjects the moving elements of the plasma to energy dissipation by magnetic pumping, which damps the rotation in a period of the order of the ion‐ion collision time. The problem is analyzed for the “plateau” and “banana” regimes by applying the drift kinetic equation, with a simple relaxation collision term, to a slab‐model low‐β plasma. The calculation may be more generally applied to the problem of momentum dissipation for any low‐β long‐mean‐free‐path plasma in a periodic or stochastic magnetic field.

On the generation of potential differences across the membranes of ellipsoidal cells in an alternating electrical field.

Abstract: Particles with a nonconducting membrane, oriented in an alternating electrical field, will show the behaviour of electrical dipoles. Across the membranes there will be generated alternating electrical potential differences, which may be calculated for confocal ellipsoidal cells by solving Laplace's equation. We have evaluated a formula valid generally for single confocal ellipsoidal cells under physiological conditions, the cells being placed with one of their semi-axes parallel to an external electrical field. The values of the generated potential difference, considered at the position of their maximum values, are dependent on the shape and size of the cells, on their orientation to the electrical field and on the frequency and strength of the field. The relaxation frequency depends also on cell shape, size and orientation, but furthermore on the membrane properties and on the conductivities inside and outside the cells. For simple cases like spheres and cylinders perpendicular to the electrical field, our formula will correspond to known expressions. Values for the generated potential differences, form-factors and relaxation frequencies are given for different types of spheroids and at different orientations. Of some practical importance are long prolate spheroids with their long semi-axes parallel to the external field, because only small field strengths are necessary in order to generate large potential differences which may evoke action potentialse.g. in muscle or nerve cells. The significance of this mechanism concerning the determination of protection and safeguard standards for the exposure to low-frequency electrical fields is discussed.

Smith–Purcell radiation from a point charge moving parallel to a reflection grating

Abstract: A rigorous solution is obtained for the problem of radiation from an electric point charge that moves, at a constant speed, parallel to an electrically perfectly conducting grating. The relevant vectorial electromagnetic problem is reduced to two two-dimensional scalar ones. A Green’s-function formulation of the two problems is employed. For both cases, an integral equation of the second kind for the remaining unknown function is derived. This integral equation is solved numerically by a method of moments. Some numerical results for the radiation from a moving point charge above a sinusoidal grating are presented; in particular, the power losses of the point charge have been estimated.

Runaway electrons in a plasma

Abstract: r a uniform electric field is calculated by solving the Fokker-Planck equation numerically. Comparison with other theoretical and experimental results is made. (auth)

Dielectric constant of non-polar fluids

Abstract: The theory of the static dielectric constant of non-polar fluids is re-examined using graph-theoretical techniques. A sample of arbitrary shape in an applied static electric field E 0 is considered...

Power Deposition in a Spherical Model of Man Exposed to I-20-MHz Electromagnetic Fields

Abstract: The induced fields and the associated power deposition in mail exposed to HF electromagnetic (EM) fields have been investigated theoretically using spherical models. The induced electric fields inside the model exposed to either plane wave or near fields can be described adequately by a combination of quasi-static electric and magnetic induction solutions. It is shown that for field impedances less than 1200/spl pi//spl Omega/ the magnetically induced energy absorption predominates. Therefore, H fields must be measured to obtain any estimate of the hazards due to HF exposure. For a 70-kg model of man exposed to a plane wave field, the theory indicates that the time-average power absorption per unit volume is less than 2.5x10/sup -3/ mW/g for each milliwatt per square centimeter incident at 20 MHz and below. This suggests that the thermal safe-exposure levels for the HF band are many orders of magnitude in excess of the 10-mW/cm/sup 2/ level recommended for the microwave region.

Electric field observations by incoherent scatter radar in the auroral zone

Abstract: Analysis of ion drift velocity measurements, made for a 24-hour period in February 1972 by the incoherent scatter radar at Chatanika, Alaska (L = 57), provides a detailed view of electric fields and currents in the auroral zone Large northward electric fields were seen in the evening sector, and an abrupt change to southward occurred at the start of a midnight sector substorm The westward electric field was generally much smaller than the north-south electric field but showed a rapid increase at the time of a westward auroral surge Study of global magnetograms and all-sky camera photographs has led to the identification of five substorms during the 24-hour observation period These substorms were sufficiently separated in time to allow identification of the electric field and current variations in late afternoon, evening, and morning local time sectors

Analyses of techniques for measuring DC and AC electric fields in the magnetosphere

Abstract: Methods for measuring the amplitudes and directions of DC electric fields and the directions, power spectra, and dispersion relations of AC electric fields in the magnetosphere are discussed with emphasis on their applicability in various regimes of the magnetospheric plasma. The two classes of techniques that are discussed are measurement of the bulk flow of the plasma and the potential difference between pairs of separated conductors. The plasma bulk flow discussion includes measurements by ionospheric radar backscatter, whistler mode wave propagation, energetic or thermal particle trajectories, artificial ion cloud motion, probe measurements of bulk flow, vehicle wake analyses, effects of bulk flow on the coupling of antennas, and the bulk flow of an artificial electron beam.

Calculated frequencies and intensities associated with coupling of the proton motion with the hydrogen bond stretching vibration in a double minimum potential surface

Abstract: The influence of the coupling of the proton movement and the H bond stretching vibration in a double minimum potential energy surface on the energy levels, transitions, induced dipole moments and polarisabilities is calcualted ab initio as a function of an electric field for the H5O+2 system. The high polarisability of the hydrogen bonds remains to a large extent unchanged due to the coupling. New types of transitions occur, particularly when the tunnelling frequency and the frequency of the bond stretching vibration are comparable in size. Especially in this case numerous Fermi resonances occur due to the shift of the energy levels in the electric field, which leads to a considerable increase in the number of transitions. It is shown that the change of the frequencies of the transitions due to the induced dipole interaction of the bonds with fields from their environment is a decisive cause of the variety of energy level differences observed as a continuous absorption in the i.r. spectrum of such systems.

Intrinsic photoconduction in anthracene single crystals: Electric field dependence of hole and electron quantum yields

Abstract: For electric fields up to 2 × 104 V/cm applied normal to the a b plane of virgin anthracene crystals, both the hole and electron photocarrier quantum yields increase linearly with field Field‐dependence plots exhibit a slope to intercept ratio of 31 × 10−5 cm/V, a value which is in quantitative agreement with that predicted by Onsager's theory of geminate recombination In nonvirgin crystals, sharply reduced photocarrier quantum yields at low fields are found to result from recombination of free carriers with oppositely charged trapped carriers left behind in the excitation region from previous experiments The free carrier‐trapped charge recombination rates are found to be diffusion controlled