Showing papers on "Electric field published in 1981"

Neoclassical transport of impurities in tokamak plasmas

Abstract: Tokamak plasmas are inherently comprised of multiple ion species. This is due to wall-bred impurities and, in future reactors, will result from fusion-born alpha particles. Relatively small densities nI, of highly charged non-hydrogenic impurities can strongly influence plasma transport properties whenever . The determination of the complete neoclassical Onsager matrix for a toroidally confined multispecies plasma, which provides the linear relation between the surface averaged radial fluxes and the thermodynamic forces (i.e. gradients of density and temperature, and the parallel electric field), is reviewed. A closed set of one-dimensional moment equations is presented for the time evolution of thermodynamic and magnetic field quantities which results from collisional transport of the plasma and two-dimensional motion of the magnetic flux surface geometry. The effects of neutral-beam injection on the equilibrium and transport properties of a toroidal plasma are consistently included.

Evidence for magnetic field reconnection at the Earth's magnetopause

Abstract: Eleven passes of the ISEE satellites through the frontside terrestrial magnetopause were identified, where the plasma velocity in the magnetopause and boundary layer was substantially larger than in the magnetosheath. The nature of the plasma flow, magnetic field, and energetic particle fluxes in these regions were examined, with a view to determining whether the velocity enhancements can be explained by magnetic field reconnection.

A Point Defect Model for Anodic Passive Films I . Film Growth Kinetics

Abstract: A model based on the movement of point defects in an electrostatic field is proposed to interpret the growth behavior of a passive film on a metal surface. This model results in a logarithmic growth law. The theoretical equations derived from the model readily account for experimental data for the growth of a passive film on iron. It is found that the field strength of the film is . The dependence of film/solution interface potential difference on the applied potential (α) was found to be 0.743, and is independent of the identity of the anion in solution. However, the dependence of the potential difference across the film/solution interface on the solutionpH (β) is strongly dependent on the identity of the solution anion.

Estimation of ionospheric electric fields, ionospheric currents, and field-aligned currents from ground magnetic records

Abstract: An approximate method of separating the effects of ionospheric currents from those of field-aligned currents in ground magnetic perturbations observed in high latitudes is developed. The distribution of ionospheric electric fields can also be estimated. The procedure includes the following steps: (1) the calculation of the equivalent ionospheric current function on the basis of magnetic H and D component records on the earth's surface, (2) the computation of the electric potential distribution from the equivalent ionospheric current function by using a simple model of the ionospheric conductivity, (3) the derivation of ionospheric current vectors as well as electric fields and, (4) the derivation of the field-aligned current intensity by taking the divergence of the ionospheric currents. Several examples for both quiet and disturbed conditions are utilized to demonstrate how our method is successful in estimating the intensities of the electric fields and the ionospheric and field-aligned currents in the sense that the estimated values are in good agreement with those observed recently by radar and satellite methods. Significant portions of the H component in nightside auroral latitudes appear to result from the east-west ionospheric currents, called the auroral electrojets, while both the north-south ionospheric current and field-aligned current are almost equally important in producing the D component excursions. It is found that the ionospheric and field-aligned current distributions obtained are not very sensitive to the choice of the ionospheric conductivity model, unless the auroral enhancement is not given in an appropriate place. This indicates that even a simple conductivity distribution inferred from the distribution of the magnetic perturbations can make it possible to estimate the three-dimensional current system with a reasonable accuracy.

The direction of growth of differentiating neurones and myoblasts from frog embryos in an applied electric field.

Abstract: 1. Disaggregated single neurones and myoblasts obtained from the neural tube and somites of Xenopus laevis embryos (stages 17-21) were cultured in the presence of steady small electric fields. 2. Neurites grew preferentially towards the negative pole, or cathode, in field strengths of 7-190 mV/mm. Many turned through considerable angles to do so. This effect disappeared below a threshold level of about 7 mV/mm. 3. Greater numbers of neurones sprouted neurites in cultures exposed to an electric field compared to control cultures. The difference could be as much as tenfold. The threshold level of this phenomenon was about 6-8 mV/mm. Other cell types such as pigment cells and fibroblasts were also stimulated to differentiate in culture by an electric field, although to a lesser extent than neurones. 4. Applied electric fields had no effect on the location of the origin of neurites on the cell body. 5. Spherical myoblasts cultured in applied electric fields (36-170 mV/mm) elongated with a bipolar axis of growth which was perpendicular to the electric field. The response was graded and disappeared at field strengths below 36 mV/mm. 6. It is suggested that in vivo, the direction of neural outgrowth from the neural tube and the strict spatial organization of somites might be under the control, in part, of endogenous electric fields. Possible sources of these are discussed.

Image display apparatus of liquid crystal valve projection type

Abstract: A liquid crystal light valve projection type image display apparatus comprises an electro-optic element and a Schlieren optical system. The electro-optic element has a liquid crystal layer having a dielectric and optical anisotropy. An electric field having a spatial intensity distribution according to an image signal is applied to said liquid crystal at a spatial period, so that a spatially phase-modulated phase diffraction grating is formed in the liquid crystal layer. Thus, a projected image in enlarged form is obtained. The fact that the electric field with a spatial period is applied to the liquid crystal leads to a constant light diffraction angle, and the modulation of the diffraction light intensity in the applied electric field enables an image corresponding to the input image signal to be projected at high light utilization.

Anomalous heating of the polar E region by unstable plasma waves 1. Observations

Abstract: With the incoherent scatter facility at Chatanika, Alaska, we have measured electron temperatures of up to 1200/sup 0/K near 110-km altitude in the polar E region in the presence of strong electric fields. No classical heat process can account for these high temperatures, which are clearly correlated with the dc electric field strength. We show that the enhancement is most probably caused by the unstable plasma waves known to exist in the disturbed polar E region.

Quantitative simulation of a magnetospheric substorm 2. Comparison with observations

Abstract: Results of the computer simulation of the behavior of the inner magnetosphere during the substorm-type event of September 19, 1976, are discussed. The computed electric fields are found to compare satisfactorily with electric fields measured from S3-2, although there are detailed differences. The three general features on which the model and observations are in good agreement are (1) the magnitude and direction of the high-latitude electric field, (2) the degree to which the low-latitude ionosphere is shielded from the high-latitude convection electric field, and (3) the fact that the poleward electric field on the duskside is significantly larger, on the average, than the equatorward electric field on the dawnside. Simple formulas are presented that give rough estimates of global Joule heating rates from observable parameters.

Electric field enhanced emission from non‐Coulombic traps in semiconductors

Abstract: Electric field enhancement of emission from three non‐Coulombic traps has been calculated: the shielded Coulombic potential, the polarization potential, and the dipole potential. Both the Poole‐Frenkel effect and phonon‐assisted tunneling have been included, and both were found to be important. The field effect can be used to distinguish between these potentials on the basis of their long range character. This effect is most important in interpreting the results of capacitance transient studies of deep levels.

Stress-Wave Probing of Electric Field Distributions in Dielectrics

Abstract: The spatial distribution of the electric field within a dielectric sample is shown to be obtainable unambiguously from the time dependence of the open-circuit voltage or short-circuit current during the propagation of a stress wave across the sample. Experiments in which the pressure wave is generated by the impact of a pulsed laser beam on a metal target bonded to the dielectric plate under investigation have led to the first straightforward visualization of electric field distributions in solid dielectrics.

Diffraction efficiency and energy transfer in two-wave mixing experiments with Bi 12 SiO 20 crystals

Abstract: The diffraction efficiency and energy transfer are investigated in photorefractive Bi12SiO20 crystals (BSO). Dependence on fringe spacing, electric fields, light intensity and rise-time constants are reported. The optimum crystallographic orientation for each effect is determined for vertical polarization of the recording beams. It is shown that beam coupling is a very sensitive phenomenon in BSO crystals where charge transport lengths are equivalent to usual fringe spacings. Experimental results are interpreted on the basis of the nonlinear theory of self-diffraction developed by Kukhtarev et al. [10].

Hot-electron injection into the oxide in n-channel MOS devices

Abstract: In recent years, interest in hot-electron injection current in MOS devices has increased due to advances in device concepts and technology. The injection current to the gate is the mechanism for programming FAMOS devices and determines the potential degradation of short-channel MOS devices due to electron trapping in the oxide. This work presents an accurate indirect current measurement technique based on charge transport to the floating gate in a FAMOS structure. The measurement bypasses effects of trapping and local heating, allowing full characterization of parameter, voltage, and temperature dependence down to gate current levels of 10-16A. Based on this characterization, a new qualitative model of hot-electron injection into the oxide is proposed. The basic assumption in the model is the spherical symmetry of the momentum distribution function of the hot electrons. This assumption leads to the experimentally observed dominant role of the lateral electric field in the pinchoff region in determining gate current behavior. The model provides an explanation of gate current parameter and voltage dependence, and suggests correlation between gate current and substrate impact ionization current in a range of operating voltages. This correlation is substantiated experimentally for a range of device parameters and voltages.

Mode suppression means for gyrotron cavities

Abstract: In a gyrotron electron tube of the gyro-klystron or gyro-monotron type, having a cavity supporting an electromagnetic mode with circular electric field, spurious resonances can occur in modes having noncircular electric field. These spurious resonances are damped and their frequencies shifted by a circular groove in the cavity parallel to the electric field.

Microscopic simulation of a strongly coupled hydrogen plasma

Abstract: Results of "molecular dynamics" simulations are reported for a model of a fully ionized strongly coupled hydrogen plasma. Quantum effects are taken into account through the use of effective pair potentials; at short distances, these differ significantly from the bare Coulomb potential. Static properties of the plasma are shown to be well described by hypernetted chain theory. The ion- and electron-velocity autocorrelation functions have been computed and the electrical conductivity turns out to be roughly twice that expected on the basis of the electron self-diffusion coefficient. The predictions of Vlasov theory for the damping and dispersion of the plasmon mode are found to be in generally poor agreement with the results of the computer "experiments", but the collective dynamical properties are successfully described by a memory-function scheme in which explicit account is taken of ion-electron correlations. Prospects for future work are briefly reviewed.

Discrete aurora as the direct result of an inferred high‐altitude generating potential distribution

Abstract: In a previous paper it was shown that spatial changes in the high-altitude magnetospheric electric field E with ▽ · E <0 can result in the generation of large-scale ‘inverted V’ regions of auroral electron precipitation. In the present paper it is shown that smaller-scale precipitation regions, as are required to account for discrete aurora, result from the basic analysis in the previous paper if appropriate structure is introduced in the high-altitude electric field distribution. Using observations of electric fields and precipitating electrons from a rocket flight over discrete aurora the required structure in the electric field is inferred to exit at high altitudes along magnetic field lines connected to the aurora. By using this inferred high-altitude electric potential distribution the ionospheric current continuity equation is solved for the ionospheric potential. The analysis assumes that the field-aligned current is governed by single-particle motion along field lines. The solution gives ionospheric potentials and precipitating electron energy fluxes in good quantitative agreement with those observed throughout the auroral rocket flight. The results in this and the previous paper imply that the ‘inverted V’ scale size (order of 200 km in width) is a natural result of the current versus electric potential relations along auroral field lines and in the ionosphere. This scale size need not be imposed by structure in the high-altitude electric field distribution. Smaller-scale (tens of kilometers) discrete auroral precipitation regions require the same current versus electric potential relations, but the scale size is imposed by structure in the high-altitude electric potential distribution. The cause of this structure is not considered in the present analysis.

Shape of a drop in an electric field

Abstract: The shape of an axisymmetric dielectric drop in a uniform electric field is computed numerically. The problem is formulated as a nonlinear integro‐differential system of equations. They are discretized and the resulting algebraic system is solved by Newton’s method. The results show that when the dielectric constant e is larger than a critical value ec, the drop develops two obtuse‐angled conical points at its ends for a certain field strength. For e

The small‐scale structure of electrostatic shocks

Abstract: It is noted that small-scale regions of large electric fields have been observed above the auroral zone by the S3-3 satellite. The data from five such electrostatic shocks are examined in great detail. The three higher altitude shocks (all above 5,700 km) are found to be associated with upward-going ion beams, indicating that the potential associated with the shock closed below the satellite to give rise to the parallel electric field required for the acceleration of the ion beam. In all these cases, electrostatic ion cyclotron waves are found to be adjacent to the shock and to extend throughout the upward-going ion beam region. The lack of noticeable Doppler shift in the electrostatic ion cyclotron waves in association with large convective drift velocities is seen as indicating that the wavelength of the electrostatic ion cyclotron wave can be several kilometers and that the potential difference within the wave can be on the order of 100 V.

Optical electric-field enhancement at a metal surface arising from surface-plasmon excitation.

Abstract: Surface plasmons can be excited on a metal by an external plane-wave beam through the use of prism or grating couplers or by introducing roughness. This can enhance the electric field at the surface compared with that in the incident beam, and it has been suggested that this effect is an important aspect of surface-enhanced Raman scattering. A general upper limit for this field enhancement is derived on the basis of energy conservation. Numerical results are given for Ag, Au, and Cu. With a perfect coupler on a Ag surface, the maximum increase of the square of the electric field in the 2–3-eV range is ≅300. On randomly roughened surfaces, the estimated enhancements are of the order of unity.

Electric birefringence of restriction enzyme fragments of DNA: Optical factor and electric polarizability as a function of molecular weight

Abstract: The electric birefringence of restriction enzyme fragments of DNA has been investigated as a function of DNA concentration, buffer concentration, and molecular weight, covering a molecular weight range from 80 to 4364 base pairs (bp) (6 × 104–3 × 106 daltons). The specific birefringence of the DNA fragments is independent of DNA concentration below 20 μg DNA/ml, but decreases with increasing buffer concentration, or conductivity, of the solvent. At sufficiently low field strengths, the Kerr law is obeyed for all fragments. The electric field at which the Kerr law ends is inversely proportional to molecular weight. In the Kerr law region the rise of the birefringence is accurately symmetrical with the decay for fragments ≤ 389 bp, indicating an induced dipole orientation mechanism. The optical factor calculated from a 1/E extrapolation of the high field birefringence data is −0.028, independent of molecular weight; if a 1/E2 extrapolation is used, the optical factor is −0.023. The induced polarizability, calculated from the Kerr constant and the optical factor, is proportional to the square of the length of the DNA fragments, and inversely proportional to temperature. Saturation curves for DNA fragments ≤ 161 bp can be described by theoretical saturation curves for induced dipole orientation. The saturation curves of larger fragments are broadened, because of a polarization term which is approximately linear in E, possibly related to the saturation of the induced dipole in high electric fields. This “saturated induced dipole” is found to be 6400 D, independent of molecular weight. The melting temperature of a 216-bp sample is decreased 6°C in an electric field of 8 kV/cm, because the lower charge density of the coil form of DNA makes it more stable in an electric field than the helix form.

Measurements of ferroelectric switching characteristics in polyvinylidene fluoride

Abstract: The ferroelectric switching characteristics of polyvinylidene fluoride have been investigated by the time domain measurement of electric displacement under a step‐function field up to 200 MV/m at temperatures between −100 and 20 °C. Almost complete reversal of polarization is found to occur in a fairly short time if the applied field is sufficiently high. The switching time is 4 μsec at 20 °C under a field of 200 MV/m and increases significantly as either field or temperature decreases. The rate of change of polarization is greater than the rate associated with a single relaxation process. This is an indication of cooperative effects in the switching process of this ferroelectric polymer.

Nature of the charge distribution in proteins

Abstract: The significance of the fairly strong electric fields produced by the electric macrodipole of the α-helix and by ionic charges in stabilizing globular proteins has been recognized for some years1–4. These electrostatic interactions are involved at the active sites of functional proteins in binding a substrate or a coenzyme, or in enhancing enzymatic reaction rates2–5, and are unique among the many interactions affecting protein structure and function because of their long range, extending over the whole protein molecule. We have now analysed the distribution of the distances separating the ionic charges (ionized groups and the apparent charges at the termini of the α-helices) for more than 44,000 charge pairs in 14 proteins. Our results show that charges in the proteins are, on average, surrounded by charges of opposite sign. Previous calculation of the electric potential near the helix termini has shown that the electrostatic effect of the α-helix dipole is equivalent to the effect of one-half of a positive unit charge at the N-terminus of the α-helix and one-half of a negative unit charge at the C-terminus3. We report here that the macrodipole of the α-helix has the same order of contribution to stabilizing the native protein conformation as ionized groups.

The plasma wave and quasi-static electric field instrument /PWI/ for dynamics Explorer-A

Abstract: It is explained that the Plasma Wave Instrument (PWI) on Dynamics Explorer-A measures both plasma wave phenomena and quasi-static electric fields. The quasi-static electric fields are measured parallel to the spin axis of the spacecraft in a range of 2 mV/m to 2 V/m and perpendicular to the spin axis 0.5 mV/m to 2 V/m at 16 samples/s. The ac electric field sensors include a 200-m tip-to-tip long wire antenna and a 0.6-m short electric antenna, both of which are perpendicular to the spin axis, and a 9-m tip-to-tip tubular antenna parallel to the spin axis. AC electric wave fields are measured over a frequency range of 1 Hz to 2 MHz and over an amplitude range of 0.03 microvolt/m to 100 mV/m.

Theory of a plasma column sustained by a surface wave

Abstract: A self-consistent theory of a cylindrical plasma column sustained by a surface wave is derived which gives absolute values and radial profiles of electron density, electron temperature, HF electric field intensity and atomic excited state densities as a function of gas pressure, wave frequency and HF absorbed power. The basic equations are the continuity and the momentum transfer equations for both electrons and ions, the equations for the wave electric field and the power balance equation for electrons. The theory is applicable in the low attenuation regime. The plasma and field profiles are significantly different from the classical Bessel type and the field profiles of surface waves in homogeneous media, respectively. Depending on pressure the radial distribution of excited atoms is either flat or increases to reach a maximum near the wall.