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Showing papers on "Electric field published in 1998"


01 Mar 1998
TL;DR: The quantum-confined Stark effect in single cadmium selenide (CdSe) nanocrystallite quantum dots was studied, suggesting the potential use of these dots in electro-optic modulation devices.
Abstract: The quantum-confined Stark effect in single cadmium selenide (CdSe) nanocrystallite quantum dots was studied. The electric field dependence of the single-dot spectrum is characterized by a highly polarizable excited state (∼10 5 cubic angstroms, compared to typical molecular values of order 10 to 100 cubic angstroms), in the presence of randomly oriented local electric fields that change over time. These local fields result in spontaneous spectral diffusion and contribute to ensemble inhomogeneous broadening. Stark shifts of the lowest excited state more than two orders of magnitude larger than the linewidth were observed, suggesting the potential use of these dots in electro-optic modulation devices.

696 citations


Journal ArticleDOI
TL;DR: In this article, a nematic liquid crystal cell associated with a homogeneously aligned to twisted transition of a liquid crystal director was fabricated, which exhibits a high transmittance ratio as well as a wide viewing angle.
Abstract: We have fabricated a nematic liquid crystal cell associated with a homogeneously aligned to twisted transition of a liquid crystal director. In the absence of an electric field, the liquid crystal molecule is homogeneously aligned under the crossed polarizers, and thus the cell appears to be black. When a fringe field induced by interdigital electrodes is applied, liquid crystal molecules rotate in plane even above electrodes and thus the cell transmits light. The device exhibits a high transmittance ratio as well as a wide viewing angle, which solves a long standing problem of low transmittance existing in the conventional in-plane switching mode. We show that the distance between electrodes smaller than the width of an electrode and cell gap is required for generating fringe field with applied voltage and rotating molecules above electrodes. We also investigate the mechanism of fringe-field switching and dependence of electro-optic effect on different cell conditions and dielectric anisotropy of liquid ...

656 citations


Journal ArticleDOI
TL;DR: In this paper, the authors report observations of fast solitary waves that are ubiquitous in downward current regions of the mid-altitude auroral zone and propose that these nonlinear structures play a key role in supporting parallel electric fields.
Abstract: We report observations of “fast solitary waves” that are ubiquitous in downward current regions of the mid-altitude auroral zone. The single-period structures have large amplitudes (up to 2.5 V/m), travel much faster than the ion acoustic speed, carry substantial potentials (up to ∼100 Volts), and are associated with strong modulations of energetic electron fluxes. The amplitude and speed of the structures distinguishes them from ion-acoustic solitary waves or weak double layers. The electromagnetic signature appears to be that of an positive charge (electron hole) traveling anti-earthward. We present evidence that the structures are in or near regions of magnetic-field-aligned electric fields and propose that these nonlinear structures play a key role in supporting parallel electric fields in the downward current region of the auroral zone.

531 citations


Journal ArticleDOI
TL;DR: The rotational excitation of small interstellar grains and the resulting electric dipole radiation from spinning dust was discussed in this paper, where the authors discussed the excitation and damping of grain rotation by collisions with neutrals, collisions with ions, plasmas drag, and formation of H2 on the grain surface.
Abstract: We discuss the rotational excitation of small interstellar grains and the resulting electric dipole radiation from spinning dust Attention is given to excitation and damping of grain rotation by collisions with neutrals, collisions with ions, "plasma drag," emission of infrared radiation, emission of electric dipole radiation, photoelectric emission, and formation of H2 on the grain surface Electrostatic "focusing" can substantially enhance the rate of rotational excitation of grains colliding with ions Under some conditions, "plasma drag"—due to interaction of the electric dipole moment of the grain with the electric field produced by passing ions—dominates both rotational damping and rotational excitation Emissivities are estimated for dust in different phases of the interstellar medium, including diffuse H I clouds, warm H I, low-density photoionized gas, and cold molecular gas Spinning dust grains could explain much, and perhaps all, of the 14-50 GHz background component recently observed by Kogut et al, de Oliveira-Costa et al, and Leitch et al Future sensitive measurements of angular structure in the microwave sky brightness from the ground and from space should detect this emission from high-latitude H I clouds It should be possible to detect rotational emission from small grains by ground-based pointed observations of molecular clouds, unless these grains are less abundant there than is currently believed

505 citations


Journal ArticleDOI
TL;DR: In this paper, the underlying physics behind the success of the thermochemical E model in describing time-dependent dielectric breakdown (TDDB) in SiO2 thin films is presented.
Abstract: The underlying physics behind the success of the thermochemical E model in describing time-dependent dielectric breakdown (TDDB) in SiO2 thin films is presented. Weak bonding states can be broken by thermal means due to the strong dipolar coupling of intrinsic defect states with the local electric field in the dielectric. This dipole-field coupling serves to lower the activation energy required for thermal bond-breakage and accelerates the dielectric degradation process. A temperature-independent field acceleration parameter γ and a field-independent activation energy ΔH can result when different types of disturbed bonding states are mixed during TDDB testing of SiO2 thin films. While γ for each defect type alone has the expected 1/T dependence and ΔH shows a linear decrease with electric field, a nearly temperature-independent γ and a field-independent ΔH can result when two or more types of disturbed bonding states are mixed. The good agreement between long-term TDDB data and the thermochemical model su...

438 citations


Journal ArticleDOI
TL;DR: The POLAR plasma wave instrument often detects coherent electric field structures in the high altitude polar magnetosphere, which are found to move both up and down the ambient magnetic field as mentioned in this paper.
Abstract: The POLAR plasma wave instrument often detects coherent electric field structures in the high altitude polar magnetosphere. The structures appear to be positively charged potentials which are found to move both up and down the ambient magnetic field. Typical estimated velocities and parallel scale sizes are the order of 1000 km/s and 100-1000 meters, respectively. We have observed the structures at radial distances of 2.02 to 8.5 Re and L shells of 6 - 12+, although the they are likely to occur over a broader range of space than suggested by this initial study. The structures are responsible for some of the the spectral features of broadband electrostatic noise, and are similar to recent GEOTAIL and FAST observations of solitary waves.

351 citations


Journal ArticleDOI
TL;DR: In this article, an analytic theory for dark injection from a metallic electrode into a random hopping system, e.g., a conjugated polymer or a molecularly doped polymer, is presented.
Abstract: An analytic theory is presented for dark injection from a metallic electrode into a random hopping system, e.g., a conjugated polymer or a molecularly doped polymer. It encompasses injection of a charge carrier from the Fermi level of the electrode into tail states of the distribution of hopping states of the dielectric followed by either return of the charge carrier to the electrode or diffusive escape from the attractive image potential. The latter process resembles Onsager-type geminate pair dissociation in one dimension. The theory yields the injection current as a function of electric field, temperature and energetic width of the distribution of hopping states. At high electric fields it resembles that the current calculated from Fowler-Nordheim tunneling theory although tunneling transitions are not included in the theory. Good agreement with experimental data obtained for diode structures with conjugated polymers as a dielectric is found.

300 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present observations of intense, bipolar, electrostatic structures in the transition region of the terrestrial bow shock from the Wind spacecraft and interpret the observations as small scale convecting unipolar potential structures, consistent with simulations of electron phase space holes.
Abstract: We present observations of intense, bipolar, electrostatic structures in the transition region of the terrestrial bow shock from the Wind spacecraft. The electric field signatures are on the order of a tenth of a millisecond in duration and greater than 100 mV/m in amplitude. The measured electric field is generally larger on the smaller dipole antenna, indicating a small spatial size. We compare the potential on the two dipole antennas with a model of antenna response to a Gaussian potential profile. This result agrees with a spatial scale determined by convection and gives a characteristic scale size of 2–7 λd. We interpret the observations as small scale convecting unipolar potential structures, consistent with simulations of electron phase space holes and discuss the results in the context of electron thermalization at strong collisionless shocks.

294 citations


Proceedings ArticleDOI
17 Aug 1998
TL;DR: In this article, the authors investigated the degradation of the breakdown electric field resulting from surface roughness, the effect of gas pressure and the performance of the insulator structure under bipolar stress.
Abstract: The authors investigate a novel insulator concept which involves the use of alternating layers of conductors and insulators with periods less than 1 mm. These structures perform many times better (about 1.5 to 4 times higher breakdown electric field) than conventional insulators in long pulse, short pulse and alternating polarity applications. They present their ongoing studies investigating the degradation of the breakdown electric field resulting from surface roughness, the effect of gas pressure and the performance of the insulator structure under bipolar stress. Further, they present their initial modeling studies.

283 citations


Journal ArticleDOI
TL;DR: In this article, the authors demonstrate that parallel electric fields may be a fundamental particle acceleration mechanism in astrophysical plasmas by comparing the inferred parallel potentials of electrostatic shocks with particle energies.
Abstract: Electric field and energetic particle observations by the Fast Auroral Snapshot (FAST) satellite provide convincing evidence of particle acceleration by quasi-static, magnetic-field-aligned (parallel) electric fields in both the upward and downward current regions of the auroral zone. We demonstrate this by comparing the inferred parallel potentials of electrostatic shocks with particle energies. We also report nonlinear electric field structures which may play a role in supporting parallel electric fields. These structures include large-amplitude ion cyclotron waves in the upward current region, and intense, spiky electric fields in the downward current region. The observed structures had substantial parallel components and correlative electron flux modulations. Observations of parallel electric fields in two distinct plasmas suggest that parallel electric fields may be a fundamental particle acceleration mechanism in astrophysical plasmas.

282 citations


Journal ArticleDOI
TL;DR: The FAST satellite mission as discussed by the authors investigates plasma processes occurring in the low altitude auroral acceleration region, where magnetic field-aligned currents couple global magnetospheric current systems to the high latitude ionosphere.
Abstract: The FAST satellite mission investigates plasma processes occurring in the low altitude auroral acceleration region, where magnetic field-aligned currents couple global magnetospheric current systems to the high latitude ionosphere. In the transition region between the hot tenuous magnetospheric plasma and the cold, dense ionosphere, these currents give rise to parallel electric fields, particle beams, plasma heating, and a host of wave-particle interactions. FAST instruments provide observations of plasma particles and fields in this region, with excellent temporal and spatial resolution combined with high quantitative accuracy. The spacecraft data system performs on-board evaluation of the measurements to select data “snapshots” that are stored for later transmission to the ground. New measurements from FAST show that upward and downward current regions in the auroral zone have complementary field and particle features defined by upward and downward directed parallel electric field structures and corresponding electron and ion beams. Direct measurements of wave particle interactions have led to several discoveries, including Debye-scale electric solitary waves associated with the acceleration of upgoing electron beams and ion heating, and the identification of electrons modulated by ion cyclotron waves as the source of flickering aurora. Detailed quantitative measurements of plasma density, plasma waves, and electron distributions associated with auroral kilometric radiation source regions yield a consistent explanation for AKR wave generation.

Journal ArticleDOI
TL;DR: In this paper, a modification of dipole emission that is due to its optical environment is calculated for planar layered structures, and the dipole is included by using additive source terms for the electric field that depend on dipole orientation and wave polarization.
Abstract: Modification of dipole emission that is due to its optical environment is calculated for planar layered structures. The layers are optically described by standard matrix techniques, and the dipole is included by using additive source terms for the electric field that depend on dipole orientation and wave polarization. These source terms also allow coupling through evanescent waves. We emphasize the applicability of this method to cases in which the power distribution into various modes is affected: dipole emission into guided modes and emission distribution into the various modes of structures that contain multilayer reflectors, such as microcavities.

Journal ArticleDOI
TL;DR: In this article, a new type of spatially coherent plasma structure that is associated with quasistatic, magnetic-field-aligned electric fields in space plasmas is reported.
Abstract: We report a new type of spatially coherent plasma structure that is associated with quasistatic, magnetic-field-aligned electric fields in space plasmas. The solitary structures form in a magnetized plasma, are multidimensional, and are highly supersonic. The size along ${\mathbf{B}}_{0}$ is a few ${\ensuremath{\lambda}}_{D}$ and increases with increasing amplitude, unlike a classical soliton. The perpendicular size appears to be influenced by ion motion. We show that the structures facilitate ion-electron momentum exchange and suggest that an aggregate of structures may play a role supporting large-scale, parallel electric fields.

Journal ArticleDOI
TL;DR: In this article, it was shown that the sub-Alfvenic, low-beta interaction can be described by an anisotropic conducting atmosphere joined to an Alfven wing as one extreme case and the Jovian ionosphere as the other extreme case.
Abstract: Recent observations by the Galileo spacecraft and Earth-based techniques have motivated us to reconsider the sub-Alfvenic interaction between the Galilean satellites of Jupiter and the magnetosphere. (1) We show that the atomic processes causing the interaction between the magnetoplasma and a neutral atmosphere can be described by generalized collision frequencies with contributions from elastic collisions, ion pickup, etc. Thus there is no fundamental difference in the effect of these processes on the plasma dynamics claimed in the recent literature. For a magnetic field configuration including possible internal fields, we show that the sub-Alfvenic, low-beta interaction can be described by an anisotropically conducting atmosphere joined to an Alfven wing as one extreme case and the Jovian ionosphere as the other extreme case. (2) The addition of a small magnetic field of internal origin does not modify the general Alfven wing model qualitatively but only quantitatively. All magnetic moments discussed in the literature for In are small in this sense. For an aligned internal dipole and ambient Jovian magnetic field the interaction will be enhanced by focusing of the electric field. (3) A qualitative change occurs by the additional occurrence of closed magnetic field lines for larger internal magnetic fields as in the case of Ganymede. Here the focusing is even enhanced. (4) The first discussion of nonstationary plasma flows at the satellites shows that electromagnetically induced magnetic fields may play an important role if the satellite interiors are highly conducting. From the point of view of the external excitation, induction effects may be strong for Callisto, In, Europa, and Ganymede in order of decreasing importance. The magnetic field observations at the first Callisto encounter can be explained by these effects.

Journal ArticleDOI
TL;DR: In this paper, the authors investigate self-consistent particle acceleration near a pulsar polar cap by the electrostatic field due to the effect of inertial frame dragging and find that stable acceleration zones may occur at some distance above the surface, where curvature radiation dominates the electron and positron energy losses.
Abstract: We investigate self-consistent particle acceleration near a pulsar polar cap (PC) by the electrostatic field due to the effect of inertial frame dragging. Test particles gain energy from the electric field parallel to the open magnetic field lines and lose energy by both curvature radiation (CR) and resonant and nonresonant inverse Compton scattering (ICS) with soft thermal X-rays from the neutron star (NS) surface. Gamma rays radiated by electrons accelerated from the stellar surface produce pairs in the strong magnetic field, which screen the electric field beyond a pair formation front (PFF). Some of the created positrons can be accelerated back toward the surface and produce γ-rays and pairs that create another PFF above the surface. We find that ICS photons control PFF formation near the surface, but because of the different angles at which the electron and positron scatter the soft photons, positron-initiated cascades develop above the surface and may screen the accelerating electric field. Stable acceleration from the NS surface is therefore not possible in the presence of dominant ICS energy losses. However, we find that stable acceleration zones may occur at some distance above the surface, where CR dominates the electron and positron energy losses and there is up-down symmetry between the electron and positron PFFs. We examine the dependence of CR-controlled acceleration zone voltage, width, and height above the surface on parameters of the pulsar and its soft X-ray emission. For most pulsars, we find that acceleration will start at a height of 0.5-1 stellar radii above the NS surface.

Journal ArticleDOI
TL;DR: DNA molecules can be manipulated in aqueous solution in a manner analogous to optical trapping by mixing static and oscillating electric fields, which should be useful in microdevices for manipulation of small quantities or single molecules of DNA.

Journal ArticleDOI
TL;DR: In this article, the authors show that dispersionless injections can be understood as a consequence of changes in the electric and magnetic fields by modeling an electron injection event observed early on January 10, 1997 by means of a test-particle simulation.
Abstract: The term “dispersionless injection” refers to a class of events which show simultaneous enhancement (injection) of electrons and ions with different energies usually seen at or near geosynchronous orbit. We show that dispersionless injections can be understood as a consequence of changes in the electric and magnetic fields by modeling an electron injection event observed early on January 10, 1997 by means of a test-particle simulation. The model background magnetic field is a basic dipole field made asymmetrical by a compressed dayside and a weakened nightside. The transient fields are modeled with only one component of the electric field which is westward and a consistent magnetic field. These fields are used to model the major features of a dipolarization process during a substorm onset. We follow the electrons using a relativistic guiding center code. Our simulation results, with an initial kappa electron energy flux spectrum, reproduce the observed electron injection and subsequent drift echoes and show that the energization of injected electrons is mainly due to betatron acceleration of the preexisting electron population at larger radial distances in the magnetotail by transient fields.

Journal ArticleDOI
TL;DR: In this paper, the authors used ac-coupled sensors, induction coils for the magnetic field, and an electric field amplifier developed for marine controlled-source applications for seafloor magnetotelluric measurements.
Abstract: Induction in electrically conductive seawater attenuates the magnetotelluric (MT) fields and, coupled with a minimum around 1 Hz in the natural magnetic field spectrum, leads to a dramatic loss of electric and magnetic field power on the sea floor at periods shorter than 1000 s. For this reason the marine MT method traditionally has been used only at periods of 103 to 105 s to probe deep mantle structure; rarely does a sea‐floor MT response extend to a 100-s period. To be useful for mapping continental shelf structure at depths relevant to petroleum exploration, however, MT measurements need to be made at periods between 1 and 1000 s. This can be accomplished using ac-coupled sensors, induction coils for the magnetic field, and an electric field amplifier developed for marine controlled‐source applications. The electrically quiet sea floor allows the attenuated electric field to be amplified greatly before recording; in deep (1-km) water, motional noise in magnetic field sensors appears not to be a proble...

Journal ArticleDOI
01 Oct 1998-Nature
TL;DR: In this paper, it is shown that the rate at which metal-induced crystallization takes place is markedly enhanced in the presence of an electric field, and a thin-film transistor fabricated from such a film exhibits a field-effect mobility of 58 cm2.
Abstract: Thin films of polycrystalline silicon are of great importance for large-area electronic applications, providing, for example, the switching electronics in many flat-panel displays. Polycrystalline silicon is typically produced by annealing films of amorphous silicon1 that have been deposited from the vapour phase, and much research is focused on lowering the crystallization temperature. It is known that the solid-phase crystallization temperature of amorphous silicon can be reduced by the addition of certain metals2, such as nickel3. Here we show that the rate at which this metal-induced crystallization takes place is markedly enhanced in the presence of an electric field. For example, the crystallization time at 500 °C decreases from 25 hours to 10 minutes on application of a modest (80 V cm−1) electric field. No residual amorphous phase can be detected in the films. A thin-film transistor fabricated from such a film exhibits a field-effect mobility of 58 cm2 V−1 s−1, thereby demonstrating the practical utility of these materials.

Journal ArticleDOI
TL;DR: In this paper, numerical simulations were performed to predict the performance of microwave plasma reactors with various reactor geometries, including the calculation of the electric field distribution using the finite integration theory and the determination of the plasma density distribution based on a breakdown field algorithm.
Abstract: Numerical simulations were performed to predict the performance of microwave plasma reactors with various reactor geometries. The simulations include the calculation of the electric field distribution using the finite integration theory and the determination of the plasma density distribution based on a breakdown field algorithm. One reactor geometry with a cavity having the shape of a rotational ellipsoid turned out to be very promising. The electric field within this cavity exhibits two pronounced maxima at the two focal points of the ellipsoid. By coupling microwave energy into one maximum via an antenna, large electric field strengths can be generated in the counter maximum. This effect has been used to excite intense discharges that are very stable, spatially extended, homogeneous, and free from wall contact. These discharges were employed for the chemical vapor deposition of large area diamond wafers.

Journal ArticleDOI
TL;DR: In this article, the authors derived the energy release rate for an elliptical cylinder cavity or a crack inside an infinite piezoelectric medium under combined mechanical-electrical loadings via the Stroh formalism and well confirmed by finite element analysis.

Journal ArticleDOI
TL;DR: In this paper, a polarization switching model for polycrystalline ferroelectric ceramics was developed, in which a single ferro-electric crystallite in a ceramic, which is subjected to an electric field and/or a stress, undergoes a complete polarization change and a corresponding strain change if the resulting reduction in potential energy exceeds a critical value per unit volume of switching material.
Abstract: A polarization switching model for polycrystalline ferroelectric ceramics has been developed. It is assumed that a single ferroelectric crystallite in a ceramic, which is subjected to an electric field and/or a stress, undergoes a complete polarization change and a corresponding strain change if the resulting reduction in potential energy exceeds a critical value per unit volume of switching material. The crystallite’s switch causes a change in the interaction of its field and stress with the surrounding crystallites, which is modeled by the Eshelby inclusion method to provide a mean field estimate of the effect. Thus the model accounts for the effects of the mean electric and stress fields arising from the constraints presented by surrounding crystallites as well as the externally applied mechanical and electrical loads. The switching response of the ceramic polycrystal is obtained by averaging over the behavior of a large number of randomly oriented crystallites. The model, along with the linear dielect...

Journal ArticleDOI
06 Feb 1998-Langmuir
TL;DR: In this paper, the authors investigated the physical ground of the electrorheological (ER) effect and found that the slow polarization, especially the interfacial polarization rather than the Debye polarization, might be responsible for the observed phenomena.
Abstract: The conductive, dielectric, and surface properties of several water-free polymer or inorganic material based ER fluids, as well as their response times, are investigated to elucidate the physical ground of the electrorheological (ER) effect. It is found that the slow polarization, especially the interfacial polarization rather than the Debye polarization, might be responsible for the observed phenomena. A possible ER mechanism is proposed as follows: a large interfacial polarization would facilitate the particle to attain a large amount of charges on the surface, then leading to the turn of particle along the direction of an electric field to form a fibrillation structure; the strength of fibrillation chains is thus determined by the particle polarization force, i.e., the particle dielectric constant. The rationality that the marked interfacial polarization would likely drive the particles to turn is theoretically addressed on the basis of experimental results.

Journal ArticleDOI
TL;DR: In this article, the radial structures of plasma rotation and radial electric field in toroidal plasmas are reviewed and the anomalous perpendicular viscosity, which is dominant in dictating the toroidal rotation in tokamaks, is discussed.
Abstract: Experimental studies on radial structures of plasma rotation and radial electric field in toroidal plasmas are reviewed. In this context, the perpendicular and parallel viscosities that determine the toroidal/poloidal rotation velocity and radial electric field profiles are discussed. Experimental studies of parallel viscosity and the comparison with the neoclassical values in heliotron/torsatron and stellarator devices, are described. The anomalous perpendicular viscosity, which is dominant in dictating the toroidal rotation in tokamaks, is also discussed. Even without external momentum input, plasma rotation and radial electric field are sustained by non-ambipolar flux of off-diagonal terms of the transport matrix. The effects of radial electric field shear and the bulk rotation velocity shear on the improvement of particle, momentum and heat transport in bulk and edge plasma regimes are also discussed.

Journal ArticleDOI
TL;DR: In this article, the spatial extent of the plasma wave and the spectrum of the accelerated electrons are simultaneously measured when the relativistic plasma wave associated with Raman forward scattering of an intense laser beam reaches the wave breaking limit.
Abstract: The spatial extent of the plasma wave and the spectrum of the accelerated electrons are simultaneously measured when the relativistic plasma wave associated with Raman forward scattering of an intense laser beam reaches the wave breaking limit. The maximum observed energy of 94 MeV is greater than that expected from the phase slippage between the electrons and the accelerating electric field as given by the linear theory for preinjected electrons. The results are in good agreement with 2D particle-in-cell code simulations of the experiment.

Journal ArticleDOI
TL;DR: In this paper, the authors present the first simultaneous in situ measurements of the large-scale convection electric field and the ring current induced magnetic field perturbations in the equatorial plane of the inner magnetosphere and compares them to the evolution of major geomagnetic storms as characterized by Dst.
Abstract: This paper presents the first simultaneous in situ measurements of the large-scale convection electric field and the ring current induced magnetic field perturbations in the equatorial plane of the inner magnetosphere and compares them to the evolution of major geomagnetic storms as characterized by Dst. The measurements were obtained from the University of California, Berkeley double-probe electric field experiment and the Air Force Geophysics Laboratory fluxgate magnetometer on the CRRES spacecraft. This spacecraft had an apogee near geosynchronous orbit and a perigee near 300 km altitude. We focus on the major geomagnetic storm on March 24, 1991, for which the maximum negative excursion of Dst was about −300 nT. During the main phase of the storm, the large-scale electric field repeatedly penetrated earthward, maximizing between L = 2 and L = 4 with magnitudes of 6 mV/m. These magnitudes were larger than quiet time values of the electric field by a factor of 60 or more. Electric potential drops across the dusk region from L = 2 to L = 4 ranged up to 50–70 kV in concert with increases in Kp up to 9 and dDst/dt (an indicator of the net ring current injection rate) which ranged up to −50 nT/hr. These electric fields lasted for time periods of the order of an hour or more and were capable of injecting ring current ions from L = 8 to L = 2.4 and energizing particles from initial plasma sheet energies of 1–5 keV up to 300 keV through conservation of the first adiabatic invariant. The data obtained during the recovery phase of this storm provide the first direct experimental evidence in the equatorial plane that the electric field is systematically diminished or shielded earthward of the inner edge of the ring current during this phase of the geomagnetic storm. Also observed during the 2-week recovery phase were episodic enhancements in the electric field which coincided and were colocated with enhancements of in situ ring current intensity and which also coincided with decreases in Dst. These enhancements in the electric field and in the ring current magnetic field perturbation occurred at progressively larger radial positions as the recovery phase continued. Evidence for regions of reversed convection near midnight during the recovery phase is provided. An unexpected and important feature of this data set, during both main and recovery phases, near 1800–2100 MLT, is that electric fields are often much stronger earthward of L = 4 or L = 5 than at positions more distant than L = 6. This suggests important features of the interaction between the hot ring current plasma and the large-scale electric field in the inner magnetosphere are not yet understood.

Journal ArticleDOI
TL;DR: In this article, the average structure of the inner magnetospheric electric field for different geomagnetic activity levels was determined using measurements made with the University of California, Berkeley/Air Force Geophysics Laboratory electric field instrument on the CRRES spacecraft.
Abstract: Measurements made with the University of California, Berkeley/Air Force Geophysics Laboratory electric field instrument on the CRRES spacecraft are examined to determine the average structure of the inner magnetospheric electric field for different geomagnetic activity levels. Data were gathered between L=2.5 and L=8.5 over the period from January to October 1991 in the local time sector between 1200 and 0400 magnetic local time. The average dawn-dusk component of the electric field was nearly always duskward, scaling in magnitude from 0.05 mV/m to 1.5 mV/m as Kp increased from 0 to 9-. The data indicate that the electric field is shielded out of the inner magnetosphere, with the shielding distance starting at about L=5.0 for Kp=1 and moving 0.5 RE earthward for every unit increase in Kp. There is evidence that the electric field penetrates below L=2.5 for Kp ≥ 5. The most interesting aspect of this statistical study is the development for moderate to high Kp of a region of enhanced electric field between L=3.5 and L=6. For moderately active conditions the electric field does not decrease monotonically as one moves earthward. Instead, it increases to a broad local maximum near the position where the ring current is typically observed to be the strongest, falling off earthward of that position. The electric field magnitude can be a factor of 2 or more larger at this location than at higher L values. These results are discussed in the context of large-scale flows and the effects of hot plasma in the inner magnetosphere.

Journal ArticleDOI
TL;DR: In this article, the authors used the pulsed electroacoustic method to obtain time-dependent space charge profiles in 3-mm thick XLPE (crosslinked low-density polyethylene) cable insulation under dc electric fields.
Abstract: This report deals with space charge behavior in PE (polyethylene) under dc fields. Direct observation of time-dependent space charge profiles in 3-mm thick XLPE (crosslinked low-density polyethylene) cable insulation under dc electric fields was performed using the pulsed electroacoustic method. Stable hetero charges were formed when the field was as low as 0.2 MV/cm, and intermittent generation of packet shaped space charges and their propagation through the insulation were observed when the field was as high as 0.7 MV/cm. These phenomena were reproduced in sheet specimens of XLPE and LDPE (low-density polyethylene). It was found that hetero charges resulted from heat treatment of the XLPE specimen containing antioxidant and acetophenone, which is one of the crosslinking by-products, suggesting dissociation of the antioxidant through solvation at high temperature by acetophenone. The packet charges were easily detected when acetophenone was diffused into the LDPE specimen. However, uniformity of acetophenone distribution prevented the packet charge generation. It is suggested on the basis of several experimental results that local ionization of impurities in the insulation through solvation by acetophenone takes place assisted by high field and leads to the packet charge generation. A numerical simulation was carried out based on the above model.

Journal ArticleDOI
TL;DR: In this paper, a single-surface multipactor discharge on a dielectric, such as an rf window, was investigated using a Monte Carlo simulation, and the susceptibility diagram, applicable to a wide range of materials, in terms of the rf electric field and of the dc electric field, was constructed.
Abstract: This paper proposes a novel theory of single-surface multipactor discharge on a dielectric, such as an rf window. Using a Monte Carlo simulation, we obtain the susceptibility diagram, applicable to a wide range of materials, in terms of the rf electric field and of the dc electric field that may result from dielectric charging. The electron multiplication mechanism assumes realistic yield curves of secondary electrons, including distributions of emission velocities and angles for these electrons. The susceptibility diagram thus constructed allows an immediate assessment of the range of rf power over which multipactor may be expected to occur. A simple analytic theory is constructed to explain the simulation results.

Journal ArticleDOI
Wen Yang1, Ting Zhu1
TL;DR: In this paper, a model of stress-assisted 90-polarization switching was proposed to quantify the fracture toughness of a mono-domain ferroelectric crystal undergoing a confined polarization switch.
Abstract: Electric fields can influence the fracture toughness of ferroelectrics. For example, poled ferroelectrics exhibit fracture toughness anisotropy: the material is tougher for a crack parallel to the poling direction but less tough for a crack perpendicular to it. When an electric field is applied to a poled sample, a positive field reduces its fracture toughness but a negative field enhances it. Previous investigations attribute these phenomena to polarization switching. This paper proposes a model of stress-assisted 90 polarization switching to quantify the toughening process. Small scale switching and uniform electric fields are assumed. An analytical solution is presented for a mono-domain ferroelectric crystal undergoing a confined polarization switch. This solution and the domain orientation pattern enable us to estimate the fracture resistance against the steady state crack growth in ferroelectrics by a Reuss-type multiple-domain assembly. A dimensionless group of material parameters and an electric field function emerge, and form the key ingredients of switch-toughening. The model is used to delineate several observations, including: poling-induced anisotropy of the fracture toughness, asymmetric variation of the fracture toughness under positive and negative electric fields of a poled specimen; upside-down butterfly loop for the fracture toughness response under cyclic electric loading.