Electric Field Component Parallel Research Articles

Effect of Electric-Field Components on the Flashover Characteristics of Oil-Paper Insulation Under Combined AC-DC Voltage

Flashover characteristics are closely related to the electrical field distribution on the surface of oil-paper insulation. In this study, the effects of electrical field and DC voltage components on the creepage flashover characteristics of oil-paper insulation under combined AC-DC voltage (CADV) are investigated using two electrode models. The results demonstrate that when the DC voltage component is large, the flashover voltage under the influence of strong parallel electric field component is approximately 1.2 times higher than that under the influence of strong normal electric field component. When the DC voltage component value increases under the influence of strong normal electric field component, the value of corresponding AC voltage component of the creepage flashover voltage exhibits a decreasing trend. It is believed that due to the strong normal electric field component, the electrons intensify the collision on the surface of the insulating pressboard. Under the influence of the DC voltage component and due to the presence of space charge on the insulating pressboard, the distribution shape of carbonized particles on the surface of the insulating pressboard after creepage flashover is different. Furthermore, the instantaneous energy release during creepage flashover under CADV is higher than that under AC voltage, and the greater the DC voltage component value, more severe is the damage to the fibers on the insulating pressboard surface.

Nanometer-sensitive wideband opto-mechanical switching concept

The present paper is concerned with the mechanically extremely sensitive reflection switching concept of a free-space wave impinging on an array of dielectric or semiconductor pillars. Splitting the pillars of a 2D periodic array in its resonant reflection regime at a prescribed wavelength into two parts with a low-index gap of a few nanometers between parts cancels the reflection of a plane wave under normal incidence. The underlying principle lies in the strong and abrupt discontinuity of the electric field component parallel to the pillar axes caused by the gap. The electromagnetic field distribution is consequently deeply perturbed and no longer corresponds to that of an optical resonance of the array; this suppresses the reflection. The electromagnetic analysis of a silicon pillar array leads to the design of a gapless experimental model fabricated by microsystem technologies that exhibits a broad reflection maximum of a few tens of nm at a prescribed wavelength in the visible and near-IR range, and of a pillar structure with nanometer-thick low-index gap exhibiting no reflection peak over this wide wavelength range. A transmission ratio of 1:30 at a 1080 nm peak wavelength between a gapless and a 1.5 index, 30 nm-thick gap structures was measured.

Analysis and Experimental Verification of the Peaking Capacitor’s Flashover Process in an EMP Simulator

The flashover process of the peaking capacitor in the electromagnetic pulse (EMP) simulator is studied based on theoretical analyses and experimental verification in this paper. There are deeper and denser ablation spots on the film surface near the inner core of the destroyed peaking capacitor, while the damage of the outer film is relatively slight, which indicates that the flashover current along the inner film is larger. Besides, the circuit simulation analyses show that the earlier the flashover occurs on the film of the peaking capacitor, the smaller the flashover current. The electric field on the non-conical surface of the capacitor is mainly occupied with normal component. Differently, for the conical surface, the electric field on the outer layer is dominated by the normal component and the parallel component is the main part on the inner layer. It is considered that the flashover on the conical surface originates from outer layers and develops gradually to the inner until the flashover penetrates through all layers. Furthermore, the images of flashover show that the flashover firstly occurs on the outermost layers and develops to the inner layers with the increase of the voltage. For such special structure of the peaking capacitor, the parallel component of electric field is more likely to facilitate the flashover under nanosecond pulse. These results may exhibit specific reference implication in the design of insulation for the peaking capacitor used in EMP simulator.

Gap-type Particle Acceleration in the Magnetospheres of Rotating Supermassive Black Holes

Abstract The detection of rapidly variable gamma-ray emission in active galactic nuclei has generated renewed interest in magnetospheric particle acceleration and emission scenarios. In order to explore its potential, we study the possibility of steady gap acceleration around the null surface of a rotating black hole magnetosphere. We employ a simplified (1D) description along with the general relativistic expression of Gauss’s law, and we assume that the gap is embedded in the radiation field of a radiatively inefficient accretion flow. The model is used to derive expressions for the radial distribution of the parallel electric field component, the electron and positron charge density, the particle Lorentz factor, and the number density of γ-ray photons. We integrate the set of equations numerically, imposing suitable boundary conditions. The results show that the existence of a steady gap solution for a relative high value of the global current is in principle possible if charge injection of both species is allowed at the boundaries. We present gap solutions for different choices of the global current and the accretion rate. When put in context, our results suggest that the variable very-high-energy γ-ray emission in M87 could be compatible with a magnetospheric origin.

Essential differences between TE and TM band gaps in periodic films at the first Bragg condition.

In photonic lattices with thin-film geometry, TE modes possess an in-plane electric field component parallel to the film surface, whereas TM modes have a magnetic field component similarly oriented. This study reports the essential properties of, and differences between, TE and TM band gaps induced by laterally periodic thin-film photonic lattices at the first Bragg condition. Because TE and TM guided waves obey different wave equations, TE and TM band gaps exhibit different evolution as the film thickness varies. The first TM band exhibits both band gap closure and band flips wherein the symmetry properties of the band-edge modes are reversed by variation of film thickness. In the first TE band, in contrast, there is neither band gap closure nor band flip. The work provides an insightful semianalytical formulation whose results are verified by rigorous computations.

Effects of reconnection downstream conditions on electron parallel acceleration during the merging start-up of a spherical tokamak

The axial merging method is one of the candidates to provide a center-solenoid-free start-up of high-beta spherical tokamak (ST) plasma. Two initially formed STs merge through magnetic reconnection in the presence of the guide (toroidal) magnetic field, which is perpendicular to the reconnection (poloidal) magnetic field. During ST merging start-up, electrons are effectively accelerated near the reconnection point where the reconnection electric field is almost parallel to the magnetic field. In order to evaluate the effectivity of this acceleration process on electron heating, the temporal and spatial distributions of generated energetic electrons are observed by a soft x-ray fast imaging system equipped on the UTST device. The energetic electrons were generated not only in the vicinity of the reconnection point but transiently in the inboard-side downstream region until the static electric field by charge separation grew to cancel the reconnection electric field component parallel to the magnetic field line. Adequate control of the downstream condition could enhance the generation of energetic electrons and provide a more effective conversion from the released magnetic energy to electron energy.

Electron Heating by Kinetic Alfvén Waves in Coronal Loop Turbulence

Abstract A test-particle model describing the energization of electrons in a turbulent plasma is presented. Parameters are chosen to represent turbulence in a magnetic structure of the solar corona. A fluctuating electric field component parallel to the background magnetic field, with properties similar to those of Kinetic Alfvén Waves, is assumed to be present at scales of the order of the proton Larmor radius. Electrons are stochastically accelerated by multiple interactions with such fluctuations, reaching energies of the order of 102 eV within tens to hundreds of seconds, depending on the turbulence amplitude. For values of the large-scale plasma velocity fluctuation of the order of tens of kilometers per second, the power absorbed by electrons per surface unit is of the order of that typically necessary to heat the corona. The power that electrons absorb from fluctuations is proportional to the third power of the large-scale velocity amplitude, and is comparable with the power associated with the turbulent cascade. Therefore, this mechanism can be considered as an equivalent kinetic dissipation for turbulence, and it can play a relevant role in the heating of electrons in the corona.

Tight focusing properties of a circular partially coherent Gaussian beam.

Tight focusing properties of a circular partially coherent Gaussian (CPCG) beam with linear polarization have been studied based on vectorial Debye theory. Expressions for the intensity distribution and degree of coherence near the focus are derived. Numerical calculations are performed to show the intensity distribution and degree of coherence of the CPCG beam in the focal region. It is interesting to find that after focusing the CPCG beam through a high numerical-aperture objective we can obtain a super-length optical needle (>12λ) with homogeneous intensity along the propagation axis and wavelength beam size (∼λ). Moreover, the numerical calculations of coherence illustrate that, in the range of full width at half-maximum of the optical needle, for any two of the parallel electric field components of the optical needle the coherence is close to 1, but for any two of orthometric electric field components the value of coherence is between 0.4 and 0.9. Such a non-diffracting optical needle may have potential applications in atom optical experiments, such as in atom traps and atom switches.

Polarized SERS on linear arrays of silver half-shells: SERS re-radiation modulated by local density of optical states

This work investigates polarization effects in surface-enhanced Raman scattering (SERS) on a particular kind of hybrid colloidal plasmonic-photonic crystal consisting in linear arrays of polystyrene colloids coated by a silver film forming caps (half-shells). The polarization of Raman scattering of adsorbed molecules is found to be imposed by the linear morphology of the plasmonic nanostructures, independent of the incident polarization. Specifically, it is demonstrated that the electric field component parallel to the linear plasmonic nanostructures brings the main contribution to the SERS enhancement for both parallel and perpendicular excitation. The stronger plasmon resonance, polarized along the chain of metal half-shells, is the one that determines the polarization of the SERS scattering, even if this resonance is not directly excited by the incident laser, but only re-radiated photons couple to it. The observed dependences indicate a strong contribution of the second part of the E4 enhancement, related to the enhancement at the frequency of the Raman scattered photons. FDTD electromagnetic simulations, taking into account both the excitation enhancement at the location of the scatterer and the enhancement of the scattering (re-radiation) by local density of optical states (LDOS) effects, support the experimental results. The presented results emphasize the practical importance of knowing and controlling the excitation/detection conditions in SERS experiments with nanostructures possessing well-defined and oriented morphological features. The LDOS approach employed here for the theoretical analysis, despite not being common for this purpose, proves its potential for becoming a useful ingredient in the analysis of plasmon-enhanced spectroscopies.

Dissipation, energy transfer, and spin-down luminosity in 2.5D PIC simulations of the pulsar magnetosphere

We perform 2.5D axisymmetric simulations of the pulsar magnetosphere (aligned dipole rotator) using the charge conservative, relativistic, electromagnetic particle in cell code PICsar. Particle in cell codes are a powerful tool to use for studying the pulsar magnetosphere, because they can handle the force-free and vacuum limits and provide a self-consistent treatment of magnetic reconnection. In the limit of dense plasma throughout the magnetosphere, our solutions are everywhere in the force-free regime except for dissipative regions at the polar caps, in the current layers, and at the Y-point. These dissipative regions arise self-consistently, since we do not have any explicit dissipation in the code. A minimum of $ \approx 15-20\%$ of the electromagnetic spindown luminosity is transferred to the particles inside 5 light cylinder radii. However, the particles can carry as much as $\gtrsim 50 \%$ of the spindown luminosity if there is insufficient plasma in the outer magnetosphere to screen the component of electric field parallel to the magnetic field. In reality, the component of the spindown luminosity carried by the particles could be radiated as gamma rays, but high-frequency synchrotron emission would need to be implemented as a sub-grid process in our simulations and is not present for the current suite of runs. The value of the spindown luminosity in our simulations is within $\approx 10\%$ of the force-free value, and the structure of the electromagnetic fields in the magnetosphere is on the whole consistent with the force-free model.

Superposition principle for nonlinear Josephson plasma waves in layered superconductors

We show that a specific superposition principle is valid for \emph{nonlinear} Josephson plasma waves in layered superconductors. We study theoretically the reflection and transmission of terahertz waves through a finite-size superconducting slab placed inside a rectangular waveguide with ideal-metal walls. We assume that the superconducting layers are parallel to the waveguide axis. We show that there exist two specific mutually-orthogonal polarizations for waves which, in spite of the nonlinearity, reflect and transmit through the superconductor \emph{independently}. The wave of the first polarization causes a strong shielding current along the crystallographic \textbf{ab}-plane of the superconductor. Therefore, this wave reflects nearly completely from the superconductor and excites only an evanescent mode inside it. The wave of the other polarization does not contain the electric field component parallel to both the sample surface and the crystallographic \textbf{ab}-plane, and excites much weaker shielding currents. Therefore, it partially reflects and partially transmits through the sample. Moreover, this wave excites the nonlinear mode in the layered superconductor, and the transmission coefficient of the superconductor depends on the amplitude of the incident wave of this polarization.On the basis of the discussed superposition principle, we suggest a new method for solving nonlinear problems of waves interaction in layered superconductors. Namely, it is reasonably to represent incident, reflected, and transmitted waves of any polarizations as superpositions of the modes with the two specific polarizations considered here, and then solve the problem separately for these modes. We apply this method to the case of nonlinear interaction and mutual transformation of the transverse electric and transverse magnetic modes in layered superconductors.

Self-consistent stationary MHD shear flows in the solar atmosphere as electric field generators

Magnetic fields and flows in coronal structures, for example, in gradual phases in flares, can be described by 2D and 3D magnetohydrostatic (MHS) and steady magnetohydrodynamic (MHD) equilibria. Within a physically simplified, but exact mathematical model, we study the electric currents and corresponding electric fields generated by shear flows. Starting from exact and analytically calculated magnetic potential fields, we solveid the nonlinear MHD equations self-consistently. By applying a magnetic shear flow and assuming a nonideal MHD environment, we calculated an electric field via Faraday's law. The formal solution for the electromagnetic field allowed us to compute an expression of an effective resistivity similar to the collisionless Speiser resistivity. We find that the electric field can be highly spatially structured, or in other words, filamented. The electric field component parallel to the magnetic field is the dominant component and is high where the resistivity has a maximum. The electric field is a potential field, therefore, the highest energy gain of the particles can be directly derived from the corresponding voltage. In our example of a coronal post-flare scenario we obtain electron energies of tens of keV, which are on the same order of magnitude as found observationally. This energy serves as a source for heating and acceleration of particles.

Direct observation of radiation-belt electron acceleration from electron-volt energies to megavolts by nonlinear whistlers.

The mechanisms for accelerating electrons from thermal to relativistic energies in the terrestrial magnetosphere, on the sun, and in many astrophysical environments have never been verified. We present the first direct observation of two processes that, in a chain, cause this acceleration in Earth's outer radiation belt. The two processes are parallel acceleration from electron-volt to kilovolt energies by parallel electric fields in time-domain structures (TDS), after which the parallel electron velocity becomes sufficiently large for Doppler-shifted upper band whistler frequencies to be in resonance with the electron gyration frequency, even though the electron energies are kilovolts and not hundreds of kilovolts. The electrons are then accelerated by the whistler perpendicular electric field to relativistic energies in several resonant interactions. TDS are packets of electric field spikes, each spike having duration of a few hundred microseconds and containing a local parallel electric field. The TDS of interest resulted from nonlinearity of the parallel electric field component in oblique whistlers and consisted of ∼ 0.1 msec pulses superposed on the whistler waveform with each such spike containing a net parallel potential the order of 50 V. Local magnetic field compression from remote activity provided the free energy to drive the two processes. The expected temporal correlations between the compressed magnetic field, the nonlinear whistlers with their parallel electric field spikes, the electron flux and the electron pitch angle distributions were all observed.

Role and origin of the poleward Alfvénic arc

AbstractAlfvénic arcs are often found adjacent to the poleward border of the substorm bulge. They are created by precipitating narrow electron beams with a broad energy distribution, mainly below 1 keV, and dominated by Alfvénic structures of small scales and frequencies in the 1 Hz range. They are also associated with transverse ion heating. A balanced field‐aligned current system accompanying the poleward Alfvénic arc reveals its underlying structure being a broad channel of primary energy inflow of several tens of kilometers width. The associated magnetic shear stresses drive a flow along the poleward side of the substorm current wedge. Polar cap convection passes through this channel before entering the substorm bulge. The small‐scale electromagnetic structures are developing from the primary energy inflow by scale breaking and multiple reflections in the ionospheric Alfvén resonator. By their parallel electric field components these structures decouple effectively from the ionosphere. Their energy content is converted into kinetic energy of auroral particles in the topside ionosphere. A selected data set from FAST, DE 2, and Cluster is presented for characterizing the energetic and electromagnetic properties of the Alfvénic arc. Its function in the substorm can be summarized as a preconditioning of the polar cap plasma and magnetic field for entry into the magnetosphere through the poleward arc. This occurs under substantial density depletion.

PARALLEL ELECTRIC FIELD SPECTRUM OF SOLAR WIND TURBULENCE

By searching through more than 10 satellite-years of THEMIS and Cluster data, three reliable examples of parallel electric field turbulence in the undisturbed solar wind have been found. The perpendicular and parallel electric field spectra in these examples have similar shapes and amplitudes, even at large scales (frequencies below the ion gyroscale) where Alfvenic turbulence with no parallel electric field component is thought to dominate. The spectra of the parallel electric field fluctuations are power laws with exponents near -5/3 below the ion scales (~ 0.1 Hz), and with a flattening of the spectrum in the vicinity of this frequency. At small scales (above a few Hz), the spectra are steeper than -5/3 with values in the range of -2.1 to -2.8. These steeper slopes are consistent with expectations for kinetic Alfven turbulence, although their amplitude relative to the perpendicular fluctuations is larger than expected.

Plasma transport induced by kinetic Alfvén wave turbulence

At the Earth's magnetopause that separates the hot-tenuous magnetospheric plasma from the cold dense solar wind plasma, often seen is a boundary layer where plasmas of both origins coexist. Plasma diffusions of various forms have been considered as the cause of this plasma mixing. Here, we investigate the plasma transport induced by wave-particle interaction in kinetic Alfvén wave (KAW) turbulence, which is one of the candidate processes. We clarify that the physical origin of the KAW-induced cross-field diffusion is the drift motions of those particles that are in Cerenkov resonance with the wave: E×B-like drift that emerges in the presence of non-zero parallel electric field component and grad-B drift due to compressional magnetic fluctuations. We find that KAW turbulence, which has a spectral breakpoint at which an MHD inertial range transits to a dissipation range, causes selective transport for particles whose parallel velocities are specified by the local Alfvén velocity and the parallel phase velocity at the spectral breakpoint. This finding leads us to propose a new data analysis method for identifying whether or not a mixed plasma in the boundary layer is a consequence of KAW-induced transport across the magnetopause. The method refers to the velocity space distribution function data obtained by a spacecraft that performs in situ observations and, in principle, is applicable to currently available dataset such as that provided by the NASA's THEMIS mission.

Unidentified transitions in one-photon intrashell dynamics in Rydberg atoms

One-photon intrashell transitions in strongly driven Li ($n=25$) atoms are studied experimentally. The degeneracy of the $n$ shell is lifted by orthogonal dc electric and magnetic fields, which also define the eccentricity of the initial coherent elliptic state. The transitions are driven by a radio frequency pulse linearly polarized parallel to the major axis of the ellipse. A small dc electric field component parallel to the magnetic field splits the one-photon resonance into two, and transitions in between are studied by state-selective field ionization. Unexpected lines in the ionization spectra relating to unknown transitions are found and discussed.

TOWARD A REALISTIC PULSAR MAGNETOSPHERE

We present the magnetic and electric field structures as well as the currents and charge densities of pulsar magnetospheres which do not obey the ideal condition, ${\bf E \cdot B =0}$. Since the acceleration of particles and the production of radiation requires the presence of an electric field component parallel to the magnetic field, ${\bf E}_\parallel$, the structure of non-Ideal pulsar magnetospheres is intimately related to the production of pulsar radiation. Therefore, knowledge of the structure of non-Ideal pulsar magnetospheres is important because their comparison (including models for the production of radiation) with observations will delineate the physics and the parameters underlying the pulsar radiation problem. We implement a variety of prescriptions that support nonzero values for ${\bf E}_\parallel$ and explore their effects on the structure of the resulting magnetospheres. We produce families of solutions that span the entire range between the vacuum and the (ideal) Force-Free Electrodynamic solutions. We also compute the amount of dissipation as a fraction of the Poynting flux for pulsars of different angles between the rotation and magnetic axes and conclude that this is at most 20-40% (depending on the non-ideal prescription) in the aligned rotator and 10% in the perpendicular one. We present also the limiting solutions with the property $J=\rho c$ and discuss their possible implication on the determination of the "on/off" states of the intermittent pulsars. Finally, we find that solutions with values of $J$ greater than those needed to null ${\bf E}_\parallel$ locally produce oscillations, potentially observable in the data.

Spatial, temporal, and amplitude characteristics of parallel electric fields associated with subsolar magnetic field reconnection

The electric field experiment on the Polar satellite collected bursts of data at rates of 1600 and 8000 samples/second to measure the parallel and perpendicular components of the vector electric field. Because data at these rates are required for full resolution measurements of the parallel component associated with subsolar magnetic field reconnection, some 150 such bursts from 2000 through 2003 were examined during 5 month intervals when the spacecraft was on the dayside of the Earth and the apogee of 9.5 RE was near the equator. Seventeen events were found at reconnecting magnetopauses with perpendicular electric field components as large as 200 mV/m and parallel electric field components as large as 80 mV/m. The parallel electric fields were associated with significant plasma density depletions, and they all appeared on the magnetospheric side of the current sheet. The large magnitudes of the parallel fields and their anticorrelations with plasma density are not found in simulations. For one example, the speed of the parallel electric field structure was 1.2 times the local Alfven speed. The directions of the parallel fields were such as to accelerate electrons moving along the magnetic field toward the reconnection site. The full widths at half maxima of the parallel field events ranged from less than 0.2 to 15 ms, in general agreement with simulations. Although the events occurred over ±20 degrees of magnetic latitude and for clock angles of 100 to 180 degrees, their statistics suggest that the X line for these events was within a few degrees of the magnetic equator.

Lorentz Mapping of Magnetic Fields in Hot Dense Plasmas

Unique detection of electromagnetic fields and identification of field type and strength as a function of position were used to determine the nature of self-generated fields in a novel experiment with laser-generated plasma bubbles on two sides of a plastic foil. Field-induced deflections of monoenergetic 15-MeV probe protons passing through the two bubbles, measured quantitatively with proton radiography, were combined with Lorentz mapping to provide separate measurements of magnetic and electric fields. The result was absolute identification and measurement of a toroidal magnetic field around each bubble and determination that any electric field component parallel to the foil was below measurement uncertainties.