Axial Component Of Electric Field Research Articles

Surface-standing-wave formation via resonance interaction of a finite-length conductive rod with microwaves

The resonant response of a thin conducting rod with a finite length irradiated by microwaves polarized along its axis is observed. By using a thermoelastic optical indicator microscope it is shown that rod with a length of several half- wavelengths can serve as a resonator for axial surface waves. It is facilitated by noticeable reflections (approximately 30%) from the rod edges conditioned by the unique distributions of Sommerfeld wave fields along a rod. The presence of a weak axial electric field component of surface waves ensures an easy coupling with the incident plane wave polarized along the rod axis and excites the resonator. Visualization of distributions of the near-field magnetic component of surface standing waves in the vicinity of a rod allows the exploration of three longitudinal modes of a resonator with low orders. The possibility of controlling the resonant frequency by changing the length and diameter of the rod, as well as the electromagnetic characteristics of the environment, are studied. The phenomenon under study can be used to create wavefront shaping metasurfaces and for studies of the properties of a dielectric medium in the microwave region. As Sommerfeld waves propagate on the surface of a cylindrical resonator, the resonant properties are sensitive to the dielectric permittivity of the surrounding medium, which will open up the potential for using the suggested resonator in sensing applications, which is experimentally demonstrated.

Characterisation of surface charge density and net electric field during parallel-plate dielectric barrier discharge generated in atmospheric-pressure air

We measured the surface charge density in a parallel-plate dielectric barrier discharge (DBD) using the Pockels effect, and the axial and lateral components of the net electric field were evaluated for different gap lengths and applied voltages. The DBD was driven by a 5 kHz sinusoidal voltage in gap lengths of 0.5, 0.3, and 0.1 mm at atmospheric pressure with Bi4Ge3O12 crystal as a dielectric. Typical microdischarges (MDs) were observed for every gap length, and the number of MDs increased with the increasing applied voltage. As the gap length decreased, the spot radius of a single MD decreased, whereas the peaks of charge density were almost the same, indicating that the amount of charge transported per unit MD is limited for short gaps. The spatial memory effect, in which MDs occur at the same position in successive cycles, was not always observed under the experimental conditions, and it was evaluated considering the surface charge density distributions. Whether the memory effect works is determined by the surface charge density, and it is likely to occur under a balance between positive and negative charges across successive half-cycles. The net electric field was estimated from surface charge measurements. The axial component of the net electric field strength increased up to 150–170 Td before the MD occurred, and it decreased below 100 Td by the surface charge deposited by MD, being approximately 50%–60% of the external field amplitude. The maximum value of the lateral component of the electric field was approximately 150 Td at the edge of the MD spot with a gap length of 0.5 mm, and it decreased as the gap length decreased. As a negative surface charge generated a weaker lateral field than a positive one, the electric field distribution differed between anodic and cathodic dielectrics.

A High-Power Sheet Beam Slow-Wave Structure of Traveling Wave Tubes

In future electronic devices, the trade-off between power capacity and thermal management will be a severe challenge. In this letter, a sheet beam slow-wave structure (SB-SWS) has been proposed to realize high-power output while taking into account cooling design inside the traveling-wave tubes (TWT). The design of the modified structure ensures a sufficient axial electric field component to realize efficient interaction, meanwhile expands the width of the metal vanes by 327% to design micro-channel cooling. The power load capacity for electronic interception increased by 25%. Utilizing all-period optimization technology, the maximum output power can reach 4 kW, corresponding 18.8% electronic extraction efficiency. Also presented further is a proof-of-concept design model of Ka-band for practical test. The consistency between experiment and theory shows that this SWS is not only suitable for microwave frequency band, but more suitable for future miniaturized devices in sub-millimeter wave and terahertz bands.

Electric field induced second harmonic (E-FISH) generation for characterization of fast ionization wave discharges at moderate and low pressures

The electric field in an ionization wave discharge in nitrogen at 20–100 mbar, initiated by positive polarity, high-voltage, ns duration pulses, is measured by ps second harmonic generation. The axial electric field component is determined both during the propagation of the ionization wave along the discharge tube, and after the wave reaches the grounded electrode, spanning the entire discharge gap. The temporal resolution of the present measurements is 200 ps, with the spatial resolution in the axial direction of approximately 0.5 mm. The second harmonic signal exhibits a quadratic dependence on the Laplacian electric field but indicates that in this pressure range most of the signal is generated within the wall of the tube. Absolute calibration of the signal is obtained from the current shunt data, after the ionization wave has reached the grounded electrode. Comparison of the data taken at different pressures shows that the peak value of the axial electric field in the wave front, 8–11 kV cm−1, has a fairly weak dependence on pressure, with the peak reduced electric field reaching ≈2000 Td at 20 mbar. Reducing the pressure from 100 to 20 mbar, while keeping the discharge pulse voltage waveform the same, steepens the ionization wave front considerably, from 3.0 to 1.0 ns full width at half maximum. The results demonstrate that ps second harmonic generation may be employed for electric field measurements in low-pressure discharges, discharges sustained in small diameter capillary tubes, and discharges sustained in gas mixtures with low nonlinear susceptibility, at the conditions when the detection of the signal generated directly in the plasma is challenging. High temporal resolution of the present measurements indicates a possibility of detection of non-local electron kinetics effects induced by a rapidly varying, high peak value electric field in low and moderate pressure ionization wave discharges.

Investigation of a plasma–target interaction through electric field characterization examining surface and volume charge contributions: modeling and experiment

Numerical simulations and experiments are performed to better understand the interaction between a pulsed helium plasma jet and a dielectric target. The focus of this work lies on the volume and surface charge influence on the electric field distribution. Experimentally, the electric field due to surface charges is measured inside an electro-optic target under exposure of a plasma jet, using the optical technique called Mueller polarimetry. For the first time, the time-resolved spatial distributions of both the axial and radial components of electric field inside the target are obtained simultaneously. A 2D fluid model is used in a complementary way to the experiments in order to study separately the contribution of volume charges and surface charges to the spatio-temporal evolutions of the electric field during the plasma–surface interaction. The experimental investigation shows that the average axial and radial components of electric field inside the dielectric target, only due to surface charges, are lower than generally reported for electric field values in the plasma plume. Thanks to the phenomenological comparison with experiments, simulations show that during the plasma–surface interaction two effects sequentially determine the electric field inside the target: firstly, a relatively high electric field is observed due to the proximity of the ionization front; afterwards, in longer timescales, lower electric fields are induced due to the contribution of both leftover volume charges close to the target and surface charges deposited on its surface. The experimental technique provides a unique way to examine this second phase of the plasma–surface interaction.

Imaging axial and radial electric field components in dielectric targets under plasma exposure

This work presents new ways to investigate the individual electric field components in a dielectric target induced by a non thermal atmospheric pressure plasma jet. Mueller polarimetry is applied to investigate electro-optic crystals under exposure of guided ionization waves produced by a plasma jet. Three different cases are examined to visualize the different electric field components induced in the crystals by charges deposited on the surface by impact of the ionization waves. Investigating a (BSO) crystal at normal incidence allows measurement and visualization of the axial field, while if the crystal is examined at 45° both radial and axial electric field components are combined. For the first time, a Fe:LiNbO3 (Felinbo) crystal is examined using Mueller polarimetry under influence of a plasma jet. In this case, exclusively the patterns and local values of the radial field are obtained and not the axial field. These unique imaging options in the target for the individual electric field components allow a new and more complete investigation of the dynamics of surface discharges on dielectric materials.

Large-signal field analysis of a linear beam travelling wave tube amplifier for the anisotropically conducting tape helix slow-wave structure supported by dielectric rods

The large-signal behavior of traveling wave tube amplifier for a linear beam dielectric loaded anisotropically conducting tape helix slow wave structure (SWS) is realized through a swift and reliable field analysis. Using Green’s function sequence, the field components in the SWS are designated as nonlinear functionals of electron arrival time. The electron arrival time in the beam region is formulated into a nonlinear operator in the Banach space mapping form by substituting the axial electric field component into the electron ballistic equation. The nonlinear beam–wave interaction is then obtained by determining the electron arrival time through extensive successive approximations, and thus exact electric and magnetic field components in the tape helix SWS are attained. The numerical computation of the proposed model yields definitive analytical results for the electron exit velocity, induced surface current density, power gain, conversion efficiency, and optimum interaction length.

Electric field measurements on plasma bullets in N2 using four-wave mixing

Atmospheric pressure plasma jets generated by kHz nanosecond voltage pulses typically consist of guided streamer discharges called plasma bullets. In this work, plasma bullets are generated in a pulsed plasma jet using N2 as feed gas and their electric field distribution is investigated by polarization-resolved four-wave mixing. The method and its analysis have been extended to resolve radial profiles of non-uniform, but radially symmetric, electric field distributions. In addition, a calibration procedure using an electrode geometry different from the discharge geometry has been developed. A radially resolved profile of the axial electric field component of a plasma bullet in N2 is presented, as well as the temporal development of the (line-integrated) radial and axial components of the electric field. To verify the results, they are compared to a streamer model adapted to the conditions of the experiment. The peak values obtained from the experiment are in the range expected from streamer literature. However, there are some quantitative differences with the model, which predicts values approximately a factor two lower than those found in the experiment, as well as a faster radial decay. The temporal development shows similar features in both the experiment and the model. Explanations for these differences are provided and further improvements for the method are outlined.

Analytical model of the field of super-resolution focal spot based on sink-source model

The expressions of non-paraxial tightly focused vector beams propagating along a certain direction are given based on the sink-source model by using the spatiotemporal translation technology. The singularities on the beam waist plane are eliminated in the model. The field of a super-resolution focal spot with strong axial electric field component can be simulated by the model. The full width at half maximum (FWHM) of the intensity of focal spot where the field can be simulated by the model can be as small as 0.44 wavelength. The FWHM information of focal spot is preserved in the sink-source model. The refocusing phenomena of a focal laser spot by the 4f optical imaging system is also studied. The change of FWHM of an initial focal spot can be reflected from the refocused spot.

Fields of an ultrashort tightly focused radially polarized laser pulse in a linear response plasma

Analytical expressions for the fields of a radially polarized, ultrashort, and tightly focused laser pulse propagating in a linear-response plasma are derived and discussed. The fields are obtained from solving the inhomogeneous wave equations for the vector and scalar potentials, linked by the Lorenz gauge, in a plasma background. First, the scalar potential is eliminated using the gauge condition, then the vector potential is synthesized from Fourier components of an initial uniform distribution of wavenumbers, and the inverse Fourier transformation is carried out term-by-term in a truncated series (finite sum). The zeroth-order term in, for example, the axial electric field component is shown to model a pulse much better than its widely used paraxial approximation counterpart. Some of the propagation characteristics of the fields are discussed and all fields are shown to have manifested the expected limits for propagation in a vacuum.

Modal analysis of graphene microtubes utilizing a two-dimensional vectorial finite element method

The propagation properties of surface plasmon polariton waves on graphene microtubes were investigated in this paper. A precise vectorial finite element modal solver that models graphene as a surface boundary condition is devised for the graphene microribbon case. The solver extracts the dispersion curves through the effective index of various supported modes, while its propagation length, compared to the microstrip’s one, unveils a notable behavior of surface waves. Also, radial and axial electric field components are evaluated at different frequencies, indicating the strong confinement at the surface of graphene and the impact of the microtubes’ diameter on the propagating modes.

Dispersion relation for space-charge waves in a warm plasma-filled elliptical waveguide in an infinite axial magnetic field

A perfectly conducting elliptical cylinder filled with a warm plasma and immersed in an infinite axial magnetic field is considered. Using Maxwell’s equations and dielectric tensor, a Mathieu differential equation for axial component of electric field is obtained. Considering the boundary conditions, dispersion relation for waves in a plasma of warm electrons and immobile ions, which fills an elliptical waveguide and it is under the action of infinite axial magnetic field are calculated. Furthermore, dispersion relation and scalar potential in the quasi-static approximation in a cold magnetized plasma elliptical waveguide is calculated. The obtained results are graphically presented.

Breaking Bullseye’s Symmetry for Axial Field Focusing

We propose a bullseye type device capable of coupling the incident linearly polarized THz waves and focusing the axial electric field component. In order to avoid the destructive interference of the axial field occurring at the center of classic bullseyes, we introduce a spatial π-phase shift on half part of it. The device is a simpler alternative than the use of classic bullseyes illuminated by a radially polarized incidence wave for the generation of axial field.

Focusing properties of the vector beam with complicated polarization and helical phase

We report a vector beam with complicated polarization and helical phase and derive the corresponding focusing model of the aplanatic system, where the 10 variables optimized provide a more powerful and flexible tool to construct various interesting focal spots. By optimizing these 10 variables, we directly construct some specific focal spots, including the single focal spot with lateral resolution beyond the Abbe diffraction limit and without axial electric field component and the focal spots with unique structures in the intensity, such as the square and triangular bright spots, the various double lines, the cross lines, the ring-shaped square, the ring-shaped hexagon, and so on. Some of those focal spots with unique structures in the intensity have high resolution, even beyond the Abbe diffraction limit. We conclude the functions of some variables affecting the structures of the focal spots, draw some regulars constructing the focal spot with high quality, and indicate how to find the new values of various variables optimized in order to rotate the focal spot distribution. Although only the focal spot structures of the intensity distribution are discussed in this paper, the ideas and the developed focusing model can be used for the investigations of the various focal spot structures of polarizations, gradient forces, and spin and orbital angular momentums.

Seismoelectric waves in a borehole excited by an external explosive source

The conversion of energy between seismic and electromagnetic wave fields has been described by Pride's coupled equations in porous media. In this paper, the seismoelectric field excited by the explosive point source located at the outside of the borehole is studied. The scattering fields inside and outside a borehole are analyzed and deduced under the boundary conditions at the interface between fluid and porous media. The influences of the distance of the point source, multipole components of the eccentric explosive source, and the receiving position along the axis of vertical borehole, on the converted waves inside the borehole are all investigated. When the distance from the acoustic source to the axis of a borehole is far enough, the longitudinal and coseismic longitudinal wave packets dominate the acoustic and electric field, respectively. The three components of both electric field and magnetic field can be detected, and the radial electric field is mainly excited and converted by the dipole component. Owing to the existence of borehole, the electric fields and magnetic fields in the borehole are azimuthal. The distance from the point where the maximum amplitude of the axial components of electric field is recorded, to the origin of coordinate indicates the horizontal distance from the explosive source to the axis of vertical borehole.

Optical trapping and polarization-controlled scattering of dielectric spherical nanoparticles by femtosecond laser pulses

Abstract We present optical trapping behavior of 50-nm-sized polystyrene beads, suspended in water medium, by femtosecond pulsed laser beam. In addition to a higher number of nanoparticles trapped at the focal spot by the ultrashort laser pulses compared with that by continuous-wave laser, the nanoparticles are scattered out of the focal spot by the laser pulses to the surrounding area. The scattered particles form a partially opened folding fan-shaped bright locus in two opposite directions, in an alternating manner, perpendicular to the laser polarization. To understand those phenomena, we analyzed radiation (gradient and scattering) force of femtosecond laser pulses and their temporal force exerted on the dielectric spherical nanoparticles by taking into account the impulsive peak power and the axial component of electric light field produced by high numerical aperture of objective lens. We show that the axial electric field is responsible for lateral components of the scattering and temporal forces, and hence, controls the scattering directions of the Rayleigh particles. These findings provide important information about the dynamic optical trapping of the Rayleigh particles by highly focused ultrashort laser pulses.

The 2D plasma potential distribution in a HiPIMS discharge

Using an emissive probe the spatial-temporal distribution of the plasma potential Vp in a high power impulse magnetron sputtering discharge has been measured. The magnetron (with a planar circular titanium target) was operated in argon gas at a fixed pressure of 0.54 Pa, a pulse frequency of 100 Hz with a 100 µs on-time and average power of 650 W. In the early part of the voltage pulse (∼6–8 µs), Vp attains deep negative values (∼−150 V) at positions close to the target (10 mm) and above the racetrack, diminishing with distance, but never reaching ground potential, even at excursions of 80 mm. In the confined plasma region, extraordinarily high axial and radial electric field components, up to several kV m−1, are calculated from the plasma potential measurements.As the plasma develops and the discharge current reaches a maximum (at ∼40 µs), Vp is elevated everywhere in the plasma, however, still with deep negative values (down to −40 V) at positions closest to the target. From the derived electric fields and modelled (vacuum) magnetic field, the 2D distribution of E × B electron drift velocities has been determined. During the early discharge phase, a broad drift channel is predicted above the racetrack, with drift speeds up to ∼3 × 105 ms−1 centred ∼30 mm above the target racetrack. As the discharge develops, these speeds reduce by about a factor 3 and the centre of the velocity distribution moves further away from the target and inwards towards the discharge axis, resembling that observed in dc and pulsed-dc magnetron operation.

A high-power high-efficiency klystronlike relativistic backward wave oscillator with a dual-cavity extractor

A klystronlike relativistic backward wave oscillator (RBWO) with a dual-cavity extractor is presented. The phase of the axial electric field component Ez varies by 0° in the dual-cavity extractor, and a larger electric field appears in the second extraction cavity, in comparison with a single-cavity extractor. Such an improved field distribution is beneficial for converting modulated beam power into microwave power. The particle in cell simulation results reveal that microwaves with power of 10 GW, frequency of 4.3 GHz are generated, and conversion efficiency is 48% when diode voltage is 1.2 MV and beam current 17.3 kA.

QUANTITATIVE EVALUATION OF FORMATION PERMEABILITY FROM ACOUSTIC AND ELECTRIC STONELEY WAVES

Numerical experiments based on Pride's model of electrokinetic phenomena have shown that electromagnetic Stoneley waves as well as pressure Stoneley waves are most sensitive to permeability variations. A new way for quantitative evaluation of any value of formation permeability is presented. It is based on simultaneous measurement of pressure field and axial component of electric field excited by an acoustic source in fluid-filled borehole with help from a set of receivers in borehole. Frequency dependence of ratio of the complex-valued amplitudes of the electric Stoneley wave to the pressure Stoneley wave obtained as a result of plane waves decomposition of pressure field and mentioned component of electric field carries important information about permeability. The ratio of the real part of this ratio to its imaginary part is very sensitive to permeability variations. The approximate analytical expressions for this ratio derived for open and sealed pores on borehole wall are base for construction of a new way of quantitative evaluation of formation permeability.

BOREHOLE ACOUSTIC AND ELECTRIC STONELEY WAVES AND PERMEABILITY

New way for quantitative evaluation of any value of formation permeability based on numerical experiments with Pride's model of electrokinetic phenomena is presented. This approach is based on simultaneous measurement of pressure field and axial component of electric field excited by an acoustic source in fluid-filled borehole with help a set of receivers in borehole. Frequency dependence of ratio of the complex-valued amplitudes of the electric Stoneley wave to the pressure Stoneley wave obtained as a result of plane-wave decomposition of pressure field and mentioned component of electric field carries important information about permeability. In case of open and sealed pores on borehole wall were obtained enough simple analytical expressions for this ratio.