Axial Electric Field Research Articles

Models for estimating nanoparticle transmission efficiency through an adverse axial electric field

An adverse electric field is often encountered or utilized when classifying charged nanoparticles or ions according to their electrical mobility. For instance, the classified charged particles usua...

Stark Tuning of the Silicon Vacancy in Silicon Carbide.

We present a versatile scheme dedicated to exerting strong electric fields up to 0.5 MV/cm on color centers in hexagonal silicon carbide, employing transparent epitaxial graphene electrodes. In both the axial and basal direction equally strong electric fields can be selectively controlled. Investigating the silicon vacancy (VSi) in ensemble photoluminescence experiments, we report Stark splitting of the V1' line of 3 meV by a basal electrical field and a Stark shift of the V1 line of 1 meV in an axial electric field. The spectral fine-tuning of the VSi, being an important candidate for realizing quantum networks, paves the way for truly indistinguishable single-photon sources.

Structure and phase transition behaviors of water in carbon nanotube under the electric field and high pressure

The structure and phase transition behaviors of the confined water in a (3, 15) carbon nanotube (CNT) (diameter = 1.26 nm) under the different axial electric fields and the ultra-high pressure P = 1 and 10 GPa were studied by perform molecular dynamics simulations. Depending on the pressure and the strength of the applied fields, the confined water presents four ice structures. Under zero of fields, the hollow 〈7, 0〉 ice nanotube (ice-NT) is the unique ice phase to the water confined in (3, 15) CNT. Applying an electric field triggers a helical water chain forming on the axis of the ice-NT. The structural order of water competes with its degree of polarization in its first–order solid-liquid phase transition. Therefore, high-intensity fields are not conductive to the formation of the ice. However, continuous phase transition tends to occur in the case of ultra-high pressure.

Highly Efficient Gyrotron with Multi-Stage Recuperation of Residual Electron Energy

The results of complex modeling of physical processes in a gyrotron of moderate power in the 4-mm wavelength range have been presented. Methods for improving the quality of the helical electron beam and gyrotron electronic efficiency based on the optimization of the electric field distribution in the cathode region have been implemented. The design of a collector with four-stage recuperation of residual beam energy based on the method of spatial separation of electrons in crossed azimuthal magnetic and axial electric fields has been developed. A gyrotron total efficiency equal to 71.8% has been achieved by improving the quality of the electron beam and efficient energy recuperation in the collector region.

Extension–torsion–inflation coupling in compressible electroelastomeric thin tubes

We present an axisymmetric and axially homogeneous variational formulation to obtain coupled extension–torsion–inflation deformation in compressible electroelastomeric tubes in the presence of axial and radial electric fields. We show that such deformations occur under the following two conditions: (1) only the axial electric field is imposed, with the electric poling direction in the tube (if present) lying in the radial plane; and (2) only the radial electric field is imposed within the tube, with the electric poling direction (if present) also along the radial direction. The poling direction in condition (1) generates helical anisotropy in the tube. We then obtain the governing differential equations necessary to solve the above deformation problem for thick tubes. We further apply the thin tube limit to obtain simplified algebraic equations to solve the same deformation problem. The effect of applied electric field parameters on the extension–inflation coupling and induced internal pressure vs. imposed inflation behavior is finally presented through numerical solution of the above obtained algebraic equations. The study will be useful in designing soft electroelastic tubular actuators.

Current-Free Electric Double Layer in a Small Collisional Plasma Thruster Nozzle Simulation

A computational fluid dynamics and plasma model of a collisional (∼ a few Torr) radiofrequency (at 13.56 MHz) argon plasma capacitively coupled in a converging-diverging nozzle (applied to the optimisa- tion of electrothermal plasma thrusters for space use) shows the formation of a strong stationary current-free double layer (CFDL) at the 1.5 mm diameter nozzle throat for a downstream pressure of ∼ 0.1 Torr. The cycle average magnitude of the double layer potential is ∆ΦDL = 77 V and the electron temperature at the high potential edge of the double layer is kBTe = 2.64eV, yielding a strength of ∆ΦDL/(kBTe) ∼ 30. The double layer is 1.2 mm wide which corresponds to ∼ 90 Debye lengths. The axial electric field of the double layer accelerates ions along the nozzle to a maximum drift velocity of 17 km s−1, about 3.3 times the ion sound speed, and their kinetic energy is transferred to neutrals by ion-neutral charge exchange col- lisions. The ion transit time τi through the potential structure spontaneously forming at the nozzle throat is about 5 times the radiofrequency excitation period τRF. These findings are discussed in the broader context of double layer physics and the dynamics of their formation as well as in the context of electrothermal thruster optimisation in which neutral propellant heating via ion-neutral charge exchange collisions is the main source of thrust.

Theoretical research on the transport and ionization rate coefficients in glow discharge dusty plasma

The electron kinetic model for investigating the transport and ionization rate coefficients of argon glow discharge dusty plasma is developed from the Boltzmann equation. Both of the electron–neutral and electron–dust collisions are considered as collision terms in the kinetic equation. The kinetic equation is simplified by employing the local approximation and nonlocal approach under the same discharge conditions, and the corresponding simplified kinetic equations are known as local and nonlocal kinetic equations respectively. Then the electron energy distribution function (EEDF) is obtained by numerically solving the local and nonlocal kinetic equations and the dust charging equations simultaneously. Based on the obtained EEDFs, the effective electron temperature, electron mobility, electron diffusion coefficient and ionization rate coefficient are calculated for different discharge conditions. It is shown that the EEDFs calculated from the local kinetic model clearly differ from the nonlocal EEDFs and both the local and nonlocal EEDFs are also clearly different with Maxwellian distributions. The appearance of dust particles results in an obvious decrease of high energy electrons and increase of low energy electrons when axial electric field is low. With the increase of axial electric field, the influence of dust particles on the EEDFs becomes smaller. The electron mobility and diffusion coefficients calculated on the basis of local and nonlocal EEDFs do not differ greatly to the dust-free ones. While, when dust density nd = 106 cm−3, the electron mobility increases obviously compared with the dust-free results at low axial electric field and decreases with the increasing axial electric field until they are close to the dust-free ones. Meanwhile, electron diffusion coefficients for dusty case become smaller and decrease with the increasing axial electric field. The ionization rate coefficients decrease when dust particles are introduced and they approach the dust-free results gradually with the increasing axial electric field.

Simulations of the glow discharge positive column parameters in helium

The self-consistent model for the positive column of a glow discharge is presented. The model is based on the simultaneous solution of the nonlocal Boltzmann equation for electron energy distribution function, continuity equation for ions and Poisson equation for electric field. Calculations were performed for a discharge tube similar to the Plasma Kristall-4 experiments for plasma forming gas helium for the range of pressures of 20-70 Pa and the range of discharge currents of 0.5-2.5 mA. Axial electric field strength, electron temperature and electron density dependences on the discharge current and the gas pressure are obtained. The results show a good correlation with the data obtained by the other authors.

High-Efficiency Study of an SBEIO Based on the SAA Optimization

The improvement of the beam–wave interaction efficiency of the sheet beam extended interaction oscillator (SBEIO) is studied and presented in this article. A novel multi-parameter optimization scheme is developed, which is based on the simulated annealing global optimization algorithm, the nonlinear theory, and 3-D simulations, including the axial electric field distribution and the distances between each gap. The 3-D particle-in-cell (PIC) simulations are performed to verify the scheme. A $\textit {Ka}$ -band SBEIO with nine gaps is optimized with a 36.25-kV and 3.5-A electron beam. The final optimized efficiency obtained from the developed code is 31%, which shows a good agreement with the 32.6% results of the PIC simulation. Compared with the uniform axial electric field distribution, the optimized design increased the efficiency from 15.8% to 32.6%.

Perturbation of Reflective Discharge Plasma with a Hollow Cathode upon the Emission of Plasma Electrons

Perturbation of a reflective discharge plasma with a hollow cathode upon the emission of plasma electrons through a small channel is studied experimentally. The energy spectrum of emitted electrons expands as the external accelerating electric field grows. This could be due to the emergence of an axial electric field in the discharge plasma of the inter-cathode space.

Piezopotential in a composite cantilever of piezoelectric dielectrics and nonpiezoelectric semiconductors produced by shear force through e 15

We propose a specific composition of a beam of a piezoelectric dielectric layer sandwiched between two nonpiezoelectric semiconductor layers. A one-dimensional theoretical model is established for the bending of the beam with shear deformation. A theoretical analysis of a cantilever of such a beam under an end shear force is performed. Results show that an axial electric field develops in the beam because of the shear deformation accompanying bending via the piezoelectric constant e 15. The axial electric field drives the charge carriers to the two ends of the beam. Thus the proposed composite beam can be used as a new and basic structure with potential applications in piezotronics when the shear force is present or dominant, differing from the homogeneous beam and the composite beam using e 33 in the literature which are more suitable when bending moment is dominant.

Transmission of charged nanoparticles through the DMA adverse axial electric field and its improvement

AbstractCharged particles can be classified according to their electrical mobility using electrical methods. These particles are often transported against an adverse electric field from a region of...

Linear instability of a charged non-Newtonian liquid jet under an axial electric field

A theoretical model is established to study the breakup of a charged power law liquid jet, which is moving in stationary air. Furthermore, the effect of a uniform axial electric field is considered in this mathematical model. The liquid non-Newtonian behavior is explained by the power law model, which is assumed to be a Taylor–Melcher leaky dielectric material in this case. The corresponding dispersion relation is derived through a linear analysis. Besides, the effects of the axial electric field with a low and a high density of surface charge, the asymmetric disturbances, and relaxation time on the charged power law liquid jet instability are investigated. Results show that the effects of the axial electric field intensity on the charged power law liquid jet are different when the density of charge on the liquid surface is set as low and high. Besides, the asymmetric disturbances dominate the jet instability when the charge density is set as low, and the axisymmetric disturbance dominates the jet instability when the surface charge density is set as high. The flow model in this paper can be used for designing and operating the electrospraying and spinning systems.

Analysis of entropy generation in biomimetic electroosmotic nanofluid pumping through a curved channel with joule dissipation

Biomimetic designs are increasingly filtering into new areas of technology in recent years. Such systems exploit characteristics intrinsic to nature to achieve enhanced adaptivity and efficiency in engineering applications. Peristaltic propulsion is an example of such characteristics and in the current article it is explored as a feasible mechanism for deployment in electrokinetic pumping of nanofluids through a curved distensible conduit as a model for a bioinspired smart device. The unsteady mass, momentum, energy and nanoparticle concentration conservation equations for a Newtonian aqueous ionic fluid under an axial electrical field are formulated and simplified using lubrication approximations and low zeta potential (Debye Hückel linearization). A dilute nanofluid is assumed with Brownian motion and thermophoretic body forces present. The reduced non-dimensional conservation equations are solved with the symbolic software, Mathematica 9 via the NDSolve algorithm for velocity, temperature, nano-particle concentration distributions for low zeta potential. An entropy generation analysis is also conducted. The influence of curvature parameter, maximum electroosmotic velocity (Helmholtz-Smoluchowski velocity), inverse EDL thickness parameter, zeta potential ratio and Joule heating parameter on transport characteristics is evaluated with the aid of graphs and contour plots. Temperature profiles are elevated with positive Joule heating and reduced with negative Joule heating whereas the opposite behaviour is observed for the nano-particle concentrations.

2D axial-azimuthal particle-in-cell benchmark for low-temperature partially magnetized plasmas

The increasing need to demonstrate the correctness of computer simulations has highlighted the importance of benchmarks. We define in this paper a representative simulation case to study low-temperature partially-magnetized plasmas. Seven independently developed particle-in-cell codes have simulated this benchmark case, with the same specified conditions. The characteristics of the codes used, such as implementation details or computing times and resources, are given. First, we compare at steady-state the time-averaged axial profiles of three main discharge parameters (axial electric field, ion density and electron temperature). We show that the results obtained exhibit a very good agreement within 5% between all the codes. As discharges are known to cause instabilities propagating in the direction of electron drift, an analysis of these instabilities is then performed and a similar behaviour is retrieved between all the codes. A particular attention has been paid to the numerical convergence by varying the number of macroparticles per cell and we show that the chosen benchmark case displays a good convergence. Detailed outputs are given in the supplementary data, to be used by other similar codes in the perspective of code verification.

Nonlinear optical properties of cylindrical quantum dot with Kratzer confining potential in the presence of axial homogeneous electric field

Electronic states of an electron localized in a cylindrical quantum dot with Kratzer confining potential in the presence of axial electrostatic field are considered. The dependences of the dipole matrix elements on the geometrical parameters and values of the electric field are calculated. Nonlinear optical effects such as second harmonic generation and optical rectification in this structure are studied. The electric field values, at which double resonance condition are satisfied, have been found. Optical rectification and the second harmonic generation coefficients of energy dependence curves are obtained. Specificity of the Kratzer confinement potential profile leads to vanishing of the mean displacement of the electron in intraband transitions. This fact is reflected in the behavior of optical rectification coefficient, which has a deep dip around certain values of the electric field.

Numerical Study of Electron Cyclotron Drift Instability: Application to Hall Thruster

We study the cross-field electron transport in Hall thruster induced by ExB cyclotron drift instability. The investigation tool, consisting of one-dimensional Particle-in-Cell model in the azimuthal drift direction, has been subjected to a convergence study to verify the effects of numerical parameters. The instability evolves keeping the discrete nature of its cyclotron harmonics only for low wavenumbers. A resonance broadening mechanism induced by the electron heating and velocity distribution deformation makes the high-wave numbers disappear in the long non-linear stage. A large wavelength modulation, comparable to the entire azimuthal domain considered is always superimposed. The saturation mechanism is conducted by ions that, due to friction with electrons and trapping in the potential well, heat up and rotate along the electron drift direction. With the best numerical parameters found, the scaling of anomalous mobility with the most important physical quantities (gas and plasma density, magnetic field, accelerating axial electric field and ion mass) has been obtained. Results show that the electron cross-field mobility has a strong dependence from the plasma density and ion mass: for large plasma density, the system undergoes an abrupt change entering in a mode dominated by fluctuation-induced transport, while lighter ions present larger mobility. The scaling of the dominant wavelength detected is compatible with the first harmonic and no transition towards ion acoustic like instability has been observed.

Parametric study of the radial plasma-wall interaction in a Hall thruster

An investigation on the influence of relevant parameters on an annular Hall effect thruster plasma discharge is performed using a radial particle-in-cell simulation code with secondary electron emission from the walls and prescribed axial electric and radial magnetic fields. A simulation with true-secondary electrons only is taken as reference. First, the near-wall conductivity effects on the magnetized secondary electrons are illustrated by doubling the , allowing a further code validation. Second, when secondary backscattered electrons are included, the enhanced secondary emission yields lower sheath potential drops and primary electron temperature. Moreover, the dominant backscattered electrons increase the average secondary electrons emission energy, greatly affecting its temperature anisotropy ratio and increasing the replenishment level of the wall collectable tails of the primary electrons velocity distribution function. Third, the effect of the true-secondary electrons emission energy on the potential profile is shown to be negligible, the latter being mainly set by the dominant magnetic mirror effect. Finally, a planar case featuring symmetric plasma profiles permits to confirm the validity of the large cylindrical asymmetries present in the reference case, induced by the combined effects of the geometric expansion, the magnetic mirror and the centrifugal force (due to the drift). A smaller deviation of the primary electron momentum equation from the Boltzmann relation along the magnetic lines is still found in the planar case, induced by the parallel temperature non-uniformity.

The dynamics of discharge propagation and x-ray generation in nanosecond pulsed fast ionisation wave in 5 mbar nitrogen

In this work, the propagation of fast ionisation wave (FIW) discharges driven by negative nanosecond high-voltage (HV) pulses and the x-ray spectrum from the FIW discharges are investigated. The measurement using a capacitive probe shows that the peak axial electric field () at each position rises with the increase of the applied voltage amplitude (Umax), resulting in an increase of the FIW velocity (VFIW). The influence of the pre-ionisation on the FIW propagation is estimated from the relationship between VFIW and The pre-ionisation effect appears to be enhanced with the increase of Umax and it is suspected to be due to the presence of more high energy electrons. This is supported by the measured x-ray spectrum, showing a higher count rate and a more elevated high energy tail with a larger Umax. The spatially resolved measurement of the x-ray spectrum shows that, with the increase of the distance away from the HV electrode (as the cathode), the lower energy part (< ∼15 keV) of the x-ray spectrum keeps decaying, while its high energy tail (> ∼25 keV) rises at first and then decays. Based on the spatially resolved x-ray spectrum, it is inferred that, as high energy electrons move away from the HV electrode, the peak of their energy distribution is shifted toward a higher value, while their total number decreases. Further analysis implies that the electrons emitted from the cathode obtain a large percent of the applied potential in the vicinity of the cathode and become runaway electrons. The electrons with a high initial energy travel freely in the discharge region, due to a decreasing electron collisional cross section with its energy.

Tunnel ionization of diatomic atmospheric gases (N2, O2) by laser radiation

We present the results of calculation of the rates of tunnel ionization of N2 and O2 molecules from the ground and excited vibrational states by linearly polarized laser radiation. These data are necessary for the theoretical description of filamentation. For N2, we consider ionization from the and shells, which give comparable contributions. For O2, we consider ionization from both the ground and excited electronic terms. We demonstrate that for N2, the ionization rate is maximum when the electric field vector of laser radiation is directed along the molecular axis (for shell) or perpendicular to it (for shell), whereas for the O2 molecule, for both electronic states considered, the rates have maxima when the angle between the electric field and molecular axis is equal to 45°.