Space Charge Density Research Articles

Особенности анализа вод, почв и донных отложений в масс-спектрометрии с индуктивно-связанной плазмой

The paper discusses the possibilities and limitations of the method of mass spectrometry with inductively coupled plasma on the example of elemental analysis of natural and drinking waters, soils and grounds. It is shown that the combination of this method with the simpler atomic emission method makes it possible to expand the range of determined elements, simplify the mass-spectral analysis and increase its reliability. It is shown that the use of the ICP-MS method in the analysis of various objects makes it possible to determine the majority of elements with extremely low detection limits. The reason for the manifestation of matrix effects is the positive space charge formed between the interface and the extractor, the composition of which is determined by the composition of singly charged argon ions. The increase in the concentration of ions in this region is the appearance of a matrix element, which facilitates the scattering of ions from this region. It was found that the heavier the ions of the matrix element, the more the space charge density increases and the scattering occurs. A serious limitation of the method is associated with interferences due to the presence of a certain amount of two and three-charged ions in the plasma. These ions, which have approximately the same mass as the isotopes of the element being determined, are formed as a result of various plasma-chemical reactions and interfere with the determination.

Design and optimization of the shape of electrostatic precipitator system

The electro hydrodynamic (EHD) flows in “Optimization of The Shape of Electrostatic Precipitator System” which also known as “Cup shape W type electrostatic precipitator system” is simulated on Ansys Fluent 6.1. The “Cup shape” and W type electrostatic precipitator System is comparing with old flat plate Electrostatic precipitator system. According to theoretical analysis model particle flow is analyze by time-averaged conservation equations of mass and momentum, the electric field and current flow equations. The W-type collecting surface space charge density is more uniform rather than the flat plate. It is seen that on W- type circular wire plate number of trap particle is more than the flat plate type, whereas number of escapes is more in flat type. Which state that increasing the voltage of this design increase the efficiency of the system. In Cup design electrode release greater number of ion or electric field than the circular type electrode. Together using of w type and cup type electrode increase the ionization and collection area, which improve the efficiency of the ESP design. Separate work on practical design already done in previous work for Cup shape electrode with the flat collecting plate design and w type collecting plate with circular wire which give much better results.

Negative differential resistance and rectification effect of the benzoquinone molecules junction sandwiched between the graphene nanoribbon electrodes

Based on the first-principles calculation method combining the density functional theory (DFT) and the nonequilibrium Green’s function (NEGF) method, the negative differential resistance (NDR) and rectification effect of the benzoquinone molecules junction sandwiched between the graphene nanoribbon electrodes are systematically investigated. The current of the device with the central o-benzoquinone and p-benzoquinone molecule has been demonstrated to decrease with the increase of the bias voltage in the range of [± 0.9 V, ± 1.5 V] and [± 0.6 V, ± 1.1 V], respectively, exhibiting a significant NDR effect. In addition, the interesting NDR effect of the device with the central carbon (C) and nitrogen (N) connected o- and p-benzoquinone molecules has been observed in the bias voltage range of [0.9 V, 1.2 V] and [ $$-0.8$$ V, $$-1.0$$ V] , respectively. The current of the device with the central sulfur (S) and oxygen (O) connected o- and p-benzoquinone molecules should decrease with the increase of the bias voltage at the regime of [0.8 V, 1.0 V] while that should be forbidden when a negative bias voltage is applied, illustrating an interesting rectification effect, and the maximum rectification ratio is observed to be up to 57.85 and 55.85, respectively. The obtained NDR and rectification effect are physically explained from the integral of the transmission coefficient in the bias voltage window and the distribution of the real space charge density, and the demonstrated results are believed to be vital for the designing of the molecular switches, molecular rectifying devices and negative differential resistance devices based on benzoquinone molecules junction.

Evolution Characteristics of Electric Field for AC Corona Modes in Atmospheric Air

Electric field is one of the key parameters to study the charge dynamics for corona discharge. To study the motion characteristics of space charge in different corona modes of ac corona, electrooptic (EO) modulation technique was used to obtain the electric field in corona space. This article focuses on the time-varying characteristics of electric field for ac corona discharge modes. The step phenomenon is observed and the evolution characteristics of electric field for corona modes, from the Trichel pulses to the stable glow, are obtained. It was found that the background field could not remove the space charge generated by the discharge completely within half a cycle, which directly proved the existence of retained charge. And it is proposed that the continuous and fast rising electric field is the characteristic of positive glow in ac corona, which may be an effective method to judge the positive glow. Additionally, electric fields at different spatial locations were studied. The electric field step at the migration zone is suppressed, and as the space charge density increases, the suppression phenomenon becomes more obvious. This article provides more information on the physical mechanisms of the ac corona modes and gives support for the research of corona plasma.

Modeling of space charge dynamics in polyethylene under AC stress based on bipolar charge transport model

Space charge dynamics under AC stress is of importance as a majority of high voltage cables are under AC stress, and space charge is the driving mechanism of dielectric degradation under these conditions. Bipolar charge transport model is used to simulate space charge dynamics in polyethylene under AC stress. The current density, electroluminescence intensity and space charge density under sinusoidal, triangular and square voltages are compared. It is found that there is no phase shift between current density, electroluminescence intensity and applied voltages, which disagrees the results of Baudoin et al. The thickness of space charge layer under AC stress is much thinner that under DC stress.

Impact of accelerated aging of epoxy‐Ni nanocomposites on space charge variation adopting pulsed electro acoustic technique

AbstractEpoxy‐Ni nanocomposites of different weight percentages are subjected to accelerated aging by water aging, thermal aging and UV irradiation to understand the influence of aging conditions on their space charge behavior. Homo‐charge accumulation is observed for unaged epoxy‐Ni nanocomposites. The magnitude of accumulated space charge is found to be lesser in 0.5 wt% epoxy‐Ni nanocomposite specimen compared to other unaged specimens. Water diffusion coefficient of epoxy‐Ni nanocomposites decreased with increasing weight percentage of filler addition. Space charge accumulation tends to increase with water aging. Increment in the space charge accumulation of 0.25 wt% epoxy‐Ni nanocomposite specimen is lesser compared to other water aged specimens. Exposure to thermal stress resulted in deterioration of the molecular structure of insulating material leading to an increase in trap‐controlled mobility, further leading to the reduction in space charge density with aging period. UV irradiation marginally assisted the charge transportation phenomenon, which resulted in the slight decrease of space charge density of epoxy‐Ni nanocomposites after UV irradiation. Hetero‐charge formation is found for all the three aging procedures. Overall, the specimen S1 reflected better space charge characteristics after being subjected to different aging conditions.

Improved Rectification and Osmotic Power in Polyelectrolyte-Filled Mesopores.

Ample studies have shown the use of nanofluidics in the ionic diode and osmotic power generation, but similar ionic devices performed with large-sized mesopores are still poorly understood. In this study, we model and realize the mesoscale ionic diode and osmotic power generator, composed of an asymmetric cone-shaped mesopore with its narrow opening filled with a polyelectrolyte (PE) layer with high space charges. We show that, only when the space charge density of a PE layer is sufficiently large (>), the considered mesopore system is able to create an asymmetric ionic distributions in the pore and then rectify ionic current. As a result, the output osmotic power performance can be improved when the filled PE carries sufficiently high space charges. For example, the considered PE-filled mesopore system can show an amplification of the osmotic power of up to 35.1-fold, compared to the bare solid-state mesopore. The findings provide necessary information for the development of large-sized ionic diode and osmotic power harvesting device.

Space charge profile study of AlGaN-based p-type distributed polarization doped claddings without impurity doping for UV-C laser diodes

The space charge density profile of the nondoped AlGaN-based p-type cladding layer for UV-C laser diodes realized by distributed polarization doping is examined theoretically and experimentally. The analysis of the capacitance-voltage measurement revealed that the average effective acceptor density of 4.2 × 1017 cm–3 is achieved even without impurity doping, and it is in good agreement with the theoretical prediction from the measured Al composition profile. This result suggests that the cladding layer is ideal for UV-C LDs because it provides sufficient hole injection while potentially avoiding internal losses due to impurity doping.

Effect of particle segregation on non-uniform electrostatic charge distribution in cylindrical silo during loading binary particles with size ratio of 2.5:1 centrally

This paper is aimed to study the effect of particle segregation on the non-uniform electrostatic charge distribution in the silo. By using the DEM method, the flow patterns at different repose angles α and volume fractions of the small particle in the feeding mixture χS is obtained. Results show that the space charge density level is higher at the silo center and smaller near the silo wall when particles have negative saturation charges. The increase of α can increase the space charge density difference between the silo center and the wall side. Increasing χS will increases the space charge density level in the silo as well as the risk of the electrostatic discharge in the silo. Furthermore, the electrostatic charge distribution in the silo is related to the charging efficiency of particles. The electrostatic charge distribution in the bipolar charging system was compared with that in the monopolar charging system.

Reconstructing the electrical structure of dust storms from locally observed electric field data

While the electrification of dust storms is known to substantially affect the lifting and transport of dust particles, the electrical structure of dust storms and its underlying charge separation mechanisms are largely unclear. Here we present an inversion method, which is based on the Tikhonov regularization for inverting the electric field data collected in a near-ground observation array, to reconstruct the space-charge density and electric field in dust storms. After verifying the stability, robustness, and accuracy of the inversion procedure, we find that the reconstructed space-charge density exhibits a universal three-dimensional mosaic pattern of oppositely charged regions, probably due to the charge separation by turbulence. Furthermore, there are significant linear relationships between the reconstructed space-charge densities and measured PM10 dust concentrations at each measurement point, suggesting a multi-point large-scale charge equilibrium phenomenon in dust storms. These findings refine our understanding of charge separation mechanisms and particle transport in dust storms.

Fluid simulation model and analysis of partial discharge characteristics of tip defects

The tip discharge is modeled and the micro discharge characteristics are studied. The hydrodynamic model of tip discharge in transformer oil is established. The development process of streamer discharge under pulse voltage is analyzed. The distribution of space charge density and space electric field under different pulse voltage amplitude and rising edge is obtained. The numerical results show that: with the increase of applied voltage amplitude, the average velocity of streamer development changes more significantly with the same discharge spacing; the steeper the rising edge pulse is, the faster the average discharge development speed is and the larger the discharge radius is. At the same time, according to the change law of streamer morphology development under AC voltage, the discharge frequency is less, the amplitude is higher, and the phase distribution is narrow when the applied voltage is positive half cycle. When the applied voltage is negative half cycle, the discharge times are more and the phase distribution is wide, and the tip discharge has obvious polarity effect.

The structure of an electronegative magnetized plasma sheath with non-extensive electron distribution

In this paper, an electronegative magnetized plasma sheath model with non-extensive electron distribution is established, and the Bohm criterion affected by the non-extensive parameter q is theoretically derived. The ion Mach number varies with q. The numerical simulation results show that compared with electronegative magnetized plasma sheath with Maxwell distribution (q = 1), the sheath structures with super-extensive distribution (q < 1) and sub-extensive distribution (q > 1) are different. The physical quantities including the sheath potential distribution, ion density distribution, the electron density distribution, negative ion density distribution and the net space charge density distribution are discussed. It is shown that the non-extensive parameter q has a significant influence on the structure of the electronegative magnetized plasma sheath. Due to the Lorentz force, both the magnitude and the angle of the magnetic field affect the structure of the sheath, whether the electrons are Maxwell distributed or non-extensively distributed.

Ionic Current Rectification of Porous Anodic Aluminum Oxide (AAO) with a Barrier Oxide Layer.

Synthetic nanofluidic diodes with highly nonlinear current-voltage characteristics are currently of particular interest because of their potential applications in biosensing, separation, energy harvesting, and nanofluidic electronics. We report the ionic current rectification (ICR) characteristics of a porous anodic aluminum oxide membrane, whose one end of the nanochannels is closed by a barrier oxide layer. The membrane exhibits intriguing pH-dependent ion transport characteristics, which cannot be explained by the conventional surface charge governed ionic transport mechanism. We reveal experimentally and theoretically that the space charge density gradient present across the 40-nm-thick barrier oxide is mainly responsible for the evolution of ICR. Based on our findings, we demonstrate the formation of a single 5-8-nm-sized pore in each hexagonal cell of the barrier oxide. The present work would provide valuable information for the design and fabrication of future ultrathin nanofluidic devices without being limited by the engineering of the nanochannel geometry or surface charge.

Efficiency enhancement in InGaN-based laser diodes using an optimized Al0.12Ga0.88N electron blocking layer

In this paper, a design for an electron blocking layer (EBL) is proposed to enhance the wall plug efficiency of InGaN-based laser diodes. Using calibrated 3D simulations (including thermal models), a comprehensive analysis of various design aspects (composition, thickness and p-doping) of EBLs is conducted, including their impact on carrier (electron and hole) wavefunction overlap and stimulated recombination rate in the quantum wells (QWs) along with the space charge density, electric field and free carrier absorption (FCA) at the interface of the p-side waveguide/EBL. The results indicate that Poole–Frenkel emission is vital for consideration of FCA in the p-doped layers of the epitaxial structure. Consequently, the proposed EBL design reduces electron overflow, improves hole injection, decreases the internal absorption losses and thus, enhances the internal quantum efficiency of the device. The threshold current is reduced from 230 mA to 205 mA as compared to the reference structure. The hole barrier is reduced by 23.93%. Hence, the output power is increased from 1.746 W to 1.95 W, and the voltage drop as well as the device temperature is reduced. These improvements enhance the efficiency from 37.4% of the reference structure to 42.1% in the proposed structure (corresponding to a bias current of 1 A).

Transformed two-fluid equations of low-pressure plasmas with non-vanishing ion temperature without the singularity at the ionic sound barrier and several methods to solve these equations numerically

The equations of the two-fluid model of low-pressure plasmas with warm ion gas are taken into consideration including collisions between charged particles and neutrals, the charge exchange, and the ionization. The basic equations contain a removable singularity at the ion sonic speed. These equations are ill-conditioned in the subsonic interval of the ion flux, but they are well-conditioned in the transsonic one. First, several transformations and auxiliary functions are introduced in order to eliminate the singularity at the ion sound speed. The resulting boundary value problem is numerically solved by a multi-shooting method for one of the versions of the transformed equations. Second, an improved one-fluid-model is well-conditioned wherein the space charge density is calculated additionally using the electric field and the Poisson equation. The numerical solution yields usable approximated results in the subsonic interval and suitable initial values for the solution of the two-fluid model in the transsonic interval. Third, the unknown functions are expanded as a power series in the relation of the ion temperature to the electron temperature. These equations can be numerically integrated throughout both intervals without serious difficulties. A set of parameters is given describing subsonic intervals extending over the whole plasma. Results obtained by means of the used methods confirm that Bohm's sheath criterion loses its meaning in collision-dominated plasmas. The scopes of application of the different methods are treated by means of examples.

Theoretical study on the anomalies of the magnetic susceptibility in the honeycomb lattice compound Na2Co2TeO6

In this paper, based on ab initio molecular dynamics and the exchange-interaction model, the magnetic order transition phenomenon of ${\mathrm{Na}}_{2}{\mathrm{Co}}_{2}\mathrm{Te}{\mathrm{O}}_{6}$ material under different temperatures is investigated. Our results exclude the effect of lattice distortion as a factor for magnetic susceptibility under different temperatures in ${\mathrm{Na}}_{2}{\mathrm{Co}}_{2}\mathrm{Te}{\mathrm{O}}_{6}$. Furthermore, we found that the charge transfer is not a main factor to effectively explain the magnetic phase transition. We proposed a method based on radial distribution function to analyze the space-charge density (SCD) to explore the thermal fluctuations. Our analysis of SCD implies that the thermal fluctuations induced by the variation of atomic vibration under different temperatures are responsible for the anomalies of magnetic susceptibility in ${\mathrm{Na}}_{2}{\mathrm{Co}}_{2}\mathrm{Te}{\mathrm{O}}_{6}$ below the N\'eel temperature.

An insight into effect of front surface field on the performance of interdigitated back contact silicon heterojunction solar cells

The development of interdigitated back contact silicon heterojunction has been flourishing in the field of solar cells. The front surface field has a decisive influence on the electrical field effect passivation of interdigitated back contact silicon heterojunction solar cells, and the effect of passivation layers on the performance of solar cells needs to be clarified. In this study, the two-dimension TCAD models of the doped n+-a-Si: H layer and SiNx with a fixed charge layer were established by the Sentaurus code, respectively. The space charge density and electric field intensity, carrier transportation, and distribution of current density were numerically analyzed to evaluate the effect of these two front surfaces on the performance of interdigitated back contact silicon heterojunction solar cells. The results show that for SiNx, the root cause of the field passivation is the surface fixed charge density. The combination of the doping concentration and layer thickness directly affects the field passivation of n+-a-Si: H. Based on the intuitive carrier transport vector, the selective transportation of the carrier near the surface is proved by the front surface field, which effectively inhibits the recombination. The current density distribution on the cross-section reveals that a strong front surface field is an effective way to reduce the internal recombination in particular. Considering practical operating conditions, a doping concentration of 1e20 cm−3, in combination with 7 nm layer thickness, potentially improves the front surface field of n+ a-Si: H leading to the maximum conversion efficiency of 27.41%, with the voltage increased by 32.8 mV and the fill factor reaching 86.84%.

Quasi-stationary modeling of the DBD plasma flow control around airfoil

This paper presents the results of numerical simulation of a dielectric barrier discharge (DBD) plasma actuator and shows its effectiveness to control air flow around the NACA(National Advisory Committee for Aeronautics)0015 airfoil. The actuator consists of two tape electrodes separated by a dielectric layer, and it is mounted on the suction side of the airfoil at 18% of the chord length. An alternating voltage with 20 kV magnitude and 10 kHz frequency is applied between both electrodes. The physical model of the DBD includes the drift of two ionic species, positive and negative, and the Poisson equation for the electric potential distribution. The spatio-temporal distribution of the electric field, the space charge density in the ambient air, and the surface charge density on the dielectric layer have been determined. The time average electric body force was entered into the air flow model, which was solved using the Spalart–Allmaras turbulence technique. The simulation of the air flow was performed for the free-stream velocities between 5 m/s and 20 m/s (Reynolds numbers 1.65 × 105–6.61 × 105 based on the chord length). The results of computations show the effect of the electrohydrodynamic actuation on the flow pattern, the lift and drag coefficients, the pressure coefficient, and the flow fluctuation near the airfoil. The ability of the DBD actuation to effectively control the aerodynamic airfoil characteristics has been confirmed, and its limitations for the discussed case have been determined.

On the nature of optical flashes observed aboard Universitetsky-Tatyana and Vernov satellites

A model of electric discharges at mesospheric altitudes has been developed to explain the nature of optical flashes/transient atmospheric events (TAEs) observed aboard the Russian microsatellites “Universitetsky-Tatyana-1”, “Universitetsky-Tatyana-2” and “Vernov”. The model is based on assumption that large-scale areas with a low space charge density and a low electric breakdown threshold can occur in the mesosphere thereby producing electric discharges between the charged areas. Variations in the number densities of electrons and ions in the discharge channel connecting these areas are described by kinetic equations, in which spatial derivatives are disregarded. The discharge parameters, such as mobility of charged particles, rate of ionization and rate of electron attachment to neutral molecules are assumed to depend on altitude in the atmosphere. Numerical simulation and analytical solutions of the basic equation set make it possible to analyze the time dependences of electric field, conductivity, current and number densities of electrons and ions in the discharge channel at various altitudes in the atmosphere. Theoretical estimates of the TAEs parameters are best suited to the onboard observations under assumptions that, first, the charged areas of 10−15km in size are situated at altitudes of 60−70km and, second, their total charge is about 1 C. The theory predicts that the energy dissipated during a single electric discharge under these parameters can reach a value from tenths to several MJ while the discharge duration can be on the order of several milliseconds.

Impact of Temperature on the Transient DC Field Distribution of ±1100 kV UHVDC Wall Bushing

UHV DC wall bushing is the only channel connecting the valve hall and the DC electric field in the converter station. For the epoxy - SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> gas composite insulation wall bushing, the main insulation material is the epoxy/crepe paper core and SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> gas. The transient process of establishing the DC electric field for the wall bushing is impacted by the temperature gradient. In this paper the 3-D temperature field of the wall bushing has been simulated considering the effect of heat conduction, convection and radiation. The simulation results have been confirmed using a temperature rise experiment. The transient process of the wall bushing under the actual operation condition has been simulated using the gas saturation current density method. The temperature impact on space charge density in the core, the surface charge on the interface, and the electric field distribution on the bushing is investigated. In this way a theoretical basis is developed for the optimal design of the bushing that is conductive to the safe operation of the bushing.