Influence Of Space Charge Research Articles

Long-Term Stable Cycling of Dendrite-Free Lithium Metal Batteries Using ZIF-90@PP Composite Separator.

Lithium metal batteries (LMBs) are anticipated to meet the demand for high energy density, but the growth of lithium dendrites seriously hinders its practical application. Herein, we constructed a kind of composite separator (ZIF-90@PP) consisting of zeolite imidazole framework-90 (ZIF-90) and polypropylene (PP) to promote the uniform deposition of Li+ and inhibit the growth of lithium dendrites. The aldehyde groups interacting with TFSI- and the nitrogen-containing negative groups attracting Li+ of ZIF-90 can facilitate the dissociation of LiTFSI to release more Li+, thus alleviating the influence of space charge near the electrode surface and accelerating the transfer of Li+. Not only does the excellent electrolyte wettability of ZIF-90 enhance the electrolyte retention capacity of the separator, but the orderly nano-channels in ZIF-90 also restrict the free migration of anions and homogenize the distribution of Li+. Consequently, the functional separator achieves a long-term stable Li plating/stripping cycling for over 780 h at 2 mA cm-2. Moreover, an impressive average coulombic efficiency of 98.67% at 0.5 C after 300 cycles is realized by Li || LFP full cells based on ZIF-90@PP with a capacity retention rate of 71.22%. The high-rate and long cycling performance of the modified Li || LFP cells further demonstrates the advantages of the ZIF-90@PP composite separator.

Multiturn Injection Design and Optimization for XiPAF-Upgrading Synchrotron

XiPAF (Xi’an 200MeV proton application Facility) synchrotron is using H- stripping injection and phase space painting scheme. With the demand of more particle species for single event effect study, XiPAF synchrotron has been upgraded to multiturn injection from stripping injection, the injection system must be redesigned. This paper report XiPAF-Upgrading synchrotron multiturn injection scheme, simulation results by PyORBIT[1] show that the injection efficiency is ∼85% for proton and ∼80% for heavy ions. The influence of space charge and magnet errors on accumulated particle number has been studied by simulation.

Influence of mixed-frequency medium-voltage and environmental stress on the aging of epoxy

Recent developments in power electronic technologies lead to new challenges for insulation systems. This contribution aims to clarify the influence of a broad range of mixed-frequency (MF) medium-voltage and environmental stress parameters on the aging of epoxy insulation. For this purpose, test samples are stressed with an AC (50 Hz) or a DC voltage, superimposed with a pulse-width-modulated (PWM) voltage (kHz range). An analysis of the samples’ health state is carried out after the aging by the evaluation of potential aging markers (AC breakdown strength, dielectric permittivity, glass transition temperature, Fourier-transform infrared spectroscopy spectra). Although the main focus of this work is on aging below the inception of partial discharges (PDs), it was first confirmed that PD-related aging depends mainly on the peak voltage stress. In contrast, the results obtained by aging below PD inception suggests a dependence on the root-mean-square of the applied voltage stress, and consequently on the energy dissipation. Aging in the PD-free regime was only observed at alternating electric field stress and high relative humidity or elevated temperatures. No influences of space charge and of the slew rate of the PWM voltage were observed. Remarkably, higher PWM frequencies lead to less insulation aging. This might be attributed to the increasing hindrance of polymer side chain movement at higher frequencies, as observed by dielectric spectroscopy. In addition, it is indicated that the aging mechanisms under MF voltage stress result from superimposed single-frequency aging mechanisms and that aging is activated after a latency period. Of the investigated potential aging markers, only the residual breakdown strength revealed aging effects, which correlates with lifetime observations in the PD-free voltage stress regime. It is hypothesized that the aging mechanism is associated with a rearrangement of the free volume in the polymer, followed by a localized breaking of van der Waals bonds.

Effect of Space Charge on Stationary and Transient Electric Field Distribution of HVDC Cable Joint

The conversion of AC XLPE cable lines into direct-current (DC) operation has been proven to be an effective means to improve the transmission capacity of the system. Prefabricated joints are the weakest points of a cable line because of the complex structures, and composite interfaces contained. Therefore, it is of great theoretical and engineering significance to study the field strength distribution of XLPE AC cable prefabricated joints under DC voltage, effectively evaluate their DC tolerance characteristics, and provide a basis for the construction and transformation of XLPE cable DC distribution network system. This paper takes the silicone rubber (SIR), and ethylene-propylene-diene monomer (EPDM) prefabricated joints of 10kV XLPE cables as an example, the cable joint temperature field, and electric field coupling simulation model is established by the finite element analysis software COMSOL Multiphysics. The steady and transient electric field simulation of the joints under different DC voltages and load conditions are carried out considering the influence of space charge. The results show that with the increase of applied voltages and load level, the space charge injection increases, and the maximum steady state field strength in the joint is concentrated at the root of the stress cone, showing an increasing trend. Compared with the SIR joint, the field strength in the EPDM joint is higher. The capacitive component of the field strength in the joint is proportional to the peak value of the impulse voltage under the DC superimposed impulse voltage. In other words, the transient electric field equation meets the superposition principle applied.

Discharge characteristics of positive and negative polarity streamers with submillimeter gap based on fractal theory

In order to study the characteristics of streamer discharge in sub-millimeter gap, an experimental system and an image acquisition system of positive and negative polarity streamer discharge in the gap of 100–500 μm at atmospheric pressure are built, and the initial breakdown voltages and breakdown images of positive and negative polarity streamer discharge in a gap range of 100–500 μm are collected, and the fractal dimension of the experimental discharge images is calculated by Matlab. The experimental analysis shows that the air breakdown discharge in the gap range of 100–500 μm still conforms to the stream theory, and the polarity effect between the breakdown voltage of positive and negative streamers and the fractal dimension of the discharge image is obvious. The influence of space charge and photoionization on the meandering degree and coverage of the discharge channel in stream theory increase with the increase of the gap, and jump at 300 μm. The fractal simulation of positive and negative streamer discharge with a gap of 500 μm is established by using WZ (Wiesmann-Zeller) model based on fractal theory in Matlab. It is found that the development probability index <i>η</i> is inversely proportional to the fractal dimension, and that the <i>η</i> is smaller in positive streamer than in negative streamer under the same discharge condition.

Glycerol as an efficient plasticizer to increase the DC conductivity and improve the ion transport parameters in biopolymer based electrolytes: XRD, FTIR and EIS studies

In the current work Plasticized sodium ion conducting solid polymer electrolytes (SPEs) based on polyvinyl alcohol: methylcellulose (PVA: MC) and sodium iodide (NaI) as the electrolytic salt are fabricated. The SPE films are created using a renowned solution casting procedure, and the results of the experiments are provided. The development of polymers-salt complexes is supported by the Fourier-transform infrared transform (FTIR) analysis. The degrees of crystallinity of the polymers are noticeably decreased as a result of the glycerol plasticizer, according to X-ray diffraction test. The sample inserted with 40 wt% glycerol has the maximum ionic conductivity, according to electrical impedance spectroscopy (EIS). Electrical equivalence circuits (EEC) are used to explore the electrolytes circuit components. For the highest conducting electrolyte, the number density ( n ), mobility (µ), and diffusion coefficient (D) of ions are found to be 2 × 10 21 , 1.79 × 10 −6 , and 4.59 × 10 −8 , respectively. A high dispersion of the real component of dielectric permittivity at a lower frequency are used to infer the space charge influence induced by stainless-still (SS) electrodes. The tangent loss spectra show that the bouncing chance per unit time decreases as the glycerol concentration rises.

Linear electron accelerator for energy 8-50 MeV with injection from an electron source based on cluster plasma systems

For many years, one of the key problems of modern accelerator physics has been an increase of the rate of the energy gain in RF linear electron accelerators. The physical limits of the accelerating field intensity for metallic accelerating structures have been practically reached; therefore, new acceleration schemes are being considered, primarily acceleration in plasma and wakefield acceleration. The second aim is the generation of ultrashort (100 fs and less) electron bunches, for which RF photoguns are traditionally used. In this case, for RF photoguns, a serious problem that limits the intensity of electrons in a bunch is the influence of the own space charge during emission and acceleration in the near-cathode region, where the beam is weakly relativistic and the influence of the space charge on its dynamics plays the determinative role. The possibility of using a plasma cathode source as an injector for RF accelerator will considered. In the future, this may make it possible to bypass the limitations inherent in RF photoguns (sufficient influence of the space charge on the beam dynamics in the near-cathode region) and acceleration in the laser-plasma channel (low electron capture coefficient in the acceleration mode, wide energy spectrum - 10% or more at energies of tens and hundreds of megaelectrons). It is proposed to develop a combined accelerator in which a bunch generated in a laser-plasma channel is injected into a traditional metal structure. It is supposed that could be possible to generate a short (from 0.1 to 1.0 ps) electron bunches with an energy of several hundred kiloelectrons, which will make it possible to consider such source as an alternative to the photocathode. Next, the beam must be captured in the acceleration mode in a normally conducting section and accelerated to an energy of 50 MeV with the possibility of energy tuning. The features of such accelerator, the features of the electron bunch capturing in the acceleration mode, and the possible values of the energy spectrum in such a system will considered.

Accurate and Efficient Calculation Method for Ion Flow Field Near Direct Current Voltage Divider

The surface of grading rings in DC voltage divider may cause surface wear or scratch, resulting in corona phenomenon. Due to the influence of space charges and surface charges, the total electric field near DC voltage divider is different from the nominal electric field. For the problem of solving the ion-flow field near the DC voltage divider, this paper proposes an improved method based on upwind Finite Element Method (FEM). According to the nominal electric field results, the updated switch state of the charge density is determined, and then the upwind FEM is used to update the node charge density. This method uses a dual-scene iterative method to converge for the multiple grading rings, which improves the convergence. The correctness of the method is verified by the coaxial cylindrical electrode. Finally, the ion-flow field near 500 kV DC voltage divider is calculated. The results show that the total electric field near the grading ring becomes more uniform due to the effect of space charges and surface charges. In the space far from or close to the grading rings, the total electric field will increase or decrease compared with the nominal electric field. The method in this paper provides guidance for the calculation of the ion-flow field near the DC divider and its insulation design.

Numerical calculation of transient electric field considering space charge in oil-paper insulation of converter transformers

PurposeThe purpose of this paper is to develop a numerical simulation method based on the transient upstream finite element method (FEM) and Schottky emission theory to reveal the distribution characteristics of space charge in oil-paper insulation.Design/methodology/approachThe main insulation medium of the converter transformer in high voltage direct current transmission is oil-paper insulation. However, the influence of space charge is difficult to be fully considered in the insulation design and simulation of converter transformers. To reveal the influence characteristics of the space charge, this paper proposes a numerical simulation method based on Schottky emission theory and the transient upstream FEM. This method considers the influence of factors, such as carrier mobility, carrier recombination coefficient, trap capture coefficient and diffusion coefficient on the basis of multi-physics field coupling calculation of the electric field and fluid field.FindingsA numerical simulation method considering multiple charge states is proposed for the space charge problem in oil-paper insulation. Meanwhile, a space charge measurement platform based on the electrostatic capacitance probe method for oil-paper insulation structure is built, and the effectiveness and accuracy of the numerical simulation method is verified.Originality/valueA variety of models are calculated and analyzed by the numerical simulation method in this paper, and the distribution characteristics of the space charge and total electric field in oil-paper insulation medium with single-layer, polarity reversal of plate voltage and double-layer are obtained. The research results of this paper have the guiding significance for the engineering application of oil-paper insulation and the optimal design of converter transformer insulation.

Generation of ultrashort ion pulses in the keV range: Numerical simulations

In order to gain a direct experimental access to the ultrafast dynamics induced by an impact of an energetic particle onto a solid surface, we set out to utilize a pump–probe technique using an ultrashort ion pulse as a stimulus (“pump”) in combination with a synchronized and time delayed analysis (“probe”). As a necessary prerequisite, we have recently developed a concept to generate ultrashort ion pulses with (sub-)picosecond temporal duration in the keV ion energy range which is interesting in many applications of ion–solid interactions. Here, we present further numerical simulations, where we focus on identifying pathways to decrease the space charge broadening of pulses containing more than one ion. As a result, we find that the influence of space charge can be significantly decreased using a defocused and properly shaped laser beam, thereby allowing to generate picosecond pulses containing up to ∼100 ions.

Influence of space charge on the conductivity of nanocrystalline SrTiO3

A grand canonical multiscale space-charge model has been developed to study and predict the electrical properties of polycrystalline perovskites with complex defect chemistries. This model combines accurate data from hybrid exchange-correlation functional density functional theory calculations (defect formation energies, resultant grand canonical calculations of defect concentrations, and ionization states) with finite-element simulation of the electric field and its coupling to defect redistribution and reionization throughout the grain. This model was used to simulate the evolution of the oxygen partial pressure-dependent conductivity of polycrystalline acceptor-doped strontium titanate as the grain size decreases, and the results were compared to previous experiments. These results demonstrate that as the grain size is reduced from the microscale to nanoscale, the experimentally observed disappearance of ionic conductivity and forward shift of the oxygen partial pressure of the n–p crossover are successfully reproduced and explained by the model. Mechanistically, the changes to conductivity stem from the charge transfer from the grain boundary core into the grain interior, forming a space-charge layer near the grain boundary core that perturbs the local defect chemistry. The impact of the grain size on the electrical conductivity and the underlying defect chemistry across the grain are discussed. In addition to the findings herein, the model itself enables exploration of the electrical response of polycrystalline semiconductor systems with complex defect chemistries, which is critical to the design of future electronic components.

Fast Corona Discharge Assessment Using FDM integrated With Full Multigrid Method in HVDC Transmission Lines Considering Wind Impact

A novel approach for solving the monopolar corona in high voltage direct current (HVDC) transmission line systems is proposed by the finite difference method (FDM) and a full multigrid method (FMG). Specifically, the FMG is implemented as a fast solver with respect to existing iterative solutions for the FDM to solve the Poisson equation, particularly on fine grids. The advantage features of the proposed approach are that it avoids the hypothesis of a constant electric field around the conductor’s surface. Further, it considers the influence of space charge on both the magnitude and the direction of the electrical field. The proposed approach is employed for computing the electric field and current density on the ground plane with and without wind effect. Considering the impact of wind in the present study, the findings confirm that both corona current density and electric field on the ground plane are influenced by the transverse wave. Eventually, the effect of changing the wind speed on the electric field profiles and the current density is deeply studied in HVDC transmission line systems. To prove the efficacy of the proposed approach, it is compared with previous experimental results where a better agreement is reached rather than other numerical techniques.

Space Charge Transport Characteristic Considering the Non-Uniform Electric Effect of Ion Mobility

Oil-paper insulation is the main insulating medium of converter transformers. Space charge can result in the distortion of electric field in oil-paper insulation, hence it's necessary to analyze the space charge transport characteristic and its influence on the oil-paper insulation. In the paper, the space charge transport characteristic considering the electric field is investigated, and an upstream finite element method is presented to calculate the space charge distribution in oil insulation of converter transformer considering the influence of injection barrier, ion mobility, trapped coefficient and carrier recombination coefficient. Finally, the insulation state of tortuous oil-path is evaluated. Experiments were conducted to analyze the relationship between ion mobility and electric field intensity, the results indicate that the influence of space charge on the electric field intensity in the tortuous oil-path can not be ignored for the design of converter transformer.

Effect of Thickness on the Space Charge Behavior and DC Breakdown Strength of Cross-Linked Polyethylene Insulation

In high voltage direct current (HVDC) cable systems, study of electric field distortion created by space charge accumulation is very important for examining insulation performance. Therefore, in this paper the influence of space charge on short-time breakdown characteristics of cross-linked polyethylene (XLPE) are studied. Trap energy distribution is an important factor affecting space charge behavior in dielectrics. Dielectrics with various thicknesses exhibit different space charge phenomena due to various trap distribution characteristics, which regulate the injection, migration and accumulation processes of charges. Consequently, trap characteristics can affect many parameters, such as charge accumulation depth and injection barrier. XLPE with thickness less than 100 μm show lower density of deep traps which can accumulate homogeneous bulk charges as compared to thick XLPE with thickness greater than 100 μm. This phenomenon determines the internal field strength distortion rate which is 20% larger for thin XLPE and it is much higher than that for thick XLPE. The external factor which is considered for analysis is applied field strength and it shows a linear proportional affect on the electric field distortion. A quantitative relationship model between applied field strength and distortion field strength of XLPE with different thicknesses was established. Linear extrapolation was used to obtain the trend of applied, distortion, and actual field strengths at different XLPE thicknesses when breakdown occurred. When the thickness of XLPE is less than 100 μm, distortion field strengths is higher than 50kV/mm and increases with decreasing thickness, resulting in a significant effect on the breakdown phenomenon and breakdown strength increases with increasing thickness. And when the thickness of XLPE is greater than 100 μm, the distortion field strengths is less than 50 kV/mm which also confirms the volume effect on breakdown phenomenon and breakdown strength decreases with increasing thickness.

Помножувач частоти у субміліметровому діапазоні хвиль. Частина 2. Обґрунтування моделі компактних електронних ущільнень, які існують тривалий час

Subject and Purpose. Part 1 of the present paper presents a feasibility study of a submillimeter frequency multiplier based on a clinotron with a single slow-wave structure. The aim of Part 2 is to gain a better insight into the electron bunching mechanism, seeking for efficient energy exchange between the electron bunches and the RF field in the multiplier of the sort. Methods and Methodology. The research method is a theoretical analysis given to the electron bunching process in a BWO-type oscillator with rigorous numerical models involved. The bunch longitudinal size is calculated in steady state regime with regard to the space charge influence. The necessary conditions for compact electron bunching are sought via numerical integration of the motion equations of electrons subject to the interaction with the RF field of the slow-wave structure. Results. A mechanism of compact electron bunching has been revealed by numerical modeling and described. The pattern of long-lived compact electron bunches continuously moving along the surface of the clinotron comb-type slow-wave structure holds owing to the continuous deposition of compact electron bunches on the comb surface. The compact bunches are formed in electron beam layers farthest from the comb surface but moving to it in consequence of the electron beam inclination under magnetic field action (the clinotron effect). The bunch size and its dependence on the problem parameters have been specified. The research results find use in analysis of operational regimes of conventional clinotrons. Clinotron designers are provided with relevant recommendations. Conclusion. A model of electron bunching in clinotron-type oscillators has been developed with regard to the process of deposition of electron beam layers on the comb-type slow-wave structure surface. It is the existence of a system of compact electron bunches continuously moving along the comb surface that makes possible efficient electron beam interaction with the high-frequency electromagnetic field of multiplied-mode oscillations. We justifiably claim that multipliers of the kind can be advanced to the short-wave end of the submillimeter band.

Corona discharge pulse pattern and audible noise on hybrid AC/DC transmission lines under electric field bias, ripple and ion coupling

Hybrid AC/DC overhead lines offer a significant increase in transmission capacity compared to existing HVAC infrastructure. While corona phenomena and audible noise are crucially important for public acceptance, they are affected by mutual AC/DC coupling. While the underlying phenomena need to be clearly understood and predicted accurately, only few experimental studies exist. The corona effects are therefore studied in detail on a large laboratory setup under the influence of electric field bias, ripple and space charges. The results show a clear trend in the phase resolved partial discharge (PRPD) pattern and repetition rate which can explain the change in audible noise.

Interaction between electrospray using ionic liquid and simultaneous corona discharge under positive and negative polarity

One kind of ionic liquid, 1-ethyl-3-methylimidazolium tetrafluoroborate, is used to investigate the interaction between electrospray and corona discharge under positive and negative polarity. A high-speed camera, a digital camera, and an oscilloscope are applied to observe the shape of the meniscus and the jet, photograph the discharge plume, and observe the current waveform of discharge, respectively. The electrospray and discharge modes are studied under different flow rates and voltage conditions, and the experimental results show that there is only corona discharge with no jet at a low flow rate, while the intermittent jet or droplet emission is accompanied by corona discharge at a high flow rate, and no steady cone jet mode is obtained under all experimental conditions. The inevitability of corona discharge in the electrospray process of 1-ethyl-3-methylimidazolium tetrafluoroborate is analyzed from the viewpoint of electric field. Pulse discharge at low voltage depends on the oscillation of the meniscus. The frequency of pulse discharge can be changed indirectly by changing the voltage to control the oscillation of the meniscus. The influence of corona discharge and resultant space charge is not only on the electric field strength, but also on the shape, which is the reason why the liquid surface morphology is significantly different under positive and negative polarities.

A concept to generate ultrashort ion pulses for pump-probe experiments in the keV energy range

The impact of an energetic particle onto a solid surface generates a strongly perturbed and extremely localized non-equilibrium state, which relaxes on extremely fast time scales. In order to facilitate a time-resolved observation of the relaxation dynamics using established ultrafast pump-probe techniques, it is necessary to pinpoint the projectile impact in time with sufficient accuracy. In this paper, we propose a concept to generate ultrashort ion pulses via femtosecond photoionization of rare gas atoms entrained in a supersonic jet, combined with ion optical bunching of the resulting ion package. We calculate the photoion cloud generated by an intense focused laser pulse and show that Arq+ ions with q = 1–5 can be generated with a standard table-top laser system, which are then accelerated to energies in the keV range over a very short distance and bunched to impinge onto the target surface in a time-focused manner. Detailed ion trajectory simulations show that single ion pulses of sub-picosecond duration can be generated this way. The influence of space charge broadening is included in the simulations, which reveal that flight time broadening is insignificant for pulses containing up to 10–20 ions and starts to increase the pulse width above ∼50 ions/pulse.

Aging mechanisms of polymeric materials under DC electrical stress: A new approach and similarities to mechanical aging

The main fundamental mechanisms proposed for the aging of polymeric insulation to breakdown at the DC design field are reviewed. A correlation between the action of static mechanical stress affecting the whole insulation volume, and DC electric-mechanical stress providing local strain large enough to bring the polymer to plastic deformation is hypothesized. With the corollary that local plastic deformation leads to the formation of cavities, or crazes, of size large enough to trigger highly energetic phenomena and bring about insulation failure, an inter-relationship between mechanical and electrical life models can be obtained and supported by calculation and fitting to experimental results. The influence of space charge is discussed and it is argued that it would play a central role in DC ageing even if its presence is not a precondition.

The Influence of Space Charge on the Transport of Charged Particles Generated during Electrospray in Crossed Gasdynamic and Electric Fields

The transport of charged particles generated during electrospray in a longitudinal gasdynamic field has been studied in a model system comprising two coaxial electrodes and a collector grid. The process has been numerically simulated with omission of the role of a space charge. A comparison of the results shows that the space charge is a key factor determining the transport of charged particles: the model transport efficiency in the absence of space charge reaches 80–100%. In experiment, the efficiency strongly depends on the space charge and amounts to 70–80% for its minimum values, while decreasing to 20–30% with increasing electrospray current.