Research on corona discharge suppression of high-voltage direct-current transmission lines based on dielectric-film-covered conductor

Corona discharge suppression for high-voltage direct-current(HVDC) transmission lines at line terminals such as converter stations is a subject that requires attention. In this paper, a method based on a conductor covered with dielectric film is proposed and implemented through a bench-scale setup. Compared with the bare conductor, the corona discharge suppression effect of the dielectricfilm-covered conductor under positive polarity is studied from the composite field strength and ion current density using a line-plate experimental device. The influences of film thickness and film material on the corona discharge suppression effect are investigated. The charge accumulation and dissipation characteristics of different film materials are also studied. The results show that the conductor covered with dielectric film has excellent ability to inhibit corona discharge. The groundlevel composite field strength of the conductor covered with dielectric film is lower than its nominal field strength, and its ion current density is at the n A m~(-2) level. The corona threshold voltage can be promoted by increasing the film thickness, but the ability to inhibit corona discharge becomes weak.The larger the surface electric field strength, the more charge accumulated, but the faster the charge dissipation rate. Compared with polyvinyl chloride film, cross-linked polyethylene film has stronger charge accumulation ability and slower charge dissipation rate, which can better restrain the corona discharge of HVDC transmission lines.     

Study on influencing factors of ion current density measurement in corona discharge of HVDC transmission lines

The ground level ion current density produced by corona discharge in high voltage direct current(HVDC) transmission lines can reflect the operation status of the lines, but the distorted electric field at the edge of the Wilson plate seriously affects the measurement results of ion current density. In order to measure the ground level ion current density accurately and directly, a new reduced scale wire-plate experimental device in which the Wilson plate is flush with the grounding plate is designed. The influence of protective annulus width and the height of the Wilson plate from the grounding plate on ground level ion current density are studied. In addition, the differences between the micro-current galvanometer method and the sampling resistance method in the measurement of ion current density are compared. Finally, the ground level ion current density distributions of unipolar and bipolar HVDC transmission lines are measured. The results show that the edge effect of the Wilson plate can be neglected when the width of protective annulus is less than 2 mm, and the ion current density is nonlinear with the height of the Wilson plate from the grounding plate. Moreover, the internal resistance of the digital voltmeter seriously affects the measurement results and it is necessary to correct the results. Finally, at the same applied voltage, the ground level ion current density in the negative conductor region is higher than that in the positive conductor region.     

Humidity effects on the ground-level resultant electric field of positive DC conductors

The effects of humidity on the ground-level resultant electric field around positive DC conductors were studied both experimentally and numerically. Experiments were carried out in an artificial climate chamber, the results of which showed that the photon count and the groundlevel resultant electric field strength both increased with increasing relative humidity. Numerical calculations for different values of relative humidity were carried out, including solutions of the positive corona inception voltage and the ion-flow field, for which a photoionization model and the upstream finite element method were employed, respectively. In order to analyze the effects of humidity, three main factors were considered: the ionization coefficient, the attachment coefficient in the photoionization model and the modified ion mobility of the charged water particles. The results indicated that, with increasing relative humidity, increasing values of the effective ionization coefficient were responsible for a reduction in the inception voltage, and the reduction reinforced the ground-level resultant electric field. Moreover, due to the charged water particles and the lower ion mobility with increasing relative humidity, the space charge density distribution was enhanced, which also strengthened the ground-level resultant electric field.     

The Effect of Gas Flow Rate on Radio-Frequency Hollow Cathode Discharge Characteristics

It is known that gas flow rate is a key factor in controlling industrial plasma processing. In this paper, a 2D PIC/MCC model is developed for an rf hollow cathode discharge with an axial nitrogen gas flow. The effects of the gas flow rate on the plasma parameters are calculated and the results show that： with an increasing flow rate, the total ion（N＋2, N＋） density decreases, the mean sheath thickness becomes wider, the radial electric field in the sheath and the axial electric field show an increase, and the energies of both kinds of nitrogen ions increase;and, as the axial ion current density that is moving toward the ground electrode increases, the ion current density near the ground electrode increases. The simulation results will provide a useful reference for plasma jet technology involving rf hollow cathode discharges in N2.     

Study on water treatment effect of dispersion discharge plasma based on flowing water film electrode

To improve the utilization rate of plasma active species,in this study,a closed non-uniform air gap is formed by a flowing water film electrode and a sawtooth insulating dielectric layer to realize the diffuse glow discharge in the atmosphere.Firstly,the electric field distribution characteristics of non-uniform air gap in the sawtooth dielectric layer are studied,and the influence of aspect ratio on the characteristics of diffuse discharge plasma is discussed.Subsequently,the effects of wire mesh,the inclination angle of the dielectric plate,and liquid inlet velocity on the flow characteristics of the water film electrode are analyzed.The results show that the non-uniform electric field distribution formed in the sawtooth groove can effectively inhibit the filamentous discharge,and the 1 mm flowing water film is directly used as the electrode,and high-active plasma is formed directly on the lower surface of the water film.In addition,a plasma flowing water treatment device is built to treat the methyl orange solution and observe its decolorization effect.The experimental results show that after 50 min of treatment,the decolorization rate of the methyl orange solution reaches 96％,which provides a new idea for industrial applications of wastewater treatment.     

400 kV强流中子发生器的物理设计

对400 kV强流中子发生器进行了物理设计。采用Poisson/Superfish软件对中子发生器高压电极和加速管的电场分布进行了模拟,结果显示,各关键区域的空间电场最大值远低于击穿电场限值。以强流束旁轴包络方程为基本模型,发展了强流束传输系统束包络的计算机模拟程序IONB1.0,模拟了中子发生器传输系统中40 mA的D束流包络。结果显示,设计方案中所采取的两间隙高梯度加速结构有较强的聚焦性能,能有效抵消强流束空间电荷效应造成的束流发散,加速管出口处的束包络半径约3 cm,由加速管出口处的空间电荷透镜和三重四极磁透镜组成的传输系统能将束流聚焦在约140 cm处的靶上,且束斑直径小于2 cm。     

A low-cost, accurate and non-intercepting continuous method for beam current measurements in a high-current ion implanter

The development of a low-cost, accurate, non-intercepting continuous method for measuring the beam current in a high-current ion implanter is described. The method, named a differential current monitor, is based on the electric charge conservation principle, applied to the currents that flow in the implanter electrical system, due to the acceleration voltage applied to the ion beam and the leakage currents to ground. This method allows for continuous measurement of the ion beam current without intercepting it. Since its installation, it is possible to accurate measure ion beam currents from tens of μA to mA, which is the normal range for this type of system.     

特高压交流输电线路对人体电场效应的对比分析

摘要本文通过有限元分析方法计算了1000kV输电线路下方简化人体模型的电场效应,比较分析了不同塔型时人体中的感应电场及其分布情况。结果表明：人体周围电场并不是均匀分布的,而是产生了畸变;人体较细的部位（如颈部与腿部）电流密度较大;与普通型输电线路相比,紧凑型线路下人体内感应电流密度较小;中枢神经系统组织的最大感应电流为远小于2mA·mt安全限值;与紧凑型线路相比,普通型线路中枢神经系统组织的电场强度较大,但其最大感应电场仍小于20mV·m-1的光幻视阈值。研究表明,特高压交流输电线路下人体感应电流及电场均低于根据ICNIRP导则推荐的安全限值。     

Characteristic studies on positive and negative streamers of double-sided pulsed surface dielectric barrier discharge

The mechanisms of streamer generation and propagation in double-sided pulsed surface dielectric barrier discharge (SDBD) on both sides have been analyzed and investigated by experiment and numerical simulation. The fully exposed asymmetric SDBD has two discharge processes located on the high voltage electrode (HVE) side and the ground electrode (GE) side. Discharge images of the HVE side and GE side are taken by a digital camera under continuous pulse and ICCD (Intensified Charge Coupled Device) is utilized to diagnose the generation and propagation of streamers in single pulse discharge. In order to understand the physical mechanisms of streamer evolution more deeply, we establish a 2D simulation model and analyze it from the aspects of electron density, ion density, reduced electric field and electron impact ionization source term. The results show that the primary and secondary discharges on the HVE side and the GE side of the double-sided SDBD are composed of positive streamer and negative streamer, respectively. On the HVE side, the accumulation of positive charges on the dielectric surface causes the direction of the electric field to reverse, which is the principal factor for the polarity reversal of the streamer. On the GE side, both the negative charges accumulated on the dielectric surface and the falling voltage are the key factors for the streamer polarity switch.     

Correlation between surface charge and creepage discharge on polymeric dielectrics under high-frequency high-voltage stress

In the present work, creepage discharge characteristics, i.e. amplitudes, phases, and repetitiveness, and surface charge dynamic behaviors under a 20 kHz high-frequency sinusoidal waveform high-voltage electrical stress were captured in a discharge chamber with temperature and humidity control. The results showed that the creepage discharges mostly occurred in the positive half phase, whose maximum amplitude increased with the development of discharge. The inception voltage of the creepage discharge is independent of the frequency of the external electrical stress. Once the discharge occurred, there were a large number of positive and negative particles ionized by a high electric field. Because of the much higher velocity of electrons than positive ions, the energetic discharge-produced electrons are likely to disperse away along the surface and be accumulated through adsorption, collision, and reactions. Moreover, the positive ions join the high-conductive discharge channel and disappear though the ground electrode. Thus, after high-frequency creepage discharge, only negative charges remained on the dielectric surface, as measured. Particularly, the creepage discharges mostly occurred in the positive half phase, owing to the reverse electric field induced by the accumulated negative charges. With the development of creepage discharge, some large-amplitude discharges began to occur in the positive-peak-phase region. The research concluded that the synergistic effect of negative surface charges and large-amplitude discharges eroded the dielectrics and excited the streamer to creep toward the ground electrode until flashover along the surface. Therefore, the correlation between high-frequency creepage discharge and surface charge is preliminarily revealed.     

蒸汽湿度电容传感器内部电场与流场耦合特性数值研究

基于电介质极化和蒸汽流动的基本理论,利用FLUENT软件的二次开发功能,对蒸汽湿度电容传感器内部蒸汽流场和电场进行了理论分析和耦合特性的数值模拟。湍流模型采用标准k-ε模型,近壁区采用壁面函数法,电场和流场方程均使用SIMPLE算法。研究结果表明：当蒸汽为单相饱和蒸汽时,电容传感器内部电势由正极板向负极板逐渐减小,且变化较均匀,电荷主要分布在极板附近,内部区域无极化电荷;电场对流场的影响主要体现在极板附近蒸汽的径向流速上,最外层极板附近电场对流场的影响最大;流场对电场的影响主要体现在电极板的边缘效应上,有流场时极板附近的电场强度较无流场时低;数值模拟结果与实验结果的相符程度较好。     

Pulsed extraction of ionization from helium buffer gas

The migration of intense ionization created in helium buffer gas under the influence of applied electric fields is considered. First the chemical evolution of the ionization created by fast heavy-ion beams is described. Straight forward estimates of the lifetimes for charge exchange indicate a clear suppression of charge exchange during ion migration in low pressure helium. Then self-consistent calculations of the migration of the ions in the electric field of a gas-filled cell at the National Superconducting Cyclotron Laboratory (NSCL) using a particle-in-cell computer code are presented. The results of the calculations are compared to measurements of the extracted ion current caused by beam pulses injected into the NSCL gas cell.     

Surface Effects of Radiation on Transistors

Surface effects caused by ionizing radiation have been found to result in serious parameter changes in certain transistors. These effects include large increases in leakage current, changes in gain, and increases in noise. Studies have been made of the effects of dose, dose rate, bias, transistor environment, and surface protection, in addition to the phenomena of recovery and memory. The greatest changes occur when bias and radiation are applied simultaneously to a gas-encapsulated silicon transistor with unprotected surfaces. Most of these effects can be qualitatively explained through the use of a simple model of the process. Radiation ionizes the encapsulating gas, and the resulting ions and electrons are directed to transistor surfaces by electric fields at the junction surfaces and between the transistor and its can. Inversion layers are produced at the surface which grossly change certain transistor parameters. The great variability among devices of the same type suggests that the gas ions interact with the surface by imparting charge to surface contaminants. Detailed investigation of the influence of electric fields between a transistor structure and its can have been carried out on special gas-encapsulated mesa and planar transistors which are electrically insulated from their cans. Results indicate that inversion layers on both collector and base are affecting ICBO. while, as would be expected, gain is altered principally by an inversion layer on the base. In the gasencapsulated planar devices the effect of can bias on ICBO is greatly reduced and its effect on gain is practically zero.     

Techniques for Investigating Integrated Circuit Dielectric Isolation Media

This paper describes two different techniques for investigating the dielectric isolation of integrated circuits manufactured by this method of isolation. The study concentrates on the two radiation effects of induced transient conductivity and charge storage in silicon dioxide. The first technique is theoretical involving a mathematical model which considers some of the physical processes in silicon dioxide under irradiation. A system of partial differential equations is derived from a consideration of some of the possible mechanisms and carrier kinetics occurring in the oxide as a result of radiation. A sub-routine was then written for an existing computer program (SCEPTRE) which was used to numerically solve the continuity equations describing the model. Primary outputs of the computer program are the transient current density, total charge in the oxide, and the surface charge induced in the silicon by the charge in the oxide which then allows one to also calculate the induced charge in the gate electrode. In addition, available as outputs are the local electric field, local charge density, and the instantaneous density of electron and hole charge carriers throughout the dielectric. The other technique is an empirical method of nondestructively determining an existing nominal electric field in unirradiated, irradiated and then annealéd silicon-silicon dioxide-polycrystalline silicon (SOS) structures. This method of investigation is based on the quadratic electro optical Kerr effect. From results obtained by applying external bias voltage on these SOS-structures it was concluded that the nominal internal electric field in the oxide is directed toward the polycrystalline silicon region.     

Ion-induced electrostatic charging of ice

We studied electrostatic charging on amorphous ice films induced by the impact of 100 keV Ar⁺ ions at 45° incidence. We derived the positive surface electrostatic potential from the kinetic energy of sputtered molecular ions. Measurements were performed as a function of film thickness, ion flux and accumulated fluence. The main results are (a) films charge up to a saturation value, following an exponential time dependence. (b) The time constant for charging is approximately proportional to the reciprocal of the ion flux. (c) The maximum surface voltage depends on film thickness and ion flux. (d) Charging does not occur for films thinner than the maximum range of projectile. (e) Dielectric breakdown is observed for surface potentials above ∼100 V. We explain the measurements with a model in which charges can drift into the substrate or be trapped temporarily near the ionization range of the projectiles. A charge can be released from the trap by the electric field produced by a nearby charge injected by subsequent projectiles.     

The influence of charge characteristics of suspension droplets on the ion flow field in different temperatures and humidity

In order to clarify the charging characteristics of suspension droplets in ion flow field under different temperatures and humidity, the effective charging factor used to characterize the charging characteristics of suspension droplets is introduced in this paper, and a calculation method of charging factor is proposed based on the upstream finite element method (FEM). Then, the charging factor under different temperatures and humidity is calculated, and the analytic expression of the charging factor considering the influence of temperature and humidity is obtained by fitting the calculation results. The influence of suspension droplets on the ion flow field is analyzed. The results show that the charging factor is small and increases little with the relative humidity when the relative humidity is less than 60%, and the charging factor is large and increases rapidly with the relative humidity when the relative humidity is more than 60%. At the same relative humidity, the charging factor increases linearly with the temperature. The influence of charged suspension droplets on the ion flow field can be ignored when the relative humidity is less than 60% and must be considered under high temperature and humidity. The calculation method and analytic expression of the charging factor proposed in this paper can be used to model of ion flow field considering the influence of temperature and humidity and provide technical support for the construction of HVDC transmission lines across high temperature and humidity.     

Impact and energy deposition of slow, highly charged ions on a solid surface

A plasma region in nanometer scale may be created by a highly charged ion impact on solid surface. The charge imbalance leads to enormous electric fields and may further induce Coulomb explosion due to electrostatic repulsion in the region. Thus, the highly charged ion is thus expected to be a powerful tool to induce surface modification in the nanometer scale. The Coulomb explosion model is applied in order to interpret the interaction mechanism and to understand the impact and energy deposition of highly charged ions on a solid surface, and to obtain the energy deposited by the ion. The energy deposition ratio is dependent on the material and charge. A high temperature and high pressure environment will be formed by the deposited energy, causing the atoms to swell up and a hillock nano-defect to be formed on surface. The height of hillock is estimated from the Coulomb explosion.     

Exploration of a MgO cathode for improving the intensity of pulsed discharge plasma at atmosphere

With regard to the lower density and energy of electrons in pulsed discharge plasma (PDP) at atmosphere, leading to the lower energy utilization of plasma, we propose a MgO cathode to enhance the plasma intensity according to field emission principle. The MgO cathode is prepared by an electro-depositing MgO film on a stainless steel plate. This way, the positive charges come to the cathode and accumulate on the surface of the MgO film, leading to the enhancement of the electric field intensity between the cathode and MgO film, and result in the strong emission of secondary electrons from the MgO cathode. As a result, the intensity of plasma can be enhanced. Herein, the effect of the MgO cathode on the intensity of PDP is investigated. It was shown that the discharge peak current was improved by 20% compared with that of without the MgO cathode. With increasing the MgO film thickness, discharge intensity, including the peak current, transforming charge and spectrum intensity first increased and then decreased. Higher enhancement of peak current, transforming charge and spectrum intensity were acquired with a higher peak voltage. Compared to a cathode without MgO film, the ozone production is higher with MgO cathode employed. The research proposes a novel approach for improving the intensity of discharge plasma, and also provides a reference for further application of PDP.     

Gas pressure effect on plasma transport in a magnetic-filtered radio-frequency plasma source

Volume negative ion production relies on a magnetic filter(MF), where the plasma downstream of the MF is characterized by a strip-like pattern that consists of a bright and dense plasma region. In this work, we study, in a radio-frequency plasma source, the effects of operating pressure on this strip. This investigation, conducted using a Langmuir probe, shows that the plasma uniformity might be controlled through the gas pressure. Moreover, the operating pressure determines on which hemi-cylinder(side of magnetic field lines) the strip forms. This side inversion of the high-density plasma hemi-cylinder is due to an inversion of an ambipolar electric field that changes the E?×?B drift direction.     

Effect of insulating oil covering electrodes on the characteristics of a dielectric barrier discharge

In this study, the effects of the fluid cooling and electric field line deformation were investigated in a dielectric barrier discharge (DBD) plasma source. The DBD plasma jet is improved by covering the ground electrode and a power electrode with insulating oil. We obtained positive results as insulating oil prevents arc formation, while it improved the supplied power and plasma jet length, and increased radical production. Radical production of this nonthermal plasma jet is studied with polyvinyl alcohol–potassium iodide liquid.