Diagnostic of capacitively coupled radio frequency plasma from electrical discharge characteristics: comparison with optical emission spectroscopy and fluid model simulation

The capacitively coupled radio frequency(CCRF)plasma has been widely used in various fields.In some cases,it requires us to estimate the range of key plasma parameters simpler and quicker in order to understand the behavior in plasma.In this paper,a glass vacuum chamber and a pair of plate electrodes were designed and fabricated,using 13.56 MHz radio frequency(RF)discharge technology to ionize the working gas of Ar.This discharge was mathematically described with equivalent circuit model.The discharge voltage and current of the plasma were measured atdifferent pressures and different powers.Based on the capacitively coupled homogeneous discharge model,the equivalent circuit and the analytical formula were established.The plasma density and temperature were calculated by using the equivalent impedance principle and energy balance equation.The experimental results show that when RF discharge power is 50–300 W and pressure is 25–250 Pa,the average electron temperature is about 1.7–2.1 e V and the average electron density is about 0.5?×?10~(17)–3.6?×?10~(17)m~(-3).Agreement was found when the results were compared to those given by optical emission spectroscopy and COMSOL simulation.     

Modelling effect of magnetic field on material removal in dry electrical discharge machining

One of the reasons for increased material removal rate in magnetic field assisted dry electrical discharge machining(EDM) is confinement of plasma due to Lorentz forces.This paper presents a mathematical model to evaluate the effect of external magnetic field on crater depth and diameter in single-and multiple-discharge EDM process.The model incorporates three main effects of the magnetic field,which include plasma confinement,mean free path reduction and pulsating magnetic field effects.Upon the application of an external magnetic field,Lorentz forces that are developed across the plasma column confine the plasma column.Also,the magnetic field reduces the mean free path of electrons due to an increase in the plasma pressure and cycloidal path taken by the electrons between the electrodes.As the mean free path of electrons reduces,more ionization occurs in plasma column and eventually an increase in the current density at the inter-electrode gap occurs.The model results for crater depth and its diameter in single discharge dry EDM process show an error of 9%-10%over the respective experimental values.     

Characterization and comprehension of corona partial discharge in air under power frequency to very low frequency voltage

For the partial discharge test of electrical equipment with large capacitance, the use of lowfrequency voltage instead of power frequency voltage can effectively reduce the capacity requirements of test power supply. However, the validity of PD test under low frequency voltage needs to be evaluated. In order to investigate the influence of voltage frequency on corona discharge in the air, the discharge test of the tip-plate electrode under the frequency from 50 to 0.1 Hz is carried out based on the impulse current method. The results show that some of the main features of corona under low frequency do not change. The magnitude of discharge in a positive half cycle is obviously larger than that in a negative cycle. The magnitude of discharge and interval in positive cycle are random, while that in negative cycle are regular. With the decrease of frequency, the inception voltage increases. The variation trend of maximum and average magnitude and repetition rate of the discharge in positive and negative half cycle with the variation of voltage frequency and magnitude is demonstrated, with discussion and interpretation from the aspects of space charge transportation, effective discharge time and transition of discharge modes. There is an obvious difference in the phase resolved pattern of partial discharge and characteristic parameters of discharge patterns between power and low frequency. The experimental results can be the reference for mode identification of partial discharge under low frequency tests. The trend of the measured parameters with the variation of frequency provides more information about the insulation defect than traditional measurements under a single frequency (usually 50 Hz). Also it helps to understand the mechanism of corona discharge with an explanation of the characteristics under different frequencies.     

A novel double dielectric barrier discharge reactor with high field emission and secondary electron emission for toluene abatement

Dielectric barrier discharge (DBD) has been extensively investigated in the fields of environment and energy, whereas its practical implementation is still limited due to its unsatisfactory energy efficiency. In order to improve the energy efficiency of DBD, a novel double dielectric barrier discharge (NDDBD) reactor with high field emission and secondary electron emission was developed and compared with traditional DDBD (TDDBD) configuration. Firstly, the discharge characteristics of the two DDBD reactors were analyzed. Compared to TDDBD, the NDDBD reactor exhibited much stronger discharge intensity, higher transferred charge, dissipated power and gas temperature due to the effective utilization of cathode field emission and secondary electron emission. Subsequently, toluene abatement performance of the two reactors was evaluated. The toluene decomposition efficiency and mineralization rate of NDDBD were much higher than that of TDDBD, which were 86.44%–100% versus 28.17%–80.48% and 17.16%–43.42% versus 7.17%–16.44% at 2.17–15.12 W and 1.24–4.90 W respectively. NDDBD also exhibited higher energy yield than TDDBD, whereas the overall energy constant ${k}_{{\rm{overall}}}$ of the two reactors were similar. Finally, plausible toluene decomposition pathway in TDDBD and NDDBD was suggested based on organic intermediates that generated from toluene degradation. The finding of this study is expected to provide reference for the design and optimization of DBD reactor for volatile organic compounds control and other applications.     

A two-dimensional air streamer discharge modified model based on artificial stability term under non-uniform electric field at low temperature and sub-atmospheric pressure

In this paper, an improved air discharge fluid model under non-uniform electric field is constructed based on the plasma module COMSOL Multiphysics with artificial stability term, and the boundary conditions developed in the previous paper are applied to the calculation of photoionization rate. Based on the modified model, the characteristics of low temperature subatmospheric air discharge under 13 kV direct current voltage are discussed, including needle-plate and needle-needle electrode structures. Firstly, in order to verify the reliability of the model, a numerical example and an experimental verification were carried out for the modified model respectively. Both verification results show that the model can ensure the accuracy and repeatability of the calculation. Secondly, according to the calculation results of the modified model, under the same voltage and spacing, the reduced electric field under low temperature subatmosphere pressure is larger than that under normal temperature and atmospheric pressure. The high electric field leads to the air discharge at low temperature and sub atmospheric pressure entering the streamer initiation stage earlier, and has a faster propagation speed in the streamer development stage, which shortens the overall discharge time. Finally, the discharge characteristics of the two electrode structures are compared, and it is found that the biggest difference between them is that there is a pre-ionization region near the cathode in the needle-needle electrode structure. When the pre-ionization level reaches 10~(13) cm~(-3), the propagation speed of the positive streamer remains unchanged throughout the discharge process, and is no longer affected by the negative streamer. The peak value of electric field decreases with the increase of pre-ionization level, and tends to be constant during streamer propagation. Based on the previous paper, this paper constructs the air discharge model under non-uniform electric field, complements with the previous paper, and forms a relatively complete set of air discharge simulation system under low temperature and sub atmospheric pressure, which provides a certain reference for future research.     

高压偏移栅PMOSFET击穿电压的电离辐照响应

揭示了辐照引起击穿电压变化的机制,提出了提高高压偏移栅PMOSFET击穿电压抗电离辐照的方法。对辐照后击穿电压退火特性进行了研究。     

CFD analysis for thermal mixing in a subcooled water tank under a high steam mass flux discharge condition

A Computational Fluid Dynamics (CFD) analysis for a thermal mixing test was performed for 30 s to develop the methodology for a numerical analysis of the thermal mixing between steam and subcooled water and to apply it to Advanced Power Reactor 1400 MWe (APR1400). In the CFD analysis, the steam condensation phenomenon by a direct contact was simulated by the so-called condensation region model. Thermal mixing phenomenon in the subcooled water tank was treated as an incompressible flow, a free surface flow between the air and the water, and a turbulent flow, which are implemented in the CFX4.4. The comparison of the CFD results with the test data showed a good agreement as a whole, but a small local temperature difference was found at some locations. A sensitivity analysis was performed to find the reason of the temperature difference. The commercial CFD code of CFX4.4 together with the condensation region model can simulate the thermal mixing behavior reasonably well when a sufficient number of mesh distributions and a proper numerical method are selected.     

A novel strategy for quantitative analysis of soil pH via laser-induced breakdown spectroscopy coupled with random forest

pH is one of the significant properties of soil,and is closely related to the decomposition of soil organic matter,anion-cation balance,growth of plants and many other soil processes.In the present work,laser-induced breakdown spectroscopy(LIBS) technique coupled with random forest(RF) was proposed to quantify the pH of soil.First,LIBS spectra of soil was collected,and some common elements in soil were identified based on the National Institute of Science and Technology database.Then,in order to obtain a better predictive result,the influence of different input variables(full spectrum,different spectral ranges,the intensity of characteristic bands and characteristic lines) on the predictive performance of RF calibration model was explored with the evaluation indicators of root mean square error(RMSE) and coefficient of determination(R2),the characteristic bands of four elements(AI,Ca,Mg and Si) were determined as the optimal input variables.Finally,the predictive performance of RF calibration model was compared with partial least squares calibration model with the optimal input variables and model parameters,and RF calibration model showed a better predictive performance,and the four evaluation indicators of R_p~2,RMSEP,mean absolute error and mean relative error were 0.9687,0.1285,0.1114 and 0.0136,respectively.It indicates that LIBS technique coupled with RF algorithm is an effective method for pH determination of soil.     

A calculation model for breakdown time delay and jitter of gas switches under hundred-nanosecond pulses and its application in a self-triggered pre-ionized switch

In this paper,a calculation model for the breakdown time delay and jitter of gas switches under hundred-nanosecond pulses is proposed and applied in a self-triggered pre-ionized switch.The effects of injection time of pre-ionization,pulse rise time,and the pre-ionization jitter are discussed and verified through experiments.It indicates that the pre-ionization should be injected when the electric field is high enough in the gap,injection after 80％peak-time can ensure its effectiveness.Then the statistical time delay jitter will be determined by the pre-ionization jitter,which is an intrinsic restriction of the self-triggered switch.However,when the changing rate of the pulsed electric field exceeds a certain value,the breakdown time delay jitter can be partly offset in the formative stage because the formative time delay has an exponential relationship with the electric field.Therefore,lower time jitter can be obtained under pulses with a shorter pulse rise time.In general,the results of the calculation model agree with the experimental results,and the experimental parameters which lead to a low jitter can also be used as a reference.     

Application of the thin layer activation technique to study surface erosion under high voltage electrical spark discharges

The thin layer activation technique using a heavy ion beam has been applied to measure the erosion loss of materials by electrical spark discharges with a discharge current in the mA range. Since the range of heavy ions such as ¹⁴N, ¹⁶O and ²⁰Ne, is about one order less than that of light ions such as p, d and α, the total activity can be generated within a narrow layer by activation with heavy ions. In the present work, a narrow layer of activity of ∼27 μm thickness was produced in copper-based materials by heavy ion induced nuclear reactions using 110 MeV ¹⁶O ions to measure the surface erosion in the range of hundreds of nanometers to few microns. The sensitivity can be enhanced to tens of nanometers using suitable heavy ions.     

3.0MeV高频高压电子加速器计算机监控系统的研制

描述了基于PLC的高频高压电子加速器的计算机监控系统。在满足加速器正常操作的基础上,增加了能量反馈控制回路,提高了输出能量的稳定度(1％);保证了扫描电流的大小随输出能量变化的自动跟踪调节：在故障诊断方面也提供了有效的手段帮助排除故障或分析故障原因。     

Remote open-path laser-induced breakdown spectroscopy for the analysis of manganese in steel samples at high temperature

A remote open-path laser-induced breakdown spectroscopy(LIBS) system was designed and studied in the present work for the purpose of combining the LIBS technique with the steel production line. In this system, the relatively simple configuration and optics were employed to measure the steel samples at a remote distance and a hot sample temperature. The system has obtained a robustness for the deviation of the sample position because of the open-path and alloptical structure. The measurement was carried out at different sample temperatures by placing the samples in a muffle furnace with a window in the front door. The results show that the intensity of the spectral lines increased as the sample temperature increased. The influence of the sample temperature on the quantitative analysis of manganese in the steel samples was investigated by measuring ten standard steel samples at different temperatures. Three samples were selected as the test sample for the simulation measurement. The results show that, at the sample temperature of 500 ℃, the average relative error of prediction is 3.1% and the average relative standard deviation is 7.7%, respectively.     

The effect of substrate holder size on the electric field and discharge plasma on diamond-film formation at high deposition rates during MPCVD

The effect of the substrate holder feature dimensions on plasma density(ne), power density(Qmw) and gas temperature(T) of a discharge marginal plasma(a plasma caused by marginal discharge) and homogeneous plasma were investigated for the microwave plasma chemical vapor deposition process. Our simulations show that decreasing the dimensions of the substrate holder in a radical direction and increasing its dimension in the direction of the axis helps to produce marginally inhomogeneous plasma. When the marginal discharge appears, the maximum plasma density and power density appear at the edge of the substrate. The gas temperature increases until a marginally inhomogeneous plasma develops. The marginally inhomogeneous plasma can be avoided using a movable substrate holder that can tune the plasma density, power density and gas temperature. It can also ensure that the power density and electron density are as high as possible with uniform distribution of plasma. Moreover, both inhomogeneous and homogeneous diamond films were prepared using a new substrate holder with a diameter of 30 mm. The observation of inhomogeneous diamond films indicates that the marginal discharge can limit the deposition rate in the central part of the diamond film. The successfully produced homogeneous diamond films show that by using a substrate holder it is possible to deposit diamond film at 7.2 μm h~(–1)at 2.5 kW microwave power.     

Surface modification of silicone rubber by CF4 radio frequency capacitively coupled plasma for improvement of flashover

The flashover performance of insulating materials plays an important role in the development of high-voltage insulation systems. In this paper, silicone rubber(SIR) is modified by CF₄ radio frequency capacitively coupled plasma (CCP) for the improvement of surface insulation performance. The discharge mode and active particles of CCP are diagnosed by the digital single-lens reflex and the spectrometer. Scanning electron microscopy and x-ray photoelectron spectroscopy are used for the surface physicochemical properties of samples, while the surface charge dissipation, charge accumulation measurement, and flashover test are applied for the surface electrical characteristics. Experimental results show that the fluorocarbon groups can be grafted and the surface roughness increases after plasma treatment. Besides, the surface charge dissipation is decelerated and the positive charge accumulation is inhibited obviously for the treated samples. Furthermore, the surface flashover voltage can be increased by 26.67% after 10 min of treatment. It is considered that strong electron affinity of C–F and increased surface roughness can contribute to deepening surface traps, which not only inhibits the development of secondary electron emission avalanche but also alleviates the surface charge accumulation and finally improves the surface flashover voltage of SIR.     

Comparison of two models for a high temperature reactor coupled to a gas turbine

This paper presents two independent dynamic models of a nuclear gas turbine power plant. Both the high temperature nuclear reactor (HTR) and its energy conversion system (ECS) based on a direct Brayton cycle have been modelled. One model utilises RELAP5 for the ECS, the other Aspen Custom Modeler (ACM). The reactor model used in both models is a point kinetic model derived from a detailed reactor model. The ECS model is described and compared componentwise, with an emphasis on the turbomachinery. The total plant models are compared with each other by calculating two representative transients: one load rejection transient and one transient with the system at part load.     

高压脉冲辉光放电内表面注入及等离子体特征研究

为了提高内表面注入的剂量及深度均匀性,作者将脉冲高压辉光放电机制引入到内表面改性的研究中.利用发射光谱法及静电探针法对该方法获得的离子体参数进行了诊断,并在特定的内筒中采用氮气为工作气,进行了离子注入实验.结果显示,采用这种方法可以在内筒获得连续存在的等离子体.Ar等离子中含有大量激发态原子,而N等离子体中N2+离子占离子数量的绝大多数.等离子密度随着电压的提高显著提高,当电压从10kV增加到15kV时,Ar等离子体中离子密度增加约4倍,N等离子中离子密度增加约2倍.内表面获得均匀性良好的改性层,对于直径56mm的圆筒在电压20kV、气压1.5Pa条件下注入深度达到16.9nm,剂量均匀性可达到87.3%.     

Study of electromagnetic noise influence on quench detection system under different discharge conditions for EAST

EAST is the first Tokamak device whose toroidal and poloidal magnet are superconducting. The enormous magnetic field energy stored in the magnet system will transfer into thermal energy and cause the damage of superconducting magnet, if a quench happened. Therefore, reliable quench detection is a key issue for steady-state operation. In addition to electromagnetic noise from poloidal magnet fields and plasma current which will experience fast current ramp rate, radio frequency noise from heating system also have some interference on quench detection system to a certain degree. The most difficult point for quench detection system is required to have more detail evaluation on electromagnetic noise interference.Recently experiments have been carried out successfully in EAST device. The steady-state operation with 1 MA of plasma current and more than 100-s plasma duration has been obtained. In the paper, the electromagnetic noise interference on quench detection system under different discharge conditions are analyzed and relative process methods are also introduced. The technological experience and experimental data are significant for the constructing ITER and similar superconducting device have been mentioned which will supply significant technological experience and experimental data for constructing ITER and similar superconducting device.     

超灵敏小型回旋加速器质谱计高频三角波加速电源系统的改进

高频三角波加速电源系统的改进是为了实现交替加速的需要和减少高频干扰对磁场稳流电源的影响.前者实际上是改造一台斜坡电压产生器.描述了高精度连续可调直流稳压电源的改制及动态响应;高频机电源工艺的改进减少了高频对磁场电源的干扰,满足了SMCAMS的测试要求.