Investigation of variable aperture on the performance and lifetime of ion thruster

Beam flatness is an important parameter that determines the performance and the lifetime of a gridded ion thruster.To improve the beam flatness of the 30 cm (LIPS-300) ion thruster,variable aperture ion optics that adapts to the decreasing ion density as the radius increases is proposed.It is the ion optics that the screen grid surface is divided into several zones,where the aperture diameter in each zone is determined by the ion density and the electron temperature upstream of the screen grid.The beam current density in the central area is artificially reduced.A particle in cell-Monte Carlo collision model is applied in this work to investigating the effect of variable aperture on the perveance and the maximum beam current per aperture by simulating the extraction,focusing and acceleration processes of ions.Taking into account the engineering implementability,the screen grid surface is divided into four zones.The hole diameter in each zone is decreased from 1.95 mm to 1.8 mm,1.9 mm,1.8 mm and 1.7 mm,respectively.The simulation results show that the maximum ion density in the center area of grid is decreased by 10.6％ and 6.99％,while it is increased by 6.49％ and 22.3％ in the edge region,respectively.The beam flatness of the variable aperture ion optics is improved from 0.69 to 0.88.The erosion rate is decreased by 31.9％,but the total beam current is also decreased by 7.15％.The simulation results can provide a valuable reference of the development of the ion thruster.     

Discharge Simulation and Fabrication Process of an Aluminum Electrode and an Alumina Layer in AC-PDP

A larger space PDP cell with patterned aluminum as the addressing electrode and alumina as the dielectric layer was proposed. The aluminum electrode and the alumina dielectric layer formed on the aluminum electrode were prepared separately by magnetron sputtering and anodic oxidation for plasma display panel. The properties of the aluminum electrode and the alumina dielectric layer were tested and can meet the demand of PDP application. The resistivity of the aluminum electrode is about 5×10 8 ·m, the voltage withstanding of the alumina dielectric layer exceeds 100 V/μm and the relative permittivity is about 3.5 at 1 MHz. With this structure, the manufacturing cost of PDP could be cut and the addressing discharge formative delay is reduced by 0.67%, which is proved by PIC-MCC simulation.     

Parametric investigation of stationary plasma thruster performance

A particle-in-cell Monte Carlo collision method is used to carry out parametric investigations on the performance of a stationary plasma thruster (SPT). The effects of applied voltage, channel length, working gas pressure and the peak magnetic field are studied. The evolution of the plasma density, electron temperature, discharge current etc. are observed under various operating conditions. The performance of the SPT is evaluated in terms of specific impulse and thrust efficiency. The results are compared with existing theoretical and computational results, wherever possible. An attempt is made to understand the nature of the variations in terms of the physical processes involved.     

荫罩式等离子体显示单元阳极条纹现象的研究

等离子体显示单元中的阳极条纹现象,即等离子体密度沿阳极分布不均匀的现象,对于提高等离子体显示屏的显示性能具有重要影响.在许多等离子体显示单元的实验和模拟过程中,都观察到了条纹现象,但对于条纹形成的机理还没有定论.本文采用基于粒子模拟的PIC-MCC(Particle in Cell Monte Carlo Collide)模型,对荫罩式等离子体显示单元中阳极条纹产生过程进行了模拟,并结合放电过程中粒子浓度、等位线分布以及壁电荷积累分布等的变化情况,详细研究了荫罩式等离子体显示单元中阳极条纹的形成机理,通过对阳极条纹现象及其机理的研究,可以更好地理解等离子体放电单元的放电特性和机理,为我们寻找提高放电效率的途径提供一定的理论指导和依据.     

Kinetic simulation of the transition from a pulse-modulation microwave discharge to a continuous plasma

The generation of a very strong peak current in the first period(PCFP) in a pulse-modulated microwave discharge has been discussed in previous studies. In this paper we focus on the transition process from a pulsed discharge to a fully continuous one driven by the pulsed microwave power source by means of a kinetic model. The computational results show that by increasing the duty cycle or voltage modulation rate(VMR), the discharge eventually becomes fully continuous and PCFP can no longer be observed. In the transition process, the distributions of the electric field, electron energy probability function(EEPF) and plasma density are discussed according to the simulation data, showing different discharge structures. The simulations indicate that many high-energy electrons with electron energy larger than 20 eV and low-energy electrons with electron energy less than 3 eV could be generated in a pulsed microwave discharge, together with a reversal electric field formed in the anode sheath when PCFP occurs. However, only medium-energy electrons could be observed in a fully continuous discharge. Therefore, by investigating the transition process the pulse-modulated microwave discharges can be further optimized for plasma applications at atmospheric pressure.     

Influence of the axial magnetic field on sheath development after current zero in a vacuum circuit breaker

After current zero,which is the moment when the vacuum circuit breaker interrupts a vacuum arc,sheath development is the first process in the dielectric recovery process.An axial magnetic field (AMF) is widely used in the vacuum circuit breaker when the high-current vacuum arc is interrupted.Therefore,it is very important to study the influence of different AMF amplitudes on the sheath development.The objective of this paper is to study the influence of different AMF amplitudes on the sheath development from a micro perspective.Thus,the particle in cell-Monte Carlo collisions (PIC-MCC) method was adopted to develop the sheath development model.We compared the simulation results with the experimental results and then validated the simulation.We also obtained the speed of the sheath development and the energy density of the ions under different AMF amplitudes.The results showed that the larger the AMF amplitudes are,the faster the sheath develops and the lower the ion energy density is,meaning the breakdown is correspondingly more difficult.     

107cm荫罩式PDP实际单元和放大单元放电特性的研究

利用基于PIC-MCC(Particle in cell-Monte Carlo collision)模型的OOPIC-PRO软件计算了107 cm荫罩式PDP实际单元和放大单元的放电,模拟结果表明相似放电单元具有相同的伏安特性,放电相对应时刻的空间粒子浓度分布相同,从数值实验角度验证了气体放电的重要定律:相似定律.在理论模拟的基础上,利用实际单元和放大单元的实验测试系统,测量并比较了放大单元和实际单元的放电电流,结果表明放大单元和实际单元的放电电流强度相当,但实际单元较放大单元的放电快约20倍.     

等离子体平板背光源单元放电特性的研究

采用粒子网格-蒙特卡罗碰撞(PIC-MCC)方法对等离子体平板背光源单元的放电过程进行了数值模拟,获得了放电过程中各带电粒子在空间区域的分布以及各区域的形成和性质,并结合模拟结果,详细分析了等离子体平板背光源单元的放电特性.结果表明,放电单元采用大电极间距可获得正柱区放电,正柱区的形成是正离子在阴极鞘层区不断积累将电位抬高所致.通过增加电极间距以增加正柱区的长度,可以有效地改善放电特性,从而提高背光源的发光效率.     

大气压射频微等离子体放电结构演化的粒子模拟

大气压射频微等离子体放电具有较大的潜在应用价值,但实验研究较困难。为此借助于粒子模拟的方法,在给定的放电间隙下,研究了电流密度及二次电子发射系数(SEEC)对射频微等离子体的放电结构的影响。模拟结果表明,随着输入电流密度的增大,放电空间逐渐由鞘层主导的结构转变为辉光放电结构,电子密度也会随之增大,鞘层电场逐渐增强,同时电子能量概率函数(EEPF)曲线会随之整体向上偏移;而在给定的电流密度下,随着SEEC的增大,放电结构也会逐渐由鞘层主导的结构转变为辉光放电的结构,电子密度会随之增大,同时鞘层电场会逐渐变小,高能电子(20 eV)比例也随之减小。最后分析了在大间隙下出现鞘层主导结构的可能性。     

The Numerical Simulation Study of Pseudospark Hollow Cathode Discharge

Pseudospark discharges are sources of intense electron beams. Reported in this paper are theoretical studies of the Pseudospark discharges. A theoretical and computational model has been adopted to study the initiation phase of Pseudospark discharges via a two-dimensional electrostatic particle-in-cell plus Monte Carlo (PIC-MCC) collision method. From the numerical results, a sequence of physical events has been identified. It has been found that the ionization processes determined by local electric field and hollow cathode effect. The growth phenomena is dependent of α ionization multiplication due to local space charge from initial ionization growth to onset of the hollow cathode effect, and then hollow cathode effect become leading factor.