平等板等离子体鞘层演化过程的PIC模拟研究

为了详细描述等离子体形成过程中鞘层的产生、演化过程,建立了平等板内部等离子体流动过程的PIC模型。在考虑壁面二次电子发射的前提下,模拟得到了放电开始直到放电稳定后的平板等离子体内部和边界处的电场强度、电子密度、离子密度、电势等一系列参数分布,并分析了二次电子发射系数对鞘层厚度的影响分析。模拟结果表明:平等板内部电势相对于边界处较高,中部的电场强度为零,电子密度近似等于离子密度,而在边界处电子密度略低于离子密度,电场方向指向边界处,在等离子体边界处有明显的鞘层。     

二次电子对高压太阳电池阵裸露互联鞘层的影响研究

低轨道高压太阳电池阵与空间冷稠等离子体相互作用是复杂的非线性过程,对该相互作用占支配影响地位的是电池阵裸露互联附近的鞘层特性,而电池盖片的二次电子发射又影响着电池阵裸露互联附近的鞘层特性。基于介质-导体结构的简化模型,通过PIC仿真分析和一阶渐进边界条件研究了介质二次电子发射对裸露导体鞘层的影响,仿真分析结果表明,二次电子发射主要通过影响介质表面充电电位来影响鞘层结构,对鞘层的影响随着导体偏置电压增加而增大。     

聚变等离子体鞘层能量传输系数分析

对于磁约束聚变装置来说,可以用离子和电子的鞘层能量传输系数来预测和计算到达面向等离子体部件(PFC)的等离子体能量通量。文章推导并详细分析了悬浮态和非悬浮态的等离子体鞘层区域能量传输系数关系式。结果表明此系数随着边界等离子体的参数的变化而变化。并且当探针处于负偏压态时,探针面处的能量传输系数随着负偏压的增大而近似线性的增大。同时,也对发生在鞘层区域的能量转移过程进行了仔细分析,表明鞘层对于穿越的电子和离子分别相当于能量的冷却和加热装置。     

等离子体鞘层中朗缪尔探针吸收离子电流理论的数值模拟

为了研究朗缪尔静电圆柱型探针半径对等离子体密度测量的影响以及鞘层空间电势分布等特性,在非热平衡条件下采用等离子体鞘层中探针吸收离子模型,对朗缪尔静电探针周围等离子体鞘层空间中的修正玻姆电流、OML理论鞘层空间电势分布、ABR理论鞘层空间电势分布、BRL理论鞘层空间电势分布以及三种理论对应的探针吸收离子电流进行了系统的数值模拟研究。计算结果显示,电子温度和等离子体密度对ABR理论鞘层空间电势分布存在显著影响,离子温度小于0.1倍电子温度时离子的温度效应对BRL理论鞘层空间电势分布的影响可以忽略;探针半径为1~3倍德拜长度时,OML理论、ABR理论及BRL理论预测的归一化离子电流近似相等,即三种理论给出近似相等的等离子体密度。     

等离子体浸没离子注入球形靶的鞘层尺度

对于等离子体浸没离子注入（PIII）技术,球形靶鞘层尺度预测对真空室设计,批量处理研究先进是十分有用的,但由于球形靶鞘层Child-Langmuir定律数学表达的非线笥使得工程应用较为困难,本文对球形靶的鞘层尺度进行了数值求解,讨论了注入参数对鞘层尺度的影响,计算结果表明,鞘层厚度（包括离子阵鞘层和稳态鞘层）随球体半径或注入电压增加而增加,随等离子体密度增加而减小,但对于不同的参数区间,鞘层特性对参数的变化表现出不同的敏感性,当离子体密度较高,注入电压较低时,稳态鞘层厚度对于靶体半径的变化有不敏感,相反鞘层厚度对靶体大小变化较为敏感,虽然平面靶与球形靶的离子辄鞘层尺度比值与等离子体密度及球体半径有关,但平面靶稳态鞘层尺度总是大于球形靶的,这对于实际的PIII应用具有重要的指导意义。     

等离子体浸没离子注入球形靶的鞘层尺度

对于等离子体浸没离子注入(PIII)技术,球形靶鞘层尺度预测对真空室设计、批量处理研究等是十分有用的。但由于球形靶鞘层Child-Langmuir定律数学表达的非线性使得工程应用较为困难。本文对球形靶的鞘层尺度进行了数值求解、讨论了注入参数对鞘层尺度的影响。计算结果表明,鞘层厚度(包括离子阵鞘层和稳态鞘层)随球体半径或注入电压增加而增加,随等离子体密度增加而减小。但对于不同的参数区间,鞘层特性对参数的变化表现出不同的敏感性。当等离子体密度较高、注入电压较低时,稳态鞘层厚度对于靶体半径的变化极不敏感。相反鞘层厚度对靶体大小变化较为敏感。虽然平面靶与球形靶的离子阵鞘层尺度比值与等离子体密度及球体半径有关,但平面靶稳态鞘层尺度总是大于球形靶的。这对于实际的PIII应用具有重要的指导意义。     

两种正离子对磁化等离子体鞘层中尘埃颗粒的影响

建立了包含两种不同种类正离子的磁化等离子体鞘层的流体模型,通过四阶龙格库塔法数值模拟了含有两种不同种类正离子对等离子体鞘层中尘埃粒子的影响.结果表明对于含有He+和Ar+的稳态等离子体来说,随着离子温度的升高和Ar+密度的增加,尘埃粒子充电所带电量越多;尘埃密度越高,其带电量越低.此外,对于带有一定负电的尘埃粒子来说,离子的温度、鞘边Ar+的含量以及鞘层中离子与中性粒子的碰撞对鞘层中尘埃粒子的密度和速度都产生一定的影响.     

真空断路器弧后鞘层发展过程仿真分析

以真空断路器弧后鞘层发展过程为对象,采用等离子体流体力学模型,求解电子、离子密度和平均电子能量的漂移扩散方程和耦合电场的泊松方程,引入粒子间碰撞反应,仿真分析其弧后介质恢复变化和鞘层发展阶段电子和离子的空间分布、密度分布以及间隙电势分布.采用对比分析法,研究不同初始条件对鞘层发展的影响,结果表明:在保持其余参数不变的条...     

PDP放电单元Si掺杂MgO保护层二次电子发射系数理论研究

采用基于密度泛函理论的原子轨道展开方法的第一性原理计算了Mg1-xSixO体系的电子结构、用SIESTA软件包计算了Mg1-xSixO体系的晶胞结构,体系基态总能,确定了MgO的最优晶格常数。同时,计算了Mg1-xSixO的能带结构、态密度、分波态密度等。针对采用氖氙混合气体的PDP放电单元,分析了Si掺杂对MgO晶体的电子结构以及氖离子和氙离子二次电子发射系数的影响。结果表明,掺入微量的Si(掺杂浓度小于0.06)可提高MgO保护层氖离子和氙离子的二次电子发射系数,其中氙离子的二次电子发射系数的提高尤为显著。同时由分析结果表明,Si掺杂量存在最优化值为0.0185。     

第二十讲 真空离子镀膜

正(接2018年第4期第80页)(1)等离子体鞘:基片(工件)放进等离子体云中,不与等离子体直接接触。基片与等离子体之间隔了一层电中性被破坏了的薄层,是一个负电位区,称等离子体鞘,或称鞘层。在等离子体与容器壁之间,放置在等离子体中的任何绝缘体表面,或插入等离子体中的电极近旁都会形成鞘层。轰击基片的离子的能量部分或大部分是在离子鞘内获得,所以在离子镀中调节离子鞘的电位     

Ion dynamics in plasma sheath under the effect of E×B and collisional forces

Using the fluid model, we investigated the velocity, kinetic energy and the density distribution of the ions in collisional and collisionless magnetized plasma sheath. Considering an external magnetic field, the ion movement under the effect of magnetic, electric and collisional forces has been analyzed numerically. The nonexistence of fluctuations in ions kinetic energy in collisionless strong magnetized plasma sheath and increasing the ions velocity in depth direction due to the collisions in some positions in the sheath are shown. The fluctuations of ion velocity in weak magnetized plasma sheath are shown too when ions enter the sheath with oblique incident angle.     

Effects of dielectric substrate thickness on plasma immersion ion implantation

A one-dimensional plasma fluid model is developed for investigating the effects of dielectric substrate thickness on plasma immersion ion implantation. By considering the effects of secondary electron emission from the dielectric substrate and using finite difference schemes, evolution of plasma sheath, ion fluence and dielectric surface potential versus time and substrate thickness are evaluated. It was demonstrated that with the increasing dielectric thickness, sheath width and ion fluence over the dielectric surface decrease and surface potential reduces. These effects can be attributed to the accumulation of positive ions and ejection of secondary electrons from the dielectric surface and thereby lessening the strength of the electric field over the dielectric substrate. It is also shown that the secondary electrons have a profound effect on implantation results and must be considered in plasma immersion ion implantation of dielectric materials.     

Direct recovery of ion beam energy using magnetic electron suppression: I. Analysis of ORNL energy recovery experiments

The charge-exchange neutralization efficiency of positive ion-based neutral beams used in plasma heating applications decreases as the beam energy increases. Direct energy recovery from the remaining charged particles can be accomplished by electrostatically decelerating the positive ions; the space-charge neutralizing electrons are constrained from being accelerated by the application of a transverse magnetic field. A finite difference nonlinear sheath analysis is used to analyze the transverse magnetic field electron suppression experiments carried out at Oak Ridge National Laboratory in the early 1980s. A double plasma model, which assumes an equilibrium Boltzmann distribution of electrons at both the neutralizer potential and the ion collector potential, is used to study the experimental data obtained from operating 40 keV, 10 A ion beam energy recovery experiments. The effects of the magnetic field strength, ion “boost” energy, and ion beam current density are examined in detail.     

Equilibrium states of an ion-beam plasma with magnetized electrons at low pressures

Results are presented of an experimental investigation of an ion-beam plasma with magnetized electrons in the cathode channel of an ion accelerator with an anode layer. New data are reported on the spatial distributions of the local plasma parameters (plasma potential, electron temperature, electron and ion densities) as functions of the external parameters of the discharge (magnetic field strength, anode voltage, and working gas pressure) in regions with strong, nonuniform electric and magnetic fields. Pis’ma Zh. Tekh. Fiz. 24, 33–38 (March 12, 1998)     

Two-dimensional kinetic model of short high-current vacuum-arc discharge

A two-dimensional mathematical model of a short high-current vacuum-arc discharge is developed, according to which magnetized electrons move in a hydrodynamic regime and fast cathode ions propagate in a free flight regime in a two-dimensional electric field. The proposed model takes into account the distribution of ions with respect to their escape angles from the cathode plasma boundary. A method for calculation of the plasma density distribution in the interelectrode gap is proposed. Two-dimensional distributions of the plasma density, electric field, and discharge current density in an external magnetic field are calculated. It is shown that ion trajectories exhibit mutual intersections, partly return to the cathode, and partly rotate in the oppositely oriented electric field at the side boundary of plasma. A decrease in the applied magnetic field intensity leads to a decrease in the number of ion trajectories reaching the anode (ion starvation), which can result in the violation of a stationary current transfer.     

The hydrodynamic theory of a positive discharge column in an axial magnetic field

The influence of an axial magnetic field on the performance of a low-pressure cylindrical positive discharge column is studied from the hydrodynamic point of view. It is shown that the magnetic field affects the distribution of the plasma density, its speed, and the energy of electrons. The energy of electrons, the concentration and the speed of plasma, and the azimuth speed of electrons and ions as functions of the radius have been found for a helium atom in a magnetic field of varying intensity. It has been noticed that the electron and ion azimuth movement equations should account for inertia. The obtained hydrodynamic results significantly deviate from the ones obtained in the wide-spread diffusion model of a positive column. It is shown that the distribution of plasma concentration and the radial speed in the positive column are generally close to the results using the diffusion approach, if the axial inductance of the magnetic field and the gas density are increased. However, major differences are found near the walls.     

The ion density distribution in a magnetized plasma sheath

The ion density distribution of plasma sheath in an oblique magnetic field is investigated with a fluid model. We performed numerical simulations of the sheath. The results reveal that the magnetic field has significant effects on the plasma sheath, including ion density distribution and space charge density distribution. Two cases of ion incidence are considered here. Under suitable conditions, Lorentz force induces fluctuations in the ion density. And the magnetic field parallel to the board is responsible for these changes. The action states of ions are more complicated while the ions enter the sheath with an oblique incidence angle. Ions could gather in some regions, so that it leads to small peaks of the density curve. Also the space charge density in such regions is slightly higher.     

Characteristics of ions in a magnetized plasma sheath with two species of positive ions

Using the hydrodynamic model, the effects of an external oblique magnetic field and the second ion species density on the characteristics of a three-component (electrons and two species of positive ions) plasma sheath are investigated. It is seen that depending on the magnetic induction of the external field, the velocity and the ion density distributions of both ion species begin to fluctuate. Furthermore, it is shown that density of the second ion species affects the amplitudes of these fluctuations. It is also found that the electrostatic potential of the sheath region depends on the density ratio of positive ion species and by increasing this ratio the electrostatic potential falls down.     

耦合腔行波管多级降压收集极的模拟设计

本文中较全面地讨论了多级降压收集极的物理模型.通过分析3个工作频率点高频输出端的电子注特性来设计多级降压收集极:借助电子注层流性参量,对带有再聚焦磁场的散群聚区进行优化,得到磁场参量的初始值;运用电子轨迹等效电位图,确定各电极的初步电位,通过收集极区结构和电极电位的优化得到较高的收集极效率;通过收集极的全面优化使收集极效率得到了进一步的提高;在考虑二次电子发射情况下,对收集极结构和电极电位进行优化,在保证收集极效率的情况下使二次电子回流率为零.模拟结果表明:借助电子注层流参量设计出带有再聚焦磁场的散群聚区使电子轨迹层流性得到较大改善;合理的结构和电极电位能得到较高的收集极效率;二次电子发射对收集极效率影响较大,合理的调节外凸锥形电极的倾角能避免二次电子回流.此设计运用于一耦合腔行波管收集极的模拟计算,达到了良好的效果.