Behaviour of fully ionized seed plasma excited by microwave

Nonequilibrium plasmas with cesium metal vapor ionization in helium and argon gases at moderate pressures are excited with microwave power. The structures and behaviour of the seeded plasmas are experimentally examined, particularly under the condition of Full seed (cesium atoms) ionization. By cesium seeding, the minimum power sustaining the plasma is reduced markedly, and both a broad plasma observed in pure helium and unsteady filament-like plasmas in pure argon change to the steady and broad plasma locating close to the inner surface of a discharge tube, it is revealed from the electron temperature measurements that the plasma can be in the regime of full seed ionization for suitable microwave powers, where the electron density is kept almost constant. The thickness of the fully ionized seed (FIS) plasma decreases with increasing the mole fraction of cesium vapor, and is almost independent of noble gas pressure. The thickness almost coincides with the skin depth determined from the electrical conductivity almost uniform in the FIS plasma. These facts suggest that the FIS plasma will be easily produced and maintained as long as the microwave power is consumed to the electron heating     

高功率微波输出窗内侧击穿动力学的PIC/MCC模拟研究

高功率微波在受控热核聚变加热、微波高梯度加速器、高功率雷达、定向能武器、超级干扰机及冲击雷达等方面有着重要的应用.本文针对高功率微波输出窗内侧氩气放电击穿过程,建立了二次电子倍增和气体电离的一维空间分布、三维速度分布（1D3V）模型,并开发了相应的PIC/MC程序代码.研究了气压、微波频率、微波振幅对放电击穿的影响.结果表明：在真空情况下,介质窗放电击穿只存在二次电子倍增过程;在低气压和稍高气压时,二次电子倍增和气体电离共存;在极高气压时,气体电离占主导.给出了不同气压下电子、离子的密度和静电场的空间分布.此外还观察到,在500 mTorr时,随着微波振幅或微波频率的变化,气体电离出现的时刻和电离产生的等离子体峰值位置有较大差异,尤其是当微波频率（GHz）在数值上是微波振幅（MV/m）的2倍时,气体电离出现的较早.     

电子回旋共振放电电离特性的PIC/MCC模拟

A theoretical and computational model is presented to study the ionization of the argon electron cyclotron resonance(ECR)microwave discharge using a quasi-three-dimensional electromagnetic particle-in- cell plus Monte Carlo collision method.The interaction between the charged particles and microwave fields are described by the electromagnetic mode of particle-in-cell method.The collision processes are treated with Monte Carlo method.The simulation code is the original work.The results of the particle simulation for the ECR discharge of argon gas which include the microscopic features of charged particles and the electromagnetic characteristics of the ECR discharge plasma,and also the transient phenomena have been presented.     

微波瑞利散射法测定空气电火花激波等离子体射流的时变电子密度

大气压空气电火花激波等离子体射流的电子密度在亚微秒时间尺度上瞬变,其电子密度的测定很难.基于微波瑞利散射原理,本文测量了空气电火花冲击波流注放电等离子体射流的时变电子密度.实验结果表明:测量系统的标定参数A为1.04 × 105 V·Ω·m–2;空气流注放电等离子体射流的电子密度与等离子体射流的半径和长度有关,结合高速放电影像展示的等离子体射流的等效半径和等效长度,测定的电子密度在1020 m–3的量级,且随时间先快速增长至峰值再成指数衰减.此外,本文还探讨了等离子体射流的不同等效尺度对测定结果的影响;分析结果表明,采用时变等效半径和时变等效长度的计算结果最有效,且第1个快速波峰是由光电离的电离波导致的.     

共面双对称条件下电子碰撞Ar原子单电离的一阶扭曲波Born近似

在共面双对称几何条件下,利用一阶扭曲波Born近似计算了中低能电子碰撞Ar原子(3p壳层电子)单电离的三重微分截面,并与最近的实验数据做了比较.结果表明,对于Ar原子,当入射电子能量比电离阈高40 eV以上,随着入射能量的增加,binary和recoil碰撞机理逐渐占据支配地位;在近阈能量范围,上述碰撞机理不再处于支配地位,扭曲效应明显.要完备地描述中低能入射条件下Ar原子的电子碰撞电离过程,理论模型必须同时考虑多种散射机理.     

Long‐Time Evolution of a Low Pressure Laboratory Plasma after Application of Transient high Voltage Positive Pulses

The long‐time evolution of weakly‐collisional plasma with application of high voltage positive pulses to an electrode immersed in plasma, with pulse widths less than as well as more than ion plasma periods, is studied. The plasma is produced by electron impact ionization of argon or helium gas, where electrons are coming out from dc biased hot thoriated tungsten filaments. It is observed that during the temporal evolution of argon plasma, a beam component exists along with temporal bulk electrons giving rise to a double hump profile of transient Electron Distribution Function (EDF). However, in the case of temporal evolution of helium plasma, only a bulk electron population is present. The obtained results are explained by understanding the role played by thermionically emitted electrons during the plasma evolution, the role of the difference of ionization rates of helium and argon, and the higher temporal plasma potential. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

强流电子束碰撞电离背景气体研究

利用数值计算与粒子模拟两种方法,结合实际的实验数据,对高功率微波二极管中相对论电子束与背景气体相互作用碰撞产生的等离子体密度进行了研究.研究结果表明：碰撞产生的等离子体密度数值计算结果与粒子模拟结果基本一致,背景气压在0.01 Pa—0.05 Pa时,碰撞产生的等离子体密度在4—12×10⁹cm^-3,即便在考虑电子离子复合的情况下,数值计算结果与粒子模拟结果依然符合得很好.另外,粒子模拟结果表明：随着气压的增加,等离子体密度呈现先增大再减小然后又逐渐增大的过程, 关键词： 相对论电子束 等离子体 数值计算 粒子模拟     

Effect of argon ion activity on the properties of Y2O3 thin films deposited by low pressure PACVD

Yttrium oxide thin films are deposited by microwave electron cyclotron resonance (ECR) plasma assisted metal organic chemical vapour deposition process using an indegeneously developed Y(thd)₃ {(2,2,6,6-tetramethyl-3,5-heptanedionate)yttrium} precursor. Depositions were carried out at two different argon gas flow rates keeping precursor and oxygen gas flow rate constant. The deposited coatings are characterized by X-ray photoelectron spectroscopy (XPS), glancing angle X-ray diffraction (GIXRD) and infrared spectroscopy. Optical properties of the films are studied by spectroscopic ellipsometry. Hardness and elastic modulus of the films are measured by load depth sensing nanoindentation technique. Stability of the film and its adhesion with the substrate is inferred from the nanoscratch test.It is shown here that, the change in the argon gas flow rates changes the ionization of the gas in the microwave ECR plasma and imposes a drastic change in the characteristics like composition, structure as well as mechanical properties of the deposited film.     

A multi-fluid stagnation-flow plasma model with self-consistenttreatment of the collisional sheath

A two-temperature, multifluid model of a plasma in stagnation flow against a cooled, electrically biased surface is presented. The model couples bulk fluid motion, species diffusion and convection, electron and bulk energy equations, and net finite-rate ionization with Poisson's equation for the electric field in a generalized formulation. Application of the model to argon flow reveals important interactions between thermal, hydrodynamic, chemical and electrical boundary layers, with implications for current-limiting regimes of arcjet operation. The response of a planar Langmuir probe in contact with a collisional, flowing plasma is examined. Determinations of current-voltage behavior compare well with simple theory, including dependence on incident plasma velocity. Departures from this theory arise from boundary-layer perturbations near the electrode surface, away from free-stream conditions. The computational model incorporates a finite-rate catalytic recombination of ions and electrons at the electrode surface together with a specified current     

Cross sections of electron capture and electron capture ionization versus the impact parameter in collisions of a proton with multielectron atoms

The absolute differential cross sections of scattering of hydrogen atoms resulting from an electron capture and an electron capture ionization are measured for collisions of 4.5- and 11-keV protons with argon and xenon atoms. The range of scattering angles is 0°–2°. From the scattering differential cross section found experimentally, the probabilities of single-electron capture and electron capture ionization as a function of the impact parameter are calculated. The dependences of the incident particle scattering angle on the impact parameter (deviation function) for interactions with Ar and Xe atoms are calculated in terms of classical mechanics using the Moliére—Yukawa potential to describe the interaction of atomic particles. Analysis is given to the probabilities of electron capture and electron capture ionization versus the impact parameter and to the distribution of the electron density on different electron shells in a target atom versus a distance to the core. It is concluded that only electrons from the outer shell of the target atom are involved in the process of electron capture ionization. The cross section of electron capture ionization is calculated in the proton energy range 5–20 keV.     

Similarity principle of microwave argon plasma at low pressure

In order to validate the similarity principle of microwave breakdown, a two-dimensional(2 D) fluid model of lowpressure microwave argon plasma is established and solved by the finite-element method. Proportional conditions are used in this model to build three different breakdown processes that meet the premise of a similarity principle, and these breakdown processes are called "similar cases" in this paper. Similar cases have proportionately sized breakdown regions,where the ratio of frequency of incident microwave f to gas pressure p( f/p), and the reduced field E/p in them are kept the same. All the important physical parameters such as electron density, electron temperature, and reduced electric field can be obtained from the simulation of this model. The results show that the parameters between similar cases are in constant ratio without changing with time, which means that the similarity principle is also valid in microwave breakdown.     

大气压微波等离子体射流装置放电特性研究

基于同轴传输线结构设计了两种不同喷嘴结构的大气压微波等离子体射流(MW-APPJ)装置,其工作频率2.45 GHz,工作气体为氩气,分别研究了两种不同喷嘴结构对等离子体放电特性产生的影响。仿真结果表明,MW-APPJ在气体喷嘴处会产生高强度的电场,经过优化结构,实现在频率2.45 GHz下,喷嘴处的场强满足氩气电离的击穿场强阈值要求。同时,利用多物理场耦合仿真软件对装置的气流分布进行了稳态模拟,并通过实验对比分析了两种喷嘴结构下大气压氩等离子体射流的基本特性。实验结果表明,不同的喷嘴结构会影响等离子体装置的反射系数随输入功率的变化规律,但并不影响等离子体射流长度随输入功率的变化规律和反射功率随进气流量的变化规律;同时,在大气压下,稳态微波等离子体射流呈现出类金属性,等离子体中的电子只能在很薄的区域中吸收微波能量,因而造成微波的反射功率较大。     

Beam-Plasma Heating Model

A one-dimensional ionization and heating model is applied to results of several electron-beam-plasma interaction experiments. Beam energy is deposited resistively in the plasma at a rate ?j2, where j is the return current density and ? the plasma resistivity both classical and anomalous due to ion acoustic or e-e-mode turbulence. Principal energy losses include ionization, line radiation, inelastic electron impact excitation, bremsstrahlung and radiative recombination. The level of ionization and plasma heating are computed as a function of neutral gas pressure, beam rise time, pulsewidth and current density, and resistivity model. Plasma dynamics and kinetic effects such as expansion and end loss are not explicitly included in the model.     

氩气直流放电等离子体中三稳现象的半经典理论

本文从粒子间的电离、复合、激发和去激发等基本相互作用出发,解释了实验中观察到的各类三稳现象,并对更为复杂的现象如分岔、混沌等作了讨论。     

Numerical simulation of nonlinear ionization nonuniformities innonequilibrium disk MHD generator

The formation and evolution of the ionization nonuniformities from initial disturbances of finite amplitude in the nonequilibrium Ar-Cs plasma in a disk magnetohydrodynamic (MHD) generator is studied by the numerical simulation, The simulations are carried out in the wide interval of electron temperatures corresponding to the region at which the seed partially ionizes, the region of the linear plasma stability at the fully ionized seed, and the region of the instability corresponding to the partial ionization of Ar at high electron temperatures. Initial disturbances of finite amplitude in electron temperature and density are introduced at the time t=0 into the homogeneous plasma distribution, and the critical amplitudes determining the development of the instability are calculated. The initial disturbances are constructed using random functions with different spatial scales, The results are compared with the calculation of the critical amplitudes from the nonlinear theory of the plane ionization waves, It is found that at electron temperatures lower than 5500 K, the temperature dependence of the critical amplitudes and the structure of the nonlinear waves agree well with the nonlinear theory, In the electron temperature region corresponding to the partial ionization of the noble gas (T_e>5500 K), the finite ionization rate of argon atoms is essential for analysis of the instability, In this region the margin of the plasma stability is wider than it is predicted by the nonlinear theory, The nonuniformity in the argon ion number density plays the dominating role in the instability development at high electron temperatures (T_e>5500 K) in comparison with the nonuniformity in T_e in the initial disturbances,     

One-dimensional fluid model of ECR discharge with inhomogeneityeffects of external magnetic field

A one-dimensional fluid model of the microwave electron cyclotron resonance (ECR) discharge, which includes the inhomogeneity effects of the external magnetic field, is developed. We use fluid equations which are obtained from the one-dimensional Bolzmann equation expressed in terms of magnetic moment and parallel velocity. We model the plasma and sheath separately, and appropriate plasma-sheath boundary conditions are utilized. Microwave is represented by an energy flow, and treated by a ray tracing technique. For the argon discharge, we obtain various quantities such as the axial profiles of plasma density, electron temperature, electrostatic potential, fluid velocity, and microwave power deposition. The results of simulation compare well with the experimental observation of the mirror field effects on the plasma parameters     

蒙特卡罗方法模拟薄膜电致发光器件中碰撞离化的作用

基于经验赝势法得到的能带结构数据，采用分段多项式拟合获得ZnS能带结构的解析表达式 ，建立解析能带模型.使用建立的模型计算得到各能谷的态密度和总的散射速率,并与文献 的计算结果进行了对比，验证该解析能带模型既具有非抛物型多能谷能带模型运算速度快、 使用方便的优势,又具有与采用全导带模型相近的计算精度.进一步利用该模型进行蒙特卡罗 模拟，得到第一导带和第二导带中电子数随电场强度的变化、不同电场中能量分布函数以及 包含与不包含碰撞离化情况下电子能量随时间变化的曲线.讨论在外加电场下，电子在导带 内各个能谷间和 关键词： 蒙特卡罗模拟 解析能带模型 多项式拟合 碰撞离化     

Collective Scattering of Electromagnetic Waves from a Relativistic Magnetized Plasma

Recently, laser and microwave scatterings have become one of the important diagnostic means for plasma. Laser and microwave correlative scattering spectrum is determined by particle-density fluctuations in a weak turbulent plasma. In a relativistic plasma, on the basis of complete electromagnetic interaction between particles, a general expression for particle density fluctuations and spectra of laser and microwave scattering from a magnetized plasma are derived. The laser and microwave scattering spectra provide information on electron density and temperature, ion temperature, resonance and nonresonance effects.     

Modelling of the Positive Column in an Argon-Hexamethyl-disiloxane dc Glow Discharge

A model is presented of the positive column of a dc glow discharge in argon with small admixtures of hexamethyldisiloxane (HMDS). The axial electric field, the ion production rates for direct-, stepwise-, pair-, and Penning ionization, the densities of metastable Ar atoms and of electrons, and the wall current of HMDS ions are calculated in dependence on HMDS admixture and discharge current density. For the calculations particle balance equations were used for a diffusion determined plasma in a mixture of two gaseous components. The reaction rates for the electron collision processes were determined applying the electron distribution function calculated for pure argon. Taking into account PENNING ionization of HMDS molecules by metastable argon atoms the decrease of electric field for increasing HMDS admixtures is according to the experimen-tally measured values. Also ion wall currents and electron densities are compared with experimen-tal values for thin film formation rate and results of probe measurements.     

氩原子近LⅡ,Ⅲ边结构和振子强度密度

在入射电子能量2500eV，平均散射角为0°的条件下测量了氩原子内壳层2p电子激发和电离的高分辨电子能量损失谱，确定了分立态的有效量子数和电离边的能量．同时确定了两组分立跃迁和电离连续区的振子强度密度． 关键词：