直流辉光和磁控增强放电等离子体的空间分辨发射光谱技术

光学发射光谱(OES)方法是等离子体诊断的有力工具之一,可以定量地给出等离子体的多种重要参数,如等离子体中的物种成分、粒子能态分布、激发温度、粒子相对密度等.本文介绍了一种用于电子回旋共振(ECR)微波等离子体磁控溅射靶附近的增强放电和直流辉光放电等离子体空间分辨诊断的发射光谱装置.其特点是光学收集系统的位置可以水平精细移动,因而可以对放电区域进行空间分辨发射光谱测量.作者利用这套装置对氩气的ECR微波等离子体和直流辉光放电等离子体进行诊断.在ECR微波等离子体的下游区内氩离子谱线的发射强度很弱,主要是高激发态原子的辐射.在磁共振增强放电区,离子谱线强度有所增加但仍比原子谱线弱,类似于直流辉光放电正柱区的光发射特性.     

空间环境模拟用ECR等离子体源标准装置研究

研究了以微波ECR等离子体源作为等离子体发生器的空间环境模拟装置。试验以氩气为放电气体,通过分析气压、微波功率、磁场等放电条件对微波ECR等离子体源的耦合作用,并结合COMSOL软件进行仿真验证,实现了等离子体电子密度、电子温度等特征参数的大范围可控调节。在等离子体源放电腔的出口处设计了扩散杯和栅网两种引出结构,使用不同类型和尺寸的Langmuir探针分别测量了两种引出结构下真空腔室内等离子体参数的径向变化,得到了引出结构对等离子体均匀性和稳定性的影响,分析比对了不同Langmuir探针的测试结果,得到一组最优等离子体诊断方式。这些工作对后续等离子体源标准装置研制和校准技术研究具有参考意义。     

ECR微波等离子体特性的实验研究

着重介绍采用一段真空波导耦合的ECR微波等离子体装置，以及在CH4－H2混合气体放电情况下，诊断了内部等离子体参数，给出了等离子体密度、电子温度、基板鞘附近的空间电位以及在类金刚石膜合成条件下等离子体中的基团情况，同时研究了它们与工艺参数之间的关系。     

不同流速对LTE态下氢等离子体特性的研究

采用二维流体力学模型研究了多级直流弧放电装置中流速对处于局部热平衡状态下氢等离子体特性的影响.分析了氢等离子体中心轴线处电场和压强的分布情况;各粒子密度在通道中的分布状态;通道出口处等离子体温度以及电导率的分布情况.模拟结果表明,随着流速的增大,中心轴线处电场和压强均增大;通道中氢等离子体的各粒子密度变化很小;通道出口处等离子体温度以及电导率在出口处沿径向的分布影响不大.     

用于中子管的微波离子源放电特性的仿真研究

微波离子源作为一种无阴极离子源,与潘宁离子源相比具有电离度高、形成的等离子体密度高、寿命长等优点。为了深入了解用于中子管微波离子源的放电特性,根据微波离子源的放电原理,设计中子管微波离子源的几何结构和所需磁铁的结构。结合Comsol多物理场仿真软件中的二维轴对称的AC/DC模块和微波等离子体模块,采用控制变量法,通过仿真实验探究了放电气压、微波输入功率、放电腔室大小以及放电腔室外壁材料对电子密度的影响,总结了电子密度在不同参数下的规律,将为中子管微波离子源的实验和设计提供重要支撑。     

用于中子管的微波离子源放电特性的仿真研究北大核心CSCD

微波离子源作为一种无阴极离子源,与潘宁离子源相比具有电离度高、形成的等离子体密度高、寿命长等优点。为了深入了解用于中子管微波离子源的放电特性,根据微波离子源的放电原理,设计中子管微波离子源的几何结构和所需磁铁的结构。结合Comsol多物理场仿真软件中的二维轴对称的AC/DC模块和微波等离子体模块,采用控制变量法,通过仿真实验探究了放电气压、微波输入功率、放电腔室大小以及放电腔室外壁材料对电子密度的影响,总结了电子密度在不同参数下的规律,将为中子管微波离子源的实验和设计提供重要支撑。     

ECR微波等离子体特性的实验研究

着重介绍采用一段真空波导耦合的ＥＣＲ微波等离子体装置，以及在ＣＨ４－Ｈ２沸合气体放电情况下，诊断了内部等离子体参数，给出了等离子体密度，电子温度，基板鞘附近的空间电位以及在类金刚石膜合成条件下等离子体中的基团情况，同时研究了它们与工艺参数之间的关系。     

利用准光腔对辉光放电等离子体诊断分析

利用建立的准光腔谐振系统对辉光放电空气等离子体中电子密度参数进行了诊断分析。通过测试加载等离子体前后准光腔谐振系统的谐振参数,计算得到被测等离子体的等效复介电常数及电子密度。实验结果表明:采用准光腔诊断辉光放电空气等离子体,测试结果重复性好;当工作气压在30~35 Pa,放电电流在2~8 A时,等离子体密度范围在10~(16)m~(-3)量级,且在相同气压下,电子密度随放电功率增加而增加;与采用标准Langmuir探针的诊断结果相比较,二者差别不大。证明了采用准光腔谐振系统诊断辉光放电等离子体的可靠性与准确性。     

常压微波等离子体激发过程的数字研究

基于常压微波等离子体产生装置的三维数字模型用于分析等离子体产生过程中电场、反射系数等物理参数的变化和等离体的特性。三维数字模型建立在包括气体放电物理过程、边界条件和工作气体碰撞反应等大量的电磁学、流体力学、化学以及分子动力学的学科理论模型基础上，对多个参数进行耦合计算。计算结果表明：等离子体的激发是一个快速、剧烈的过程，在2.5×10-7^s时，放电区域的气体电离达到最高峰，0.1 s时等离子体就已趋于稳定。同时激发气体产生等离子体所消耗的微波功率在等离子体激发过程中先急速增大，到达峰值后缓慢减小。     

大气压宽径向空气等离子体射流装置的设计、实验和仿真研究

大气压空气等离子体射流 (空气APPJ) 能够在开放的大气环境中产生高活性低温等离子体, 在细菌灭活、材料表面处理和生物医学应用等方面有广泛应用前景, 但是目前空气放电击穿电压高, 放电稳定性较差, 射流长度较短、径向尺寸小等限制了它的应用。为了降低放电电压及维持放电稳定性, 本文在高压电极上包裹一层介质, 设计出一种介质包覆的针-金属喷嘴结构的空气APPJ枪, 利用COMSOL的静电场模块对枪体的电学特性进行仿真, 研究针尖曲率半径、电极间距以及针电极直径等参数对电势和电场的空间分布的影响, 发现针尖曲率半径对于场强最大值有较大影响。据此, 选择合适的参数, 设计并制备了枪体。该枪在交流驱动下能够稳定放电, APPJ径向尺寸3 mm左右、长度达到17 mm。分析了射流长度、功率和气体温度随气流流速的变化, 并与氮气和氩气放电进行了比较, 其放电参数与氮气基本相当, 与氩气相比, 放电功率大, 温度高, 但射流长且径向尺寸宽, 更适合活性反应场合的应用。     

Spectra of microwave oscillations in an SPD-ATON stationary plasma thruster

The spectra of microwave oscillations and electromagnetic radiation in an SPD-ATON stationary plasma thruster have been measured. Using the results of determination of the spectral characteristics and the spatial distribution of microwave intensity, features of the plasma jet instability manifestations related to the trapping of electrons in a magnetic field of the acceleration channel are analyzed. A method for the evaluation of the spectral and energy parameters of microwave oscillations and electromagnetic radiation generated by the operating plasma thruster is proposed.     

Electromagnetic field decay in high-frequency flare discharge plasma

Axial profiles of the amplitudes of harmonic components in the electric field of a flare discharge in air and argon have been measured. The frequency dependence of the coefficient of electromagnetic field decay in the discharge plasma exhibits a nonmonotonic character.     

Field-emission diode with tangential current takeoff from thin-film nanodiamond/graphite emitter

Dependence on the performance characteristics of a field-emission diode with tangential current takeoff from thin-film nanodiamond/graphite (NDG) emitter on the design parameters has been studied. Thin-film NDG emitter structures were formed in the plasma of microwave low-pressure gas discharge. Field-emission current densities up to 20 A/cm² at a voltage of 300 V were obtained. For the optimum diode design parameters, the tangential current takeoff scheme allows the threshold electric field strength for the onset of field emission to be decreased to less than half of the value typical of the planar field emission from the same NDG structures.     

Inhomogeneous microwave discharge in oxygen

Results are given of one-dimensional quasi-static simulation of steady microwave discharge in a system of electrodes with spherical symmetry in oxygen at pressures of 1 to 8 torr. The model includes the equation for electric field intensity in quasi-static approximation, Poisson equation, balance equations defining the kinetics of charged and neutral particles of plasma, and steady-state homogeneous Boltzmann equation for electrons. The well-known analytical expression for vibrational distribution of molecules, derived in diffusion approximation, is used for including the processes which involve vibrationally excited particles. It is demonstrated that the presence of negative ions does not result in differences of the electrodynamics of discharge from those of discharge in nitrogen. The composition of heavy component of plasma is investigated and, in particular, it is demonstrated that the concentration of molecules in the O₂(a ¹Δ) state may be as high as 20%.     

Investigation of the processes of periodic plasma structure formation in transverse nanosecond discharge with a slotted cathode

A periodic standing-like plasmic striation in inert gases has been observed and investigated under transversal nanosecond electric discharges. The pressure limits relevant for formation of a periodic plasma structure have been established, and the critical values for the voltage amplitude and discharge current have been found corresponding to the upper boundary of the range in which the plasma structure is formed. The external magnetic field effect on the parameters of the periodic plasma structure has been studied. It is stated that the plasma structure is formed at the stage of steady-state discharge and that the lifetime of the periodic structure considerably increases when the transversal magnetic field is applied.     

Modelling and Analysis of Power Distribution of Electromagnetic Waves on Plane Surfaces Using Lock-in IR Thermography

The electric field distribution (magnitude only) near a radiating source (antenna) can be easily determined using infrared thermography. A thin screen (made of carbon fiber reinforced polymers) is placed in front of a microwave source. The electromagnetic waves impinging on the screen are partially absorbed, resulting in temperature rise of the screen. This temperature rise is monitored by an infrared camera. The temperature distribution thus observed is mapped to the electric field strength (magnitude of electric field) of the electromagnetic waves. Points on the screen where the temperature rise is low correspond to weak electromagnetic fields whereas points with high temperature rise correspond to strong electromagnetic fields. In this paper electro-thermal modelling is done so as to obtain the temperature distribution over the screen, when an electromagnetic field is incident on it. This model can conversely be used for finding electromagnetic field distributions from IR thermal images.     

Influence of a DC field on the near-electrode zone of nonuniform microwave discharge in hydrogen

We investigate, by the emission spectroscopy, the influence of the DC electric field on the nearsur-face plasma of the electrode microwave hydrogen discharge (EMD) at pressures of 1 to 5 Torr. We obtain the DC current-voltage characteristics of the EMD, the strength values of the microwave field, and its spatial distributions in the EMD near-electrode zone. Under a positive voltage on the electrode as against the chamber, the variation in the discharge structure are minor, and, at the particular voltages depending on the pressure and the microwave power, the spatial charge layer breakdown takes place near the discharge chamber surface. Under a negative voltage on the electrode (the plasma cathode microwave mode), the discharge structure and dimensions vary and, at high currents, the discharge cancels.     

Plasma parameters in the vicinity of the quartz window of a low pressure surface wave discharge produced in O2

Plasma parameters in the vicinity of the dielectric window of a low density, microwave discharge produced in O₂ at 915 MHz are investigated by a spherical probe and optical emission spectroscopy while the microwave field distribution is measured by a spectrum analyzer. The electron energy distribution function is found to be strongly dependent on the position with respect to the slot antenna, exhibiting a group of energetic electrons at locations where the electric field and the optical intensity exhibit maximum values. The density of energetic electrons decreases sharply just a few cm away from the dielectric.