柱面天线射频感性耦合等离子体放电模式特性的实验研究

利用Z-scan、电流、电压探头,通过测量等离子体吸收功率、天线电流、电压、等离子体直流悬浮电位等多种参数,研究了匹配网络、天线耦合强度、导电地面积、气压等多种因素对E,H放电模式特性及模式转化行为的影响.基于Γ型阻抗匹配网络中串联电容对射频电源输出功率的影响,提出了E—H放电模式转化的正负反馈区概念.研究发现：在相同的其他放电条件下,处于正反馈区时等离子体放电易于产生跳变型模式转化,而且模式跳变的临界天线电流、回滞宽度、跳变临界功率、跳变功率差等参数均随阻抗匹配网络参数产生明显变化;在负反馈区内,模式转化过程趋于连续.由于阻抗匹配网络的影响,E—H模式的跳变电流并不是总大于H—E模式的跳变电流.在不同导电地面积、阻抗匹配网络、气压下,模式转化过程中等离子体直流悬浮电位的变化呈现多样性. 关键词： 射频等离子体 感性耦合 容性耦合 模式转化     

Effects of nonlocal electron kinetics and transition from αto γ regime in an RF capacitive discharge in nitrogen

The electron kinetics and regime of operation of asymmetrically coupled RF (27-MHz) nitrogen discharges in two vessels with different interelectrode gaps over the range of 0.20-0.35 torr gas pressure are studied in terms of the electron energy distribution function (EEDF). The latter is measured by means of a computer-controlled data acquisition system, a Langmuir probe with cross-modulation second derivative technique applied. The experiments are performed with an axial resolution along the RF electric field and accompanied with a measurement of electrical discharge characteristics. The effects of local and nonlocal plasma response are considered. The transition between α and γ discharge regimes is registered by measuring the EEDF and its moments' changes with the increase of the RF discharge current density     

An experimental study of the plasma parameters of a hybrid low-pressure RF discharge

This paper presents an experimental study of the plasma parameters of a hybrid radio-frequency (RF) discharge, which is a new modification of an RF discharge. The discharge is maintained by both vortex and potential RF electrical fields. To generate a hybrid RF discharge, an RF power input unit is used in the form of a parallel-connected inductor and capacitor coatings. A blocking capacitor is included in the capacitive channel of the discharge. The paper presents data from the study of the influence of power coupled to the plasma, argon pressure, and blocking capacitance on the plasma parameters, i.e., the electron energy distribution, temperature, and density and plasma potential. The role of the capacitive channel in the variations in properties and the characteristics of the discharge are considered.     

The inductive channel effect on the parameters of the space-charge electrode sheaths in a hybrid RF discharge

The physical properties of a new modification of RF discharge—hybrid RF discharge (HRFD)—are studied experimentally. A HRFD is sustained by both the vortical RF electric field and the potential one generated by the inductive and capacitive channels of the discharge. The inductive channel effect on the parameters of the space-charge electrode sheaths, which determine the capacitive component of the physical mechanism of a HRFD, is discussed.     

The influence of external parameters on the peculiarities of a hybrid low-pressure radio-frequency discharge

This paper deals with the experimental study of the patterns of the RF power input into the plasma of a hybrid RF discharge that was sustained by an RF power unit, which consisted of a spiral antenna connected in parallel with capacitor electrodes. At low values of RF generator power, RF power has been shown to be derived in the hybrid discharge through the capacitive channel; the role of the inductive channel becomes more significant at higher RF generator power as the power of the RF generator increases. It was demonstrated that at a low power of the RF generator the RF power occurs in the hybrid discharge essentially through the capacitive channel and then increases as the power of the RF generator increases. The larger the contribution of the inductive channel is, the smaller the value of the dividing capacity included in the capacitive discharge chain is.     

Plasma parameters in a dual-camera low-power inductive RF discharge with an external magnetic field

The results from studying a dual-camera inductive radio-frequency (RF) discharge that was placed in an external magnetic field are presented. The operating conditions were as follows: an argon pressure of 5 × 10^–5–6 × 10^–2 Torr, an external magnetic field strength of 0–60 G, and an RF generator power supply of 25–300 W. During the experiment the resonant RF power consumption and the correspondence between the local power-consumption maxima and spatial maxima of the plasma concentration as a function of the external magnetic field were observed. The comparison of the experimental results with the results of the mathematical simulation indicates that the resonant character of the discharge is associated with the excitation of helicons and Trivelpiece–Gould waves.     

RF breakdown by toroidal helicons

Bounded whistlers are well-known for their efficient plasma production capabilities in thin cylindrical tubes. In this paper we shall present their radio frequency (RF) breakdown and discharge sustaining capabilities in toroidal systems. Pulsed RF power in the electronmagnetohydrodynamic (EMHD) frequency regime is fed to the neutral background medium. After the breakdown stage, discharge is sustained by toroidal bounded whistlers. In these pulsed experiments the behaviour of the time evolution of the discharge could be studied in four distinct phases of RF breakdown, steady state attainment, decay and afterglow. In the steady state average electron density of ≈10¹² per cc and average electron temperature of ≈20 eV are obtained at 10⁻³ mbar of argon filling pressure. Experimental results on toroidal mode structure, background effects and time evolution of the electron distribution function will be presented and their implications in understanding the breakdown mechanism are discussed.     

射频功率对氢气与反式二丁烯的低压电感耦合等离子体的影响（英）

利用等离子体聚合技术制备的GDP壳层是目前ICF靶丸的主要烧蚀层材料。为了了解GDP薄膜沉积过程中的CH等离子体的状态,采用朗缪尔探针和质谱仪对C4H8/H2等离子体的组分和状态参数进行了诊断,并对等离子体的电子能量分布函数、电子密度、电子温度等进行了深入分析。同时讨论了等离子体状态与放电参数之间的关系。研究发现,射频功率对等离子体参数有明显的影响。从10 W到35 W,电子密度正比于射频功率。随着射频功率的增加,在两步电离机制作用下,电子温度和等离子体电势呈现先减小后增大的变化趋势。另外,在高气压下,质谱诊断中发现了大量的稳定的小质量碎片离子,这表明在高气压下等离子体气相中的离子碎片聚合反应被抑制。     

射频电感性耦合等离子体调谐基片自偏压特性

采用调节射频电感性耦合等离子体中基片电极与地之间的外部电路阻抗的方法,控制基片电极的射频自偏压。研究了调谐基片自偏压随外部调谐电容值的变化特征,得到了调谐基片射频自偏压随射频放电功率、气压的变化曲线。在一定放电参数区域内,调谐基片射频自偏压随调谐电容的变化曲线呈现跳变、双稳、迟滞现象。     

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为探究射频离子源驱动器线圈电气参数对射频放电的影响,主要进行了射频离子源等离子体激发的物理分析,并计算了射频电源的频率选择与线圈放电电流、线圈匝间电压以及放电气压之间的关系,设计了射频离子源驱动器的主要参数。研制的射频离子源驱动器装置,成功获得氢等离子体射频放电。实验结果和理论计算结果符合很好。     

大面积NBI 射频离子源电气参数设计分析

为探究射频离子源驱动器线圈电气参数对射频放电的影响,主要进行了射频离子源等离子体激发的物理分析,并计算了射频电源的频率选择与线圈放电电流、线圈匝间电压以及放电气压之间的关系,设计了射频离子源驱动器的主要参数。研制的射频离子源驱动器装置,成功获得氢等离子体射频放电。实验结果和理论计算结果符合很好。     

Wave diagnostics of plasmas using a dielectric waveguide

We study the dispersion characteristics of a planar dielectric waveguide in a magnetized plasma. A method is proposed to determine the parameters of an RF discharge plasma by comparing experimental and theoretical dependences of the transmission coefficient of the sounding microwave signal through a dielectric waveguide on the external magnetic field. Experimental tests showed good agreement between the results of measurements of the plasma density in the discharge by the method proposed and using Langmuir probes. The possibilities of using metal-oxide (dielectric)-semiconductor (MOS) structures as tunable rejector filters, phase rotators, and modulators are discussed. N. I. Lobachevsky State University of Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 3, pp. 215–224, March, 1999.     

Electrical characteristics of parallel-plate RF discharges in argon

Electrical characteristics were measured in a parallel-plate, capacitively coupled (E-type), low-pressure, symmetrical RF discharge driven at 13.56 MHz. The discharge voltage, current, and phase shift between them were measured over a very wide range of discharge parameters (gas pressures between 3 mtorr and 3 torr with discharge power between 20 mW and 100 W). From these measurements the discharge impedance components, the power dissipated in the plasma and in the sheaths, the sheath width, and the ion current to the RF electrodes were found over a wide range of discharge conditions. Some of the general relationships between the various measured and determined parameters are discussed. The experimental results can be used as a database for straightforward comparison with existing RF discharge models and numerical simulations     

Synthesis of well-aligned carbon nanotubes by inductively coupled plasma chemical vapor deposition

Uniform and well-aligned carbon nanotubes (CNTs) have been grown using a high density inductively coupled plasma chemical vapor deposition (ICP-CVD) system. A gas mixture of methane-hydrogen was used as the source and Ni as the catalyst for the CNT growth. The effect of process parameters, such as inductive RF power, DC bias voltage and CH₄/H₂ ratio, on the growth characteristics of CNTs was investigated. It was found that both plasma intensity and ion flux to the substrate, as controlled by the inductive RF power and DC bias voltage, respectively, can greatly affect the growth of CNTs. The relative importance of the generation of ions and the subsequent transport of ions to the substrate as serial process steps are considered as the two underlying factors in determining the growth characteristics of CNTs. PACS 81.05.Uw; 81.07.De; 81.15.Gh     

具有空心阴极放电特征的射频放电的两电子组模型

 运用两电子组模型，考虑了射频放电中的α过程和γ过程两种电离机制，并结合流体模型，研究了中等气压下窄电极间隙容性耦合射频放电在运行模式转变区的等离子体密度以及电离速率分布等特性。理论研究表明，γ电离过程在高电流模式运行中起主要作用，并证实了此类放电中存在显著的电子摆钟效应，具有类似于空心阴极放电的特征。     

Aerodynamic actuation characteristics of radio-frequency discharge plasma and control of supersonic flow

In this paper, aerodynamic actuation characteristics of radio-frequency(RF) discharge plasma are studied and a method is proposed for shock wave control based on RF discharge. Under the static condition, a RF diffuse glow discharge can be observed; under the supersonic inflow, the plasma is blown downstream but remains continuous and stable.Time-resolved schlieren is used for flow field visualization. It is found that RF discharge not only leads to continuous energy deposition on the electrode surface but also induces a compression wave. Under the supersonic inflow condition, a weak oblique shock wave is induced by discharge. Experimental results of the shock wave control indicate that the applied actuation can disperse the bottom structure of the ramp-induced oblique shock wave, which is also observed in the extracted shock wave structure after image processing. More importantly, this control effect can be maintained steadily due to the continuous high-frequency(MHz) discharge. Finally, correlations for schlieren images and numerical simulations are employed to further explore the flow control mechanism. It is observed that the vortex in the boundary layer increases after the application of actuation, meaning that the boundary layer in the downstream of the actuation position is thickened. This is equivalent to covering a layer of low-density smooth wall around the compression corner and on the ramp surface, thereby weakening the compressibility at the compression corner. Our results demonstrate the ability of RF plasma aerodynamic actuation to control the supersonic airflow.     

Plasma characteristics and broadband electromagnetic wave absorption in argon and helium capacitively coupled plasma

A one-dimensional self-consistent calculation model of capacitively coupled plasma(CCP) discharge and electromagnetic wave propagation is developed to solve the plasma characteristics and electromagnetic wave transmission attenuation.Numerical simulation results show that the peak electron number density of argon is about 12 times higher than that of helium, and that the electron number density increases with the augment of pressure, radio frequency(RF) power, and RF frequency. However, the electron number density first increases and then decreases as the discharge gap increases. The transmission attenuation of electromagnetic wave in argon discharge plasma is 8.5-d B higher than that of helium. At the same time, the transmission attenuation increases with the augment of the RF power and RF frequency, but it does not increase or decrease monotonically with the increase of gas pressure and discharge gap. The electromagnetic wave absorption frequency band of the argon discharge plasma under the optimal parameters in this paper can reach the Ku band. It is concluded that the argon CCP discharge under the optimal discharge parameters has great potential applications in plasma stealth.     

Discontinuity of mode transition and hysteresis in hydrogen inductively coupled plasma via a fluid model

A new type of two-dimensional self-consistent fluid model that couples an equivalent circuit module is used to investigate the mode transition characteristics and hysteresis in hydrogen inductively coupled plasmas at different pressures,by varying the series capacitance of the matching box. The variations of the electron density, temperature, and the circuit electrical properties are presented. As cycling the matching capacitance, at high pressure both the discontinuity and hysteresis appear for the plasma parameters and the transferred impedances of both the inductive and capacitive discharge components, while at low pressure only the discontinuity is seen. The simulations predict that the sheath plays a determinative role on the presence of discontinuity and hysteresis at high pressure, by influencing the inductive coupling efficiency of applied power. Moreover, the values of the plasma transferred impedances at different pressures are compared, and the larger plasma inductance at low pressure due to less collision frequency, as analyzed, is the reason why the hysteresis is not seen at low pressure, even with a wider sheath. Besides, the behaviors of the coil voltage and current parameters during the mode transitions are investigated. They both increase(decrease) at the E to H(H to E) mode transition, indicating an improved(worsened) inductive power coupling efficiency.     

Spatial variation behaviors of argon inductively coupled plasma during discharge mode transition

A Langmuir probe and an ICCD are employed to study the discharge mode transition in Ar inductively coupled plasma. Electron density and plasma emission intensity are measured during the E (capacitive discharge) to H (inductive discharge) mode transitions at different pressures. It is found that plasma exists with a low electron density and a weak emission intensity in the E mode, while it has a high electron density and a strong emission intensity in the H mode. Meanwhile, the plasma emission intensity spatial (2D image) profile is symmetrical in the H mode, but the 2D image is an asymmetric profile in the E mode. Moreover, the electron density and emission intensity jump up discontinuously at high pressure, but increase almost continuously at the E to H mode transition under low pressure.     

Characteristics of an atmospheric‐pressure radio frequency‐driven Ar/H2 plasma discharge with copper wire in tube

This paper investigates a plasma discharge driven by a 13.56 MHz radio frequency (RF) power supply at atmospheric pressure, in which a copper wire is inserted in the discharge tube for the deposition of Cu films. The results show that the jet plasma formation originates from the discharge between the copper wire and induction coil because of its electrostatic field. The axial distribution of the plasma parameters in the RF plasma jet, namely the gas temperature, excitation temperature, and electron number density, is determined by diatomic molecule OH fitting, Boltzmann slope, and H_β Stark broadening, respectively. The discharge current significantly declines when a small amount of hydrogen is added to the argon as the plasma‐forming gas, and the gas temperature of discharge plasma increases considerably.