Power loss to generating ion current in radio-frequency ion thrusters and technological sources of ions

The balance of power in a radio-frequency ion source is constructed by calculating the inevitable power loss at surfaces bordering the inductive discharge plasma and power loss to the generation and preliminary acceleration of working-gas ions. The relationship between the specific radio-frequency power consumption per ion-current unit emerging from the source and electron temperature and geometric parameters of the gas discharge chamber is determined.     

Particle-in-cell/Monte Carlo simulation of radio frequencySiH4/H2 discharges

In this paper we report on a study of SiH₄/H₂ radio-frequency discharges using the particle-in-cell/Monte Carlo (PIC/MC) method. A special procedure based on the rate balance for negative ions has been developed to speed up the simulation for this kind of electronegative discharge. The electron energy distribution function and the angular and energy distribution function of ions arriving at the substrate have been studied at different discharge settings (frequency, pressure, voltage, and power). The simulations show that the electrons are heated ohmically, so the average electron energy can be increased only by increasing the voltage. A high radical density, a high and more directional ion flux, and a low average ion energy can be obtained by a combination of a high frequency and a low RF voltage. The behavior of the dissociation rate with the discharge parameters is consistent with the experimentally observed consumption of SiH₄. The simulated ion energy distribution functions are in good agreement with experimental results     

Supersonic CO2 laser excited by RF discharge in closed cycle

A supersonic gas flow having a Mach number of 2 has been realized in a closed-cycle radio-frequency (RF)-discharge-excited supersonic CO₂ laser system. Stable RF discharge at a high CO₂ gas concentration has become possible using supersonic gas flow and RF discharge generated between dielectric electrodes. As a result, high RF input power density has been obtained. In addition, a high small-signal gain has been obtained in the supersonic section through decreases in gas pressure and gas temperature due to supersonic gas flow.This revised version was published online in August 2005 with a corrected cover date.     

Study of motion of atoms in direct-current discharge of ring laser

Using a ring laser, we experimentally study the motion of atoms caused by their collisions with electrons and ions in a direct-current discharge. We find the dependences of the frequency difference between counterpropagating light waves on the discharge current and parameters of the gas mixture. It is found that, depending on the parameters of the discharge and excitation mechanism of energy levels, the sign of the frequency difference can be reversed. We show that recombination processes are mainly responsible for the occurrence of the frequency difference in the ring laser. The method of investigation makes it possible to detect at least 100 atoms, the velocity of the directed motion of which is comparable with the velocity of ions.     

On the ion drift in gas mixtures

The features of the velocity distribution function of ions during their drift in a mixture of different gases are analyzed. Examples of drift of heavy ions in light gas, a mixture of two gases with equal concentrations, and drift of light ions in heavy gas are considered. It was shown that the transition to discharge in mixtures of different gases allows the formation of an ion flux with characteristics unattainable for discharge in single-component gas under typical conditions under which experiments with dust structures in plasma are performed.     

发射光谱研究氩气/空气混合气体介质阻挡放电能量传递过程

使用水电极介质阻挡放电装置,对比氩气与氩气/少量空气的混合气体以及空气与空气/少量氩气的混合气体放电的发射光谱,研究了氩气与空气相混合时气体放电中的能量传递过程。实验发现, 当氩气中加入少量的空气时,氩原子谱线均变弱,说明空气中的氮分子对氩原子的各激发态具有猝灭作用。并且随着空气含量的增加,各谱线变弱的速率不同。越是与氮分子的激发电位接近的氩原子的激发态被猝灭的作用越明显。另一方面,当空气中加入少量氩气时,发现氮分子第二正带系和氮分子离子第一负带系的谱线均被增强。说明在空气/少量氩气放电中,氮分子的激发由于亚稳态氩原子的潘宁激发传能而增强。因此在氩气/空气混合气体放电中,气体成分及比例影响放电的发光特性和能量传输特性。     

激光诱导荧光方法对SiH4／N2混合气体放电等离子体的研究

用激光诱导荧光方法对SiH_4/N_2混合气体射频放电等离子体进行了研究,实验上首次检测到SiH_4分子射频放电离解过程的中间产物Si_2.     

碰撞效应对入射到射频偏压电极上离子能量分布和角度分布的影响

考虑了离子与中性粒子的弹性碰撞和电荷交换碰撞效应,建立了一套描述射频等离子体鞘层动力学特性的自洽模型,并利用MonteCarlo模拟方法研究了入射到电极上的离子的能量分布和角度分布.数值结果表明:随着放电气压增加,入射到电极上离子的能量分布逐渐地由双峰分布变成单峰分布,而且低能离子的数目也逐渐地增加.入射到电极上的离子呈小角分布,而且放电气压等参数对角度分布的影响不是太明显. 关键词： 射频放电 等离子体 离子 鞘层     

基于共振型高灵敏度光声光谱技术探测痕量乙炔气体浓度

乙炔气体作为判断变压器运行状态的一种故障气体,其浓度的高低反映了变压器的运行状况,因此对其浓度的探测在变压器的维护中具有重要意义。为了准确探测变压器运行过程中产生的乙炔气体浓度,为变压器的维护提供技术参数,针对基于DFB激光器的共振型光声光谱技术痕量乙炔气体检测技术开展研究,对传统的光声光谱探测系统进行改进。根据光声光谱技术的理论可知,光声信号的强度与入射激光的功率成正比,所以在光声池的出射窗口采用一个平面反射镜将红外光再次反射到光声池中以增加入射光功率,增强光声信号强度,进一步提高了光声系统的探测灵敏度。通过一定浓度的乙炔气体在不同调制频率和不同调制深度下光声信号强度的变化,确定光声探测系统的最佳调制频率和最佳调制深度为767 Hz和0.3 mV。利用不同浓度乙炔气体对系统进行标定,然后采用最小二乘法对光声信号与气体浓度进行拟合,二者具有很好的线性度。通过Allan方差计算可知,系统在平均时间达到200 s时,能够达到最低探测极限浓度。实验表明,在一个大气压下,积分时间为10 ms时,改进后的共振型光声光谱探测系统对乙炔气体的最低探测极限浓度达到了0.3 μL·L-1。还将小波去噪技术引入到低浓度下乙炔气体的光声信号处理中,有效消除了低浓度气体光声信号中的噪声,提高了信噪比。设计的共振型光声光谱探测系统操作简单,最低探测浓度符合国标中对变压器维护过程中对乙炔气体的探测需求,在变压器维护领域具有广阔的应用前景。     

The influence of discharge parameters on the generation of ions H<Subscript>3</Subscript><Superscript>+</Superscript> in the source based on reflective discharge with hollow cathode

For hydrogen ions source based on reflective discharge with hollow cathode the investigations of the effect of discharge current and gas pressure on the component composition of the ion beam have been performed. It has been shown that the optimization of the discharge parameters makes it possible to achieve up to 70% triatomic hydrogen ions H₃ ⁺ in the beam.     

Simulation of nanoparticle coagulation in radio-frequency capacitively coupled C_2H_2 discharges

A self-consistent fluid model is employed to investigate the coagulation stage of nanoparticle formation, growth,charging, and transport in a radio-frequency capacitively coupled parallel-plate acetylene(C2H2) discharge. In our simulation, the distribution of neutral species across the electrode gap is determined by mass continuity, momentum balance, and energy balance equations. Since a thermal gradient in the gas temperature induced by the flow of the neutral gas, a careful study of the thermophoretic force on the spatial distribution of the nanoparticle density profiles is indispensable. In the present paper, we mainly focus on the influences of the gas flow rate, voltage, and gas pressure on the spatial distribution of the nanoparticle density. It appears that the resulting density profile of the 10-nm particles experiences a significant shift towards the upper showerhead electrode once the neutral equations are applied, and a serious shift is observed when increasing the gas flow rate. Thus, the flow of neutral gas can strongly influence the spatial distribution of the particles in the plasma.     

Discharge characteristics of an atmospheric-pressure capacitively coupled radio-frequency argon plasmas

In this Letter, the electrical discharge characteristics of plasmas generated in coaxial cylindrical electrodes capacitively powered by radio-frequency power supply at atmospheric pressure are investigated with respect to argon gas. The electrical discharge parameters, the current and voltage characteristics (I–V) and the current and power characteristics (I–P), are measured for argon plasmas, and the electron temperatures and electron densities are estimated based on the equivalent circuit model and by making use of the power balance equation. Furthermore, the influence of the additive gas, oxygen gas, on the electrical discharge characteristics is also investigated in the argon plasmas, which is closely related to the electron temperature of plasmas.     

电激励脉冲HF激光SF_6/C_2H_6工作气体的放电特性

研究了电激励脉冲HF激光工作介质SF6/C2H6混合气体的放电特性。通过对放电等离子体荧光图像和放电波形的测量,分析比较了不同条件下放电稳定性、剩余电压、能量沉积效率等特性参数的变化情况。实验结果表明:混合气体的放电过程存在主放电、剩余电压维持和电弧放电3个阶段,各阶段的放电特性有所差异;提高充电电压有利于放电能量的有效沉积,也会使不稳定的电弧放电提前;增加C2H6原子分数能起到抑制电弧放电的作用;混合气体总压的增加会导致剩余电压的提高以及辉光放电的能量沉积效率的降低;最佳的能量沉积出现在电弧放电阶段与辉光放电阶段即将融合的临界状态。     

Plasma-dust structures in He-Ar DC glow discharge

The gas mixture discharge has a number of features which can appear in experiments with dusty plasma. For example, in the case of a significant difference in atomic masses of ions and atoms, strong anisotropy of the distribution function over ion velocities takes place, which in turn can cause a significant change in properties of dust structures. In this work, experiments on the study of the dust structures in the gas discharge of a mixture of light and heavy gases, i.e., helium and argon, are analyzed. The results of numerical simulation of ion and electron drift in the mixture of these gases and dust particle charging processes are presented.     

Modeling of the nanoparticle coagulation in pulsed radio-frequency capacitively coupled C_2H_2 discharges

The role of pulse parameters on nanoparticle property is investigated self-consistently based on a couple of fluid model and aerosol dynamics model in a capacitively coupled parallel-plate acetylene(C2H2) discharge. In this model, the mass continuity equation, momentum balance equation, and energy balance equation for neutral gas are taken into account.Thus, the thermophoretic force arises when a gas temperature gradient exists. The typical results of this model are positive and negative ion densities, electron impact collisions rates, nanoparticle density, and charge distributions. The simulation is performed for duty ratio 0.4/0.7/1.0, as well as pulse modulation frequency from 40 k Hz to 2.7 MHz for pure C2H2 discharges at a pressure of 500 m Torr. We find that the pulse parameters, especially the duty ratio, have a great affect on the dissociative attachment coefficient and the negative density. More importantly, by decreasing the duty ratio, nanoparticles start to diffuse to the wall. Under the action of gas flow, nanoparticle density peak is created in front of the pulse electrode,where the gas temperature is smaller.     

氧气放电等离子体温度测量研究

为了考察电激励氧碘激光器中放电腔内的宏观气体温度,由两片蚌形铜电极和一根长30 cm内径1.65 cm的耐热玻璃管构成放电腔装置,用一台最高功率500 W,频率13.56 MHz的射频装置对压力1 330Pa的纯氧气体进行了介质阻挡放电研究。利用O2(b,ν=0)的P支发射光谱,分别采用波尔兹曼直线作图法和计算机模拟发射光谱法,测量了氧气射频放电等离子体的宏观气体温度。对于低分辨率光谱,利用高斯拟合进行了分峰处理,利用峰面积表征发光强度,通过波尔兹曼作图法得到了宏观气体温度。利用氦氖激光器测得的光谱仪狭缝函数获得了计算1机模拟发射光谱,以最小二乘法作为判据,通过比较计算机模拟发射光谱和实测光谱获得了宏观气体温度。     

Effect of helium/argon gas ratio in a He-Ar-Cu<Superscript>+</Superscript> IR hollow-cathode discharge laser: modeling study and comparison with experiments

The He-Ar-Cu⁺ IR laser operates in a hollow-cathode discharge, typically in a mixture of helium with a few-% Ar. The population inversion of the Cu⁺ ion levels, responsible for laser action, is attributed to asymmetric charge transfer between He⁺ ions and sputtered Cu atoms. The Ar gas is added to promote sputtering of the Cu cathode. In this paper, a hybrid modeling network consisting of several different models for the various plasma species present in a He-Ar-Cu hollow-cathode discharge is applied to investigate the effect of Ar concentration in the gas mixture on the discharge behavior, and to find the optimum He/Ar gas ratio for laser operation. It is found that the densities of electrons, Ar⁺ ions, Ar_m ^* metastable atoms, sputtered Cu atoms and Cu⁺ ions increase upon the addition of more Ar gas, whereas the densities of He⁺ ions, He₂ ⁺ ions and He_m ^* metastable atoms drop considerably. The product of the calculated Cu atom and He⁺ ion densities, which determines the production rate of the upper laser levels, and hence probably also the laser output power, is found to reach a maximum around 1–5 % Ar addition. This calculation result is compared to experimental measurements, and reasonable agreement has been reached. Received: 14 October 2002 / Revised version: 28 November 2002 / Published online: 19 March 2003 RID="*" ID="*"Corresponding author. Fax: +32-3/820-23-76, E-mail: annemie.bogaerts@ua.ac.be     

XeO luminescence in a self-sustained slab radio-frequency discharge

We report the observation of bright luminescence and registration of luminescence spectrum of a XeO molecule in the green spectral region upon excitation of a Xe:O₂ gas mixture in a self-sustained slab radio-frequency discharge.     

射频感应耦合Ar-N2等离子体物理特性的Langmuir探针测量及理论研究

分别通过Langmuir探针测量和动力学模型模拟方法研究了射频感应耦合Ar-N₂等离子体中电子能量分布、电子温度、电子密度等物理量随N₂含量的变化规律.实验研究结果表明：电子能量分布呈现出非Maxwell型分布,并由双温分布向三温分布过渡;电子温度在不同的气压下随N₂含量的增加呈现出不同的变化规律.在放电气压小于1.3 Pa时,电子温度随N₂含量的增加而下降;当气压大于1.3 Pa时,电子温度随N₂关键词： 感应耦合等离子体 2混合气体放电')" href="#">Ar-N₂混合气体放电 电子能量分布 Langmuir探针     

Monte carlo simulation of gas ionization in the interelectrode gap of a low-current discharge in an argon-mercury mixture

Kinetics of electrons, ions and metastable excited atoms in a low-current gas discharge between flat electrodes in the mixture of argon with mercury vapors was simulated. The motion of electrons was calculated using the Monte Carlo method, while that of ions and metastables was described on the basis of their transport equations. The ionization coefficient of the mixture was calculated as a function of relative mercury density. The dependence of discharge ignition voltage on the interelectrode distance was determined.