氩气压力对螺旋波放电影响的发射光谱诊断及仿真研究

螺旋波等离子体源以其高电离效率与高密度优势受到多个领域的青睐。螺旋波放电高电离效率的机理或者功率耦合模式,一直是困扰该领域学者的难点之一,对于放电过程与特性的诊断则是揭示其物理机制的重要途径。光谱诊断能够克服介入式诊断手段对等离子体的干扰同时受等离子体烧蚀等弊端,且响应速度快、操作灵活。为研究螺旋波等离子体的放电特性以及气体压力的影响,开展了以氩气为工质气体的光谱实验研究,并针对实验开展了Helic程序数值模拟。通过改变光纤探头焦距调整径向诊断位置,得到谱线强度的径向分布。由氩原子4p-4s能级跃迁产生的谱线主要集中在740～920 nm区间,谱线相对强度较离子激发谱线较强。实验研究发现,在较低氩气压力范围（0.2 Pa<P_Ar<1.0 Pa）,随着压力增加,放电光强迅速增加,但是当压力增加到大于1.0 Pa之后,光强增长的趋势变缓,甚至部分谱线的相对强度不再增长,达到类饱和状态,朗缪尔探针测量得到离子密度变化趋势与其相似。光强分布在靠近径向边界处（r≈4 cm）存在凸起,且随压力增加,该凸起分布更为明显。通过对电子温度的计算发现,压力增加到一定程度将影响放电均匀性。仿真结果显示,增大压力,功率沉积密度的径向分布逐渐向径向边界处积累,与实验观察到的谱线强度径向凸起相一致,螺旋波与TG波的耦合效率增加。随着气体压力的增加,E_r的径向边界峰值降低,原因是波所受阻尼增强,TG波被有效地局限于径向较窄的边界处。电流密度轴向分量J_z在等离子体内部和边界处的峰值呈显著的减小趋势,可见,虽然压力增加一定程度上提高了等离子体密度,但却相应的减小了电离率,导致轴向电流密度受限。但是径向电流密度J_r却呈现先减小后增大的趋势,且增长幅度明显,综合来看,放电效率有所提高。可见适当增加气体压力,有助于提高放电的功率耦合效率和强度,增加等离子体密度。光强比值法是针对线性谱线参数计算的典型方法,Helic程序亦是专业领域内认可度很高的计算工具,结果可靠,分析方法具有可借鉴性。实验及仿真结果对于提高氩气工质下的螺旋波放电强度提供了一定的参考价值。     

气体放电系统中多臂螺旋波的数值分析

采用Purwins的三变量模型, 在二维空间对气体放电系统中多臂螺旋波的形成和转化进行了数值研究. 通过分析方程参数对系统空间的影响, 确定了系统获得稳定螺旋波的参数空间; 得到了斑图由简单静态六边形到螺旋波的演化过程, 分析了螺旋波的形成机制和时空特性; 进一步获得六种不同臂数的多臂螺旋波斑图(例如: 双臂、三臂、四臂、五臂、六臂和七臂螺旋波). 结果表明: 螺旋波斑图出现在图灵-霍普夫(Turing-Hopf)空间, 是Turing模和Hopf模相互竞争、相互作用的结果; 不同臂数的螺旋波波头均在持续地旋转运动, 其运动速度随螺旋波臂数的增加而增大; 随着螺旋波臂数的增加, 其波头的运动形式愈加复杂; 由于受微扰及边界条件的影响, 多臂螺旋波可以向臂数少一的螺旋波发生转变, 数值模拟结果与实验结果符合较好. 关键词： 螺旋波 数值模拟 气体放电     

束—等离子体放电中低频等离子体波的非稳定性研究

本文采用非中性冷等离子体模型,研究了沿磁场入射的电子束和等离子体相互作用引起的低频等离子体波的非稳定性。计算表明,在束-等离子体放电情况下,振动频率和增长率都随电子束密度增加而增加,当束电流一定时,它们随l增加而略有增加。l=1时其频率数量级与离子迴旋频率相同。l≥3时,振动频率几乎不随k_z变化,其振动频率和增长率数量级与低混杂振荡频率相同,实质是低混杂漂移非稳定性。理论结果与实验一致。     

螺旋波等离子体制备多种碳基薄膜原位诊断研究

利用自行研制的强磁场螺旋波等离子体化学气相沉积装置(HWP-CVD),通过改变等离子放电参数,实现多种碳基薄膜制备.利用朗缪尔探针、发射光谱以及质谱对Ar/CH4等离子体放电进行原位诊断;用扫描电子显微镜和拉曼光谱对碳基薄膜进行表征.结果表明:在给定参数下,等离子体放电模式均为螺旋波放电模式;在给定CH4流量下,等离子...     

发射光谱法测量常压介质阻挡放电氩等离子体的放电参数

介绍发射光谱法测量常压介质阻挡氩等离子体的放电参数的方法,通过常压介质阻挡放电氩等离子体的光谱图,测量和计算了等离子体的电子温度和电子浓度.     

脉冲放电产生螺旋流注的等离子体特性研究

通过脉冲放电方式产生三维螺旋形的等离子体放电通道,在高速摄像机拍摄下观察到放电通道中的发光电离体以流注形式沿螺旋轨迹快速传播.建立电磁模型解释螺旋放电的形成机制,对造成对称性破缺及影响其手性性质的极向电场进行分析.研究表明,螺旋放电产生的放电通道存在两种不同的手性特征,而脉冲重复频率等放电参数及边界条件对螺旋流注的传播特性存在影响.脉冲电源驱动的电磁场在介质管内所形成的波模是极向电场形成的一个重要来源,当极向电场与轴向电场强度相近时则形成螺旋流注放电.     

磁场对螺旋波等离子体波和能量吸收影响的数值研究

本文考察在径向电子数密度呈抛物形分布的情况下,外加稳恒磁场,射频通过螺旋波天线在等离子体中激发电磁波的传播性质.采用线性扰动波假设,数值求解Maxwell方程组,得到80—800 G(1 G=10-4T)磁场条件下等离子体中径向电、磁场强度及能量沉积密度的分布情形.计算结果表明,磁场增大(80→800G)时,螺旋波受到的阻尼较小,可深入等离子体传播;Trivelpiece-Gould(TG)波受到的阻尼增大,在等离子体-真空边界处衰减增强;整体的能量吸收向边界集中.磁感应强度小于100 G时,TG波可深入主等离子体区传播,等离子体径向能量吸收相对均匀.     

高气压氩气辉光放电条纹等离子体的形成和演化

辉光放电等离子体正柱区内的自组织条纹现象是气体放电物理中的基础性问题,涉及电子动力学、输运过程、放电不稳定性、非线性现象等丰富的物理内容,是基础物理及其应用中备受关注的重要课题.本文报道了一种在千帕量级气压下产生的氩气辉光放电条纹等离子体,重点关注了条纹等离子体的电学、光学及电离波传播特征,从物理上分析了氩气条纹等离子体的产生及消除机制.研究结果表明,在此气压下产生的氩气条纹等离子体,其条纹长度约为1.5 mm,且随气压减小;电离波波速为1.87 m/s,频率为1.25 kHz.发射光谱诊断证实,条纹等离子体的产生与丰富的亚稳态原子密切相关,亚稳态原子导致的分步电离过程会引起电离不稳定性,这种不稳定性以电离波的形式传播,使得等离子体参数发生纵向调幅,从而形成明暗相间的条纹等离子体.加入氮气可有效猝灭亚稳态氩原子,调整电子能量分布函数,这使得等离子体的不稳定性条件被破坏,因此,条纹等离子体消失.本工作可为人们进一步认识和理解高气压下辉光放电条纹等离子体的形成及消除机制提供新的思路和实验依据.     

复Ginzburg-Landau方程中模螺旋波的稳定性研究

研究了复Ginzburg-Landau方程系统中模螺旋波与其他斑图在同一平面内的竞争行为,发现演化结果在系统参数平面内可分为四个主要区域:在I区和III区中,模螺旋波与相螺旋波相比稳定性较差,模螺旋波的空间被相螺旋波所入侵.在II区中,模螺旋波具有较强的稳定性,相螺旋波的空间被模螺旋波所入侵.在IV区内,由于时空混沌所导致的频率不稳定性,演化的结果较为复杂.我们通过对模螺旋波、相螺旋波以及时空混沌的频率分析,发现当模螺旋波的系统参数为α1=-1.34,β1=0.35时,较高频率的模螺旋波具有较好的稳定性,高频模螺旋波可以入侵低频斑图空间.竞争结果主要受系统变量实部的频率影响,频率分析所得到的理论结果与数值实验结果符合得非常好.     

电子温度对螺旋波等离子体中电磁模式能量沉积特性的影响

采用考虑粒子热效应及粒子温度各向异性的温等离子体介电张量模型,借助绝缘边界条件下径向密度均匀分布等离子体柱中螺旋波与Trivelpiece-Gould (TG)波的本征模色散关系,理论分析了螺旋波等离子体中典型电子温度范围内中等密度、低磁场情形下m=–1, 0,+1角向模的能量沉积特性.研究结果表明:在w/2π=13.56 MHz, T_i=0.1T_e参量条件下,存在一个临界轴向静磁场值B_0,c,当B₀ 0,c时螺旋波变为消逝波;存在一个临界电子温度值T_e,c,当Te e,c时TG波变为消逝波;当波频率靠近电子回旋频率时, TG波的回旋阻尼开始显著陡升;当电子横纵向温度比T_e⊥/T_ez大于某一临界值时, TG波变为增长波;在螺旋波放电典型电子温度T_e∈(3 eV, 5 eV)范围内, TG波朗道阻尼和碰撞阻尼致使的能量沉积在不同范围内占据主导地位.     

Diagnosis of a low pressure capacitively coupled argon plasma by using a simple collisional-radiative model

This paper proposes a simple collisional-radiative model to characterise capacitively coupled argon plasmas driven by conventional radio frequency in combination with optical emission spectroscopy and Langmuir probe measurements. Two major processes are considered in this model, electron-impact excitation and the spontaneous radiative decay. The diffusion loss term, which is found to be important for the two metastable states (4s[3/2]₂, 4s'[1/2]₀), is also taken into account. Behaviours of representative metastable and radiative states are discussed. Two emission lines (located at 696.5 nm and 750.4 nm) are selected and intensities are measured to obtain populated densities of the corresponding radiative states in the argon plasma. The calculated results agree well with that measured by Langmuir probe, indicating that the current model combined with optical emission spectroscopy is a candidate tool for electron density and temperature measurement in radio frequency capacitively coupled discharges.     

Kinetic study of instability growth rate in a helicon plasma discharge source

In this work, a kinetic model is developed to study the effects of the radio frequency antenna wavenumber, helicon plasma electron density, as well as their drift velocity and temperature on the instability increment rate of the helicon wave in both longitudinal and transverse directions. The ion acoustic (IA) wave frequencies and wavenumbers of the helicon waves are obtained when the maximum wave energy is deposited on the plasma ions. Moreover, it is shown that, at the IA wavenumber and frequencies, while the longitudinal instability increment rates for both the helicon and IA waves are ignorable, the transverse instability increment rate for both the helicon and IA wave increases. Besides, the longitudinal instability increment rate for the helicon or IA wave has non‐zero resonant frequencies. On the other hand, the transverse instability increment rate of helicon or IA wave can be neglected. Furthermore, it is observed that, while both the imaginary part of longitudinal permittivity and longitudinal instability increment rate are not influenced by the electron temperature, their transverse component increases linearly with the electron temperature. In addition, the imaginary part of transverse permittivity increases almost linearly with the drift velocity of the plasma electrons.     

双频容性耦合等离子体相分辨发射光谱诊断

采用相分辨发射光谱法, 对双频容性耦合纯Ar和不同含O₂量的Ar-O₂混合气体放电等离子体的鞘层激发模式进行了探究. 在射频耦合电源上极板的鞘层区域处观察到两种电子激发模式: 鞘层扩张引起的电子碰撞激发模式和二次电子引起的电子碰撞激发模式; 并发现这两种激发模式均受到低频射频电源周期的调制. 在纯Ar放电等离子体中, 两种激发模式的激发轮廓相似; 而在Ar-O₂混合气放电等离子体中, 随着含O₂量的增加, 二次电子的激发轮廓变弱. 此外, 利用相分辨发射光谱法对不同含O₂量的Ar-O₂混合气放电下Ar的 750.4 nm谱线的平均低频电源周期轴向分布进行了研究, 得到了距耦合电源上极板约3.8 mm处为双频容性耦合射频等离子体的鞘层边界. 关键词： 双频容性耦合等离子体 等离子体鞘层 发射光谱     

Aspects of the upstream region in a plasma jet with dielectric barrier discharge configurations

A plasma column with a length of about 65 cm is generated in the upstream region of a plasma jet using dielectric barrier discharge configurations. The effects of experimental parameters such as the amplitude of the applied voltage and the driving frequency are investigated in aspects of the plasma column by the optical method. Results show that both the plasma length and the propagating velocity, as well as the discharge current, increase with the increase in the applied voltage or its frequency. The discharge mechanism is analysed qualitatively based on streamer theory, where photo-ionization is important. Furthermore, optical emission spectroscopy is used to investigate the electric field intensity of the upstream region.     

Aspects of the dielectric upstream region barrier discharge in a plasma jet with configurations

A plasma column with a length of about 65 cm is generated in the upstream region of a plasma jet using dielectric barrier discharge configurations. The effects of experimental parameters such as the amplitude of the applied voltage and the driving frequency are investigated in aspects of the plasma column by the optical method. Results show that both the plasma length and the propagating velocity, as well as the discharge current, increase with the increase in the applied voltage or its frequency. The discharge mechanism is analysed qualitatively based on streamer theory, where photo-ionization is important. Furthermore, optical emission spectroscopy is used to investigate the electric field intensity of the upstream region.     

等离子体刻蚀工艺的物理基础

介绍了等离子体刻蚀工艺背景以及有关等离子体刻蚀机理的研究进展,综述了等离子体刻蚀机理的研究方法,着重阐述了电容耦合放电和电感耦合放电等离子体物理特性,特别是双频电容耦合放电等离子体和等离子体鞘层研究中的关键问题.     

Synthesis of SiC/graphene nanosheet composites by helicon wave plasma

We report an approach to the rapid, one-step, preparation of a variety of wide-bandgap silicon carbide/graphene nanosheet(Si C/GNSs) composites by using a high-density helicon wave plasma(HWP) source. The microstructure and morphology of the Si C/GNSs are characterized by using scanning electron microscopy(SEM), Raman spectroscopy, x-ray diffraction(XRD), x-ray photoelectron spectroscopy(XPS), and fluorescence(PL). The nucleation mechanism and the growth model are discussed. The existence of Si C and graphene structure are confirmed by XRD and Raman spectra.The electron excitation temperature is calculated by the intensity ratio method of optical emission spectroscopy. The main peak in the PL test is observed at 420 nm, with a corresponding bandgap of 2.95 e V that indicates the potential for broad application in blue light emission and ultraviolet light emission, field electron emission, and display devices.     

Calculation of ion energy distributions of argon excimer ions generated in helicon plasma

A program is developed to calculate the ion energy distributions （IEDs） of Ar2^＋ making use of a simplified kinetic model with a combination of Monte Carlo method. Several coefficients are used to realize good match between the calculated and measured results. Some important assumptions are confirmed： argon excimer ions have short lifetime, hence they are formed in a short range before the collecting electrode. The excimer ions that encounter collisions will be discarded because they turn to other ion species after they collide with argon atoms. From the calculated results some plasma parameters such as the cross section or neutral density in discharge could be evaluated.     

螺旋波等离子体推进器中双层形成的PIC模拟

建立了螺旋波等离子体推进器中双层等离子体形成过程的一维全粒子PIC模型,讨论了放电过程中电子加热模型和等离子体膨胀模型,计算了不同条件下螺旋波等离子体推进器中双层等离子体的分布。结果表明：采用氩气工质,在射频电流90 A/m2和工作压强0.05~0.15 Pa的条件下,可产生双层等离子体,其密度为1.31015~2.81015 m-3,双层电势降为10~30 V,可加速氩离子束流,喷射速度为3~12 km/s,双层加速效应对推进器的性能具有一定影响。