HT-7托卡马克slide-away放电充气对等离子体行为的影响

本文研究了slide-away放电条件下的等离子体约束性能;分析了充气对等离子体约束性能以及反常多普勒共振不稳定性的影响.研究了等离子体密度的提升对slide-away放电过程中逃逸电子辐射行为的影响.研究结果发现:slide-away放电充气可以抑制逃逸电子反常多普勒不稳定性,但是使得等离子体约束状态变差,逃逸电子辐射增强.     

提高等离子体密度抑制逃逸电子束不稳定性的实验研究

利用ECE电子回旋辐射和Ha线辐射等托卡马克物理诊断系统,研究了Slide-away放电过程中提高等离子体密度对非麦克斯维尔分布的逃逸电子所激发的逃逸电子束不稳定性影响作用.实验结果表明:在Slide-away放电模式下,提高等离子体密度能有效抑制逃逸电子束的不稳定性.     

提高等离子体密度抑制逃逸电子束不稳定性的实验研究

利用ECE电子回旋辐射和Ha线辐射等托卡马克物理诊断系统,研究了Slide-away放电过程中提高等离子体密度对非麦克斯维尔分布的逃逸电子所激发的逃逸电子束不稳定性影响作用。实验结果表明：在Slide-away放电模式下,提高等离子体密度能有效抑制逃逸电子束的不稳定性。     

标准有限元方法模拟大气压流注等离子体中数值振荡与伪扩散问题研究与改进

基于商用软件的等离子体数值模拟方案大多是基于标准Galerkin格式的有限元方法,在计算大气压流注放电时,存在数值振荡和伪扩散的问题,计算结果可靠性不高.针对针-板体流注放电结构,构建了修正的COMSOL Multiphysics等离子体模型.修正模型与COMSOL Multiphysics内置等离子体模块的区别主要在于增加了基于弱形式的人工稳定项.利用修正模型复现了经典的雪崩-流注转捩算例,并与经典纳秒秒冲过电压针板放电实验结果进行了对比验证.结果表明,引入修正后的商用软件模型能够克服数值振荡和伪扩散缺陷,确保等离子体数值计算的准确性和可复现性.      

Coupling Between the Discharge Plasma Instability and the Laser Oscillation in a He—Cd Laser

The investigation of the output of a He–Cd laser with electrically floating hollow electrodes shows that the discharge plasma instability plays an important role in the generation of the population inversion. The experimental evidence is presented and a qualitative interpretation is given by considering the plasma instability as equivalent to a radio frequency component of the discharge voltage.     

Thermal Instability of Non-Ideal Current-Carrying Plasmas of Metal Vapors

As a result of Ohmic heating the transition proceeds from the liquid metal state to the state of the gaseous plasma. The conductivity drops rapidly. This paper reports on the thermal instability of such a discharge. The instability results in the plasma stratification across the current direction. The discussion is given of the experiment by DIKHTER and ZEIGARNIK. The discharge is layered under the isobaric heating of cesium wire in the argon atmosphere.     

Thermal ionization instability of an air discharge plasma in a microwave field

Results are presented from experimental studies of the initial stage of an air discharge initiated in a linearly polarized quasi-optical microwave beam. The discharge was excited at an air pressure at which the electron-neutral collision frequency in the discharge plasma was considerably higher than the circular frequency of the electromagnetic field and at a microwave field amplitude close to the threshold field for air breakdown. The experiments revealed relatively bright plasma channels stretched along the microwave electric field. The development rate of these channels and their characteristic transverse dimensions are estimated. A comparison of the experimental data and theoretical estimates indicates that the channels observed arise due to the onset of thermal ionization instability in the microwave discharge plasma.     

Recombination instability of dust plasma of a non-self-sustained discharge in the collision regime

Recombination instability of a dust plasma of a non-self-sustained discharge maintained by an ionizing radiation beam has been studied for the conditions when the collisions of ions with atoms in the charged layer of a dust particle considerably affect the ion current to the particle. It has been shown that the collisions of ions elevate the stability of the plasma. The dependence of the conditions for the evolution of instability and its increment on the discharge parameters has been analyzed.     

Emission from a sulfur-hexafluoride volume discharge induced by attachment instability

Characteristics of a low-pressure volume discharge in SF₆ are investigated. The discharge with a spherical anode-plane cathode electrode system was induced by attachment instability. It is found that applying a dc voltage (U _ch≤1.3 kV) to the anode in the absence of a confining dielectric wall results in the ignition of a repetitive discharge (f=0.1–120 kHz). The spatial, frequency, and current-voltage characteristics of the volume discharge; plasma emission in the spectral range 200–700 nm; and the waveforms of the discharge voltage, current, and plasma emission are investigated. It is shown that the plasma under study exists in the form of a domain (autosoliton) and that the volume discharge is self-induced because, during attachment instability, the plasma itself acts as a switch enabling repetitive pulsed operation. The results obtained can be applied to studying the physics and technology of electric-discharge chemical HF (DF) lasers based on nonchain reactions and to developing high-aperture low-pressure repetitive Ar-, Kr-, and Xe-fluoride lamps with low-corrosive working media (low-pressure mixtures of Ar, Kr, and Xe with SF₆).     

Physical aspects of dust–plasma interactions

Low-pressure gas discharge plasmas are known to be strongly affected by the presence of small dust particles. This issue plays a role in the investigations of dust particle-forming plasmas, where the dust-induced instabilities may affect the properties of synthesized dust particles. Also, gas discharges with large amounts of microparticles are used in microgravity experiments, where strongly coupled subsystems of charged microparticles represent particle-resolved models of liquids and solids. In this field, deep understanding of dust–plasma interactions is required to construct the discharge configurations which would be able to model the desired generic condensed matter physics as well as, in the interpretation of experiments, to distinguish the plasma phenomena from the generic condensed matter physics phenomena. In this review, we address only physical aspects of dust–plasma interactions, that is, we always imply constant chemical composition of the plasma as well as constant size of the dust particles. We also restrict the review to two discharge types: dc discharge and capacitively coupled rf discharge. We describe the experimental methods used in the investigations of dust–plasma interactions and show the approaches to numerical modelling of the gas discharge plasmas with large amounts of dust. Starting from the basic physical principles governing the dust–plasma interactions, we discuss the state-of-the-art understanding of such complicated, discharge-type-specific phenomena as dust-induced stratification and transverse instability in a dc discharge or void formation and heartbeat instability in an rf discharge.     

Ionization-overheating instability threshold in the electrodeless microwave discharge plasma

Experiments with a pulsed freely localized electrodeless microwave discharge in air under a pressure corresponding to the ascending branch of the pressure dependence of the breakdown field are described. The discharge is initiated in a focused quasi-optical electromagnetic beam. The minimal threshold values of the electromagnetic field (for which a brighter plasma channel extended along the field is formed in the initially spatially homogeneous diffuse discharge plasma) are determined by varying air pressure for several fixed values of this field in the focal region of the beam. In accordance with the prevailing theory, this phenomenon is interpreted as the result of evolution of ionization-overheating instability in the microwave discharge plasma.     

Experiments on the injection of dust jets into plasma

An experimental technique for studying the injection of dust jets into the plasma of a glow discharge in air is developed. The velocity and flight time of a dust jet are measured under different initial conditions. It is shown that the propagation of dust grains in plasma is accompanied by self-contraction instability along and across the discharge, which leads to dust agglomerization and clusterization.     

Cathode Sheath Instability at Frequencies Near the Ion Plasma Frequency

We consider steady-state and nonstationary processes in a near-cathode region. Equations describing the plasma dynamics near a cathode at frequencies close to the ion plasma frequency are derived, and solutions of these equations for various zones of a discharge gap are found. A piecewise-uniform model of a cathode sheath is developed, which points out the possibility of an instability at a frequency slightly less than the near-cathode ion plasma frequency. The gas pressure effect on the instability threshold with respect to the discharge current is considered. The obtained results are in good agreement with the data of experimental studies of the cathode sheath in a hollow-cathode discharge.     

Modulation instability in pulsed surface-wave sustained discharges

Experimental results showing development of modulation instability and tendency to soliton formation in pulsed gas discharges sustained by surface waves are presented. The measurements are performed in argon discharges at gas pressure 13-1.3·10³ Pa sustained by pulsed microwave power at 2.45 GHz, The changes along the discharge length of the shape of the pulses of the total light emission, which is an indication for the plasma density, and of the wave electric field creating the discharge, are registrated. The cases when the modulation instability arises from the level of fluctuations in the plasma and when it is forced by the applied signal producing the discharge are demonstrated. The obtained results are discussed in terms of weak nonlinearity superimposed on the mechanism of strong ionization nonlinearity responsible for the discharge creation itself. A separation of a solitary-like wave front the leading edge of the pulse is also reported as an experimental result     

Observation of Potential Relaxation Instability in a Bounded Discharge Plasma

A potential relaxation instability (PRI), which causes a periodic motion of a potential jump and plasma expansion accompanying a high-density fluctuation level (?60 percent), is observed in a bounded discharge plasma. The instability is found to create a high electron drift velocity and a spatial growth of density and potential fluctuations, and to accelerate a test wave. An additional supplement of a plasma into the boundary suppresses the instability. At the same time, the fluctuation decreases (<5 percent) and the frequency difference of the wave spectrum between nth and (n - 1) th (n is an integer) higher harmonics decreases as the frequency increases. However, when the potential relaxation instability is excited, this frequency difference keeps constant.     

Characteristics of a reflex discharge in hydrogen in a magnetic field

The properties of an extensive reflex discharge of large power with one heated and one cold cathode in a magnetic field of 10 to 1500 Gauss were measured. At a neutral hydrogen pressure of 10^–4 to 10^–3 torr a plasma column was obtained which was 100 cm long, 10 cm in diameter and had a density greater than 10^–11 cm^–3. The dependence of the radial profile of the potential in the plasma was measured by a heated probe, and the temperature and electron density by Langmuir probes calibrated by a microwave interferometer.The dependence of the origin of low-frequency rotational instability on the parameters of the discharge was studied and the measured critical magnetic field was compared with theory. Apart from this low-frequency instability, intensive oscillations were also found in the discharge current in a frequency band up to 30 MHz, and the dependence of their spectrum on the magnetic field was measured.     

Experimental Analysis of a Low Frequency Instability in a Magnetized Discharge Plasma

In the paper we present the results of an investigation of a low frequency (30-100 kHz) instability in a weakly magnetized discharge plasma. The instability is triggered by a disc electrode which terminates the magnetized plasma column and is biased above the plasma potential. Frequency dependence on various parameters, e.g. electrode diameter, electrode bias, neutral gas pressure and plasma density is measured. Space and time dependence of the plasma potential and density in the perturbed region during one period of the electrode current oscillation are measured. During the phase of the current decrease a potential structure moves in axial direction from the edge of the perturbed region towards the electrode. During the phase of current saturation the motion of ions is mostly radial. The observed phenomenon is approximately modeled as a two dimensional potential relaxation instability (PRI).     

The Theory of Ionization Waves in the Contracted Discharge of Noble Gases

Positive column plasma in noble gases at middle pressures is analysed for stability in the frames of the linear hydrodynamic theory. At critical values of pressure and current the discharge becomes unstable to radial contraction (contraction) and to wave disturbances of the type of current pinch constrictions (contraction ionization waves). Ionization waves in the contracted discharge are three-dimensional formations with electron concentration oscillations on the axis in the opposite phase with current pinch cross section. The discharge diffuse-recombination theory was used for analysing the problem of instability arising.     

Spatial structure of the lower mode of ion-acoustic instability in the plasma of a high-current ion laser

The spatial structure of the lower mode of ion-acoustic instability in the plasma of the continuous discharge of a high-current argon ion laser is studied experimentally. The oscillations in the intensity of the spontaneous ArII line radiation from the plasma are recorded in different directions in cross sections perpen-dicular to the discharge axis. The power spectra of the integral projections of radiation are obtained and used to reconstruct the two-dimensional spatial structure of the mode, which is identified by using the available theoretical models.     

非链式化学HF（DF）激光器工作气体中电子分离的非稳定性和气体放电等离子体的自组织现象

报道了放电引发的非链式HF（DF）激光器中的激活介质由电子碰撞负离子分离引起的电离非稳定性。这种非稳性出现在电极空间分离、脉冲CO2激光加热的基于sF6的混合气体的大体积放电中。实验研究了自引发体放电过程中由激光加热引起的放电等离子体的自组织现象以及由此在放电间隙的大部分区域形成的准周期等离子体结构。重点分析了等离子体结构随气体温度和注入能量的变化,讨论了等离子体自组织对电子碰撞分离不稳定性所产生的影响,解释了混合气体中由于电子碰撞使负离子消失导致的单等离子体通道移动的产生机理。