氮气中空心阴极放电条纹的发光特性

利用发射光谱法,在氮气环境下研究了圆柱型空心阴极放电条纹的特性。测量得到了气压为20 Pa,放电电流为1.3 mA时条纹区的发射光谱,结果表明发射光谱主要为氮分子的第一正带系(B3П_g →A3П_u)和 第二正带系(C3П_u→B3П_g )。利用双原子光谱发射理论,计算得到了氮分子振动温度的空间分布特性。结果表明光谱线强度呈周期性分布,明纹中心处的谱线强度高于暗纹中心处的谱线强度。明纹中心处的N₂分子振动温度为3 500～4 400 K,并且从阴极到阳极,明纹中心处光谱线强度和分子振动温度逐渐下降。同时测量得到了放电电流为1.0和1.5 mA时的发光条纹特性,研究了放电电流对条纹特性的影响。随着放电电流的增加,明纹中心处的分子振动温度升高,条纹间距增加。另外,利用测量得到的发光条纹,计算得到了条纹区的平均约化电场强度为44～49 m-1·Pa-1,并且由阴极向阳极逐渐降低。对于揭示气体放电中发光条纹的形成机理和促进空心阴极放电的稳定性有重要的参考价值。     

Behavior of the spatial phase of modulated ionization waves in a glow discharge

Work is described in which it was shown experimentally that a modulated glow discharge with striations acquires an additional characteristic which can be called spatial phase of the oscillations. In fact, this characteristic reflects the spatial distribution of the maxima of the time-averaged integrated plasma luminescence on the tube axis which arises due to the influence of the current modulation on traveling striations. It was discovered that for fixed discharge conditions such a distribution remains constant when the discharge is switched off and on, i.e., it is not random. An experimental investigation was made of the influence of a magnetic field on the spatial phase of the modulated ionization waves. It was found that in a low-pressure glow discharge with small currents the striations are initiated in the cathode region. The anode region does not directly initiate the striations but it influences their spatial phase characteristics through a feedback mechanism. State University, St. Petersburg. Ukhtinskii Industrial Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 108–113, January, 1997.     

Stationary Striations due to Interaction of Two Ionization Waves in Xenon Glow Discharge

Experimental observations on stationary striations in the positive column of xenon discharge are reported. Stationary striations are observed when two ionization waves exist simultaneously in the positive column at low pressure and high current region. These stationary striations are caused by nonlinear interference of two backward ionization waves of which frequencies are either equal or are in the ratio 1:2. The spatial intervals for the striated pattern are equal to the reciprocal of the difference between the wave-numbers of two ionization waves.     

Mechanism of Striation in Dielectric Barrier Discharge

The mechanism of striations in dielectric barrier discharge in pure neon is studied by a two-dimensional particle- in-cell/Monte Carlo collision （PIC-MCC） model. It is shown that the striations appear in the plasma background, and non-uniform electrical field resulting from ionization and the negative wall charge appear on the dielectric layer above the anode. The sustainment of striations is a non-local kinetic effect of electrons in a stratified field controlled by non-elastic impact with neutral gases. The striations in the transient dielectric barrier discharge are similar to those in dc positive column discharge.     

Origin of laser-output noise of cataphoretic HeSe+ lasers

We investigated noise and fluctuations of the output power of cataphoretic HeSe⁺ lasers in positive column plasma. Direct coupling of laser output power noise and fluctuations of the local population inversion was found. An investigation of the positive column plasma showed moving striations being responsible for the gain fluctuations. Whereas the local plasma properties are dominated by high frequency striations in the 100 kHz range, integrated quantities such as laser gain per pass are most strongly influenced by low-frequency waves with a continuous noise spectrum below 200 kHz. External modulation of the discharge voltage or current at a frequency near thehf striations reduces laser noise and increases laser output power.     

The successive production of striations in a glow discharge in hydrogen

The manner of successive production of striations moving from the cathode to the anode in a glow discharge in hydrogen is experimentally investigated. For this purpose use is made of the method of an artifically produced transient process in the positive column. It is shown that the fundamental phenomenon in the production of these striations, similarly as with an inert gas, is the wave of stratification. The wave of stratification in hydrogen, however, differs from that in the plasma of an inert gas in the direction of motion of the striations. This direction in a hydrogen discharge is the same as the direction of the successive production of striations, i. e. from cathode to anode. The phenomenological theory of the successive production of moving striations elaborated earlier is also applicable for the wave of stratification in hydrogen.     

空心阴极放电条纹特性的光谱诊断

利用发射光谱法,研究了圆柱型空心阴极放电条纹的特性.测量了条纹区的发射光谱,在此基础E计算得到r电子激发温度、相对电子密度和电子平均能量的空间分布特性.结果表明条纹区的光强、电子激发温度和电子密度均呈非等幅的周期性变化.与暗纹中心处相比,明纹中心具有较高的电子激发温度和较低的电子密度.由阴极向阳极,明纹中心处的电子激发温度幅值逐渐减小.此外,条纹区的电子激发温度随着电流的增加而增加.     

Investigations about the Influence of the External Circuit Elements on the Propagation of Ionization Waves in the Positive Column of a Neon Glow Discharge

Our investigations have been motivated by former works of Michel and Achterberg [1]. They described the important influence of the external circuit elements and connected therewith the mechanism of feedback (Barkhausen k · v ≧ 1). The properties of external and self-excited moving striations (threshold current, fundamental frequency) are strongly influenced by the feedback. This paper demonstrates the differences occuring either a voltage or a current source in the external circuit is used in order to perturb the discharge and to realize different degrees of feedback by changing the external resistor R_ext. of the discharge. It is shown the impact on the fields of existence of self excited striations in a non driven discharge. Furthermore our investigations yield differences in the width of Arnol'd tongues [2] of periods one and two in the perturbed discharge depending on a varied degree of feedback. Last not least its influence on the behaviour of quasiperiodic and chaotic states is demonstrated. The investigations permit first information concerning the sensivitity of one parameter variation (feedback controll by external resistor) which might be used e.g. for a stabilization of unstable periodic orbits (controlling chaos).     

The positive column in a high-molecular atmosphere

The positive column of a low-pressure discharge is investigated in organic substances that form macromolecules. The method by which such macromolecules are formed is studied and the method for verifying them in a discharge space is described. It is proved that in the discharge space these macromolecules form negative ions. The irreversibility of the volt-ampere characteristic was found for a low-pressure discharge in organic gases and vapours. Standing striations were found in the positive column of such a discharge, some being conical and others, as a consequence of radial space charges, special plate-like striations.     

Moving striations in tapered discharge tube

Moving striations in the tapered tube with smoothly changing radius are studied experimentally. The frequency depends on local tube radius by nature and increases toward the narrow end of the tube, independent of direction and magnitude of the discharge current. Radius-frequency versus radius-pressure is compatible with the similarity law for striations in cylindrical tubes. When there appears synchronization, the frequency becomes apparently constant throughout the tube column. The wavelength shows different dependences on radius without and with the synchronization. An important role is played by the feedback through an electric circuit. Also, direction and magnitude of the current have influence on the phenomena. Steady states in the tubes are compared with those in cylindrical tubes. An attempt is made to explain the observed synchronizations and then the remarkable discrepancies between the previous experiments can be eliminated.     

Stability of spherical striations

It is found experimentally that spherical striations in volume low-pressure glow discharges are stable. Measurements are carried out for a cylindrical-anode discharge. The floating potential distribution indicates that the striations represent double electrical layers.     

Structural properties of complex plasmas in a homogeneous dc discharge

We report on the first three-dimensional (3D) complex plasma structure analysis for an experiment that was performed in an elongated discharge tube in the absence of striations. The low frequency discharge was established with 1 kHz alternating dc current through a cylindrical glass tube filled with neon at 30 Pa. The injected particle cloud consisted of monodisperse microparticles. A scanning laser sheet and a camera were used to determine the particle position in 3D. The observed cylindrical-shaped particle cloud showed an ordered structure with a distinct outer particle shell. The observations are in agreement with performed molecular dynamics simulations.     

Unstable regime of the excitation of kinetic striations in a gas-discharge plasma

Chaotic striations in a low-pressure discharge in the regime corresponding to an unstable periodic orbit singled out of a chaotic attractor are stabilized. A specific feature of the wave process in question is the change in the type of some striations in the course of their motion in the positive column.     

The influence of acoustic waves on the positive column of a glow discharge with standing striations

The influence was investigated of low-frequency standing acoustic waves on the positive column of a glow discharge in air and nitrogen in a regime in which spontaneous formation of standing striations readily occurs. Experimental information is presented proving that an acoustic wave of sufficient energy propagating along the discharge axis has a great influence on physical processes creating standing striations in a molecular gas.In conclusion the author would like to thank Prof. J. Kracík for his support and his interest in this work and Mr. P. Slovák for his assistance with the experimental work.     

Forced modulation of self excited striations in a discharge tube of varying diameter

Observations on striations contained in a discharge tube of varying diameter are reported and explained in terms of forced modulation.     

高气压均匀直流辉光放电等离子体的光学特性

在高气压(大于100 Torr, 1 Torr=1.33322×10² Pa)平板位形的均匀直流辉光放电中, 一定条件下观察到平行排列的明暗相间的等离子体辉纹. 结合等离子体的光发射谱诊断, 研究了气体组分对等离子体光学特性的影响. 研究发现, 随着甲烷浓度的增加, 辉纹间距减小, 相应的电子激发温度降低. 当甲烷浓度增加时, 等离子体中低电离能的粒种增加, 粒子平均电离能减小, 这种情况下, 电子被电场加速较短的距离所获得的能量就可以激发粒子, 产生可见的光发射, 表现为辉纹间距缩短. 随着氩气的引入, 能够观察到明显的辉纹, 且增大氩气含量, 辉纹间距增加, 这与氩的较高电离能有关, 而相应的电子激发温度增加. 研究结果表明, 随着工作气体的改变, 等离子体辉纹间距呈现出一种对电子温度的响应.     

Field reversal in an electronegative plasma containing moving striations

Evidence is presented to show that under some conditions the radial ambipolar field, in a diffuse positive column containing moving striations, reverses near the discharge tube axis.     

Factors affecting the self-excitation of low-frequency oscillations in an electric discharge

The influence of the individual factors affecting the production of low-frequency oscillations connected with moving striations in a discharge is analysed and experimentally verified. From the conception of two mechanisms of feedback, which leads to self-excitation of these oscillations, it follows that the following influence the production of oscillations: 1) the tendency of the plasma to stratification, 2) the length of the positive column, 3) processes in regions at the electrodes, 4) the external electric circuit.The measurements confirm the influence of all these factors. It is shown that the main factor conditioning the production of oscillations is the property of the plasma of the positive column — its tendency to stratification. The plasma of a glow discharge in neon — in the region of low pressures and currents investigated — has a very strong tendency to stratification with the exception of a small interval in the neighbourhood of the pressure of 4 mm Hg and current 3 . Low-frequency oscillations and moving striations are therefore very often present in a discharge in neon.The influence of the external circuit on the oscillations investigated was also experimentally proved, but it is very weak.     

Striations als Eigenlösungen der Elektronenbewegung im elektrischen Feld

A simple model for the motion of electrons in an inhomogeneous electric field is derived. With this model the striations in a weakly ionized low pressure discharge can be explained as a phenomenon of the energy relaxation. In a periodical electric field resonances occur, for which the voltage across one striation equals the average energy gain of an electron between two inelastic collisions, divided by an integer. These resonances are recognized as eigensolutions in the homogeneous field. The influence of the elastic and ineiastic collisions on the damping of the striations is discussed. In a first approximation the energy loss at the elastic collisions can be taken into account by a frictional contribution to the voltage across one striation. This voltage and the energy distribution function in moving striations are calculated and compared with measurements of other authors.     

A study of the propagation of moving striations in inert gases by means of artificial feedback

A study is made of the propagation of moving striations in inert gases. The method elaborated in [6] combined with the optical method of photo-multipliers was used. The results of the measurements show that despite the fact that the striations themselves move from anode to cathode, their propagation takes place in the opposite direction. Measurements with artificial feedback further confirmed the conclusions reached in [1] and [2] on the mechanism of self-excitation of the striations by means of feedback over the external discharge circuit.In conclusion the authors thank Prof. V. Kunzl and M. Novák for valuable remarks and K. Jakoubková for help in the experiments.