Plasma parameters of a spherically stratified gas discharge

Basic parameters of spherically stratified gas-discharge plasma are studied. Radial distributions of the electron concentration and temperature are measured by the method of an electric probe. It is shown that the electron concentration and temperature in an unstratified discharge monotonically decrease from the anode to cathode, while, in a stratified one, they have discontinuities on the strata borders, which can be caused by the appearance of double layers in such a discharge.     

Temperature time dependence in nitrogen pulse excited microwave discharge

A detailed analysis of the population of the N₂ vibrational states for the N₂ (C ³ II _u,X ¹ _g ⁺ ) electronic states has been carried out. Quantitative spectral and microwave measurements of vibrational temperatures and electron densities were performed for 2400 MHz non-isothermic pulsed discharges in flowing nitrogen at pressures (60–2700) Pa. From the time dependent peak intensities of the second positive system of N₂, the temperature of neutral gas during the h.f. pulses has been determined.     

Plasma parameters of microarcs towards minuscule discharge gap

This paper describes the behaviour of the plasma parameters of microarcs generated between a cooled copper anode and a ceriated tungsten cathode by means of a one-dimensional unified non-equilibrium model for gap lengths between 15 and 200 μm and current densities from 2 × 10⁵ up to 10⁶ A/m². The results obtained show that the decrease of the gap length to a few tens of micrometres for a given current density results in a progressive shrinking of the quasi-neutral bulk in the microplasma and its complete disappearance. The decrease of the gap length further leads to an increase of the discharge voltage and the electron temperature and to slightly less heating of the gas.     

大气压介质阻挡放电超四边形斑图的等离子体参量

本工作利用双水电极介质阻挡放电装置,采用发射光谱方法,在大气压氩气介质阻挡放电中研究了由不同空间尺度 微放电通道构成的超四边形斑图的等离子体参量.实验发现直径较大的微放电通道(大点)和直径较小的微放电通道(小点)亮度不同.采用氮分子第二正带系谱线计算了分子振动温度,利用谱线强度比方法得到了电子激发温度,用氩原子696.54 nm谱线的Stark展宽估算了电子密度.结果显示小点的电子密度和分子振动温度均高于大点,而电子激发温度低于大点.这说明稳定超四边形斑图中不同尺度微放电的等离子体状态不同.     

Distributions of ions in a cluster plasma created by a laser pulse

Energy and charge distributions of ions are calculated for a cluster beam irradiated by a high-power ultrashort laser pulse. It is shown that the self-consistent field of a cluster ionized by the laser beam strongly affects the characteristics of the ion distributions obtained after the cluster explodes. The mean concentration of atoms bound into clusters in a beam, the cluster size distribution, and the focal-spot diameter are found to have a weak effect on both energy and charge distributions of the ions, whereas the energy spectrum of the produced ions is determined by the mean cluster size.     

The theory of microwave detection by a discharge

The presented paper tries to establish a compact theory of the hitherto only slightly explored effect of modulated electro-magnetic microwave field detection in a glow discharge. Apart from theoretical analyses aimed at maximum possible generality and applicability also for other types of discharges, the paper presents the most important results of experimental verifications. The whole theory is divided into two parts: the macroscopic part where the discharge is studied as a disrupted macroscopic system, and the microscopic one dealing with the change in the discharge structure caused by a microwave field. Apart from discovering the mechanism of the detection effect, the theory also provides possibilities of application for plasma diagnostics.The field of plasma physics is so developed now that all other considerations would depart from the aim and scope of this paper. Finally, the author thanks Dr. A. Tálský for support and interest in this work and Mr. F. Frainic for his devoted assistance in constructing the discharge tubes and the vacuum apparatus.     

Gas dynamics modeling of a plasmoid created by the Gatchina discharge

Whether plasmoids produced by the Gatchina discharge has a gas-dynamic nature is examined. The analysis is performed using two models for the formation of hot gas flows in the discharge region. The heating of the gas by a bulk heat source near the central electrode and by hot jet formed over the surface of the discharge region and having a maximum velocity in an area above the central electrode are considered. Predictions of the second model are demonstrated to be in closer agreement with experimental data.     

Pulsed microwave damage trend of bipolar transistor as a function of pulse parameters

In the present paper we conduct a theoretical study of the thermal accumulation effect of a typical bipolar transistor caused by high power pulsed microwave (HPM), and investigate the thermal accumulation effect as a function of pulse repetition frequency (PRF) and duty cycle. A study of the damage mechanism of the device is carried out from the variation analysis of the distribution of the electric field and the current density. The result shows that the accumulation temperature increases with PRF increasing and the threshold for the transistor is about 2 kHz. The response of the peak temperature induced by the injected single pulses indicates that the falling time is much longer than the rising time. Adopting the fitting method, the relationship between the peak temperature and the time during the rising edge and that between the peak temperature and the time during the falling edge are obtained. Moreover, the accumulation temperature decreases with duty cycle increasing for a certain mean power.     

The pulsed microwave damage trend of a bipolar transistor as a function of pulse parameters

In the present paper we conduct a theoretical study of the thermal accumulation effect of a typical bipolar transistor caused by high power pulsed microwaves(HPMs),and investigate the thermal accumulation effect as a function of pulse repetition frequency(PRF) and duty cycle.A study of the damage mechanism of the device is carried out from the variation analysis of the distribution of the electric field and the current density.The result shows that the accumulation temperature increases with PRF increasing and the threshold for the transistor is about 2 kHz.The response of the peak temperature induced by the injected single pulses indicates that the falling time is much longer than the rising time.Adopting the fitting method,the relationship between the peak temperature and the time during the rising edge and that between the peak temperature and the time during the falling edge are obtained.Moreover,the accumulation temperature decreases with duty cycle increasing for a certain mean power.     

Plasma parameters at nanosecond breakdown and capillary discharge in a solid insulator

The subject of investigation is the energy-mass composition of a plasma resulting from the breakdown of KCl single crystals and from discharges in capillaries produced by the breakdown of KCl and high-pressure polyethylene samples. The plasma flux formed by the head of the discharge channel in KCl is found to be much less intense than the plasma flux due to the capillary and surface discharges. Also, the first breakdown of KCl does not produced multiply charged ions of the related material. It is revealed that the energies and charge numbers for the capillary and surface discharges are close to each other.     

Photoelectron imaging on time-dependent molecular alignment created by a femtosecond laser pulse

Rotational wave packet revivals on an excited electronic state have been measured by femtosecond time-resolved photoelectron imaging for the first time. The first full revival at 82 ps of S1 (n,pi*) pyrazine was clearly observed in the time dependencies of the photoelectron intensity and the photoelectron angular distribution (PAD). The PAD, measured for laser aligned pyrazine, clearly reflects the different characters of pi* and 3s molecular orbitals.     

Distribution and evolution of electrons in a cluster plasma created by a laser pulse

We analyze the properties and the character of the evolution of an electron subsystem of a large cluster (with a number of atoms n～10⁴?10⁶) interacting with a short laser pulse of high intensity (10¹⁷?10¹⁹ W/cm²). As a result of ionization in a strong laser field, cluster atoms are converted into multicharged ions, part of the electrons being formed leaves the cluster, and the other electrons move in a self-consistent field of the charged cluster and the laser wave. It is shown that electron-electron collisions are inessential both during the cluster irradiation by the laser pulse and in the course of cluster expansion; the electron distribution in the cluster therefore does not transform into the Maxwell distribution even during cluster expansion. During cluster expansion, the Coulomb field of a cluster charge acts on cluster ions more strongly than the pressure resulting from electron-ion collisions. In addition, bound electrons remain inside the cluster in the course of its expansion, and cluster expansion therefore does not lead to additional cluster ionization.     

Ignition of a nonresonant microwave discharge

The ignition of a 2.45 GHz microwave plasma source by a temporary local magnetic field quenching to ECR value has been studied. The source operates at high magnetic fields (ω_ce > ω) and at overcritical electron densities (ω_pe > ω). This ignition method appears to be attractive also for microwave plasma sources in toroidal devices.     

Initiation of self-propagating high-temperature synthesis by a pulsed microwave discharge

It is shown that a metal plasma with a temperature of 10 kK arises on the surface of a metal-insulator powder subjected to a 0.3-to 1.0-ms-long microwave pulse. The pulse triggers an exothermal chemical reaction in the Ti-B or Al-Fe₂O₃ powder mixture, the delay between the end of the pulse and inflammation of the mixture reaching 10–20 ms. The microwave irradiation results in a high local energy deposition causing evaporation and rapid mixing of the reactants. This distinguishes the early stage of the reaction triggered by microwave radiation from the reaction in the case of conventional thermal initiation.     

Plasma torches and electrophysical parameters of the diaphragm discharge in water

This work is aimed at studying plasma torch formation, voltages, currents, power distribution, and resistance variation in the case of the little understood low-energy (≤10 J) diaphragm discharge initiated in water and salt solutions. Plasma torches associated with this type of discharge differ considerably from those of other discharges. Different shapes of anode and cathode torches, breakdowns between the diaphragm and one of the electrodes, and a specific form of cathode breakdown are observed. It is found that the electrical conductivity of the medium influences the parameters of the plasma formations, current pulses, dielectric strength of the medium, current pulse variation at “semibreakdowns,” etc. Based on the experimental data, it is concluded that the process of discharge initiation differs from that described in the literature.     

Numerical modeling of a XeCl laser excited by microwave discharge

12 , 169 (1987). Reasonably good agreements in the peak output power and laser efficiency have been achieved. Model calculations also predict that an efficiency as high as 2.7% can be obtained once the conditions of the above-mentioned experiments have been optimized. From the consideration that the skin depth effectively limits the absorption length of the microwave pumping and hence the excitable volume, it is concluded that high input power densities (>2 MW/cm³) and higher gas pressures (between 3 and 10 atm) are the preferable conditions to achieve higher efficiency. Preliminary calculations on CCl₄ containing XeCl gas mixtures show that improvement in laser efficiency by several folds may be achieved as a result of the higher intrinsic efficiency of excimer formation. Received: 23 September 1996 / Revised version: 25 March 1997     

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.     

Excitation of a cavity by a microwave pulse transmitted through a nonreflective cavity compressor

Excitation of a cavity by a phase-modulated pulse transmitted through a chain of nonreflective cavities is considered. It is shown that for a linear frequency-modulated rectangular pulse, the use of a two-cavity compressor increases the energy stored in the cavity fourfold for the same efficiency of its excitation.