Dusty plasma structures in magnetic fields in a dc discharge

The formation of dusty plasma structures has been experimentally investigated in a cylindrical dc discharge in axial magnetic fields up to 2500 G. The rotation of the dusty plasma structures about the discharge symmetry axis with a frequency depending on the magnetic field has been observed. When the field increases to 700 G, the displacement of dust particles from the axial region of the discharge to the periphery, along with the continuation of the rotation, has been observed. The kinetic temperatures of the dust particles, the diffusion coefficients, and the effective nonideality parameter have been determined for various magnetic fields. The explanation of the features in the behavior of the dust particles in the discharge in the magnetic field has been proposed on the basis of the analysis of ambipolar diffusion in the magnetized plasma. The maximum magnetic field at which the levitation of the dust particles in the discharge is possible has been estimated.     

Threshold for a cumulative resonant microwave streamer discharge in a high-pressure gas

Results are reported from experiments aimed at investigating how the structure of a microwave streamer discharge depends on the gas pressure. The formation of a bright core in the streamer channel is shown to be of a threshold nature: in discharges initiated in the field of a standing electromagnetic wave of an open two-mirror cavity, a bright core forms in air and hydrogen in the pressure ranges p ₀≥540±50 torr and p ₀≥740±70 torr, respectively. Estimates are presented, according to which the appearance of a bright core can be attributed to the onset of a local microwave pinch effect.     

Two-mirror resonator for studying high-pressure electrodeless microwave discharge

An electromagnetic centimeter-wave quasi-optical two-mirror open resonator is studied. The eigen-frequency spectrum of the resonator is determined and the Q factor is measured. The structure of a standing wave in the resonator is visualized by an electrodeless microwave discharge. The experimental results are compared with theoretical values.     

Thermodiffusional stratification of a continuous microwave discharge plasma

We report the results of investigations of a continuous microwave discharge ignited in a quasioptical resonant cavity. We study a new phenomenon for such a discharge: a small-scale stratification of the plasma in the direction perpendicular to the electric field vector. This stratification is observed in a plasma with electron density higher than the critical density at the microwave frequency and is due to the development of a thermocurrent instability. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 8, 537–542 (25 April 1998)     

Spatial structures of continuous microwave discharge

The paper deals with the results of investigations of spatial structures of continuous microwave discharge in a quasi-optical resonator. The results are given of experimental observations and easurements of the parameters of plasma in discharges of different forms, and the reasons are analyzed for the formation of spatial discharge structures. It is demonstrated that, as a result of the plasma-resonance amplification of the field, the discharge makes a transition to the contracted state with a size that is much less than the microwave-frequency wavelength and with an electron concentration in excess of the critical. It is found that the stratification of the contracted state across the electric field vector, which arises in some gases, is caused by the development of thermoelectric-current instability that was not previously observed in microwave discharges.     

Formation of sub-micron size carbon structures by plasma jets emitted from a pulsed capillary discharge

We have performed an experimental investigation of the potential use of intense plasma jets produced in a repetitive pulsed capillary discharge (PCD) operating in methane gas, to irradiate Si (1 0 0) substrates. The surface modifications induced by the plasma jet using two different material inserts at the capillary end, graphite and titanium, are characterized using standard surface science diagnostic tools, such as scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) analysis and Raman spectroscopy (RS). It has been found that the application of methane plasma jet results in the formation of sub-micron size carbon structures. It is observed that the resulting plasma irradiated surface morphologies are different, depending on the different material inserts used at the capillary end, at otherwise identical operational conditions. To investigate the species responsible for the observed surface changes in different material inserts to the capillary, optical-emission spectroscopy (OES) was recorded using a 300-1000 nm spectrometer. The OES results show the presence of H, CH and C₂ Swan band in the discharge plasma, which play a significant role in the formation of the carbon structures.     

Formation of a high-current discharge plasma in metal vapor

A method of converting the energy of a capacitive store into the energy of a high-current gas discharge in aluminum vapor is investigated. The spatial and temporal characteristics of the gas-discharge plasma are studied. The electron temperature, density of charged particles, and conductivity of the plasma are determined. Zh. Tekh. Fiz. 69, 134–137 (November 1999)     

Formation of an out-of-electrode plasma in a high-voltage gas discharge

The formation of an out-of-electrode plasma in a high-voltage gas discharge is studied. The occurrence and self-maintenance of a gas discharge and its associated plasma fluxes on the straight portions of electrical field lines are predicted theoretically and confirmed experimentally. It is shown that the focusing of the gas discharge and plasma fluxes is provided by increasing the length of the field line straight portions toward the symmetry axis of a hole in the anode. It is found that, when the discharge power (more specifically, an accelerating voltage applied to the electrodes of the gas-discharge tube) rises, the straight portions of the field lines elongate and concentrate near the symmetry axis of the hole in the anode. Recommendations are given on using the out-of-electrode plasma in surface micro- and nanostructuring.     

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.     

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.     

Dusty plasma structures in He-Kr DC glow discharge

Ion drift in gas mixtures has certain properties that can be used to generate ion flows with desired characteristics. For example, when the field is strong, ion heating is significant, and there is a large difference in atomic weight between ions and atoms, the ion velocity distribution can be highly anisotropic. Ion distribution anisotropy, in turn, can cause a substantial change in properties of dust structures in plasmas. Experiments on dusty plasma structures in glow discharge in mixtures of light and heavy gases (helium and krypton) are performed, and results of numerical simulations of ion and electron drift in the mixture are presented.     

Corona discharge as a temperature probe of atmospheric air microwave plasma jet

We developed and tested a new method for temperature measurements of near-LTE air plasmas at atmospheric pressure. This method is specifically suitable for plasmas at relatively low gas temperature (800–1700 K) with no appropriate radiation for direct spectroscopic temperature measurements. Corona discharge producing cold non-equilibrium plasma is employed as a source of excitation and is placed into the microwave plasma jet. The gas temperature of the microwave plasma jet is determined as the rotational temperature of N₂? produced in the corona discharge. The corona probe temperature measurement was tested by the use of a thermocouple. We found a fairly good agreement between the two methods after correcting the thermocouple measured temperatures for radiative losses. The corona probe method can be generally applied to determine the temperature of the near-LTE plasmas and contrary to the thermocouple it can be used for higher plasma temperatures and is not affected by radiative losses and problems of interaction with the microwave plasma and electromagnetic fields.     

垂直入射电磁波在大气压非平衡等离子体层中的传播特性

用数值模拟的方法对大气压非平衡等离子体薄层中，不同的电子密度分布对微波反射、吸收和透射的影响进行了研究。所采用的理论分析方法是分层模型和镶嵌不变原理。计算中考虑了微波在子层间的多次反射和吸收。数值结果表明，对于电磁波的吸收来说，等离子体中具有二次分布的电子密度，其效果要高于线性分布10%左右；而对于反射来说，线性分布效率更高。功率反射系数随波长的增大而增大，功率吸收系数A也不是单调的，当电子密度不变时，A存在一个峰值，随着电磁波波长的增加而增加，达到最大值后，缓慢降低。     

Efficiency of the microwave energy absorption in a plasma at high magnetic fields

It was shown experimentally that the efficiency of the microwave energy absorption in an inhomogeneous magnetoactive plasma strongly depends on the polarization of electromagnetic waves entering the plasma. At high magnetic fields satisfying the condition _ce />1 the RHCP wave (right-hand circularly polarized wave) is absorbed most effectively; here _ce and are the electron cyclotron frequency and the angular frequency of an electromagnetic wave respectively. The experimental results are in a good qualitative agreement with theory.On leave fromA. F. Ioffe Physico-Technical Institute, Acad. Sci. USSR, Leningrad. The authors wish to express their appreciation to Drs. V. I.Fedorov and A. D.Pilija from A. F. Ioffe Physico-Technical Institute, Leningrad, for many valuable discussions.     

垂直入射电磁波在大气压非平衡等离子体层中的传播特性

用数值模拟的方法对大气压非平衡等离子体薄层中,不同的电子密度分布对微波反射、吸收和透射的影响进行了研究。所采用的理论分析方法是分层模型和镶嵌不变原理。计算中考虑了微波在子层间的多次反射和吸收。数值结果表明,对于电磁波的吸收来说,等离子体中具有二次分布的电子密度,其效果要高于线性分布10%左右;而对于反射来说,线性分布效率更高。功率反射系数随波长的增大而增大,功率吸收系数A也不是单调的,当电子密度不变时,A存在一个峰值,随着电磁波波长的增加而增加,达到最大值后,缓慢降低。     

Theory of a normal high-pressure glow discharge

In the present work, a theoretical model considering the processes of generation and losses of charged particles in the cathode region of a glow discharge in the drift approximation for ion and electron motion is developed. Exact analytical solutions, which can be used to calculate the current-voltage characteristics of the glow discharge in an arbitrary gas with the known Townsend ionization coefficient, are derived. The calculated parameters of the normal glow discharge (the current density, discharge burning voltage, and width of the space charge region) for different gases are in good agreement with the available experimental data. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 71–77, February, 2006.     

Faraday rotation of microwave fields in an electron cyclotronresonance plasma

An electron cyclotron resonance (ECR) plasma is created with 2.45-GHz linearly polarized microwaves, which propagate in the direction of the magnetic field. Measurements of the relative power and polarization angle versus z have been made within the first few centimeters of the quartz entry window. As the microwave electric field enters the plasma, it rotates while becoming elliptically polarized then circularly polarized. The rotation angle versus z and the component of the microwave field along the major axis of the polarization ellipse versus z are explained by cold plasma dispersion theory     

Electron kinetics in a discharge plasma produced by a focused microwave beam in free space

A study is made of the electron kinetics in a discharge plasma produced by a high-power beam of electromagnetic radiation in the centimeter-wave region under conditions approaching free space, when the dimensions of the chamber are much greater than the wavelength of the microwave radiation. Two regimes of discharge production are investigated: the regime of short microsecond pulses at a repetition rate of 200 Hz, and a single millisecond pulse regime. It is shown that at threshold values of the microwave energy flux density the electron density in the initial stages of discharge formation reaches the critical value, and that the average energy of the electrons is of the order of 1.5–3 eV. Zh. Tekh. Fiz. 67, 10–14 (June 1997)     

Formation of atomically clean silicon surfaces in a low-energy low-pressure microwave plasma

The influence of the regimes and chemical composition of the low-energy highly ionized ECR plasma of a low-pressure microwave gas discharge on the etch rate and nanomorphology of differently oriented single-crystal silicon surfaces is studied. Model mechanisms of the processes controlling the etch rate and etch quality of atomically clean silicon surfaces with a desired orientation are considered.