Effect of the gas dynamic structure of a flow on the parameters of a self-sustained discharge. II

The limiting current of a self-sustained glow discharge is calculated. Two-dimensional equations for the flow of a viscous, vibrationally nonequilibrium gas and a model of the cathode sheath are used. The validity of the approximations which form the basis of the cathode sheath model was tested with experimental data for anomalous and normal currents. The effects of laminar and turbulent gas flow and of the geometric dimensions of the channel on the limiting discharge current are examined. Zh. Tekh. Fiz. 69, 49–55 (November 1999)     

Effect of the gas dynamic structure of a flow on the parameters of a self-sustained discharge. I

A study is made of self-sustained glow discharges in transverse gas flows and jets. The distributions of the discharge current and voltage over the elements of a sectioned cathode array are measured along with the temperature of the cathode array. The limiting current and discharge voltage corresponding to the transition from a uniformly burning discharge to a contracted state are measured. Two-dimensional and one-dimensional systems of equations for the gas dynamics and vibrational kinetics are used for a numerical analysis of the experimental data, and the results are used to determine the character of the distribution of E/N in the discharge, where E is the electric field and N is the molecular density. The heat balance of the cathode array is calculated. A model is proposed for self-consistently calculating the parameters of the gas flow, the distribution of the current over the cathode array, and the discharge voltage, as well as the values of the ballast resistances. Zh. Tekh. Fiz. 69, 42–48 (November 1999)     

Self-sustaining discharges in needle-to-plane geometry with hundreds of microns electrode gaps

Atmospheric pressure needle-to-plane discharges have been explored experimentally in electrode gaps from 100 μm to 400 μm. These discharges can be self-sustained and follow the form of existing empirical formulae describing the current-voltage characteristics of corona discharge. The discharge can also be self-sustained by its lower sustaining voltage applied between the two electrodes once it is ignited by the initial high output voltage from power supply. The experiments of charging aerosol particles by the self-sustaining discharge operating with a lowered power have shown that for particles with a diameter of 46 nm, the charging efficiency attained 43.6%.     

Microwave streamer discharge in a supersonic air flow

Data are presented from experiments on the ignition of a pulsed, triggered microwave streamer discharge at the focus of a cm-band TEM wave in an immersed supersonic air jet. It is shown experimentally that for velocities of the air in the jet up to 500 m/s, the structure of the discharge remains qualitatively unchanged and retains its streamer character. The finite size of the transverse cross section of the jet determines some features of the discharge. Zh. Tekh. Fiz. 69, 14–18 (November 1999)     

Investigation of the ozone formation process in a nanosecond microwave discharge in air and oxygen

Results are presented from an investigation of the dynamics of ozone formation in a freely localized discharge generated by a periodic train of 3-cm nanostructured microwave pulses in oxygen and air at a pressure p=3–30 Torr. Conditions for the efficient generation of ozone in air with the minimum production of nitrogen oxides are demonstrated experimentally. It is shown that when the microwave pulse repetition frequency is high, heating of the gas and the buildup of nitrogen oxides in the discharge in air reduce the ozone formation efficiency while under prolonged exposure the ozone formed initially is destroyed. The energy cost of forming ozone in oxygen and air is determined as a function of the microwave pulse length and repetition frequency and the gas pressure. The lowest energy cost of forming a single ozone molecule in these experiments is 16 eV per molecule for a discharge in air and 4 eV per molecule in oxygen. It was observed that circulating the gas through the discharge zone enhances th ozone formation efficiency. It is shown that there are optimal conditions for ozone formation as a function of the reduced electric field in the plasma. Zh. Tekh. Fiz. 67, 9–18 (March 1997)     

On the mechanism of the runaway of electrons in a gas: The upper branch of the self-sustained discharge ignition curve

Based on the results of simulation by the method of particles, it is shown that the Townsend mechanism of electron multiplication in a gas at a sufficiently large electrode spacing is valid at least up to such large values of E/p at which relativistic electrons are generated. On the other hand, the phenomenon of electron runaway in a gas is determined by the electrode spacing, which must be either comparable with or smaller than the characteristic electron multiplication length, rather than the local criteria accepted presently. It is shown that, for a particular gas, the critical voltage across the electrodes at which the runaway electrons comprise a significant fraction is a universal function of the product of the electrode spacing by the gas pressure. This function also determines the condition of self-sustained discharge ignition. It not only incorporates the known Paschen curve but also additionally contains the upper branch, which describes the absence of a self-sustained discharge at a high voltage sufficiently rapidly supplied across the electrodes.     

Characteristics of an x-ray preionized TEA CO laser

A cryogenically cooled sealed-off x-ray preionized self-sustained discharge CO laser was succesfully operated. It was found that 20 to 40% higher output energies could be obtained using x-ray instead of uv preionization. A maximum output energy of 2.9 J per pulse could be extracted from a 2×2×40cm³ discharge volume. The maximum electrical efficiency proved to be 12.6%.     

XeO luminescence in a self-sustained slab radio-frequency discharge

We report the observation of bright luminescence and registration of luminescence spectrum of a XeO molecule in the green spectral region upon excitation of a Xe:O₂ gas mixture in a self-sustained slab radio-frequency discharge.     

Efficient self-sustained pulsed CO laser

In this paper a simple sealed-off TEA CO laser is described with a self-sustained discharge without an external UV preionization source. At 77 K this system yields more than 600 mJ from a lasing volume of about 60 cm³ CO-N₂-He mixture (45 J/? atm. with 15.6% efficiency).     

Wide-aperture superatmospheric-pressure CO<Subscript>2</Subscript> laser amplifier pumped by a self-sustained volume discharge

Initiation of a self-sustained volume discharge in CO₂-containing gaseous mixtures kept under a pressure of up to 10 atm with the aim of amplifying picosecond IR pulses is considered. Experimental electricdischarge and optical characteristics of a wide-aperture high-pressure CO₂ amplifier are presented. The feasibility of designing terawatt laser equipment with a master oscillator and preamplifier is discussed.     

外粒子源注入下气体放电过程的模拟研究

利用Geant4程序建立外源注入式、低气压气体开关物理模型,通过模拟计算电子增益与极板间电场强度、电子增益与极板间隙距离的函数关系验证了模型的正确性。计算了气体种类、气体压强对电子增益的影响,分析得到形成自持放电所需最小入射电子数,计算结果表明:在相同的气压及电场条件下,氮气的电子增益远大于氦气,这与氦气的高电离能性质相吻合; 随气压增大,电子增益呈非线性增长; 为实现自持放电,外源注入电子数面密度为1×105~2×105 /cm2。     

Development of a self-sustained gas volume discharge

The development of a self-sustained volume gas discharge is studied numerically. Special attention is paid to the formation and stability of the cathode sheath. It is shown that the high-voltage threshold for the ignition of a volume discharge is determined by the onset of cathode sheath instability. The methods for suppressing cathode sheath instability are discussed.     

The role of halogen donors in discharge instability of rare-gas halide excimer lasers

Experimental results on striation instability in a self-sustained discharge-pumped XeCl laser are presented. The presence of HCl proves to be critical to the evolution of this particular mode of instability. The role of halogen donors in discharge instabilities of RGH lasers is discussed. That mixtures containing HCl will be susceptible to striation instability and those with F₂ or NF₃ will not is concluded.This work is based on experiments done when the author was at UCSD     

On the mechanism of the runaway of electrons in a gas: The upper branch of the paschen curve

Basing on the simulation results, it is shown that the Townsend mechanism of electron multiplication in a gas at sufficiently large interelectrode distances is valid at least up to such large values of E/p at which relativistic electrons are generated. Correspondingly, the runaway electron producing in a gas is determined not by the local criteria accepted presently, but by the ratio of interelectrode distance and the characteristic electron multiplication length. It is shown that the critical discharge voltage U, at which the runaway electrons appear in a given gas, is a function of the product of the interelectrode distance by the gas pressure. This function (U-pd dependence) defines not only well-known Paschen curve but also an additional branch, which describes the absence of a self-sustained discharge at a high voltages sufficiently rapidly supplied across the electrodes. Critical discharge voltage dependence for helium and xenon are presented.     

Plasma parameters of a nonself-sustained microwave discharge created by a programmed pulse

The kinetics of the electrons in the plasma of a nonself-sustained discharge formed at the focus of a microwave beam when the gas is exposed to electromagnetic radiation with an energy flux density that varies with time in a programmed-pulse mode are investigated. It is shown that the temperature of the electrons in the plasma of the localized microwave discharge is of the order of 1 eV and varies weakly during the pump pulse and as the air pressure is varied, while the electron density is an order of magnitude or more lower than the critical density and depends on the level of the pump generator power. It is shown that the degree of ionization of the plasma can be regulated by altering the programmed-pulse mode. Zh. Tekh. Fiz. 67, 19–23 (July 1997)     

Expansion of spark channels in air and possibilities of plasma crowbar in high pulsed current and magnetic field technique

The radial expansion velocities and diameters of spark channels in air are measured by the plasma-metal contact method. An LC discharge circuit with energy up to 50 kJ and with current frequencies ranging from ∼10² to ∼10⁴ Hz served as the source of the channels. It is concluded on the basis of the results obtained that the previously proposed automatic plasma crowbar based on the expansion of spark channels in gases is a universal switch for an inductive load in LC discharge circuits that could find very wide applications in high pulsed current and magnetic field technology. Zh. Tekh. Fiz. 68, 133–136 (February 1998)     

Self-sustained oscillations in a low-current discharge with a semiconductor serving as a cathode and ballast resistor: II. Theory

Current self-sustained oscillations in a Townsend discharge are studied analytically. The proposed method for solving simple equations is applicable even when the Townsend coefficient of electron reproduction g (the main factor governing the oscillations) cannot be determined theoretically. The coefficient g is related to the discharge current-voltage characteristic, which can be obtained experimentally or from numerical simulations. Self-oscillating solutions (limit cycles) are found under various conditions. The mechanisms governing the excitation and stabilization of the solutions obtained are interpreted. It is shown that the waveform of the undamped oscillations may change significantly (the current peaks are smoothed, and the oscillation period decreases) when a weak constant cathode current, which is presumably related to the emission caused by slowly diffusing metastable molecules, is included in the equations.     

A 5 cm single-discharge CO2 laser having high power output

A single-discharge self-sustained CO₂ laser has been constructed with a gap distance of 5 cm. The system has a very simple construction; it produces a very uniform discharge with an output power of 50 Joules per liter for a CO₂ : N₂ : He = 1 : 1 : 3 mixture. The efficiency can be as high as 19%.     

Experimental investigation of the influence of a posterior gap on glottal flow and sound

The influence of a posterior gap on the airflow through the human glottis was investigated using a driven synthetic model. Instantaneous orifice discharge coefficient of a glottal shaped orifice was obtained from the time-varying orifice area and the velocity distribution of the pulsated jet measured on the axial plane using a single hot-wire probe. Instantaneous orifice discharge coefficient values were found to undergo a cyclic hysteresis loop when plotted versus Reynolds number and time, indicating a pressure head increase and a net energy transfer from the air flow to the orifice wall. The net energy transferred was estimated to be around 10% of the value presumably required to achieve self-sustained oscillation. The radiated sound pressure was measured to characterize the influence of the minimum flow through the posterior gap on the broadband component of the radiated sound. The presence of a posterior gap was found to significantly increase the broadband sound level produced over the frequency range in which human hearing is most sensitive.     

Generation of VUV radiation in Lyman and Werner bands of pulsed space discharge in hydrogen mixtures with helium

A self-consistent numerical model for the self-sustained high-current pulsed discharge is constructed based on the solution of the equations of the population of H₂ electronic and vibrational states. The model accounts for electronic, ion-molecular, and vibrational kinetics, electron attachment to and detachment from the H₂ molecule, Lyman and Werner band emission, and their radiation trapping. The equations of electron-vibrational kinetics are solved simultaneously with the Boltzmann equation for the electron energy distribution function and the external electrical circuit equations.