Pulsed Gas Discharge Research Articles

On the similarity law in picosecond gas discharges

It has been shown that the product of the gas pressure p and the discharge formation time τ is unambiguously related to the reduced electric-field strength E/p for air and argon in the picosecond range of τ. This dependence was previously found for the nanosecond range. The available experimental data are satisfactorily explained in the framework of the theory of the multielectron initiation of pulsed gas discharges that was proposed in my previous works.

Initiation of Ignition by the Action of a High-Current Pulsed Discharge on a Gas

The possibility of nonthermal initiation of chemical reactions by a uniform pulsed nanosecond discharge is demonstrated. Dependences of variation of the ignition delay on initial conditions are obtained. It is shown that the main role in combustion initiation under conditions of a pulsed gas discharge in the case of moderate electric fields and low degree of ionization belongs to reactions of dissociation quenching of electron‐excited levels of nitrogen.

Decolorization of Rhodamine B in Water by Pulsed High-Voltage Gas Discharge

The red coloring in water colored by an organic dye, rhodamine B, was removed in as fast as 10 s by pulsed gas discharge. Water was atomized by air and flowed as a mist down the central part of a reactor and as a water film down the inner wall. Radicals, such as ozone, OH and O, which were produced by radial barrier discharge, decolorized rhodamine B. Color was completely removed at a low water flow rate and high total input energy, but the removal efficiency was highest at a high water flow rate and low total input energy. By using oxygen, the color removal and removal efficiency were improved due to higher ozone concentration produced than in the case of using air. The efficiency was improved in proportion to the initial concentration of rhodamine B. The highest removal efficiency of 8.2 µg/J was obtained at 22 mg/L and a water flow rate of 150 mL/min. The results of the discharge performed in Ar suggest that the radicals produced from water considerably contributed to the decolorization. By changing the reactor radius, we clarified that the water flowing down the reactor wall as a water film was decolorized as well as the atomized water in the reactor.

Diffusion model of the transport of sputtered metal atoms in a cylindrical vessel

Measurement of the diffusion loss rate of metal atoms sputtered by a pulsed gas discharge in a vessel represents a convenient method for determination of the diffusion coefficient of metal atoms in gases (J. Phys. D 30 (1997) 1878). This measurement should be combined with an appropriate diffusion model, which takes into account the experimental geometry and the interactions of the diffusing particles with the walls of the container. The effect of the latter is usually accounted for through the boundary condition used. In this work we consider a boundary condition based on a thermodynamic approach. The obtained diffusion model for cylindrical geometry is compared with experimental results for the diffusion of ground-state Mg atoms in Kr, as well as with some other model solutions.

Pulsed lasing in dysprosium vapors

For the first time lasing is obtained on dysprosium atomic transitions at 849.015 and 917.2 ± 0.1 nm under the pulsed gas-discharge excitation of dysprosium-helium vapors.

Ion beam formation in the field of double layer stabilized by spatial reversal of magnetic field

Abstract The ion beam generation and dynamics of processes in a pulsed straight high-current gas discharge at Iow pressures have been studied. The spatial reversal of a longitudinal con-fining magnetic field is used to stabilize a potential jump. The potential difference of 3–10 kV is applied to the discharge gap filled with a preliminary created plasma. Initially, the precathode potential jump is formed and, thereafter, the auasi-steady double layer arises in the region of magnetic field reversal. Potential difference is concentrated in the double layer, where formation of ion and electron beams occur. A current value of the ion beam formed in the double layer is determined by Bohm's current of the plasma in the anode part of discharge gap (J < 0.6 A/cm2). The ion beam energy is determined by a value of the potential jump (3–10kV) in the double layer. When the plasma with the density higher than the critical one is formed in the system, the magnetic field reversal is self-consistently suppressed; the dou...

Self-consistent model of a pulsed air discharge excited by surface waves

A complete self-consistent electrodynamic model of a pulsed gas discharge excited by surface waves is developed. The model allows one to calculate both the initial phase of the discharge front propagation and the parameters of the produced plasma. The spatiotemporal evolution of the electromagnetic field and plasma parameters at the discharge front is investigated for the first time. It is shown that discharge propagation is mainly governed by a breakdown wave in an inhomogeneous electric field at the leading edge of the ionization front. It is found that the effect of the electric field enhancement in the plasma resonance region significantly affects the velocity of the breakdown wave. The results of calculations agree well with experimental data.

Discharge formation processes and glow-to-arc transition in pseudospark switch

Deals with an interpretation of the current sustaining mechanisms at different stages of the high-current low pressure pulsed gas discharge with hollow cathode (pseudospark discharge). The analysis of experimental data for the stage of delay time to breakdown and the subsequent stages is presented. The principal features of glow stages are interpreted in the framework of the concept of nonmonotonic potential distribution in the near cathode regions. It is shown that in spite of extremely high current density the main fraction of the discharge current at the cathode surface is carried by the ion component. In the superdense glow stage the ion current is provided due to numerous microexplosions of the cathode surface, ionization of the metal vapor inside the cathode voltage drop region, and returning the metal vapor back to the cathode in a form of ions. The glow mode in this case is determined by a uniform distribution of the explosion centers over the cathode.

Excimer KrF laser with He buffer gas, 0.8 J energy, and 2% efficiency

An experimental investigation was made of the energy and temporal characteristics of the pump process and of the output radiation of a pulsed gas-discharge excimer KrF laser (λ =248 nm) with He as the buffer gas. An RU-65 spark gap was used as the design base. The parameters of a high-voltage excitation circuit of the LC inverter type with automatic UV preionisation were optimised. A laser efficiency (based on the stored energy) of 2.4% and an output radiation energy of 0.57 J were reached for the first time for a gaseous medium of the He:Kr:F2= 89.8:10:0.2 composition at a total pressure of 2.5 bar. The maximum output energy of the KrF laser was 0.82 J in the form of pulses of 24 ns duration at half-amplitude; the specific output energy was then 5.9 J litre-1 and the efficiency was 2.0%.

Modulation Methods of Studying Processes in Pulsed Gas-Discharge Lasers

A method for detecting step-like excitation and ionization of particles in a plasma is suggested and adapted to pulse-periodic discharges in metal vapors. The method of the resonance optical drive as applied to transient processes in a plasma is developed and is shown to yield relative values of excitation constants, criteria for applicability of various kinetic models for pulsed lasers, and so on.

The use of a high-voltage discharge at low pressure for 3D ion implantation

A high-voltage pulse gas discharge burning on the left branch of the Paschen curve is used as a basis for three-dimensional ion implantation (3DII). The 3DII technique uses a scheme whereby the target is the cathode and the anode is a vacuum chamber filled with working gas in the pressure range 0.15–2.0 Pa. The external characteristics of the gas discharge are described. Results of a probe investigation of the main discharge parameters are presented. It is found that gas discharge has a quasi-stationary spatial structure with a thin layer (less than 1 cm) of cathode fall where all voltage applied to the electrodes drops. Ions effectively accelerate in cathode fall in a collisioniess mode. A high-energy ion current density on the cathode surface is measured. Possible mechanisms of generation of ion flux on the cathode are discussed. It is shown that the near-anode plasma is not a general supplier of ions on the cathode. The main parameters measured and the discharge features make it possible to use the 3DII technique for technological applications.

Reply To "Comments On "The Time Evolution Of The Resistances And Inductances Of The Discharges In A Pulsed Gas Laser Through Its Current Waveforms'"

The physics of a pulsed gas discharge introduces adequate restrictions into the mathematical problem for the definition of the time evolution of the resistance and inductance. These restrictions permit the determination of the above-mentioned parameters uniquely. In a previous paper, 1 we had published a method for finding the time evolution of the resistance and inductance of a pulsed discharge. According to this method, the elaboration of the current waveforms through the integrodifferential equations of the system leads to the revelation of the time history of the resistance and inductance. However, two objections in our method have arisen in a paper by Friedman. According to the first objection, the definition of the time evolution of the resistance and inductance through the oscillograms of the current and voltage is not one-valued, but it has a set of solutions. As a verification, the author of the above Comments gave an example (an - - circuit) of various temporal dependencies of inductance and resistance corresponding to the identical current and voltage oscillograms. The set of solutions and consisted of the fundamental solutions plus oscillatory terms with frequencies multiples of the fundamental frequency of the system. Two restrictions were established by the author of the above Comments for the choice of the functions and : the physical restriction, that is, and , should be positive, and the mathematical restriction, that is, when , the inductance is

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/spl middot/10/sup 3/ 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.

High current plasma electron emitter

A high current plasma electron emitter based on a miniature plasma source has been developed. The emitting plasma is created by a pulsed high current gas discharge. The electron emission current is 1 kA at 300 V with a pulse duration of 10 ms. The prototype injector described in this paper will be used for a 20 kA electrostatic current injection experiment in the Madison symmetric torus reversed-field pinch. The source will be replicated in order to attain this total current requirement. The source has a simple design and has proven to be very reliable in operation. A high emission current, small size (3.7 cm in diameter) and low impurity generation make the source suitable for a variety of fusion and technological applications.

Measurement of Excited States Density and the VUV‐Radiation in the Pulsed Xenon Medium Pressure Discharge

AbstractTime resolved absolute density measurements of the 1s5 (metastable) and 1s4 (resonance) level in the positive column of a pulsed xenon gas discharge for gas pressures between 1 and 40 Torr and currents between 100 and 300 mA are presented. The densities ranged from 1 × 1011 to 5 × 1012 cm−3 and were found to be ten times larger in the afterglow than in the active part of the discharge. The enhanced radiation obtained in the afterglow in the near infrared regions as well as in the VUV region is caused by a dissociative recombination and formation of excimer states.

Time History of the Resistance and Inductance in a Pulsed Electric Discharge

The time behavior of the electric characteristic resistance and inductance in a pulsed gas discharge is revealed through a procedure which exploits only the voltage waveform. This can be achieved combining step by step the waveform with the differential equation governing the performance of the system. This method is described analytically in the text. Its application showed that the resistance drops sheerly in the first few ns from a very high value while the inductance presents a peak in the “formation phase” of the discharge (first 40 ns). These are due to the reaction of the system to the oncoming sudden variation.

Pseudospark switches-technological aspects and application

We report results of the development of fast closing switches, so-called pseudospark switches, at Erlangen University. Two different parameter regimes are under investigation: medium power switches (32 kV anode voltage, 30 kA anode current and 0.02 C charge transfer per shot) for pulsed gas discharge lasers and high power switches (30 kV anode voltage, 400 kA anode current and 3.4 C charge transfer per shot) for high current applications. The lifetime of these switches is determined by erosion of the cathode. The total charge transfer of devices with one discharge channel is about 220 kC for the medium and 27 kC for the high power switch. At currents exceeding 45 kA a sudden increase in erosion rate was observed. Multichannel devices are suited to increase lifetime as the current per channel can be reduced. Successful experiments with radial and coaxial arrangements of the discharge channels were performed. In these systems the discharge channels move due to magnetic forces. A skilful use of this phenomena will result in a considerably increase of switch lifetime. Multigap devices enable an increase of anode voltage. A three gap switch has run reliably at an anode voltage of 70 kV.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Segmented ballasted electrodes for a large-volume, sub-atmospheric, transversely excited pulsed laser

Two prototype ballasted electrodes were fabricated and tested with a large-volume, reduced pressure, pulsed CO2 laser gas discharge, initiated by corona pre-ionization, and pumped by pulse widths up to 19 mu s. The design of segmented, ballasted cathodes is considered and equations are derived to quantify the degree of discharge arcing given partial collapse of the discharge. The number of segments passing the fault current was experimentally investigated as a function of the discharge power and found to increase until each segment passed the fault current. Compared with a planar-planar electrode geometry, under identical pulse excitation conditions, the ballast electrodes gave a factor of four improvement in the maximum discharge power depositions, prior to the development of instabilities. Higher frequencies were obtained with pulse trains below 50 ms, the maximum observed frequency being approximately 5 kHz. Arcing for the ballasted electrode configurations was observed in the middle of the electrodes, and its position corresponded to a measured non-uniform gas velocity.

Investigation of the active media in pulsed gas discharge lasers by the Rozhdestvenskii hook method

In this review we generalize the results of our experimental investigations in which the Rozhdestvenskii hook method was first used to look for an inverted population in new spectral transitions. An inverted population in new 3p–3s transitions of the neon atom with λ=588.1, 594.4, 650.6, and 653.2 nm was discovered in the active medium of a Penning plasma laser emitting the λ=585.3 nm neon line in Ne-H2 and Ne-H2-Ar mixtures. Results of investigations of a number of active media are given. An analysis is made of the spatial and temporal distributions of copper atoms in the ground state and of their influence on the lasing efficiency of a copper-vapor laser. Using the rhenium atom as an example, it was shown to be possible to obtain a sufficiently high concentration of refractory metal atoms (>1014 cm−3) in an active medium to form active media of lasers utilizing self-terminating transitions and also plasma lasers.

Method of physical investigation of pulsed gas-discharge lasers

Method of physical investigation of pulsed gas-discharge lasers