Gas Discharge System Research Articles

Extension of the gas-pressure operating range and increase in the lifetime of the plasma cathode grid of an ion source

A new scheme of a gas-discharge system is proposed for a basket-type ion source with a plasma cathode in which the electrons are emitted from the expanded anode part of a constricted hollow-cathode glow discharge bounded by a grid electrode. The modified electrode system of the ion source made it possible to enlarge the surface area of the plasma cathode grid and the aperture of its cells, thereby providing stable ion emission from the discharge plasma within a wide gas-pressure range and substantially (by one order of magnitude) increasing the grid lifetime. The operation of the plasma cathode in the free and forced emission modes is examined, and the energy efficiency of ion generation in the gas-discharge system under study is evaluated.

Transition from bright to dark dissipative solitons in dielectric barrier gas-discharge

In this article we deal with the experimental investigation of pattern formation in a planar ac gas-discharge system with a dielectric barrier. We report on the first observation of the transition from bright to dark current filaments and vice versa via stripe-like patterns. The observed phenomena become classified in the framework of Turing-structures and solitary objects and are compared to results obtained by numerical simulations of a two-component reaction-diffusion-system.

Axial evolution of the energy spectra of the electron beams ejected from a Penning discharge

Results are presented from experimental studies of the formation of the energy spectra of the electron beams ejected in the axial direction from a Penning discharge. The main features of the axial evolution of the time-averaged energy spectra of anomalously fast electrons are determined. The presence of several groups of electrons with different energies is revealed and explained. The influence of the electrode geometry, the difference between the cathode potentials, and the atomic mass of the working gas on the energy spectra of the ejected electron beams is investigated. A physical model describing the formation of the energy spectra of anomalously fast electrons in Penning-type gas-discharge systems is proposed.

Forced random walks with memory in a glow mode dielectric barrier discharge

In this paper, we present experimental results on dielectric barrier gas-discharge (DBD) systems in helium where the surface is prepared with some humidity. We observe well-defined solitary current filaments with self-propelled motion. The trajectories of the filaments in the discharge plane resemble a random walk motion with memory. The mechanism leading to motion is attributed to the mutual interaction of gas-discharge and local humidity at the dielectric surface. The phenomenon is a new drift mechanism for filaments in DBD and may be important in applications being related to plasma surface treatment.

Spontaneous division of dissipative solitons in a planar gas-discharge system with high ohmic electrode

In this Letter we report on the division of electrical current filaments in a planar semiconductor gas-discharge system with high ohmic electrode that we refer to as dissipative solitons. The effect is observed for stationary and propagating, as well as for isolated and for dense arrangements of filaments. For large spatial density of dissipative solitons, processes of their generation and annihilation seem to give rise to a specific kind of spatio-temporal chaotic dynamics.

Analysis of prebreakdown current in a gas discharge system with a semiconducting cathode

Results are presented of an analysis of the prebreakdown current of a Townsend discharge in a planar gas discharge system with a GaAs semiconductor cathode for a gap thickness of 45 µm and gas pressures of 6.9, 8.9, 34.2 and 36.9 kPa. IR radiation excites the cathode in the system, thus controlling the current density in the gas discharge layer. It is shown that the prebreakdown current is caused by electron emission from the semiconductor surface. The present experimental investigations show that the prebreakdown current decreases anomalously with increase of the feeding voltage and that it also decreases under the illumination of a semiconductor cathode. Both these anomalies depend on gas pressure. The current density change through the cross-section of the discharge gap, i.e. the appearance of the spatio-temporal self-organization of non-linear dissipative systems, causes these observed effects. These characteristics of the system can be applied for fast IR imaging and a high speed UV light source.

Pattern Dynamics in a Two-Dimensional Gas Discharge System

Reaction-diffusion equation model for a 2-dimensional gas discharge system is introduced in close relationship with the recent experiment by Nasuno. The model shows formation of spots, molecule-like organization of a cluster of spots, moving of spots, and intermittent collapse and recreation of spots, in agreement with experiments. The pattern dynamics are classified into distributed, localized, and moving spots, and periodic wave pattern. The phase diagram displayed against the current and pressure has some agreement with that observed in the experiment. Dynamic change of spot numbers as well as the structure of the spot cluster is studied in terms of the collective flow of charge, and discussed as chaotic itinerancy.

Silicon Doped with Sulfur as a Detector Material for High Speed Infrared Image Converters

The work aims at approaching the solution of the problem of developing sensitive silicon detectors for high speed IR imaging devices which are semiconductor – gas discharge systems. Among the requirements to detectors is their operation at the temperature which is somewhat higher than that of liquid nitrogen. To meet this requirement, a set of deep impurities is analyzed. It is emphasized that silicon doped with sulphur is a good choice to reach the aim. The doping of silicon with sulphur is done by the technique of high temperature diffusion. Data of the Hall measurements indicate the presence of large density of shallow donor levels in the material obtained. To compensate them, acceptors are introduced afterwards with using radiation doping techniques. Testing of the fabricated detectors in the converter setup shows that they provide imaging of IR fields of temperature T ~ 270 0C with the temporal resolution in the order of 3 µs.

Flow distribution and pressure of air due to ionic wind in pin-to-plate corona discharge system

An electrohydrodynamic investigation has been carried out in a pin-to-plate gas discharge system to clarify the mechanism of repulsive force generation between a pin and plate electrode at corona discharge. Numerical calculations have been conducted in two steps. First, the axi-cylindrical static corona discharge field was calculated with the finite-element method to deduce the Coulombic body force ρ E applied to the air, where ρ is the charge density and E is the electric field, and then the induced ionic wind was calculated with the finite differential method. The calculated pressure distribution on the plate electrode was on the order of 10 Pa which was in good agreement with the measured pressure distribution. The calculated air velocity at the center was several m/s and was confirmed by a time-of-flight experiment and the velocity distribution near the pin electrode also agreed with measurements using a laser Doppler velocimeter. Pressure and wind velocity were increased at high-applied voltage. These results confirm that the ionic wind is the cause of the repulsive force to the pin electrode at the corona discharge.

Electrical instability in a semiconductor gas discharge system

AbstractElectrical instability in a SI GaAs plates of the semiconductor gas discharge gap system (SGDGS) is studied experimentally in a wide range of the gas pressures, interelectrode distances and different diameters of the cathode areas. While being driven with a stationary voltage, it generates current and discharge light emission (DLE) instabilities with different amplitudes of the oscillation. It is shown that under the experimental conditions the interelectrode distance played only a passive role and was not responsible for the appearance of the DLE instability. At the same time for different diameters D of the GaAs plate areas the expanded range of current and DLE oscillations are observed. SGDGS with an N‐shaped CVC was analyzed using both the current and DLE data showing the electrical instability in the GaAs cathode. It was found that application of high feeding voltage to this cathode give rise to non‐uniform spatial distribution of the DLE, which disturbed the operation of the system. The experiment presents also a new metod to study and visualization of the electrical instabilities in high‐resistivity GaAs plates of large diameter. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Electrohydrodynamic deformation of water surface in a metal pin to water plate corona discharge system

Electrohydrodynamic deformation of water surface was investigated in a pin-to-plate gas discharge system that consisted of a pin electrode made of metal and an ion-conductive water electrode. In the condition of a lower applied voltage than the corona threshold, because an extremely small electrostatic attractive force, a Coulomb force in the order of 10 µN, was induced, water lifted up in the order of several tens of micrometres at the centre. Over the threshold voltage corona discharge took place and a relatively large repulsive force, in the order of 100 µN, was induced due to the ionic wind. It depressed water in the order of several hundred micrometres at the centre. Deformation of the water level coincided with the pressure distribution on the metal plate electrode, if the surface tension of water and the Coulomb force was included in the estimation to derive the pressure distribution from the measured deformation of the water level. If the applied voltage was lower than the corona threshold, total force to the water electrode coincided with that to the pin electrode. However, it was larger than that to the pin electrode at the corona discharge because the reaction force due to the ionic wind was applied not only to the pin electrode but also to other parts of the electrode at the corona discharge.

Current instability in a planar gas discharge system with a large-diameter semiconductor cathode

The current instability in a planar gas discharge system is studied experimentally in a wide range of the gas pressure, p (44–550 Torr), interelectrode distance, d (45–330 µm), and diameter, D (5, 9, 12, 18, 22 mm), of the electrode areas of the semiconductor cathodes. While being driven with a stationary voltage, it generates current instabilities with different amplitudes of the oscillation. Through spatially uniform irradiation of the semiconductor cathode, non-stationary states which are non-homogeneous can be generated in a system. It is shown that under the experimental conditions the discharge gap played only a passive role and was not responsible for the appearance of the current instability. At the same time, for different diameters, D, of the electrode an expanded range of current oscillations is observed. The pronounced N-type negative differential resistance is observed in the current–voltage characteristic of a planar gas discharge system with a large-diameter semiconductor cathode.

Pattern formation in planar dc-driven semiconductor–gas discharge devices: two mechanisms

The spatial and spatio-temporal patterning of the luminance distribution in laterally extended dc-driven gas-discharge systems with a semiconductor high-ohmic electrode is investigated. It is experimentally verified that a primary instability, via which a pattern is generated in the device, may be due to the active role of both the semiconductor component and the gas-discharge layer. Under the experimental conditions, formation of patterns at the expense of the semiconductor electrode is caused by the N-type negative differential conductivity (NDC) of the latter (if one plots the discharge current, I, as a function of the applied voltage, U). The critical voltage drop on the semiconductor at which NDC arises depends on the temperature in an essential way. Thus, by changing the temperature of the device, one can shift the critical supply voltage that corresponds to the onset of patterning of electrical current in the system. At conditions where the semiconductor component reveals a monotonic current–voltage characteristic, the patterning of the electric current in the device can be attributed to the active properties of the gas discharge. Presumably, it is the S-type NDC of the gas that is responsible for the formation of spatial structures in this case. The observed scenarios of pattern formation are qualitatively different for these two mechanisms.

Drift bifurcation of dissipative solitons due to a change of shape: experiment and theory

The subject of this paper is self-organized solitary current filaments being observed experimentally in a planar dc gas-discharge system with high-ohmic barrier. We report on the dynamical behavior of these objects which we refer to as dissipative solitons. An application of stochastic data analysis methods enables the separation of intrinsic dynamics from stochastic contributions. Using the externally applied voltage as control parameter, we observe a drift bifurcation that is accompanied by a change of shape of the bifurcating dissipative soliton. In order to interpret the experimental finding, a theoretical model in form of a three-component reaction–diffusion system is considered, allowing for a qualitative understanding of the obtained results. We discuss an analytical expression for the velocity of the dissipative soliton as a function of an appropriate control parameter and demonstrate that the change of the shape can induce the drift bifurcation. This analytical finding is supported by numerical simulations of the model equations.

A Large Emitting Area UV Light Source With Semiconductor Cathode

Light emission in the ultraviolet (UV) and visible (blue) range (330-440 nm) generated by a planar gas discharge system and the possibility of locally increasing the discharge light emission for a given photosensitivity of a planar GaAs semiconductor cathode has been studied. The use of metallic patched concentrators with an area of S=5/spl times/10/sup -4/ cm/sup 2/ and a density of 400 cm/sup -2/ leads to a fivefold increase in the gas light density. In a system with metallic patched concentrators, the local density of gas discharge light exceeds the density of uniform gas discharge light in the ionization system as many times as the working area of the semiconductor cathode exceeds the total area of the current concentrators. By using the infrared light to excite the semiconductor cathode of the system, we have shown that the uniform discharge light emission of the device with N/sub 2/ in the gap can serve as a source of UV radiation with a large emitting area of GaAs cathode if gas pressure and electric field are sufficiently high. Moreover, the use of metallic patched concentrators prolongs the working time of the cathode. The filamentation was primarily due to the formation of a space charge of positive ions in the discharge gap, which changed the discharge from the Townsend to the glow type.

THE FORMATION OF VORONOI DIAGRAMS IN CHEMICAL AND PHYSICAL SYSTEMS: EXPERIMENTAL FINDINGS AND THEORETICAL MODELS

The work discusses the formation of Voronoi diagrams in spatially extended nonlinear systems taking experimental and theoretical results into account. Concerning experimental systems a number of chemical systems used previously as prototype chemical processors and a barrier gas-discharge system are investigated. Although the underlying microscopic processes are very different, both types of systems show self-organized Voronoi diagrams for suitable parameters. Indeed certain chemical systems exhibit Voronoi diagrams as an output state for two distinct sets of parameters one that corresponds to the interaction of stable forced trigger waves and the other that corresponds to the spontaneous initiation and interaction of waves due to point instabilities in the system. In the case of the chemical systems front initiation, propagation and interaction (annihilation) are the primary mechanisms for Voronoi diagram formation, in the case of the barrier gas-discharge system regions of vanishing electric field define the medial axes of the Voronoi diagram. On the basis of cellular automata models the general concept of the formation of Voronoi diagrams has been explained, and related mechanisms have been simulated. Another intuitive approach towards the understanding of self-organized Voronoi diagrams has been given on the basis of reaction–diffusion models explaining the formation of Voronoi diagrams as a result of the mutual interactions of trigger fronts. The variety of systems exhibiting Voronoi diagrams as stationary states indicates that Voronoi diagrams are a generic and natural pattern formation phenomenon.

Measuring the interaction law of dissipative solitons

We investigate the interaction of self-organized solitary current filaments (dissipative solitons) under the influence of noise in a planar dc gas-discharge system with high-ohmic barrier. These localized structures exhibit interesting properties such as propagation and scattering as well as the transient formation of molecules and clusters. To quantitatively examine these interesting properties, methods of stochastic data analysis are developed to determine interaction laws from experimentally recorded data series. It turns out that in most cases, the sign of the resulting interaction functions alternates with the distance of the dissipative solitons. This phenomenon can be connected to experimentally detectable oscillatorily decaying tails of the filaments, which is in agreement with theoretical predictions.

Role of surface charges in dc gas-discharge systems with high-ohmic electrodes.

Surface charge of the electrodes is investigated for planar dc gas-discharge systems. Both analytical estimates and experimental data show that such a charge plays an important role for the dc systems with a high-ohmic electrode. This is demonstrated by several experiments concerning discharge establishment and pattern formation phenomena. The surface charge has an inhibitory role, as it diminishes the electric field in the gas. Due to the low mobility of the surface charges, their distribution can be nonuniform giving rise to the observable filamentary structure of the discharge. It is also shown that the surface charge effect can be naturally incorporated in existing phenomenological models of the planar discharge. Thereby one can explain several observable phenomena, such as stability, multiplicity, and motion of the localized structures.

Force at Spark Discharge in Pin-to-Plate Gas Discharge System

It was investigated whether the electrostatic force was generated at the spark discharge on a pin electrode in a pin-to-plate gas discharge system. Because it was not possible to measure the force directly at a short sparking period, three independent metcods were employed to evaluate the existence of the force indirectly. (1) Axial vibration was observed at the intermittent spark discharge for the softly supported pin electrode. The force was explicitly calculated in the case that the calculated vibration was well agreed with the measured. This experiment indicated that the force was almost 0 N at the spark discharge. The vibration was generated not by the force at the spark discharge but by alternative ionic wind at corona discharge. (2) A similar experiment was conducted whether the vibration magnitude depended on the spark current. The current at the spark discharge was varied by a circuit resistor. The experiment deduced that the force did not generated at the spark period and it was independent on the current. (3) Axial vibration could be observed when the voltage pattern that was common with that with the spark discharge was applied, if no force was applied to the pin electrode. To confirm it an experiment was conducted with two parallel-connected pin-to-plate gas discharge systems, one of which air gap was shorter than the other. The axial vibration of the longer air gap, in which the spark discharge did not take place, was observed and vibration also agreed quantitatively with calculated one. These three results suggested that no substantial force was generated at the spark discharge.

Micro-Driving Mechanisms Utilizing Force Generated in Pin-to-Plate Gas Discharge System

Two driving mechanisms were constructed and these characteristics were investigated. The mechanisms utilize force generated in a pin-to-plate gas discharge system that consisted of a rigid pin electrode and a plate electrode. One of the driving mechanisms utilizes force generated at dark discharge region, because attractive force, in the order of 10μN, was induced to the pin electrode due to the Coulomb force at this region. A stator consisted of parallel plate electrodes on a plastic plate and small linear movers were needle and/or plate electrodes on floating plastic plates. Experimental investigation deduced that (1) the speed of the movers was increased at high frequency of the applied voltage and a small air gap, but (2) the motion of the movers were out of tuning over a threshold frequency. Another driving mechanism utilizes force generated at corona discharge, because corona discharge took place over a certain threshold voltage and a relatively large repulsive force, in the order of 100μN, was induced to the pin electrode due to the ionic wind. The force was almost tangential to the pin electrode even when the pin electrode inclined to the plate electrode. This force was utilized for driving small linear and rotational movers on water. The linear mover was an inclined pin electrode on a floating plate and the rotational mover consisted of two inclined pin electrodes on a floating disk at point-symmetrical positions. Experimental investigation deduced that (1) the driving force was induced over the corona onset voltage, (2) the driving force or torque were maximum when the inclination angle was 45 degrees, and (3) the speed of the movers was increased at high applied voltage and a small air gap.