In this paper, a fast opto-electronic device is used to investigate a novel ultraviolet light source with an optical system.
The ultraviolet light source is generated by dielectric barrier discharge in argon at low pressure. Experimental results
indicate that the light source is uniform when the gas pressure is lower than 0.1 atm, however, localized discharge
(discharge filament) can be observed when the gas pressure is 0.4 atm. The light emission signals from the discharge are
detected by fast opto-electronic device (Hamamatsu H7826-01) with increasing the amplitude of the applied voltage. It
is shown that the discharge at low voltage (slightly above the breakdown voltage) has two discharge pulses per half cycle
of the applied voltage, and duration of each pulse is more than 1μs. The number of discharge pulses increases with
increasing the applied voltage. An intensified charge coupled device (ICCD) is usually used to investigate the mechanism
of the uniform discharge at low pressure. However, an optical system is used in our experiment. The optical system
includes an image-forming block and a fast opto-electronic device. Spatially resolved measurement of the discharge can
be achieved selectively. The research results indicate that the uniform light source is composed of many micro-discharges
that distribute randomly on the electrode. The duration of the micro-discharge is about several tens nanoseconds. These
results are of great importance for the generation and application of ultraviolet light source.
Dielectric barrier uniform discharges have attracted considerable interest because this type of discharge requires
practically no vacuum devices and plasma with good uniformity can be generated at high pressure. In this paper,
discharges are initiated in air at atmospheric pressure in a dielectric barrier discharge setup composed of two parallel
planar electrodes separated by two layers of dielectric. The characteristics of dielectric barrier discharge are studied
through collecting the emission signals from the discharge with a photomultiplier tube and a spectrometer, respectively.
The results show that the discharge consists of many micro-discharge filaments when the applied voltage is slightly
above the breakdown voltage, and the discharge is uniform when the applied voltage is very high. The waveform of
discharge emission consists of many pulses with duration of several tens nanoseconds in the filamentary discharge mode.
However, it only consists of a single broad electrical pulse (hump) lasting approximately a quarter of a discharge time
period on which significant narrow pulse peaks are superposed. Streamer breakdown mechanism is involved in the
discharge of not only filamentary discharge but also uniform discharge. Spectral emission spectroscopy is used to study
the discharge transition. The intensity ratio of 391.4nm to 337.1nm represents electron energy that is mainly determined
by the electric filed applied to the gas gap. With increasing the applied voltage, the intensity ratio of 391.4nm to 337.1nm
decreases. This experimental result indicates that electron energy decreases with the increasing of the applied voltage.
Spatio-temporal patterns in nonlinear system have been paid much attention in resent years. Among different
nonlinear systems, gas discharge system is more remarkable because proper time scale and abundance in pattern
structures. In this article, pattern formation dynamics is studied in a dielectric barrier discharge system with mixed
working gas of argon and air at pressure of 0.6 atm by optical method. A boundary condition of square structure is used
in the experiments. The experimental results show that the discharge pattern with increasing the applied voltage
undergoes a scenario: uniform discharge, hexagon structure, stochastic micro-discharge filaments, hexagon structure
again, square pattern, regular stripes that bridge the boundary, and uniform discharge again. The emission signals from
the discharge in different pattern are detected by photomultiplier tubes and results show that the waveform of total light
signals under low voltage lower than the voltage of stochastic micro-discharge filaments is only one pulse at each half
cycle of the applied voltage, while it shows two pulses at each half cycle of the applied voltage in the second hexagon
pattern and square pattern, and more pulses appear in the stripe pattern discharge and second uniform discharge. Through
analyzing the temporal sequence of the different filaments in a hexagon, it can be concluded that the hexagon pattern is
an interleaving of two rectangular sub-patterns that the micro-discharge filaments in a sub-pattern volley almost at the
same time. The temporal sequence of the two sub-patterns in consecutive half cycle alternates.
Lifetime of micro-discharge filaments in dielectric barrier discharge in air at atmospheric pressure is very short and high temporal resolution device is necessary to study time correlation between micro-discharge filaments. In this paper, a simple optical method is introduced to study time correlation between micro-discharge filaments in dielectric barrier discharge in air at atmospheric pressure by photomultiplier tubes. The waveforms of light emission indicate that the discharge burst within each half cycle of applied voltage consists of a series of discharges pulses. This experimental phenomenon shows that the discharges of two or more filaments would overlap in time. By time correlation study, it is found out that discharge filaments can be categorized to some groups according their spatial position. The filaments can volley almost at the same time within neighboring space whose dimension is less than 3x3<i>mm</i><sup>2</sup>. A discharge domain is proposed to denote the group of discharge filaments that volley at the same time and exist in a neighboring space. The temporal behavior of filaments belong to one domain is investigated in many applied voltage cycles. The probability distribution function of the intervals for the discharge filaments in a domain is given at last. The delay time between breakdown moments of two filaments in one domain varies within the range of a few ns order. The physical mechanism involved in photo-ionization is presented to interpret the domain formation.
The spatial-temporal correlation in dielectric barrier discharge is difficult to be studied in the mixed gas of air and argon. In this paper, a simple optical method is introduced to study the temporal correlation intensity between micro-discharge filaments in dielectric barrier discharges at different air concentration in mixed gas of air and argon. The relation of the breakdown voltage and air concentration (<i>Χ</i>) is measured. It's found that the breakdown voltage increases as the air concentration increasing. The experimental results show that the diameter and discharge duration of the filament decrease with the air concentration increasing, at the same time the coherence of the discharge moments of the filaments weakens with the air concentration increasing. The experimental results can be explained with the theory of electron drifting. In addition, the accumulated charges on dielectric surface created by the filament discharge create a field within very time when the duration is small, which against the filament breakdown in its neighboring region. So the coherence of the discharge moments of the filaments can't be realized. While the accumulation of the surface charges will last a long time when the duration of the filament discharge is big, the breakdown can take place in the neighboring region of the filament in the duration, which would be the factor to the coherence of the discharge moments.
The spatio-temporal behavior in pattern formation in dielectric barrier discharge system is hard to be studied in the mixed gas of air and argon at high pd product, for the discharge duration of micro-discharge (filament) in streamer mode is very short. In this paper, pattern formation phenomenon in streamer mode in dielectric barrier discharge is studied by optical method. A rich variety of patterns has been observed in streamer discharge mode in the mixed gas of air and argon. It's found that the appearance of these patterns is very sensitive to air concentration and applied voltage. Regular patterns such as hexagon and square structure can be formed in this system when the parameters space is proper. The applied voltage for obtaining the hexagon (or square) pattern increases with increasing air concentration. These regular patterns sometimes drift in a certain direction and sometimes rotate stochastically. The drifting velocity is estimated through dividing the filament trace length by exposure time of the photo. It is found that the drifting velocity increases generally with increasing air concentration and the drifting velocity of hexagon pattern is larger than that of square pattern. The light waveforms from irregular pattern or random walking filaments are un-orderly and stochastic. On the contrary, the light waveforms of regular patterns are very orderly and periodical, only two pulses in each half cycle of the applied voltage. In our experiments, it is also found that the spatial frequency of pattern increases with increasing air concentration.
The pattern formation of hexagonal and square structure is obtained in dielectric barrier discharge in argon at atmospheric pressure. The temporal behavior of total light emission of square pattern is measured with optical method. The experimental results show that there are two current spikes in each half cycle of applied voltage in waveform of total light emission. The possible structure of the pattern is proposed, which has been proved partly by late experiment.
In this paper transition between glow-like discharge and filamentary discharge are found by gas condition being changed in dielectric barrier discharge device, discharge signal is measured by the electric methods and the current waveforms were registered by usign digital oscillography in the course of the transition. The difference between two modes is analyzed and reasons resulting in such difference are discussed.
A special designed setup consisting tow water electrodes is used to investigate the temporal characteristic of micro-discharge in dielectric barrier discharge in Argon by the optical methods on the non-intrusive and in-situ measurement. The nonsymmetrical characteristic of the micro-discharge breakdown moment which the interval between two adjacent discharges varies between long one and short one alternately is discovered by the applied voltage increasing step by step, the influence of wall charges on the temporal behavior characteristic is analyzed at last.
In this paper, the filamentary pattern of dielectric barrier discharge has been processed by using Photoshop, the coordinates of each filament can also be obtained. By using Photoshop two different ways have been used to analyze the spatial order of the pattern formation in dielectric barrier discharge. The results show that the distance of the neighbor filaments at U equals 14 kV and d equals 0.9 mm is about 1.8 mm. In the scope of the experimental error, the results from the two different methods are similar.