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In this paper, the results of measurements of the characteristics of the hydrogen microdischarges from direct current to radio frequencies are presented and discussed. Two types of the electrode configurations are used: electrodes with Bruce profile and glass melting electrodes separated between 2.5 and \mathrm 100~\mu m . The breakdown voltage values for low frequencies are similar to the direct current breakdown voltage data, while the high-frequency breakdown voltages are systematically lower. As the frequency increases, the breakdown voltage decreases in the case of glass melting electrodes and increases in the case of electrodes with Bruce profile. It is observed that the breakdown voltages that correspond to the melting glass electrodes are lower due to edge issues and inability to achieve a homogenous field. The effective yields estimated from the measured breakdown voltage curves are similar for both electrode configurations. In addition to the breakdown voltage curves and current–voltage waveforms, the images demonstrating the discharge development and propagation are also recorded. Presented results reveal that secondary electrons play an essential role in sustaining the discharge in microgaps, where the relationship between breakdown voltage and gap spacing is far away from the standard scaling law at atmospheric pressure. [ABSTRACT FROM AUTHOR]

Pulsed microdischarges produced by dielectric barrier discharges (DBDs) in a submillimeter gap were investigated under 200 cycles of sinusoidal ac voltage at 5 kHz in this paper. The impulsive current in the external circuit was accurately measured by an oscilloscope with a bandwidth of 2.5 GHz and a maximum sampling rate of 40 GS/s to calculate the filamentary current in the discharge gap. The amplitude, pulse duration, and transferred charge of a single filamentary current and the microdischarge energy acquired over the 200 voltage cycles were statistically analyzed for different discharge gaps and gas pressures. The microdischarge parameters and ozone generation efficiencies for different conditions were compared. The ozone production efficiency was found to increase with increasing pressure from 1 to 2 bar absolute, and the gap length from 0.2 to 0.5 mm. The maximum ozone production efficiency achieved in the paper was 217 g/kWh, with a gap length of 0.5 mm, an absolute pressure of 2.0 bar, and an applied voltage of 5.5 kV at 5 kHz. [ABSTRACT FROM AUTHOR]

Recent studies have shown that, in microscale electrode gaps, the traditional Paschen's curve fails as the left branch sharply decreases with electrode spacing, thus resulting in the modified Paschen's curve. This deviation from Paschen's curve is attributed to ion-enhanced field emission and notably breaks pressure times distance (pd) scaling. Here, 1-D particle-in-cell/Monte Carlo collision simulations at moderately high pressures are used to predict breakdown and reproduce the modified Paschen's curve, which is in good agreement with existing theory. These simulations reveal that the net positive space charge that accumulates in the electrode gap enhances the electric field, subsequently enhancing field emission from the cathode. Because the emitted electrons generate additional ions in the discharge, a positive feedback mechanism occurs, where the field-emitted electrons produce the ions that enhance the electric field. It is revealed that this coupling between field emission and the discharge is necessary in order for breakdown to occur. [ABSTRACT FROM PUBLISHER]

In this paper, a quartz coaxial dielectric-barrier-discharge tube operated at different gas pressures and frequencies has been studied. A sinusoidal voltage up to 2.4 kVp with frequencies 34.5 and 47.5 kHz has been applied to the discharge electrodes for the generation of microdischarges. The experimental results confirm the filamentary nature of discharges when operated at different pressures (300, 600, and 1000 mbar) and at different frequencies (34.5 and 47.5 kHz). The relative influence of the given pressures and applied voltage waveforms on the discharge parameters has been analyzed. An equivalent electrical circuit model representing the multipeak phenomenon in the discharge has been developed, which validates the characteristics of the filamentary behavior. A series of simulations has been carried out in order to obtain the internal discharge parameters including discharge impedance which is not measurable during the experimental process. A close agreement between the simulated and experimental results has been obtained. From the experimental results and equivalent electrical circuit model, the dynamic nature of equivalent capacitance has also been reported. [ABSTRACT FROM PUBLISHER]

The vacuum ultraviolet (VUV) emissions from 115 to 200 nm from the effluent of an RF (1.2 MHz) capillary jet fed with pure argon and binary mixtures of argon and xenon or krypton (up to 20%) are analyzed. The feed gas mixture is emanating into air at normal pressure. The Ar excimer second continuum, observed in the region of 120-135 nm, prevails in the pure Ar discharge. It decreases when small amounts (as low as 0.5%) of Xe or Kr are added. In that case, the resonant emission of Xe at 147 nm (or 124 nm for Kr, respectively) becomes dominant. The Xe second continuum at 172 nm appears for higher admixtures of Xe (10%). Furthermore, several N I emission lines, the O I resonance line, and H I line appear due to ambient air. Two absorption bands (120.6 and 124.6 nm) are present in the spectra. Their origin could be unequivocally associated to O2 and O3. The radiance is determined end-on at varying axial distance in absolute units for various mixtures of Ar/Xe and Ar/Kr and compared to pure Ar. Integration over the entire VUV wavelength region provides the integrated spectral distribution. Maximum values of 2.2 mW·mm-2·sr-1 are attained in pure Ar and at a distance of 4 mm from the outlet nozzle of the discharge. By adding diminutive admixtures of Kr or Xe, the intensity and spectral distribution is effectively changed. [ABSTRACT FROM AUTHOR]

Devices with micrometer and submicrometer gaps can face a serious challenge due to electrical breakdown during manufacturing, handling, and operation. Therefore, it is necessary to be aware of the breakdown voltage at different gaps. Since the Paschen's law is not valid for gaps smaller than several micrometers, modified Paschen curve should be used to predict breakdown voltage for microdevices. One of the possible mechanisms responsible for the reduction of the maximum operation voltage at small gaps is the field emission (FE). In this paper, particle-in-cell/Monte Carlo collision simulations, including the ejection of electrons from the cathode due to a high electric field, have been carried out to estimate the significance of the FE effect on the breakdown voltage in microgaps. [ABSTRACT FROM AUTHOR]

We have performed simulations on a coplanar structured alternating current plasma display panel cell sustained in the ternary He-Ne-Xe gas mixture and its discharge characteristics were compared with those of the conventional binary Ne-Xe mixture, by using the two-dimensional fluid model simulator. Since plasma display panels use micro-discharges in the Xe mixed gas to generate vacuum ultraviolet light to excite phosphor for visible light emission, the condition of discharge gas mixtures is one of the main factors that determine luminous efficacy and thus, intensive studies on discharge gas mixture are essential to optimize it. As the He concentration increases in the He-Ne-Xe mixture, luminance and luminous efficacy increase but power consumption decreases, which agrees well with the recent experimental findings. We have found that the enhanced ion mobilities in the gas mixture by adding He gas to the conventional Ne-Xe mixture play an important role in increasing luminous efficacy of a plasma display panel cell, by reducing the cathode fall potential. In addition, He atoms increase the number of Xe*(3P2) in the excited state and thus, the dimer emission is increased while the resonant line is reduced with the He content. As a result, the total vacuum ultraviolet emission is increased and higher luminance and higher luminous efficacy can be obtained. [ABSTRACT FROM PUBLISHER]

Plasma display panel emission measurements are correlated with panel efficacy trends, and directions for the improvement of the discharge efficiency are derived. An increase of the ratio of the phosphor emission in the visible to the Xe emission in the infrared indicates an increased Xe excitation efficiency. Also, the time dependence and the spatial distribution of the Xe emission are important discharge characteristics. Experiments reveal that a high panel efficacy is obtained, especially for design and driving conditions that govern a fast and spatially distributed discharge development. A high sustain voltage V>200 V causes a "high efficiency discharge mode." It is proposed that in this mode, the cathode sheath is not, or is incompletely, formed during the rise of the discharge current. Then the electric field in the discharge cell is dominated not by the space charges, but by the externally applied voltage. The effective discharge field is lowered, resulting in a lower effective electron temperature and more efficient Xe-excitation. Under the fast discharge buildup conditions also the electron-heating efficiency increases due to a decrease of the ion heating losses in the cathode sheath. A high sustain voltage combines well with a high Xe content gas mixture, that further increases the discharge efficiency. Changes in the phosphor to Xe- and Ne-emission ratio show that for higher Xe content, a lower electron temperature accounts for a more efficient Xe excitation. Further, the use of a TiO2-layer underneath the phosphor causes an increase of the ratio of the phosphor emission in the visible to the Xe emission in the infrared, i.e., an increased Xe excitation efficiency. As a result, a high efficacy of 5 lm/W and a high luminance of 5000 cd/m2 have been realized in a 4-in color plasma display test panel design with a 50% Xe in Ne gas mixture, a TiO2-layer underneath the phosphor, and a high sustain voltage 260-290 V. [ABSTRACT FROM PUBLISHER]

Microscope photos of the microdischarges in dielectric barrier discharge microplasma were taken for the discharge gaps ranging from 30 to 100 \mu\m. The microdischarge formation phenomena in all the stages were observed for microplasma generated in \N2/\Ar mixture by a pulse power supply. A diffused glowlike microplasma was observed with the increase in Ar concentration in \N2/\Ar mixture. [ABSTRACT FROM PUBLISHER]

It has been recently demonstrated that microcathode sustained discharges (MCSD) are very efficient for the production of large fluxes of singlet delta oxygen (SDO). In this paper, a comparison between MCSD operation in \Ar/O2 and in \He/O2 mixtures is done. It is shown that, even if SDO production efficiency is theoretically much higher in \Ar/O2 mixtures, atmospheric pressure operation is only possible in He-based mixtures. [ABSTRACT FROM AUTHOR]

Stable microdischarges, ∼0.5-1 mm in length, are produced in atmospheric air by extracting plasma from a (50 μm)² inverted pyramidal Si microdischarge device which serves as a plasma cathode. Both metal and dielectric lips have been successfully tested as the extraction electrode and driving frequencies up to 20 kHz have been demonstrated. The plasma column, or conduit, generated is well behaved and essentially cylindrical with a diameter smaller than the width of the Si cathode device. [ABSTRACT FROM AUTHOR]

Arrays of microdischarge devices, 100 × 100 μm² in cross section, have been fabricated in a photodefinable glass, and electrically driven by interdigitated electrodes. Operated in Ne gas at pressures from 200 to 600 torr, 5 × 5 arrays of square microdise charge pixels are bright and draw a total current of 0.4-1.5 mA for direct current operating voltages of <200 V. [ABSTRACT FROM AUTHOR]

The breakdown voltage (Vs) for a discharge in Ar at pressures between 35 and 300 torr has been reduced significantly with an array of cylindrical microdischarge devices mounted behind the tungsten cathode. For PAr = 50 torr, Vs drops by approximately a factor of two, relative to that for a conventional discharge, when the microdischarge array is in operation. The injection of electron-ion pairs into the anode-cathode gap region by the array also decreases the formative and statistical time lags associated with the startup of a cold lamp. [ABSTRACT FROM AUTHOR]