Ultraviolet (UV) emissions from a unipolar submicrosecond pulsed dielectric barrier discharge (DBD) in He-Air mixtures (original) (raw)
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Journal of Advanced Oxidation Technologies, 2003
Investigations were carried out on point-to-plane dielectric barrier discharges with two different gas gap lengths (d = 0 and 2 mm), energized with two different high voltage power supplies providing one an ac signal at 15 kHz and the other a pulsed signal with a same repetition rate. Correlations between the electrical properties and the behavior of the plasma in these different situations were established through ozone generation, and by the way O radicals net production, checking for this purpose that in our operating conditions gasheating influence remained minor. Using the representation ozone concentration vs. charge amount transferred through current pulses, the specific electrical and thus physical properties of pulsed surface discharges are put in light; in these discharges, compared to ac and pulsed volume discharges, current pulses exhibit, for a given charge per pulse, the highest amplitudes and the shortest durations.
Influence of the On-time on the Ozone Production in Pulsed Dielectric Barrier Discharges
Plasma
Understanding the production mechanisms of ozone and other reactive species in atmospheric pressure dielectric barrier discharges (DBDs) has become increasingly important for the optimization and commercial success of these plasma devices in emerging applications, such as plasma medicine, plasma agriculture, and plasma catalysis. In many of these applications, input power modulation is exploited as a means to maintain a low gas temperature. Although the chemical pathways leading to ozone production/destruction and their strong temperature dependence are relatively well understood, the effect of the on-time duration on the performance of these modulated DBDs remains largely unexplored. In this study, we use electrical and optical diagnostics, as well as computational methods, to assess the performance of a modulated DBD device. The well-established Lissajous method for measuring the power delivered to the discharge is not suitable for modulated DBDs because the transients generated a...
Power consideration in the pulsed dielectric barrier discharge at atmospheric pressure
Journal of Applied Physics, 2004
Nonequilibrium, atmospheric pressure discharges are rapidly becoming an important technological component in material processing applications. Amongst their attractive features is the ability to achieve enhanced gas phase chemistry without the need for elevated gas temperatures. To further enhance the plasma chemistry, pulsed operation with pulse widths in the nanoseconds range has been suggested. We report on a specially designed, dielectric barrier discharge based diffuse pulsed discharge and its electrical characteristics. Two current pulses corresponding to two consecutive discharges are generated per voltage pulse. The second discharge, which occurs at the falling edge of the voltage pulse, is induced by the charges stored on the electrode dielectric during the initial discharge. Therefore, the power supplied to ignite the first discharge is partly stored to later ignite a second discharge when the applied voltage decays. This process ultimately leads to a much improved power transfer to the plasma.
Plasma Processes and Polymers, 2010
The reported dielectric barrier discharge (DBD) source comprises of a ceramic-covered copper electrode, and plasma can be ignited in ambient air with grounded 'opposite' electrodes or with objects of high capacitance (e.g., human body), when breakdown conditions are satisfied. Filamentary plasma mode is observed when the same source is operated using grounded opposite electrodes like aluminium plate and phosphate buffered saline solution, and a homogeneous plasma mode when operated on glass. When the source is applied on human body, both homogeneous and filamentary discharges occur simultaneously which cannot be resolved into two separate discharges. Here, we report the characterization of filamentary and homogeneous modes of DBD plasma source using the above mentioned grounded electrodes, by applying optical emission spectroscopy, microphotography and numerical simulation. Averaged plasma parameters like electron velocity distribution function and electron density are determined. Fluxes of nitric oxide, ozone and photons reaching the treated surface are simulated. These fluxes obtained in different discharge modes namely, single-filamentary discharge (discharge ignited in same position), stochastical filamentary discharge and homogeneous discharge are compared to identify their applications in human skin treatment. It is concluded that the fluxes of photons and chemicallyactive particles in the single filamentary mode are the highest but the treated surface area is very small. For treating larger area, the homogeneous DBD is more effective than stochastical filamentary discharge. -7.5 -5.0 -2.5 0.0 2.5 5.0 7.5 1E16 1E18 1E20 1E22 Flux of ozone / m -2 s -1 radius of electrode / mm 1 ppm single-filamentary DBD homogeneous DBD stochastic-filamentary DBD Plasma Process. Polym. 2010, 7, 665-675 ß
Electrical and Optical Characterization of Dielectric Barrier Discharge Produced in Atmospheric Air
Kathmandu University Journal of Science, Engineering and Technology, 2010
This paper reports the results concerning the production of Dielectric Barrier Discharge (DBD) at atmospheric pressure air and its electrical and optical characterization. The discharge was produced by applying high voltage AC source of frequency (10-30) kHz and potential difference of (0-20) kV across the electrodes. The discharge was characterized by measuring current and voltage with a high frequency digital oscilloscope. The optical characterization was made by taking the spectrums of discharge by optical emission spectrometer. The optical spectra in the range of 200 nm to 450 nm have been analyzed in order to estimate the electron temperature by intensity ratio method. Results showed that the electron temperature is about 1.9 eV.
Effects of a pulsed operation on ozone production in dielectric barrier air discharges
We have performed an experimental investigation of ozone production in a pulsed dielectric barrier discharge (DBD) reactor. Measurements of ozone in the gas-phase as a function of the power level show that in continuous mode a maximum concentration is achieved before a decrease presumably connected with gas-phase heating. When the reactor is employed in pulsed mode, by applying a definite duty cycle, a strong increase in ozone concentration is generally observed, with a maximum which happens at quite reduced duty cycles, thus requiring reduced power compared to the continuous mode.
Journal of Electrostatics, 2012
The paper presents a study on the atmospheric pressure dielectric barrier discharge plasma, generated with Teflon covered electrodes in flowing helium at a driving frequency of 1.74 MHz. Besides generation techniques and running principle, an operating stability diagram is presented for the discharge. By means of optical emission techniques, characteristic temperatures were determined and the reactive species were identified. The applicability of generated discharge was tested by surface functionalization and bacterial inactivation. It was found that even for short treatment times the plasma is efficient for surface treatment and it can inactivate Escherichia coli with a D-time of 10 s.
Journal of Electrostatics, 2009
Dielectric barrier discharge (DBD) is an important method to produce non-thermal plasma, which has been widely used in many fields. In the paper, a repetitive nanosecond-pulse generator is used for the excitation of DBD. Output positive pulse of the generator has a rise time of about 15 ns and a full width at half maximum of 30-40 ns, and pulse repetition frequency varies from single shot to 2 kHz. The purpose of this paper is to experiment the electrical characteristics of DBD driven by repetitive nanosecond pulses. The variables affecting discharge conditions, including air gap spacing, dielectric thickness, barrier fashion, and applied pulse repetition frequency, are investigated. The relationship between electric field, discharge current, instantaneous discharge power across air gap, and estimated electron density with the length of air gap, dielectric thickness, barrier fashion, and pulse repetition frequency is obtained respectively, and the experimental results are also discussed. In addition, two typical images exhibiting homogeneous and filamentary discharges are given with different experimental conditions.
Journal of Physics: Conference Series, 2010
Dielectric-barrier discharges (DBDs) are characterized by the presence of at least one insulating layer in contact with the discharge between two planar or cylindrical electrodes connected to an AC/pulse power supply. The dielectric layers covering the electrodes act as current limiters and prevent the transition to an arc discharge. DBDs exist usually in filamentary mode, based on the streamer nature of the discharges. The main advantage of this type of electrical discharges is that nonequilibrium and non-thermal plasma conditions can be established at atmospheric pressure. VUV/UV sources based on DBDs are considered as promising alternatives of conventional mercury-based discharge plasmas, producing highly efficient VUV/UV radiation. The experiments have been performed using two coaxial quartz double barrier DBD tubes, which are filled with Xe/Ar at different pressures. A sinusoidal voltage up to 2.4 kV peak with frequencies from 20 to 100 kHz has been applied to the discharge electrodes for the generation of microdischarges. A stable and uniform discharge is produced in the gas gap between the dielectric barrier electrodes. By comparisons of visual images and electrical waveforms, the filamentary discharges for Ar tube while homogeneous discharge for Xe tube at the same conditions have been confirmed. The electrical modeling has been carried out to understand DBD phenomenon in variation of applied voltage waveforms. The simulated discharge characteristics have been validated by the experimental results.