Atmospheric Pressure Radio Frequency Dielectric Barrier Discharges in Nitrogen/Argon

This work reports the experimental results on the characteristics of radio frequency dielectric barrier N2 /Ar discharges.Depending on the nitrogen content in the feed gas and the input power,the discharge can operate in two diferent modes: a homogeneous glow discharge and a constricted discharge.With increasing input power,the number of discharge columns increases.The discharge columns have starlike structures and exhibit symmetric self-organized arrangement.Optical emission spectroscopy was performed to estimate the plasma temperature.Spatially resolved gas temperature measurements,determined from NO emission rotational spectroscopy were taken across the 4.4 mm gap filled by the discharge.Gas temperature in the middle of the gas gap is lower than that close to the electrodes.     

The Role of Metastable Atoms in a Homogeneous Atmospheric Pressure Barrier Discharge in Helium

A one-dimensional fluid model for homogeneous atmospheric pressure barrier discharges in helium is presented by considering elementary processes of excitation and ionization including a metastable atom effect. Using this model we investigate the behaviours of the helium metastable atoms in discharges as well as their influence on the discharge characteristics. It is shown that the metastable atoms with a relatively high concentration during the discharge are mainly produced in the active phase of the discharge and dissolved in the off phase. It is also found that the metastable atom collisions can not only provide seed electrons for discharges but also influence the concentration of ions. A reduction of matestable atom density results in a drop in the charged particle densities and causes a qualitative change in the discharge patterns.     

Spectroscopic Study of a Radio-Frequency Atmospheric Pressure Dielectric Barrier Discharge with Anodic Alumina as the Dielectric

This paper presents the fabrication and a spectroscopic study of a stable radiofrequency dielectric barrier discharge(RF DBD) in Ar with a novel dielectric,anodic alumina,at atmospheric pressure.Dielectric electrodes are fabricated from commercially available low cost impure aluminum strips by a two-step anodization process in 0.3 M solution of oxalic acid.The discharge is found to be stable with excellent spatial uniformity for the RF input power range of 30~80 W.Excitation and rotational temperatures measured in the experiment range of 1472~3255 K and 434~484 K,respectively,as the input power changes from 30 W to 80 W.These temperature ranges are suitable for surface modification applications.     

Gas Breakdown of Radio Frequency Glow Discharges in Helium at near Atmospheric Pressure

A one-dimensional self-consistent fluid model was developed for radio frequency glow discharge in helium at near atmospheric pressure, and was employed to study the gas breakdown characteristics in terms of breakdown voltage. The effective secondary electron emission coefficient and the effective electric field for ions were demonstrated to be important for determining the breakdown voltage of radio frequency glow discharge at near atmospheric pressure. The constant of A was estimated to be 64±4 cm 1 Torr 1 , which was proportional to the first Townsend coefficient and could be employed to evaluate the gas breakdown voltage. The reduction in the breakdown voltage of radio frequency glow discharge with excitation frequency was studied and attributed to the electron trapping effect in the discharge gap.     

The Nonlinear Behaviors in Atmospheric Dielectric Barrier Multi Pulse Discharges

An in-depth and comprehensive understanding of the complex nonlinear behaviors in atmospheric dielectric barrier discharge is significant for the stable operation and effective control of the plasma. In this paper, we study the nonlinear behaviors in argon atmospheric dielectric barrier multi pulse discharges by a one-dimensional fluid model. Under certain conditions, the multi pulse discharge becomes very sensitive with the increase of frequency, and the multi pulse period-doubling bifurcation, inverse period-doubling bifurcation and chaos appear frequently. The discharge can reach a relatively steady state only when the discharges are symmetrical between positive and negative half cycle. In addition, the effects of the voltage on these nonlinear discharges are also studied. It is found that the amplitude of voltage has no effects on the number of discharge pulses in multi-pulse period-doubling bifurcation sequences; however, to a relatively stable periodic discharge, the discharge pulses are proportional to the amplitude of the applied voltage within a certain range.     

Surface Treatment of Polyethylene Terephthalate Film Using Atmospheric Pressure Glow Discharge in Air

Non-thermal plasmas under atmospheric pressure are of great interest in polymer surface processing because of their convenience, effectiveness and low cost. In this paper, the treatment of Polyethylene terephthalate (PET) film surface for improving hydrophilicity using the non-thermal plasma generated by atmospheric pressure glow discharge (APGD) in air is conducted. The discharge characteristics of APGD are shown by measurement of their electrical discharge parameters and observation of light-emission phenomena, and the surface properties of PET before and after the APGD treatment are studied using contact angle measurement, x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). It is found that the APGD is homogeneous and stable in the whole gas gap, which differs from the commonly filamentary dielectric barrier discharge (DBD). A short time (several seconds) APGD treatment can modify the surface characteristics of PET film markedly and uniformly. After 10 s APGD treatment, the     

Experimental Study of ZnO-Coated Alumina DBD in Atmospheric Pressure Air

An investigation on the discharge characteristic of a dielectric barrier discharge (DBD) device was carried out using bare and ZnO-coated alumina dielectric layer in atmospheric pressure air. Highly conductive ZnO film was first deposited on the alumina surface, and the characteristics of the dielectric barrier discharge were examined and compared. Experimental result shows that discharge behavior was definitely improved in the case of ZnO-coated dielectric barrier discharge. Relevant explanation is offered to describe its discharge physics.     

Study on the Microsecond Pulse Homogeneous Dielectric Barrier Discharges in Atmospheric Air and Its Influencing Factors

The homogeneous dielectric barrier discharge （DBD） in atmospheric air between two symmetric-columnar copper electrodes with epoxy plates as the dielectric barri...     

Operation Mode on Pulse Modulation in Atmospheric Radio Frequency Glow Discharges

The discharge operation regime of pulse modulated atmospheric radio frequency(RF) glow discharge in helium is investigated on the duty cycle and frequency of modulation pulses.The characteristics of radio frequency discharge burst in terms of breakdown voltage, alpha(α)-gamma(γ) mode transition voltage and current are demonstrated by the discharge current voltage characteristics. The minimum breakdown voltage of RF discharge burst was obtained at the duty cycle of 20% and frequency of 400 k Hz, respectively. The α-γ mode transition of RF discharge burst occurs at higher voltage and current by reducing the duty cycle and elevating the modulation frequency before the RF discharge burst evolving into the ignition phase, in which the RF discharge burst can operate stably in the γ mode. It proposes that the intensity and stability of RF discharge burst can be improved by manipulating the duty cycle and modulation frequency in pulse modulated atmospheric RF glow discharge.     

Deposition of Thin Titania Films by Dielectric Barrier Discharge at Atmospheric Pressure

A homogeneous atmospheric pressure dielectric barrier discharge is studied. It is in argon with small admixtures of titanium tetrachloride vapour and oxygen for the deposition of thin titania films on glass substrates. A special electrode configuration was applied in order to deposit the titania film uniformly. The sustaining voltage （6 kV to 12 kV）, current density （about 3 mA/cm^2） and total optical emission spectroscopy were monitored to characterize the discharge in the gap of 2 mm. Typical deposition rates ranged from approximately 30 nm/min to 120 nm/min. The film morphology was investigated by using scanning electron microscopy （SEM） and the composition was determined with an energy dispersive x-ray spectroscopy （EDS） analysis tool attached to the SEM. The crystal structure and phase composition of the films were studied by x-ray diffraction （XRD）. Several parameters such as the discharge power, the ratio of carrier gas to the precursor gas, the deposition time on the crystallization behavior, the deposition rate and the surface morphology of the titania film were extensively studied.     

Study of Atmospheric Pressure Abnormal Glow Discharge

Atmospheric pressure abnormal glow discharge （APAGD） was carried out simply with a transformer of 1 ： 500 driven by a alternating current with a frequency of 50 Hz. Typical stable discharge parameters, namely voltage of 400 V to 850 V and current of 60 mA to 110 mA were measured by oscillograph. Simulation of the discharge process suggested that the stable discharge was supported by the impedance from the secondary coil of the transformer, which offered a negative feedback to prevent the discharge from turning into an arc. An interpretation was given for the oscillogram of the sinuous discharge current and square voltage. Furthermore, the electron temperature and electron density averaged in the discharge channel of APAGD were estimated.     

Temporally-Resolved Emission Spectroscopic Diagnostics of the Atmospheric Pressure Glow Discharge in Helium

Temporally-resolved spectroscopic diagnostics of dielectric barrier discharges(DBDs) in atmospheric-pressure helium was carried out to study the discharge mechanism.Using an intensified charge-coupled device(ICCD) and a grating spectrometer,we obtained the emission spectra of homogeneous discharges and presented them in 3D graphs.We also studied the time variation of typical emissions from He,O and first negative bands of N+ 2.The results showed that the spectral lines do not develop synchronously as N+ 2(B2u+X2∑+g,0~0,λ=391.4 nm) and N∑+2(B2∑+u → X2∑+g,0~1,λ=427.8 nm) appear earlier and last for a longer time than He(33S1 → 23P1,λ=706.5 nm) and O(35P→35S,λ=777.4 nm).A certain number of He metastables produced in the initial stage of discharge.Even between adjacent pulses,the emissions from N∑+2 can still keep certain intensities while those from He and O extinguish.Since long-lifetime He metastables are produced and exist in the discharging space,it is the Penning ionization that keeps the long decay of N∑+2 emissions.     

Characteristics of RF Cold Plasma at Atmospheric Pressure

The characteristics of a stable discharge at atmospheric pressure is investigated. The plasma source consisted of two closely spaced parallel-plated perforated electrodes, driven by a radio frequency power to generate a uniform cold plasma in Helium at atmospheric pressure. Both alpha and gamma modes were clearly observed. The hollow cathode effects were found in the discharge. The influence of the dielectric barrier on the discharge was also investigated by utilizing a surface-anodized aluminium electrode as the anode.     

Simulation Study on the Self-Sustained Oscillations in DC Driven Glow Discharges at Atmospheric Pressure Under Different Gas Gaps

In this paper,a one-dimensional plasma fluid model is employed to study the selfsustained oscillations in DC-driven helium glow discharges at atmospheric pressure under different gas gaps.Our simulation results indicate that a harmonic current oscillation with tiny amplitude always occur at the onset of instability and transits into a relaxation one as the conductivity of the semiconductor is decreased.It is found that the dynamics of the oscillations are dependent on the gas gaps.The discharge can only exhibit a simple oscillation with unique amplitude and frequency at smaller gas gaps(2 mm) while it can exhibit a more complex oscillation with several different amplitudes and frequencies at larger gas gaps(2 mm).The discharge modes in these current oscillations have also been analyzed.     

Effects of Oxygen Concentration on Pulsed Dielectric Barrier Discharge in Helium-Oxygen Mixture at Atmospheric Pressure

In this work the effects of O_2 concentration on the pulsed dielectric barrier discharge in helium-oxygen mixture at atmospheric pressure have been numerically researched by using a one-dimensional fluid model in conjunction with the chosen key species and chemical reactions.The reliability of the used model has been examined by comparing the calculated discharge current with the reported experiments. The present work presents the following significant results. The dominative positive and negative particles are He_2~+ and O_2~-, respectively, the densities of the reactive oxygen species(ROS) get their maxima nearly at the central position of the gap, and the density of the ground state O is highest in the ROS. The increase of O_2 concentration results in increasingly weak discharge and the time lag of the ignition. For O_2 concentrations below 1.1%,the density of O is much higher than other species, the averaged dissipated power density presents an evident increase for small O_2 concentration and then the increase becomes weak. In particular,the total density of the reactive oxygen species reaches its maximums at the O_2 concentration of about 0.5%. This characteristic further convinces the experimental observation that the O_2 concentration of 0.5% is an optimal O_2/He ratio in the inactivation of bacteria and biomolecules when radiated by using the plasmas produced in a helium oxygen mixture.     

Exploration to generate atmospheric pressure glow discharge plasma in air

Atmospheric pressure glow discharge (APGD) plasma in air has high application value.In this paper,the methods of generating APGD plasma in air are discussed,and the characteristics of dielectric barrier discharge (DBD) in non-uniform electric field are studied.It makes sure that APGD in air is formed by DBD in alternating current electric field with using the absorbing electron capacity of electret materials to provide initial electrons and to end the discharge progress.Through designing electric field to form two-dimensional space varying electric field and three-dimensional space varying electric field,the development of electron avalanches in airgap is suppressed effectively and a large space of APGD plasma in air is generated.Further,through combining electrode structures,a large area of APGD plasma in air is generated.On the other hand,by using the method of increasing the density of initial electrons,millimeter-gap glow discharge in atmospheric pressure air is formed,and a maximum gap distance between electrodes is 8 ram.By using the APGD plasma surface treatment device composed of contact electrodes,the surface modification of high polymer materials such as aramid fiber and polyester are studied and good effect of modifications is obtained.The present paper provides references for the researchers of industrial applications of plasma.     

Characteristics of a Normal Glow Discharge Excited by DC Voltage in Atmospheric Pressure Air

Atmospheric pressure glow discharges were generated in an air gap between a needle cathode and a water anode. Through changing the ballast resistor and gas gap width between the electrodes, it has been found that the discharges are in normal glow regime judged from the currentvoltage characteristics and visualization of the discharges. Results indicate that the diameter of the positive column increases with increasing discharge current or increasing gap width. Optical emission spectroscopy is used to calculate the electron temperature and vibrational temperature. Both the electron temperature and the vibrational temperature increases with increasing discharge current or increasing gap width. Spatially resolved measurements show that the maxima of electron temperature and vibrational temperature appeared in the vicinity of the needle cathode.     

Degradation of Aniline Wastewater Using Dielectric Barrier Discharges at Atmospheric Pressure

Aniline is a toxic water pollutant detected in drinking water and surface water,and this chemical is harmful to both human and aquatic life.A dielectric barrier discharge(DBD)reactor was designed in this study to investigate the treatment of aniline in aqueous solution.Discharge characteristics were assessed by measuring voltage and current waveforms,capturing light emission images,and obtaining optical emission spectra.The effects of several parameters were analyzed,including treatment distance,discharge power,DBD treatment time,initial pH of aniline solutions,and addition of sodium carbonate and hydrogen peroxide to the treatment.Aniline degradation increased with increasing discharge power.Under the same conditions,higher degradation was obtained at a treatment distance of 0 mm than at other treatment distances.At a discharge power of 21.5 W,84.32%of aniline was removed after 10 min of DBD treatment.Initial pH significantly influenced aniline degradation.Adding a certain dosage of sodium carbonate and hydrogen peroxide to the wastewater can accelerate the degradation rate of aniline.Possible degradation pathways of aniline by DBD plasmas were proposed based on the analytical data of GC/MS and TOC.     

Surface Decontamination of Chemical Agent Surrogates Using an Atmospheric Pressure Air Flow Plasma Jet

An atmospheric pressure dielectric barrier discharge (DBD) plasma jet generator using air flow as the feedstock gas was applied to decontaminate the chemical agent surrogates on the surface of aluminum, stainless steel or iron plate painted with alkyd or PVC. The experimental results of material decontamination show that the residual chemical agent on the material is lower than the permissible value of the National Military Standard of China. In order to test the corrosion effect of the plasma jet on different material surfaces in the decontamination process, corrosion tests for the materials of polymethyl methacrylate, neoprene, polyvinyl chloride (PVC), polyethylene (PE), phenolic resin, iron plate painted with alkyd, stainless steel, aluminum, etc. were carried out, and relevant parameters were examined, including etiolation index, chromatism, loss of gloss, corrosion form, etc. The results show that the plasma jet is slightly corrosive for part of the materials, but their performances are not affected. A portable calculator, computer display, mainboard, circuit board of radiogram, and a hygrometer could work normally after being treated by the plasma jet.     

Electrical features of radio-frequency atmospheric pressure helium discharge with and without dielectric electrodes

A comparative study of radio-frequency atmospheric pressure glow discharge(rf APGD)generated in helium with and without dielectric electrodes to investigate the effect of electrodes insulation on electrical features of APGD is presented. In the α mode, both the rf APGDs remain volumetric, stable and uniform. In the γ mode, the APGD without dielectric electrodes shrinks into a constricted plasma column whereas APGD with dielectric electrodes remains stable and retains the same volume without plasma constriction even at higher densities of discharge current. A comparison of electrical features of both rf APGDs in normal and abnormal glow discharge regimes is presented. In both APGDs with and without dielectric electrodes,impedance measurements have been performed and compared with equivalent circuit models.The measured impedance data is found to be in good agreement with simulated data.