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.     

Novel Plasma Reactor with Rotary Helix Electrode Used in Coupling of CH4 at Atmospheric Pressure

At the ambient temperature and pressure a glow discharge plasma was used as a new approach for the coupling of methane with the newly-developed rotary multidentate helix electrode. In the presence of hydrogen, the effects of the input peak voltages and gas flow rates on methane conversion, C2 single pass yield and selectivity were investigated, and then the results were compared with those from the three-disc multidentate electrode. This demonstrated, on an experimental scale, that the rotary multidentate helix electrode was better than the multidentate three-disc electrode as there was little accumulation of coke, and the C2 yield per pass was 69.85% and C2 selectivity over 99.14% with 70.46% methane conversion at an input peak voltage of 2300 V and 60 ml/min gas flow rate.     

Numerical simulation of atmospheric pulse-modulated radio-frequency glow discharge ignition characteristics assisted by a pulsed discharge

A one-dimensional self-consistent fluid numerical model was developed to study the ignition characteristics of a pulse-modulated(PM) radio-frequency(RF) glow discharge in atmospheric helium assisted by a sub-microsecond voltage excited pulsed discharge. The temporal evolution of discharge current density and electron density during PM RF discharge burst was investigated to demonstrate the discharge ignition characteristics with or without the pulsed discharge. Under the assistance of pulsed discharge, the electron density in RF discharge burst reaches the magnitude of 1.87 × 10~(17) m~(-3) within 10 RF cycles, accompanied by the formation of sheath structure. It proposes that the pulsed discharge plays an important role in the ignition of PM RF discharge burst. Furthermore, the dynamics of PM RF glow discharge are demonstrated by the spatiotemporal evolution of the electron density with and without pulsed discharge. The spatial profiles of electron density, electron energy and electric field at specific time instants are given to explain the assistive role of the pulsed discharge on PM RF discharge ignition.     

Investigation of flame structure in plasma-assisted turbulent premixed methane-air flame

The mechanism of plasma-assisted combustion at increasing discharge voltage is investigated in detail at two distinctive system schemes (pretreatment of reactants and direct in situ discharge).OH-planar laser-induced fluorescence (PLIF) technique is used to diagnose the turbulent structure methane-air flame,and the experimental apparatus consists of dump burner,plasma-generating system,gas supply system and OH-PLIF system.Results have shown that the effect of pretreatment of reactants on flame can be categorized into three regimes:regime Ⅰ for voltage lower than 6.6 kV;regime Ⅱ for voltage between 6.6 and 11.1 kV;and regime Ⅲ for voltage between 11.1 and 12.5 kV.In regime Ⅰ,aerodynamic effect and slower oxidation of higher hydrocarbons generated around the inner electrode tip plays a dominate role,while in regime Ⅲ,the temperature rising effect will probably superimpose on the chemical effect and amplify it.For wire-cylinder dielectric barrier discharge reactor with spatially uneven electric field,the amount of radicals and hydrocarbons are decreased monotonically in radial direction which affects the flame shape.With regard to in situ plasma discharge in flames,the discharge pattern changes from streamer type to glow type.Compared with the case of reactants pretreatment,the flame propagates further in the upstream direction.In the discharge region,the OH intensity is highest for in situ plasma assisted combustion,indicating that the plasma energy is coupled into flame reaction zone.     

Synthesis of Poly （Butyl Methacrylate/Butyl Acrylate） Highly Absorptive Resin Using Glow Discharge Electrolysis

A highly absorptive resin poly （butyl methacrylate （BMA）-co-butyl acrylate （BA）） was prepared by emulsion polymerization, which was initiated by glow discharge electrolysis plasma （GDEP）. The effects of discharge voltage, discharge time, monomer ratio and the amounts of cross- linking agent were examined and discussed in detaiI. The chemical structure of the obtained resin was characterized by means of attenuated total reflectance Fourier transform infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy. The optimal conditions were ob- tained as： discharge voltage was 600 V, discharge time was 8 min, the ratios of BMA：BA being 2：1 for chloroform and 3：1 for xylene, with 2% N, N＇-methylenebis. Under optimal conditions, the oil absorbency was 70 g/g for chloroform and 46 g/g for xylene. Moreover, the absorptive dynamical behavior of the resulting resin was also investigated.     

Study on Glow Discharge Plasma Used in Polyester Surface Modification

To achieve an atmospheric pressure glow discharge(APGD)in air and modify the surface of polyester thread using plasma,the electric field distribution and discharge characteristics under different conditions were studied.We found that the region with a strong electric field,which was formed in a tiny gap between two electrodes constituting a line-line contact electrode structure,provided the initial electron for the entire discharge process.Thus,the discharge voltage was reduced.The dielectric barrier of the line-line contact electrodes can inhibit the generation of secondary electrons.Thus,the transient current pulse discharge was reduced significantly,and an APGD in air was achieved.We designed double layer line-line contact electrodes,which can generate the APGD on the surface of a material under treatment directly.A noticeable change in the surface morphology of polyester fiber was visualized with the aid of a scanning electron microscope(SEM).Two electrode structures–the multi-row line-line and double-helix line-line contact electrodes–were designed.A large area of the APGD plasma with flat and curved surfaces can be formed in air using these contact electrodes.This can improve the efficiency of surface treatment and is significant for the application of the APGD plasma in industries.     

The influence of grounded electrode positions on the evolution and characteristics of an atmospheric pressure argon plasma jet

An atmospheric pressure plasma jet (APPJ) in Ar with various grounded electrode arrangements is employed to investigate the effects of electrode arrangement on the characteristics of the APPJ.Electrical and optical methods are used to characterize the plasma properties.The discharge modes of the APPJ with respect to applied voltage are studied for grounded electrodepositions of 10 mm,40 mm and 80 mm,respectively,and the main discharge and plasma parameters are investigated.It is shown that an increase in the distance between the grounded electrode and high-voltage electrode results in a change in the discharge modes and discharge parameters.The discharges transit from having two discharge modes,dielectric barrier discharge (DBD) and jet,to having three,corona,DBD and jet,with increase in the distance from the grounded to the high-voltage electrodes.The maximum length of the APPJ reaches 3.8 cm at an applied voltage of 8 kV.The discharge power and transferred charges and spectral line intensities for species in the APPJ are influenced by the positions of the grounded electrode,while there is no obvious difference in the values of the electron excited temperature (EET) for the three grounded electrode positions.     

Three modes of a direct-current plasma jet operated underwater to degrade methylene blue

A direct-current air plasma jet operated underwater presents three stable modes including an intermittently-pulsed discharge, a periodically-pulsed discharge and a continuous discharge with increasing the power voltage. The three discharge modes have different appearances for the plasma plumes. Moreover, gap voltage-current characteristics indicate that the continuous discharge is in a normal glow regime. Spectral lines from reactive species(OH, N_2, N_2~+, H_α,and O) have been revealed in the emission spectrum of the plasma jet operated underwater.Spectral intensities emitted from OH radical and oxygen atom increase with increasing the power voltage or the gas flow rate, indicating that reactive species are abundant. These reactive species cause the degradation of the methylene blue dye in solution. Effects of the experimental parameters such as the power voltage, the gas flow rate and the treatment time are investigated on the degradation efficiency. Results indicate that the degradation efficiency increases with increasing the power voltage, the gas flow rate or the treatment time. Compared with degradation in the intermittently-pulsed mode or the periodically-pulsed one, it is more efficient in the continuous mode, reaching 98% after 21 min treatment.     

Various patterns in dielectric barrier glow discharges simulated by a dynamic model

In this paper, various patterns of dielectric barrier glow discharge simulated by a phenomenological dynamic model are reported. The model is constructed based on the basic dynamic process of dielectric barrier glow discharge and involves the voltage-transfer characteristic as well as the lateral inhibition effect. In simulations, different driving voltage profiles are applied to achieve one or two pulsed discharges in each half-period and the corresponding pattern evolution is investigated. The final stable patterns driven by a rectangular wave voltage organize simply as stationary striations or hexagonal lattices. The patterns driven by a multi-step wave appear to be much more complicated, with complementary striations, concentric rings and square superlattices observed. The evolutions of these patterns from the initial uniform state are described and it is found that the spreading of the inhibition effect plays a key role in these evolutions. The numerical simulations in the present work are in excellent accordance with previous experiments and fluid modeling. This dynamic model proves to be a convenient and promising approach to reproducing different pattern structures and pattern evolutions in dielectric barrier glow discharge systems.     

Planar magnetron glow discharge on copper — The Thornton relation revisited

Among the empirical and semi-empirical relations linking discharge current I and the absolute value of cathode voltage V in magnetron-assisted abnormal glow discharges, the “Thornton law” has been widely used. In the literature the model parameters were referred as depending on several characteristics as target material, discharge gas, discharge pressure, geometry and magnetic configuration. However that dependence is not normally shown. In this work, experimental results are presented that were obtained for Ar sputtering of copper target on a planar magnetron cathode of our own design and construction. The Thornton relation fits quite well to data. A change in curve behavior which is independent of the pressure, is reported at about 400 V. The variation of the model parameters with the pressure, is studied systematically. The results are discussed and physical interpretations are suggested.     

Temporal evolution of atmospheric cascade glow discharge with pulsed discharge and radio frequency discharge

Atmospheric cascade discharges with pulsed discharge and radio frequency(RF)discharge were experimentally investigated by the temporal evolution of discharge spatial profile and intensity.The indium tin oxide(ITO)coated glass was employed as the transparent electrode to capture the discharge distribution above the electrode surface.It is demonstrated that in the pulsed discharge with dielectric barrier,the first discharge at the rising edge of pulse voltage is uniformly ignited and then forms an expanding plasma ring on the ITO electrode surface,which shrinks to the same diameter as that of bare stainless steel electrode with the generation of second discharge at the falling edge of pulse voltage.The discharge profiles along the electrode surface and discharge gap of the successive RF discharge are dependent on the intensity and spatial distribution of residual plasma species generated by the pulsed discharge,which is determined by the time interval between the pulsed discharge and RF discharge.It is demonstrated that the residual plasma species before the RF discharge ignition help to achieve the stable operation of RF discharge with elevated intensity.     

A low power 50 Hz argon plasma for surface modification of polytetrafluoroethylene

The characteristics of a low power 50 Hz argon plasma for surface treatment of polytetrafluoroethylene (PTFE) film is presented in this article. The current–voltage behavior of the discharge and time-varying intensity of the discharge showed that a DC glow discharge was generated in reversed polarity at every half-cycle. At discharge power between 0.5 and 1 W, the measured electron temperature and density were 2–3 eV and ∼10⁸ cm⁻³, respectively. The optical emission spectrum of the argon plasma showed presence of some 'impurity species' such as OH, N₂ and H, which presumably originated from the residual air in the discharge chamber. On exposure of PTFE films to the argon glow plasma at pressure 120 Pa and discharge power 0.5 to 1 W, the water contact angle reduced by 4% to 20% from the original 114° at pristine condition, which confirms improvement of its surface wettability. The increase in wettability was attributed to incorporation of oxygen-containing functional groups on the treated surface and concomitant reduction in fluorine as revealed by the XPS analysis and increase in surface roughness analyzed from the atomic force micrographs. Ageing upon storage in ambient air showed retention of the induced increase in surface wettability.     

Generation scenarios of anodic structures and experimental realization of turbulence in unmagnetized plasma

In the present work, we report development of a DC glow discharge plasma(GDP) set-up to study controlled evolution of anodic structures having distinctive geometry, size and layers,generated in front of a positively biased electrode, submerged in unmagnetized plasma. For such an anodic structure, we have also investigated the condition under which the turbulence is triggered. Characteristic of these structures, generated in front of a positively biased electrode,depends on multiple parameters such as the ratio of anode to cathode size, electrode separation,gas pressure, biasing configuration such as anode bias, cathode bias and grounding schemes. We attempted to classify different anodic structures observed experimentally, as anode glow, fireball,anode spot, double layer and multiple double layers(MDLs) based on its physical characteristics.Among these structures the present investigation is focused on MDLs. The number of layers,observed in MDLs varied from as high as six to as low as zero, by controlling the operating discharge parameters, externally. Diagnostics were carried out using Langmuir probe. The analysis of floating potential fluctuations corresponds to a multiple anodic structure showed emergence of turbulence, at its critical stage, satisfying condition for self-organized criticality(SOC). This was identified with three slopes observed in the power spectrum, resembling the sand-pile model. Though, the GDP is completely different from that of the magnetically confined plasma, the nature of turbulence observed with SOC, is very similar to that observed in the scrape of layer of fusion devices. Therefore, the present investigation could provide new approach to study turbulence of similar nature, under an experimental condition that is free from the complexities of complicated field geometries used in confinement devices.     

An Experimental Study on Atmospheric Pressure Glow Discharge in Different Gases

Usually,the electrical breakdown of dielectric barrier discharge(DBD) at atmospheric pressure leads to a filamentary non-homogeneous discharge,However,it is also possible to obtain a diffuse DBD in homogeneous form,called atmospheric pressure glow discharge(APGD).We obtained a uniform APGD in helium and in the mixture of argon with alcohol,and studied the electrical characteristics of helium APGD.It if found that the relationship between discharge current and source frequency is different depending on the difference in gas gap when the applied voltage is kept constant.The discharge current shows an increasing trend with the increased frequency when gas gap is 0.8cm ,but the discharge current tends to decrease with the increased frequency when the gas gap increases.The discharge current always increases with the increased applied voltage when the source frequency is kept constant.We also observed a glow-like discharge in nitrogen at atmospheric pressure.     

Design,manufacture and testing of the glow discharge electrodes for Wendelstein 7-X

The electrodes for the Wendelstein 7-X glow discharge system have been designed, tested and manufactured. The compact design relies on a cooled housing, integrated into the first wall cooling system, and a calotte-shaped graphite anode. The new mounting concept avoids the need of active cooling of the anode due to an improved thermal conduction. Comprehensive tests of a prototype electrode had been carried out in laboratory and in the ASDEX Upgrade Tokamak during two operation campaigns. The electrode showed excellent and reliable long-time discharge behavior and fulfilled all the requirements regarding temperature limits and maintainability resulting from the steady-state operation of W7-X.     

Non-Thermal Equilibrium Atmospheric Pressure Glow-Like Discharge Plasma Jet

Non-thermal equilibrium atmospheric pressure plasma jet (APPJ) is a cold plasma source that promises various innovative applications,and the uniform APPJ is more favored.Glow discharge is one of the most effective methods to obtain the uniform discharge.Compared with the glow dielectric barrier discharge (DBD) in atmospheric pressure,pure helium APPJ shows partial characteristics of both the glow discharge and the streamer.In this paper,considering the influence of the Penning effect,the electrical and optical properties of He APPJ and Ar/NH3 APPJ were researched.A word "Glow-like APPJ" is used to characterize the uniformity of APPJ,and it was obtained that the basic characteristics of the glow-like APPJ are driven by the kHz AC high voltage.The results can provide a support for generating uniform APPJ,and lay a foundation for its applications.     

Analysis of Energetic Species Caused by Contact Glow Discharge Electrolysis in Aqueous Solution

Contact glow discharge electrolysis is a non-Faradaic electrochemical process with an abnormal relationship between the current and voltage. Hydroxyl radicals, hydrogen radicals and hydrogen peroxide can be produced under the glow discharge, which are often used to degrade organic contaminants in aqueous solution. In this study, with 4-nitrophenol taken as an example of contaminants and tert-butanol as a scavenger of hydroxyl radicals, the role of energetic species in degrading organic compounds was examined in detail. Moreover, the effects of the applied voltage, solution conductivity and pH on the formation of three energetic species were also observed. The formation rate constants of the three energetic species were calculated based on the experimental data.     

1d3v PIC/MCC simulation of dielectric barrier discharge dynamics in hydrogen sulfide

In this study, we computationally examined the dynamics of dielectric barrier discharge in hydrogen sulfide. The simulations were performed with a 1d3v particle-in-cell/Monte Carlo collision model in which a parallel-plate electrode geometry with dielectrics was used. Particle recombination process is represented in the model. The discharge mode was found to be initially Townsend discharge developing from the cathode to the anode, and at the peak of the current, a more stable glow discharge develops from the anode to the cathode. A higher applied voltage results in sufficient secondary electrons to trigger a second current peak, and then the current amplitude increases. As the frequency is increased, it leads to the advance of the phase and an increase in the amplitude of the current peak. A higher dielectric permittivity also makes the discharge occur earlier and more violently in the gap.     

Influence of the Transverse Field Component on the Edge Efect in a Short-Gap Discharge

In a general plane-parallel electrode system,the edge of the electrode will undermine the uniformity of the dielectric barrier discharge(DBD)because of the influence of the distorted electrical field.In this paper,the influence of the non-uniform electrical field on the edge efect of DBDs in a short-gap is investigated.We present some of the experimental results of DBDs produced by three kinds of convex-spherical electrodes.The results show that there is a dark area(the homogeneous discharge)in the central region of the electrode and a bright halo(the filamentary discharge)in the outer peripheral region,and the radius of the dark region is determined by the electrode geometry.The calculated results of the transverse(radial)field component distribution on the surface of the electrodes show that the edge efect does not come from the electrode edge,but the transverse field.The discharge has enough space to be fully developed and then format the filamentary discharge in the outer peripheral region because the streamer of the filamentary discharge is driven to move along the direction of the longer path by the transverse field.Thus,the homogeneous discharge(the Townsend DBD or a glow DBD)could not be produced in this area.     

Degradation of Microcystin-LR by Gas-Liquid Interfacial Discharge Plasma

In this study, we report on the degradation of microcystin-LR （MC-LR） by gas- liquid interracial discharge plasma. The influences of operation parameters such as average input voltage, electrode distance and gas flow rate are investigated. Experimental results indicate that the input voltage and gas flow rate have positive influences on MC-LR degradation, while the electrode distance has a negative one. After 6 min discharge with 25 kV average input voltage and 60 L/h air aerati by discharge both in on, the degradation rate of MC-LR achieves 75.3%. distilled water and MC-LR solution are measured H202 and 03 generated Moreover, an emission spectroscopy is used as an indicator of the processes that take place on the gas-liquid boundary and inside plasma. Varied types of radicals （O, .OH, CO, 03, etc.） are proved to be present in the gas phase during gas-liquid interfacial discharge.