A homogeneous atmospheric pressure air plasma in a 10 mm gap based on a three-electrode configuration

Generation of atmospheric pressure homogeneous air plasma in a large gap(>4 mm)is a challenge.In this study,an atmospheric pressure homogeneous air plasma generated in a gap up to 10 mm is reported,which is based on a three-electrode configuration,where a high-voltage(HV)electrode and a middle electrode form a surface dielectric barrier discharge(S-DBD),and together with the ground electrode form the main volume discharge.High-speed photographs confirm that the discharge in the main gap is homogeneous.The gas temperature of the plasma estimated from the N_(2)(C^(3)∏_(u)-B^(3)∏_(g))(Δv=-2)emission is about 320 K,which is close to room temperature.A detailed analysis shows that the discharge ignited between the HV electrode and the middle electrode is serving as an electron source,and the electrons deposited on the dielectric plate are due to the S-DBD along with the applied voltage generating a driving force,which results in a high concentration of seed electrons in the main gap and induces the homogeneous plasma.Further analysis shows that the electric field in the main gap is only about18.45 k V·cm^(-1),which is much lower than the typical breakdown electric field of 30 k V·cm^(-1)for atmospheric pressure air discharge.

Ionization process and distinctive characteristic of atmospheric pressure cold plasma jet driven resonantly by microwave pulses

In the present study,a coaxial transmission line resonator is constructed,which is always capable of generating cold microwave plasma jet plumes in ambient air in spite of using argon,nitrogen,or even air,respectively.Although the different kinds of working gas induce the different discharge performance,their ionization processes all indicate that the ionization enhancement has taken place twice in each pulsed periods,and the electron densities measured by the method of microwave Rayleigh scattering are higher than the amplitude order of 10^(18)m^(-3).The tail region of plasma jets all contain a large number of active particles,like NO,O,emitted photons,etc,but without O_(3).The formation mechanism and the distinctive characteristics are attributed to the resonance excitation of the locally enhanced electric fields,the ionization wave propulsion,and the temporal and spatial distribution of different particles in the pulsed microwave plasma jets.The parameters of plasma jet could be modulated by adjusting microwave power,modulation pulse parameters(modulation frequency and duty ratio),gas type and its flow rate,according to the requirements of application scenarios.

On the green aurora emission of Ar atmospheric pressure plasma

The Ar atmospheric pressure plasma was found to be an excellent laboratorial source for green aurora emission.However,the characteristic and production mechanism of the green aurora emission of the Ar atmospheric pressure plasma are still not clear.In this work,an Ar plasma in a long glass tube which emits intense green aurora light is investigated.With the long glass tube,it can be concluded that the green aurora emission in the Ar plasma is not owing to the mixture of Ar plasma plume with the surrounding air.It is also found that the green aurora emission often appeared beyond the active electrode when the active electrode is placed at the downstream of the gas flow.The green emission disappears when the traces amount of O_(2) or N_(2)(about 0.05%–0.07%)is added to Ar.This is because the O_(2) molecules deactivate the upper state O(^(1)S),which results in the decrease of the green emission.On the other hand,when N_(2) is added,Ar metastable atoms are quenched by N_(2),which results in the decrease of O atoms and eventually leads to the decrease of the green emission intensity.The intensity of the green aurora emission increases when the driving voltage frequency increases from 1 to 10 k Hz.More importantly,it is found that the green aurora emission is not affected when a grounded stainless steel needle is in contact with the plasma plume.Thus,the green emission is not driven electrically.All these findings are helpful for the understanding of the physics and its applications of atmospheric pressure plasma jet in space physics,laser physics and other application areas.

Plasma-activated ethanol solution and it's decontamination effect

Ethanol solution as a disinfectant has been widely used in various fields.However,it has a significant bactericidal capability only when the volume fraction of ethanol is around 70%-75%.For such high concentration of ethanol solution,it has an irritating smell.When it is used for applications such as wound disinfection,it causes a stinging sensation.Low concentrations of ethanol solution are less irritating,but it is also less effective at killing bacteria.In this study,an idea for producing a green,efficient and less irritating disinfectant is proposed.It is based on a plasma-activated low-concentration ethanol solution(PAES).It is found that the plasma-activated 10% volume fraction of ethanol solution can kill more than seven orders of magnitude of Escherichia coli,while the untreated 10% volume fraction of ethanol solution has no bactericidal effect.Besides,the PAES's activity remains unchanged after being stored at -20℃ for three days.Further investigation shows that new compositions including peracetic acid,peroxynitrite,hydrogen peroxide and acetic acid are detected in the PAES,which together are playing the main role of the excellent and prolonged bactericidal effect.

A novel flexible plasma array for large-area uniform treatment of an irregular surface

In this work,we demonstrate a flexible multi-pin plasma generator with movable electrodes,which can change the shape of the electrode array freely,and then provide a large-area uniform plasma for the treatment of surfaces of different shapes.Discharge characteristics including U-I waveforms and discharge images and sterilization performance under three different electrode configurations(flat-flat,flat-curve,curve-curve)are investigated.Very similar results are acquired between the flat-flat configuration and the curve-curve configuration,which is much better than that under flat-curve configuration.This flexible multi-pin plasma generator offers a simple method to treat different irregularly shaped surfaces uniformly with a single device.Moreover,this device provides a foundation for developing a self-adaption large-scale uniform plasma generator by further introducing automatic adjustment of the position of every electrode driven by motors with discharge current feedback in the following study.Thus it will promote the applications of atmospheric-pressure cold plasmas significantly.

Experimental study on the influence of H_(2)O vapor and O_(2)for desulfurization and denitrification of the diesel exhaust in marine application by non‐thermal plasma

To improve the pollutant removal efficiency by non‐thermal plasma(NTP),the effect of H2O vapor and O_(2)on removal efficiency of NO and SO_(2)as well as the reduction of CO was investigated in H_(2)O/O_(2)/SO_(2)/NO/C_(3)H_(6)/CO_(2)/N_(2)system.To analyse the reaction mechanism,the effects of H2O vapor and O2 on the emission intensity of Oð3p^(5)P→3s^(5)S0_(2)Þand OHðA^(2)Σþ→X^(2)ΠÞwere investigated.The experimental results show that the increase of H_(2)O vapour(0%-9.8%)promotes the generation of OH radicals,increases the removal efficiency of NO from 18.9%to 57.3%,decreases the energy per NO removed from 449.0 to 148.1 eV/NO,increases SO_(2)removal efficiency from 4.8%to 35.3%,decreases the energy per SO_(2)removed decreases from 2784.0 to 582.9 eV/SO_(2),and reduces the generation of CO from 460 to 229 ppm.In the range of 0%-15%,the increase of O_(2)content promotes the formation of O radicals,increases the removal efficiency of NO from 8.5%to 54.2%,and decreases the energy per NO removed from 994.3 to 156.4 eV/NO.In the range of 0%-5%,increasing O_(2)content promotes SO_(2)removal efficiency from 8.7%to 24.8%,and decreases the energy per SO_(2)removed from 2485.7 to 876.6 eV/SO_(2).However,CO generation increases from 200 to 350 ppm with the increase of O_(2)in 0%-5%due to the incomplete oxidation of C_(3)H_(6).In the range of 5%-15%,the increase of O2 produces more O radicals,decreases the removal efficiency of SO_(2)from 24.8%to 23.5%and the generates of CO from 350 to 311 ppm.This study is helpful for improving the efficiency of NTP for desulfurization and denitrification,while reducing the by‐product CO.

On the chronological understanding of the homogeneous dielectric barrier discharge

Dielectric barrier discharges(DBD)are widely utilised non‐equilibrium atmospheric pressure plasmas with a diverse range of applications,such as material processing,surface treatment,light sources,pollution control,and medicine.Over the course of several decades,extensive research has been dedicated to the generation of homogeneous DBD(H‐DBD),focussing on understanding the transition from H‐DBD to filamentary DBD and exploring strategies to create and sustain H‐DBD.This paper first discusses the in-fluence of various parameters on DBD,including gas flow,dielectric material,surface conductivity,and mesh electrode.Secondly,a chronological literature review is presented,highlighting the development of H‐DBD and the associated understanding of its un-derlying mechanisms.This encompasses the generation of H‐DBD in helium,nitrogen,and air.Lastly,the paper provides a brief overview of multiple‐current‐pulse(MCP)behaviours in H‐DBD.The objective of this article is to provide a chronological un-derstanding of homogeneous dielectric barrier discharge(DBD).This understanding will aid in the design of new experiments aimed at better comprehending the mechanisms behind H‐DBD generation and ultimately assist in achieving large‐volume H‐DBD in an air environment.

Ionization waves in nanosecond pulsed atmospheric pressure plasma jets in argon

Typical ionization waves(IWs)are observed during the propagation of nanosecond pulsed atmospheric pressure plasma jets(APPJs)with argon flow,combining both the measurement of the axial electric field(Ez)and the temporal resolved optical imaging.The movement of the luminous APPJ head is recognized as the development of the IW front,accompanied with the propagation of the peak electric field.Especially,the radial distribution of Ez transits from a central peak profile before the IW front arrives to a hollow profile after the pass of the IW front.As for the temporal Ez trend,there is a mode transition from the single-peak feature under a low peak voltage to the double-peak feature under a higher peak voltage,indicating the existence of both primary and secondary IWs.The effect of target conditions on the IWs in APPJs is also explored.With a metal target,no residual electric field is observed before imposing the high-voltage pulses.However,with a dielectric target,the residual surface charges generate a back-ground electric field in the opposite direction to that during IW propagation.In the free APPJ(with no target),on the voltage falling edge,a negative electric field drives the electron flow to compensate the positive ions left over during the forward IW propa-gation on the voltage rising edge.

A non‐equal gap distance dielectric barrier discharge:Between cone‐shape and cylinder‐shape electrodes

A non‐equal gap distance dielectric barrier discharge(DBD)between cone‐shape and a cylinder‐shaped electrodes is reported.The DBD is driven by a nanosecond voltage pulse.When the pulse frequency is 500 Hz or lower,ladder‐shape plasma with multiple plasma layers is generated within the gap,with a distance increasing from 1 to 7 mm.According to high‐speed photographs of the plasma captured by an intensified charge‐coupled camera detector camera,the ladder‐shaped plasma is formed owing to propa-gation of ring‐shaped plasma from the region of the short‐gap distance to the region of long‐gap distance with regular variations in its propagation speed.The propagation speed drops to zero and lasts for about 20-30 ns at the region of each plasma layer,which results in bright plasma layers.The electric field of the plasma layer at the region of the different gap distance is evaluated according to the optical emission intensity ratio R_(391)/_(394)of N_(2)^(+)at 391 nm and N_(2) at 394 nm.The obtained electric field drops from 8.1 to 6.4 kV/mm when the plasma is propagated from regions of gap distance of 2-5 mm.When the pulse frequency is increased to 1 kHz or higher,the discharge changes into a filamentary mode and the multiple‐layer plasma disappears.

On the charged aerosols generated by atmospheric pressure non‐equilibrium plasma

Recently,charged aerosols are used widely in many applications,such as fog elimination,inactivation of airborne viruses and so on.Atmospheric pressure non‐equilibrium plasma(APNP)have become an efficient way to generate charged aerosols.Except the traditional pin‐plate or wire‐plate APNP sources,the new APNP sources such as large scale corona discharge system and air plasma jet array are introduced.These sources can increase the ion density in open air and generate adjustable large plasma plume,which are helpful in increasing the charging efficiency on aerosols.Although the interactions between plasma and aerosols is quite complicated,the preliminary study suggests that the diffusion charging dominates aerosols below 0.1μm,field charging dominates aerosols larger than 1μm,and the photo charging also contributes to aerosols charging.These reactive charged aerosols have shown their potential in the artificial rain enhancement,biomedicine,and ma-terial processing.Finally,challenges and opportunities for theoretical,experimental,and application research in related cross‐disciplinary areas are presented to stimulate critical discussions and collaborations in the future.

Numerical study on propagation mechanism and bio-medicine applications of plasma jet

In this study,the propagation mechanism of plasma jet and some bio-medical applications are investigated by two-dimensional numerical model.The key equations of plasma physics and chemistry related with plasma jet are firstly introduced.The simulation results suggest that the sheath forms near the dielectric tube inner surface,which results in the plasma channel to shrink in the radial direction inside the dielectric tube.The photoionisation of air species plays a crucial role in the transition from the localised discharge to streamer.The Penning ionisation increases the electric conductivity of the plasma channel and facilitates the formation of ring-shaped plasma bullet.For the plasma jet in the open air,electronimpact dissociation of H2O,electron neutralisation of H2O+,as well as dissociation of H2O by O(1D)are found to be the main reactions to produce OH.For micro plasma jet,the higher ignition voltage as the tube diameter decreased is attributed to the deceasing pre-avalanche electron density inside the tube.The simulation of plasma treatment of bacteria biofilm indicates that the mean free path of charged species inμm scale permitted the plasma penetrate into the cavity of the biofilm,and the structure of the biofilm results in the non-uniform distribution of ROS and RNS.The simulation of plasma treatment of cells immersed in liquid suggests that the HO2 generated by plasma aqueous species is the only way for superoxide to penetrate cell membrane and damage cytosolic fumarase B.