This article provides a short review on the importance of the detailed analysis of a Langmuir probe I-V trace in a multi-Maxwellian plasma,and discuss proper procedures analyzing Langmuir probe I-V traces in bi-Maxwel...This article provides a short review on the importance of the detailed analysis of a Langmuir probe I-V trace in a multi-Maxwellian plasma,and discuss proper procedures analyzing Langmuir probe I-V traces in bi-Maxwellian and triple-Maxwellian Electron Energy Distribution Function(EEDF)plasmas.Discus⁃sion and demonstration of procedures include the treatment of the ion saturation current,electron saturation cur⁃rent,space-charge effects on the I-V trace,and most importantly how to properly isolate and fit for each electron group present in an I-V trace reflecting a mult-Maxwellian EEDF,as well as how having a multi-Maxwellian EEDF affects the procedures of treating the ion and electron saturation currents.Shortcomings of common improp⁃er procedures are discussed and demonstrated with simulated I-V traces to show how these procedures gives false measurements.展开更多
Plasma-assisted combustion technology has been a hot spot in aero-engines andscramjet-engines.The electron density is a key discharge parameter related to the active-particledensity.The latter has been considered play...Plasma-assisted combustion technology has been a hot spot in aero-engines andscramjet-engines.The electron density is a key discharge parameter related to the active-particledensity.The latter has been considered playing an important role in the above applications bythe kinetic effect.In this work,an atmospheric pressure air plasma collisional-radiative model con-sidering the excited states of atomic nitrogen and oxygen is built based on previous widely kineticinvestigations of molecules and radicals,as well as their excited states.The excited states,especiallythe atomic nitrogen and oxygen states were less investigated in previous works.The emission inten-sity distributions from the model have a good agreement with those measured in the glide arcplasma with two discharge modes,as well as the microwave plasma.Based on the kinetics of molec-ular and atomic emitting states,the line-ratio method is presented to determine the electron density.The N_(2)(337 nm)/O(844 nm)and N_(2)(337 nm)/NO(γ)line ratios are used for the glide arc plasma andmicrowave plasma torch,respectively.Besides,the kinetics of the excited states involved with twoline-ratios are also investigated in the two types of discharges.Combined with the atmospheric pres-sure actinometry method,the kinetic effect of the plasma-assisted combustion can be revealed quan-titatively in the future.展开更多
We study the Rayleigh-Taylor instability(RTI)of electrostatic plane wave perturbations in compressible relativistic magnetoplasma fluids with thermal ions under gravity in three different cases of when(ⅰ)electrons ar...We study the Rayleigh-Taylor instability(RTI)of electrostatic plane wave perturbations in compressible relativistic magnetoplasma fluids with thermal ions under gravity in three different cases of when(ⅰ)electrons are in isothermal equilibrium,i.e.,classical or nondegenerate,(ⅱ)electrons are fully degenerate(with Te=0),and(ⅲ)electrons are partially degenerate or have finite temperature degeneracy(with Te≠0).While in the cases of(ⅰ)and(ⅲ),we focus on the regimes where the particle's thermal energy is more or less than the rest mass energy,i.e.,βe≡kBTe/mec2<1or>1,the case(ⅱ)considers from weakly to ultra-relativistic degenerate regimes.A general expression of the growth rate of instability is obtained and analyzed in the three different cases relevant to laboratory and astrophysical plasmas,which generalize and advance the previous theory on RTI.展开更多
Recent experiments at the National Ignition Facility and theoretical modeling suggest that side stimulated Raman scattering(SSRS)instability could reduce laser–plasma coupling and generate considerable fluxes of supr...Recent experiments at the National Ignition Facility and theoretical modeling suggest that side stimulated Raman scattering(SSRS)instability could reduce laser–plasma coupling and generate considerable fluxes of suprathermal hot electrons under interaction conditions envisaged for direct-drive schemes for inertial confinement fusion.Nonetheless,SSRS remains to date one of the least understood parametric instabilities.Here,we report the first angularly and spectrally resolved measurements of scattered light at laser intensities relevant for the shock ignition scheme(I×10^(16)W/cm^(2)),showing significant SSRS growth in the direction perpendicular to the laser polarization.Modification of the focal spot shape and orientation,obtained by using two different random phase plates,and of the density gradient of the plasma,by utilizing exploding foil targets of different thicknesses,clearly reveals a different dependence of backward SRS(BSRS)and SSRS on experimental parameters.While convective BSRS scales with plasma density scale length,as expected by linear theory,the growth of SSRS depends on the spot extension in the direction perpendicular to laser polarization.Our analysis therefore demonstrates that under current experimental conditions,with density scale lengths L_(n)≈60–120μm and spot sizes FWHM≈40–100μm,SSRS is limited by laser beam size rather than by the density scale length of the plasma.展开更多
We employ the Green–Kubo(G-K)and Einstein relations to estimate the self-diffusion coefficients(denoted as D_(G)and D_(E),respectively)in two-dimensional(2D)strongly coupled dusty plasmas(SC-DPs)via equilibrium molec...We employ the Green–Kubo(G-K)and Einstein relations to estimate the self-diffusion coefficients(denoted as D_(G)and D_(E),respectively)in two-dimensional(2D)strongly coupled dusty plasmas(SC-DPs)via equilibrium molecular dynamics(EMD)simulations.D_(G)and D_(E)are computed for a broad domain of screening length(κ)and coupling parameters(Γ)along with different system sizes.It is observed that both D_(G)and D_(E)decrease linearly with increasing Г in warm liquid states and increase with increasingκ.In cold liquid states,the Einstein relation accurately predicts D_(E)in 2D SC-DPs because diffusion motion is close to normal diffusion,but the G-K relation provides overestimations of D_(G),because VACF indicates anomalous diffusion;thus,D_(G)is not accurate.Our new simulation outcomes reveal that D_(G)and D_(E)remain independent of system sizes.Furthermore,our investigations demonstrate that at higher temperatures,D_(G)and D_(E)converge,suggesting diffusion motion close to normal diffusion,while at lower temperatures,these two values diverge.We find reasonable agreement by comparing current and existing numerical,theoretical and experimental data.Moreover,when normalizing diffusion coefficients by the Einstein frequency and testing against the universal temperature scaling law,D_(G)deviates from theoretical curves at low temperatures and κ,whereas D_(E)only disagrees with theory at very smallκ(■0.10).These findings provide valuable insight into diagnosing dust component parameters within 2D DP systems and contribute to the broader understanding of diffusion processes in DP environments.展开更多
Atmospheric-pressure argon plasmas have received increasing attention due to their high potential in many industrial and biomedical applications. In this paper, a 1-D fluid model is used for studying the particle dens...Atmospheric-pressure argon plasmas have received increasing attention due to their high potential in many industrial and biomedical applications. In this paper, a 1-D fluid model is used for studying the particle density characteristics of the argon plasmas generated by the pulsed dielectric barrier discharges. The temporal evolutions of the axial particle density distributions are illustrated, and the influences of changing the main discharge conditions on the averaged particle densities are researched by independently varying the various discharge conditions. The calculation results show that the electron density and the ion density reach two peaks near the momentary cathodes during the rising and the falling edges of the pulsed voltage. Compared with the charged particle densities, the densities of the resonance state atom Arr and the metastable state atom Arm have more uniform axial distributions, reach higher maximums and decay more slowly. During the platform of the pulsed voltage and the time interval between the pulses, the densities of the excited state atom Ar＊ are far lower than those of the Arr or the Arm. The averaged particle densities of the different considered particles increase with the increases of the amplitude and the frequency of the pulsed voltage. Narrowing the discharge gap and increasing the relative dielectric constant of the dielectric also contribute to the increase of the averaged particle densities. The effects of reducing the discharge gap distance on the neutral particle densities are more significant than the influences on the charged particle densities.展开更多
Cold atmospheric-pressure He +N2 and He +O2 plasmas are chosen as the representatives for electropositive andelectronegative plasmas, of which the discharge characteristics are studied and then compared to each other ...Cold atmospheric-pressure He +N2 and He +O2 plasmas are chosen as the representatives for electropositive andelectronegative plasmas, of which the discharge characteristics are studied and then compared to each other by fluidmodels. As the increase of the impurity (N2 or O2) fraction from 0 to 10%, for He + N2 plasmas the electron density andion density increase, the spatiotemporal distributions of electron density, ion density, electron temperature and electrongeneration rate change a little. On contrast, for He + O2 plasmas the electron density decreases, the ion density firstincreases and then decreases, the electron temperature increases in the bulk region, but decreases in the sheath region,and the plasmas transform from g mode to α mode as the significant change of electron generation rate distributions.Larger electric field is needed in the bulk region to sustain the electronegative plasma, so the electrical characteristics ofHe + O2 plasmas transform form capacitive to resistive with increasing O2 fraction. Meanwhile, the ion-coupling powerincreases dramatically, which can be estimated by a formula based on the electronegativity. A new criterion fordetermining the sheath boundary, |∇E| = 5 kV/cm2, is put forward, which is found suitable for both the electropositive andelectronegative plasmas.展开更多
Membrane surfaces modified with poly（N-vinyl-2-pyrrolidone） （PNVP） can be endowed with hydrophilicity, biocompatibility and functionality. In this work, atmospheric pressure dielectric barrier discharge plasma gra...Membrane surfaces modified with poly（N-vinyl-2-pyrrolidone） （PNVP） can be endowed with hydrophilicity, biocompatibility and functionality. In this work, atmospheric pressure dielectric barrier discharge plasma graft polymerization of N-vinyl-2-pyrrolidone （NVP） onto polypropylene （PP） microporous membrane surface was studied. The experimental results reveal that plasma treatment conditions, such as discharge power, treatment time and adsorbed NVP amount, have remarkable effects on the grafting degree of NVP. Structural and morphological changes on the membrane surfaces were characterized by attenuated total reflection-Fourier transform infrared spectroscopy （FT-IR/ATR）, X-ray photoelectron spectroscope （XPS） and field emission scanning electron microscopy （FE-SEM）. Water contact angles of the membrane surfaces were also measured by the sessile drop method. Water contact angles on the membrane surfaces decrease with the increase of NVP grafting degree, which indicates an enhanced hydrophilicity for the modified membranes. The effects of grafting degrees on pure water fluxes were also measured. It is shown that pure water fluxes increase with grafting degree firstly and then decrease adversely. Finally, filtration of bovine serum albumin （BSA） solution and platelets adhesion of the PNVP modified membranes show good protein resistance and potential biocompatibility due to the enhancement of surface hydrophilicity.展开更多
The key plasma parameters under different discharge modes, such as heavy-particle and electron temperatures, electron number density, and nonequilibrium volume of plasmas, play important roles in various applications ...The key plasma parameters under different discharge modes, such as heavy-particle and electron temperatures, electron number density, and nonequilibrium volume of plasmas, play important roles in various applications of gas discharge plasmas. In this study, a self-consistent two-dimensional nonequilibrium fluid model coupled with an external circuit model is established to reveal the mechanisms related to the discharge modes, including the normal glow, abnormal glow,arc, and glow-to-arc transition modes, with an atmospheric-pressure direct-current(DC) argon discharge as a model plasma system. The modeling results show that, under different discharge modes, the most significant difference between the preceding four discharge modes lies in the current and energy transfer processes on the cathode side. On one hand, the current to the cathode surface is mainly delivered by the ions coming from the plasma column under the glow discharge mode due to the low temperature of the solid cathode, whereas the thermionic and secondary electrons emitted from the hot cathode surface play a very important role under the arc mode with a higher cathode surface temperature and higher ion flux toward the cathode. On the other hand, the energy transfer channel on the cathode side changes from mainly heating the solid cathode under the glow mode to simultaneously heating both the solid cathode and plasma column under the arc mode with an increase in the discharge current. Consequently, the power density in the cathode sheath(P_c) was used as a key parameter for judging different discharge modes, and the range of(0.28–1.2) × 10^(12) W m^(-3) was determined as a critical window of P_c corresponding to the glow-to-arc-mode transition for the atmospheric-pressure DC argon discharge, which was also verified by comparison with the experimental results in this study and the data in the previous literature.展开更多
Cold plasma generated by dielectric barrier discharge （DBD） at atmospheric pressure was adopted for preparation of commercial TiO2 Degussa P25 supported Au catalysts （Au/P25- P） with the assistance of the depositi...Cold plasma generated by dielectric barrier discharge （DBD） at atmospheric pressure was adopted for preparation of commercial TiO2 Degussa P25 supported Au catalysts （Au/P25- P） with the assistance of the deposition-precipitation procedure. The influences of the plasma reduction time and calcination on the performance of the Au/P25-P catalysts were investigated. CO oxidation was performed to investigate the catalytic activity of the Au/P25 catalysts. The results show that DBD cold plasma for the fabrication of Au/P25-P catalysts is a fast process, and Au/P25-P （4 min） exhibited the highest CO oxidation activity due to the complete reduction of Au compounds and less consumption of oxygen vacancies. In order to form more oxygen vacancies active species, Au/P25-P was calcined to obtain Au/P25-PC catalysts. Interestingly, Au/P25- PC exhibited the highest activity for CO oxidation among the Au/P25 samples. The results of transmission electron microscopy （TEM） indicated that the smaller size and high distribution of Au nanoparticles are the mean reasons for a high performance of Au/P25-PC. Atmospheric- pressure DBD cold plasma was proved to be of great efficiency in preparing high performance supported Au catalysts.展开更多
TiO2 decorated with partially crystallized Pd nanoparticles （Pd/TiO2-P） was successfully prepared by atmospheric-pressure dielectric barrier discharge cold plasma. The XRD and XPS analyses proved that Pd ions were r...TiO2 decorated with partially crystallized Pd nanoparticles （Pd/TiO2-P） was successfully prepared by atmospheric-pressure dielectric barrier discharge cold plasma. The XRD and XPS analyses proved that Pd ions were reduced to partially crystallized metallic Pd nanoparticles in Pd/TiO2-P. The XPS spectra also indicated that an enhanced metal-support interaction was formed due to the existence of partially crystallized Pd nanoparticles with lower coordination number in Pd/TiO2-P. Photocatalytic activity of Pd/TiO2-P was much higher than that of TiO2 samples decorated with well crystallized Pd nanoparticles.展开更多
To deposit TiO2 films through plasma CVD, the partial pressure ratio of O2 to TIC14 should be greater than the stoichiometric ratio （PO2/PTiCl4 〉 1）. However, this may lead to the formation of powder instead of fil...To deposit TiO2 films through plasma CVD, the partial pressure ratio of O2 to TIC14 should be greater than the stoichiometric ratio （PO2/PTiCl4 〉 1）. However, this may lead to the formation of powder instead of film on the substrate when using volume dielectric barrier discharge （volume-DBD） at atmospheric pressure. In this study, by adding N2 into the working gas Ar, TiO2 photocatalytic films were successfully fabricated in the presence of excess O2 （PO2/PTiC14 = 2.6） by using a wire-to-plate atmospheric-pressure volume-DBD. The tuning effect of N2 on the deposition of TiO2 film was studied in detail. The results showed that by increasing the N2 content, the deposition rate and particle size of the TiO2 film were reduced, and its photocatalytic activity was enhanced. The tuning mechanism of N2 is further discussed.展开更多
A 2D axial symmetry fluid model is applied to study the features of an atmospheric-pressure argon(Ar) plasma jet propagating into ambient nitrogen(N_(2)) driven by a pulsed voltage,emphasizing the influence of gas vel...A 2D axial symmetry fluid model is applied to study the features of an atmospheric-pressure argon(Ar) plasma jet propagating into ambient nitrogen(N_(2)) driven by a pulsed voltage,emphasizing the influence of gas velocity on the dynamic characteristics of the jet. The results show that the Ar jet exhibits a cylindrical-shaped channel and the jet channel gradually shrinks with the increase in propagation length. The jet propagation velocity varies with time. Inside the dielectric tube, the plasma jet accelerates propagation and reaches its maximum value near the nozzle. Exiting the tube, its velocity quickly decreases and when approaching the metal plane,the decrease in jet velocity slows down. The increase in gas speed results in the variation of jet spatial distribution. The electron density presents a solid structure at lower gas flow speeds,whereas an annular structure can be observed under the higher gas flow velocity in the ionization head. The jet length increases with the flow velocity. However, when the flow velocity exceeds a critical value, the increase in the rate of the plasma jet length slows down. In addition, the gas velocity effect on the generation and transport of the reactive particles is also studied and discussed.展开更多
In order to form an atmospheric-pressure plasma jet without airflow, a needle–ring electrode structure is proposed in this paper. When heteropolar potentials are applied to a needle and a ring, a marked electric fiel...In order to form an atmospheric-pressure plasma jet without airflow, a needle–ring electrode structure is proposed in this paper. When heteropolar potentials are applied to a needle and a ring, a marked electric field strength enhancement around the needle’s pointed end has been found. When the same potential is applied to both the needle and the ring, the lateral electric field strength for the needle can be weakened. By using the above two methods, an increase of the difference between the pointed end electric field strength and the lateral one is achieved and stable plasma jets are formed. A symmetrical space electric field distribution is established at the pointed end of the needles when several sets of heteropolar needle–ring electrodes are uniformly arranged, which is conducive to forming a uniform array plasma jet. Under DC discharge conditions, a safe and stable plasma jet of high density and an array plasma jet are successfully achieved.展开更多
In this work,the super-hydrophobic(SH)surface was prepared through chemical vapor deposition process by an argon atmospheric pressure plasma jet source with HMDSN(hexamethyldisilazane)as the polymerization precursor.P...In this work,the super-hydrophobic(SH)surface was prepared through chemical vapor deposition process by an argon atmospheric pressure plasma jet source with HMDSN(hexamethyldisilazane)as the polymerization precursor.Plasma synthesized organosilicon(SiOxCyHz)thin films with water contact angle over 160°and sliding angle below 5°,were able to be achieved.FTIR and XPS analysis indicates a large number of hydrocarbon compositions were polymerized in the thin films enduing the latter very-low surface free energy.SEM shows the SH films display micro-nanostructure and with high degree of averaged surface roughness 190 nm evaluated by AFM analysis.From experiments under controlled low-temperature and moisture conditions,the prepared SH surface exhibits good anti-icing effects.Significantly prolonging freezing time was achievable on the SH thin films for both static and sliding water droplets.This investigation demonstrates the anti-icing potentials of SH surface prepared through low-cost simple atmospheric-pressure plasma polymerization process.展开更多
The sterilizing effect of the non-equilibrium atmospheric pressure plasma jet by applying it to the Bacillus subtilis spores is invesigated. A stable glow discharge in argon or helium gas fed with active gas （oxygen...The sterilizing effect of the non-equilibrium atmospheric pressure plasma jet by applying it to the Bacillus subtilis spores is invesigated. A stable glow discharge in argon or helium gas fed with active gas （oxygen）, was generated in the coaxial cylindrical reactor powered by the radio-frequency power supply at atmospheric pressure. The experimental results indicated that the efficiency of killing spores by making use of an Ar/O2 plasma jet was much better than with a He/O2 plasma jet. The decimal reduction value of Ar/O2 and He/O2 plasma jets under the same experimental conditions was 4.5 seconds and 125 seconds, respectively. It was found that there exists an optimum oxygen concentration for a certain input power, at which the sterilization efficiency reaches a maximum value. It is believed that the oxygen radicals are generated most efficiently under this optimum condition.展开更多
An atmospheric-pressure air plasma is employed to treat C6 glioma cells in vitro. To elucidate on the mechanism causing cell death and role of reactive species （RS） in the medium produced by the plasma, the concentr...An atmospheric-pressure air plasma is employed to treat C6 glioma cells in vitro. To elucidate on the mechanism causing cell death and role of reactive species （RS） in the medium produced by the plasma, the concentration of the long-lived RS such as hydrogen peroxide, nitrate, and ozone in the plasma-treated liquid （phosphate-buffered saline solution） is measured. When vitamin C is added to the medium as a ROS quencher, the viability of C6 glioma cells after the plasma treatment is different from that without vitamin C. The results demonstrate that reactive oxygen species （ROS） such as H2O2, and O3 constitute the main factors for inactivation of C6 glioma cells and the reactive nitrogen species （RNS） may only play an auxiliary role in cell death.展开更多
The quantum hydrodynamic model for electrons and ions and the generalized hydrodynamic model for the strongly coupled dust particles are proposed in the strongly coupled quantum dusty plasma, where the combined quantu...The quantum hydrodynamic model for electrons and ions and the generalized hydrodynamic model for the strongly coupled dust particles are proposed in the strongly coupled quantum dusty plasma, where the combined quantum effects of quantum diffraction, quantum statistic pressure,as well as electron exchange and correlation effects are all considered in the quantum hydrodynamic model. The shear and bulk viscosity effects are included in the viscoelastic relaxation, which leads to the decay of the dust-ion-acoustic waves. The approximate time-dependent solitary solution is obtained by the momentum conservation law in the presence of viscosity.展开更多
Objective： A direct-current, cold atmospheric-pressure air plasma microjet （PMJ） was performed to inactivate Staphylococcus aureus （S. aureus） and Enterococcusfaecalis （E. faecalis） in air. The process of steri...Objective： A direct-current, cold atmospheric-pressure air plasma microjet （PMJ） was performed to inactivate Staphylococcus aureus （S. aureus） and Enterococcusfaecalis （E. faecalis） in air. The process of sterilization and morphology of bacteria was observed. We wish to know the possible inactivation mechanisms of PMJ and explore a potential application in dental and other temperature sensitive treatment. Methods： In this study, we employed a direct current, atmospheric pressure, cold air PMJ to inactivate bacterias. Scanning electron microscopy was employed to evaluate the morphology of S. aureus and showed rupture of cell walls after the plasma treatment and Optical emission spectrum （OES） were used to understand the possible inactivation mechanisms of PMJ. Re- suits＂ The inactivation rates could reach 100% in 5 min. When the distance between the exit nozzle of the PMJ device and Petri dish was extended from 1 cm to 3 cm, effective inactivation was also observed with a similar inactivation curve. Conclusion： The inactivation of bacteria is attributed to the abundant reactive oxygen and nitrogen species, as well as ultroviolet radiation in the plasma. Different life spans and defensibilities of these killing agents may hold the key to understanding the different inactivation curves at different treatment distances.展开更多
An atmospheric-pressure microplasma plume of diameter 10 μm is generated inside a long tube. The length of the microplasma plume reaches as much as 2 cm. First, with the assistance of an air dielectric barrier discha...An atmospheric-pressure microplasma plume of diameter 10 μm is generated inside a long tube. The length of the microplasma plume reaches as much as 2 cm. First, with the assistance of an air dielectric barrier discharge （DBD）, the ignition voltage of the microplasma decreases from 40 kV to 23.6 kV. Second, although the current density reaches as high as （1.2-7.6）× 10 4A cm-2, comparable to the current density in transient spark discharge, the microplasma plume is nonthermal. Third, it is interesting to observe that the amplitude of the discharge current in a positive cycle of applied voltage is much lower than that in a negative cycle of applied voltage. Fourth, the electron density measured by the Stark broadening of Ar spectral line 696.5 nm reaches as high as 3× 10 16 cm-3, which yields a conductivity of the microplasma column of around 48 S m-1. In addition, the propagation velocity of the microplasma plume, obtained from light signals at different axial positions, ranges from 1 × 10 5 m s-1 to 5× 10 5m s-1. A detailed analysis reveals that the surface charges deposited on the inner wall exert significant influence on the discharge behavior of the microplasma.展开更多
文摘This article provides a short review on the importance of the detailed analysis of a Langmuir probe I-V trace in a multi-Maxwellian plasma,and discuss proper procedures analyzing Langmuir probe I-V traces in bi-Maxwellian and triple-Maxwellian Electron Energy Distribution Function(EEDF)plasmas.Discus⁃sion and demonstration of procedures include the treatment of the ion saturation current,electron saturation cur⁃rent,space-charge effects on the I-V trace,and most importantly how to properly isolate and fit for each electron group present in an I-V trace reflecting a mult-Maxwellian EEDF,as well as how having a multi-Maxwellian EEDF affects the procedures of treating the ion and electron saturation currents.Shortcomings of common improp⁃er procedures are discussed and demonstrated with simulated I-V traces to show how these procedures gives false measurements.
基金supported by the National Key Lab of Aerospace Power System and Plasma Technology Foundation,China(No.6142202210101)the National Science and Technology Major Project,China(No.J2019-Ⅲ-0013-0056)+2 种基金the National Natural Science Foundation of China(No.52025064)supported by the National Natural Science Foundation of China(Nos.52350072 and 52277167)the Beijing Natural Science Foundation,China(No.1242030)。
文摘Plasma-assisted combustion technology has been a hot spot in aero-engines andscramjet-engines.The electron density is a key discharge parameter related to the active-particledensity.The latter has been considered playing an important role in the above applications bythe kinetic effect.In this work,an atmospheric pressure air plasma collisional-radiative model con-sidering the excited states of atomic nitrogen and oxygen is built based on previous widely kineticinvestigations of molecules and radicals,as well as their excited states.The excited states,especiallythe atomic nitrogen and oxygen states were less investigated in previous works.The emission inten-sity distributions from the model have a good agreement with those measured in the glide arcplasma with two discharge modes,as well as the microwave plasma.Based on the kinetics of molec-ular and atomic emitting states,the line-ratio method is presented to determine the electron density.The N_(2)(337 nm)/O(844 nm)and N_(2)(337 nm)/NO(γ)line ratios are used for the glide arc plasma andmicrowave plasma torch,respectively.Besides,the kinetics of the excited states involved with twoline-ratios are also investigated in the two types of discharges.Combined with the atmospheric pres-sure actinometry method,the kinetic effect of the plasma-assisted combustion can be revealed quan-titatively in the future.
基金support from the University Grants Commission(UGC),Government of India,for a Senior Research Fellowship(SRF)with Ref.No.1161/(CSIR-UGC NET DEC.2018)and 16-6(DEC.2018)/2019(NET/CSIR)。
文摘We study the Rayleigh-Taylor instability(RTI)of electrostatic plane wave perturbations in compressible relativistic magnetoplasma fluids with thermal ions under gravity in three different cases of when(ⅰ)electrons are in isothermal equilibrium,i.e.,classical or nondegenerate,(ⅱ)electrons are fully degenerate(with Te=0),and(ⅲ)electrons are partially degenerate or have finite temperature degeneracy(with Te≠0).While in the cases of(ⅰ)and(ⅲ),we focus on the regimes where the particle's thermal energy is more or less than the rest mass energy,i.e.,βe≡kBTe/mec2<1or>1,the case(ⅱ)considers from weakly to ultra-relativistic degenerate regimes.A general expression of the growth rate of instability is obtained and analyzed in the three different cases relevant to laboratory and astrophysical plasmas,which generalize and advance the previous theory on RTI.
基金financial support from the LASERLAB-EUROPE Access to Research Infrastructure Activity (Application No. 23068)carried out within the framework of EUROfusion Enabling Research Projects AWP21-ENR-01-CEA02 and AWP24-ENR-IFE-02-CEA-02+3 种基金received funding from Euratom Research and Training Programme 2021–2025 under Grant No. 633053supported by the Ministry of Youth and Sports of the Czech Republic [Project No. LM2023068 (PALS RI)]by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant Nos. XDA25030200 and XDA25010100)supported by COST (European Cooperation in Science and Technology) through Action CA21128 PROBONO (PROton BOron Nuclear Fusion: from energy production to medical applicatiOns)
文摘Recent experiments at the National Ignition Facility and theoretical modeling suggest that side stimulated Raman scattering(SSRS)instability could reduce laser–plasma coupling and generate considerable fluxes of suprathermal hot electrons under interaction conditions envisaged for direct-drive schemes for inertial confinement fusion.Nonetheless,SSRS remains to date one of the least understood parametric instabilities.Here,we report the first angularly and spectrally resolved measurements of scattered light at laser intensities relevant for the shock ignition scheme(I×10^(16)W/cm^(2)),showing significant SSRS growth in the direction perpendicular to the laser polarization.Modification of the focal spot shape and orientation,obtained by using two different random phase plates,and of the density gradient of the plasma,by utilizing exploding foil targets of different thicknesses,clearly reveals a different dependence of backward SRS(BSRS)and SSRS on experimental parameters.While convective BSRS scales with plasma density scale length,as expected by linear theory,the growth of SSRS depends on the spot extension in the direction perpendicular to laser polarization.Our analysis therefore demonstrates that under current experimental conditions,with density scale lengths L_(n)≈60–120μm and spot sizes FWHM≈40–100μm,SSRS is limited by laser beam size rather than by the density scale length of the plasma.
基金support of the Fundamental Research Funds for the Central Universities of China(Grant No.2019ZDPY16).
文摘We employ the Green–Kubo(G-K)and Einstein relations to estimate the self-diffusion coefficients(denoted as D_(G)and D_(E),respectively)in two-dimensional(2D)strongly coupled dusty plasmas(SC-DPs)via equilibrium molecular dynamics(EMD)simulations.D_(G)and D_(E)are computed for a broad domain of screening length(κ)and coupling parameters(Γ)along with different system sizes.It is observed that both D_(G)and D_(E)decrease linearly with increasing Г in warm liquid states and increase with increasingκ.In cold liquid states,the Einstein relation accurately predicts D_(E)in 2D SC-DPs because diffusion motion is close to normal diffusion,but the G-K relation provides overestimations of D_(G),because VACF indicates anomalous diffusion;thus,D_(G)is not accurate.Our new simulation outcomes reveal that D_(G)and D_(E)remain independent of system sizes.Furthermore,our investigations demonstrate that at higher temperatures,D_(G)and D_(E)converge,suggesting diffusion motion close to normal diffusion,while at lower temperatures,these two values diverge.We find reasonable agreement by comparing current and existing numerical,theoretical and experimental data.Moreover,when normalizing diffusion coefficients by the Einstein frequency and testing against the universal temperature scaling law,D_(G)deviates from theoretical curves at low temperatures and κ,whereas D_(E)only disagrees with theory at very smallκ(■0.10).These findings provide valuable insight into diagnosing dust component parameters within 2D DP systems and contribute to the broader understanding of diffusion processes in DP environments.
基金supported by Natural Science Foundation of Shandong Province,China(No.ZR2015AQ008)Project of Shandong Province Higher Educational Science and Technology Program of China(No.J15LJ04)
文摘Atmospheric-pressure argon plasmas have received increasing attention due to their high potential in many industrial and biomedical applications. In this paper, a 1-D fluid model is used for studying the particle density characteristics of the argon plasmas generated by the pulsed dielectric barrier discharges. The temporal evolutions of the axial particle density distributions are illustrated, and the influences of changing the main discharge conditions on the averaged particle densities are researched by independently varying the various discharge conditions. The calculation results show that the electron density and the ion density reach two peaks near the momentary cathodes during the rising and the falling edges of the pulsed voltage. Compared with the charged particle densities, the densities of the resonance state atom Arr and the metastable state atom Arm have more uniform axial distributions, reach higher maximums and decay more slowly. During the platform of the pulsed voltage and the time interval between the pulses, the densities of the excited state atom Ar＊ are far lower than those of the Arr or the Arm. The averaged particle densities of the different considered particles increase with the increases of the amplitude and the frequency of the pulsed voltage. Narrowing the discharge gap and increasing the relative dielectric constant of the dielectric also contribute to the increase of the averaged particle densities. The effects of reducing the discharge gap distance on the neutral particle densities are more significant than the influences on the charged particle densities.
基金the National Science Foundation of China(Grant No.51521065)the Fundamental Research Funds for the Central Universities and the State Key Laboratory of Electrical Insulation and Power Equipment(Grant No.EIPE14123).
文摘Cold atmospheric-pressure He +N2 and He +O2 plasmas are chosen as the representatives for electropositive andelectronegative plasmas, of which the discharge characteristics are studied and then compared to each other by fluidmodels. As the increase of the impurity (N2 or O2) fraction from 0 to 10%, for He + N2 plasmas the electron density andion density increase, the spatiotemporal distributions of electron density, ion density, electron temperature and electrongeneration rate change a little. On contrast, for He + O2 plasmas the electron density decreases, the ion density firstincreases and then decreases, the electron temperature increases in the bulk region, but decreases in the sheath region,and the plasmas transform from g mode to α mode as the significant change of electron generation rate distributions.Larger electric field is needed in the bulk region to sustain the electronegative plasma, so the electrical characteristics ofHe + O2 plasmas transform form capacitive to resistive with increasing O2 fraction. Meanwhile, the ion-coupling powerincreases dramatically, which can be estimated by a formula based on the electronegativity. A new criterion fordetermining the sheath boundary, |∇E| = 5 kV/cm2, is put forward, which is found suitable for both the electropositive andelectronegative plasmas.
基金Funded by the Foundation for University Young Key Teacher by Zhejiang Province
文摘Membrane surfaces modified with poly（N-vinyl-2-pyrrolidone） （PNVP） can be endowed with hydrophilicity, biocompatibility and functionality. In this work, atmospheric pressure dielectric barrier discharge plasma graft polymerization of N-vinyl-2-pyrrolidone （NVP） onto polypropylene （PP） microporous membrane surface was studied. The experimental results reveal that plasma treatment conditions, such as discharge power, treatment time and adsorbed NVP amount, have remarkable effects on the grafting degree of NVP. Structural and morphological changes on the membrane surfaces were characterized by attenuated total reflection-Fourier transform infrared spectroscopy （FT-IR/ATR）, X-ray photoelectron spectroscope （XPS） and field emission scanning electron microscopy （FE-SEM）. Water contact angles of the membrane surfaces were also measured by the sessile drop method. Water contact angles on the membrane surfaces decrease with the increase of NVP grafting degree, which indicates an enhanced hydrophilicity for the modified membranes. The effects of grafting degrees on pure water fluxes were also measured. It is shown that pure water fluxes increase with grafting degree firstly and then decrease adversely. Finally, filtration of bovine serum albumin （BSA） solution and platelets adhesion of the PNVP modified membranes show good protein resistance and potential biocompatibility due to the enhancement of surface hydrophilicity.
基金supported by National Natural Science Foundation of China (No. 12075132)。
文摘The key plasma parameters under different discharge modes, such as heavy-particle and electron temperatures, electron number density, and nonequilibrium volume of plasmas, play important roles in various applications of gas discharge plasmas. In this study, a self-consistent two-dimensional nonequilibrium fluid model coupled with an external circuit model is established to reveal the mechanisms related to the discharge modes, including the normal glow, abnormal glow,arc, and glow-to-arc transition modes, with an atmospheric-pressure direct-current(DC) argon discharge as a model plasma system. The modeling results show that, under different discharge modes, the most significant difference between the preceding four discharge modes lies in the current and energy transfer processes on the cathode side. On one hand, the current to the cathode surface is mainly delivered by the ions coming from the plasma column under the glow discharge mode due to the low temperature of the solid cathode, whereas the thermionic and secondary electrons emitted from the hot cathode surface play a very important role under the arc mode with a higher cathode surface temperature and higher ion flux toward the cathode. On the other hand, the energy transfer channel on the cathode side changes from mainly heating the solid cathode under the glow mode to simultaneously heating both the solid cathode and plasma column under the arc mode with an increase in the discharge current. Consequently, the power density in the cathode sheath(P_c) was used as a key parameter for judging different discharge modes, and the range of(0.28–1.2) × 10^(12) W m^(-3) was determined as a critical window of P_c corresponding to the glow-to-arc-mode transition for the atmospheric-pressure DC argon discharge, which was also verified by comparison with the experimental results in this study and the data in the previous literature.
基金supported by National Natural Science Foundation of China(Nos.11505019,21173028)the Science and Technology Research Project of Liaoning Provincial Education Department(No.L2013464)+1 种基金the Scientific Research Foundation for the Doctor of Liaoning Province(No.20131004)the Dalian Jinzhou New District Science and Technology Plan Project(No.KJCX-ZTPY-2014-0001)
文摘Cold plasma generated by dielectric barrier discharge （DBD） at atmospheric pressure was adopted for preparation of commercial TiO2 Degussa P25 supported Au catalysts （Au/P25- P） with the assistance of the deposition-precipitation procedure. The influences of the plasma reduction time and calcination on the performance of the Au/P25-P catalysts were investigated. CO oxidation was performed to investigate the catalytic activity of the Au/P25 catalysts. The results show that DBD cold plasma for the fabrication of Au/P25-P catalysts is a fast process, and Au/P25-P （4 min） exhibited the highest CO oxidation activity due to the complete reduction of Au compounds and less consumption of oxygen vacancies. In order to form more oxygen vacancies active species, Au/P25-P was calcined to obtain Au/P25-PC catalysts. Interestingly, Au/P25- PC exhibited the highest activity for CO oxidation among the Au/P25 samples. The results of transmission electron microscopy （TEM） indicated that the smaller size and high distribution of Au nanoparticles are the mean reasons for a high performance of Au/P25-PC. Atmospheric- pressure DBD cold plasma was proved to be of great efficiency in preparing high performance supported Au catalysts.
基金supported by the National Natural Science Foundation of China(21173028)the Science and Technology Research Project of Liaoning Provincial Education Department(L2013464)+1 种基金the Scientific Research Foundation for the Doctor of Liaoning Province(20131004)the Program for Liaoning Excellent Talents in University(LR2012042)
文摘TiO2 decorated with partially crystallized Pd nanoparticles （Pd/TiO2-P） was successfully prepared by atmospheric-pressure dielectric barrier discharge cold plasma. The XRD and XPS analyses proved that Pd ions were reduced to partially crystallized metallic Pd nanoparticles in Pd/TiO2-P. The XPS spectra also indicated that an enhanced metal-support interaction was formed due to the existence of partially crystallized Pd nanoparticles with lower coordination number in Pd/TiO2-P. Photocatalytic activity of Pd/TiO2-P was much higher than that of TiO2 samples decorated with well crystallized Pd nanoparticles.
基金supported by National Natural Science Foundation of China(Nos.10835004,51077009)the Fundamental Research Funds for the Central Universities
文摘To deposit TiO2 films through plasma CVD, the partial pressure ratio of O2 to TIC14 should be greater than the stoichiometric ratio （PO2/PTiCl4 〉 1）. However, this may lead to the formation of powder instead of film on the substrate when using volume dielectric barrier discharge （volume-DBD） at atmospheric pressure. In this study, by adding N2 into the working gas Ar, TiO2 photocatalytic films were successfully fabricated in the presence of excess O2 （PO2/PTiC14 = 2.6） by using a wire-to-plate atmospheric-pressure volume-DBD. The tuning effect of N2 on the deposition of TiO2 film was studied in detail. The results showed that by increasing the N2 content, the deposition rate and particle size of the TiO2 film were reduced, and its photocatalytic activity was enhanced. The tuning mechanism of N2 is further discussed.
基金supported by National Natural Science Foundation of China(Nos.11775043,11675095 and 11505020)the Fundamental Research Funds for the Central Universities(No.DUT18LK31)。
文摘A 2D axial symmetry fluid model is applied to study the features of an atmospheric-pressure argon(Ar) plasma jet propagating into ambient nitrogen(N_(2)) driven by a pulsed voltage,emphasizing the influence of gas velocity on the dynamic characteristics of the jet. The results show that the Ar jet exhibits a cylindrical-shaped channel and the jet channel gradually shrinks with the increase in propagation length. The jet propagation velocity varies with time. Inside the dielectric tube, the plasma jet accelerates propagation and reaches its maximum value near the nozzle. Exiting the tube, its velocity quickly decreases and when approaching the metal plane,the decrease in jet velocity slows down. The increase in gas speed results in the variation of jet spatial distribution. The electron density presents a solid structure at lower gas flow speeds,whereas an annular structure can be observed under the higher gas flow velocity in the ionization head. The jet length increases with the flow velocity. However, when the flow velocity exceeds a critical value, the increase in the rate of the plasma jet length slows down. In addition, the gas velocity effect on the generation and transport of the reactive particles is also studied and discussed.
基金supported by National Natural Science Foundation of China (No. 51577011)
文摘In order to form an atmospheric-pressure plasma jet without airflow, a needle–ring electrode structure is proposed in this paper. When heteropolar potentials are applied to a needle and a ring, a marked electric field strength enhancement around the needle’s pointed end has been found. When the same potential is applied to both the needle and the ring, the lateral electric field strength for the needle can be weakened. By using the above two methods, an increase of the difference between the pointed end electric field strength and the lateral one is achieved and stable plasma jets are formed. A symmetrical space electric field distribution is established at the pointed end of the needles when several sets of heteropolar needle–ring electrodes are uniformly arranged, which is conducive to forming a uniform array plasma jet. Under DC discharge conditions, a safe and stable plasma jet of high density and an array plasma jet are successfully achieved.
基金partly supported by the State Key Laboratory of Advanced Electromagnetic Engineering and Technology(No.AEET 2018KF003)National Natural Science Foundation of China(Nos.51637002,11405144)+3 种基金the Fundamental Research Funds for the Central Universities(Nos.2018CDXYTW0031,20720150022)the Construction Committee of Chongqing(No.2018-1-3-6)the International Science&Technology Cooperation Program of China(No.2015DFR70390)the Natural Science Foundation of Hunan Province(No.2018JJ3587)
文摘In this work,the super-hydrophobic(SH)surface was prepared through chemical vapor deposition process by an argon atmospheric pressure plasma jet source with HMDSN(hexamethyldisilazane)as the polymerization precursor.Plasma synthesized organosilicon(SiOxCyHz)thin films with water contact angle over 160°and sliding angle below 5°,were able to be achieved.FTIR and XPS analysis indicates a large number of hydrocarbon compositions were polymerized in the thin films enduing the latter very-low surface free energy.SEM shows the SH films display micro-nanostructure and with high degree of averaged surface roughness 190 nm evaluated by AFM analysis.From experiments under controlled low-temperature and moisture conditions,the prepared SH surface exhibits good anti-icing effects.Significantly prolonging freezing time was achievable on the SH thin films for both static and sliding water droplets.This investigation demonstrates the anti-icing potentials of SH surface prepared through low-cost simple atmospheric-pressure plasma polymerization process.
文摘The sterilizing effect of the non-equilibrium atmospheric pressure plasma jet by applying it to the Bacillus subtilis spores is invesigated. A stable glow discharge in argon or helium gas fed with active gas （oxygen）, was generated in the coaxial cylindrical reactor powered by the radio-frequency power supply at atmospheric pressure. The experimental results indicated that the efficiency of killing spores by making use of an Ar/O2 plasma jet was much better than with a He/O2 plasma jet. The decimal reduction value of Ar/O2 and He/O2 plasma jets under the same experimental conditions was 4.5 seconds and 125 seconds, respectively. It was found that there exists an optimum oxygen concentration for a certain input power, at which the sterilization efficiency reaches a maximum value. It is believed that the oxygen radicals are generated most efficiently under this optimum condition.
基金jointly supported by the Education and Research Foundation of Anhui Province(KJ2015A327)Science Foundation of Institute of Plasma Physics,Chinese Academy of Sciences No.DSJJ-14-YY02Hong Kong Research Grants Council(RGC)General Research Funds(GRF)No.CityU 11301215
文摘An atmospheric-pressure air plasma is employed to treat C6 glioma cells in vitro. To elucidate on the mechanism causing cell death and role of reactive species （RS） in the medium produced by the plasma, the concentration of the long-lived RS such as hydrogen peroxide, nitrate, and ozone in the plasma-treated liquid （phosphate-buffered saline solution） is measured. When vitamin C is added to the medium as a ROS quencher, the viability of C6 glioma cells after the plasma treatment is different from that without vitamin C. The results demonstrate that reactive oxygen species （ROS） such as H2O2, and O3 constitute the main factors for inactivation of C6 glioma cells and the reactive nitrogen species （RNS） may only play an auxiliary role in cell death.
基金supported by the National Natural Science Foundation of China (NSFC) (Grant No. 11974043)the Fundamental Research Funds for the Central Universities (Grant No. FRF-BR-19-002B)。
文摘The quantum hydrodynamic model for electrons and ions and the generalized hydrodynamic model for the strongly coupled dust particles are proposed in the strongly coupled quantum dusty plasma, where the combined quantum effects of quantum diffraction, quantum statistic pressure,as well as electron exchange and correlation effects are all considered in the quantum hydrodynamic model. The shear and bulk viscosity effects are included in the viscoelastic relaxation, which leads to the decay of the dust-ion-acoustic waves. The approximate time-dependent solitary solution is obtained by the momentum conservation law in the presence of viscosity.
基金supported by Bioelectrics Inc.(USA),Peking University Biomed-X Foundation and China International Science and Technology Cooperation(No.2008KR1330)
文摘Objective： A direct-current, cold atmospheric-pressure air plasma microjet （PMJ） was performed to inactivate Staphylococcus aureus （S. aureus） and Enterococcusfaecalis （E. faecalis） in air. The process of sterilization and morphology of bacteria was observed. We wish to know the possible inactivation mechanisms of PMJ and explore a potential application in dental and other temperature sensitive treatment. Methods： In this study, we employed a direct current, atmospheric pressure, cold air PMJ to inactivate bacterias. Scanning electron microscopy was employed to evaluate the morphology of S. aureus and showed rupture of cell walls after the plasma treatment and Optical emission spectrum （OES） were used to understand the possible inactivation mechanisms of PMJ. Re- suits＂ The inactivation rates could reach 100% in 5 min. When the distance between the exit nozzle of the PMJ device and Petri dish was extended from 1 cm to 3 cm, effective inactivation was also observed with a similar inactivation curve. Conclusion： The inactivation of bacteria is attributed to the abundant reactive oxygen and nitrogen species, as well as ultroviolet radiation in the plasma. Different life spans and defensibilities of these killing agents may hold the key to understanding the different inactivation curves at different treatment distances.
基金partially supported by National Natural Science Foundation of China (No. 51607090)the Natural Science Foundation of Jiangsu Province (No. BK20160796)+2 种基金the Delta Research and Educational Foundation (No. DREG2017008)Fundamental Research Funds for the Central Universities (No. XCA17003–03)financial support from the China Scholarship Council
文摘An atmospheric-pressure microplasma plume of diameter 10 μm is generated inside a long tube. The length of the microplasma plume reaches as much as 2 cm. First, with the assistance of an air dielectric barrier discharge （DBD）, the ignition voltage of the microplasma decreases from 40 kV to 23.6 kV. Second, although the current density reaches as high as （1.2-7.6）× 10 4A cm-2, comparable to the current density in transient spark discharge, the microplasma plume is nonthermal. Third, it is interesting to observe that the amplitude of the discharge current in a positive cycle of applied voltage is much lower than that in a negative cycle of applied voltage. Fourth, the electron density measured by the Stark broadening of Ar spectral line 696.5 nm reaches as high as 3× 10 16 cm-3, which yields a conductivity of the microplasma column of around 48 S m-1. In addition, the propagation velocity of the microplasma plume, obtained from light signals at different axial positions, ranges from 1 × 10 5 m s-1 to 5× 10 5m s-1. A detailed analysis reveals that the surface charges deposited on the inner wall exert significant influence on the discharge behavior of the microplasma.
