In this paper, a 1D fluid model is developed to study the characteristics of a discharge in argon with small admixtures of oxygen at atmospheric pressure. This model consists of a series of equations, including contin...In this paper, a 1D fluid model is developed to study the characteristics of a discharge in argon with small admixtures of oxygen at atmospheric pressure. This model consists of a series of equations, including continuity equations for electrons, positive ions, negative ions and neutral particles, the energy equation, and the Poisson equation for electric potential. Special attention has been paid to the electron energy dissipation and the mechanisms of electron heating, while the admixture of oxygen is in the range of 0.1%-0.6%. It is found that when the oxygen-to-argon ratio grows, the discharge is obviously divided into three stages： electron growth, electron reduction and the electron remaining unchanged. Furthermore, the cycle-averaged electric field, electron temperature, electron Ohmic heating, electron collisionless heating, electron energy dissipation and the net electron production are also studied in detail, and when the oxygen-to- argon ratio is relatively larger （R = 0.6%）, double value peaks of electron Ohmic heating appear in the sheath. According to the results of the numerical simulation, various oxygen-to-argon ratios result in different amounts of electron energy dissipation and electron heating.展开更多
Using a one-dimensional fluid model, the pulse-modulated radio-frequency dielectric barrier discharge in atmospheric helium is described. The influences of the pulse duty cycle on the discharge characteristics are stu...Using a one-dimensional fluid model, the pulse-modulated radio-frequency dielectric barrier discharge in atmospheric helium is described. The influences of the pulse duty cycle on the discharge characteristics are studied. The numerical results show that the dependence of discharge characteristics on the duty cycle is sensitive in the region of around 40% duty cycle under the given simulation parameters. In the case of a larger duty cycle, the plasma density is higher, the discharge becomes more intense, but the power consumption is higher. When the duty cycle is lower, one can get a weaker discharge, lower plasma density and higher electron temperature in the bulk plasma. In practical applications, in order to get a higher plasma density and a lower power consumption, it is more important to choose a suitable duty cycle to modulate the RF power supply.展开更多
The generation of a very strong peak current in the first period(PCFP)in a pulse-modulated microwave discharge has been discussed in previous studies.In this paper we focus on the transition process from a pulsed disc...The generation of a very strong peak current in the first period(PCFP)in a pulse-modulated microwave discharge has been discussed in previous studies.In this paper we focus on the transition process from a pulsed discharge to a fully continuous one driven by the pulsed microwave power source by means of a kinetic model.The computational results show that by increasing the duty cycle or voltage modulation rate(VMR).the discharge eventually becomes fully continuous and PCFP can no longer he observed.In the transition process,the distributions of the electric field,electron energy probability function(EEPF)and plasma density are discussed according to the simulation data,showing different discharge structures.The simulations indicate that many high-energy electrons with electron energy larger than 20eV and low-energy electrons with electron energy less than 3eV could he generated in a pulsed microwave discharge,together with a reversal electric field formed in the anode sheath when PCFP occurs.However,only medium-energy electrons could be observed in a fully continuous discharge.Therefore,by investigating the transition process the pulse-modulated microwave discharges can be further optimized for plasma applications at atmospheric pressure.展开更多
As a spatially extended dissipative system with strong nonlinearity,the radio-frequency(rf)dielectric-barrier discharges(DBDs)at atmospheric pressure possess complex spatiotemporal nonlinear behaviors.In this paper,th...As a spatially extended dissipative system with strong nonlinearity,the radio-frequency(rf)dielectric-barrier discharges(DBDs)at atmospheric pressure possess complex spatiotemporal nonlinear behaviors.In this paper,the time-domain nonlinear behaviors of rf DBD in atmospheric argon are studied numerically by a onedimensional fluid model.Simulation results show that,under appropriate controlling parameters,the rf DBD can undergo a transition from single-period state to chaos through period doubling bifurcation with increasing discharge time,i.e.,the regular periodic oscillation and chaos can coexist in a long time series of the atmosphericpressure rf DBD.With increasing applied voltage amplitude,the duration of the periodic oscillation reduces gradually and chaotic zone increases,and finally the whole discharge series becomes completely chaotic state.This is different from conventional period doubling route to chaos.Moreover,the spatial characteristics of rf perioddoubling discharge and chaos,as well as the parameter range of various discharge behaviors occurring are also investigated in this paper.展开更多
Radio-frequency microdischarge in acetylene is investigated by use of a fluid model and an aerosol dynamics model in a cylindrical discharge chamber.In this article,the results at a pressure of 100–500 Torr,a voltage...Radio-frequency microdischarge in acetylene is investigated by use of a fluid model and an aerosol dynamics model in a cylindrical discharge chamber.In this article,the results at a pressure of 100–500 Torr,a voltage of 80–150 V,and an electrode gap of 400–1000μm are carefully analyzed and discussed.It is shown that two electron heating modesαandγappear in the microdischarge,and the pressure-dependent transition fromαtoγwas accompanied by the abrupt decrease of electron density and electron temperature.The mode transition phenomenon is further confirmed by the variation of the electron temperature axial profiles,the profiles vary continuously from a center high at the pressure of 100 Torr to an edge high at the pressure of500 Torr.Furthermore,in theαmode(100 Torr)the plasma density increases linearly with the increase of electrode gap,but decreases sharply with the increase of electrode gap in theγmode(>100 Torr).The gas pressure and applied voltage effects on the nanoparticle density and degree of nonuniformity are also investigated.It has been shown that the gas pressure greatly influences the axial profiles of nanoparticle density and the values of the degree of nonuniformity,while the values of the plasma parameters(electron density and nanoparticle density)strongly depend on the applied voltage.展开更多
Experimental study of the low-pressure hybrid RF discharge with both inductive and capacitive channels was carried out. The RF power unit consists of inductor(antenna) and capacitor plates connected in parallel to the...Experimental study of the low-pressure hybrid RF discharge with both inductive and capacitive channels was carried out. The RF power unit consists of inductor(antenna) and capacitor plates connected in parallel to the same RF power source. A separating capacitor Csepis included into the circuit between the antenna ends and the lead connected to the discharge capacitor plate in order to prevent the closing of the capacitive circuit through direct current by inductor and to control the contribution of capacitive channel to discharge sustaining. It is shown that at low power of the RF power source, power coupling to the discharge mainly occurs through the capacitive channel. Increasing the power of the RF power source increases the power coupled in the inductive channel, electron density, and current flowing through the capacitive channel. This leads to increasing voltage drop on the separating capacitor and partial cutoff of the capacitive channel. At separating capacitance values below certain value(below 50 pF in the present experiments), the self-bias of the loaded plate of the discharge capacitor becomes positive indicating that the thickness of the electrode sheath of the loaded electrode decreases compared to thickness of the sheath of the grounded electrode. The thickness of the space-charge sheath of the grounded electrode decreases with increasing power coupled to the plasma. At separating capacitance below 50 pF, higher harmonics of the RF voltage and current are actively generated in the capacitive discharge channel. Increasing the separating capacitance leads to decreasing electron density, increasing effective electron temperature and more effective RF energy coupling to plasma due to increasing relative importance of the capacitive discharge channel.展开更多
The efficiency of radio-frequency(RF)power absorption,RF magnetic field structure and plasma parameters were measured in cylindrical inductive RF plasma sources 20 cm in diameter and 22,32,53 cm in length with a low v...The efficiency of radio-frequency(RF)power absorption,RF magnetic field structure and plasma parameters were measured in cylindrical inductive RF plasma sources 20 cm in diameter and 22,32,53 cm in length with a low value external magnetic field.The experiments were carried out in argon at pressures of 13-140 m Pa.The RF power supply changed from 200 W to 800 W.The spiral antenna was used for sustaining the discharge.It was shown that efficiency of RF power absorption depended nonlinearly on the external magnetic field values.At maximal values of the RF power absorption efficiency,the axial distributions of longitudinal Bzand azimuthal Bφcomponents of RF magnetic field manifested the formation of the partially standing wave with a half wavelength close to 8 cm.At the same conditions,the axial dependence of the radial RF magnetic field component Brdiffered drastically.It was concluded that the Bz and Bφamplitudes were largely determined by the RF field of Trivelpiece-Gould wave,while Br amplitude represented the radial RF field of the helicon wave.展开更多
针对磁流体流动控制技术对大体积、均匀放电等离子体的需要,开展了低气压下平板型电容耦合放电特性实验研究,并基于均匀射频放电模型,联立能量平衡方程建立诊断模型对等离子体参数进行诊断。结果表明:气压较低时,放电为α模式,整个放电...针对磁流体流动控制技术对大体积、均匀放电等离子体的需要,开展了低气压下平板型电容耦合放电特性实验研究,并基于均匀射频放电模型,联立能量平衡方程建立诊断模型对等离子体参数进行诊断。结果表明:气压较低时,放电为α模式,整个放电空间发光较为均匀,当气压大于500 Pa时,放电转变为γ模式,在电极附近出现负辉光区,但负辉光区较厚占据了整个放电空间,随着气压增大,负辉光区、法拉第暗区厚度减小,并在放电区域中心出现明显正柱区,正柱区面积随负载功率的增大而增大;放电为γ模式时,电流将随负载功率增大而增大,而电压先不变后增大,并且转折点负载功率随着气压增大而增大;电子数密度ne随负载功率的增大线性增大,而电子温度T_e只是略有增大,约为5500 K(0.47 e V)。展开更多
Cold atmospheric plasmas(CAPs)have shown great applicability in agriculture.Many kinds of CAP sources have been studied in agricultural applications to promote plant growth and cure plant diseases.We briefly review th...Cold atmospheric plasmas(CAPs)have shown great applicability in agriculture.Many kinds of CAP sources have been studied in agricultural applications to promote plant growth and cure plant diseases.We briefly review the state-of-the-art stimulating effects of atmospheric-pressure dielectricbarrier-discharge(AP-DBD)plasmas,after the direct or indirect treatment of plants for growth promotion and disease control.We then discuss the special demands on the characteristics of the CAP sources for their applications in plant mutation breeding.An atmospheric and room temperature plasma(ARTP)jet generator with a large plasma irradiation area,a high enough concentration of chemically reactive species and a low gas temperature is designed for direct plant mutagenesis.Experimental measurements of the electrical,thermal and optical features of the ARTP generator are conducted.Then,an ARTP-P(ARTP for plant mutagenesis)mutation breeding machine is developed,and a typical case of plant mutation breeding by the ARTP-P mutation machine is presented using Coreopsis tinctoria Nutt.seeds.Physical and agricultural experiments show that the newly-developed ARTP-P mutation breeding machine with a large irradiation area can generate uniform CAP jets with high concentrations of chemically reactive species and mild gas temperatures,and have signiflcant mutagenesis effects on the Coreopsis tinctoria Nutt.seeds.The ARTP-P mutation breeding machine may provide a platform for systematic studies on mutation mechanisms and results for various plant seeds under different operating conditions in future research.展开更多
基金supported by National Natural Science Foundation of China (No. 11505089)
文摘In this paper, a 1D fluid model is developed to study the characteristics of a discharge in argon with small admixtures of oxygen at atmospheric pressure. This model consists of a series of equations, including continuity equations for electrons, positive ions, negative ions and neutral particles, the energy equation, and the Poisson equation for electric potential. Special attention has been paid to the electron energy dissipation and the mechanisms of electron heating, while the admixture of oxygen is in the range of 0.1%-0.6%. It is found that when the oxygen-to-argon ratio grows, the discharge is obviously divided into three stages： electron growth, electron reduction and the electron remaining unchanged. Furthermore, the cycle-averaged electric field, electron temperature, electron Ohmic heating, electron collisionless heating, electron energy dissipation and the net electron production are also studied in detail, and when the oxygen-to- argon ratio is relatively larger （R = 0.6%）, double value peaks of electron Ohmic heating appear in the sheath. According to the results of the numerical simulation, various oxygen-to-argon ratios result in different amounts of electron energy dissipation and electron heating.
基金supported jointly by National Natural Science Foundation of China （No. 10835004） and National Basic Research Program of China （No. 2010CB832901）
文摘Using a one-dimensional fluid model, the pulse-modulated radio-frequency dielectric barrier discharge in atmospheric helium is described. The influences of the pulse duty cycle on the discharge characteristics are studied. The numerical results show that the dependence of discharge characteristics on the duty cycle is sensitive in the region of around 40% duty cycle under the given simulation parameters. In the case of a larger duty cycle, the plasma density is higher, the discharge becomes more intense, but the power consumption is higher. When the duty cycle is lower, one can get a weaker discharge, lower plasma density and higher electron temperature in the bulk plasma. In practical applications, in order to get a higher plasma density and a lower power consumption, it is more important to choose a suitable duty cycle to modulate the RF power supply.
文摘The generation of a very strong peak current in the first period(PCFP)in a pulse-modulated microwave discharge has been discussed in previous studies.In this paper we focus on the transition process from a pulsed discharge to a fully continuous one driven by the pulsed microwave power source by means of a kinetic model.The computational results show that by increasing the duty cycle or voltage modulation rate(VMR).the discharge eventually becomes fully continuous and PCFP can no longer he observed.In the transition process,the distributions of the electric field,electron energy probability function(EEPF)and plasma density are discussed according to the simulation data,showing different discharge structures.The simulations indicate that many high-energy electrons with electron energy larger than 20eV and low-energy electrons with electron energy less than 3eV could he generated in a pulsed microwave discharge,together with a reversal electric field formed in the anode sheath when PCFP occurs.However,only medium-energy electrons could be observed in a fully continuous discharge.Therefore,by investigating the transition process the pulse-modulated microwave discharges can be further optimized for plasma applications at atmospheric pressure.
基金This work was supported by the National Natural Science Foundation of China under Grant No.10775026 and 50537020 and Science Research Foundation of Dalian University of Technology.
文摘As a spatially extended dissipative system with strong nonlinearity,the radio-frequency(rf)dielectric-barrier discharges(DBDs)at atmospheric pressure possess complex spatiotemporal nonlinear behaviors.In this paper,the time-domain nonlinear behaviors of rf DBD in atmospheric argon are studied numerically by a onedimensional fluid model.Simulation results show that,under appropriate controlling parameters,the rf DBD can undergo a transition from single-period state to chaos through period doubling bifurcation with increasing discharge time,i.e.,the regular periodic oscillation and chaos can coexist in a long time series of the atmosphericpressure rf DBD.With increasing applied voltage amplitude,the duration of the periodic oscillation reduces gradually and chaotic zone increases,and finally the whole discharge series becomes completely chaotic state.This is different from conventional period doubling route to chaos.Moreover,the spatial characteristics of rf perioddoubling discharge and chaos,as well as the parameter range of various discharge behaviors occurring are also investigated in this paper.
基金supported by National Natural Science Foundation of China(Nos.11805107 and 21703112)the Fundamental Research Funds in Heilongjiang Provincial Universities of China(No.135209312).
文摘Radio-frequency microdischarge in acetylene is investigated by use of a fluid model and an aerosol dynamics model in a cylindrical discharge chamber.In this article,the results at a pressure of 100–500 Torr,a voltage of 80–150 V,and an electrode gap of 400–1000μm are carefully analyzed and discussed.It is shown that two electron heating modesαandγappear in the microdischarge,and the pressure-dependent transition fromαtoγwas accompanied by the abrupt decrease of electron density and electron temperature.The mode transition phenomenon is further confirmed by the variation of the electron temperature axial profiles,the profiles vary continuously from a center high at the pressure of 100 Torr to an edge high at the pressure of500 Torr.Furthermore,in theαmode(100 Torr)the plasma density increases linearly with the increase of electrode gap,but decreases sharply with the increase of electrode gap in theγmode(>100 Torr).The gas pressure and applied voltage effects on the nanoparticle density and degree of nonuniformity are also investigated.It has been shown that the gas pressure greatly influences the axial profiles of nanoparticle density and the values of the degree of nonuniformity,while the values of the plasma parameters(electron density and nanoparticle density)strongly depend on the applied voltage.
文摘Experimental study of the low-pressure hybrid RF discharge with both inductive and capacitive channels was carried out. The RF power unit consists of inductor(antenna) and capacitor plates connected in parallel to the same RF power source. A separating capacitor Csepis included into the circuit between the antenna ends and the lead connected to the discharge capacitor plate in order to prevent the closing of the capacitive circuit through direct current by inductor and to control the contribution of capacitive channel to discharge sustaining. It is shown that at low power of the RF power source, power coupling to the discharge mainly occurs through the capacitive channel. Increasing the power of the RF power source increases the power coupled in the inductive channel, electron density, and current flowing through the capacitive channel. This leads to increasing voltage drop on the separating capacitor and partial cutoff of the capacitive channel. At separating capacitance values below certain value(below 50 pF in the present experiments), the self-bias of the loaded plate of the discharge capacitor becomes positive indicating that the thickness of the electrode sheath of the loaded electrode decreases compared to thickness of the sheath of the grounded electrode. The thickness of the space-charge sheath of the grounded electrode decreases with increasing power coupled to the plasma. At separating capacitance below 50 pF, higher harmonics of the RF voltage and current are actively generated in the capacitive discharge channel. Increasing the separating capacitance leads to decreasing electron density, increasing effective electron temperature and more effective RF energy coupling to plasma due to increasing relative importance of the capacitive discharge channel.
文摘The efficiency of radio-frequency(RF)power absorption,RF magnetic field structure and plasma parameters were measured in cylindrical inductive RF plasma sources 20 cm in diameter and 22,32,53 cm in length with a low value external magnetic field.The experiments were carried out in argon at pressures of 13-140 m Pa.The RF power supply changed from 200 W to 800 W.The spiral antenna was used for sustaining the discharge.It was shown that efficiency of RF power absorption depended nonlinearly on the external magnetic field values.At maximal values of the RF power absorption efficiency,the axial distributions of longitudinal Bzand azimuthal Bφcomponents of RF magnetic field manifested the formation of the partially standing wave with a half wavelength close to 8 cm.At the same conditions,the axial dependence of the radial RF magnetic field component Brdiffered drastically.It was concluded that the Bz and Bφamplitudes were largely determined by the RF field of Trivelpiece-Gould wave,while Br amplitude represented the radial RF field of the helicon wave.
文摘针对磁流体流动控制技术对大体积、均匀放电等离子体的需要,开展了低气压下平板型电容耦合放电特性实验研究,并基于均匀射频放电模型,联立能量平衡方程建立诊断模型对等离子体参数进行诊断。结果表明:气压较低时,放电为α模式,整个放电空间发光较为均匀,当气压大于500 Pa时,放电转变为γ模式,在电极附近出现负辉光区,但负辉光区较厚占据了整个放电空间,随着气压增大,负辉光区、法拉第暗区厚度减小,并在放电区域中心出现明显正柱区,正柱区面积随负载功率的增大而增大;放电为γ模式时,电流将随负载功率增大而增大,而电压先不变后增大,并且转折点负载功率随着气压增大而增大;电子数密度ne随负载功率的增大线性增大,而电子温度T_e只是略有增大,约为5500 K(0.47 e V)。
基金supported by the National Key Research and Development Program of China(No.2016YFD0102106)National Natural Science Foundation of China(Nos.11475103,21627812)。
文摘Cold atmospheric plasmas(CAPs)have shown great applicability in agriculture.Many kinds of CAP sources have been studied in agricultural applications to promote plant growth and cure plant diseases.We briefly review the state-of-the-art stimulating effects of atmospheric-pressure dielectricbarrier-discharge(AP-DBD)plasmas,after the direct or indirect treatment of plants for growth promotion and disease control.We then discuss the special demands on the characteristics of the CAP sources for their applications in plant mutation breeding.An atmospheric and room temperature plasma(ARTP)jet generator with a large plasma irradiation area,a high enough concentration of chemically reactive species and a low gas temperature is designed for direct plant mutagenesis.Experimental measurements of the electrical,thermal and optical features of the ARTP generator are conducted.Then,an ARTP-P(ARTP for plant mutagenesis)mutation breeding machine is developed,and a typical case of plant mutation breeding by the ARTP-P mutation machine is presented using Coreopsis tinctoria Nutt.seeds.Physical and agricultural experiments show that the newly-developed ARTP-P mutation breeding machine with a large irradiation area can generate uniform CAP jets with high concentrations of chemically reactive species and mild gas temperatures,and have signiflcant mutagenesis effects on the Coreopsis tinctoria Nutt.seeds.The ARTP-P mutation breeding machine may provide a platform for systematic studies on mutation mechanisms and results for various plant seeds under different operating conditions in future research.
