不同初始温度下氩等离子体演化过程研究

本文对不同初始温度下氩等离子体中主要粒子随时间的演化规律进行数值模拟,跟踪各主要成分粒子的浓度随时间的变化,得到放电后氩等离子体中主要带电粒子和中性粒子浓度随时间的变化规律。计算结果表明,氩等离子体化学反应达到平衡所需时间随初始温度升高逐渐减少,活性粒子Ar⁺浓度随时间不断增大,Ar^*、Ar^**浓度随时间先增大后减小,最终趋于稳定值达到平衡状态。     

Surface Treatment of PET Nonwovens with Atmospheric Plasma

In this study, polyethylene-terephthalate (PET) nonwovens are treated using an atmospheric plasma and the effects of the treatment time, treatment power and discharge distance on the ability of water-penetration into the nonwovens are investigated. The result indicates that the method can improve the wettability of PET nonwovens remarkably, but the aging decay of the sample’s wettability is found to be notable as a function of the storage time after treatment due to the internal rotation of the single bond of surface macromolecules. As shown by SEM and XPS analysis, the etching and surface reaction are significant, and water-penetration weight is found to increase remarkably with the increasing power. This variation can be attributed to momentum transfer and enhanced higher-energy particle excitation.     

Electromagnetic Wave Attenuation in Atmospheric Pressure Plasma

When an electromagnetic （EM） wave propagates in an atmospheric pressure plasma （APP） layer, its attenuation depends on the APP parameters such as the layer width, the electron density and its profile and collision frequency between electrons and neutrals. This paper proposes that a combined parameter -the product of the line average electron density n and width d of the APP layer （i.e., the total number of electrons in a unit volume along the wave propagation path） can play a more explicit and decisive role in the wave attenuation than any of the above individual parameters does. The attenuation of the EM wave via the product of n and d with various collision frequencies between electrons and neutrals is presented.     

Compact High-Velocity Atmospheric Pressure Dielectric Barrier Plasma Jet in Ambient Air

In this paper,a non-thermal atmospheric pressure plasma jet at high streaming velocity operating with ambient air is highlighted.In the present technological approach,the employment of air poses a significant challenge.The high oxygen concentration in air results in a reduced concentration of reactive species in combination with a short species lifetime.The plasma jet assembly presented here contains a special dielectric barrier with a high secondary emission coefficient.In this way,the electron density and in turn the density of reactive species is increased.In addition,the plasma jet assembly is equipped with a short electrode.This leads to a higher voltage across the discharge gap and in turn to an increased density of reactive plasma species.The plasma jet is formed within and emitted by a small conical nozzle.A high-speed gas flow with gas velocity of 340 m/s was achieved at the end of the nozzle.In the jet the concentration of toxic and unwanted neutral plasma species like O_3 or NO_x is significantly reduced because of the shorter residence time within the plasma.The range of short-lived active plasma species is in turn considerably enhanced.The jet efficiency and action range measured through the oxidation of a test surface were determined by measuring the increase of surface tension of a polypropylene substrate via contact angle measurements after plasma treatment.Numerical modeling of the plasma plume indicates that oxygen atoms are in fact the main active species in the plasma plume.     

A New Atmospheric Pressure Microwave Plasma Source （APMPS）

An atmospheric pressure microwave plasma source （APMPS） that can generate a large volume of plasma at an atmospheric pressure has been developed at Tsinghua University. This paper presents the design of this APMPS, the theoretical consideration of microwave plasma ignition and the simulation results, including the distributions of the electric field and power density inside the cavity as well as the accuracy of the simulation results. In addition, a method of producing an atmospheric pressure microwave plasma and some relevant observations of the plasma are also provided. It is expected that this research would be useful for further developing atmospheric pressure microwave plasma sources and expanding the scope of their applications.     

拟合目标反应谱的高精度人工加速度时程生成算法及应用

加速度时程是核电厂结构和部件开展抗震分析和试验的重要输入。本文基于改进的窄带时程构造形式,综合应用频域法和时域法,提出一种拟合目标反应谱的高精度人工加速度时程生成算法,通过RG1.60标准反应谱和两个复杂度不同的楼层反应谱拟合测试以验证算法的有效性和稳健性。结果表明：对目标反应谱的拟合相对偏差最大不超过10%;迭代次数少,拟合收敛性好。本文提出的算法可生成高精度的符合法规要求的人工加速度时程,对于核电工程抗震设计具有重要的应用价值。     

Mechanisms of Streamer Propagation Affected by Driven Voltage Polarity in a Cold Atmospheric Pressure Plasma Jet

A two-dimensional self-consistent fluid model is used to investigate the effects of DC-voltage polarity in plasma initiation and propagation of helium plasma jet.The simulation results indicate that the difference in initial breakdown for the positive jet and negative jet leads to a difference in the electron density of about 4 orders of magnitude,even with the same initial electric field,which also influences the subsequent propagation.In the propagation process of negative jets,the ionization process exists in a longer gas channel behind the streamer head.In addition,the drift process to the infinite grounded electrode driven by the electric field results in higher energy consumption in the ionization process.However,in the positive jet,the ionization process mainly exists in the streamer head.Therefore,the differences in the initial breakdown and propagation process make the electric field intensity and the ionization weaker in the streamer head of the negative jet,which explains the weaker and shorter appearance of the negative jet compared to the positive jet.Our model can adequately reproduce the experimental results,viz.a bullet-like propagation in the positive jet and a continuous plasma plume in the negative jet.Furthermore,it also indicates that the streamer velocity shows the same variations as the electron drift velocity for both positive and negative jets.     

N2 Mole Fraction Dependence of Plasma Bullet Propagation in Premixed He/N2 Plasma Needle Discharge at Atmospheric Pressure

In this work, a computational modeling study on the mechanism of the acceleration behavior of a plasma bullet in needle-plane configuration is presented. Above all, in our model,two sub-models of time-dependent plasma dynamics and laminar flow are connected using a oneway coupled method, and both the working gas and the surrounding gas around the plasma jet are assumed to be the same, which are premixed He/N_2 gas. The mole fractions of the N_2(NMF)ingredient are set to be 0.01%, 0.1% and 1% in three cases, respectively. It is found that in each case, the plasma bullet accelerates with time to a peak velocity after it exits the nozzle and then decreases until getting to the treated surface, and that the velocity of the plasma bullet increases at each time moment with the peak value changing from 0.72×10~6m/s to 0.80×10~6m/s but then drops more sharply when the NMF varies from 0.01% to 1%. Besides, the electron impact ionizations of helium neutrals and nitrogen molecules are found to have key influences on the propagation of a plasma bullet instead of the penning ionization.     

Observation of the Emission Spectra of an Atmospheric Pressure Radio-frequency Plasma Jet

An atmospheric pressure plasma jet （APPJ） using radio-frequency （13.56 MHz） power has been developed to produce homogeneous glow discharge at low temperature. With optical emission spectroscopy, we observed the excited species （atomic helium, atomic oxygen and metastable oxygen） generated in this APPJ and their dependence on gas composition ratio and RF power. O and O2（b1∑g^＋） are found in the effluent outside the jet by measuring the emission spectra of effluent perpendicular to the jet. An interesting phenomenon is found that there is an abnormal increase of O emission intensity （777.4 nm） between 10 mm and 40 mm away from the nozzle. This observation result is very helpful in practical operation.     

The Oblique Incident Effects of Electromagnetic Wave in Atmospheric Pressure Plasma Layers

The propagating behaviours, i.e. phase shift, transmissivity, reflectivity and absorp- tivity, of an electromagnetic （EM） wave in a two-dimensional atmospheric pressure plasma layer are described by the numerical solutions of integral-differential Maxwell＇s equations through a generalized finite-difference-time-domain （FDTD） algorithm. These propagating behaviours are found to be strongly affected by five factors： two EM wave characteristics relevant to the oblique incident and three dimensionless factors. The two EM wave factors are the polarization mode （TM mode or TE mode） and its incident angle. The three dimensionless factors are： the ratio of the maximum electron density to the critical density no/nor, the ratio of the plasma layer width to the wave length d/λ, and the ratio of the collision frequency between electrons and neutrals to the incident wave frequency veo/f.     

Sterilization of Staphylococcus Aureus by an Atmospheric Non-Thermal Plasma Jet

An atmospheric non-thermal plasma jet was developed for sterilizing the Staphylococcus aureus (S. aureus). The plasma jet was generated by dielectric barrier discharge (DBD), which was characterized by electrical and optical diagnostics. The survival curves of the bacteria showed that the plasma jet could effectively inactivate 10 6 cells of S. aureus within 120 seconds and the sterilizing efficiency depended critically on the discharge parameter of the applied voltage. It was further confirmed by scanning electron microscopy (SEM) that the cell morphology was seriously damaged by the plasma treatment. The plasma sterilization mechanism of S. aureus was attributed to the active species of OH, N 2 + and O, which were generated abundantly in the plasma jet and characterized by OES. Our findings suggest a convenient and low-cost way for sterilization and inactivation of bacteria.     

Spatial and Excitation Variations for Different Applied Voltages in an Atmospheric Neon Plasma Jet

A neon plasma jet was generated in air,driven by a 9 kHz sinusoidal power supply.The characteristics of the plasma plume and the optical spectra with plasma propagation for different applied voltages were investigated.By increasing the applied voltage,the plasma plume first increases and then retracts to become short and bulky.The shortened effect of Ne plasma plume(about 10 mm) for the further voltage increasing is more apparent than that of He(about3 mm) and Ar(about 1 mm).Emission intensity of the N_2(337 nm) increases with the applied voltage,gradually substituting the emission intensity of Ne(702 nm and 585 nm) as the noticeable radiation.At the nozzle opening,the Ne(702 nm) emission dominates,while the Ne(585 nm)emission is most noticeable around the tip of the plasma plume.The spatial distribution of the three spectral lines indicates that Ne(702 nm) emission decreases dramatically with plasma propagation while Ne(585 nm) and N_2(337 nm) emissions reach their maxima at the middle of the plasma plume.The results indicate that the Ne(702 nm) emission is much more sensitive to the average electron temperature and the density of the high-energy electrons,so it changes greatly at the tube nozzle and little at the tip region as the voltage increases.The population of high-energy electrons,the average electron temperature,the collision with air molecules and the Penning effect between Ne metastables and air molecules may explain their different variations with plasma propagating and voltage increasing.     

Polymer Surface Treatment by Atmospheric Pressure Low Temperature Surface Discharge Plasma： Its Characteristics and Comparison with Low Pressure Oxygen Plasma Treatment

The polymer treatment with a low-temperature plasma jet generated on the atmospheric pressure surface discharge （SD） plasma is performed. The change of the surface property over time, in comparison with low pressure oxygen （O2） plasma treatment, is examined. As one compares the treatment by atmospheric pressure plasma to that by the low pressure O2 plasma of PS （polystyrene） the treatment effects were almost in complete agreement. However, when the atmospheric pressure plasma was used for PP（polypropylene）, it produced remarkable hydrophilic effects.     

Sterilization of Turmeric by Atmospheric Pressure Dielectric Barrier Discharge Plasma

In this study atmospheric pressure dielectric barrier discharge （DBD） plasma has been employed for sterilizing dry turmeric powders. A 6 kV, 6 kHz frequency generator was used to generate plasma with Ar, Ar/Ou, He, and He/O2 gases between the 5 mm gap of two quartz covered electrodes. The complete sterilization time of samples due to plasma treatment was measured. The most important contaminant of turmeric is bacillus subtilis. The results show that the shortest sterilization time of 15 rain is achieved by exposing the samples to Ar/O2 plasma. Survival curves of samples are exponential functions of time and the addition of oxygen to plasma leads to a significant increase of the absolute value of time constant of the curves. Magnitudes of protein and DNA in treated samples were increased to a similar value for all samples. Taste, color, and solubility of samples were not changed after the plasma treatment.     

Study on the Property Evolution of Atmospheric Pressure Plasma Jets in Helium简

Nowadays atmospheric pressure plasma jets （APPJs） are being widely applied to many fields and have received growing interests from cold plasma community. A helium APPJ with co-axial double ring electrode configuration is driven by an AC high voltage power with an adjustable frequency of 1-60 kHz. Experiments are conducted for acquiring the electrical and optical properties of APPJ, including the discharge mode, current peak＇s phase and APPJ＇s length, etc. Moreover, the actions of Penning effect on APPJ are discussed by adding impurity nitrogen into highly pure helium. The results may contribute to further research and aPPlications of APPJs.     

Experimental Study of a Minitype Atmospheric Non-equilibrium Plasma Source

A mini-type of plasma source was studied experimentally. The results showed that the plasma density, which was generated by an atmospheric non-equilibrium plasma source, rises with the increase in driving electric-field and the momentum of gas particles. For a driving electricfield of 56 kV/cm and a gas particles＇ momentum of 10^9 × 10^-22 g·m/s, the ion density can exceed 10^10/cm^3 while the effective volume of the plasma source is only 2.5 cm^2. This study may help develop a method to generate a minitype plasma source with low energy consumption but high ion concentration. This source can be used in chemical industry, environmental engineering and military applications.     

Atmospheric Pressure Plasma Processing of Fused Silica in Different Discharge Modes

One of the major advantages of utilizing atmospheric pressure plasma processing(APPP) technology to fabricate ultra-precision optics is that there is no subsurface damage during the process.In APPP,the removal footprint and removal rate are critical to the capability and efficiency of the figuring of the optical surface.In this paper,an atmospheric plasma torch,which can work in both remote mode and contact mode,is presented.The footprints and the removal rates of both modes are compared by profilometer measurements.The influences of process recipes and substrate thickness for both modes are investigated through a series of experiments.When the substrate is thinner than 12 mm,the removal rate in contact mode is higher.However,the removal rate and width of the footprint decrease dramatically as the substrate thickness increases in contact mode.     

Gravitational Effects on Plasma Waves in Environment of Sun and Neutron Star

Local plasma phenomena in environment of Sun are observed closely by spacecrafts in recent years. We provide a new method to apply general relativity to astro-plasma physics in small local area. The relativistic dispersion relations of Langmuir, electromagnetic and cyclotron waves are obtained. The red shifts of Langmuir and cyclotron frequencies are given analytically. A new equilibrium velocity distribution of particles soaked in local gravitational field is suggested. The gravitational effect of a neutron star is also estimated.     

A Brief Study on the Ignition of the Non-Thermal Atmospheric Pressure Plasma Jet from a Double Dielectric Barrier Configured Plasma Pencil

To understand the self sustained propagation of the plasma jet/bullet in air under atmospheric pressure, the ignition of the plasma jet/bullet, the plasma jet/bullet ignition point in the plasma pencil, the formation time and the formation criteria from a dielectric barrier configured plasma pencil were investigated in this study. The results were confirmed by comparing these results with the plasma jet ignition process in the plasma pencil without a dielectric barrier. Electrical, optical, and imaging techniques were used to study the formation of the plasma jet from the ignition of discharge in a double dielectric barrier configured plasma pencil. The investigation results show that the plasma jet forms at the outlet of the plasma pencil as a donut shaped discharge front because of the electric field line along the outlet’s surface. It is shown that the required time for the formation of the plasma jet changes with the input voltage of the discharge. The input power calculation for the gap discharge and for the whole system shows that 56% of the average input power is used by the first gap discharge. The estimated electron density inside the gap discharge is in the order of 1011cm-3 . If helium is used as a feeding gas, a minimum 1.48×10-8C charge is required per pulse in the gap discharge to generate a plasma jet.     

Study on an Atmospheric Pressure Plasma Jet and its Application in Etching Photo-Resistant Materials

An atmospheric pressure radio-frequency plasma jet that can eject cold plasma has been developed. In this paper, the configuration of this type of plasma jet is illustrated and its discharge characteristics curves are studied with a current and a voltage probe. A thermal couple is used to measure the temperature distribution along the axis of the jet stream. The temperature distribution curve is generated for the He/O2 jet stream at the discharge power of 150 W. This jet can etch the photo-resistant material at an average rate of 100 nm/min on the surface of silicon wafers at a right angle.