Gas Breakdown of Radio Frequency Glow Discharges in Helium at near Atmospheric Pressure

A one-dimensional self-consistent fluid model was developed for radio frequency glow discharge in helium at near atmospheric pressure, and was employed to study the gas breakdown characteristics in terms of breakdown voltage. The effective secondary electron emission coefficient and the effective electric field for ions were demonstrated to be important for determining the breakdown voltage of radio frequency glow discharge at near atmospheric pressure. The constant of A was estimated to be 64±4 cm 1 Torr 1 , which was proportional to the first Townsend coefficient and could be employed to evaluate the gas breakdown voltage. The reduction in the breakdown voltage of radio frequency glow discharge with excitation frequency was studied and attributed to the electron trapping effect in the discharge gap.     

Atmospheric Pressure Radio Frequency Dielectric Barrier Discharges in Nitrogen/Argon

This work reports the experimental results on the characteristics of radio frequency dielectric barrier N2 /Ar discharges.Depending on the nitrogen content in the feed gas and the input power,the discharge can operate in two diferent modes: a homogeneous glow discharge and a constricted discharge.With increasing input power,the number of discharge columns increases.The discharge columns have starlike structures and exhibit symmetric self-organized arrangement.Optical emission spectroscopy was performed to estimate the plasma temperature.Spatially resolved gas temperature measurements,determined from NO emission rotational spectroscopy were taken across the 4.4 mm gap filled by the discharge.Gas temperature in the middle of the gas gap is lower than that close to the electrodes.     

RC-Coupled Atmospheric Glow Discharge in Air

Resistance and capacity-coupled glow discharge （RCCGD） is a new method to produce atmospheric pressure glow discharge in air. In RCCGD, each electrode is connected with both a resistor R and a capacitor C. The R and C can provide a negative feedback to prevent the transition from glow to spark discharge. The influence of coupled resistance, coupled capacity, inter-electrode gap and power source frequency on the discharge is studied and discussed.     

Electrical Characteristics of Pseudoglow Discharges in Helium under Atmospheric Pressure

A pseudoglow discharge behaviour is achieved at a 2.0-mm dielectric-dielectric electrode gap in pure helium under atmospheric pressure. An experimental study of the pseudoglow discharges is presented. The electrical characteristics and the discharge photos of the pseudoglow discharges are analyzed and discussed. The current-voltage parameters of the pseudoglow dis- charges are considered in regard to the influence on their behaviour.     

The Role of Metastable Atoms in a Homogeneous Atmospheric Pressure Barrier Discharge in Helium

A one-dimensional fluid model for homogeneous atmospheric pressure barrier discharges in helium is presented by considering elementary processes of excitation and ionization including a metastable atom effect. Using this model we investigate the behaviours of the helium metastable atoms in discharges as well as their influence on the discharge characteristics. It is shown that the metastable atoms with a relatively high concentration during the discharge are mainly produced in the active phase of the discharge and dissolved in the off phase. It is also found that the metastable atom collisions can not only provide seed electrons for discharges but also influence the concentration of ions. A reduction of matestable atom density results in a drop in the charged particle densities and causes a qualitative change in the discharge patterns.     

Transition from Spark Discharge to Constricted Glow Discharge in Atmospheric Air by Capacitor Coupled Discharge

The transition from a spark discharge to a constricted glow discharge in atmospheric air was studied with a capacitor coupled pin-to-water plasma reactor. The reason of the transition is considered to be of various factors, namely the change of the air gap due to the polarization of water molecules by the electric field, the feedback effect of the capacitors, and the ion trapping mechanism. The effects of the frequency of the power supply, inter-electrode gap, and coupled capacitance on the discharge transition were also investigated.     

Self-Consistent Model for Pulsed Direct-Current N2 Glow Discharge

A self-consistent analysis of a pulsed direct-current (DC) N2 glow discharge is presented. The model is based on a numerical solution of the continuity equations for electron and ions coupled with Poisson‘s equation. The spatial-temporal variations of ionic and electronic densities and electric field are obtained. The electric field structure exhibits all the characteristic regions of a typical glow discharge (the cathode fall, the negative glow, and the positive column). Current-voltage characteristics of the discharge can be obtained from the model. The calculated current-voltage results using a constant secondary electron emission coefficient for the gas pressure 133.32 Pa are in reasonable agreement with experiment.     

Study of Atmospheric Pressure Abnormal Glow Discharge

Atmospheric pressure abnormal glow discharge （APAGD） was carried out simply with a transformer of 1 ： 500 driven by a alternating current with a frequency of 50 Hz. Typical stable discharge parameters, namely voltage of 400 V to 850 V and current of 60 mA to 110 mA were measured by oscillograph. Simulation of the discharge process suggested that the stable discharge was supported by the impedance from the secondary coil of the transformer, which offered a negative feedback to prevent the discharge from turning into an arc. An interpretation was given for the oscillogram of the sinuous discharge current and square voltage. Furthermore, the electron temperature and electron density averaged in the discharge channel of APAGD were estimated.     

Simulations and Measurement of Electron Energy and Effective Electron Temperature of Nanosecond Pulsed Argon Plasma

The behavior of argon plasma driven by nanosecond pulsed plasma in a low-pressure plasma reactor is investigated using a global model, and the results are compared with the experimental measurements. The time evolution of plasma density and the electron energy probability function are calculated by solving the energy balance and Boltzmann equations. During and shortly after the discharge pulse, the electron energy probability function can be represented by a bi-Maxwellian distribution, indicating two energy groups of electrons. According to the effective electron temperature calculation, we find that there are more high-energy electrons that play an important role in the excitation and ionization processes than low-energy electrons. The effective electron temperature is also measured via optical emission spectroscopy to evaluate the simulation model. In the comparison, the simulation results are found to be in agreement with the measure- ments. Furthermore, variations of the effective electron temperature are presented versus other discharge parameters, such as pulse width time, pulse rise time and gas pressure.     

高压脉冲辉光放电内表面注入及等离子体特征研究

为了提高内表面注入的剂量及深度均匀性,作者将脉冲高压辉光放电机制引入到内表面改性的研究中。利用发射光谱法及静电探针法对该方法获得的离子体参数进行了诊断,并在特定的内筒中采用氮气为工作气,进行了离子注入实验。结果显示,采用这种方法可以在内筒获得连续存在的等离子体。Ar等离子中含有大量激发态原子,而N等离子体中N2+离子占离子数量的绝大多数。等离子密度随着电压的提高显著提高,当电压从10kV增加到15kV时,Ar等离子体中离子密度增加约4倍,N等离子中离子密度增加约2倍。内表面获得均匀性良好的改性层,对于直径56mm的圆筒在电压20kV、气压1.5Pa条件下注入深度达到16.9nm,剂量均匀性可达到87.3%。     

Filament Discharge Phenomena in Fingerprint Acquisition by Dielectric Barrier Discharge

In this paper, the dielectric barrier discharge fingerprint acquisition technique is introduced. The filament discharge phenomena were observed in the process of fingerprint acquisition. The filament discharge reduced the quality of fingerprint images. Obviously, it was necessary to eliminate streamer discharges in order to get good fingerprint images. The streamer discharge was considered to be the cause of the filament discharge in the experiment. The relationship between the critical electric field and the discharge gap was calculated with the Raether＇s model of streamer discharge. The calculated results and our experiment proved that it would be difficult for the streamer discharge to occur when the discharge gap was narrow. With a narrow discharge gap, the discharge was homogeneous, and the fingerprint images were clear and large in area. The images obtained in the experiment are very suitable for fingerprint identification as they contain more information.