Simulation And Experiments On Electrical Character Of Atmospheric Low-temperature Plasma Jet

Plasma refers to the state that when gas is influenced by external factor, some of all the electrons of the gas molecule absorb enough energy to ionize. The ways lead to generating plasma including heating, energetic particle's bombarding and gas discharge. Atmospheric plasma jet is a typical kinds of gas discharge that is a king of cold and non-equilibrium plasma. Low temperature means temperature is lower than 108 K, while non-equilibrium means the temperature of electron is lower than the temperature of gas. And the greater the difference between them, the higher the level of non-equilibrium.As atmospheric plasma jet technology has advantages of low discharge temperature and high concentration of active particle, it is widely used in material modification, biomedicine sterilization, environment protection, etc. It attract much attention in the field of plasma. In essence, plasma jet is generated in a limit cavity by external source and sprays out of it by means of supporting gas.Plasma jet has the following advantage:(1) low condition of generation, only by applying several kilovolts voltage in atmosphere can it generate;(2) the jet away from the high voltage electrode to guarantee the safety of the operator;(3) the high spaying speed of jet, which makes it possible for active particles to arrive the treated substance's surface before they diminish;(4) the temperature of jet out of the cavity close to the room temperature and its energy low so as not to improve the treated substance's temperature;(5) no more shape and size acquirement for the treated substance, if moving the jet device, we can treat the substance in three dimension.So far, the research in homeland and overseas is including following three aspects:(1) the research of discharge feature, build the equivalent circuit model to simulate the oscillography of voltage and current as well as lissajous figures;(2) design of electrode structure including needle-ring, ring-ring, spiro-ring and micro-hollow cathode structure and make experiment to identify and analyze discharge feature base on this, but lack of research on its mechanism;(3) production diagnoses making use of electrostatic probe and emission spectrum to measure the jet's concentration, electron temperature and density,but cannot find the correspondence to the influencing factor. In conclusion, since the requirement of plasma jet will change with different applications, exploring the rule of plasma jet's generation can be used for generating different jets aiming for certain use, which has value of engineering application.Aiming at the above issues, this paper begins with the common needle-ring structure, analyze the circuit feature through circuit simulation, analyze electric fluent and plasma fields through FEM simulation and analyze the discharge influencing factor experimentally. Then study further and modify the electrode structure and test its performance. The paper's main study contents lists below:First, utilize the matlab's Simulink tool to build the equivalent circuit model to analyze its characteristics of voltage and current. The paper shows that plasma jet's discharge and DBD's discharge both display the microdischarge. And because of the polarity effects on strengthing the gap electric strength, the initial discharge voltage in the next half period will be advanced.Second, build the plasma jet device's FEM model. The paper first simulates the distribution of electric field and space charge in the quartz tube before and after discharge, and research the structure and source properties' effects on the electric field. And we find altering the gap distance and size of electrode will have a strong influence in the electric field. And then, the paper simulates the fluent field on the conditions of side and one end ventilation. We find the gas flow rate near the nozzle will be faster by side ventilation then by one end ventilation. But in this way, in a small scale, the change of atmosphere pressure is greater. Then the paper uses the Plasma module in COMSOL to simulate the development of plasma bullet. Eventually, the paper uses the Jet&Poudures software to simulate the jet out of the tube. We find that the temperature decreases rapidly along diameter and the gas flow rate in redius is lower than in axial.Third, set up plasma jet's discharge platform with supporting gas of argon and analyze structure and external properties that influence jet's length and initial discharge voltage and explain why the jet length will not be always extended with increasing of voltage and gas flow rate and calculate device's equivalent capacitor and effective power and analyze its regulation.Then, according to the simulation and experiment's regulation, we study further the factor that influence jet's length and intensity then introduce the external ground electrode to realize and identify by experiments. The paper refers the change of the plasma jet is related to the space polarity.