The Researches On The Nitrogen Plasma Electron Behaviors In Microwave Pulsed Discharge At The Low Pressure Of The Open Space

Microwaves generating plasmas technology is applied to industry production every early. Recently people are more and many researches have further discussions on the plasma's characteristics generated by microwaves. But people mostly care about the functions of the steady plasmas after the microwave generating the plasmas, and they don't care about the process of plasmas forming and the variation of plasmas state during the discharge. On the other hand, the researches of the microwave gas breakdown are involved in many microwave transmission or microwave component researches, but the most of them on the microwave gas breakdown are aimed at preventing the effects of microwaves inducing breakdown (sparks), so this kind researches mostly care about the microwave parameters and environmental factors at the moment of the microwave breakdown, but don't discuss and study the configuration after the microwave breakdown in detail.This paper is mainly aiming at discuss the whole process from the beginning of the microwave breakdown, generating plasmas, to finally forming the steady plasmas in detail. Thus, the core point of studying this whole process is the researches of how the electrons absorbing energies from the microwave electric field. Due to the much complexity of this process, the simplification of the unimportant factors is very necessary. In the experiment, this paper chooses the condition of the open space to avoid the interactions between the electrons and the wall of the vessel. Besides, the state of the background gas is more steady, and meanwhile, the diffusion effect of the electrons is dominant. But the condition of the open space induces a non-neutralized process of forming plasmas in the microwave discharge, this is because the movement of the electrons is much more faster than the ions. And in the experiment, the low pressure nitrogen is selected as the background gas to make the collision process between the electrons and the nitrogen molecules more important, for avoiding the severe influence of the collision process between the electrons or the electrons and the ions at the extreme low pressure, or the collision process between the nitrogen molecules coming out as the main collision process at the extreme high pressure. This paper selects the method of the pulsed microwave discharge to clearly and directly observe the process from the plasmas generation to finally forming the steady plasmas. The method of the pulsed microwave discharge provides the references of the measurements and diagnostics.In the theory, this paper firstly starts from the movement model of the single electron, and then, educes the fluid equation of the single electron's movement in the microwave electric field and discusses the application conditions and attentions of the equation. Then, the each collision processes between the electrons and the nitrogen molecules, the collision processes between the nitrogen molecules, the collision processes between the electrons, the electrons and the ions, and the diffusion of the electrons are discussed in detail. The each collision processes are studied for the conditions of the open space and the low pressure, and their application conditions are analyzed, and finally the supplementary specification of the single electron model is done with the collision behaviors of the electrons. At last, the single electron model is developed to the Global Model, and the collision behaviors of the electrons are analyzed concretely and the application conditions of the model are discussed from the viewpoint of statistics.Eventually, the variation process of the plasma electron temperature and density generated by pulsed microwaves in open space at low pressure and what affects them are analyzed and discussed according to comparing the measured results and the theoretic results.In the experiment, the pressure is 300Pa, and the nitrogen is selected as the background gas to be discharged at the gas temperature of 300K. The C band 5.3GHz microwave is used to produce the plasmas via focusing with the pulse width of 1?s and the repetition frequency of 500Hz and the peak power of 600-800kW. In diagnostics, the X band continues wave is used for the variation of the electron density as the microwave transmission diagnostic, and meanwhile, the emission spectroscopic diagnostic is adopted to measure the vibrational and rotational temperatures of the nitrogen.At last, according to comparing the experimental results and the theoretic results, it's found that in the process from the microwave breakdown to forming the steady plasmas, the electron temperature increases rapidly to a higher value firstly, and then the higher electron temperature makes the ionization process act severely to form the avalanche effect, and at this moment, the electron density starts rising rapidly. When the electron density increases above the critical density of the discharge microwave, the plasmas start to block the discharge microwave's entrance, which causes the microwave electric field entering the plasmas starts to attenuate, and the attenuation of the microwave electric filed will make the energies of the electrons absorbed from the microwave electric field decrease, and then make the electron temperature decrease. The decrease of the electron temperature will result in the decrease of the ionization rate, and then lead to the decrease of the electron density's rising rate. Finally, the steady plasmas are formed at the equilibrium of the gain and loss of the electron numbers and energies.The whole discharge process is a non-equilibrium and non-linear process. But tracing it to the physical essence, it's the result of the interactions between plasmas and microwaves. This is a unique characteristic of plasmas contrast to the other three states.