Research On The Plasma In High Power Microwave Devices And Its Effects On The Microwave Transmission Properties

High-power microwave technology has a broad development perspective both in military and civilian fields.Recently,with the rapid development of high-power microwave source technologies,the amplitude of the electric field transmitting in microwave devices is getting closer to the breakdown threshold of the working gas.Once there are discontinuous structures(such as coupling holes)in these devices,gas breakdown occurs frequently.Plasma generated in this progress will have significant influence on the transmission properties of the incident wave,and then affects the performance of microwave devices.Therefore,it is of great significance to study the plasma in high power microwave devices and its effects on the microwave transmission properties by combining the knowledge of electromagnetic theory and plasma physics.This paper simulated high power microwave gas breakdowns under different conditions,calculated the important parameters of generated plasma and investigated the influence of plasma on microwave transmission properties.The results of this paper are of great significance for revealing the physical mechanism of high power microwave gas breakdowns,and can provide theoretical support for the design of high power microwave devices and for the rational utilization of microwave plasma.The main innovations of this paper are as follows:1.A 3-D fluid model to simulate the gas breakdown happened in high power microwave devices was established.Results including the change rules and distribution of electron density,electron temperature and electric field were obtained,the breakdown threshold and breadown time with different gas pressures and microwave frequencies were calculated.These results can be used to describe the detailed breakdown process.2.The influence of the plasma on the transmission properties of microwave was studied.Based on the research scenario of microwave propagates through breakdown region in rectangular waveguide,the reflection and absorption of microwave caused by the plasma generated under different conditions were simulated using 3-D fluid model.The impacts of gas pressure,microwave frequency and the thickness of plasma slab on the microwave transmission properties were calculated.3.The similarity principle in microwave breakdowns was proposed based on the similarity principle in DC discharges.The validity of this principle was varified,the precondition and the application scope were clarified using fluid model.A scaling substitution method was proposed based on this principle which can provid an efficient method to study the breakdowns happened in ultra-size environments.4.A microwave plasma torch based on rectangular waveguide was designed,which can be an equipment to produce plasma for experiments.