The Diagnosis And Microwaves Propagation Characteristics Of The Coaxial Gridded Hollow Cathode Discharge

In recent years,the interaction between electromagnetic wave and plasma has become a hot topic because of its application in microwave attenuation of rocket exhaust,reentry vehicle communication and microwave diagnosis for plasma.Ground-based experimental study on the interaction between electromagnetic wave and plasma,which is economic,repeatable and stable,is widely used in various kinds of simulation experiments.These experimental studies can lay a solid foundation for the theoretical model.Although the theoretical framework of the interaction between electromagnetic wave and plasma has been perfected,but there are few experimental studies on the interaction between electromagnetic wave and plasma.Based on this,this paper designs and builds hollow cathode discharge plasma with coaxial gridded electrodes and the microwave transmission system to study the transmission characteristics of electromagnetic waves in different plasma environment,the use of electromagnetic waves through the plasma phase and amplitude of the plasma after the diagnosis.In this paper,a new type of hollow cathode discharge plasma is designed and built,and the coaxial gridded electrode is used to produce large-scale uniform weakly ionized collisional plasma.The whole plasma system includes the inlet gas system,the vacuum system,the intermediate frequency AC power supply system and Langmuir probe diagnostic system.The working condition of the whole system and the working states with different atmosphere were studied and the basic parameters were diagnosed by the Langmuir probe.The method was compared with the spectral diagnosis method,and a poly diagnosis method is established for plasma,which lays the experimental foundation for the research of electromagnetic wave and plasma interaction.The propagation characteristics of coaxial gridded hollow cathode plasma are analyzed theoretically,and the transmission model of the interaction between electromagnetic wave and plasma is established.The time domain finite difference of electromagnetic field is established.The effects of plasma electron density,plasma collision frequency and the size of plasma on the transmission characteristics of electromagnetic waves were studied.The physical mechanism of the interaction between electromagnetic wave and plasma was explained,which provides theoretical guidance for the experimental study on the interaction between electromagnetic wave and plasma.The broadband microwave transmission system is designed and built.The coaxial gridded hollow cathode discharge device is used to study the transmission of electromagnetic waves in the hollow cathode plasma.The influence factors of the electromagnetic wave transmission coefficients under different discharge input power and discharge pressure are analyzed.The influence factors of the electromagnetic wave transmission characteristics under the limited the volume of the plasma are analyzed and compared with the theoretical calculation model.It is proved that the electromagnetic waves are transmitted in the plasma which is directly related to the electron density and the collision frequency.At the same time,it is proved that the electron density and the collision frequency of the plasma play a decisive role in the phase change of the electromagnetic wave transmission in different plasma conditions.Finally,the microwave attenuation and the phase change of the microwave after plasma are studied.A microwave diagnosis method for coaxial gridded hollow cathode discharge plasma is proposed.The transmission of electromagnetic waves in plasma under different discharge conditions is messured for electronic density and temperature.Compared with Langmuir probe diagnosis method,the accuracy of microwave diagnosis is proved,and the poly diagnosis method of plasma is improved.