Research On The Properties Of Plasma Based On Microwave Transmit System

Plasma diagnostics based on microwave is a kind of important plasma diagnostic method, which includes microwave interferometer method, microwave reflectmeter method, electron cyclotron emission method and microwave transmit method. Plasma diagnostics with microwave is nonintrusive, which would not pollute the plasma and is of high accuracy in measuring. So, it’s widely used in plasma diagnostic environment.Plasma diagnostics with microwave transmit method is studied mainly, include microwave transmit diagnostic theory, then, this method is used in shock tube plasma diagnostics. The dissertation is arranged as follow:Firstly, electromagnetic wave transmit in plasma is discussed, the attenuation constant and phase constant of electromagnetic wave in plasma is computed with analytic method, the reflect constant and transmit constant of wave incident on plasma boundary is also calculated. The effect of electron density and collision frequency on these constant is simulated, the result of which indicate that: high electron density leads to more reflection and less transmission, high collision frequency leads to less reflection and transmission and more attenuation.Secondly, double frequency microwave transmit attenuation method is introduced, this kind of method is limited in diagnostic of steady plasma, which would cause error while measuring fast changing plasma. Then microwave transmit diagnostic theory is proposed based on this method, which both measure the attenuation and phase shift of microwave through plasma, the attenuation constant and phase shift constant is also used to calculate the electron density and collision frequency of plasma. The range of electron density is obtained from simulation. There is also a kind of situation that the shape of plasma could be cylinder, so this kind of plasma is also analyzed. The scatter field of cylinder plasma is calculated, the effect of electron density to the field is introduced, the possibility to measure this kind of plasma is also estimated.Then, a kind of plasma-shock tube plasma, is analyzed, the model of shock tube is build. From which, the shock tube is divide into five slab, the field at each slab is analyzed, the total reflect coefficient and transmit coefficient is calculated, the simulation result show the attenuation of shock tube as a function of electron density.Finally, the microwave transmit measuring system based on microwave transmit theory is introduced, the diagram of amplitude and phase at reflect channel and transmit channel is plotted. The microwave transmit system is used to measure electron density of shock tube plasma, the characteristics of this kind of plasma is also analyzed.