The Research Of Electromagnetic Wave Propagation In Collisional Plasma And Microwave Probe Diagnostic Technique

This paper calculates the interaction between electromagnetic waves and plasma in theory and analyses the amplitude and phase of the electromagnetic waves'propagation in plasma. In addition, two new methods of diagnosing local plasma density by microwave , which are free of collision and sheath, are introduced.We simulated the electromagnetic waves'propagation in the non-uniformed plasma using MAFIA and analyzed the attenuation and phase shift of the electromagnetic waves. Through the simulation, we found that the attenuation of electromagnetic waves is related with the integral of the plasma density on the path of transmission, while not with the shape of the density profile. We proposed a method to measure the density profile of plasma using microwave.In addition, the simulation shows that the collision frequency is inversely proportional to attenuation at this time, which provides a theoretical basis to diagnostic the collision frequency in experiment.Last, through the simulation of two-dimensional oblique plasma layer and three-dimensional spherical plasma, we found that when the pulse electromagnetic wave goes through the plasma, the propagation direction remains unchanged, only the amplitude decays. So the electromagnetic waves'propagation formula in three-dimensional distributed plasma and be approximately resolved by WKB, and can be simplified to one-dimensional issue, which will greatly simplify the working in the future.We starts our analyzing from the electromagnetic waves'dispersion formula, calculates the attenuation and phase shift of electromagnetic waves, and divide the plasma into three zones: the reflection zone, the transmission zone and the collision platform zone, in which the collision platform zone is divided into strong ones and weak ones according to the collision strength. We provide the basis of the division and detailed analyzing of the relationship between the attenuation and phase shift of electromagnetic waves and its frequency, plasma density and collision frequency for each zone. We propose the concept of the relaxation frequency for the first time. All the theoretical work provides a theoretical basis for experimental study of plasma diagnosis using microwave in the future.A new method called microwave point antenna, which is used in local plasma density diagnosis with high-resolution, is proposed. This method can avoid the impact of the collision and the sheath. Point microwave antenna is made of the terminal of the coaxial cable. For its small physical size, it can be reached into the plasma, and used for plasma density diagnosis based on the cut-off phenomenon of microwave propagation in the plasma. We analyze the diagnostic results and believe it's feasible in principle to diagnose the plasma density using the cut-off frequency, and the transmission coefficient changes with the frequency in the cut-off area are decided by the density gradient primarily.Besides, we verified our measurement results using the existing microwave interferometry and the double-probe, and proved that the microwave point antenna is not only a effective diagnostic tool of the plasma density, but also can be used for calibrating the dual-probe measurements through its accuracy.We proposed a new diagnostic tool of the plasma density called microwave monopole antenna, which is based on the characteristic of the transmission of the antenna. We verified its feasibility from the aspect of the theory, experiment and simulation.From the theory, we analyzed the relationship between the characteristic of the transmission of the microwave monopole antenna and the dielectric constant of the surrounding media, so as to provide a theoretical basis for using microwave monopole antenna as a diagnostic toolFrom the experiment, we analyzed the production of microwave antennas monopole as well as its characteristic of the transmission based on our measurement. We improved its measuring performance and verified its feasibility in the non-dispersive medium. The microwave monopole antenna got the consistent results with electrostatic double-probe when measuring the plasma density under different air pressures, which proved the feasibility of using microwave monopole as a diagnostic tool of the plasma density.We also proposed the correction factor to the collision from the measurement principle, as well as a solution to revise the collision of the measurement results of the plasma density by the microwave monopole antenna.As it is a new diagnostic tool, we analyzed its measurement accuracy and measurement range from the experiment. In addition to the experiment, we verified its feasibility through simulation, and analyzed the sheath correction method and the spatial resolution of the microwave monopole antenna.