Research On The Diagnostics Of Plasma’s Density With Fabry-perot Cavity

As the development of science and technology, plasma technology is widely applied in many professional field and plays important roles. To handle and apply plasma technology better, it is especially important to research its physical properties and basic parameters. The plasma diagnostic is trying to figure out the parameters of plasma through different ways. There are a lot of ways to diagnose plasma studied by researchers from different countries, basically these methods can be divided into touch and no-touch class. This thesis based on the issue from astronautic association,adopts Quasi-optical cavity to diagnostic plasma in millimeter wave band, to carry out the test and set standard. The Quasi-optical cavity is cheap and the construction is simple. The method can figure out result instantaneity and stably.First of all this thesis research the basic physical characteristic of plasma, study the parameters of plasma that to be measured and understand the physical significance of the parameters. The mathematical relationship of plasma density, collision frequency and permittivity is obtained.Secondly, this thesis make a further study on the quasi-optical resonator’s theoretical knowledge and the characteristic of electromagnetic field within it. Based on the perturbation theory, the formula of quasi-optical cavity diagnostic is deduced. With these knowledge, a quasi-optical cavity with symmetric spherical mirror is designed. Coupling the microwave into the cavity with little circle. The designed cavity can work well from 15 to 40 GHz.Programing the algorithm of diagnostic into a GUI to make experiment convenient. Glow discharge is studied and a glow discharge equipment is applied as the plasma resource of experiment. Collect the glow discharge equipment, the quasi-optical cavity diagnostic system and Langmuir probe to build a diagnostic system. Experiment in this diagnostic system, different kinds of data and curve under diverse discharge current are got. The result of the Quasi-optical cavity system agree well with theory. The designed system owns high accuracy. Large number of repeated experiment data and curves shows that the quasi-optical cavity has excellence stability.Finally, experimental error is analyzed, the advantage and disadvantage is surmised and suggests that can make the system work better are offered. The questions that need to be further studied are summarized.