Research On The Diagnostics Of Plasma’s Density In Real-time

With the rapid development of science and technology, people become more familiar with plasma. Since plasma has many considerate properties, such as high electron concentration, high ionization, no electrode contamination and capable of operating over a wide pressure range, in recent years, plasma technology has been applied to chemical vapor deposition, plasma stealth, plasma surface treatment and achieved an unprecedented development. In certain applications, the requirements of the plasma parameters are different. In order to accurately apply plasma technology, plasma parameters such as electron density, ion concentration, energy distribution must be grasped accurately.Plasma diagnose is the mean that apply specific diagnostic method to measure the characteristic parameters of the target plasma in a particular environment. At present, plasma diagnostic methods in the world are divided into non-contact and contact diagnostics, which non-contact diagnostics for high temperature plasma diagnose and contact diagnostics for low temperature plasma diagnose. In this paper, plasma source is a xenon lamp. Since the lamp temperature will be very high after the lamp be lighted, the plasma arc temperature between the poles can up to about 5000 K. So, non-contact diagnostics will be preferred, and this paper ultimately determined applies the quasi-optical cavity measurement system to the plasma diagnostics after a comprehensive comparison of various plasma diagnostics methods.Quasi-optical cavity is a test device with a very high quality factor; meanwhile, it has many other advantages, such as ease of processing, good stability and low cost. With these properties, quasi-optical cavity is widely applied to microwave and millimeter wave testing. This paper aims to design a high-precision quasi-optical cavity diagnostic system, and applied to plasma diagnostics both in 3mm and 8mm band. Firstly, plasma foundation and physical meaning of various plasma parameters are studied. Also, the relationships between different parameters are deduced. Secondly, the relationship between electric field, energy distribution and cavity dimensions is analyzed in this paper. According to the project requires, a quasi-optical resonator can work at both 3mm and 8mm band is designed. Also, the cavity coupling device and Xenon mobile platforms are designed. Then, the principle of plasma diagnostics with quasi-optical cavity is studied and a physical diagnostic model of partially longitudinal filled plasma is established. Meanwhile, the test software is written.In addition, in this paper, plasma generation principal of Xenon discharge is studied and the electron concentration in Xenon lamp is theoretically estimated. Finally, the quasi-optical cavity diagnostic system is build, and this system is applied to 3mm and 8mm band. Experiment shows that quasi-optical cavity can stable resonance in both bands and diagnose values are close to theoretical values. At the end of this article, error analysis of diagnostic system is provided, the advantages and disadvantages of quasi-optical cavity system as well as areas where can be improved are also have been analyzed.