Research On The Microwave Diagnostics Of Plasma Density Profile

As the rapid development of plasma technology,people urgently need to know the plasma parameters.Especially in fields of national defense,how to break through blackout has been puzzling scientists for a long time.Without plasma diagnostic techniques,the development of plasma technology cannot develop.Microwave technology is the effective method in plasma diagnostic,which can be divided into contact type and un-contact type.Based on microwave reflection method,multiple frequency antenna is adapted to detect plasma for non-contact diagnostic in this article.Mainly,microwave reflection method using cutoff feature to distinguish the profile of plasma electron density,it always ignore the type of low density in ages and high in middle.Basing on multilayer model,the paper presents high sensitive multi-frequency antenna to realize multilayer testing.Firstly,after introducing plasma parameters and define their significance,the thesis studies dielectric property of plasma,parameter of which is influenced by electron density and collision frequency.Different methods of plasma diagnostic are compared.Secondly,by analyzing the interactions between plasma and electromagnetic wave,the character of electromagnetic waves in plasma is introduced.Using equivalent input impedance method,the electron density,collision frequency and plasma thickness are considered as the main element for microwave reflection character in plasma.And on this basis,the paper propose multiple frequency radiating antenna to detect plasma through theoretical analysis and simulation.Thirdly,an antenna working in three frequencies has been designed in this paper.Choosing the glow discharge device as plasma source to fulfill the system integration,this thesis has performed the experiment.Finally,experimental data are analyzed to calculate the plasma density.After analyzing the source of error,existent deficiency and improved method are pointed out.Using multiple frequency antenna,electron density was calculated to be in the range of 1015~1016/m3 and three multilayers of data was proposed.