Algorithm On Plasma Characteristics Based On Multi-Channel Microwave Interferometer

When intercontinental missile enters the atmosphere or stealth aircraft flies through the atmosphere,plasma wake will be generated after the friction between the aircraft surface and the atmosphere.Plasma wake is of great significance to the research of stealth and anti-stealth technology,so it is necessary to study the electromagnetic characteristics of plasma wake.Plasma diagnosis is an important means to study the characteristic parameters of plasma.In the traditional diagnosis methods,the probe method will disturb the plasma,thus affecting the diagnosis results.The distribution function of plasma electron density needs to be assumed when microwave interferometry is used to solve the problem,which results in rough diagnosis.To solve the above problems,this thesis adopts the diagnosis method based on multi-channel microwave interferometer and puts forward the relevant algorithm.The specific content of the thesis is divided into the following parts:Firstly,in view of the limitation of the traditional single-channel microwave interferometer method in diagnosing the plasma electron density,a multi-channel microwave interferometer is adopted in this thesis,which can collect the electromagnetic wave variation information at different positions in the radial direction of the plasma at the same time when the plasma electron density distribution is unknown.It is possible to accurately diagnose the radial distribution of plasma electron density.Then,according to the electromagnetic wave signal collected by multi-channel microwave interferometer,the phase information of 0°?360° is obtained by using the if digital receiver technology and I\Q demodulation,which is processed by using the Abelian inverse conversion method based on Taylor expansion.The algorithm solves the problem of singularity in the traditional Abelian inverse transformation results.Finally,the feasibility and correctness of the method are verified by simulation using several functions.Furthermore,aiming at the limitation that the calculation accuracy of inverse Abelian transformation based on Taylor expansion is affected by the number of expanded terms,this thesis proposes a hierarchical recursive method based on inverse Abelian transformation.This method constructs a multi-layer medium model,and the calculation method is simple,without polynomial expansion and normalization operation.It can overcome the limitation of the calculation accuracy of the inverse Abel transform by the number of expanded terms and better suppress the discrete error caused by the drastic fluctuation of plasma electron density in radial direction.Then,the principle of this method and the derivation of recursive formula are introduced in detail.Finally,using the mentioned above two algorithms for diagnosis of multiple sets of ballistic target and shock tube experiment environment,experimental data were collected to solve out the plasma under the environment of the two kinds of different location of the electron density distribution,and the fitting is studied by using gaussian distribution,the plasma in the shock tube and ballistic target under the environment of electron density radial distribution.