High Accuracy Diagnostics For Plasma Electron Density In Near Space Device

In recent years,technology of aerospace developing very fast,the near space which is not only a flight corridor for hypersonic vehicles but also a place for spacecraft entering and leaving space,has been paid more and more attention.Due to the effects of viscosity and shock waves,air molecules near the surface of the aircraft will ionize to form plasma due to intense thermal motion,and cover the surface of the aircraft to form a plasma sheath,which contains a large number of neutral particles,positive ions and free electrons.Charged particles(mainly free electrons)will absorb,reflect,and scatter electromagnetic waves,triggered a series of electromagnetic effects which generate distortion in communication signals.Ground simulation is an effective method to study the high-speed target plasma in near space,so that an Experimental Research Apparatus for Electromagnetic Science(ERAES)forhypersonic vehicle plasma in near space has been developed,in the background.ERAES mainly studies the interaction mechanism between electromagnetic wave and plasma.Abnormal communication problem of high-speed aircraft.The problem of reliable radar detection under plasma cladding.All of these problems require reliable electron density data.In this paper,two kinds of electron density diagnosis systems are developed for ERAES:three-channel HCN interferometer and electrostatic probe system,of which the electrostatic probe system is divided into quick moving probe system and probe array system.The interferometer mainly measures the integral electron density of the plasma,and the fast moving probe measures the radial distribution of the electron density.In the first chapter,the research background,research purpose and parameter range of ERAES are introduced.The research status of HCN interferometer and electrostatic probe is introduced.In chapter 2,the physical basis of plasma electron density measured by HCN interferometer is introduced in detail.The principles of electrostatic probes and the modified theory of non-ideal probe are introduced.The third chapter mainly introduces the development of three-channel HCN interferometer,including the choice of interferometer wavelength,the choice of interferometer structure,the choice and development of IF(intermediate frequency)modulation system,optical path design,mechanical design and probe selection.The fourth chapter introduces the development of electrostatic probe,including the design of probe bracket.Since the probe bracket is placed in the ERAES,so the probe works in the high-temperature flow field,so we used ANSYS software to analyze the bracket stress and thermal distribution on the probe,and the results show that our design is reasonable and effective.In chapter 5,the HCN interferometer and the electrostatic probe system are tested.First,wedge is used to replace the plasma for the mesa test.Then the HCN interferometer and electrostatic probe system were tested by multi-cavity combined inductively coupled plasma.The measurement results are consistent with each other.At last,we summarize the whole paper and look into the future.