| In the near space,with the continuous increase of the flying speed of the aircraft,the aircraft will rub violently with the air,causing the gas coated on the surface of the aircraft to undergo a thermochemical ionization reaction,resulting in a layer of "plasma sheath".The plasma sheath on the periphery of the aircraft will cause scattering and attenuation of incident electromagnetic waves,interfere with the normal communication,measurement and control,navigation process of the aircraft,and in serious cases,the communication will be interrupted,and the outside world can not keep in touch with the aircraft,namely the "black barrier" phenomenon.Therefore,it is of great significance to study the electromagnetic characteristics of plasma sheath to suppress the "black barrier".In this paper,based on the ground inductively coupled plasma device,ground experiments are carried out to simulate some characteristics of the plasma in aerospace,and the spectroscopic method is used to diagnose the plasma parameters generated by the inductively coupled plasma device,and combined with theoretical simulation to analyze the complex problems of electromagnetic wave propagation in inductively coupled plasma,it can provide theoretical basis for the communication,navigation,detection and other technologies of hypersonic vehicles.The main work of the paper is as follows:1.Measurement of electron temperature distribution in an inductively coupled plasma device.The intensity information of the spectral line is collected by the spectrometer,and the change trend of the intensity of the spectral line with the coil power,air pressure and intake air volume is analyzed.The inductively coupled plasma electron temperature model was established by the method of electron collision interface,and the electron temperature was calculated under different coil power,different air pressure and different intake air volume.And design the cavity axial and radial plasma parameter measurement experiments to analyze the distribution law of plasma electron temperature in the cavity.2.Measurement of electron density distribution in an inductively coupled plasma device.By analyzing the broadening mechanism of the spectral line,the electron density of the inductively coupled plasma was measured by the Stark broadening method and the probe-calibrated emission spectrometry.For the Stark broadening method,the influence of Doppler broadening on the spectral line broadening is considered,which improves the measurement accuracy of the electron density.For the probe calibration emission spectrometry,the Langmuir probe was used to measure the distribution of the plasma density in the axial direction of the 300 W and 500 W cavity.Combined with the spectral line intensity collected by the spectrometry method,the value of the proportionality coefficient "K" was obtained.Then,the diagnosis of electron density is carried out.Based on the above two methods,the law of electron density changing with different parameter conditions and the distribution of electron density in the axial,radial and vertical directions of the cavity are analyzed.Finally,the electron densities diagnosed by Stark broadening method,probe calibration emission spectrometry and Langmuir probe method were compared and analyzed.3.Carry out research on the transmission characteristics of electromagnetic waves in inductively coupled plasma.Based on the ICP plasma device,a patch antenna is used to measure the S21 parameters of electromagnetic waves of different frequencies transmitted in plasmas with different densities and different distributions.At the same time,based on the axial electron density distribution of the cavity measured by the Stark broadening method,the equivalent transmission line method was used to calculate the reflection coefficient and transmission coefficient of the electromagnetic wave propagation in the inductively coupled plasma.Finally,the influence of the ablation effect on the electromagnetic wave propagation characteristics is analyzed. |
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