Spectral Diagnosis Of High Power Inductively Coupled Plasma

When the aircraft is flying near the atmosphere of space at high speed,a layer of"plasma sheath"covering the surface of the aircraft will be produced due to the friction between the surface of the aircraft and the atmosphere.Communication signals and radar waves will cause a series of special electromagnetic phenomena when passing through the plasma sheath.Therefore,studying the distribution of parameters such as electron temperature and electron density inside the sheath is useful for exploring and breaking through the communication"black barrier problem"and"detecting abnormal problems"It is of great significance.At present,ground simulation is an effective method to study the plasma of high-speed targets in nearby space.In this paper,the plasma electromagnetic scientific experimental research device for high-speed targets in nearby space is used as the plasma spectrum generation system,an experimental platform is built,and emission spectroscopy is adopted.The working medium gas is N atom,N⁺characteristic spectrum and N₂molecular band in the ICP quartz tube cavity.The spectral characteristics of plasma under discharge voltage of 6～12k V and discharge pressure of 300～1200Pa are studied,and important parameters such as electron temperature,gas temperature and electron density are calculated and analyzed.The spectral characteristics of plasma include spectral line wavelength,spectral line intensity,spectral line type and spectral line broadening,including the types of particles present in the discharge plasma,the energy state and collision frequency of the electrons in the plasma,and the radiation particles in space Information such as the state of exercise.This paper reveals the corresponding relationship between the spectral line intensity and the transition frequency and transition energy level,analyzes the influence of the discharge voltage and discharge pressure on the spectral line intensity,and finds that the spectral line intensity increases with the increase of the discharge voltage and pressure.By fitting the line types of multiple characteristic lines,it is found that the plasma line type in the experiment is more in line with the Lorentz line type.The analysis reason is that the discharge voltage is relatively high and the external electric field has a significant Stark effect on the radiating particles.,The broadening of the spectral line is mainly based on the broadening of Stark.The influence of discharge voltage and discharge gas pressure on the spectral line broadening is further analyzed.The results show that the spectral line broadening increases with the increase of the discharge voltage,and the influence of the discharge gas pressure on the broadening is not obvious.The Boltzmann slope method is used to study the electron temperature of air discharge plasma.Under the experimental conditions in this article,the electron temperature is in the range of 1.18～1.62e V,and the discharge voltage,discharge pressure and other experimental conditions have a greater impact on the electron temperature.The N₂⁺（B-X）band was fitted by LIFBASE software,and then compared with the spectrum obtained in the experiment,the vibration temperature was 0.58e V and the rotation temperature was0.75e V.In addition,the second positive band of N₂C³（?）_u-B³（?）_gwas selected and the Boltzmann graph method was used.The vibration temperature is calculated,and the result is not much different from the fitting result of LIFBASE software.Combining the calculation results of electron temperature and gas temperature,it is found that the plasma is in a state of local thermodynamic equilibrium.In addition,the Saha equation method is used to calculate the electron density under different experimental conditions.The results show that the electron density at the center axis of the quartz tube is in the range of10²⁰～20²¹m^-3.The spatial distribution of the electron density is studied,and the plasma diameter is found.The directional distribution is Gaussian distribution.During the experiment,it was observed that the electron density increased suddenly when the discharge voltage increased from 10k V to 11kv.The reason is that the E-H mode conversion occurred in the plasma generator near the discharge voltage of 11kv.