Study On Spectral Characteristics Of RF Capacitively Coupled Plasma

The plasma in the space environment has a great influence on the wireless transmission of signals between the spacecraft and the ground.At present,the research on plasma electromagnetic science has been in-depth at home and abroad.How to achieve effective communication between spacecraft and the ground under the condition of plasma sheath is still in the research stage.Radio frequency capacitive coupled discharge can produce large and uniformly distributed plasma,which can be used to study the interaction mechanism between plasma and electromagnetic wave.Therefore,the radio frequency capacitively coupled plasma（CCP）is studied by emission spectroscopy to obtain the information of plasma electron density and establish the relationship between radiation spectral line intensity and electron density.Radio frequency capacitively coupled plasma（RCP）is a common method to produce large and uniform plasma.In this paper,the discharge mechanism of RF capacitively coupled plasma is analyzed.The characteristic spectra of different wavelengths emitted in different physical and chemical reactions during plasma discharge are analyzed.Spectral lines originate from the transition of external energy between different energy levels,which excites or ionizes the photons with different energy,corresponding to spectral frequencies.Using 13.56MHz RF capacitively coupled plasma discharge device and Ar gas as working gas,the effects of gas pressure and power on plasma radiation spectral intensity,electron excitation temperature and spectral line broadening caused by optical energy shift were studied.This paper innovatively analyzed the intensity difference of the spectrum and the reasons for the broadening phenomenon.At the same time,the corresponding relationship between the broadening of low temperature plasma and the electron density was analyzed.At the same time,the corresponding relationship between several spectral lines and the electron density was established,and the error analysis was given.In the range of power 100-400W and pressure 5-9Pa,the intensity and broadening of plasma emission spectrum at the center of the cavity increase with the increase of power,but decrease with the increase of pressure,and the effect of pressure on broadening is small.The phase change of microwave signal before and after discharge is calculated by microwave interferometry.The range of electron density is 1.2×10¹⁶³.3×10¹⁶m^-3 under different working conditions.The quantitative function relationship between spectral line strength and electron density is established,and the error is analyzed.The results show that the error of electron density calculated by intensity calibration method is less than 0.1 order of magnitude compared with microwave interference method.The uniformity of the radial distribution and the distribution of the radial electron density of the plasma produced by capacitive coupled discharge are also investigated.The electron density at the edge electrode is higher than that at the center of the cavity,and the density decreases from 8×10¹⁶m^-3 to1×10¹⁶m^-3.Finally,the plasma electron excitation temperature is calculated by using the relative intensity of several characteristic lines.The range of electron excitation temperature is 0.4².2eV.