Research on Inductively Coupled Low-Temperature Plasma Spectroscopy Diagnosis

The electron density distribution of a closed-cavity inductively coupled plasma (ICP), along the incident direction of electromagnetic waves, is a key factor affecting its electromagnetic wave attenuation effect. Therefore, an investigation of the various parameters of the ICP, including the electron density inside a closed cavity, is of great significance in the advancement of plasma technology. In this study, an ICP generator was used to generate argon plasma, and the radiation intensity and full-width at half-maximum (FWHM) of the spectral line were measured using emission spectroscopy. The electron collision section model was then used to calculate the electron temperature of the plasma, which was found to be above 0.9 eV. In addition, the electron temperature was found to decrease as the pressure increases and increase significantly as the power increases. The Stark broadening method was used to calculate the electron density, where the Doppler broadening of spectral lines was considered, and the Voigt convolution function was introduced. An accurate value for the Stark broadening was obtained through the convolution calculation, which improves the accuracy of the plasma electron density. Subsequently, the FWHM of the 794.82-nm spectral line was used to obtain the electron density of the plasma. The influence of different power levels and pressures on the electron density was analyzed under pure argon conditions. Finally, the distributions of the plasma electron temperature and electron density in the axial and radial directions of the cavity were investigated. In order to verify the accuracy of spectral diagnosis in the current experimental environment, the diagnostic results of Langmuir single probe were used to verify it. The electron density of argon plasma measured by the probe method and spectroscopic method is of the order of
$10^{17}\,\,\text {m}^{-3}$
, and the axial distribution of the electron density and the variation trend with the pressure tend to be consistent. The reliability of spectral diagnosis under the current experimental conditions is verified.