Determining Electron Density of Atmospheric Microwave Air Plasma Torch by Microwave Power Measurement

In this article, a cheap and simple method to determine the electron density of atmospheric microwave air plasma torch (AMAPT) is proposed, which avoids the complex and costly spectrum diagnosis methods. First, the incident and reflected microwave (MW) power of the AMAPT are measured to obtain the MW power reflection ratios. Then, a 3-D Gaussian electron density distribution is built to simulate the AMAPT, especially in calculating the MW power reflection ratios. By adjusting the electron density distribution to make the calculated MW power reflection ratios equal to the measured results, the electron density can get calculated. Finally, to verify this calculation, a system of a 2.45-GHz AMAPT is built up to measure the electron density with optical emission spectroscopy (OES) in different gas flow rates and gas compositions. The results show that the electron density determined by this method agrees well with the experimental measurements by OES with a relative error of 8% which is competent for engineering applications. The simplicity and accuracy make it a promising approach to obtaining the electron density of MW plasma in engineering applications.