Gas Temperature Measurements and Imaging Analysis in Atmospheric-Pressure Microwave Air Induced Plasma Torch

Abstract

As a type of plasma can be an efficient source of highly active species, atmospheric microwave plasma torch (MPT) has achieved good results in many fields. <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1, 2</sup> Although the gas temperature of MPT has been studied by previous research, they don't realize that MPT may have two parts what we called “Plasma Core” and “Outer Shell” because the clear boundary of it has been captured in visible light. <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> We can imagine that the phenomenon would influence the results of the previous studies. In this experiment, the core of an atmospheric microwave induced plasma torch is resolved and measured by calibration of the exposure time of a high-speed camera. The molecular emission spectrometry of the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$A^{2}\Sigma^{+}\rightarrow X^{2}\Pi_{1}$</tex> , electronic system of OH radicals has been applied to measure the gas temperature of plasma core. How the geometric features and gas temperature of the plasma core are related to the magnetron power and gas flow rate is explored, and the radial temperature distribution of the microwave plasma is measured. In the experiment, we show that (i) An atmospheric microwave plasma torch has two parts, namely a core and an outer shell, which can be distinguished by visible boundary and gas temperature. (ii) The core can reach 8000K whereas the outer shell cools down from about 5500K. (iii) Gas temperature of the plasma core does not change with the magnetron power or the gas flow rate. (iv) Radial distribution of the gas temperature can be controlled by the waveform of the power supply. At last, a method to control the radial distribution of gas temperature of microwave plasma is presented.