Photographic Analysis and Optical Diagnosis of Kilowatt Microwave Plasma Torch with Air Carrier Gas

The spatiotemporal motion characteristics of the kilowatt argon microwave plasma torch with the air carrier gas (kW-AC-ArMPT) and the behavior of the plasma filaments are investigated with a digital single-lens reflex (SLR) camera and a high-speed camera. Along with the introduction of the air, both the volume of the central channel and the rotational frequency of the plasma filament are increased. Besides, the excitation temperature (Texc), rotational temperature (Trot), and density of electron number (ne) of the kW-AC-ArMPT are measured with optical diagnosis. It is clearly shown that the introduction of air contributed to the rise of Trot and ne of the plasma, which is beneficial to improving the analytical performance of the plasma. Then the detection limits of some heavy metal elements are measured by kW-AC-ArMPT, which are in the ppb range. The experimental results show that the kW-ArMPT has a high tolerance to air injection at least 1.0 L/min, which allows the direct extraction of air from the environment for analysis and therefore has the potential for online and in-situ detection of ambient air quality and industrial exhaust gases.