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

T he 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 ( T exc ), rotational temperature ( T rot ), and density of electron number ( n e ) of the kW-AC-ArMPT are measured with optical diagnosis. It is clearly shown that the introduction of air contributed to the rise of T rot and n e 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.