Gas temperature measurement of argon glow discharge at atmospheric pressure using the Mach-Zehnder interferometer

Gas temperature distribution is one of the most important parameters in chemical processes using atmospheric pressure plasma. In this study, the dependencies of the gas temperature distribution in atmospheric-pressure argon DC glow discharge on the discharge current and gas flow rate were measured using a Mach-Zehnder interferometer. A spatial resolution of 25 µm was achieved by adjusting the interference fringe density. Sphere and nozzle electrodes were used as discharge electrodes with a gap distance of 3 mm. DC glow discharge was generated by flowing argon gas from the nozzle electrode into the air. The measured gas temperature in the nozzle anode condition with a discharge curent of 15 mA and gas flow rate of 0.5 L/min was 400-500 K from 0-2.5 mm away from nozzle anode and 800 K near the sphere cathode. The measured gas temperature distribution showed that the gas temperature increased only near the cathode in the nozzle anode case. However, the gas temperature increased near both electrodes in the nozzle cathode case. By changing the discharge gap with the nozzle cathode condition, the gas temperature near the anode decreased as the gap distance increased. As a wider discharge gap should lead to larger air-mixing ratio near the sphere electrode, this result indicates that a high air-mixing ratio near the sphere electrode induces significant gas heating.