Interferometry Diagnostics of Gas Temperature in a Discharge Sustained by Microwave Radiation from a 24-GHZ Gyrotron in an Argon Flow at Atmospheric Pressure

We study experimentally an atmospheric pressure discharge sustained by the millimeter-wave gyrotron radiation in an argon flow. The spatial distribution of gas temperature in the plasma jet emerging from the conical nozzle of a waveguide plasmatron has been measured by two independent methods. Using the method of optical interferometry and the method of thermosondes, it is shown that even with a microwave heating power of several tens of watts, it is possible to create a weakly ionized plasma at the nozzle exit, in which the gas temperature reaches about 1000 K and declines uniformly in the postdischarge area. The interferometric method applied in this work makes it possible to obtain an instantaneous complete spatial picture of the gas temperature distribution in the plasma torch during a single passage of a probing laser beam through the medium under study. This permits one to observe the complex dynamics of convective processes during the outflow of plasma and hot gas from the hole in the plasmatron.