Optical emission spectroscopy of non-equilibrium microwave plasma torch sustained by focused radiation of gyrotron at 24 GHz

The excitation and gas temperature of a non-equilibrium argon plasma torch sustained by a focused 24 GHz microwave beam in the external atmosphere of air was measured by optical emission spectroscopy. The excitation temperature of argon atoms was found about 5000 K, while the vibrational and rotational temperatures of ambient nitrogen molecules were respectively estimated at 3000 K and 2000 K. The effective mixing of the external gas atmosphere into the plasma torch is experimentally demonstrated. The vibrational and rotational temperatures of nitrogen molecules slightly increased with the distance from the nozzle exit. Experimental results demonstrate that microwave discharge at atmospheric pressure may be relevant for the decomposition of highly stable molecules, e.g. carbon dioxide, in non-equilibrium conditions.