Characterizations on a 2.45 GHz microwave induced atmospheric pressure plasma torch

Summary form only given. The Center for Plasma-Material Interactions (CPMI) at the University of Illinois at Urbana-Champaign has developed a greater than 10 mm diameter 2.45 GHz microwave-induced atmospheric pressure plasma torch (APPT) for use in various manufacturing applications. The APPT has the ability to generate various atmospheric pressure plasmas (helium, argon, nitrogen) with a gas temperature range from room temperature (30°C) to more than 3,000 °C at the ignition area. The diagnostics of the electron temperature T_e, electron density n_e, and the plasma gas temperature T_g are based on the optical emission spectroscopy (OES) technique. The detailed dependence of the T_e, n_e and T_g on the microwave power, radial distance referred to the ignition point, gas type and gas flow rate will be presented individually. The validity of the OES technique, including the local thermal equilibrium conditions and the model for H_β calculation, has been verified and analyzed by the OES measured results. OES results has shown that T_e is in the range of 0.5-1.5 eV, n_e is in the range of 10¹⁴-10¹⁶ cm^-3 and T_g is in the range of 900-3000 K by varying the power from 200-3000 W, depending on the type and the mixture ratio of the plasma gases. The spatial dependence of T_e, n_e and T_g has shown a drastic decrease in T_g but relatively slower changes in T_e and n_e. This provides possibility on both thermal and non-thermal operation conditions for applications of selectable material processes.