Characterizations on a 2.45 GHz microwave induced atmospheric pressure plasma torch

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.