Modeling of atmospheric gas-stream processing using a microwave excited all-dielectric resonant plasma discharge

Abstract

Computational modeling of an all-dielectric resonant plasma discharge for the processing of atmospheric air streams is presented. A single dielectric resonator (DR) pair separated by a small gap is considered. Governing equations for plasma, flow and electromagnetics are coupled to resolve the entire process characterized by fast timescale plasma breakdown followed by slow timescale transport of radicals catalyzed in the discharge. The resonant frequencies of the DR system are determined by solving for the electromagnetic wave across a range of microwave frequencies in the absence of the plasma. The DR operating at the resonant frequency (on-resonance mode) results in 12 times larger electric field amplification in the dielectric gap as compared to its operation in an off-resonance mode. Plasma breakdown occurs in the DR gap where the electric field amplification is the highest, due to constructive interference of electromagnetic wave modes from the adjoining cylindrical dielectrics. The plasma frequency in on-resonance mode is smaller than the resonant frequency of the DR. This inhibits the formation of surface wave modes and results in a uniform electromagnetic power deposition and volumetric plasma generation in the dielectric gap. It is seen that oxygen radicals (O) and oxygen metastable states O2 a1 and O2 b1 are dominant products of the plasma catalysis process. The active radical species are transported with the flow where they can be used in downstream plasma processing applications.