Microwave-generated plasma in air under standard conditions

The possibility and feasibility of microwave-excited plasmas in air under s tandard conditions, as well as under moderate pressures of up to 5 bar, is demonstrated by using a quarter-wave coaxial resonator. The microwave energ y is coupled into the resonator by an inductive loop attaining a match of b etter -15 dB. The equivalent circuit of the resonator allows to determine i ntrinsic resistance, inductance, and capacitance. Additionally, the quality factor and, finally, the field strength inside the resonator can be deduct ed. By using this approximation a breakdown field of 300 kV/m is computed. The power levels used for exciting microwave plasmas are low enough to be m anageable, e.g., 35 W.