Direct current glow discharges in atmospheric air

Abstract

Summary form only given, as follows. Research on atmospheric pressure glow discharges in air is motivated by applications such as instantly activated reflectors and absorbers for electromagnetic radiation, remediation and detoxification of gaseous pollution, and surface treatment. One of the major obstacles in obtaining stable glow discharges at high electron densities (> 10/sup 11/ cm/sup -3/) is the glow-to-arc-transition, which develops generally in the cathode fall region. The use of a microhollow cathode discharge as independent electron emitter, has been shown to reduce the cathode fall drastically, and has therefore allowed us to generate direct current, atmospheric-pressure air glow discharges. The millimeter size plasmas, studied in earlier experiments, have been scaled to centimeter dimensions by operating MHCD sustained air glows in parallel and extending the electrode distance up to 2 cm. The electric field in these discharge plasmas, varies between 1.2 kV/cm, for a discharge current of 13 mA, to 2 kV/cm at 5 mA. The current density varies between 50 mA/cm/sup 2/ for high currents (13 mA) and 500 mA/cm/sup 2/ for low currents (5 mA), corresponding to electron densities between 10/sup 11/ cm/sup -3/ and 10/sup 12/ cm/sup -3/. The MHCD supported air glow discharge has a negative differential resistance. Parallel operation of the individual discharges therefore requires individual ballast. Two parallel discharges were generated, with their axes 0.4 cm apart. It was found that for this configuration the positive columns merged for currents exceeding 10 mA, creating a homogeneous plasma. The required electrical power density for electron densities of 1.5 /spl times/ 10/sup 11/ cm/sup -3/ was measured as 100 W/cm/sup 3/. By pulsing the plasma this power dissipation can be reduced considerably without sacrificing on the time-average value of the electron density.