Plasma cathode sustained filamentary glow discharges in atmospheric air

Summary form only given, as follows. Glow-to-arc transitions in filamentary glow discharges in atmospheric air can be largely avoided by use of a plasma cathode, as has been demonstrated in short filamentary discharges in air. In these experiments a dc-driven microhollow cathode discharge (MHCD) was used as a plasma cathode to sustain a stable, direct current discharge between the plasma cathode and a third positively biased electrode. We have, using the same concept, extended the gap distance (distance between plasma cathode and third electrode) from previously 2 mm to the range from 6 mm to 20 mm and have studied the electrical, optical and plasma properties of such long filamentary glow discharges in atmospheric air. The MHCD is ignited between closely spaced molybdenum electrodes, separated by a 130 /spl mu/m thick alumina layer, with a 130 /spl mu/m hole through the sample. The filamentary discharge was ignited at small gap distances, in order to keep the ignition voltage at a low level, and then the gap was extended to the desired distance. In a certain range of current the filamentary glow discharge (FGD) current was found to be identical to the microhollow cathode discharge current. In this range control of the FGD by the MHCD is possible. From previous measurements of short gap filamentary discharge the gas temperature was found to be approximately 2000 K], the electron density was estimated as close to 10/sup 13/ cm/sup -3/. We will report on the results of measurements of these plasma parameters in long filamentary air discharges, and the electrical parameters, which determine the current range of MHCD control of the FGD. Parallel operation of these controlled filamentary glow discharges by using individual or distributed ballast might allow the generation of large volume, high pressure glows in air.