Runaway electron preionized diffuse discharges in atmospheric pressure air with point-to-plane and point-to-point gaps in repetitive pulsed mode

Summary form only given. The paper presents the results of experimental studies of a pulsed discharge in air at 1 atm in an inhomogeneous electric field for various parameters of voltage pulses. The studies show that the diffuse form of atmospheric-pressure air discharges in the repetitive pulsed mode is kept over a wide range of experimental conditions, including those with pulser voltages of tens of kilovolts and positive electrode of small curvature radius. In this work, a REP diffuse discharge was ignited with voltage pulse amplitude of 25 kV across a high-resistance load at a pulse repetition frequency of 1 kHz. At a voltage of 150 kV, the FWHM of the voltage pulse was 1 ns. With voltage pulses of amplitude 220 kV and low repetition frequencies, an extended (70 cm) diffuse discharge was observed in gaps of 13-40 mm. It is confirmed that the diffuse form of discharges in an inhomogeneous electric field at increased pressures owes to the generation of runaway electrons and X-rays. Increasing the voltage pulse duration simplifies the pulser design and extends the applicability of REP diffuse discharges. Under our experimental conditions, the ignition of a diffuse discharge in atmospheric pressure air depended weakly on the polarity of the electrode of small curvature radius and owed to the generation of runaway electrons and X-rays. In the repetitive pulsed mode, like in the single pulse mode, a corona discharge followed by a REP diffuse discharge was ignited. With fixed voltage pulse parameters, pressure, and gas kind, decreasing the interelectrode gap with an increase in pulse repetition frequency and pulser operation time decreases the time it takes for the REP diffuse discharge to transform into a spark. In the spark discharge, broadband visible and UV radiation with pulse duration of tens-to-thousands of nanoseconds was detected form the spark channel. In the REP diffuse discharge in atmospheric pressure air at 200-800 nm, most of the emission is from second- positive system of N₂ lines with a maximum intensity at a wavelength of 337.1 nm.