Current spots in an obstructed planar glow discharge

Pattern formation in a gas discharge operating on the left-hand branch of the Paschen curve (obstructed discharge) is investigated. Such a discharge (in contrast to that operated on the right-hand branch) has a monotonic current-voltage characteristic and is believed to occupy the whole electrode area and to evolve continuously with current increase. This theoretical picture sharply contradicts a recent experiment (Nasuno S 2003 Chaos 13 1010-13) where both current constriction and current patterns have been observed for an obstructed dc discharge. We demonstrate experimentally in this paper that such a behaviour is indeed possible, but is always accompanied by current pulsation. We also suggest that the current pulsation, constriction and pattern formation are caused by local current-heating of the gas. This process explains the observed time-scales, occurrence and multiplicity of current spots