ABSTRACT
Glow discharges are likely the most studied and widely used gas discharges. They are found in numerous applications ranging from light sources to plasma reactors for materials processing (Liebermann and Lichtenberg 1994, Roth 2001). The simplest version is the direct current (DC), self-sustaining glow discharge. The discharge is established when a sufficiently high voltage is applied between the two electrodes, that is, the cathode and the anode. After the electrical breakdown, space charge-dominated boundary layers develop at the cathode and anode, that is, the cathode and anode fall regions. They are connected by a uniform plasma, the positive column. How small can we make such a discharge before conditions in voltage and current density are reached that make it difficult to sustain the discharge? An estimate can be obtained from data on glow discharges between two plane-parallel electrodes published in a book by one of the pioneers in discharge physics, von Engel (1965). Because we are interested in high-pressure glow discharges, we will extrapolate his results to discharges at 1 atmosphere-a high-pressure microglow discharge.
