FREQUENCY, CURRENT, AND AMPLITUDE MAPS OF OSCILLATING-PLASMA GLOW-DISCHARGE GC DETECTORS

This study maps the complex relationships between the oscillating freq uency (210-800 kHz), amplitude (to 4 V p-p), and current 0.18-0.7 mA) for an oscillating-plasma glow discharge GC detector as a function of pressure (0.35-0.85 Torr), electrode spacing (0.8-2.8 cm), and cathode shape in order to show the range of useful operating conditions and t o gain insight into cell mechanisms. Concave cathodes lead to amplitud e roll-offs and appear to cause an increase in local pressure between the electrodes when the gas enters via a hole in the anode. The simila rity principle explains pressure-induced shifts in frequency gaps and amplitude roll-offs. A simple dispersion equation helps to account for frequency maxima. There appears to be more that one mode of oscillati on in regions where the current is relatively constant, indicating tha t the mechanisms that control frequency and current have significant d ifferences.