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

This study maps the complex relationships between the oscillating frequency (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 to gain insight into cell mechanisms. Concave cathodes lead to amplitude 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 similarity 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 oscillation in regions where the current is relatively constant, indicating that the mechanisms that control frequency and current have significant differences.