Electrical characteristics of a millisecond pulsed glow discharge

Abstract

A μs and ms pulsed argon glow discharge was investigated with respect to the breakdown condition (Paschen curve). Moreover, current–voltage profiles were acquired for different discharge frequencies, pulse durations, cathode–anode spacing and discharge pressures. The breakdown voltage was dependent on the cathode material (Cu, steel, Ti and Al). No severe change in the breakdown voltage was observed for a 1 ms pulse at different frequencies. However, the theoretical breakdown curve, calculated based on the Paschen equation did not fit the experimental data. The current plots for different cathode–anode spacing showed a maximum at intermediate distance (8–10 mm). These data were consistent with mass spectrometric data acquired using the same instrument in a GC-GD-TOFMS chemical speciation study. A higher discharge frequency with constant pulse duration leads to an increase in discharge current, probably due to a more dense plasma during the pulse. This is supported by the total emission of the plasma, which was not reaching the baseline for short delays in-between the plasma pulses. In addition, the total emission of the plasma shows that at least 2 ms is needed for the plasma to reach a stable quasi steady-state. The current–voltage (traces) for different discharge pressures show a constant relationship for different pulse durations. The current–voltage relation is pressure dependent and similar to dc-glow discharges. A fast photodiode was used for precise observation of the entire Penning ionization in the afterpeak at different pressure settings.