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High intensity discharge (HID) lamps are often initiated by the application of one or more short, high-voltage, breakdown pulses superimposed on a 50 or 60 Hz generator voltage. A successful transition from the breakdown event to steady-state operating conditions in HID lamps requires that the lamp-circuit system be adequate to sustain the plasma created during breakdown until the electrodes are heated to thermionic temperatures. In this article, we use a one-dimensional (in the axial direction) transient discharge model to study the conditions needed to sustain the cold-cathode discharge after a breakdown event has occurred. While the application of our one-dimensional model to real lamps is approximate, we find that the model predictions are consistent with experimental results in HID lamps, a few of which are presented here. The main conclusion from this work is that, after breakdown, the voltage necessary to sustain a glow discharge is dependent on the source impedance, the gas composition, and on the plasma density created by the breakdown event.

The response of a probe with varying applied potential is studied by numerical simulation. Each particle is followed in turn in its path through the test volume and leaves a space charge in its track for the next overall iteration. The space charge is inversely proportional to its local speed [L.W. Parker and E.C. Whipple, Ann. Phys. 44 (1967) 126]. Preliminary results indicate that the effects of a magnetic field is strong and consistent with an anomalous diffusion, indicating that we may be simulating some process in real plasmas, in spite of the fact that the simulation method employed in principle gives no information on the temporal development of the plasma. On the other hand, effects of collisions seem to be slight.

A simple experimental technique for measuring the sheath length in a low-pressure glow discharge has recently been proposed in which the sheath length is determined from measurement of the transient current resulting from a rapidly rising voltage pulse applied to a steady-state discharge. In this comment, the sheath length deduced from a simulation of this experimental technique is compared with the sheath length determined directly from self-consistent calculations of the electric field profile. The excellent agreement found between these two calculations of the sheath length provides validation of the experimental technique.

Summary form only given. HID lamps are often ignited by one or more short, high voltage pulses (trigger pulses) superimposed on the low frequency, generator voltage. We have developed a self-consistent, fluid model of transient glow discharges to study the breakdown and glow phases in HID lamps from the time of the application of the trigger pulse(s) to the time when there is a fully-developed, quasi-steady state glow discharge. The transition to the thermionic arc is not considered here. Using this model we have investigated the influence of the height, width and number of trigger pulses on the generator voltage required to achieve a steady-state glow discharge. The model we use is one-dimensional, and the fundamental variables are the charged particle densities and the potential as functions of distance between the electrodes and time. The charged particles are described by their continuity equations and these are solved simultaneously with Poisson's equation for the potential distribution. We suppose that there are free electrons present in the gap when the trigger pulse is applied. Results are given for Ar and Ar-Hg discharges.