Stability and Bifurcation of Cathode Arc Attachment in AC Operated High-Intensity Discharge Lamps

A. Lenef
Osram Sylvania

High-intensity discharge (HID) lamps are highly-efficient light sources with many applications. Depending on the dimensions of the electrode, lamp current, and waveforms, the plasma may attach to the cathode in a diffuse mode, that covers the electrode tip surface, or a localized mode where heating and current transfer occur in a local region of the electrode surface.

The localized mode is often deleterious to lamp operation because the electrode becomes locally overheated. We examine part of this problem for a simple case with DC and AC current waveforms. We use FEMLAB to simulate diffuse to localized mode transitions for a cathode and consider the results in terms of linear stability theory.