Near-cathode phenomena in HID lamps

A brief review is given of the present understanding of cathode phenomena in arc discharges. A model of a near-cathode plasma region of high-pressure arcs with hot cathodes is described. Possible ways of integration of the model into numerical codes describing a lamp on the whole are discussed. An approach is suggested allowing one to estimate the upper limit of the cathode temperature and the lower limit of the temperature inside a cathode spot without detailed calculations of a temperature distribution inside the cathode. Solutions describing a diffuse and spot modes of current transfer to a thin thermionic cathode are presented and found to compare favorably with available experimental data.