摘要

When high-pressure discharge lamps are operated at frequencies higher than the line frequency, arc instabilities are occasionally observed. This phenomenon, attributed to the excitation of standing pressure waves inside the discharge vessel, is called an acoustic resonance. A theoretical treatment of these acoustic resonances in the cylindrical cavity is first presented, in which the pressure distributions are calculated. These pressure fields can also explain the particular deformation of the discharge, which is powered by a current inverter (square wave current) working at adjustable frequency and duty cycle. It is shown that the strength of acoustic resonances must have certain magnitudes to excite an arc instability. The strength of acoustic resonances is a function of a critical or threshold duty cycle, above which no arc instabilities occur in the power frequency range investigated (from 0 to 100 kHz). In the last part of the presentation, the influence of the discharge tube radius and length is studied : it is found a wider space of utilisation without inconvenient instabilities when the tube size decreases.