Effect of Operating Frequency of Fluorescent Lamp on Barium Sputtering from Electrode

Abstract

The plasma density, electron temperature, and spectral line intensities from barium atoms and ions in the vicinity of the fluorescent lamp electrode in addition to the hot spot temperature have been measured as a function of the lamp operating frequency. The plasma density increased, while the hot spot temperature decreased, as the operating frequency was increased. This caused an increase in the spectral line intensities emitted from the barium atoms and ions at high operating frequencies, which might lead to a serious sputtering of the emitter material coated on the electrode. These phenomena can be well explained as follows. The high density plasma near the electrode produced during the cathode cycle can be sustained when the ambipolar diffusion time in the anode cycle is longer than the period of the operating frequency. In turn, the high density plasma around the electrode can effectively reduce the anode fall, so that the hot spot temperature is decreased. Thus, the cathode fall voltage develops under high operating frequency, and the ions are accelerated to enhance the sputtering of the emitter material during the cathode cycle. Consequently, the auxiliary electrode heating should reduce the amount of sputtering and extend the life of the fluorescent lamp.