Oscillations at the Anode of Low Pressure Sodium Lamps

Abstract

Aanalysis of the anode voltage pulsations for low pressure sodium lamps containing starting rare gases is made with regard to the electron temperature of positive column plasmas. The electron temperature and the anode voltage pulsations of sodium lamps at the wall tempernture 0 to 150°C are related to ionization of rare gases alone, on the contrary the electron temperature at the wall temperature of more than about 150°C is inversely proportional to the vapor pressure of sodium while the anode voltage pulsations are still caused by ionization of rare gas alone from transport phenomena of sodium ions and no pulsations over 250°C. The electron currents in the anode sheaths converge to the hot spots on barium oxide compound layers of double coiled anodes, and consequently cause abrupt ionization around the hot spots of anodes, followed stoppage of the ionization immediatly by quenching of anode sheaths partially with high density charges generated locally. That is followed to recover for the anode drop voltage by ambipolar diffusion of high density local charges and reconbination of them at the walls of tubes. It is shown that the periods (T) of anode voltage pulsations are related to the mean decay time constant (τ) of ambipolar diffusion, T∝τ=γa2/π2Da where γa is radius of anode bulb-wall and Da is ambipolar diffusion constant; and that the electrode life and D lines may be shortened more by anode voltage pulsation of rare gas than by sodium vapor.