A compact high-intensity microwave discharge lamp and ignition system have been investigated using a couple of antennas and a solid-state microwave generator. It is found that the antenna-excited microwave discharge lamps can sustain mercury discharges at pressures higher than 100 atm with 2.45 GHz microwave power lower than 80 W, and that a stable plasma column is generated isolated from the lamp wall. The radial radiant profile is much different from that of conventional microwave discharge lamps without electrodes.
An antenna-excited microwave discharge (AEMD) lamp has shown attractive properties compared with conventional AC discharge or electrodeless microwave discharge lamps. This paper concerns a compact AEMD sulfur lamp with such a unique structure that a pair of antennas are covered with thin quartz glass. It is found that a stable plasma is generated between the antennas regardless of whether the antennas are coated by dielectrics. The microwave power supplied into the AEMD sulfur lamp is approximately 50 W, which is much lower than that of conventional sulfur lamps that require higher microwave power to start and maintain the discharge. Observed spectral features showed that the radiant power distribution was in the UV range at low sulfur pressure and shifted to the visible light range with increasing sulfur pressure. Finally, the possibility of obtaining a compact AEMD sulfur lamp is discussed.
A novel type of high pressure microwave discharge has been investigated to feed the microwave power at the centre of the compact high pressure discharge lamps using the antenna effect. This method of microwave discharge is named as the antenna excited microwave discharge (AEMD). The 2.45 GHz microwave of around 50 W from the solid state microwave generator can sustain a stable plasma column in the small gap between a couple of antennas fitted on the compact lamp filled with discharge gases at a pressure higher than atmosphere. The AEMD has been applied to a compact metal halide lamp and an extremely high pressure mercury discharge lamp. As a result, the metal halide lamp showed high luminous efficacy of around 130 lm W−1. The excellent lamp properties obtained here can be explained by the low heating loss at the antennas and the lamp wall. The profiles of the microwave electric field in the lamp and the microwave launcher have been numerically calculated to consider the microwave power supply into the lamp.
A compact ignition system for antenna-excited microwave discharge lamps filled with extremely high pressure mercury has been investigated using 2.45 GHz microwave power from a solid-state microwave generator. The properties of the present lamps were compared with those of conventional lamps ignited by AC electric power. It was found that the emission spectra were almost the same as each other. As a consequence, antenna-excited microwave discharge can be applied to the ignition for so-called superhigh-pressure mercury lamps, inside which the pressure is around 200 to 300 atm during lamp ignition.
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