Investigation of the moving striation in a low pressure mercury discharge

Summary form only given. A moving striation in a low pressure discharge is well known phenomena. However, its mechanism has not been cleared until now. In this paper, the moving striation under various discharge conditions is measured by a high-speed camera and the formation mechanism of the striation shape is investigated. A fluorescent lamp with U-shape tube (FPL36) is employed as a test lamp. The inner diameter of the test lamp is 16 mm and discharge length is 700 mm. The mixture gas of mercury and argon at 2.5 Torr is filled in it. The operation conditions are as follows. The operation frequency is from DC to 200 kHz of sinusoidal wave. The discharge current is from 0.1A to 0.3A. The ambient temperature of the lamp is from -20°C to 20°C. The moving striation is always observed over the wide range of the test condition. The speed and shape of the moving striation depends on the operation frequency and the stationary striation is observed around 2 kHz. The ionized medium in the discharge tube turns from mercury to argon at low temperature of -20°C, however the striation is still observed. Three types of the striation shape, beads-like, peanut-like and oval-like, are found in the moving striation by viewing. The measurement by the high-speed camera shows that only one shape like a comet is observed and the comet moves always from anode to cathode direction. The velocity of the comet like striation is measured as about 80 m/s at DC operation. When discharge tube is operated by AC current, the comet like striation vibrates due to the current oscillation since its drift direction is always from the anode to the cathode. Then, three types of the striation shape are observed due to the relationship between the lighting interval based on the current frequency and the vibration width of the lighting comet. The vibration width is the distance in which the comet can travel during the half-period of the discharge frequency. A beads-like shape is form- d when the vibration width is longer than the distance between adjacent comets. On the other hand, a peanut-like shape is formed when the vibration width is shorter than the distance between adjacent comets. An oval-like shape is formed when the vibration width is much shorter than the distance between adjacent comets.