Optical detection of pre-breakdown discharges in gas mixtures under DC, AC, and impulse voltages

Investigates the light pulses in several gas mixtures in a point-plane gap using a photomultiplier system (PM) and an image intensifier. A photomultiplier of type GB333 (RCA 7265) with 25 Ω K anode resistance was used for light pulse measurements. The output of the PM was measured by a storage oscilloscope (Tektronix 466, 100 MHz). The values of the anode resistance and anode voltage were adjusted to increase the sensitivity of the PM system. The PM was adjusted such that it received light only directly from the region around the point electrode through one of the quartz windows of the chamber. Thus the expected sensitivity and a high signal/noise ratio were obtained. An image intensifier was also used to observe the weaker light phenomena in gas mixtures under d.c. applied voltages through the second quartz window of the chamber. It consisted of a photocathode, electrostatic lens and microchannel plates (MCP). This system enabled the observation of light intensity down to 10^-4 to 10^-5 lux, and the wavelength of peak emission was about 560 nm. The gases used were dry air, N₂, CO₂ and SF₆ and the mixtures used were SF₆/N₂, SF₆/CO₂ and SF₆/N₂/c-C₄F₆ at pressures 100 to 400 kPa