Radial cataphoresis in a low-pressure neon-mercury positive column

The process of radial cataphoresis is investigated in the positive column o f a low-pressure neon-mercury discharge. The emission spectrum and the elec tric field are measured for several discharge tube diameters, neon pressure s, mercury pressures and electric currents. From the results of these measu rements, the current from which the emission spectrum of the lamp starts to contain a significant amount of neon radiation is determined. At this crit ical current, the mercury density profile in the tube is assumed to be sign ificantly depleted due to the process of radial cataphoresis. The measured trends in the critical current are compared to an approximate discharge mod el.