OPTICAL STUDIES OF PREBREAKDOWN ELECTRON AVALANCHES

This paper reviews the work carried out at Flinders University over a number of years in relation to the light output from pre-breakdown Townsend discharges and isolated electron swarms. This 'luminous flux' technique has important advantages over conventional current measurements since regions remote from electrode boundaries can be studied yielding values of electron drift velocity, diffusion coefficients and ionisation/attachment rates from a single experiment. For the first time the internal structure of a single swarm has been studied by observing the light from different excited states. From these results it is clear that, in many cases, the diffusion equation does not give an adequate description of the spatial and temporal development of electron concentration, and higher order transport parameters are required in the analysis of experiments.