Plasma emission imaging of a low-pressure argon breakdown

Breakdown in a low-pressure argon discharge was investigated experimentally by time-resolved plasma emission imaging with an intensified charge coupled device camera. Basic features of plasma breakdown, such as light emission in front of the anode and crossing of an emission front from anode to cathode, were observed. The observations were in agreement with the standard Townsend theory on breakdown into a glow discharge. In addition, a pre-breakdown light flash was observed. This light flash, which occurred at a voltage below the static breakdown voltage, was thought to originate from charges from previous discharges deposited on dielectric surfaces close to the discharge gap. Finally, the time delay as a function of the afterglow period of the discharge was measured. The densities of charged particles at the time of ignition influenced the measured time delay. For afterglow periods increasing from 1 to 20?ms, volume recombination of charged particles caused a sharp increase in the time delay from 1 to 9?µs. For longer afterglow periods (20-200?ms), diffusion became increasingly important and caused a slower increase in time delay (9-11?µs).