Modelling of charged particle decay in nitrogen afterglow

In this paper we extend the available experimental data for breakdown delay times as a function of the afterglow time to short afterglow times for a pulsed obstructed discharge in nitrogen. Measurements were performed at 6.6 mbar in research grade nitrogen by application of a high-vacuum procedure. The delay times are separated into formative and statistical time lags and their dependence on the afterglow time is discussed. A model is developed that is able to reproduce the breakdown delay time behaviour for short afterglow times which is based on ion density decay through the diffusion. A transition from the effective diffusion coefficient of 110 cm(2) s(-1) to the free diffusion of ions is observed at times of the order of 20 ms. The model was applied both in a simple approximate analytical form and in a numerical form with accurate representation of the geometry of the tube. When applied in conjunction with our earlier model of the breakdown delay appropriate for longer afterglow times the theory can predict the behaviour of the breakdown delay times between 0.5 ms and several hours.