Boundary wall effects on electron swarm parameters in a short-gap discharge

The nature of the helium breakdown at atmosphere pressure is strongly dependent on the interelectrode distance, d. In fact, experimental observation shows that for d<0.15 mm and d>2.5 mm, a spark-type breakdown occurs but for intermediate values the discharge is of glow-type. In a short-gap, the presence of the electrodes can influence factors such as secondary emission, spatial non-equilibrium effects and hence be responsible of an eventual disturbance of the hydrodynamic regime. The short-gap modelling described by Novak and Bartnikas (NB) is developed as a 2D fluid model, which includes explicitly the conservation equations for charged and excited particles and takes into consideration the effects of Penning and stepwise ionisation, for the first instants of helium plane-parallel short-gap discharges. In fact, the assumption of cold gas approximation (i.e. transport coefficients determined uniquely by the local electric field) must be verified in order to apply a fluid model. The aim of this paper is to verify the validity of the cold gas approximation in a 0.48mm helium short-gap at atmospheric pressure and 293K, by means of a Monte Carlo method, based on the classical null collision technique. It should be noted that the open-quote electron-field close-quote equilibrium is studied under exterior field conditions and thus it is not self-consistent