Abstract
Gas breakdown in electronegative gases and short non-uniform field gap is studied with a set of equations taking into account the spatio-temporal changes of the conductivity along the discharge axis and the variation of the neutral species density due to hydrodynamic processes. This simulation from a precise configuration to a general conclusion shows how the spark formation is controlled by electron energy dissipation, and in particularly the fraction of this energy which dissipates as thermal energy and by the attachment process via the field redistribution.