Threshold current density for homogeneous excitation of pulsed xenon excimer DBD

Xe excimer DBD operate in a filamented or homogeneous mode depending on several parameters, e.g. the electrical excitation. The need of a pulsed excitation for homogenous discharge is well known from literature. However, the role of the electrical excitation to homogenize the DBD is not complete understood. In this work the transfer from filamented to homogenous mode is investigated for sub-microsecond pulses. Measurements of the gap voltage and plasma current show the influence of reignition for a homogeneous operation. The correlation between short time NIR images and current measurements point out that filamentation is depending on current density during ignition. It is shown that the filaments wide up with increasing current, like in an arc discharges. The filament expands with increasing ignition current and form a 2-dimensional pattern which goes finally over to a complete homogeneous discharge. It can be shown, that the current density through the ignited area is constant and a threshold current density for homogenous discharges can be defined depending on the strength of reignition and Xe pressure. The constant current density in the ignited area explains the transition from filamented to homogenous mode. This shows that current during ignition is the critical electrical parameter and not the rise time of the lamp voltage. To display the dependency of threshold current density and reignition, sub-microsecond pulses with a negative lamp voltage undershoot are shown. The threshold current lowers with increasing reignition. This behavior could be explained with accumulated remaining charges on the barriers from the last excitation pulse. Based on the need of a high current during ignition a novel DBD pulse gear with enforced reignition is presented with good system efficiency.