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 [1].
Based on the need of a high current during ignition a novel
DBD pulse gear with enforced reignition is presented with
good system efficiency.
[1] Paravia M and Trampert K E, "Homogenisation of a
pulsed dielectric barrier Xe discharge using falling
voltage edge for secondary ignition", LS 11, 2007, pp.
499-500