VizGlow Application Note
Nanosecond Pulsed Dielectric Barrier Discharge (DBD) in Atmospheric Air

Dielectric Barrier
Discharges (DBD) arestabledischarges
capableofair
generating reactive
non-equilibrium
plasmas at highpressures. Operationof these discharges
Figure 1: Geometry for simulation of dielectric barrier discharge (DBD) inat
atmospheric
air.
pressure
isparticularly attractive for a number of applications including vacuum-chamber free materials
processing, chemical processing of gas streams, and plasma actuators for aerodynamic flowcontrol. In non-ideal gases such as air, DBD’s produce large volume plasmas through theformation of a multitude of thin streamer channels that can fill the available space in thedischarge. DBD’s are essentially pulsed discharges that are produced by applying a high voltage
oscillating waveform or a series of repeated sharp-rising pulses at an electrode in an electrodepair system. One or both of the electrodes must be covered by a dielectric solid layer so as toprevent a direct conducting channel between the electrodes. The dielectric layer traps charge
from the plasma which in turn limits a large current density in the plasma. The self-limiting
behavior of the dielectric barrier keeps the currents low enough that glow-to-arc (GAT)
instabilities are prevented, thereby
maintaining a stable non-equilibrium
Applied Voltage
discharge at high pressures. The self3 kVlimiting behavior also means that thedischarge is necessarily pulsed withthe formation of streamer channels
that are quenched rapidly during aTime
4 ns
8 ns
single pulse. An oscillating excitationis therefore necessary to maintain aFigure 2: Single pulse waveform applied at the poweredsemi-continuous discharge.
Thiselectrode.
application note discusses theCopyright © Esgee Technologies Inc.

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simulation of a prototypical DBD in air. The VizGlow Plasma Modeling Software Package is used.
The geometry for the DBD is shown in Fig. 1 and comprises a bare powered electrode (red),a surrounding ground electrode (green) that is covered by a dielectric layer (black). A sharprising triangular positive pulse is applied at the electrode as shown in Fig. 2. The pulse duration
last about 8 ns and therefore the discharge is called a “nanosecond pulsed DBD”. The DBD isgenerated at atmospheric pressure in air. Since the high pressure imposes a very fineresolution requirement, over 80,000 cells are required in the mesh. The mesh comprises pure
quadrilateral cells. Simulation domain is 2.5 mm x 0.5 mm (see Fig. 1). The air is represented
by a finite-rate chemistry with 21 gas-phase reactions among 11 species (electrons E, oxygen
radical O, nitrogen molecule N2, oxygen molecule O2, nitrogen dimer ion N2+, oxygen dimerion O2+, nitrogen cluster ion N4+, oxygen cluster ion O4+, ion complex O2+N2, oxygen dimer
negative ion O2-, oxygen ion O-).
Since air species comprise radiativestates that emit in the ultra-violet,
photoionization
becomesanimportant mechanism by whichelectrons are generated andtherefore this mechanism isincluded in the simulation.
1 ns
The pulsed excitation results inthe formation of a positive
streamer channel that propagatesfrom the powered electrode to thegrounded electrode. However, thepresence of the dielectric barrier on
the grounded electrode results inthe deposition of a positive charge
on the dielectric surface. This
locally trapped positive charge
causes a self-induced electric fieldthat pushes the streamer further
down the dielectric surface
resulting in a streamer channel that
propagates significant distancesfrom away from the powered
electrode. Essentially, the dielectriccharge trapping is the cause for thelarge volume filling property of theDBD. Figure 3 shows a series ofsnap-shots of the electron density
in the streamer channel formed by

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|3 ns

5 ns

7 ns9 ns
Figure 3: Electron density transient in air streamer
channel formed in the nanosecond pulsed DBD.

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1 ns

3 ns

5 ns

7 ns

9 ns
Figure 4: Electrostatic potential in the nanosecond
pulsed DBD.

the nanosecond pulsing of the DBD inair. Note that the streamer channel
is thin (~ 100 microns). However, amuch broader region of electron
densities is observed surrounding thestreamer. This is essentially a cloudofelectrons
resultingfromphotoionization surrounding thestreamer. Note that the streamer
propagates about 1 mm from thepowered electrode in about 7 ns andthen extinguishes once the power isturned off.
Figure 4 shows the evolution ofelectrostatic
potential
inthedischarge. The potential starts out
looking like a vacuum potential
profile during the early part of thetransient (~ 1 ns). However as thestreamer develops the self-consistentnature of the electric field induced by
the streamer channel becomes
evident. The streamer head (leadingedge of the propagating streamer) is
electronegative due to an excess ofelectrons that distorts the potential
imposed by the powered electrode.
At the end of the transient thepotential collapses with the quenching of the plasma.
Finally, a comparison is made of the streamer propagation with the photoionization andwithout the photoionization. Figure 5 shows propagation of the streamer for the two cases atthree different times during the transient. Note that the case without the photoionization
results in a much weaker streamer that propagates a very short distance away from thepowered electrode before being quenched at the end of the pulse. Also note that the absenceof photoionization results in a strongly confined electron density profile without the cloud ofelectrons that surrounds that streamer in the case with photoionization. This directcomparison emphasizes the role of photoionization in streamer propagation in air DBD’s.

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With Photoionization

Without Photoionization

3 ns

5 ns

7 ns
Figure 5: Comparison of streamer propagation with and without including the photoionization
model.

In summary, the VizGlow Plasma Modeling Software Package provides robust capability forthe high-fidelity simulation of high-pressure non-equilibrium discharges such as DBD’s.
Simulation of DBD’s is a particularly challenging problem because of the highly disparate timescales involved in the problem and the potentially wide range of length scales imposed by thesmall region of discharge formation in the context of a larger application domain. Furthermore,
the high pressure results in very restrictive resolution requirements since the thin propagating
streamer must be resolved accurately in order to model the DBD discharge. This kind ofmodeling is very much the state-of-the-art in plasma computational modeling community.
In closing we note that VizGlow Plasma Modeling Software Package is part of the Overviz
framework suite which provides an intuitive interface to set-up a project to be solved using
VizGlow, manipulate multiple projects for parametric studies. VizGlow is provably fast, robust,and easy-to-use software and currently a leading industrial plasma simulation tool.
For further information on this application note or details about the VizGlow and othersoftware packages you may contact us atEsgee Technologies Inc.
14, North PeakAustin, Texas 78746, USA
info@esgeetech.com
www.esgeetech.com

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