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Transcript PPT - DOE Plasma Science Center
OPTIMIZING PULSE WAVEFORMS IN PLASMA
JETS FOR REACTIVE OXYGEN SPECIES (ROS)
PRODUCTION*
Seth A. Norberga), Natalia Yu. Babaevab) and Mark J. Kushnerb)
a)Department
of Mechanical Engineering
University of Michigan, Ann Arbor, MI 48109, USA
[email protected]
b)Department
of Electrical Engineering and Computer Science
University of Michigan, Ann Arbor, MI 48109, USA
[email protected], [email protected]
http://uigelz.eecs.umich.edu
65th Annual Gaseous Electronics Conference
Austin, TX, October 22-26, 2012
* Work supported by Department of Energy Office of Fusion Energy Science and
National Science Foundation
AGENDA
Atmospheric Pressure Plasma Jets (APPJ)
Description of model
Plasma jet model
Propagation of plasma bullet
Radical production at fringes of jets
Planar plasma jet model
Concluding remarks
Special Acknowledgement –
Prof. Annemie Bogaerts
Mr. Peter Simon
GEC2012
University of Michigan
Institute for Plasma Science & Engr.
ATMOSPHERIC PRESSURE PLASMA JETS (APPJ)
Plasma jets provide a means to remotely deliver reactive species to
surfaces.
In the biomedical field, low-temperature non-equilibrium
atmospheric pressure plasma jets are being studied for use in,
Sterilization and decontamination
Destruction of proteins
Bacteria deactivation
Plasma jets typically consist of a rare gas seeded with O2 or H2O
flowing into room air.
Plasma produced excited states and ions react with room air
diffusing into plasma jet to generate ROS (reactive oxygen species)
and RNS (reactive nitrogen species).
In this talk, we present results from computational investigation of
He/O2 plasma jets flowing into room air.
GEC2012
University of Michigan
Institute for Plasma Science & Engr.
ATMOSPHERIC PRESSURE PLASMA JETS (APPJ)
Coaxial He/O2 plasma jets into
room air were addressed.
Needle powered electrode with
and without grounded ring
electrode.
In these configurations,
plasma bullets propagate into
a flow field.
•
Figures from X. Lu, M. Laroussi, and V. Puech,
Plasma Sources Sci. Technol. 21 (2012)
GEC2012
University of Michigan
Institute for Plasma Science & Engr.
FORMATION OF EXCITED STATES IN APPJ
Prior experimental and
modeling results have shown
that jet produced excited states
undergo reaction with air at
boundary of jets.
For example, excitation transfer
from He* to N2 creates a ring of
N2(C3π).
Ref: G. V. Naidis, J. Phys. D:
Appl. Phys. 44 (2011).
GEC2012
University of Michigan
Institute for Plasma Science & Engr.
MODELING PLATFORM: nonPDPSIM
Poisson’s equation: ( q j N j )
j
Transport of charged and neutral species:
N
t
Charged Species: = Sharffeter-Gummel
Neutral Species: = Diffusion
Surface Charge:
j
S
q j S
t
j
material
Electron Temperature (transport and rate coefficients from 2-term
spherical harmonic expansion solution of Boltzmann’s Eq.):
3
5
n e kT e S T e L T e kT e T e T e
t 2
2
GEC2012
University of Michigan
Institute for Plasma Science & Engr.
MODELING PLATFORM: nonPDPSIM
Radiation transport and photoionization:
S m ( ri ) N m ( ri )
k
mk
Ak
3
N k r j ' G k r j ' , ri d r j '
G r j ' , ri
Poisson’s equation extended into materials.
q j j
t
j
exp
l
surface
ri
lk N l r j 'd r j '
rj '
2
4 r j ' ri
Solution: 1. Unstructured mesh discretized using finite volumes.
2. Fully implicit transport algorithms with time slicing
between modules.
GEC2012
University of Michigan
Institute for Plasma Science & Engr.
nonPDPSIM: NEUTRAL FLUID TRANSPORT
Fluid averaged values of mass density, mass momentum and
thermal energy density obtained using unsteady, compressible
algorithms.
( v ) ( inlets , pumps )
t
v
NkT v v
t
c p T
t
qi N i Ei
i
T v c p T Pi v f R i H i
i
ji E
i
Individual neutral species diffuse within the single fluid, and react
with surfaces
Ni
t
GEC2012
( N i v ) D i N i S i
University of Michigan
Institute for Plasma Science & Engr.
PLASMA JET: GEOMETRY AND CONDITIONS
Quartz tube with inner pin
electrode and grounded
rink electrode.
Cylindrically symmetric
He/O2 flowed through tube.
Air flowed outside tube as
shroud.
-30 kV, 1 atm
He/O2 = 99.5/0.5, 20 slm
Surrounding humid air
N2/O2/H2O = 79.5/20/0.5, 0.5
slm
Fluid flow field first
established (5.5 ms) then
plasma ignited.
Ring electrode is dielectric
in analyzed case.
GEC2012
University of Michigan
Institute for Plasma Science & Engr.
PLASMA JET: DIFFUSION OF GASES
Flow field is established
by initializing “core” of He
in room air, and allowing
gas to intermix.
Room air is entrained into
jet, thereby enabling
reaction with plasma
excited species.
The mixing layer is due to
diffusion at the boundary
between the He/O2 and air.
He/O2 = 99.8/0.2, 20 slm
Air = 0.5 slm
Animation Slide
MIN
GEC2012
Log scale
University of Michigan
MAX Institute for Plasma Science & Engr.
PLASMA JET
One DC pulse, 25 ns rise time,
-30 kV, 1 atm, He/O2 = 99.8/0.2,
no ground electrode.
Plasma bullet moves as an
ionization wave propagating
the channel made by He/O2.
Te has peak value near 8 eV in
tube, but is 2-3 eV during
propagation of bullet.
[e] and ionization rate Se
(location of optical emission)
transition from hollow ring to
on axis.
Bullet stops when mole
fraction of He is less than 40%.
Plasma has run for 66 ns.
Animation Slide
GEC2012
MIN
Log scale
University of Michigan
MAX Institute for Plasma Science & Engr.
ELECTRON DENSITY
One DC pulse, 25 ns rise time, -30 kV,
1 atm, He/O2 = 99.8/0.2, no ground
electrode. Plasma has run for 66 ns.
Electron density transitions from
annular in tube and exit to on axis.
As air diffuses into He, the self
sustaining E/N increases,
progressively limiting net ionization
to smaller radii.
Penning ionization (He* + N2 He +
N2+ + e) at periphery aids plasma
formation, but air diffusion and
increase in required E/N dominates.
MIN
GEC2012
Log scale
MAX
Animation Slide
University of Michigan
Institute for Plasma Science & Engr.
PLASMA BULLET SHAPE
A few slides on “waveform”
One DC pulse, 25 ns rise time, -30 kV, 1 atm, He/O2 = 99.8/0.2, no ground
electrode. Flow at 5.5 ms. Plasma has run for 66 ns.
Bullets propagate at speeds similar to conventional ionization waves (107
cm/s).
•
GEC2012
Figure from X. Lu, M. Laroussi, and V. Puech,
Plasma Sources Sci. Technol. 21 (2012)
University of Michigan
Institute for Plasma Science & Engr.
ROS/RNS PRODUCED IN PLASMA
RONS produced by
plasma jet plasma
include NO, OH, O, O3
and O2(a). (Densities
shown are from 1 pulse.)
O2(a) and O are formed in
tube.
NO and OH are in plume,
resulting from diffusion
of humid air into jet.
Significant RONS
production outside core
partly due to
photoionization &
photodissociation.
1 atm, He/O2 = 99.8/0.2,
-30 kV, 20 slm, no ground
electrode.
Animation Slide
GEC2012
MIN
Log scale
MAX
University of Michigan
Institute for Plasma Science & Engr.
ROS PRODUCED IN PLASMA
ROS densities
increase along the
jet with increase of
diffusion of air
into the jet.
O2(a) and O3 are
longed lived (for
these conditions),
and will
accumulate pulseto-pulse, subject
to advective flow
clearing out
excited states.
1 atm, He/O2 =
99.8/0.2, -30 kV, 20
slm, no ground
electrode.
GEC2012
University of Michigan
Institute for Plasma Science & Engr.
RNS DENSITIES
RNS are created through the
interaction of the He/O2 jet
with air.
N2* [N2(A) and N2(C)] have
peak densities of 1014 cm-3
(from 1 pulse).
Due to high thresholds of
these electron impact
processes, densities are
center high where Te is
maximum in spite of higher
density of N2 near periphery.
1 atm, He/O2 = 99.8/0.2, -30 kV,
20 slm, no ground electrode.
Animation Slide
GEC2012
MIN
Log scale
MAX
University of Michigan
Institute for Plasma Science & Engr.
RNS PRODUCED IN
PLASMA
Annular to center peaked
RNS densities from exit of
tube to end of plume.
1 atm, He/O2 = 99.8/0.2, -30
kV, 20 slm, no ground
electrode.
GEC2012
University of Michigan
Institute for Plasma Science & Engr.
Cathode
PLANER GEOMETRY: Te SEQUENCE
Fluid module is
run first (8 ms)
to establish
steady-state
mixing of Helium
and ambient air.
Then, a pulse of
different rise
time (tens of ns)
is applied.
GEC2012
1 atm, He/O2 = 99.8/0.2, 35 kV, 20 l/min
Surrounding humid air N2/O2/H2O = 79.5/20/0.5
Pulse rise time 25 ns
University of Michigan
Institute for Plasma Science & Engr.
EFFECT OF PULSE RISE TIME
Rise time 75 ns
Rise time 25 ns
Bullet formation time
inside tube 7 ns
Bullet formation time
inside tube 22 ns
Bullet formation time
inside tube 47 ns
Propagation time 13 ns
Propagation time 17 ns
Propagation time 33 ns
Cathode
Cathode
Rise time 5 ns
Bullet formation time inside the tube and propagation time increases with
the increase of the pulse rise time.
Shorter rise time results in more intensive IW: higher electron impact
sources Se and electron temperature Te
1 atm, He/O2 = 99.8/0.2, 35 kV, 20 l/min, surrounding humid air N2/O2/H2O =
79.5/20/0.5
GEC2012
University of Michigan
Institute for Plasma Science & Engr.
CONCLUDING REMARKS
Conducted a proof of concept for modeling the plasma bullet and gained
information about radical species in the trail of the bullet.
Significant densities of reactive oxygen and nitrogen species are created
by the dry chemistry of the atmospheric pressure plasma jet.
Future modeling work includes:
Plasma bullet behavior for different polarities.
Varying discharge geometry to reproduce results.
Different mixtures of feed gas to optimize desired ROS/RNS production.
Impact effects of jet on a surface.
GEC2012
University of Michigan
Institute for Plasma Science & Engr.
Back Up Slides
1.
2.
3.
DEPENDENCE ON
VOLTAGE WAVEFORM
4.
• In each plot, electron
temperature is used to
represent the plasma bullet.
• 1 atm, He/O2 = 99.8/0.2, 20 slm
1. 25 ns rise to -30 kV pulse
with no ground electrode
2. 25 ns rise to -10 kV pulse
with ground electrode
3. 25 ns rise to -30 kV pulse
with ground electrode
4. 50 ns rise to -30 kV pulse
with ground electrode.
Animation Slide
GEC2012
MIN
Log scale
MAX
University of Michigan
Institute for Plasma Science & Engr.