OPTIMIZING PULSE WAVEFORMS IN PLASMA JETS FOR REACTIVE OXYGEN SPECIES (ROS) PRODUCTION*

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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 norbergs_at_umich.edu b)Department of
Electrical Engineering and Computer
Science University of Michigan, Ann Arbor, MI
48109, USA nbabaeva_at_umich.edu, mjkush_at_umich.edu
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
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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

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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.

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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)

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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(C3p).
• Ref G. V. Naidis, J. Phys. D Appl. Phys. 44
  (2011).

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MODELING PLATFORM nonPDPSIM

• Poissons equation
• Transport of charged and neutral species
• Charged Species ?? Sharffeter-Gummel
• Neutral Species ? Diffusion
• Surface Charge
• Electron Temperature (transport and rate
  coefficients from 2-term spherical harmonic
  expansion solution of Boltzmanns Eq.)

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MODELING PLATFORM nonPDPSIM

• Radiation transport and photoionization
• Poissons equation extended into materials.
• Solution 1. Unstructured mesh discretized using
  finite volumes.
• 2. Fully implicit transport
  algorithms with time slicing
• between modules.

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nonPDPSIM NEUTRAL FLUID TRANSPORT

• Fluid averaged values of mass density, mass
  momentum and thermal energy density obtained
  using unsteady, compressible algorithms.
• Individual neutral species diffuse within the
  single fluid, and react with surfaces

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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.

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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
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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
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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.

Animation Slide
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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).

• Figure from X. Lu, M. Laroussi, and V. Puech,
  Plasma Sources Sci. Technol. 21 (2012)

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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
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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 pulse-to-pulse,
  subject to advective flow clearing out excited
  states.
• 1 atm, He/O2 99.8/0.2, -30 kV, 20 slm, no
  ground electrode.

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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
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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.

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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.

Cathode

• 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

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EFFECT OF PULSE RISE TIME

• Rise time 75 ns

• Rise time 25 ns

• Rise time 5 ns

Cathode
Cathode

• Bullet formation time inside tube 7 ns
• Propagation time 13 ns

• Bullet formation time inside tube 22 ns
• Propagation time 17 ns

• Bullet formation time inside tube 47 ns
• Propagation time 33 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

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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.

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Back Up Slides
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DEPENDENCE ON VOLTAGE WAVEFORM
1.
2.
3.
4.

• In each plot, electron temperature is used to
  represent the plasma bullet.
• 1 atm, He/O2 99.8/0.2, 20 slm
• 25 ns rise to -30 kV pulse with no ground
  electrode
• 25 ns rise to -10 kV pulse with ground electrode
• 25 ns rise to -30 kV pulse with ground electrode
• 50 ns rise to -30 kV pulse with ground electrode.

Animation Slide
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