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

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 EngineeringUniversity of Michigan, Ann Arbor, MI 48109, USA

[email protected]

b)Department of Electrical Engineering and Computer ScienceUniversity of Michigan, Ann Arbor, MI 48109, USA

[email protected], [email protected]

http://uigelz.eecs.umich.edu

65th Annual Gaseous Electronics ConferenceAustin, 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

University of MichiganInstitute for Plasma Science & Engr.

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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)

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

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.


FORMATION OF EXCITED STATES IN APPJ

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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).


MODELING PLATFORM: nonPDPSIM

Poisson’s 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 Boltzmann’s Eq.):

)( j

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Radiation transport and photoionization:

Poisson’s equation extended into materials.

Solution: 1. Unstructured mesh discretized using finite volumes. 2. Fully implicit transport algorithms with time slicing between modules.

jsurfacejjqt

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)()(3j

kijkjkkmk

imim

rdrrGrNA

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MODELING PLATFORM: nonPDPSIM

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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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nonPDPSIM: NEUTRAL FLUID TRANSPORT

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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

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Animation Slide

MIN MAX Log scale


Animation Slide

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.

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Log scale


ELECTRON DENSITY

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Animation SlideMIN MAX Log scale


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.

PLASMA BULLET SHAPE

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A few slides on “waveform”

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

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).

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.

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Animation Slide University of MichiganInstitute for Plasma Science & Engr.MIN MAX

Log scale

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.


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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.


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Animation Slide University of MichiganInstitute for Plasma Science & Engr.

MIN MAX Log scale

RNS PRODUCED IN PLASMA

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Annular to center peaked RNS densities from exit of tube to end of plume.


PLANER GEOMETRY: Te SEQUENCE

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

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.

University of MichiganInstitute for Plasma Science & Engr.GEC2012

Cat

hode

EFFECT OF PULSE RISE TIME

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 University of Michigan

Institute for Plasma Science & Engr.GEC2012

Cat

hode

Cat

hode

Rise time 25 ns Rise time 75 ns Rise time 5 ns

Bullet formation time inside tube 7 ns

Propagation time 13 ns





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.

CONCLUDING REMARKS

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Back Up Slides

DEPENDENCE ON VOLTAGE

WAVEFORM

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• 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 MIN MAX Log scale

1. 2. 3. 4.

Documents

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