* Work supported by US Department of Energy Office of Fusion Energy Science and the National Science Foundation.

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THE LONG TERM EFFECTS OF RANDOM DBD STREAMERS ON
THIN LIQUID LAYERS OVER TISSUES
Wei Tiana) and Mark J. Kushnerb)
University of Michigan, Ann Arbor, MI USA
48109 a)Department of Nuclear Engineering and
Radiological Science, bucktian_at_umich.edu b)Depart
ment of Electrical Engineering and Computer
Science, mjkush_at_umich.edu October 2014
Work supported by US Department of Energy
Office of Fusion Energy Science and the National
Science Foundation.
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MODELING OF PLASMA INTERACTION WITH TISSUE

• Plasma treatment of tissue involves
• Plasma kinetics, dynamics and gas phase plasma
  chemistry
• Plasma-liquid interactions and liquid phase
  chemistry
• Biological functionality
• Plasma treatment of tissue usually operates from
  seconds to minutes, consisting of 100s to
  10,000s pulses.
• To investigate the plasma treatment of tissue,
  modelling of multiple pulses followed by
  long-term afterglow is necessary.

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MODELING IN PLASMA MEDICINE DBD TREATMENT

• Multi-scale, multi-phenomena, multi-disciplinary
• Many desired outcomes.

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AGENDA

• In this poster, we present results from a
  computational investigation of DBDs interacting
  with liquid covering tissue for up to 100 pulses.
• Radical production with time (or pulses),
  terminal species and transit species.
• Stationary scheme locally repeated streamers
• Memory-effect scheme streamers are repeated at
  selected locations
• Random scheme streamers are repeated randomly

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MODELING PLATFORM nonPDPSIM

• Poissons equation
• Transport of charged and neutral species
• Surface Charge
• Electron Temperature (transport coefficient
  obtained from Boltzmanns equation)
• Radiation transport and photoionization

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TREATMENT OF LIQUID

• Liquid plasma is treated identically to gas as a
  partially ionized substance.
• Higher density
• Specified susceptibility/atom to provide known
  permittivity
• Surface tension is addressed by specifying
  species able to pass through vapor/liquid
  interface.
• Diffusion into water is limited by Henrys law
  equilibrium at the surface layer.
• Liquid evaporates into gas with source given by
  its vapor pressure.

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WATER REACTION MECHANISM
Plasma
H,OH,O,O3, O2,NO,NO2
Photons, M
M
e
M-
R?
Water
RH
H
H2
H
OH-
OH
O2-
(H2O)e
H2O
H,OH,O,O3, O2,NO,NO2
OH
O,O-
H3O
O3,O3-
RH
R?
H3O
H2O2
RH
N2O3,N2O4
R?
R?
RH
O2
H
HO2
H3O
NO2-
NO3-
reaction with H2O
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GEOMETRY

• DBD, 1.5 mm gap
• 200 mm thick liquid layer with plasma water.
• Humid air (N2/O2/H2O79.0/20.9/0.1) at 1 atm with
  H2O evaporating from the liquid surface.
  Dissolved O2aq in liquid 8 ppm

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DBD DISCHARGE DYNAMICS

• DBDs in contact with water act like traditional
  DBDs with a lossy floating electrode underneath.
• After the discharge channel establishes, the ne,
  Te and Se are concentrated on the top.
• -18 kV, 5 ns pulse, 200 ?m water, O2aq 8 ppm in
  water

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SCHEME FOR MULTI-PULSES
10 ms Water evaporation
10 ns Plasma
Time
The source functions are recorded and used for
following pulses.

1 s afterglow
10 ms
10 ms
2nd pulse
3rd pulse
100th pulse
Time

• Before the first pulse, water is evaporated into
  the gap for 10 ms.
• The plasma is computed for the 1st pulse.
• The source functions at the end of plasma pulse
  are recorded and used as initial conditions for
  later pulses.
• Poissons equation is not solved and
  quasi-neutrality is assumed after the pulse.

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THREE MULTI-PULSES SCHEMES
Stationary repeated streamers

• Different multi-pulses schemes
• Repeated single streamers
• Memory-effect streamers
• Random streamers

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ELECTRON DENSITY (1015 cm-3)
Stationary
Memory-Effect
Random

• Electron density is shown for each multi-pulses
  scheme.
• In stationary scheme, plasma is concentrated at
  the center.
• In memory-effect scheme, 5 striking locations
  are shown.
• In random scheme, plasma appears randomly.

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TERMINAL SPECIES IN LIQUID
Memory-effect
Stationary

• O3aq accumulates during 100 pulses, up to 1016
  cm-3.
• In stationary scheme, NOaq and H2O2aq both
  increase with time.
• In memory-effect scheme, NOaq and H2O2aq still
  increase but with lower densities.
• In random scheme, NOaq is almost consumed up and
  H2O2aq starts to fall after 20 pulses.

Random
Density the average density in liquid layer
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TRANSIT SPECIES IN LIQUID

• Different from terminal species, OHaq , HO2aq and
  Haq can hardly accumulate during multi-pulses.
• OHaq reacts with NO2aq to form HNO3aq and
  HOONOaq.
• Haq forms HO2aq, which then reacts with NOaq to
  form HNO3aq and HOONOaq.

Density the average density in liquid layer
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HYDROGEN PEROXIDE EVOLUTION

• In stationary scheme, H2O2aq narrows to the
  width of streamer after 5 pulses.
• In memory-effect scheme, H2O2aq shows two
  significant high density region.
• In random scheme, H2O2aq is more uniform.

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NITROGEN OXIDE EVOLUTION

• In stationary scheme, NOaq is consumed at the
  center but diffuse deep aside, since NOaq reacts
  with H2O2aq.
• In memory-effect scheme, NOaq and H2O2aq are
  mixed at selected locations leaving NOaq only
  remaining at selected locations.
• In random scheme, H2O2aq is well-stirred with
  NOaq, which is no longer able to diffuse to
  tissues.

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FLUENCES TO UNDERLYING TISSUE

• In stationary scheme, the fluences profiles show
  non-uniform distributions.
• In memory-effect scheme, fluences profiles peak
  at selected locations.
• In random scheme, fluences profiles become
  uniform.

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FLUENCES TO UNDERLYING TISSUE

• The fluences profiles of charged species
  basically have the similar characteristics as
  that of neutral species.
• In memory-effect and random schemes,
  well-stirred radicals produce more ONOO-aq.

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CONCLUDING REMARKS

• Results from modeling of multiple DBD pulses
  incident onto thin water layers followed by
  long-term afterglow are discussed.
• The accumulation of reactivity, such as O3aq and
  H2O2aq, depend significantly on the multi-pulses
  schemes.
• Locally stationary streamers result in
  non-uniform fluences. NOaq can reach tissue by
  avoiding reacting with H2O2aq.
• Memory-effect scheme concentrates the
  reactivity at selected locations.
• Randomly placed streamers result in more uniform
  fluences.
• Random streamers provide a well-stirred
  environment of precursors in gas phase, resulting
  in NOaq being consumed by H2O2aq before reaching
  the tissue.

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