Transcript Document
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,
[email protected]
b)Department of Electrical Engineering and Computer Science,
[email protected]
October 2014
* Work supported by US Department of Energy Office of Fusion Energy Science and
the National Science Foundation.
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 100’s to 10,000’s pulses.
To investigate the plasma treatment of tissue, modelling of multiple
pulses followed by long-term afterglow is necessary.
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Institute for Plasma Science & Engr.
MODELING IN PLASMA MEDICINE: DBD TREATMENT
Powered Electrode
Dielectric
Air
Plasma
Evaporation
Ionization Wave
(ns - ms)
hn
E-Field
Plasma-liquid
Interaction (ms - s)
Tissue
Multi-scale, multiIntratissue Transport
phenomena, multi(mins – days, mm - cm)
disciplinary
Many desired outcomes.
Membrane
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Kinetics
Cellular
response
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
Poisson’s equation: (
q
j
N j s )
j
Transport of charged and neutral species:
Surface Charge: s
N j
t
j S j
q j j S j
t
j
material
Electron Temperature (transport coefficient obtained from
Boltzmann’s equation)
ne
5
j E ne i K i N i e Te Te
t
2
i
Radiation transport and photoionization:
S m (ri ) N m (ri )
3
mk Ak N k r j 'Gk r j ' , ri d r j '
k
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ri
exp lk N l rj 'drj '
l r '
j
G rj ' , ri
2
4 rj 'ri
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Institute for Plasma Science & Engr.
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
Henry’s law equilibrium at the surface
layer.
Liquid evaporates into gas with source
given by its vapor pressure.
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Evaporation
Ions
Dissolved
gases
Solvated
Liquid
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WATER REACTION MECHANISM
Plasma
Photons, M*
e
H2O+
(H2O)e
M-
R
Water
H2
M+
H,OH,O,O3,
O2,NO,NO2
H
RH
H
OH
OH
R
RH
O2- OH-
H,OH,O,O3,
O2,NO,NO2
O,O-
H3O+
O3,O3H 3 O+
H 2 O2
R
H
O2
RH
N2O3,N2O4
R
RH
HO2
H3O+ NO2- NO3-
= reaction with H2O
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Institute for Plasma Science & Engr.
GEOMETRY
DBD, 1.5 mm gap
200 mm thick liquid layer with “plasma water”.
Humid air (N2/O2/H2O=79.0/20.9/0.1) 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 mm water, O2aq 8
ppm in water
MIN
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MAX
Log scale
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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.
10 ms
10 ms
2nd pulse 3rd pulse
••• •••
1 s afterglow
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.
Poisson’s equation is not solved and quasi-neutrality is assumed after
the pulse.
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THREE MULTI-PULSES SCHEMES
Stationary: repeated streamers
“Memory-effect”: 5 selected locations
Dielectric
Evaporation
Repeated
Streamer
Plasma
Air
E-Field
hn
E-Field
Random Streamers
Plasma
Air
Random
Locations
E-Field
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Plasma
Air
Selected
hn
Locations
Different multi-pulses
schemes
Repeated single streamers
“Memory-effect” streamers
Random streamers
hn
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ELECTRON DENSITY (1015 cm-3)
“Memory-Effect”
Stationary
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.
MIN
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MAX
Log scale
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TERMINAL SPECIES IN LIQUID
“Memory-effect”
Stationary
Random
Density: the average density in liquid layer
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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.
TRANSIT SPECIES IN LIQUID
Density: the average density in liquid layer
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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.
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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.
MIN
MAX
Log scale
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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.
MIN
MAX
Log scale
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In “memory-effect” scheme, NOaq
and H2O2aq are mixed at selected
locations leaving NOaq only
remaining at selected locations.
In random scheme, H2O2aq is “wellstirred” with NOaq, which is no
longer able to diffuse to tissues.
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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University of Michigan
Institute for Plasma Science & Engr.