ATMOSPHERIC PRESSURE PLASMA TRANSFER OF
JETS AND BULLETS ACROSS DIELECTRIC TUBES
AND CHANNELS*
Zhongmin Xiong(a), Eric Robert(b), Vanessa Sarron(b)
Jean-Michel Pouvesle(b), Mark J. Kushner(a)
(a) University
of Michigan
Department of Electrical Engineering and Computer Sciences
Ann Arbor, MI 48109
zxiong@umich.edu, mjkush@umich.edu
(b) GREMI,
CNRS-Polytech’Orléans,
45067 Orléans Cedex 2, France
eric.robert@univ-orleans.fr, vanessa.sarron@univ-orleans.fr
jean-michel.pouvesle@univ-orleans.fr
65th Gaseous Electronics Conference 2012, Austin, Texas, USA
* Work at UoM is supported by the DOE OFES and NSF. Work at GREMI is supported
through APR "Plasmed" and ANR Blanc "PAMPA"
AGENDA
 Experimental studies of atmospheric pressure plasma transfer across
two perpendicular dielectric tubes.
 Numerical modeling of atmospheric pressure plasma transfer across
two perpendicular dielectric channels
 Primary ionization wave (IW) with positive polarity:
 Top-down transfer process, polarity preserving
 Primary IW with negative polarity:
 Bottom-up transfer process, polarity reversing
Effects of rise-time of the primary IW
 Concluding Remarks
GEC2012
University of Michigan
Institute for Plasma Science & Engr.
PLASMA TRANSFER EXPERIMENTS
 Atmospheric pressure plasma transfer refers to the production of an
ionization wave (IW) in a tube or channel by impingement on the outer
surface of a separately produced IW.
X. Lu et al, J. Appl. Phys.
105, 043304 (2009)
S. Wu et al, IEEE TPS 39, 2292 (2011)
E. Robert et al (GREMI, 2011)
V. Johnson et al, IEEE TPS 39, 2360 (2011)
GEC2012
University of Michigan
Institute for Plasma Science & Engr.
PLASMA TRANSFER  POSITIVE POLARITY
 Neon plasma, atmospheric pressure, 10 ns snapshots, filament penetration
« filaments » across
the transfer pipe
No« thin plasma layer »
E. Robert et al (GREMI, 2011)
GEC2012
University of Michigan
Institute for Plasma Science & Engr.
PLASMA TRANSFER  NEGATIVE POLARITY
 Neon plasma, atmospheric pressure, 10 ns snapshots
 Formation of thin plasma layer in the transfer tube
plasma « plume »
« thin plasma layer »
« thin plasma layer »
E. Robert et al (GREMI, 2011)
GEC2012
University of Michigan
Institute for Plasma Science & Engr.
TWO DIMENSIONAL PLASMA MODELING
 Channels filled with Ne/Xe =
99.9/0.1
 Channels 4 mm wide, separated by
4 mm in air.
 25 kV pulse of either polarity is
applied on the powered electrode.
 The pulse rise-time varies from 25
to 400 ns. The pulse duration is
100 ns.
 Initial electron density [e] in the
lower (transfer) channel is [e]0 = 1
x 107 (cm-3).
 Surrounding air is treated as
dielectric material (e = 1).
 The mole fraction of neon is
computed using ANSYS FLUENT
v.12.0.
GEC2012
University of Michigan
Institute for Plasma Science & Engr.
MODELING PLATFORM: nonPDPSIM
e    ( q j N j   )
 Poisson’s equation:
j
N j
 Transport of charged and neutral species:
 Surface charge:
t

     S


 
  q j     S     
t  j
 material


 Electron temperature:
3

5

 ne kTe  / t  S Te   LTe      kTe   Te   Te 
2

2

 Radiation transport and photoionization:


Sm (ri )  N m (ri ) 

k
GEC2012
mk
Ak 

ri

  

exp     lk N l rj 'drj '
 l r '

j

  3  G r ' , r  


j
i
N k rj ' Gk rj ' , ri d rj '
 2
4 rj 'ri
  

University of Michigan
Institute for Plasma Science & Engr.
POSITIVE POLARITY  Se AND [e]
 Electron impact ionization source Se, electron density [e], and electric
potential contours (spacing = 2 kV)
 Plume from primary tube charges the top surface of the transfer channel.
 Plasma in the transfer channel develops from top to bottom.
GEC2012
Animation Slide
University of Michigan
Institute for Plasma Science & Engr.
POSITIVE POLARITY  TRANSFER PROCESS (I)
 Primary IW front crosses the
gap at speed of 7 x 107 cm/s.
 IW in primary channel “shorts”
out the electric field,
translating applied potential to
surface of transfer tube with
additional charging of surface
of transfer tube.
 Large E/N in transfer tube
ignites the secondary IWs.
 Two secondary IWs propagate
sideways and gradually fill the
whole width of the channel.
 The peak electric field is
associated with IW front due to
the space charge effect.
 E-field penetrates the dielectric
wall with minor distortion.
GEC2012
University of Michigan
Institute for Plasma Science & Engr.
POSITIVE POLARITY  TRANSFER PROCESS (II)
 Initial electron avalanche in the
transfer channel starts directly
underneath where IW from
primary channel intersects.
 Transferred avalanche front
propagates downwards and
sideways.
 Electrons inside the transfer
channel are heated even before
the primary IW front impinges
on the top surface.
 Electric potential expands
following the propagation of
the primary/secondary IWs.
 The secondary IWs are driven
by the same polarity as that of
the primary IW.
GEC2012
University of Michigan
Institute for Plasma Science & Engr.
POSITIVE POLARITY  COMPARISONS
 Contours of time integrated Ne* density in the simulation show a similar
shape to the plasma emission image in the experiments.
 Positive plasma transfer is thus a top-down process and the secondary
IWs preserve the polarity of the primary IW.
 Time integrated Ne* density
(University of Michigan)
GEC2012
 Plasma emission in experiments
(GREMI)
University of Michigan
Institute for Plasma Science & Engr.
NEGATIVE POLARITY  Se AND POTENTIAL
 Electrons are deposited by the primary IW on the top transfer channel wall.
 Plasma inside the transfer channel develops from bottom to top.
 Positive electric potential emerges in the transfer channel.
GEC2012
Animation Slide
University of Michigan
Institute for Plasma Science & Engr.
NEGATIVE POLARITY  [e],  AND POTENTIAL
 A positive IW emerges from the bottom of the transfer tube and impinges
upon the top wall.
 A positive charge layer forms underneath the top transfer channel wall,
turning the negative potential (dash line) into positive potential (solid line).
GEC2012
Animation Slide
University of Michigan
Institute for Plasma Science & Engr.
NEGATIVE POLARITY  TRANSFER PROCESS
 Initial electron avalanche in the
transfer channel starts from
the bottom wall.
 A positive IW front propagates
upwards and then impinges on
the top wall.
 The impingement of the
positive IW front forms a
strong positive charge layer on
the top inner surface.
 The space charge layer
generates positive potential
inside the transfer channel.
 The secondary IWs are driven
by the potential with a reversed
polarity of the primary IW.
GEC2012
University of Michigan
Institute for Plasma Science & Engr.
NEGATIVE POLARITY  COMPARISONS
 Both simulations and experiments show the existence of an intensive
plasma layer underneath the inner top wall.
 Negative plasma transfer is thus a bottom-up process and the secondary
IWs reverse the polarity of the primary IW.
 Time integrated Ne* density
(University of Michigan)
GEC2012
 Plasma emission in experiments
(GREMI)
University of Michigan
Institute for Plasma Science & Engr.
EFFECTS OF PULSE RISE-TIME
 Negative IWs are more sensitive to the pulse rise time than positive IWs .
 Increasing pulse rise-time slows down both primary and secondary IWs.
 For a negative primary IW, a threshold in its rise-time exists beyond which
secondary IWs can not be generated.
GEC2012
University of Michigan
Institute for Plasma Science & Engr.
CONCLUDING REMARKS
 Experiments demonstrate atmospheric pressure plasma transfer by the
impingement of a plasma jet produced in a source tube onto the outer
surface of a transfer tube which is electrodeless and not connected
electronically to the source tube.
 For positive polarity, plasma transfer is facilitated by a direct penetration
of the electric field through the tube wall. For negative polarity, it is
characterized by the formation of a thin space charge layer inside the
transfer tube.
 Two dimensional numerical modeling with two channels demonstrates
that for a positive primary IW, the secondary IWs are produced in a topdown process and preserve the polarity of the primary IW.
 For a negative primary IW, the secondary IWs are produced in a bottomup process and reverse the polarity of the primary IW.
 Longer rise-time of the voltage pulse induces a slowing down of both
primary and secondary IWs. For a negative primary IW, there is a
threshold risetime beyond which secondary IWs can not be generated.
GEC2012
University of Michigan
Institute for Plasma Science & Engr.