Low-temperature non-thermal plasma configurations for medical application
Ruixue Wang1,3,4, WeiDong Zhu2,3, Jose L. Lopez2,3
Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, China;
2Center for Microplasma Science and Technology, Saint Peter’s College, Jersey City, NJ, USA
3
Department of Applied Science and Technology, Saint Peter’s College, Jersey City, NJ, USA
4
Department of Physics, Polytechnic Institute of NYU, Brooklyn, NY, USA
1
Abstract
Atmospheric pressure non-thermal helium plasmas are generated in flexible tubings (Teflon, Peek) as
well as in glass tubings. Plasma is ignited when a low frequency (a few tens of kilohertz) AC voltage (1525 kV) was supplied to two annular electrodes on the tubing. “Plasma brush” (or plasma jet array) is
realized by opening circular holes on the side walls of the tubings. Individual ballasting on each hole is
not necessary, although better stability can be achieved with it. Jets in the jet array can be delivered to
various distances from the tubing wall by connecting to the openings dielectric tubings with smaller inner
diameters. Electrical and optical characteristics of the plasmas are studied. The flexibility and low
temperature operation of these devices make them more attractive in applications such as disinfection of
catheters and cleaning of irregular surfaces.
Keywords: Non-thermal plasma flexible tubing
1. Introduction
2. Plasma Configurations
Non-thermal plasma produced at atmospheric
pressure has received considerable attention due to
their potential in various industrial and scientific
applications such as material treatment and
1
biomedical applications[ ]. A large number of
designs has been developed and tested already, such
as DBD, Plasma Jet, Plasma Torch [2]. Among these,
plasma jet has attracted extensive attention due to
excellent plasma stability and also rich reaction
chemistry with downstream [3]. The low temperature
feature of these plasma jets makes it possible for
them to be placed in direct contact with plant, animal
and human tissues, in particular for localized
treatment. However, to achieve widespread use in
medicine, the typically small plasma jet must be
scaled up and be capable of treating uneven surfaces,
such as complex surgical instruments. Twodimensional arrays of spatially confined plasma jets
have been reported particularly by Tachibana group
[4] and MG Kong group [3,5,6]. Here we developed
atmospheric pressure non-thermal helium plasmas in
flexible tubings (Teflon, Peek) as well as in glass
tubings driven by a low frequency (a few tens of
kilohertz) AC voltage (15-25KV) power supply. The
plasma jet can be expanded to 3-D when openings
are created on the side walls of the tubings.
2.1 Plasma Brush
Plasma Brush in this study is shown schematically
in figure 1(a). The dielectric tube was made of
Teflon with an inner diameter of 1/4” and outer
diameter of 1/2”, through which He gas flows. A
pair of tubular electrodes (copper) is attached to
the dielectric tubing, and connected to the HV
power supply and ground, respectively. While the
end of tubing is sealed, several holes can be drilled
through the sidewall (1/8”thick) in different
positions to let out working gas. The plasma
generated in the Teflon tubing can expel from
these holes. Dielectric (such as alumina) tubings
with the same outer diameter as these holes can be
inserted to the holes to further extend the emerging
plasma and the length of the tubing can vary from
0.5” to 2”. Holes can be drilled in both upstream
and downstream of the dielectrics, the maximum
plasma branches can be supported depending on
the applied voltage, the arrangement of the holes
and also the distance between adjacent holes. In
one example, six holes were drilled in a row –
three before the powered electrode and three after
(Figure 1(b)). In another example, eight holes
were drilled in 2 sets of 4 every 90° around the
tube in a circular fashion (Figure1(c)). In the six-
emissions from NO, N2, N 2 (Figure 3 (b) inset),
He and O.
A
15
B
C
D 10
E
F
0.03
(b)
0.02
(
(c)
Current(mA)
(a)
0.01
5
0.00
0
-0.01
-5
-0.02
-10
-0.03
-15
-20
0
20
40
60
80
Voltage(KV)
hole case, all of the alumina tubings can be ignited
(have a visible plasma jet) except the one in the
middle of upstream. The plasma started between
the two tubular electrodes and then spread to the
branches when voltage was increased.
100
Time(ns)
Figure 2. Voltage (blue) and currents for plasma brush in
different position (as noted in figure 1 (a))
1000000
2.2 Characterization of plasma brush
Optical emission was monitored via a
monochromater (Princeton Instrument Acton 2750)
connected with an Intensified Charge Coupled
Device camera (Princeton Instrument IMAX-1024)
at alumina port A and B (as noted in figure 1 (a))
to determine the composition of the plasma. The
light was introduced via a quartz fiber optics
bundle placed at ~1 cm away from the exit of the
alumina tubings. Figure 3 shows the emission
spectra taken at these two locations. The overall
emission intensity from A (downstream) is higher
than that from B (upstream) although same
emission lines are found in both. Identifiable are
600000
400000
200000
(a)
0
120000
B_upstream
800000
600000
400000
v=0 v=-1 v=-2 v=-3
N2 2 +
+
N2 1
(0,0)
1000000
-
100000
v=-4
(2,3)
(1,2)
(0,1)
(3,5)
(2,4)
(1,3)
(0,2)
(2,2)
(1,1) (3,6)
(0,0) (2,5)
(1,4)
(0,3)
(4,5) (3,7)
(2,3) (2,6)
(1,2)
(0,1) (1,5)
(0,4)
Emission Intensity(a.u)
The electrical characteristics of the plasma brush
were evaluated with a high voltage probe
(Tektronix 6015A) connected to the powered
electrode and a current probe (Pearson 6585)
placed at six different locations (A-F, as noted in
figure 1(a)). The results at Vp=10 kV without any
ballasting capacitor are shown in figure 2. The
discharge currents at all six locations are more or
less the same. One current pulse is observed for
every half cycle of the applied voltage, which
resembles what was typically observed in
dielectric-barrier discharges [7].
A_dowstream
800000
v=0
Intensity(A.U)
Figur .1. (a) Schematic diagrams of the plasma brush; (b)
ignited plasma brush with six holes and (c) 2 sets of 4 every
90° holes around the tube
80000
60000
40000
20000
NO
0
200000
200
(b)
250
300
350
400
450
Wavelength(nm)
0
200
300
400
500
600
700
800
900
Wavelength(nm)
Figure 3. Optical Emission Spectra taken at alumina port
(a) A (downstream) and (b) B (upstream) (A and B are as
noted in figure 1 (a)). Inset: light emission from 200-450nm
showing emission from NO, N2 and N2+
2.3 Plasma in various forms in Teflon
Plasma can be generated in flexible tubings made
of Teflon or Peek (OD: ¼” and ID: ½”). Figure 4
(a) and (b) show helium plasma generated in a
single loop and a spiral tubing arrangement. For
the single loop arrangement (Figure 4 (a)), helium
was introduced through a three way insulating
connector and evenly spread to both branches.
Light emission from one branch appears to be
stronger than the other due to the electrode
arrangement. At the far end of the loop, an
opening was made and connected to an alumina
tube, where a plasma jet was created as expected.
For the spiral tubing case, helium plasma could
not bend over one single loop if the copper
electrode was attached only to a section on one
loop. A strip of copper electrode (1” wide) was
then attached across all loops. A seemingly
continuous plasma through the spiral tubing was
then generated (Figure 4 (b)).
He gas
(b)
(a)
Powered
electrode
(a)
alumina ranking the highest in the materials used in
this study). Charge accumulation eventually reached
a critical value at which the electric field was strong
enough to break down air around it at the presence
of a third electrode.
Figure 4. Plasma generated in (a) a single loop and (b)
spiral tubing
2.4 Plasma with a third electrode
It has been well documented that these helium
plasmas can be generated in glass/quartz tubings at
various diameters [ 8 , 9 ].
We repeated those
experiments in glass tubings of different sizes: 1) ID:
0.218” and OD: 3/8”; 2) ID: 0.312”, OD: 0.5” and 3)
ID: 0.376” and OD: 0.5” with our AC power supply.
The appearance of the plasma in the glass tubing is
highly dependent on the size of the tubing and the
input voltage. At a low voltage, the luminescence of
the plasma is confined to an axial filament of
diameter below 1 mm at the center of the tubing (as
shown in figure 5 (a), dashed line represents the
glass boundary). The diameter as well as the
brightness of the filament increase with the applied
voltage. At a voltage of Vp= 25 kV, the plasma fills
the whole glass tube with the axial filament
remaining at the center (as shown in figure 5 (b).
Also worth noting is that at approximately the same
peak voltage, when a metal object (such as a razor
blade or a round head hex Allen wrench) was
brought close to the glass tubing wall, far away from
the powered electrode (either upstream or
downstream), air breakdown was observed. This
phenomenon was more clearly observed when
ceramic tubings were used (as shown in figure 5 (c)
and (d)). It is very likely that charges in the plasma
accumulated on the tubing walls, which was
essentially proportional to the applied voltage and
the dielectric constant of the tubing material (with
Figure 5.Plasma generated in glass tubing (ID: 0.218,OD:
03/8”) at (a) Vp= 7 kV: a clear axial filament is seen and (b)
Vp= 25 kV: plasma fills the whole glass with an axial filament
present; Air break down outside of the alumina tubings were
observed at Vp= 25 kV when (c) a razor blade and (d) a round
head hex Allen wrench was brought close
Figure 6. At Vp=7 kV, a spiral shape plasma develops
when a round head hex Allen wrench is brought close to
the glass tubing
In the case of lower voltage (Vp=7 kV) while the
plasma was still sustained, no air break was
observed. However, when moving close a round
head hex Allen wrench, a spiral shape plasma
form along the inner surface of the tubing (Figure
6). This could be that the electric field due to the
charges accumulated on the tubing walls being
locally perturbed by the metal item. Further
investigation of this phenomenon is underway. It
has to be noted that this spiral shape plasma
appears only toward the grounded electrode or in
the case of the gas was expelled into air, it appears
toward the tubing opening (where we consider as a
virtual ground). Meanwhile, the filament in the
middle of the tubing became weak but still visible.
Conclusion
(d)
(b)
In conclusion, we demonstrated the generation
of helium plasma in flexible tubings as well as in
glass tubings. The plasma can be split into many
branches by opening holes on flexible tubings.
OES show emission mostly from NO, N2, N2+,
He and O. The appearance of the plasma in glass
tubing depended on the size of the tubing and
the applied voltage. Clear axial filament were
observed at both high voltage (Vp=25 kV) and
low voltage (Vp=7 kV). At Vp=25 kV, air
breakdown between the tubing and third
electrode was observed due to the strong electric
field from the accumulated charged on the
tubing walls. Different plasma geometry and low
temperature property make it suitable for
medical applications where instruments with
irregular surfaces are involved.
Acknowledgement
This research was funded in part by the ElectroEnergetic Physics Program of the U.S. Air Force
Office of Scientific Research (AFOSR) under
grant
number
FA9550-08-1-0332.
Acknowledgment is also made to the Donors of
the American Chemical Society Petroleum
Research Fund and Council Scholarship of
China for support of this research. RW would
like to thank Drs. Jue Zhang and Jing Fang for
their constructive advices.
References
1
K.H.Becker, U.Kogelschatz, K.H.Schoenbach,
and R.J.Barker, Non-Equilibrium Air Plasma at
Atmospheric Pressure(IOP, Bristol, 2004)
2
M G Kong, G Kroesen, G Morfill, T Nosenko,
T Shimizu, J van Dijk and J L Zimmermann.
Plasma medicine: an introductory review. New
J.Phys. 11(2009) 115012.
3
Z. Cao, J.L. Walsh, and M.G. Kong.
Atmospheric plasma jet array in parallel electric
and gas flow fields for three-dimensional surface
treatment. APL. 94, 021501(2009)
4
O Sakai, T Sakaguchi and K Tachibana.
Photonic bands in two-dimensional microplasma
arrays.I. Theoretical derivation of band
structures of electromagnetic waves. JAP 101,
073304(2007).
5
QY Nie, Z Cao, C S Ren, DZ Wang and MG
Kong. A two-dimensional cold atmospheric
plasma jet array for uniform treatment of largearea surfaces for plasma medicine. NJP. 11(2009)
115015.
6
Z Cao, Q Nie, DL Bayliss, JL Walsh, CS Ren,
DZ Wang and MG Kong. Spatially extended
atmospheric plasma arrays. PPST. 19(2010)
0250030.
7
U Kogelschatz, Dielectric-barrier Discharges:
Their History, Discharge Physics, and Industrial
Applications. Plasma Chemistry and Plasma
Processing. Vol.23, No1, March 2003.
8
KD Weltmann, R Brandenburg, T von
Woedtke, J Ehlheck, R Foest, M Stieber and E
Kindel. Antimicrobial treatment of heat sensitive
products by miniaturized atmospheric pressure
plasma jets(APPPs). J.Phys.D: Appl.Phys.
41(2008)194008
9
N Jiang, A Ji and Z Cao, Atmospheric pressure
plasma jet: Effect of electrode configuration,
discharge behavior, and its formation
mechanism. JAP, 2009.