U.S. patent application number 15/795714 was filed with the patent office on 2018-05-10 for apparatus and method for augmenting the volume of atmospheric pressure plasma jets.
This patent application is currently assigned to The Government of the United States of America, as represented by the Secretary of the Navy. The applicant listed for this patent is The Government of the United States of America, as represented by the Secretary of the Navy, The Government of the United States of America, as represented by the Secretary of the Navy. Invention is credited to David R. Boris, Eric D. Gillman, Tzvetelina Petrova, Scott G. Walton.
Application Number | 20180130641 15/795714 |
Document ID | / |
Family ID | 62064806 |
Filed Date | 2018-05-10 |
United States Patent
Application |
20180130641 |
Kind Code |
A1 |
Walton; Scott G. ; et
al. |
May 10, 2018 |
Apparatus and Method for Augmenting the Volume of Atmospheric
Pressure Plasma Jets
Abstract
An apparatus and methods to increase and direct the spatial
volume of atmospheric pressure plasma jets. One or more additional
gas flows is introduced to intersect the plasma jet. As the plasma
jet interacts with these additional gas flows, the direction of
propagation of the plasma jet is altered, the plasma expands into
the volume defined by the additional gas flow, and the volume and
effective surface area of the plasma jet increases accordingly,
while the power increase needed to drive the increase in plasma
volume scales sub-linearly with the increase in volume.
Inventors: |
Walton; Scott G.; (Fairfax,
VA) ; Boris; David R.; (Silver Spring, MD) ;
Petrova; Tzvetelina; (Gaithersburg, MD) ; Gillman;
Eric D.; (Arlington, VA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
The Government of the United States of America, as represented by
the Secretary of the Navy |
Arlington |
VA |
US |
|
|
Assignee: |
The Government of the United States
of America, as represented by the Secretary of the Navy
Arlington
VA
|
Family ID: |
62064806 |
Appl. No.: |
15/795714 |
Filed: |
October 27, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62417372 |
Nov 4, 2016 |
|
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|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01J 2237/327 20130101;
H05H 1/3405 20130101; H01J 37/32449 20130101; H05H 1/34
20130101 |
International
Class: |
H01J 37/32 20060101
H01J037/32 |
Claims
1. An apparatus for augmenting a volume of a plasma jet,
comprising: a plasma jet source configured to produce a plasma jet
propagating in a first direction; and at least one gas nozzle
configured to produce a corresponding neutral gas stream extending
towards the plasma jet propagating in a second direction different
from the first direction of the plasma jet; wherein the neutral gas
stream intersects the plasma jet at an arbitrary angle and
interacts with the plasma jet; wherein when the neutral gas stream
interacts with the plasma jet, an extended volume of plasma from
the plasma jet extends into the neutral gas stream, the extended
volume of plasma flowing in a direction of increasing gas density
within the neutral gas stream; and wherein a geometry of the gas
nozzle, an identity of the neutral gas, a speed of the neutral gas,
or a volume of the neutral gas is configured to produce a
predetermined augmented volume of plasma having at least one
predetermined spatial characteristic.
2. The apparatus for augmenting a volume of a plasma jet according
to claim 1, wherein the neutral gas stream extends in a direction
orthogonal to a direction of the plasma jet.
3. The apparatus for augmenting a volume of a plasma jet according
to claim 1, comprising two gas nozzles configured to produce two
neutral gas streams extending towards the plasma jet opposite from
one another, wherein the common axis of both neutral gas streams
intersects the plasma jet at an arbitrary angle; and wherein when
the neutral gas streams interact with the plasma jet, an extended
volume of plasma from the plasma jet extends into the each neutral
gas stream, the extended volume of plasma flowing in a direction of
increasing gas density within each neutral gas stream.
4. The apparatus for augmenting a volume of a plasma jet according
to claim 4, wherein both neutral gas streams flow in a direction
orthogonal to the direction of the plasma flow from the plasma
jet.
5. The apparatus for augmenting a volume of a plasma jet according
to claim 1, comprising a plurality of neutral gas nozzles, the gas
nozzles being configured to produce a corresponding plurality of
neutral gas streams extending towards the plasma jet, each of the
neutral gas streams intersecting the plasma jet at an arbitrary
angle.
6. The apparatus for augmenting a volume of a plasma jet according
to claim 1, comprising a plurality of neutral gas nozzles, the gas
nozzles being configured to produce a corresponding plurality of
neutral gas streams extending towards the plasma jet, each of the
neutral gas streams being orthogonal to the plasma jet.
7. The apparatus for augmenting a volume of a plasma jet according
to claim 1; wherein the gas nozzle has a flattened shape; and
wherein extended volume of plasma is in the form of a sheet of
plasma flowing in a direction of increasing gas density within each
neutral gas stream.
8. The apparatus for augmenting a volume of a plasma jet according
to claim 1, wherein the neutral gas comprises a noble gas.
9. The apparatus for augmenting a volume of a plasma jet according
to claim 1, wherein the neutral gas comprises helium.
10. The apparatus for augmenting a volume of a plasma jet according
to claim 1, wherein the neutral gas comprises neon.
11. The apparatus for augmenting a volume of a plasma jet according
to claim 1, wherein the neutral gas comprises a mixture of
gases.
12. A method for producing an augmented plasma volume from a plasma
jet, comprising: providing a plasma jet from a plasma jet source;
and directing at least one neutral gas stream into the plasma jet;
wherein each neutral gas stream intersects the plasma jet at an
arbitrary angle and interacts with the plasma jet; wherein when the
neutral gas stream interacts with the plasma jet, an extended
volume of plasma from the plasma jet extends into the neutral gas
stream, the extended volume of plasma flowing in a direction of
increasing gas density within the neutral gas stream; and wherein a
geometry of the gas nozzle, an identity of the neutral gas, a speed
of the neutral gas, or a volume of the neutral gas can be
configured to produce a predetermined extended volume of plasma
having at least one predetermined spatial characteristic.
13. The method for producing an augmented plasma volume according
to claim 12, wherein the at least one neutral gas stream intersects
the plasma jet at an arbitrary angle.
14. The method for producing an augmented plasma volume according
to claim 12, wherein the at least one neutral gas stream extends in
a direction orthogonal to a direction of the plasma jet.
15. The method for producing an augmented plasma volume according
to claim 12, wherein the at least one neutral gas stream is
produced from gas nozzles having a flattened shape; and wherein
extended volume of plasma is in the form of a sheet of plasma
flowing in a direction of increasing gas density within each
neutral gas stream.
16. The method for producing an augmented plasma volume according
to claim 12, wherein the neutral gas comprises a noble gas.
17. The method for producing an augmented plasma volume according
to claim 12, wherein the neutral gas comprises helium.
18. The method for producing an augmented plasma volume according
to claim 12, wherein the neutral gas comprises neon.
19. The method for producing an augmented plasma volume according
to claim 12, wherein the neutral gas comprises a mixture of gases.
Description
CROSS-REFERENCE
[0001] This Application is a Nonprovisional of and claims the
benefit of priority under 35 U.S.C. .sctn. 119 based on U.S.
Provisional Patent Application No. 62/417,372 filed on Nov. 4,
2016. The Provisional Application and all references cited herein
are hereby incorporated by reference into the present disclosure in
their entirety.
TECHNICAL FIELD
[0002] The present disclosure relates to atmospheric pressure
plasma jets, and in particular to apparatuses that can be used to
increase and control the volume of such plasma jets.
BACKGROUND
[0003] Over the past two decades, there has been a surge of
interest in atmospheric pressure plasmas. These include glow
discharges, high frequency and dielectric barrier discharges,
microwave sustained plasmas, plasma jets and torches, microplasmas,
laser-induced plasmas, electron beam generated plasmas, and many
others. Typically, their design and operation are tailored for
specific applications or to enable different technologies in areas
as varied as biology and medicine (see D. B. Graves, "Low
temperature plasma biomedicine: A tutorial review," Phys. of
Plasmas 21, 080901 (2014); M. G. Kong, et al., "Plasma medicine: an
introductory review," New J. Phys. 11, 115012 (2009); and X. Lua,
et al., "Reactive species in non-equilibrium atmospheric-pressure
plasmas: Generation, transport, and biological effects," Physics
Reports 630, 1-84 (2016)); chemistry and material science (see D.
Pappas, "Status and potential of atmospheric plasma processing of
materials," J. Vac. Sci. Technol. A 29, 020801 (2011)); aerospace
science (see C. L. Enloe, et al., "Surface Potential and
Longitudinal Electric Field Measurements in the Aerodynamic Plasma
Actuator," AIAA Journal 46, 2730 (2008)); and environmental
engineering (see G. M. Petrov, et al., "Investigation of
industrial-scale carbon dioxide reduction using pulsed electron
beams," J. Appl. Phys. 119, 103303 (2016)).
[0004] Atmospheric pressure plasmas have certain advantages in
materials synthesis and processing that are not available with
other approaches including low-pressure plasmas. The breadth of
reactions afforded by non-equilibrium, low-temperature plasmas
makes them particularly advantageous, and when produced in full
density air, such plasmas can be used with systems and materials
that are not vacuum-compatible.
[0005] One type of non-equilibrium, atmospheric pressure plasmas,
often referred to as "plasma jets," are well-suited for such
applications given their relatively simple design, flexible
electrode geometry, and modest power requirements. Plasma jets are
created when a discharge generated in a confined gas flow, usually
a pure or diluted noble gas flowing through a dielectric tube,
leaves the region of confinement and propagates through the
surrounding ambient. See X. Lu, et al., "Guided ionization waves:
Theory and experiments," Physics Reports 540 123-166 (2016).
[0006] FIGS. 1A and 1B illustrate an exemplary conventional
apparatus developed at the U.S. Naval Research Laboratory for
generating a plasma jet. As shown in the block schematic of FIG. 1A
and the photographic image in FIG. 1B, a plasma jet can be
generated from a flow 101 of a noble gas such as helium (He), neon
(Ne), argon (Ar), krypton (Kr), or xenon (Xe), which passes into a
cylinder 102 within an outer casing 106, in which is situated an
electrode 103 connected to a voltage source 104. As the gas 101
passes over the electrode 103, it is ionized and forms the plasma
jet 105 that is output from the cylinder 102.
[0007] Plasma jets can be made quite small, which is good for
high-precision applications. See Lua, supra. However, it is
difficult to produce jet systems that can scale to treat large
surface areas, and as a result, the maximum treatment areas are
generally limited to about 1 cm.sup.2. See M. Ghasemi, et al.,
"Interaction of multiple plasma plumes in an atmospheric pressure
plasma jet array," Journal of Physics D: Applied Physics 46, 052001
(2013).
[0008] To address the desire for plasma treatment in larger areas,
several researchers have constructed one- and two-dimensional
arrays of plasma jets, where the treatment area scales with the
number of jets. See Ghasemi, supra; see also Q. Y. Nie, et al., "A
two-dimensional cold atmospheric plasma jet array for uniform
treatment of large-area surfaces for plasma medicine," New J. Phys.
11 115015 (2009). However, this approach requires increases in
power and gas flow, and these increases in power and gas flow also
scale with the number of jets. For example, two jets operating in
parallel will require twice the gas flow and power input.
[0009] It has also been shown that combining two
counter-propagating plasma jets effectively extends the length of a
plasma discharge. See C. Douat, et al., "Interactions Between Two
Counter Propagating Plasma Bullets," IEEE Trans Plasma Sci. 39,
2298-2299 (2011); see also C. Douat, G. et al., "Dynamics of
colliding microplasma jets," Plasma Sources Sci. Technol. 21,
034010-8 (2012). The two plasma jets can be produced using either
two opposing gas flows, each with a corresponding power source and
electrode or a single gas stream flowing between two electrodes. In
either case, the power requirements effectively double.
[0010] Although these approaches clearly work in the sense that the
volume and/or effective treatment area increases, the power needed
to produce the plasma volume increases as the plasma volume
increases. In addition, device complexity increases since both the
driving circuit and gas delivery system must be carefully designed
so that all of the plasma jets are driven simultaneously and with
equal intensity.
SUMMARY
[0011] This summary is intended to introduce, in simplified form, a
selection of concepts that are further described in the Detailed
Description. This summary is not intended to identify key or
essential features of the claimed subject matter, nor is it
intended to be used as an aid in determining the scope of the
claimed subject matter. Instead, it is merely presented as a brief
overview of the subject matter described and claimed herein.
[0012] The present invention provides an apparatus and methods to
increase the spatial volume of atmospheric pressure plasma jets
without the use of additional power supplies, circuits or
electrodes. Instead, only one or more additional neutral gas
streams that are not aligned with the plasma jet axis and intersect
the plasma jet at an arbitrary angle are used. As the plasma jet
interacts with these additional gas flows, the direction of
propagation of the plasma jet is altered, the plasma expands into
the volume defined by the additional gas flow, and the effective
volume and thus surface area of the plasma jet increases
accordingly, while the power increase needed to drive the increase
in plasma volume scales sub-linearly with the increase in
volume.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIGS. 1A and 1B depict aspects of plasma jet generation in
accordance with the prior art.
[0014] FIGS. 2A-2D depict aspects of an apparatus and method for
production of a spatially modified plasma jet volume in accordance
with the present invention.
[0015] FIG. 3 is a block diagram illustrating aspects of an
apparatus for measuring voltage and current in an apparatus for
generation of a spatially modified plasma jet volume in accordance
with the present invention.
[0016] FIGS. 4A-4C are plots illustrating voltage and current
measured by an apparatus such as that illustrated in FIG. 3 in "no
jet," "plasma jet," and "plasma jet+gas stream" cases.
[0017] FIGS. 5A and 5B are additional plots illustrating driving
current and driving power associated with the production of a
plasma jet volume with and without one or more orthogonal neutral
gas streams in accordance with the present invention.
[0018] FIGS. 6A and 6B are photographic images illustrating
production of extended plasma jet volumes in accordance with the
present invention using helium (FIG. 6A) and neon (FIG. 6B) gas
streams.
[0019] FIGS. 7A-7C are photographic images illustrating aspects of
an extended plasma jet volume produced in accordance with the
present invention using four neutral gas streams, flowing
orthogonally to one another and intersecting at the jet axis.
[0020] FIGS. 8A and 8B are photographic images illustrating aspects
of an extended plasma jet volume produced in accordance with the
present invention using flattened gas tubes to shape and direct the
neutral gas streams into the plasma jet.
[0021] FIGS. 9A-9C are photographic images illustrating aspects of
an extended plasma jet volume produced in accordance with the
present invention using neutral gas streams situated between two
parallel plates.
DETAILED DESCRIPTION
[0022] The aspects and features of the present invention summarized
above can be embodied in various forms. The following description
shows, by way of illustration, combinations and configurations in
which the aspects and features can be put into practice. It is
understood that the described aspects, features, and/or embodiments
are merely examples, and that one skilled in the art may utilize
other aspects, features, and/or embodiments or make structural and
functional modifications without departing from the scope of the
present disclosure.
[0023] This disclosure describes a means to increase the volume of
atmospheric pressure plasma jets without the use of additional
power supplies, driving circuitry, or physical confinement.
Instead, the plasma volume is increased and its spatial profile can
be tailored by controlling the background gas density through the
injection of one or more neutral gas streams. Increasing the plasma
volume through this approach provides more useful charged and
reactive neutral gas species and increases the effective surface
treatment area.
[0024] Thus, the present invention provides an apparatus and
methods to increase the volume of atmospheric pressure plasma jets
and tailor their spatial distribution without the use of additional
power supplies, circuits or electrodes. Instead, we use only one or
more additional gas flows that intersect the plasma jet.
[0025] As the plasma jet interacts with these additional gas flows,
the direction of propagation of the plasma jet is altered, the
plasma expands into the volume defined by the additional gas flow,
and the effective surface area of the plasma jet increases
accordingly, while the power increase needed to drive the increase
in plasma volume scales sub-linearly with the increase in volume.
In many embodiments, these additional gas flows will flow in a
plane orthogonal to the plasma jet axis, but such orthogonality is
not required, and gas flows in any direction not aligned with the
plasma jet axis, intersecting the plasma jet at an arbitrary angle,
can also be used.
[0026] The simplest embodiment of this invention includes a plasma
jet and a neutral gas stream, propagating at right angles to one
another. This configuration and an extension of it, two neutral gas
streams propagating in opposite directions (but still orthogonal to
the plasma jet axis), are shown in FIGS. 2A-2D.
[0027] FIG. 2A is a block schematic illustrating aspects of the
generation of a plasma jet in accordance with the present
invention. As shown by the block schematic in FIG. 2A and the
photographic image in FIG. 2B, a plasma jet 205 can be generated
from a flow of helium gas 201 travelling in a cylinder 202 within
an outer casing 206, past an electrode 203 connected to an AC
(f=25-35 kHz), high voltage (Vpp=500-2000 V) signal (not shown). In
accordance with the present invention, one or more neutral gas
streams 207a/207b are directed through tubes 208a/208b so as to
propagate in directions not aligned with the axis of the plasma jet
205. In most embodiments described, neutral gas streams 206a/206b
will be helium, though other neutral gases may be used as
appropriate.
[0028] As described in more detail below, in accordance with the
present invention, the neutral gas stream(s) interact with the
plasma jet and produce a volumetric distribution of the plasma from
the plasma jet that is not aligned with the plasma jet's original
direction of propagation. By tuning any one or more of the
parameters of the gas stream, such as the shape and spatial
distribution of the neutral gas streams, flow direction, and the
gas used, a desired spatial distribution of the plasma volume can
be achieved.
[0029] The photographic images in FIGS. 2B-2C illustrate how the
presence of a neutral gas stream orthogonal to a plasma jet can
produce a spatially altered distribution of plasma volume in
accordance with the present invention.
[0030] Thus, FIG. 2B shows the case with no gas exiting from either
of gas tubes 208a/208b, and shows plasma jet 205 exiting from the
chamber in a substantially straight stream in the direction of the
original helium gas flow through the chamber.
[0031] FIGS. 2C and 2D illustrate what happens when one or more
orthogonal gas streams are directed into the plasma jet.
[0032] As can be seen in FIG. 2C, with the presence of a gas stream
206a exiting from gas tube 208a, part of the plasma volume from
plasma jet 205 interacts with the neutral gas, producing an
additional plasma volume 209a that extends into the gas stream. As
shown in the photographic image in FIG. 2D, when the neutral gas
stream 207a/207b propagates from both gas tubes 208a/208b,
additional plasma volumes 209a/209b are created.
[0033] As can be seen from both FIG. 2C and FIG. 2D, the additional
plasma volumes 209a/209b propagates in the direction of the neutral
gas density rather than in the direction of flow. The total plasma
volume is increased by the introduction of the neutral gas streams
into the plasma jet in accordance with the present invention, with
the increase in plasma volume typically being on the order of a
two-fold increase if one gas stream is present, and three-fold if
two gas streams are used.
[0034] To better understand this system, current-voltage
measurements were performed using the configuration shown in FIG.
3, where the voltage and current from the power supply driving the
plasma could be monitored along with the current collected on
grounded collar 320 at the exit of the opposing gas tubes.
[0035] As described in more detail below, the results of these
voltage and current measurements for three operational schemes, "no
jet," "plasma jet," and "plasma jet+gas stream," are shown by the
plots in FIGS. 4A-4C, where FIG. 4A shows the driving voltage (in
kV) for the three operational schemes, FIG. 4B shows the driving
current (in mA), FIG. 4C shows the current (in mA) measured at the
exit of the gas stream tube. Additional aspects of the three
operations schemes are shown by the plots in FIGS. 5A and 5B, where
FIG. 5A shows the difference in driving current (in mA) between the
"plasma jet" vs. "no jet" case and the "plasma jet+gas stream" and
"no jet" case and FIG. 5B shows the difference in driving power (in
W) between the "no jet," "plasma jet," and "plasma jet+gas stream"
schemes.
[0036] For the "no jet" case, shown by the hollow square dotted
line in the FIGURES, power is applied to the electrode but no gas
flows past the electrode; without such flow a plasma jet cannot be
produced. The "plasma jet" case, shown by the solid round dotted
line in the FIGURES reflects typical operation for the production
of a plasma jet, where gas flows past a powered electrode to
produce a plasma jet that emerges from the tube as a freely
propagating plasma. For both the "no jet" and "plasma jet"
operational modes, no additional gas streams are intersecting with
the plasma jet. For the "plasma jet+gas stream" case, shown by the
hollow triangle dotted line in the FIGURES, gas streams emerge from
the gas tubes causing the discharge to propagate toward both gas
tubes, as discussed above with respect to FIG. 2D.
[0037] The I-V measurements in the absence of plasma (no jet)
represent the baseline values for the driving circuit, where the
displacement currents at the driven electrode and gas tube collars
are due to the oscillating high voltage signal. In the presence of
flowing helium, small deviations from these baselines signals
represent the contributions due to the plasma resistivity. In
particular, the current spikes at 2-3 .mu.s and 17-18 .mu.s on the
electrode current shown in FIG. 4B represent the ignition of
streamer-like discharges that form the plasma jets. Similar current
spikes are also measured at the ground collars after a small time
delay, commensurate with the discharge propagation time. Note, that
while current on the collars is measured without the orthogonal gas
streams, no emission (light) is observed in the volume between the
jets axis and the gas tubes, suggesting a very weak, if not
negligible plasma current. The presence of helium is critical to
the production of plasma ("no jet" vs. "plasma jet" operating
modes) and so, the increase in current measured on the collars with
the helium gas streams flowing is not surprising.
[0038] An increase in volume is expected to require an increase in
applied power. The discharge current along with instantaneous power
measured at the driven electrode is shown in FIGS. 5A and 5B,
respectively. The difference between the instantaneous power curves
for the cases with and without plasma jet is the power required to
drive the discharge. This power is found to increase when the gas
streams are introduced, with this increase being largely due to an
increase in discharge current, as seen in FIG. 5A. The average
power per period is found to increase by approximately 50% when the
gas streams are turned on. From earlier then, we see that a 3-fold
increase in plasma volume comes at a relatively modest 50% increase
in power.
[0039] FIGS. 6A-6B, 7A-7C and 8A-8B, and 9A-9C illustrate
additional exemplary embodiments of the use of neutral gas streams
to increase and tailor a plasma jet volume in accordance with the
present invention. The embodiments described herein fall into two
broad categories, the use of different gases and different gas flow
geometries. In addition, although not described in detail herein,
one skilled in the art would readily understand that tailoring
other parameters of the neutral gas flow, such as its speed,
volume, or composition, can also be used in accordance with the
present invention to obtain a desired plasma jet volume.
[0040] FIGS. 6A and 6B show the effect of the use of different
gases on the plasma jet volume in accordance with the present
invention. FIG. 6A shows a plasma jet 605 produced in a helium
background interacting with opposing helium gas streams 607a/607b
to produce additional plasma volumes 609a/609b extending into the
direction of the helium gas density, while FIG. 6B shows the plasma
jet 605 produced in a helium background interacting with neon gas
streams 607a/607b that originate farther from the plasma jet than
do the helium gas streams. As can be seen from these FIGURES, the
use of neon gas streams produces an additional plasma volume that
extends farther from the plasma jet than when compared to the
helium gas stream. Other gases may also be used to obtain a desired
spatial distribution of the plasma volume.
[0041] Plasmas are often used to treat large surfaces. Since a
plasma jet is only able to treat a very small area, roughly that
determined by the radius of the plasma jet, in current practice,
large area treatments require that one or more plasma jets must be
scanned over the entire surface. As described below, the concepts
and embodiments discussed above can be further utilized to increase
the treatment area of a plasma jet.
[0042] FIGS. 7A-7C illustrates aspects of a different geometry that
can be used to produce an enhanced plasma jet volume in accordance
with the present invention. In the embodiment illustrated in FIGS.
7A-7C, a plasma jet 705 can be subjected to gas flow from four
equally spaced gas nozzles, each at a 90.degree. angle from one
another, and in a plane orthogonal to the plasma jet axis, to
produce four extended plasma volumes 709a/b/c/d. Such a
configuration indicates a plurality of gas streams can be
interacted with a plasma jet to produce and arbitrarily large
plasma volume in a direction extending outward from the plasma jet
axis, and thus the ability to treat larger areas.
[0043] FIGS. 8A and 8B illustrate aspects of still another
embodiment of an extended plasma jet volume produced in accordance
with the present invention, which can enhance the ability of a
single plasma jet to treat larger surface areas. In the embodiment
illustrated in FIGS. 8A and 8B, a plasma jet 805 can operate in the
presence of one (FIG. 8A) or two (FIG. 8B) sheet-like gas flows
produced, e.g., by gas nozzles having a flattened shape. As can be
seen from the FIGURES, using this configuration of gas nozzles, the
additional plasma volumes 809a/809b produced also have a sheet-like
shape. It is expected that exerting fine control over gas flow
would provide a large number of possible geometries with highly
uniform plasma expansion. Such plasma configurations can be used to
treat larger surface areas in each pass, reducing the time and
energy needed to treat a large area. Additionally, sheet-like
plasmas have the added benefit of possessing a larger surface
area-to-volume ratio than cylindrical plasmas of the same
volume.
[0044] In other cases, it may be desirable to use a plasma to treat
a surface within a confined space. FIGS. 9A-9C illustrate that the
apparatus and method in accordance with the present invention can
be used to produce a spatially extended plasma volume for use in
such a confined space. Thus, as illustrated in FIG. 9A, a plasma
jet that extends between top and bottom plates 930a/930b can be
redirected to form an additional plasma volume 909a (FIG. 9B) or
909a/909b (FIG. 9C) by means of one or two neutral gas flows
directed between the plates. The symmetry created by identical top
and bottom plates largely eliminates most non-uniformities in gas
flow, leading to uniform plasma generation compared to
configurations using a single plate or surface. Such a geometry
could be used to create a plasma "line source" for the treatment of
static surfaces or with moving surfaces such as those used in
roll-to-roll polymer web treatments, where the surface area to be
treated becomes the bottom plate.
Advantages and New Features
[0045] As noted earlier, methods aimed at increasing the volume of
plasma jets typically involve simply increasing the number of jets
or powered electrodes. While these approaches are straightforward
and effective, it comes at significant increase in power and/or
driving circuit complexity. The approach described here requires no
additional circuitry and the power increase relative to the volume
increase is surprisingly low. In addition, the volume expansion can
be made orthogonal to the plasma jet axis, thereby increasing the
potential treatment area in a manner not possible with parallel
plasma jet arrays. Moreover, the use of additional external gas
flow with different gas composition is possible. For example,
diluting the neutral gas with a molecular and/or reactive gas of
choice to target specific materials processing applications.
[0046] Although particular embodiments, aspects, and features have
been described and illustrated, one skilled in the art would
readily appreciate that the invention described herein is not
limited to only those embodiments, aspects, and features.
[0047] For example, although not described in detail in the present
disclosure, one skilled in the art would readily appreciate that in
other embodiments using an apparatus and method for producing an
extended plasma volume in accordance with the present invention,
controlling one or more parameters of the neutral gas flow can also
be used to tailor the plasma volume to suit a particular
application, geometry, or environment.
[0048] All such modifications and additional embodiments are deemed
to be within the scope and spirit of the present disclosure and the
invention described and claimed herein.
* * * * *