Experimental Study of a Compact Nanosecond Plasma Gun

Full Paper

Experimental Study of a Compact NanosecondPlasma Gun

Eric Robert,* Emerson Barbosa, Sebastien Dozias, Marc Vandamme,Christophe Cachoncinlle, Raymond Viladrosa, Jean Michel Pouvesle

The paper presents a new discharge plasma setup, called plasma gun, allowing the generationof nanosecond duration plasma bullets from a pulsed dielectric barrier discharge reactor.These bullets propagate at very high velocity, up to 5� 108 cm � s�1, in flexible dielectriccapillaries flushed with neon or helium flow rates as low as 100 mL �min�1, over distances of afew tens of centimetres, before inducing plasma plume formation in ambient air. Timeresolved nanosecond ICCD imaging show evidence for the channelled structure of the bulletswhich propagate along the inner surface of the dielectric guide.A few centimetres from the DBD reactor where they aregenerated, the plasma bullets expand with no connection tothe high voltage power source. Non-thermal air plasma plumeproduction is described by spectroscopic measurements. Theplasma gun is likely to be developed for remote high voltagefast commutation or in plasma medicine applications or for thedecontamination of small diameter catheters.

Introduction

There exists today a growing interest for non-thermal

plasma source development and characterization for their

integration in new therapeutic strategies or generally

speaking plasma medicine and plasma health issues.[1]

Examples of the use of discharge plasma for medical

applications previously consisted in the argon plasma

coagulator,[2] arc discharge in saline solution,[3] and the

chemical and photochemical action of whether low

pressure plasma or afterglow ensuing from an atmospheric

pressure reactor in decontamination and sterilization

technologies.[4] More recently, the interest for the potenti-

alities of the whole plasma direct exposition for biomedical

E. Robert, E. Barbosa, S. Dozias, M. Vandamme, C. Cachoncinlle,R. Viladrosa, J. M. PouvesleGREMI, CNRS-Polytech’Orleans, 14 rue d’Issoudun, BP 6744, 45067Orleans Cedex 2, FranceFax: (þ33) 2 38 417154; E-mail: [email protected]

Plasma Process. Polym. 2009, 6, 795–802

� 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

applications was re-awakened through the investigation of

atmospheric pressure non-thermal plasma effects on living

tissue or cells.[5–9] The floating electrode DBD, the atmo-

spheric pressure torch and the plasma jets (jets, pencils,

needles and bullets) in continuous, RF, or pulsed regime are

the main discharge setups used for the production of non-

thermal rare gas plasma expanding in ambient air. They are

all more or less safe, reliable, compact and easy to handle

devices but they may suffer from two potential limitations

for their actual use in some plasma medicine protocols.

Some of the plasma torch and jets allow for surface

treatment area with typical diameters of only a few

hundreds of microns while DBD systems should be

efficiently operable on larger surfaces but require a gap

between the high voltage reactor electrode and the tissue of

only a few millimetres. The production of transient plasma

bullets or bullet trains travelling at high velocities and the

consecutive production of plasma plumes at large distances

from the plasma reactor was recently reported,[10,11] and

may open up new possibilities for the safe and extensive

DOI: 10.1002/ppap.200900078 795

E. Robert et al.

Figure 1. Plasma gun photographs in left: 50 cm long, 4 mm indiameter dielectric guide with plume formation and right: 50 cmlong, 200 mm in diameter dielectric guide, the guide is twistedonly for ‘artistic’ purpose.

Figure 2. Experimental reactor setup.

796

parametric range of operation of these non-thermal plasma

sources.

In this work, we present the experimental investigation

of a new and, to the best of our knowledge, unique pulsed

plasma gun delivering very fast moving plasma bullets of

nanosecond duration or bullet bursts from a pulsed DBD

reactor. Very fast propagation through flexible and easy to

handle capillaries over distance of tens of centimetres allow

for bullet plasma to propagate with no electrical connection

to the high voltage DBD reactor and for the long distance

remote creation of transient plasma plumes of a few

centimetres in length in ambient air. Figure 1 illustrates the

plasma generation in ambient air. In this case, the plasma is

produced through a high voltage pulsed driver, not shown

in the picture, and propagates first into a flexible polyamide

dielectric tube of 4 mm internal diameter flushed with

neon. Then the formation of a plasma plume downstream

the guide outlet is observed, on the hand of one of the

authors as shown in the left picture in Figure 1. The ruler

indicates the length of the plume of about 8 cm and also

emphasizes the production of this atmospheric air plasma

at 50 cm from the high voltage reactor, the origin of the ruler

being positioned at the reactor outlet. Preliminary studies

have shown that the light observed in Figure 1 through the

dielectric tube consists in a transient, nanosecond duration,

plasma propagating at very high velocity, of a few 107–

108 cm � s�1.[12] The propagation of the plasma together

with the remote generation of the plume was also recently

achieved through much thinner (200 mm in diameter)

flexible dielectric capillaries, a few tens of centimetres long,

as shown in the right picture in Figure 1, promoting their

potential use for endoscopic therapeutic treatment. In this

work, the design of a simplified plasma gun source and

diagnostics is proposed in the Experimental Part. The

Imaging Experiments Section presents the results and

discussion from time resolved nanosecond imaging experi-

ments. The plasma gun temporal structure and plasma

bullet velocity inferred from fast photodiode visible light

measurements are proposed in the Photodiode Measure-

ments Section. The Spectroscopic Measurements Section



provides a brief spectroscopic analysis of the plasma bullet

and the plasma plume. Main conclusions are finally

proposed in the last section of this manuscript.

Experimental Part

In this work, a very simple experimental reactor was developed to

achieve a simultaneous electrical, visible imaging and spectro-

scopic characterization of the plasma generation, propagation and

plume production. The design of this DBD-based reactor is one of

the possible setup of such devices,[12] in which the DBD reactor body

and the dielectric guide consists in a unique assembly as illustrated

in Figure 2 schematics. The main motivation was to observe the full

plasma expansion and dynamics thanks to a fast ICCD camera with

integration time as low as 2 ns. Attention was also paid to the

possibility to control the gas flow rate, the voltage peak amplitude

across the DBD reactor and, the material used for the reactor body

and the dielectric guide. These considerations lead to the

development of a DBD reactor, whether a 1 mm thick transparent

borosilicate glass or a 1 mm thick translucent alumina capillary,

equipped with a 1 mm in diameter tungsten wire as an internal

electrode defining the longitudinal axis of the capillary reactor.

High purity gas (Ne N48 or He N45) is flushed through a gas flow

controller and a polyamide tube, 4 mm in diameter, to the air-tight

connector. This connector allows the gas flow around the internal

electrode and a simple mounting, change and axing of the DBD

capillary reactor. The second DBD electrode consists of a 4 mm wide,

200 mm thick copper strip set on the capillary external surface.

Visible light imaging experiments were performed with a PIMax

ICCD camera (512� 512 pixels) equipped with a 60 mm lens. The

design of a compact atmospheric plasma reactor and capillary

guide assembly was imposed by the wish to realize the

measurement of the plasma generation, propagation in dielectric

guide and expansion in ambient air on a unique ICCD picture. This

allows for the characterization of the fast dynamics on nanosecond

time scale and the spatial topography, including the radial

dimension, of the whole atmospheric air plasma generation

processes through high aspect ratio capillaries. Main results

described in the following are obtained with a 4 mm inner

diameter and 10 cm long (aspect ratio 25) reactor but it can be

noticed that plasma propagation in 40 cm long capillaries (aspect

ratio 100) and successive plume formation were observed with the

DOI: 10.1002/ppap.200900078

Experimental Study of a Compact Nanosecond . . .

same pulsed power supply, capillary setup and gas flow conditions.

Besides imaging experiment, the plasma characterization was

complemented by voltage measurement with two P6015A 75 MHz

probes and transient light pulse duration and propagation speed

with fast, rising time of about 5 ns, PIN photodiodes connected to a

Tektronix 744 oscilloscope. Finally, time integrated spectroscopy

was performed with a UV–Visible Ocean Optics HR 2000 spectro-

meter mounted with an optical fibre cable allowing measurement

for 220 up to 900 nm.

Imaging Experiments

Figure 3 presents seven 2 ns snapshots labelled with their

respective delay to the time origin corresponding to light

appearance on the top picture in Figure 3 and correspondingly

to the rise of the voltage pulse across the DBD electrodes. The OE and

IE marks stand for the central position of the outer electrode and the

tip of the inner tungsten rod, respectively. The GO mark indicates

the guide outlet, i.e. the end of the glass capillary through which the

gas flow expands in ambient air. As described in the next section,

the time jitter between the triggering of the discharge pulse

application and the plasma ignition was of about 20 ns, so that the

Figure 3. Two nanoseconds gated ICCD images of the DBD dis-charge and transient plasma capillary propagation. The timeindicated for each picture indicates the delay from the 0 ns origin.The OE, IE, P1, P2, P3 and GO labels indicate the position of theouter electrode, inner electrode tip, transient plasma position fordelay 20, 31 and 41 ns and the dielectric guide outlet, respectively.



pictures presented in Figure 3 have been selected through a larger

set of acquisitions, obtained by tuning the delay between the

voltage pulse and the ICCD gating including the non-controllable

jitter, and measuring the real delay between both signals on

the oscilloscope. Each snapshot is displayed with a grey level values

ranging from 5 to 95% of the full pixel intensities measured for the

labelled time delay. On the two first pictures (0 and 4 ns delays) the

creation of the neon plasma in the glass capillary below the outer

electrode ring electrode is observed together with a thin glowing

plasma slab at the tip of the tungsten rod for the 4 ns time delay. For

the next two delays (9 and 13 ns), the streamer nature of the

dielectric barrier discharge is visualized along the tungsten rod

while the plasma slab at its tip expands in the direction of the guide

outlet. For the three last delays depicted in Figure 3 (20, 31 and

41 ns) the discharge splits in two regions: the first region is

composed of the DBD zone and a 4 mm thick plasma glow-like zone

at the rod tip, while the second plasma region consists in a

filamentary slab centred around the P1, P2 and P3 marks for the 20,

31 and 41 ns time delays, respectively. This latter transient plasma

slab appears as almost disconnected from the DBD zone and

propagates at very high speed up to the glass capillary outlet for

longer delays.

An overall description of the plasma formation, propagation to

the capillary outlet, plume formation in ambient air and extinction

with the end of the voltage pulse is presented through six 5 ns

snapshot images documented in Figure 4. For time delay of 7 and

16 ns, the transient plasma propagating in the glass capillary is

located around the position 30 and 20 mm, respectively. For time

delay of 25 ns the visible light from the plume observed in ambient

air at the capillary outlet is imaged with a cone shape expanding

from �20 to 0 mm positions. Finally for longer delays, the

extinction of the plume, the reduction of the plasma length in

the glass capillary and the extinction of the discharge in the DBD

zone around the outer electrode position is observed. With the DBD

reactor setup presented in this paper, matched for ICCD imaging

experiments, the plume expansion in ambient air lasts for about

40 ns while the plasma generation in the DBD outer electrode zone

vanishes simultaneously with the end of the 5 ms voltage pulse (not

shown in Figure 4). In these experimental conditions, the electrical

connection, associated with the plasma light emission, between

the plume tip and the pulsed plasma driver occurs only during the

40 ns plume expansion phase. The use of longer dielectric

capillaries and optimized pulsed drivers, previously studied

through photodiode-based analysis, indicates that the transient

plasma propagating in the capillary then appears as electrically

isolated from the plasma ignition zone before it exits from the

capillary guide and induces the plume formation. In this latter case,

the plume–plasma interaction in ambient air with any sample can

be remotely achieved through long capillaries allowing for an

electrical separation with the high voltage pulsed generator.

Figure 3 and 4 also indicate that the transient plasma

propagating in the capillary appear as filamentary structures

propagating along the internal surface of the dielectric guide and

not as a homogeneous plasma filling the whole guide volume such

as the recently reported plasma bullets.[11] The propagation of the

transient plasma can be guided on a specific path by inserting

metallic strip along the capillary outer surface. In this case, the

transient plasma in the capillary slides along the inner surface of

www.plasma-polymers.org 797

E. Robert et al.

Figure 4. Five nanoseconds gated ICCD images of the plasma propagation, plume formation in ambient air and extinction in the glasscapillary pulsed DBD reactor. The gas flow occurs from right to left, the capillary outlet coincides with the label 0, the outer electrode leftposition with about 60 mm. The time delay above each picture is measured between the voltage pulse onset and the gating of the ICCD.Corresponding radial integrated, i.e. vertically averaged, profiles extracted from the pictures are documented on the right side of the figure.

798

the glass capillary, in a very thin layer below this metallic strip, as

presented in Figure 5 (left). In the left part of the Figure 5 the

transient plasma propagates along both the upper and lower inner

surface while it is guided on the upper surface in the right side on

Figure 5 (left) where the metallic strip is sticked on the capillary

outer surface. The Figure 5 (right) presents the image of the plume

at the outlet of the capillary equipped with the top metallic strip.

The plume exhibits an asymmetric intensity vertical profile

connected to its formation through the thin sliding plasma

presented in Figure 5 (left). The plume expansion length can be

significantly enhanced by the use of a grounded metallic surface set

a few centimetres downstream the capillary outlet. All these

observations confirm the crucial role of charged species in the

transient propagation and plume formation in ambient air.



Photodiode MeasurementsThe imaging experiments mainly reveal the topography of the

plasma volume, the three generation, propagation and expansion

phases and confirm the very high speed of the plasma propagation

in the dielectric guide. In this section, the plasma time resolved

characterization and its propagation speed are studied with the use

of one and two identical PIN photodiodes collecting the UV and

visible light radiated by the plasma. The photodiodes are coupled to

a fast oscilloscope, with input impedances of 50 Ohm, by two

identical cables offering a theoretical 5 ns temporal resolution.

Figure 6 presents the signal collected by a photodiode located a few

centimetres away from the capillary wall and a few millimetres

downstream the inner electrode tip position together with the high

voltage pulse across the capillary electrodes.

DOI: 10.1002/ppap.200900078


Figure 5. Ten nanoseconds gated images in left: propagation ofthe plasma in the glass capillary with a metallic outer strip on thetop of the capillary in the right half side of the picture and right:plume formation in same capillary configuration. The gas flowoccurs from left to right.

Figure 6. Voltage waveform across the capillary electrodes (blackthick signal) and corresponding photodiode signal (grey thinsignal, an offset of 20 arbitrary units was applied to this signalbaseline for figure clarity). The black exponential calculations fitwith the experimental damping measurement. The inset pre-sents a temporal zoom of the voltage and photodiode signalstogether with a sinusoidal damped fitting curve.

Figure 7. Single shot photodiode signals at the arbitrary timeorigin (black curve), 15 min later (dashed signal) and 30 min later(grey curve). The plasma gun is continuously operated at 5 Hz.

Voltage and Light Temporal Structure

The voltage across the electrodes of the DBD reactor rapidly falls

down to about 55 kV during the first 50 ns, then it exhibits two fast

positive polarity 40 ns duration pulses and finally oscillates

following a damped waveform of about 10 ms. The peak amplitude

of the voltage is lowered to less than 5 kV during the first 5 ms. The

damping can be reduced or amplified by inserting additional

impedance, as tested with the use of resistors, in parallel with the

DBD electrodes. This matching of the electric pulsed driver output

impedance with that of the DBD reactor allows both the reduction

of the rise time of the first high voltage spike and the optimization

of the energy transfer to the DBD discharge. For the experimental

conditions of Figure 6, the inset illustrates that the voltage



experimental signal is the combination of a sinusoidal damped

waveform with transient, about 40 ns FWHM, voltage pulses as

depicted by the superposition of the experimental signal with a

pure RLC damped waveform. The appearance of these voltage

spikes coincides with the photodiode measurement of transient

light peaks superimposed over a damped envelope during the first

ten microseconds following the voltage pulse onset. These

observations are in agreement with the ICCD imaging experi-

mental results where the plasma at the inner tip electrode was

shown to lasts during time period of a few microseconds (Figure 4)

and transient filamentary structures propagating at high velocities

were imaged (Figure 4 shortest delays). High speed ICCD video

sequence, obtained with a constant gate width of a few

nanoseconds and a sliding delay with respect to the discharge

voltage triggering signal, show that secondary filamentary

transient plasmas are observed during the whole, about 10 ms,

application of the voltage across the DBD reactor. Due to the voltage

damping these secondary plasmas vanish before the dielectric

guide outlet so that no secondary plume formation in ambient air

was observed. The use of much powerful electrical drivers or shorter

dielectric guide could probably result in the possibility to induce

several transient plume formations in a MHz burst regime.

The photodiode measurements indicate that besides the

previously reported single long distance pulsed atmospheric

plasma generation,[12] the setup developed in this work allow

the generation of pulsed atmospheric pressure plasma in burst

mode, i.e. the generation of a train of transient plasmas.

If the electrical driver and the discharge reactor operation

parameters are kept constant, Figure 7 illustrates the good

reproducibility of such train production during periods of minutes.

The three photodiode signals presented in Figure 7 have been

recorded with a time delay of 15 min between each single shot

acquisition, while the plasma generator was continuously powered

for a full time of operation of 1 h at a 5 Hz repetition rate. The

production of five main transient plasma, labelled in Figure 7

during 2 ms long voltage application, is observed with both a good

intensity and timing stability.

Velocity Measurements

The propagation speed measurement of the transient plasma in the

dielectric guide was performed with the use of two similar


E. Robert et al.

Figure 8. Normalized photodiode signals at 6 cm (grey curve) andat 16 cm (black curve) downstream the inner electrode tip. Thearrows indicate a 40 ns duration time step.

Figure 9. Evolution of the plasma propagation speed in thedielectric guide as a function of the distance from the innerelectrode tip. The black trace is a fit of the experimental data.

Figure 10. Plasma velocity versus the peak voltage amplitude for100 cm3 �min�1 neon flow in glass capillary (dots), neon flow inalumina capillary (squares) and for 150 cm3 �min�1 helium flow inglass capillary (triangle).

800

photodiodes set a few centimetres apart along the dielectric guide.

Both single transient plasma propagating in dielectric guide of a

few tens of centimetres and train propagation were measured.

Figure 8 presents the photodiode signals measured 6 and 16 cm

downstream the inner electrode tip, through the glass capillary

flushed with neon at a flow rate of 100 cm3 �min�1. This

measurement first indicates that the whole burst of transient

plasmas propagates at a constant speed as the two curves exhibit

quasi-identical temporal evolution with a constant time delay of

about 40 ns between two positions where the light is detected. Such

a conservative temporal structure of the plasma burst including

several transient plasma events was verified up to 50 cm from the

inner electrode tip. This propagation of the whole burst shows that

the space charge modification, the electromagnetic field distur-

bance, or the pre-ionization effects likely to be induced by each

individual transient plasma have no significant impact on the

propagation speed on the later coming plasma events during the

burst. The time delay of 40 ns corresponds to a mean propagation

speed of 2.5�108 cm � s�1 at an average distance of 11 cm

downstream the electrode tip. This speed appears at least one

order of magnitude higher than that reported for the plasma pencil

devices[11] or plasma jets[13] and has no correlation with the gas

flow speed of a few metres per second.

Figure 9 presents the evolution of the speed of the transient

plasma burst as a function of the distance from the inner electrode

tip. A strong decrease of the propagation speed is observed with 10

times reduction from 10 to 55 cm positions, the smaller measured

speed for the 60 cm distance being nevertheless identical to the

bigger value reported for the plasma bullets elsewhere. While no

systematic measurement of the plume speed was processed yet,

the ICCD imaging experiments indicate that the expansion of the

plume in the first centimetres from the dielectric guide outlet

occurs on a few tens of nanoseconds. Such a fast plume propagation

speed indicates that its formation has no correlation with the

excited species transport in the neon gas flow occurring at a very

much lower velocity.

The evolution of the plasma propagation speed measured at an

average distance of 5 cm from the electrode tip as a function of the

peak voltage amplitude across the discharge for neon and helium

gas flow in a glass capillary and for a neon flow in glass and alumina



capillaries is depicted in Figure 10. The production of transient

plasma and plume formation was obtained with a helium flow

instead of neon. The helium operation requires a larger helium flow

rate than in the case of neon and presents a higher threshold value

of the peak voltage to be correctly sustained. Smaller propagation

speed was measured with a helium flow in comparison with neon

even if in both cases the speed is increasing with the application of a

larger high voltage amplitude. On the other hand, no significant

effect associated with the dielectric constant value of the capillary

guide (the relative permittivity changing from about 3 for glass to

about 10 for alumina reactor) was observed. The velocity and its

evolution with the high voltage peak amplitude were measured to

be quite identical when neon gas is flushed through the alumina

and the glass reactor of the same geometry, equipped with the same

electrode pair and powered by the same electrical driver. The

highest velocity value was measured to be of 5� 108 cm � s�1 for

neon flushed glass capillary. The goal of the experimental data set

summarized in Figure 10, was to determine the main parameter

having a significant impact on the plasma generation and

propagation. No definitive conclusion on the propagation mechan-

isms was inferred for our preliminary studies but the role of the gas

flow and the capillary wall material appears less critical than the

DOI: 10.1002/ppap.200900078


nature of the gas or the applied voltage amplitude. It has only been

verified that propagation was not due to photoionization.

Experiments were carried out by inserting a dielectric film not

transparent to the UV radiation, with a counter back flow in the

second part of the dielectric tube. Propagation of the bullet was not

disturbed which let suppose that ionization wave may play an

important role in the bullet movement. Nevertheless, it must be

pointed out that the gas flow rate increase results in the generation

of a larger number of transient plasmas during the voltage

microsecond duration application and also that the increase of the

voltage amplitude is associated with a larger power density in the

DBD reactor, the energy delivered by the electrical driver being

much important as the input voltage is raised.

Spectroscopic Measurements

A preliminary time integrated spectroscopic characterization of the

plasma propagating in the dielectric guide and produced at the

guide outlet where the plume expands in ambient air is proposed in

Figure 11. The spectra are averaged over 50 shots of the plasma gun,

the spectrometer being triggered from the high voltage pulsed

driver and integration time is 10 ms. The 1 mm thick borosilicate

glass capillary wall and the spectrometer assembly allow light

detection from about 300 up to 900 nm. The plasma propagating in

the dielectric guide essentially radiates the red lines from neon-

excited levels, with main peaks at 585.2, 616.3, 640.2, 703.2 and

724.7 nm. No transitions ensuing from neither the elements

constituting the dielectric reactor and guide nor other impurities

were observed. This indicates that even for the higher power

densities, i.e. higher voltage amplitudes, and during the long-term

operation at high repetition rates up to 100 Hz in this work, no

evidence for reactor or capillary ablation could be inferred from

spectroscopic measurement. This a priori pollution-free operation

of non-thermal plasma generator may indeed be a critical issue for

the use of plasma technologies in medical applications where

attention has to be paid to the material contamination. The

spectrum measured at the outlet of the glass capillary, consists in

Figure 11. Spectra of the plasma propagating in the glass dielectricguide (grey curve) and of the plasma produced at the guide outletin ambient air (black curve). The intensity of the guide outletspectrum was multiplied by a factor of 5. The acquisition wassynchronized with the pulsed driver, the integration time was10 ms and signal was averaged over 50 shots.



the neon red transitions with about 5 times less amplitude than

that during the plasma propagation, and the second positive band

system of nitrogen at 315.9, 337.1, 357.1 and 380.4 nm. This

measurement is in agreement with the visual observation of the

plume, as documented in Figure 1 (left), which reveals a violet

colour of the plasma. The generation of the plasma plume in

ambient air occurs in a mixture of air constituents with neon and

neon plasma species at the outlet of the capillary guide. As the

distance from the outlet of the capillary increases, the plume

plasma is created essentially by ambient air excitation and energy

transfer from neon metastable levels. The decay of the neon density

downstream the guide outlet and the efficient quenching of neon-

excited states probably explain the transition from an air neon

plasma to an air plasma over the first centimetres along the plume

axis for neon flow rate of 100 cm3 �min�1. For much higher neon

flow rates of a few litres per minute, the plume length is first

increased and the plume gradually appears as an oscillating string

probably due to the neon flow turbulent mixing with air. Time and

space resolved spectroscopy experiments are planned to achieve a

more comprehensive description of the plume chemistry along its

propagation path as reported in ref.[11]

Conclusion

The experimental study of a compact pulsed DBD driven

plasma gun has been performed. The design of a

transparent small size reactor allows for the simultaneous

visible light imaging of the DBD zone, i.e. the nearby

electrode region, the propagation of the plasma in the

dielectric guide and the expansion of the plasma in ambient

air. The DBD zone plasma consists in a streamer composed

plasma and a glow-like plasma at the electrode tip. This

inner electrode tip plasma expands downstream and

generates plasma slabs, designed as plasma bullets. These

plasma bullets can propagate at very high velocity, up to

5� 108 cm � s�1 in flexible large aspect ratio dielectric

capillaries. The role of floating potential of the dielectric

guide was verified by the possibility to induce the plasma

propagation through a very thin layer along a defined path

of the guide by inserting an outer metallic strip on the

dielectric guide. Fast ICCD imaging experiment reveals the

channelled structure of the bullets which appear rather as

surface guided filamentary structures and not as homo-

geneous plasma volume. The bullet expansion in open air

undergoes the formation of a transient plasma plume

which length can be monitored by the gas flow rate. The

generation of neon plasma during propagation and of air

plasma at the plume location was also described by a

preliminary spectroscopic analysis showing evidence for

the production of nitrogen second positive system radia-

tion. This air plasma is created at distances of a few tens of

centimetres from the high voltage DBD reactor and can be

produced while no electrical connection between both


E. Robert et al.

802

plasmas exists anymore. The generation of bullet bursts, a

few plasma bullets with respective delay between two

successive events of a few tens of nanoseconds, was also

proven. The study of the propagation of these trains of

bullets indicates that all the bullets move at the same

velocity so that no critical impact of the space charge, pre-

ionization, metastable species associated with each indi-

vidual bullet is assumed on the development of the next

coming bullets during the burst. A preliminary parametric

study finally indicates that the bullet propagation velocity

is lower for helium than for neon flow, that the material

constituting the capillary wall has no severe impact on this

speed and that the higher the voltage amplitude is the faster

the propagation occurs in the vicinity of the DBD reactor.

The strong decrease of the bullet velocity downstream the

location they are ignited was also measured. While

presenting a somewhat complicated temporal structure,

the bullet and the bullet bursts were shown to be very

reproducible in intensity and only exhibit a trigger jitter of a

few nanoseconds, from shot to shot for repetition rate

ranging to a few Hz up to 100 Hz during time periods of a

few tens of minutes.

Acknowledgements: This work is supported by Region Centrethrough the APR programme ‘Plasmed’.

Received: May 29, 2009; Revised: May 29, 2009; Accepted:September 2, 2009; DOI: 10.1002/ppap.200900078



Keywords: nanosecond imaging; non-thermal plasma; plasmamedicine; pulsed discharges

[1] Special Issue, Plasma Process Polym. 2006, 3, 383.[2] G. Rotondano, M. A. Bianco, R. Marmo, R. Piscopo, L. Cipolletta,

Dig. Liver Dis. 2003, 35, 806.[3] K. R. Stalder, J. Woloszko, I. G. Brown, C. D. Smith, Appl. Phys.

Lett. 2001, 79, 4503.[4] F. Clement, E. Panousis, B. Held, J.-F. Loiseau, A. Ricard, J.-P.

Sarrette, J. Phys. D: Appl. Phys. 2008, 41, 085206.[5] E. Stoffels, A. J. Flikweert, W. W. Stoffels, G. M. W. Kroesen,

Plasma Sources Sci. Technol. 2002, 11, 383.[6] I. E. Kieft, E. P. van der Laan, E. Stoffels, New J. Phys. 2004, 6,

1149.[7] M. Laroussi, X. P. Lu, Appl. Phys. Lett. 2005, 87, 113902.[8] G. Fridman, M. Peddinghaus, H. Ayan, A. Fridman, M.

Balasubramanian, A. Gutsol, A. Brooks, G. Friedman, PlasmaChem. Plasma Process. 2006, 26, 425.

[9] G. Fridman, A. Shereshevsky, M. M. Jost, A. D. Brooks, A.Fridman, A. Gutsol, V. Vasilets, G. Friedman, Plasma Chem.Plasma Process. 2007, 27, 163.

[10] J. Shi, F. Zhong, J. Zhang, D. W. Liu, M. G. Kong, Phys. Plasmas2008, 15, 013504.

[11] N. Mericam-Bourdet, M. Laroussi, A. Begum, E. Karakas,J. Phys. D: Appl. Phys. 2009, 42, 055207.

[12] FR. WO2009050240 (2009), Centre National de la RechercheScientifique (FR) and Universite d’Orleans (FR), inventors:J. M. Pouvesle, C. Cachoncinlle, R. Viladrosa, A. Khacef, E.Robert, S. Dozias.

[13] J. Kedzierski, J. Engemann, M. Teschke, D. Korzec, Solid StatePhenom. 2005, 107, 119.

DOI: 10.1002/ppap.200900078

Experimental Study of a Compact Nanosecond Plasma Gun

Documents

Transcript of Experimental Study of a Compact Nanosecond Plasma Gun