Self-deformation in a dc driven helium jet micro discharge

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by  Shaofeng Xu

Self-deformation in a dc driven helium jet micro discharge
S. F. Xu1 and X. X. Zhong1,a)
State Key Laboratory of Advanced Optical Communication Systems and Networks,
Key Laboratory for Laser Plasmas (Ministry of Education) and Department of Physics and Astronomy,
Shanghai Jiao Tong University, Shanghai 200240, China
(Dated: 5 January 2016)
We report on the experimental observation of three dimensional self-deformation in an atmospheric micro
dischargeoftheheliummicrojetthroughatubeintotheambientairuponawaterelectrode. Thegeometryof
6 the dischargesystemis axialsymmetric. While decreasingthe dischargecurrent,threedimensionalcollective
1 motion of plasma filaments are directly observed. The three dimensional configuration of the discharge self
0 changed from an axial symmetrical horn to a rectangular horn when the water acts as a cathode.
2
n PACS numbers: 52.80.Tn, 52.38.Hb, 52.35.Mw
a
J
1 Nonlinear selfformationprocessis one of the greatin-
terestsubjectsinmodernnaturalsciences. Self-focusing,

] self-similar structures, and self-organized patterns have
h
beenobservedandstudiedinnonlinearopticalsystems1,
p
strained systems2, nonlinear dissipative systems3. Non-
-
m linearspatiotemporalself-organizedpatternsoftencanbe
observed in gas discharge system such as dielectric bar-
s
a rierdischargeordc-drivenplanargasdischargesystem4,5.
pl Among them are spirals6, concentric-ring7, hexagonal
. superlattice8 and filaments9. However, all kinds of them
s
c aretwo-dimensionalpatterns. Thatis to say,the nonlin-
i ear process is located on two dimensional plane.
s
y The plasma filaments are important to the overalldy-
h namics in a variety of plasmas both in space and in fu-
p sion laboratory experiments and are recognized as the FIG.1. Sampleoftheconcentric-ringpatternobservedinthe
[ helium micro discharge when water acts as an anode. The
elements to construct above mentioned complex pat-
gap distance is about 3 mm, the helium gas flux is about 10
1 terns. The interactionand collective motion of filaments
sccm and thedischarge current is about 20 mA.
v on two dimensional plane have been reported in many
4 papers10–12. In fact, the collective motion of filaments is
7
the three dimensional effect of the discharge system.
0
0 Here a direct current driven atmospheric gas micro
0 discharge system is studied in the present work, which
1. is a three dimensional reaction-diffusionconvective axial
0 symmetricplasmasystem. Thistype ofmicrodischarges
6 has been used in engineering of nanoparticles13–15. A
1 concentric-ring pattern can be easily observed in this
:
v strongly nonlinear system when the water acts as an an-
i ode shown by Fig. 1. This pattern is still confined on
X
the two dimensional discharge-waterinterface. However,
r when the water acts as cathode, instabilities of the mi-
a
cro discharge is charged by the plasmas filaments under
weaker discharge current.
Inthisletterwereportontheexperimentalobservation
ofathreedimensionalself-deformationinaheliummicro
dischargesystemshownbyFig.2. Thethreedimensional
FIG. 2. Sample of rectangular horn observed in the micro
configurationof the dischargeself changedfrom anaxial discharge when water acts as a cathode. The gap distance is
symmetrical horn to a rectangular horn. about 1 mm, the helium gas flux is about 10 sccm and the
discharge current is about 6.5 mA.
The experimental system under consideration is
a)Electronicmail: [email protected] schematicallyshowninFig.3. Theheliumgasthrougha
2
stainless-steelcapillaryjetsintotheambientairatatmo- rectangularhorn has two symmetry planes of symmetry,
spheric pressure. The capillary acts as an electrode and whicharemuchlessthaninfinite symmetryplanesofthe
its internaldiameter is d=175µm. The other electrode axial symmetrical horn. A suitable comparison with the
is water in a quartz dish. The water is connected to the system when the water acts as an anode was shown by
power supply by a platinum electrode. The diameter of Fig. 5, where the micro discharges are in the homoge-
quartzdishis about60mm andvolume isabout25mL. neous mode.
The resistanceofwateris about1430Ω. The helium gas
fluxcontrolledbyamassfluxcontroller(MFC)isfixedto
f =10sccm. Theheliumgasvelocityv = 4f attheexit
πd2
is about 6.93 m/s and the Reynolds number Re = vρd
µ
is about 10.62, where ρ is the density of the helium gas
andµistheviscositycoefficientoftheheliumgas16. The
initial gapdistance between the exit of the capillary and
thewatersurfaceisabout1mmadjustedbya3Dmobile (a) 14 mA (b) 10 mA
platform. Adc constant-currentpowersupply drivesthe
micro discharge, which actually is helium and air mix-
ture discharge due to convective diffusion. A slanting
view CCD (Manta G201C) is installed to acquire micro
discharge image.
gas
(c) 7 mA (d) 6 mA
FIG. 4. Self-deformation process observed in the micro dis-
charge when the water acts as a cathode. The gap distance
between the exit and water surface is about 1 mm. The he-
U lium gas flux is about 10 sccm. (a) the discharge current is
14mA. (b)thedischargecurrentis10mA. (c)thedischarge
current is 7 mA. (d) thedischarge current is 6 mA.
FIG.3. Schematicrepresentationofthedischarge. Theinner
diameter of capillary is 175 µm. The helium gas flux is 10
sccm. A CCD camera is set in slanting view.
A self-deformation process in the micro discharge is
clearly shown in Fig. 4. At a larger discharge current, a
stable micro glow discharge was observed when the wa- (a) 14 mA (b) 10 mA
ter acts as cathode shown by Fig 4 (a). The three di-
mensional structure of this micro discharge luminance is
similar to that of a typical dc glow discharge. The dis-
charge looks like a three dimensional axial symmetrical
horn and is in the homogeneous mode. While decreas-
ing the dischargecurrent,for example to 10 mA, plasma
filaments emerged around the previous axial symmetri-
(c) 7 mA (d) 6 mA
cal horn shown in Fig. 4 (b). Micro plasma filaments
were not static but rotated around the inner glow dis-
FIG. 5. Images of the micro discharge when the water acts
charge, which showed the prominent instability of the as an anode. The gap distance between the exit and water
microplasma. Eventhoughthe dischargetransitedfrom surfaceisabout1mm. Theheliumgasfluxisabout10sccm.
the homogeneous mode to the mixture mode of homo- (a)thedischargecurrentis14mA. (b)thedischargecurrent
geneous and filamentary modes, the micro discharge lu- is10mA. (c)thedischargecurrentis7mA. (d)thedischarge
minance wasstillaxialsymmetricaljustexpandedinthe current is 6 mA.
radialdirection. Butdecreasingthedischargecurrentbe-
low 7 mA shown in Fig 4 (c) and (d), the axial symmet-
rical structure is destroyed, the three dimensional lumi- The mechanisms of self-deformation require further
nance configurationofthe microdischargechangedfrom studies. As known, magnetic field has an effect on
an axial symmetrical horn to a rectangular horn. The the motion of plasma filaments17. Besides instabilities
3
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discharge-liquid interactions also should be considered, (2012).
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self-deformation of a dc driven micro gas jet discharge 036211(2012).
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as a cathode. The explanation of the self-deformation 12L. Dong, C. Zhang, B. Li, X. Zhang, Y. He,
and X. Li, Physics of Plasmas 20, 123503 (2013),
mechanism is an aim of a future research.
http://dx.doi.org/10.1063/1.4838196.
13D.MariottiandR.M.Sankaran, JournalofPhysics D:Applied
Physics43,323001(2010).
ACKNOWLEDGMENTS 14X. Z. Huang, X. X. Zhong, Y. Lu, Y. S. Li, A. E. Rider, S. A.
Furman, andK.Ostrikov,Nanotechnology 24,095604(2013).
15K. Ostrikov, E. C. Neyts, and M. Meyyap-
XXZ and SFX acknowledge support from the NSFC pan, Advances in Physics 62, 113–224 (2013),
(Grant No. 11275127, 90923005), STCSM (Grant No. http://dx.doi.org/10.1080/00018732.2013.808047.
09ZR1414600). 16S.F.XuandX.X.Zhong,AppliedPhysicsLetters103,024101
(2013), http://dx.doi.org/10.1063/1.4813268.
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