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1. International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 07 Issue: 02 | Feb 2020 www.irjet.net p-ISSN: 2395-0072
© 2020, IRJET | Impact Factor value: 7.34 | ISO 9001:2008 Certified Journal | Page 2633
OpticalemissiontechniqueforunderstandingtheSparkgapDischarge
andlifetimeanalysis
CSReddy1
1AdamascienceandTechnologyUniversity, Adama,Ethiopia.
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Abstract - This paper presents the Optical Emission
Spectroscopy(OES)techniquetostudytheSparkgapdischarge
in Argon, Nitrogen and helium gasses at 0-2 kg/cm2 pressure
range. The life time is also estimated for the gas ambiance for
varyingpressureconditions.Basedonthelifetimeprofiles,the
plasmatemperatureandelectrondensityaredeterminedbythe
intensity ratio of emission lines of excited atoms. The obtained
resultsareinagreementoverawideelectrondensityrange108-
1015 cm-3.
Key Words: Spark gap, Breakdown, spectroscopy, plasma
temperature,electrondensity.
1. INTRODUCTION
One of the most conventional high peak power switching
deviceisthesparkgap.Thesparkgaphasmultipleadvantage
touseasaswitchinpulsedpowercircuitduetoitssimplicity,
wideoperatingvoltageandcurrentrange,highdv/dt.Oneof
themajordrawbackswithrepetitivepulsedpowersparkgapis
recovery of spark gap voltage. The lower pressure spark gap
recover greater than their breakdown voltage of first pulse
undercertaincondition,whichiscalled“overrecovery”[1,2].
Tounderstandthedischargepropertiesthemeasurementof
electrondensityandtemperatureisessential.
There are two major factors influences the insulation
characteristicsofgasswitch.Oneistherateofdecreaseinthe
gas temperature and the other is the vanishing of electron
followingtheextinctionofarccurrent,thevolumebetweenthe
twoelectrodesisfilledwithhotdecayingplasmainwhichthe
degreeofionizationisrapidlydecreasing.Butthemetalhotgas
remainforarelativelylongtimeandiscooledbytheheatflow
to the surrounding ambient gas and the electrodes, the
recovery characteristics are governed entirely on the gas
temperature[3].
It is essential to understand the local temperature variation
due to plasma formation during breakdown process and
influenceofvariousspeciesformedduetoconstitutionofthe
mediumontherecoveryvoltageprocesshastobeascertained.
Havingknownallthis,inthepresentstudy,anattempthasbeen
made to understand the mechanism of spark gap discharge
under the influence of different gas discharge. The emission
spectra, plasma temperature and electron density are also
investigated.
2. EXPERIMENTALSETUP
Figure 1 shows the experimental set up for the emission
spectroscopy measurements with spark gap chamber. The
supply voltage (0-230 V, AC) was stepped up using a
transformerandfedtoavoltagedoublerscircuit.Thecapacitor
was charged through the voltage doublers circuit and
dischargedthroughthesparkgapwhichwasconnectedacross
thechamber.
Animpulsegeneratorconsistsofacapacitorthatischargedto
the required voltage and discharged through a circuit. The
circuitparameterscanbeadjustedtogiveanimpulsevoltageof
the desired shapes. An equivalent circuit of an Experimental
setupisshowninFigure2,wherethecapacitorCG(10000pf)is
chargedfromaDCsourceuntilthesparkgapbreaksdown.The
voltage is then impressed upon the object using a capacitor
havingcapacitanceCL(1200pf).Thewaveshapingresistors,Rf
(416Ω)andRt (10kΩ),controlthefrontandtailoftheimpulse
voltage available across CL, respectively. Overall, the wave
shapeisdeterminedbythevaluesofthegeneratorcapacitance
(CG),theloadcapacitance(CL),andthewavecontrolresistances,
RfandRt.Ifthetailtime,Tt,issufficientlygreaterthanthefront
time,Tf,andthetotalloadcapacitance,CL,islessthan1/5ofthe
generator capacitance, CG(i.e., stage capacitance/number of
stages), then an approximation to the wave shape can be
determinedfrom
Theoutputvoltagewaveformcanbedefined
accuratelyby
3. AnalysisofOpticalEmissionSignalduringSpark
gapdischargeprocess:
TheOpticalemissionspectroscopy(OES)Techniqueisused
tostudythebehaviorofsparkgapdischargewith

2. International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 07 Issue: 02 | Feb 2020 www.irjet.net p-ISSN: 2395-0072
© 2020, IRJET | Impact Factor value: 7.34 | ISO 9001:2008 Certified Journal | Page 2634
Figure-1:ExperimentalSetup
Nitrogen, Argon and Helium gasses from zero 2 kg/cm2
pressurerange.Animpulsevoltage(doubleexponentialpulse
withafronttimeof1.2usandtailtimeof50us)isappliedtothe
sparkgapofwhichelectrodesareofrogowskyprofiletypeand
thickness of 15mm having an inter electrode gap of 10mm.
Applied voltage is measured using a CuSo4resistive divider
havingdivisionratioof1800:1.Opticalemissionduringspark
gapdischargeondifferentgassesiscollected,usingafiberlens
withafocallength150mmanditiscoupledtoaspectrometer
(Oceanoptics,USB2000)usingamultimodeopticalfiberwitha
corediameterof400um.
-50 0 50 100
0
10
20
30
40
50
Voltage(kV)
Time (us)
Figure-2:Voltagepulseappliedtothesparkgap
Anattemptwasmadetoestimatetemporaldistributionof
plasmatemperaturefromthelife-timeprofile.Fig3,4and5
showstheopticalemissionspectraofArgon,Nitrogenand
Heliumgasambienceat2kg/cm2pressure.
300 400 500 600 700 800 900
0
100
200
300
400
500
600
700
ArII
ArII
ArI
ArI
ArII
Ar 2 Kg/cm
2
Wavelength(nm)
Intensity(arbs)
Figure-3:Opticalemissionspectraobtainedduringthespark
gapdischargeintheArgonambienceat2kg/cm2
300 400 500 600 700 800 900
0
100
200
300
400
500
NII
NII
NII
Intensity(arbs)
Wavelength(nm)
N 2 Kg/cm2
NI
Figure-4:Opticalemissionspectraobtainedduringthespark
gapdischargeintheNitrogenambienceat2kg/cm2.

3. International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 07 Issue: 02 | Feb 2020 www.irjet.net p-ISSN: 2395-0072
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300 400 500 600 700 800 900
0
100
200
300
400
500
600
700
HeI
HeII
HeI
Intensity(arbs)
Wavelength(nm)
He 2 Kg/cm2
Figure-5:Opticalemissionspectraobtainedduringthespark
gapdischargeintheHeliumambienceat2kg/cm2.
4. LifetimeResults:
Life-timeprofileofaparticularemissionwavelength,givesthe
instantaneousvaluesofintensityandfromwhichtemperature
can be estimated based on Boltzmann’s distribution. Two
atomicemissionlineintensitiesofArIIat434.8and487.9nm
were sampled at different instants and estimate the plasma
temperature.Similarlytheprocedurecontinuedfornitrogen
and Helium gas line intensities to find the respective plasma
temperature. The atomic emission lines and spectroscopic
parameters used in estimating plasma temperature are
summarizedinTable1.
Line Waveleng
th (nm)
Upper energy
level Ek (c/m)
Configuration gk*Ak
(1/s)
N II 500.5 186652.49 2s22p(2P0)3p-2s22p(2P0)3d 1.03e9
N II 567.9 166678.64 2s22p(2P0)3s-2s22p(2P0)3p 3.47e8
N I 746.8 96750.840 2s22p2(3p)3s-2s22p2(3d)3p 7.84e7
Ar II 434.8 157234.0196 3s23p4(3p)4s-3s23p4(3p)4p 9.36e8
Ar II 487.9 158730.2995 3s23p4(3p)4s-3s23p4(3p)4p 4.94e8
ArI 696.5 107496.4166 3p5(2p0 )4s-3p5(2p0 )4p
3/2 1/2
1.92e7
Ar I 763.5 106237.5518 3p5(2p0 )4s-3p5(2p0 )4p
3/2 3/2
1.22e8
He I 587.6 186101.592 1s2p-1s3d 8.83e7
He II 656.1 426717.460 6.27e6
He I 667.8 186104.966 1s2p-1s-3d 3.18e8
Table1.SpectroscopicparametersofNitrogen,ArgonandHeliumusedfor
plasmatemperature
The life time was estimated at 1/e of the maximum emission
intensity. The figures 6, 7, and 8 show the lifetime profiles of
Nitrogen,HeliumandArgonrespectively. Thesefiguresshow
clearlytheeffectofpressureontheemissionlifetime.
0 10 20 30
0.00
0.02
0.04
0.06
0.08
Intensity(arbs)
N II 567.9 life time (us)
1 kg/cm
2
1.5 kg/cm
2
2 kg/cm
2
Figure-6:Life-timeprofileofNitrogenlines1kg/cm2at
NII567.9
0 10 20 30 40 50 60
0.00
0.01
0.02
0.03
0.04
Intensity(arbs)
He II 656.1 life time (us)
0.5 kg/cm
2
1 kg/cm
2
1.5 kg/cm
2
2 kg/cm
2
Figure-7:Life-timeprofileofHeliumlines0.5-2kg/cm2 atHe
II656.1
0 10 20 30 40
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
Intensity(arbs)
Ar II 487.9 life time (us)
0.5kg/cm
2
1kg/cm
2
1.5kg/cm
2
2kg/cm
2
Figure-9:Life-timeprofileofArgonlines0.5-2kg/cm2 at(d)
Ar IIat487.9

4. International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 07 Issue: 02 | Feb 2020 www.irjet.net p-ISSN: 2395-0072
© 2020, IRJET | Impact Factor value: 7.34 | ISO 9001:2008 Certified Journal | Page 2636
5.ELECTRONDENSITY
Electron density can be determined using modified Saha
equation [4] which involves ion-atom line intensity ratio.
Based on the experimentally observed emission spectra,
electrondensity,ne.
WhereEiandEaaretheenergiesoftheupperstates,EionistheIst
ionizationpotential.
TheEstimationofelectrondensityconsideringlocalthermal
equilibrium in Argon [5] ambient gas at 2 kg/cm2 pressure
valueisshowninfigure10andEstimationofelectrondensity
considering local thermal equilibrium indifferent ambient
gaseswithvariouspressurevaluesisshowninfigure11.
0 0.5 1 1.5 2 2.5 3 3.5
x 10
-5
-2
0
2
4
6
8
10
12
x 10
15
Time.
Electrondensity(cm-
3)
Figure-10:Estimationofelectrondensityconsideringlocal
thermalequilibriuminArgonambientgasat2kg/cm2
pressurevalue.
6. CONCLUSION
Optical emission spectroscopy is used to understand the
dischargeproperties.Argon,nitrogenandheliumgasseswere
usedasdielectricmediumat0-2kg/cm2.Itwasobservedthat
theelectrontemperaturewashighintheArgoncomparedwith
Nitrogenenvironment.Theaverageelectrondensityoverthe
emissiontimewasrangingfrom109 to1015 cm-3.Theplasma
temperature and density estimated from time integrated
spectra were an average value not giving any temporal
distributiondetails.
0.0 0.5 1.0 1.5 2.0
6.566E7
4.85165E8
3.58491E9
2.64891E10
1.9573E11
1.44626E12
1.06865E13
7.8963E13
5.83462E14
Electrondensity(cm^-3)
Pressure (kg/cm^2)
Nitrogen
Argon
Helium
Figure-14:Estimationofelectrondensityconsideringlocal
thermalequilibriumindifferentambientgaseswithvarious
pressurevalues.
REFERENCES
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[2] C.S.Reddy, et. al,“Voltage Recovery Characteristics of
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[3] C.S.Reddy,et.al.,,“RecoveryAnalysisofSparkgapbyAnode
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