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LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES

3rd International Workshop on RHTG,10/2/2008 , Heraklion, Crete, Greece

Definition of a new level one test case measurements of equilibrium radiation from an inductively coupled

plasma in the near-UV to near-IR spectral region for a Titan-type N2-CH4 mixture

D. Vacher, P. André, G. FaureLAEPT, Clermont University, Clermont-Ferrand, France

M. DudeckInstitut Jean Le Rond d’Alembert, University of Paris 6 , France

M. Lino da SilvaCentro de Física dos Plasmas, Instituto Superior Técnico, Lisboa, Portugal

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LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES

3rd International Workshop on RHTG,10/2/2008 , Heraklion, Crete, Greece

Contents

1. Description of the experimental set-up

2. Discussion on the problems encountered concerning the behaviour of plasma

3. Spectroscopic acquisitions in the [300-850]nm region

4. Intensity radial evolution of the C2 swan and CN violet systems

5. Estimations of temperature(s)

6. Observation of carbon formation inside the torch

7. Conclusion

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LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES

3rd International Workshop on RHTG,10/2/2008 , Heraklion, Crete, Greece

Experimental set-up

HF generator64 MHz

DEFI Systèmes

ST 138controller

CCD

Plasma gasN2 – CH4

(98%-2%)

Main characteristics

Inductively coupled plasma type : ICP-T64 Frequency : 64 MHz Tuning : Automatic adaptation Inductor : Seven-turn air-cooled coil Operating pressure : Atmospheric pressure Torch : 28 mm internal diameter quartz tube Optical set-up Spatial resolution : 0.5 mm Quartz optical fibre Spectrometer :Chromex 500 IS,

500 mm focal length, Czerny-turner mounting Entrance slit : e = 100 m Gratings : 600/1200/1800 grooves.mm-1

Detector : CCD EEV 1152 1242 pixels

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LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES

3rd International Workshop on RHTG,10/2/2008 , Heraklion, Crete, Greece

Electrical characteristics of the ICP torch

0

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0 5 10 15 20 25

-200

-100

0

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800

Time (min)

Applied power(kW)

Voltage(kV) C

urre

nt (

mA

)

applied power

grid current

applied voltage

applied current

Injection of 2% of CH4

P 1kWEncountered problem :(the ignition of plasma is realized with pure N2)

- Loss of power injected when CH4 is added- Instability of the plasma- Random extinction of the plasma

Resolution of the problem :To start the plasma directly with the N2-CH4 mixture

U = 4.09 kVIa = 724 mAIg = -017 mA

CH4 flow is cut :U = 4.57 kV

Ia = 460 mA

Ig = -042 mA

P = 2.1 kW P = 2.96 kW(a filter is placed in front of the video camera)

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LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES

3rd International Workshop on RHTG,10/2/2008 , Heraklion, Crete, Greece

Why the injection of 2% of CH4 into a pure nitrogen plasma cuts it ?

- Is it an electronic problem with the automatic adaptation of impedance ?

- Can the physical parameters explain this problem ?

Electrical conductivityViscosityThermal conductivity

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LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES

3rd International Workshop on RHTG,10/2/2008 , Heraklion, Crete, Greece

10-6

10-4

10-2

100

102

3000 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 8500 9000 9500 10000

TitanN

2

Temperature (K)

Ele

ctric

al c

ond

uctiv

ity (

S/m

)

Electrical conductivity versus temperature for 4 mixtures of plasmasElectrical conductivity

Ele

ctri

cal c

ondu

ctiv

ity

(S/m

)

Temperature (K)

Electrical neutrality :N2 e- N+

Titan e- C+ for T<6000K e- N+ for T>6000K

The electrical conductivity may be a influent parameter in order to explain the encountered problemwith the plasma of Titan atmosphere (extinction of the plasma)

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LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES

3rd International Workshop on RHTG,10/2/2008 , Heraklion, Crete, Greece

Viscosity

Temperature (K)

Vis

cosi

ty (

Pa.

s)

The viscosity is not a influent parameter in order to explain the encountered problemwith the plasma of Titan atmosphere (extinction of the plasma)

0.00006

0.00008

0.00010

0.00012

0.00014

0.00016

0.00018

0.00020

0.00022

3000 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 8500 9000 9500 10000

TitanN

2

Temperature (K)

Vis

cosi

ty (

Pa

.s)

Viscosity versus temperature for 4 mixtures of plasmas

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LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES

3rd International Workshop on RHTG,10/2/2008 , Heraklion, Crete, Greece

Thermal conductivity

Temperature (K)

The

rmal

con

duct

ivit

y (W

/m.K

)

Possible effect ?

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4.0

3000 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 8500 9000 9500 10000

TitanN

2

Temperature (K)

Th

erm

al c

on

du

ctiv

ity (

W/m

.K)

Thermal conductivity versus temperature for 4 mixtures of plasmas

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LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES

3rd International Workshop on RHTG,10/2/2008 , Heraklion, Crete, Greece

Comparison of spectra between pure N2 and N2-CH4 plasma

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0.5x105

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330 340 350 360 370 380 390 400 410 420 430

N2 - CH4N2

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1.00000x105

1.20000x105

1.40000x105

1.60000x105

1.80000x105

2.00000x105

880 890 900 910 920 930 940 950 960 970

0

0.3x105

0.6x105

0.9x105

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1.5x105

700 710 720 730 740 750 760 770 780 790

0

0.200000x105

0.400000x105

0.600000x105

0.800000x105

1.000000x105

1.200000x105

1.400000x105

1.600000x105

790 800 810 820 830 840 850 860 870 880

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LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES

3rd International Workshop on RHTG,10/2/2008 , Heraklion, Crete, Greece

Spectrum of a N2(98%)-CH4(2%) plasma : last series of measurements

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320 340 360 380 400 420 440 460 480 500 520 540 560 580 600 620 640 660 680 700 720 740 760 780 800 820 840

CN

C2 Molecular structure

Wavelength (nm)

Inte

nsit

y (a

.u.)

580 600

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LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES

3rd International Workshop on RHTG,10/2/2008 , Heraklion, Crete, Greece

Radial evolution of CN for the N2-CH4 plasma

Radial evolution of C2 for the N2-CH4 plasma

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-7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7

3021

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-7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7

453210

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405 410 415 420 425

012345

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1.25x105

375 380 385 390

0123

x (nm) x (nm)

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1.5x105

2.0x105

-7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7

x (nm)0

0.4x105

0.8x105

1.2x105

1.6x105

2.0x105

490 500 510 520

The optical acquisitions aremade between the 4th

and the 5th coil

0

3000

6000

9000

12000

370 390

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LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES

3rd International Workshop on RHTG,10/2/2008 , Heraklion, Crete, Greece

Radial profiles for C2 and CN after abel inversion

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CN

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C2

Inte

nsit

y (a

.u.)

Radial position (nm) Radial position (nm)

- No problem appear with the application of the Abel inversion with the CN specie

- Difficulty to apply the Abel inversion with the C2 specie. The value on the plasma axis is strongly dependant from the shape of the fit near the 0.

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LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES

3rd International Workshop on RHTG,10/2/2008 , Heraklion, Crete, Greece

First results in the estimation of temperature from C2 spectra (G. Faure - LAEPT)

Spectrum issued from the plasma axis

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510 511 512 513 514 515 516 517

Nor

mal

ized

inte

nsit

y

Wavelength (nm)

Measured spectrum

Simulated spectrumTROT=TVIB=4500K

Simulated spectrumTROT=4500K ; TVIB=5000K

Simulated spectrumTROT=TVIB=5500K

Apparatusfunction:0.14 nm

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LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES

3rd International Workshop on RHTG,10/2/2008 , Heraklion, Crete, Greece

0

0.5

1.0

1.5

2.0

370 372 374 376 378 380 382 384 386 388 390 392

First results in the estimation of temperature from CN spectra (G. Faure - LAEPT)

- Big disagreement Theory – experiment (self-absorption not taken into account for instant)- Strange behavior of the first band head (0-0)- Broadening phenomena of the spectral lines (not the case for the C2 lines)

- Spectral resolution must be increased

Nor

mal

ized

inte

nsit

y

Wavelength (nm)

Measured spectrum

Simulated spectrumTROT=TVIB=4500K

Simulated spectrumTROT=TVIB=6500K

Simulated spectrumTROT=TVIB=5500K

Apparatusfunction:0.14 nm

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LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES

3rd International Workshop on RHTG,10/2/2008 , Heraklion, Crete, Greece

First results in the estimation of temperature from the C2 spectra (M. Lino Da Silva-IST)

TR = 3200 KTV = 3700 K

Best agreement obtained for :

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LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES

3rd International Workshop on RHTG,10/2/2008 , Heraklion, Crete, Greece

First results in the estimation of temperature from the CN molecule (M. Lino Da Silva-IST)

Method for spectral calculations with self-absorption

1) Application of the Abel inversion

2) Estimation of Tv and Tr, followed by the calculation of emission and absorption α coefficients utilizing the line-by-line code SPARTAN

3) Calculation of the slab emitted intensity using the relationship:

I=/ α×(1-exp(α×l)

4) Convolution with a Gaussian apparatus function simulating the slit

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25000

30000

376 378 380 382 384 386 388 390

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LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES

3rd International Workshop on RHTG,10/2/2008 , Heraklion, Crete, Greece

First results in the estimation of temperature from the CN molecule (M. Lino Da Silva)

TR = 3200 KTV = 3700 K

Best agreement obtained for : Evaluation of the thermal disequilibrium :1.1 < < 1.2

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LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES

3rd International Workshop on RHTG,10/2/2008 , Heraklion, Crete, Greece

Characteristic of the plasma of Titan

Observations about the formation of "carbon " inside the ICP torch

Base of thequartz tube

Top of thequartz tube

injector

Swirl injectionof plasma gas

Carbon hair !

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LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES

3rd International Workshop on RHTG,10/2/2008 , Heraklion, Crete, Greece

Analysis of the deposited dust on the quartz tube

- Images issued from SEM (Scanning Electron Microscopy) with field effect [CASIMIR]

- The X-ray analysis didn’t work because of the lack of sample

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LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES

3rd International Workshop on RHTG,10/2/2008 , Heraklion, Crete, Greece

Analysis of the deposited dust on the quartz tube

particles with a diameter around35 nm can be observed

Similar images have been found in the thesis titled "Carbon nanoparticles synthesis by gas phase non-equilibrium plasma " [M. Moreno, 2006]

Type of the carbon compounds nano-structured : " ruffled paper "

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LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES

3rd International Workshop on RHTG,10/2/2008 , Heraklion, Crete, Greece

Plasma composition

10-6

10-4

10-2

100

1500 2000 2500 3000 3500 4000 4500 5000 5500 6000

CN

e- NO+

C

NO2

N

NO

OO2

CO

N2

CO2

Temperature (K)

Mo

lar

fra

ctio

n

Plasma formed with a Mars atmosphere

10-6

10-4

10-2

100

1500 2000 2500 3000 3500 4000 4500 5000 5500 6000

C+

e-

NCNNH

CH

C2

C2N

C2H

C2H

2

H

CHN

Ar

C(S)

H2

H

N2

Temperature (K)

Mo

lar

fra

ctio

n

Plasma formed with a Titan atmosphere

Mars atmosphere

Titan atmosphere

Mol

ar f

ract

ion

No solid carbon appears in the plasma formed with theMars atmosphere (presence of O2) whereas it is presentin the one formed with the Titan atmosphere (2700 K)

Temperature (K)

Temperature (K)(2700 K)

CCN

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LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES

3rd International Workshop on RHTG,10/2/2008 , Heraklion, Crete, Greece

Continuation of this study

- To understand why the plasma is instable when 2% of CH4 is added to a pure N2 plasma

- To acquire the spectral domain [200 – 300]nm in order to verify if carbon lines are present

- To determine axial temperature all along the inductor and above

- To realize kinetic calculation to confirm that chemical equilibrium is reached inside the inductor(as it has be done for the CO2-N2 plasma)

- To add argon (1%) in order to estimate the atomic excitation temperature

- An additional diagnostic will be soon added to the experimental set-up : LIF, Laser Interferometry