LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES 3 rd 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 N 2 -CH 4 mixture D. Vacher, P. André, G. Faure LAEPT, Clermont University, Clermont-Ferrand, France M. Dudeck Institut Jean Le Rond d’Alembert, University of Paris 6, France M. Lino da Silva Centro de Física dos Plasmas, Instituto Superior Técnico, Lisboa, Portugal

LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES 3 rd 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 [ ]nm region 4. Intensity radial evolution of the C 2 swan and CN violet systems 5. Estimations of temperature(s) 6. Observation of carbon formation inside the torch 7. Conclusion

LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES 3 rd International Workshop on RHTG,10/2/2008, Heraklion, Crete, Greece Experimental set-up HF generator 64 MHz DEFI Systèmes ST 138 controller CCD Plasma gas N 2 – CH 4 (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

LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES 3 rd International Workshop on RHTG,10/2/2008, Heraklion, Crete, Greece Electrical characteristics of the ICP torch Time (min) Applied power (kW) Voltage (kV) Current (mA) applied power grid current applied voltage applied current Injection of 2% of CH 4  P  1kW Encountered problem : (the ignition of plasma is realized with pure N 2 ) - Loss of power injected when CH 4 is added - Instability of the plasma - Random extinction of the plasma Resolution of the problem : To start the plasma directly with the N 2 -CH 4 mixture U = 4.09 kV I a = 724 mA I g = -017 mA CH 4 flow is cut : U = 4.57 kV I a = 460 mA I g = -042 mA P = 2.1 kWP = 2.96 kW (a filter is placed in front of the video camera)

LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES 3 rd International Workshop on RHTG,10/2/2008, Heraklion, Crete, Greece Why the injection of 2% of CH 4 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 conductivity Viscosity Thermal conductivity

LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES 3 rd International Workshop on RHTG,10/2/2008, Heraklion, Crete, Greece Electrical conductivity Electrical conductivity (S/m) Temperature (K) Electrical neutrality : N 2  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 problem with the plasma of Titan atmosphere (extinction of the plasma)

LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES 3 rd International Workshop on RHTG,10/2/2008, Heraklion, Crete, Greece Viscosity Temperature (K) Viscosity (Pa.s) The viscosity is not a influent parameter in order to explain the encountered problem with the plasma of Titan atmosphere (extinction of the plasma)

LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES 3 rd International Workshop on RHTG,10/2/2008, Heraklion, Crete, Greece Thermal conductivity Temperature (K) Thermal conductivity (W/m.K) Possible effect ?

LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES 3 rd International Workshop on RHTG,10/2/2008, Heraklion, Crete, Greece Comparison of spectra between pure N 2 and N 2 -CH 4 plasma

LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES 3 rd International Workshop on RHTG,10/2/2008, Heraklion, Crete, Greece Spectrum of a N 2 (98%)-CH 4 (2%) plasma : last series of measurements CN C2C2 Molecular structure Wavelength (nm) Intensity (a.u.)

LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES 3 rd International Workshop on RHTG,10/2/2008, Heraklion, Crete, Greece Radial evolution of CN for the N 2 -CH 4 plasma Radial evolution of C 2 for the N 2 -CH 4 plasma x (nm) The optical acquisitions are made between the 4 th and the 5 th coil

LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES 3 rd International Workshop on RHTG,10/2/2008, Heraklion, Crete, Greece Radial profiles for C 2 and CN after abel inversion CNC2C2 Intensity (a.u.) 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 C 2 specie. The value on the plasma axis is strongly dependant from the shape of the fit near the 0.

LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES 3 rd International Workshop on RHTG,10/2/2008, Heraklion, Crete, Greece First results in the estimation of temperature from C 2 spectra (G. Faure - LAEPT) Spectrum issued from the plasma axis Normalized intensity Wavelength (nm) Measured spectrum Simulated spectrum T ROT =T VIB =4500K Simulated spectrum T ROT =4500K ; T VIB =5000K Simulated spectrum T ROT =T VIB =5500K Apparatus function: 0.14 nm

LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES 3 rd International Workshop on RHTG,10/2/2008, Heraklion, Crete, Greece 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 C 2 lines) - Spectral resolution must be increased Normalized intensity Wavelength (nm) Measured spectrum Simulated spectrum T ROT =T VIB =4500K Simulated spectrum T ROT =T VIB =6500K Simulated spectrum T ROT =T VIB =5500K Apparatus function: 0.14 nm

LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES 3 rd International Workshop on RHTG,10/2/2008, Heraklion, Crete, Greece First results in the estimation of temperature from the C 2 spectra (M. Lino Da Silva-IST) T R = 3200 K T V = 3700 K Best agreement obtained for :

LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES 3 rd 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 T v and T r, 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

LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES 3 rd 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) T R = 3200 K T V = 3700 K Best agreement obtained for : Evaluation of the thermal disequilibrium  : 1.1 <  < 1.2

LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES 3 rd 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 the quartz tube Top of the quartz tube injector Swirl injection of plasma gas Carbon hair !

LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES 3 rd 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

LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES 3 rd International Workshop on RHTG,10/2/2008, Heraklion, Crete, Greece Analysis of the deposited dust on the quartz tube particles with a diameter around 35 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 "

LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES 3 rd International Workshop on RHTG,10/2/2008, Heraklion, Crete, Greece Plasma composition Mars atmosphere Titan atmosphere Molar fraction No solid carbon appears in the plasma formed with the Mars atmosphere (presence of O 2 ) whereas it is present in the one formed with the Titan atmosphere (2700 K) Temperature (K) (2700 K) C CN

LABORATOIRE ARC ELECTRIQUE ET PLASMAS THERMIQUES 3 rd International Workshop on RHTG,10/2/2008, Heraklion, Crete, Greece Continuation of this study - To understand why the plasma is instable when 2% of CH 4 is added to a pure N 2 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 CO 2 -N 2 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