On phenomena in ionized gases
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- LIBS technique, a useful tool for a rapid discrimination between meteorite and meteor-wrong
- Two-Dimensional Electron Density Distribution over Positive Primary Streamer Propagating in Atmospheric-Pressure Air
- 2. Experimental setup and results
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References
[1] M. Miyashita et.al. Frontier of Applied Plasma Technology Vol.5 No2 (2012) 79. [2]M. Miyashita and N. Saito. arXive: 1701.00897v1 (2017). [3]M. E. Riley. Sandia Report SAND95-0775 UC-401 (1995). [4]Alan C. F. Wu et.al. J. Appl. Phys. 101 (2007) 056105. Topic number 253
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254 XXXIII ICPIG, July 9-14, 2017, Estoril/Lisbon, Portugal
LIBS technique, a useful tool for a rapid discrimination between meteorite and meteor-wrong
G.S. Senesi P 1 P , U P. Manzari 2 P , G. Tempesta P 3 P , G. Agrosì P 3 P , A.A. Touchnt 4 , A. Ibhi 5 , O. De Pascale 1
P 1 P
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In the last years meteorite hunting and business are increasing due to the high attention given to space materials studies and discoveries. In some cases, meteorites, in particular iron meteorites, sometimes can be confused with meteor-wrongs that may consist of artifacts or terrestrial rocks or minerals. With respect to traditional techniques used to analyze geological samples, laser induced breakdown spectroscopy (LIBS) shows significant advantages, including versatility, minimal destructivity, no carbon coating, low operating costs, rapidity of analysis and sensitivity to light elements. In particular, results of LIBS analyses showed no Ni presence in analysed fragments, thus confirming the high potentiality of this technique in discriminating a meteorite from a meteor- wrong.
run-of-the-mill earth-rocks and typically show a fusion crust, i.e. a blackened, charred-looking exterior, which is the result of the meteor passage through earth atmosphere.
Meteorite business is becoming progressively important in the Saharian area. For example, nowadays Morocco is one of the main exporters of meteorites in the world. Unfortunately, a number of natural or manmade objects exist, named “meteor-wrongs”, which simulate some or all typical features of true meteorites, especially iron meteorites. Visual methods used to identify a meteorite in the field are sometimes not fully exhaustive thus the use of sophisticated analytical laboratory techniques can be required to verify the extraterrestrial origin of especially iron meteorites. These techniques are generally based on the destructive and expensive analysis of the Ni content in the sample. In this study, some whole presumed meteorite fragments collected in a dry valley located half way from two villages, Imilchil and Agoudal, in the High Atlas Mountains in Morocco, where an iron meteorite named Agoudal was discovered recently [1], were analysed quantitatively by a portable double-pulse micro-laser-induced breakdown spectroscopy (DP- µLIBS) system associated with an optical microscope to verify if they were true meteorites [2]. The morphological and chemical analyses of the fragments were also validated by SEM-EDS. No Ni presence resulted from LIBS analysis, which was confirmed by a further deeper SEM-EDS analysis and by chemical maps that showed the occurrence of
spheroidal graphite. The microstructures were consistent with P bearing iron materials. These results suggested that the fragments studied consist of possibly ancient fragments of cast iron. In conclusion, DP-µLIBS can represent a promising advanced analytical technique to obtain a fast and reliable chemical analysis able to discriminate between a true meteorite and a meteor- wrong.
Fig. 1. Meteor-wrong fragment found in Morocco. References [1] H. Chennaoui Aoudjehane, L.A.J. Garvie, C.D.K. Herd, G. Chen, M. Aboulahris, 76th Meet. Meteoritical Soc. (Edmonton, Canada), (2013) 5026. [2] G.S. Senesi, G. Tempesta, P. Manzari, G. Agrosi, Geostandards and Geoanalytical, 40 (2016) 533. 17
255 XXXIII ICPIG, July 9-14, 2017, Estoril/Lisbon, Portugal
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L. Terraz 1 , T. Silva 1 , D. Nina 1 , N. Pinhão 1 , O. Guaitella 2 and V. Guerra 1
Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, Portugal 2 LPP, Ecole Polytechnique, UPMC, Université Paris Sud-11, CNRS, Palaiseau, France Abstract: This work contributes towards a detailed kinetic model to study the plasma chemistry in CO 2 - N 2 plasmas, in order to explore the possibility of admixing nitrogen to enhance CO 2 dissociation. A particular interest is dedicated to the pumping of the asymmetric vibrational mode of CO 2 , considered as a promising way for the CO 2 dissociation at lower energy costs than by direct electronic impact. For this purpose, 0-D simulations are performed reproducing the conditions of the experiments lead in parallel at LPP. The input data of the simulations must comprise sets of reaction rates for the vibrational- translational exchanges (VT) and the vibrational-vibrational exchanges (VV) between N 2 , CO 2 and the derived products. This presentation focus on the computation and the validation of these data sets and the first results obtained from a simplified kinetic model. 1. Introduction Carbon dioxide dissociation is a way of both reducing one of the main greenhouse gases and providing a source of synthetic fuels, avoiding the carbon footprint and the restructuring problems linked to energy distribution. Non-equilibrium plasmas seem to be a very interesting medium to efficiently dissociate the CO
2 molecule, with reported energy efficiencies of about 45% under industrial conditions [1, 2]. This work explores the possibilities of admixing nitrogen to the CO 2
aim is to develop a kinetic model to study the plasma chemistry in CO 2 -N
plasmas. 2. Discussion The VT and VV reaction rates between CO 2 and N
2 molecules have been computed for the first vibrational levels, using a temperature power law which fits the results from previous experiments [3]. For the upper levels these rates have been scaled using the SSH theory [4]. In total, vibrational levels up to v≤5 for N 2 , and
v 1 ≤3, v 2 ≤6, v
3 ≤5 for the symmetric stretching, bending and asymmetric stretching modes of CO 2 , respectively, are taken into account in the model. Figure 1 shows the time evolution of the population of the CO 2 (00 0 1) level in the afterglow of a dc discharge for p=5 Torr. The gas temperature profile in the afterglow and the initial densities of CO 2 molecules in the different vibrational modes are taken from experiments in a pure CO 2 dc discharge at a current I=50 mA. The results confirm the potential of N 2
addition to enhance the vibrational pumping of the CO 2
asymmetric mode, whenever the characteristic vibrational temperature of N 2 is larger than that of the CO 2 asymmetric mode. 3. References [1] A. Fridman, Cambridge University Press (2008) 9, 54. [2] G. J. van Rooij et al., Faraday Discuss. 183 (2015) 233. [3] S. Heijkers et al., J. Phys. Chem. C (2015) 199, 12815-12828. [4] T. Kozák and A. Bogaerts, Plasma Sources Sci. Technol. 23 (2014) 045004.
Fig.1: Time evolution of the population of CO 2 (00 0 1)
level in a CO 2 -N 2 afterglow, at 5 Torr, for different N 2
Acknowledgments: This work was partially supported by the Portuguese FCT, under Projects UID/FIS/50010/2013 and PTDC/FIS-PLA/1420/ 2014 (PREMiERE). VG was partially supported by LABEX Plas@par under the project ANR-11- IDEX-0004-02. 256
XXXIII ICPIG, July 9-14, 2017, Estoril/Lisbon, Portugal
Two-Dimensional Electron Density Distribution over Positive Primary Streamer Propagating in Atmospheric-Pressure Air
Y. Inada 1 P , U R. Ono
2 P , A. Kumada 2 P , K. Hidaka 2
, M. Maeyama 1 P
P
P
P
P
Elucidating the electron density of streamer discharges propagating in atmospheric-pressure air is critical for achieving a systematic understanding of the production mechanisms of reactive species. Using Shack-Hartmann type laser wavefront sensors with a temporal resolution of 2 ns, we carried out single-shot two-dimensional electron density measurements over positive primary streamers generated in a 13-mm air gap between pin-to-plate electrodes. The electron density over the positive primary streamers decayed in a range of 10 15 cm -3 during the propagation. The decay time constant of the electron density in the primary streamer channels was estimated to be ～2 ns. The distribution widths of the electron density were in good agreement with those of the light emission, typically ranging from 0.8 to 1.5 mm.
The electron density of streamer discharges propagating in atmospheric-pressure air is crucially important for systematic understanding of the production mechanisms of reactive species utilized in wide ranging applications such as medical treatment, plasma-assisted ignition and combustion, ozone production and environmental pollutant processing. However, electron density measurement during the propagation of the atmospheric-pressure streamers is extremely difficult by using the conventional localized type measurement systems due to the irreproducibility in the discharge paths. In order to overcome the
difficulties, single-shot two-dimensional electron density measurement was conducted by using a Shack-Hartmann type laser wavefront sensor. The Shack-Hartmann sensors were applied to pulsed positive primary streamer discharges generated in an air gap.
The temporal resolution of the Shack-Hartmann sensors was 2 ns, which was equal to the exposure time of the installed two ICCD cameras. The spatial resolution was determined by the pitch of the microlens arrays, which was 300 m.
Pulsed positive streamer discharges were generated in a 13-mm gap installed in open air. The air gap was composed of a brass plate cathode and a stainless-steel pin anode, whose tip radius was 80 m.
Figure 1 shows voltage and current waveforms for the streamer discharge in atmospheric-pressure air. The voltage rise-rate was 0.83 kV/ns. Figure 2 shows that the electron densities at 5 ns after streamer initiation ranged from 5 to 7×10 15 cm -3 , while the electron density at the time of the streamer initiation was 8-9×10 15 cm -3 . In the process of streamer propagation, the electron density decreased with increasing time. On the other hand, the electron density widths distributed uniformly along the
and 5 ns after the streamer initiation. The decay time constant of the electron density in the primary streamer channels was estimated to be ～2 ns from the streamer propagation speed of 9×10 5 m/s. The half-maximum full-widths of the electron density distributions were in good agreement with those of the light emission profiles, typically ranging from 0.8 to 1.5 mm.
Figure 1. Current and voltage waveforms for air streamer discharge.
Figure 2. Two-dimensional electron density distribution at 5 ns after air streamer initiation. 10
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