PLAS@PAR Young Researcher's day 2017

Meeting of young researchers in plasma physics

May 18, 2017

Paris-Sorbonne University - Lecture hall Quinet - 46 rue St Jacques, 75005 Paris





9h - Welcome coffee

1st session: Turbulence, instabilities and energy transport
Chair: B. Khiar (LERMA)

- 9h30 - Review n°1 / F. Sahraoui (LPP) - Space plasmas

- 9h50 - A. Grassi (LULI) - Weibel-mediated collisionless shock

- 10h10 - C. Louis (LESIA) - Io-Jupiter decametric arcs observed by Juno/Waves compared to ExPRES simulations

- 10h30 - L. Nicolas (LPP/LERMA) - Collisions in the streaming instability

10h50 - Coffee break

2nd session: Shocks & Magnetic reconnection
Chair: N. Andres (LPP)

- 11h15 - A. Alexandrova (LPP) - Magnetic reconnection in the Earth's magnetotail: some aspects of evolution and dynamics

- 11h35 - R. L. Singh (LERMA/LPP) - Strong radiative shocks relevant for stellar environments

- 11h55 - M. Drouin (PLAS@PAR) - PHARE project: a 3D and AMR hybrid PIC code devoted to space and laboratory plasmas

12h15 - Lunch and poster session

3rd session: Matter under extreme conditions
Chair: A. Sgattoni (LULI)

- 13h30 - Review n°2 / J. Fuchs (LULI) - Matter under extreme conditions

- 13h50 - M. Khalal (LCPMR) - 4D inner shell ionization of Xe+ ions and subsequent Auger decay

- 14h10 - M. De Anda Villa (INSP) - Ultrafast structural dynamics of metallic targets induced by IR femtosecond laser

4th session: Plasmas in molecular gases
Chair: R. Lucken (LPP)

- 14h30 - Review n°3 / P. Chabert (LPP) - Cold plasmas

- 14h50 - A. S. Morillo-Candas (LPP) - O atom kinetics in CO2 glow discharges

- 15h05 - J.-B. Layly (ONERA/LPP) - Micro-discharges in confined media: fundamental processes and application to lightning interaction with matter

15h20 - Coffee break

- 15h40 - A. Chatterjee (LPP) - Roles of Metastable states of O2 in oxygen plasma and diagnostics

- 16h00 - S. Zhang (LPP) - Character of a pin liquid anode DC discharge in open air

- 16h20 - A. Puglisi (LCPMR) - Ab-initio spectroscopic study of silicon hydride molecular ions

- 16h40 - B. Honnorat (LPP) - Therapeutic effect of cold atmospheric plasma on oral cavity squamous cell carcinomas

- 17h00 - V. Croes (LPP) - 2D simulation of Hall effect thrusters

17h30 - End of day



Weibel-mediated collisionless shock
Anna Grassi, LULI
Weibel-mediated collisionless shock: from astrophysics to the laboratory. 
The Weibel instability of countestreaming ion currents is a basic process highly relevant for colli- sionless shock formation in astrophysics. In this Letter we investigate, via two- and three-dimensional simulations, suitable configurations for laboratory investigations of the ion Weibel instability (IWI) driving a ion current in a plasma via the radiation pressure of a ultra-high intensity laser pulse (”hole boring” process). The use of S-polarized light at oblique incidence is found to be an efficient configuration for IWI, avoiding the development of surface rippling observed at normal incidence which leads to strong electron heating favoring competing instabilities. Conditions for the evolution of IWI into a collisionless shock are also investigated.


Io-Jupiter decametric arcs observed by Juno/Waves compared to ExPRES simulations
Corentin Louis, LESIA
We compare observations from the Juno/Waves radio experiment with simulations of radio «arcs» in the time-frequency plane resulting from the Io-Jupiter interaction, performed with the ExPRES code. We identify the hemisphere of origin of the observed arcs directly from simulations and confirm this identification through comparison with Juno, Nançay, and Wind observations. The occurrence and shape of observed arcs are well modeled, at low latitudes with their usual shapes as seen from Earth, as well as at high latitudes with longer, bowl-shaped, arcs observed for the first time. Predicted emission is actually observed only when the radio beaming angle θ = (k,B) ≥ 70° ± 5°, providing new constraints on the generation of the decameter emission by the Cyclotron Maser Instability. Further improvements of ExPRES are outlined, which will then be applied to Juno and Earth-based observations of radio emissions induced by other Galilean satellites or associated to the main auroral oval.


Collisions in the streaming instability
Loïc Nicolas, LPP/LERMA
Magnetic streaming instability is a common process in many physical situations such as in diverse shock or streaming cosmic rays into the interstellar medium. It happens when a plasma beam goes trough a denser plasma along a magnetic field. This drives electromagnetic waves unstable and transfers part of the beam kinetic energy into magnetic an thermal energy for both plasmas trough wave-particle interactions. Previous analytical and numerical works show evidences of both resonant and nonresonant modes, that can compete or dominate depending the physical conditions.
In many space plasmas, Coulomb collisions are negligible, but in some situations such as in some laboratory experiments, they can become important and alter the dynamics of the system in an important way. For that reason, the study of the magnetic streaming instability in the presence of collisions is important, as it has always been treated in the collisionless case before.
This study uses a hybrid model to perform numerical simulations on the magnetic streaming instability. It first focuses on the collisionless case in order to study the main characteristics of the different generated modes, and then treats the collisional case. There are evidences of a damping of the produced waves when increasing the collisions, showing a influence of the collisions on the way energy is exchanged between both plasmas.

Magnetic reconnection in the Earth's magnetotail: some aspects of evolution and dynamics
Alexandra Alexandrova, LPP
Magnetic reconnection is a fundamental process of energy conversion in plasma. During reconnection, the magnetic energy accumulated in the current sheets is released to the energy of particles, which is accompanied with the rapid change of the magnetic field topology. In the near-Earth space, reconnection being the key mechanism responsible for the magnetic storms and substorms, can be investigated by using direct observations, which is crucial for understanding the fundamental principles of energy conversion in plasma as well as for practical applications to space weather. Based on the macro-scale remote signatures of reconnection, such as the accelerated reconnection flows far from the reconnection site, we elaborated a method to estimate the spatial characteristics and efficiency of reconnection. The in situ study based on the identification of reconnection by using its ion-scale signatures, showed that during the reconnection activity, the localized reconnection region in the magnetotail undergoes motion, which is affected by the global magnetic configurations and the local reconnection parameters. The analysis of the ion-scale in situ data revealed also that reconnection frequently evolves in the multiple sites. Among the stages of evolution, including the motion of the reconneciton site and the multiple activity, the question of the reconnection onset is yet to be fully understood. The onset problem requires the direct high-resolution measurements on the electron scales in the reconnection region, which became possible, for the first time, with the recently launched four-spacecraft Magnetospheric Multiscale Mission (NASA/MMS). We discuss the possibility of identifying the processes responsible for the reconnection onset and energization of particles by using the novel MMS observations.

Strong radiative shocks relevant for stellar environments
Raj Laxmi Singh, LERMA/LPP
Strong shocks are present in various astrophysical phenomena. Such shocks are strongly influenced by the radiation through its coupling with hydrodynamics. Thus their topology and dynamics are quite complex. Generating such hypersonic shocks in the laboratory, with controlled conditions, is thus an adequate tool to study the influence of radiation and to compare them with numerical simulations. Such shocks can be generated by intense lasers and electromagnetic devices.
The first part of this dissertation concerns the numerical and experimental study of the interaction of two counter propagating laser-driven shocks. The experiments, performed at the kJ PALS laser facility allowed to generate shocks with different speeds (~ 30-55 km/s and 10-25 km/s), in noble gases and low pressure (fraction of 1 bar). Several diagnostics were implemented: visible interferometry, time- and space- resolved visible spectroscopy, and time integrated XUV spectroscopy. Our experiment shows a strong interaction of one radiative precursor onto the second one. The physical parameters of the plasma were deduced from the diagnostics and compared with 1-D simulation results.
The second part is devoted to the design of an experiment where the shock is generated electromagnetically. The optimization of this generator is presented and also the full experimental set up which allows studying shock ~ 30 km/s in noble gas at ~ 1 mbar.


PHARE project: a 3D and AMR hybrid PIC code devoted to space and laboratory plasmas
Mathieu Drouin, PLAS@PAR
Hybrid-PIC codes are well suited to model cross-scales problems where the ions can be treated as macro-particles, while the electrons are modeled as a fluid. Such approach is of great interest to many problems in laboratory and astrophysical plasmas, where the electron temporal and spatial scales do not need to be resolved, while retaining a kinetic treatment of ions is necessary.
AMR can potentially extend the versatility of hybrid-PIC codes by allowing effective refinement strategies to increase the spatial resolution in localized regions of the computational domain, while at the same time maintaining the computational costs to a reasonable level. However, the increased complexity brought in by AMR strategies requires substantial work to adapt existing algorithms.
Project PHARE funded and fostered by Labex Plas@par was launched within this framework. An overview of the project will be given regarding both numerical and software engineering aspects.

4D inner shell ionization of Xe+ ions and subsequent Auger decay
Mehdi Khalal, LCPMR

M. A. Khalal1, P. Lablanquie1, L. Andric1,2, J. Palaudoux1, F. Penent1, K. Bucar3, M. Zitnik3, R. Püttner4, K. Jänkälä5, D. Cubaynes6,7, S. Guilbaud6,7 and J.-M. Bizau6,7

1Sorbonne Universités, UPMC Université Paris 06, CNRS, LCP-MR (UMR 7614), 4 place Jussieu, 75005 Paris, France
2Université Paris-Est, 5 boulevard Descartes, F-77454 Marne-la Vallée Cedex 2, France
3Jozef Stefan Institute, Jamova cesta 39, SI-1001 Ljubljana, Slovenia
4Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, D-14195 Berlin, Germany
5Nano and Molecular Systems Research Unit, University of Oulu, P.O. Box 3000, 90014 Oulu, Finland 5Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, 930-0194, Japan
6ISMO, CNRS UMR 8214, Université Paris-Sud, Université Paris-Saclay, 91405 Orsay, France
7Synchrotron SOLEIL, l’Orme des Merisiers, Saint-Aubin, Boîte Postale 48, 91192 Gif-sur-Yvette Cedex, France

Photoionization of free ionic species provide precious information for computational modeling of plasmas [1]. However, direct measurement of photoelectrons or Auger electrons resulting from inner-shell ionization of positive ions is extremely difficult. So far, a single experimental result was published on Xe+ 4d inner-shell photoionization [2] which is now seriously questioned by recent results obtained with the same experimental approach described in ref. [3].
We will present another way to obtain comparable information for photoionization of singly charged ions based on the study of the core-valence double ionization of the neutral atom [4]. Our experimental setup consists in a magnetic bottle time of flight spectrometer [5] that collects almost all electrons up to ~200eV in 4π solid angle. At higher kinetic energy, this collection angle slowly decreases. The detection efficiency of the electron detected by microchannel plates is about 50 to 70%. This allows the efficient detection of up to four electrons in coincidence. The energy resolution is ΔE/E=1.5% and depends on the length of the tube (here 2.1m). The experiment was carried out at the SEXTANTS beamline of the SOLEIL synchrotron facility.
The aim of the experiment was to detect the two photoelectrons emitted upon core-valence double ionization of neutral Xe atom as follows: Xe + hν (120 eV) → Xe2+* (4d-15p-1) + e−ph1 + e−ph2 Subsequently an Auger electron is emitted leading to a Xe3+ ion final state: Xe2+* (4d-15p-1) →Xe3+ + e−Auger Figure 1. shows a two-dimension coincidence map between the two photoelectrons energy sum and the Auger electron energy. The Xe2+* (4d-15p-1) states are visible in the red curve (Fig.1 right panel) and their specific Auger decay appears as horizontal line in the 2D map. The diagonal lines correspond to the final Xe3+ (5p-3, 5p-25s-1) states. The spectroscopy of intermediate Xe2+ 4d-15p-1 states and their Auger decay, state by state, have been obtained and will be presented. These spectroscopic results will be extremely useful to understand the photoelectron spectra resulting from Xe+ ions 4d photoionization.


Figure Mehdi Khalal

Figure 1. Two-dimensional coincidences map between two photoelectrons and the Auger electron. The sum of the two photoelectron energy is plotted in red.


[1] Foster A R, Smith R K, Brickhouse N S, Kallman T R and Witthoeft M C 2010 "The Challenges of Plasma Modeling: Current Status and Future Plans" Space Sci. Rev. 157 135–54
[2] Gottwald A, Gerth C and Richter M 1999 "4d Photoionization of Free Singly Charged Xenon Ions" Phys. Rev. Lett. 82 2068–70
[3] Bizau J-M, Cubaynes D, Guilbaud S, Penent F, Lablanquie P, Andric L, Palaudoux J, Al Shorman M M and Blancard C 2016 "Photoelectron Spectroscopy of Ions: Study of the Auger Decay of the 4d → nf ( n = 4 , 5 ) Resonances in Xe5+ Ion" Phys. Rev. Lett. 116 103001
[4] Huttula S-M, Lablanquie P, Andric L, Palaudoux J, Huttula M, Sheinerman S, Shigemasa E, Hikosaka Y, Ito K and Penent F 2013 "Decay of a 2 p Inner-Shell Hole in an Ar+ Ion" Phys. Rev. Lett. 110 113002
[5] Penent F, Palaudoux J, Lablanquie P, Andric L, Feifel R and Eland J H D 2005 "Multielectron Spectroscopy: The Xenon 4d Hole Double Auger Decay" Phys. Rev. Lett. 95 083002

Ultrafast structural dynamics of metallic targets induced by IR femtosecond laser
Manuel de Anda Villa, INSP
Ultrafast laser irradiation drives matter to a strong out-of-equilibrium state where the outermost electrons heat rapidly (within a few hundreds of femtoseconds) before transferring their energy to the lattice via electron-phonon interactions on a timescale of a few picoseconds. This energy transfer and the subsequent cooling down of the lattice modify the atomic structure (phase transitions, disorder, rearrangements). But, under these extreme conditions, the processes and matter properties such as electron-phonon coupling, electronic and ionic thermal conductivity and heat capacity are poorly known.
One very well suited method to study metallic materials under such conditions is to use time-resolved photoelectron spectroscopy (PES) in a pump/probe experiment with sub-picosecond resolution. The relaxation of matter can be observed within the time-dependent modification of the valence band (VB) PES spectrum.
During a first experimental campaign at the CELIA laboratory in Bordeaux measurements of the VB time-dependent evolution were obtained on a bulk gold sample using a 2ps infrared pump laser pulse and a 40eV xuv probe produced by High Harmonic Generation. As the duration of the pump pulse is restricted by the probe photon energy, we have developed and characterized a new beamline that delivers femtosecond pulses of up to 100eV in photon energy. This new beamline together with other improvements of the experiment will open perspectives in studying different materials in a wide range of excitation intensities up to the sample melting thresholds.
Parallel to these measurements on bulk samples, we have been able to obtain the VB photoelectron spectrum of stand-alone gold nanoparticles (NP) using an aerodynamic lens system (ADLS) available at the PLEIADES beamline of the SOLEIL synchrotron facility, Further developments on this technique would allow us, in fine, to study the ultrafast laser-induced structural changes and properties on metallic NP on the fly.

O atom kinetics in CO2 glow discharges
Anna Sofia Morillo-Candas, LPP

A.S. Morillo-Candas1*, B.L.M. Klarenaar2, R. Engeln2, A. Chatterjee1, J-P. Booth1, T. Silva3, V. Guerra3, C.Drag1, 4, O. Guaitella1

1Laboratoire de Physique des Plasmas, Ecole Polytechnique-CNRS-Univ Paris-Sud-UPMC 91128 Palaiseau, France
2Department of Applied Physics, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands
3Instituto de Plasmas e Fus‹o Nuclear, Instituto Superior TŽcnico, Universidade de Lisboa 1049-001 Lisboa, Portugal
4Laboratoire AimŽ-Cotton, Centre national de la recherche scientifique, universitŽ Paris-sud, Žcole normale supŽrieure de Cachan, UniversitŽ Paris-Saclay, b‰timent 505, F-91405 Orsay, France
*Contact e-mail:

1. Introduction

Different strategies have emerged to deal with the excess of CO2 emissions, whose increasing proportion in the atmosphere is the major cause of the global warming. One of these approaches is focused on CO2 recycling, which is an initial step in building more complex organic molecules, such as energy-dense hydrocarbon fuels. In this regard, the dissociation of CO2 to CO, as a first step, through the so called “vibration up-pumping mechanism” is believed to be the most efficient method, especially through the excitation of the asymmetric-stretch vibrational mode of CO2 [1]. The dissociation of CO2 results in the production of O atoms that can recombine into O2, oxidize CO back into CO2, or on the contrary dissociate further CO2. O atoms therefore play a key role, beneficial or not for the efficiency of CO2 conversion. To investigate the fundamentals of CO2 plasma kinetics, a simple glow discharge powered with continuous, pulsed or modulated voltage is studied. This simple discharge allows to measure through different techniques fundamental parameters such as dissociation rates, vibrational excitation of CO and CO2, the gas temperature and the electric field.

2. Experimental setup

The temporal evolution of the different species is studied by means of time-resolved in situ FTIR spectroscopy and actinometry. HRTALIF is introduced to measure with accuracy the gas temperature. The CO2 plasma is ignited in a cylindrical Pyrex tube (2 cm inner diameter and 22 cm or 64 cm length) plasma reactor. Water circulating around the reactor allows control of the wall temperature between 5-50°C. Different gas flows (up to 50 sccm), pressures (millibar range), currents (10 to 50 mA) and pulse durations (millisecond range) were investigated.

3. Results

The time evolution of the dissociation fraction (ratio of CO over (CO+CO2)) was determined by absorption spectroscopy (FTIR). The spectra obtained while doing FTIR experiments have been fitted using the information available in HITEMP-2010 database [2], allowing us to study the evolution over time of other relevant parameters such as rotational temperature, Trot, the pressure in the reactor or the vibration temperatures of CO2. The dissociation rate obtained for the analysed conditions is below 20%. Rotational temperature, i.e. gas temperature, can also been measured by HRTALIF, which technique is also introduced. In actinometry experiments, the ratio of the intensities of O atom lines (at 777 nm and 845 nm) over Argon line at 750 nm were recorded and fitted obtaining the O atom recombination coefficient [3]. The O atom characteristic decay time was found to be in the order of tens of milliseconds. Some differences were observed in CO2 compared to pure O2, plasma especially as a function of the wall temperature.

4. Acknowledgments

This research is conducted within the LABEX Plas@par project, and received financial state support managed by the Agence Nationale de la Recherche, as part of the programme "Investissements d'avenir", reference ANR-11-IDEX-0004-02.

5. References

[1] A. Fridman (2008), Plasma Chemistry. Cambridge University Press. 259–354.
[2] L.S. Rothman, et al., J. Quant. Spectrosc. Radiat.
[3] D. Pagnon, J. Amorim, J. Nahorny, M.Touzeau, M. Vialle J. Phys. D: Appl. Phys. 28 1856-1868 (1995).


Micro-discharges in confined media: fundamental processes and application to lightning interaction with matter
Jean-Baptiste Layly, ONERA, LPP
Lightning stroke on aircrafts induce high current levels in aeronautic assemblies which electrical resistance is mainly concentrated in the contact interfaces between the different parts. As a consequence, the maximum Joule effects, electric fields, and hence sparking probabilities take place in the electric contacts of the aeronautic assemblies. Being able to predict the behavior of electric contacts under high current levels is then necessary to provide a better understanding on sparking and out-gassing phenomena induced by lightning stroke on aeronautic structures. The present work addresses the modelling at the microscopic scale of such electric contacts under high current levels, through a simplified geometric and physical description. 2D axisymmetric and 3D finite volume simulations are used to study simplified contact geometries and examine the current distribution dynamics. Finally, a simple pseudo-analytical model is proposed that enables parametric studies on more complex and realistic electric contacts.

Roles of Metastable states of O2 in oxygen plasma and diagnostics
Abhyuday Chatterjee, LPP

Metastable Molecules in O2 Plasmas probed by High-Resolution Fourier Transform Absorption Spectroscopy

J.P. Booth1, A. Chatterjee1,2, O. Guaitella1, N. De Oliviera2 , L. Nahon2 , C.M. Western3

1 Laboratoire de Physique des Plasmas, CNRS, Ecole Polytechnique, UPMC Univ Paris 06, Univ Paris-Sud, Observatoire de Paris, UniversitŽé Paris-Saclay, Sorbonne UniversitŽés, PSL Research University, F-91128 Palaiseau, France,
2 Synchrotron SOLEIL, Gif Sur Yvette, France;
3 University of Bristol, UK

DC glow discharges in pure oxygen were studied by high resolution (~106) VUV absorption spectroscopy using synchrotron radiation and a Fourier Transform Spectrometer. O2(X), O2 (a), O2 (b) and ground state O atoms were observed, allowing their absolute densities to be determined as a function of gas pressure and discharge current. We have also developed a new way to measure O atom densities form the forbidden transition at 135.56nm

1. Introduction
Electrical discharges in oxygen-containing gases are found widely in nature and are used for many industrial processes including etching, polymer stripping and surface cleaning as well as for sterilization and other biomedical applications. Metastable molecules (a 1Δg and b 1Σg) and atomic oxygen produced in such plasmas play a vital role in the plasma characteristics. These transient species are principally lost by reactions at the chamber walls, but with surface reaction coefficients that are poorly known, limiting the predictive power of models. A significant fraction of electrons can be converted to O- negative ions by dissociative attachment on O2, strongly affecting the plasma conductivity. Associative detachment reactions with O, O2 a1Δg and O2 b 1Σg are the major destruction mechanism of O- , therefore they have a strong effect on the plasma equilibrium.
Vacuum ultraviolet absorption spectroscopy is a promising technique to measure the density of these transient species. However, their VUV spectrum of O2 a and b has not been measured since Ogawa et al. [2] in the 1970’s. We have used the excellent spectral resolution (~106) and accuracy of the DESIRS VUV Fourier-Transform (FTS) branch at synchrotron Soleil [1] to revisit these measurements. Combining with spectral simulations we can identify the best transitions for future time resolved kinetic measurements on the monochromatic branch of the DESIRS beamline. Determination of the absolute O atom density is also a challenge, since the resonance lines at 130nm are too strongly saturated to be of use. Therefore instead we detected for the first the forbidden 3P2-5S0 absorption at 135.56nm. Combined with kinetic measurements, this new data will allow models and cross-section sets for O2 plasmas to be rigorously tested.

2. Experimental Setup
The DC discharge was excited in a 40cm long, 1.9 cm id water cooling Pyrex tube, fitted with MgF2 windows to transmit the VUV beam. The transmitted light in the region 120-170 nm is analysed with the FTS [1].

3. Results
Fig 1 compares our results with the spectra of Ogawa et al. O2 X, a and b bands are observed, with high resolution, allowing the rotational temperature to be determined. The O2 X and a state densities were determined using the data of Ogawa.

Chatterjee Figure 1

Fig.1. Absorption spectrum of 50 mA discharge, 10mBar He + 0.05mBar O2

In figure 2. The forbidden transition line 3P2→ 5S2 at 135.5598 nm is visible.

4. Conclusions and perspectives
New high resolution VUV absorption spectra for a 1Δg and b 1Σg molecules and atomic oxygen are reported. As the forbidden line transition is not saturated, it will allow determination of the absolute density of O ground state atoms in O2 plasmas. In the future we will perform kinetic measurements using modulated current.

Chatterjee figure2


5. Acknowledgments
This research was conducted within the LABEX Plas@par project, and received financial state aid managed by the Agence Nationale de la Recherche, as part of the programme "Investissements d'avenir" under the reference ANR-11-IDEX-0004-02.

6. References
[1] N de Oliveira, M Roudjane, D Joyeux, D Phalippou, J-C Rodier & L Nahon, Nature Photonics 5, 149–153 (2011)
[2] S. Ogawa and M. Ogawa, Canadian Journal of Physics, 53, (1975) 1845
[3]D.H. Katayama, S. Ogawa, M. Ogawa, and Y. Tanaka, Journal of Chemical Physics, 67, (1977) 2132

New high resolution VUV absorption spectra for a 1Δg and b 1Σg molecules and atomic oxygen are reported. As the forbidden line transition is not saturated, it will allow determination of the absolute density of O ground state atoms in O2 plasmas. In the future we will perform kinetic measurements using modulated current.


Character of a pin liquid anode DC discharge in open air
Shiqiang Zhang, LPP

S. Zhang1,2, A. Rousseau1, T. Dufour1

1LPP, CNRS, UPMC Univ Paris 06, Ecole polytechnique, Univ. Paris-Sud, Observatoire de Paris, Université Paris-Saclay, Sorbonne Universités, PSL Research University, 4 place Jussieu, 75252 Paris, France
2Department of Mechanical and Aerospace Engineering, The George Washington University, Washington D.C. 20052 USA
Corresponding author:

Low temperature plasmas are promising tools for biomedical applications, such as disinfection, sterilization, cancer therapy and more recently agriculture. They can be generated using dielectric barrier discharges or plasma jets according two different approaches: (i) a direct approach where substrates or bio-tissues are directly exposed to the plasma and (ii) indirect approach where cold plasma is utilized to activate a liquid medium subsequently applied on the living system. The transported long and short-lived species, ions, UV radiation, gas temperature, transient electric field and gas flow are present in the direct approach while only long-lived species (typically hydrogen peroxide, nitrate and nitrite radicals) are present in the plasma activated medium (PAM). Plasma activated media is more flexible than direct plasma treatment in bio-applications such as cancer therapy, plasma medicine, and even the emerging plasma agriculture. As a result, it is necessary to investigate the interaction of discharge and the liquid to enhance the diffusion and production of reactive species into the media.
In this work, we present the design of a pin liquid electrode discharge in open air. We first report the emission character of the discharge and the V I character of this discharge. As the self-organized patterns are formed at the interface of water and air, we investigated the behavior of the patterns under different gap distance, current, and also liquid conductivity in future.

Keywords: pin-to-liquid discharge, self-organized patterns, emission spectrum

Ab-initio spectroscopic study of silicon hydride molecular ions
Alessandra Puglisi, LCPMR
Coming soon

Therapeutic effect of cold atmospheric plasma on oral cavity squamous cell carcinomas
Bruno Honnorat, LPP

B. Honnorat1, G. Lescaille2, M. Guillot-Delost2, R. Bouras2, J. Griffon3, C. Kikayi3, D. Le Guillou3, T.Dufour1, F.M Lemoine2, L. Bridal3, A. Rousseau1

1Laboratoire de Physique des Plasmas, UPMC, Ecole Polytechnique, CNRS, Paris/Palaiseau, France
2Centre d’Immunologie et des Maladies Infectieuses de Paris, UPMC, UMR-S INSERM 1135, ERL CNRS 8255, Paris, France
3Laboratoire d’Imagerie Biomédicale, Sorbonne Universités, UPMC, CNRS, INSERM, France

Cold Atmospheric Plasma (CAP) therapy has potential for future clinical application in oncology because CAP exposure could selectively kill cancer cells without harming normal surrounding cells. Because Oral Squamous Cell Carcinomas (OSCCs) are frequent and very aggressive despite conventional treatments (Overall survival <20% at 10 years), it is necessary to develop innovative therapeutic strategies. Since OSCCs are locally accessible to CAP treatment and relapse in a loco regional manner, we aim to investigate the therapeutic effect of local CAP therapy in a murine OSCC model.
First, we have engineered and characterized two plasma sources: a helium plasma monojet and a dielectric barrier discharge (DBD) with a low frequency (500 Hz) AC power supply. The power consumption has been measured in real-time during in vitro a n d in vivo treatments. A biochemistry study has been performed to identify reactive species from plasma-activated media (PAM) and to understand how they interplay.
In vitro plasma treatments have been carried out on TC-1 cells, a HPV16 epithelial cancer cell line used to generate a biologically relevant tumor model in mice. This cell line has been treated by (i) direct plasma exposure (ii) PAMs and (iii) calibrated solutions synthesized by admixing conventional chemical products so as to mimic PAM’s composition at matched concentrations of long-lived species (nitrites, nitrates, H2O2). Cell growth and cancer cell death have been studied 24h to 72 hours after treatments. A decrease in cell growth and an energy-dependent cell death of treated cells has been observed using both direct and indirect treatments. To confirm these results, others experiments are in progress using NR-S1 cells, a spontaneous murine oral squamous cell carcinoma cell line, and HSC4 cells, a human tongue squamous cell carcinoma cell line.
In vivo experiments have been carried out to assess the effect of time and energy deposited by direct plasma treatment using a submucosal orthotopic TC1 tumor model. The follow-up of TC1 tumors has been achieved by tumor size measurements (calipers). We observed that plasma treatment induced a slow-down of TC1 tumors. Then, a multi-channel plasma jet operating at 10 kHz AC has been recently engineered to optimize tumoral treatment in a quite shorter time. Experiments are in progress. To complete these data and to assess the effect on tumor vasculature, real-time ultrasonic echography and ultrasound will be further applied to evaluate tumor structure and tissue stiffness (Young’s Modulus).
Altogether, our preliminary data are encouraging to further develop a strategy based on plasma treatment as a therapeutic approach for oral cavity carcinomas.
This work was supported by the Institut Universitaire d’Ingénierie en Santé (IUIS), Sorbonne Université, Projet OSCC 2014/2016 by labex Plas@Par, by Canceropole, and by Ecole Polytechnique.

2D simulation of Hall effect thrusters
Vivien Croes, LPP

Bi-dimensional Particle-In-Cell simulations of Hall current thrusters: Electron drift instability and secondary electron emissions

V. Croes1;2; T. Lafleur1;3, A. Tavant1;2; A. Bourdon1, P. Chabert1

April 20, 2017

1 LPP, CNRS, Ecole polytechnique, UPMC Univ Paris 06, Univ. Paris-Sud, Observatoire de Paris, Universite Paris-Saclay, Sorbonne Universites, PSL Research University, 91128 Palaiseau, France
2 Safran Aircraft Engines, Electric Propulsion Unit, 27208 Vernon, France
3 Centre National d'Etudes Spatiales (CNES), 31401 Toulouse, France


Despite electric propulsion (EP) having its beginning in the 1960's, its full potential has only been realized in the last few years, with all-electric communication satellites and large small-satellite constellation projects [1]. Since Hall effect thrusters (HETs) are one of the most successful EP technologies, need for improved predictive models is increasing. As shown in Figure 1, typical HETs consist of three main components: (1) An external hollow cathode, providing electrons to sustain the plasma discharge and to neutralize the ion beam. (2) An annular ceramic channel where the propellant gas is injected through an anode, ionized, and accelerated (a potential difference is applied between the anode and cathode). (3) A specially designed magnetic circuit used to produce a predominantly radial magnetic field to trap electrons in the channel region. Numerous studies have shown that electron mobility across the imposed magnetic field is anomalously high in comparison to predictions from classical diffusion theories [2]. Multiple mechanisms have been proposed: Secondary electron emissions [3], sheath instabilities [3], gradient driven instabilities [4], or electron drift instabilities [5].

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[1] R. Villain. volume 18. Euroconsult Research Report, 2015.
[2] D. M. Goebel and I. Katz. Fundamentals of Electric Propulsion: Ion and Hall Thrusters. Wiley, 2008.
[3] D. Sydorenko, A. Smolyakov, I. Kaganovitch, and Y. Raitses. Phys. Plasmas, 15(053506), 2008.
[4] W. Frias, A. I. Smolyakov, I. D. Kaganovitch, and Y. Raitses. Phys. Plasmas, 19(072112), 2012.
[5] A. Heron and J. C. Adam. Phys. Plasmas, 20(082313), 2013.
[6] T. Lafleur, S. D. Baalrud, and P. Chabert. Phys. Plasmas, 23(053503), 2016.
[7] V. Croes, T. Lafleur, Z. Bonaventura, A. Bourdon, and P. Chabert. Plasma Sources Sci. Technol., 26(3):034001, 2017.



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