2nd Young Researcher Conference on Plasma Physics and applications

Organised by Sorbonne University and the Société Française de Physique (Plasma Division)
Date: 29 June 2018
Location: Sorbonne University – Pierre & Marie Curie Campus - Jussieu // International Conference Center - Room 108 - Tower 44 - 1st floor

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Context

The Labex PLAS@PAR and the Plasma Division of the SFP co-organise this year the second edition of this scientific event dedicated to research at doctoral and postdoctoral levels. All propositions are welcome from young researchers working in a French, European or International lab. The conference will last for one day and will take place in Paris.

This conference aims at bridging communities and research groups working on various aspects of plasma physics as well as promoting new innovative research and the dynamism of the upcoming generation of researchers.

Scientific focus

Plasma physics is essential to understanding a huge variety of phenomena, occurring both in nature and in man-made devices. It also provides the theoretical foundation for a wide range of key industrial applications. The recent development of new laboratory facilities and large experimental infrastructures is enabling unprecedented extreme plasma conditions to be achieved, opening the door to unexplored phenomena which will stimulate fundamental research.

Since the field of plasma science is particularly broad and its study scattered across many different disciplines, from astrophysics to fundamental plasma physics and industrial plasmas, this conference aims at promoting discussion across research groups and the diversity of scientific endeavours in the community.

Provisional program: 

9h30 - Welcome & Coffee

10h - Review n°1 with E. Robert (GREMI), Cold plasmas: physics and biomedical applications

10h30 - Session 1: Atoms & molecules in plasmas
Chair: F. Marcotte (IJLRA)

  • 10h30 - T. Loon Chng (LPP) - Time evolution of atomic nitrogen density in a nanosecond capillary discharge
  • 10h50 - B. Wurmser (LCPMR) - Photoemission delays in 2D model molecules
  • 11h10 - F. Condamine (LULI) - Very high-resolution spectroscopic study of Vanadium He-like Rydberg series of laser created plasmas
  • 11h30 - T. Miteva (LCPMR) - Interatomic Coulombic decay mediated by ultrafast superexchange energy transfer
  • 11h50 M. Deal (LESIA) - Importance of opacities for the computation of atomic diffusion in stellar models


12h10 - Session 2: Plasma applications
Chair: T. Loon Chng (LPP)

  • 12h10 - M. Zhang (2PM) - Experimental and numerical investigation of the radical chemistry within a plasma/liquid micro-reactor
  • 12h30 - F. Judée (LPP) - Are all cold plasma jet designs safe for in vivo applications? Application to cholangiocarcinoma tumors

12h50 - Lunch and poster session

  • G. Bian & J. Machado (LKB) - High-precision measurements and calculations in lithium-like ions
  • S. Colombo (LERMA) - Effects of intense flaring activities on the accretion disk of a classical T TAURI star
  • C. Ding (LPP) - Electron Temperature Measurement in Filamentary Nanosecond Surface Dielectric Barrier Discharge
  • A. Fazzini (LULI) - Pair creation in plasmas in the presence of ultra high intensity electromagnetic fields
  • N. Gilet (LPC2E) - Observation of mixed warm and cold electrons with RPC-MIP at comet 67P/Churyumov-Gerasimenko
  • S. Marini (LULI) - Surface Plasma Waves in High-Intensity Laser-Plasma Interaction
  • A. Marret (LERMA) - Kinetic study of the streaming instability in laboratory and space plasmas
  • M. Menu (LPP) - Numerical simulations of rotating turbulent dynamos
  • H. Oueslati (LPP) - Toroidal steady states in visco-resistive magnetohydrodynamics in ITER Geometry
  • S. Simon (LPP) - Investigating dry and wet plasma approaches for releasing seed dormancy
  • K. Wang (LAL) - Simulations of a LPWA with external injection of a 10 MeV electron beam
  • I. Orel (LPP) - Peculiarities of kinetics in pulsed nanosecond discharge at high and low specific deposited energy on the example of argon actinometry technique of O density measurements
  • T. Charoy (LPP) - Boundary condition influence on Hall effect thruster axial-azimuthal simulations


14h00 - Review n°2 with C. Briand (LESIA), Sun-Earth, a complex relationship

14h30 - Session 3: Waves & instabilities in plasmas

Chair: M. Deal (LESIA)

  • 14h30 - R. Hajra (LPC2E) - Comparative study on the solar wind impacts on a comet and on the Earth
  • 14h50 - F. Orain (CPHT) - Control of edge instabilities by magnetic perturbations in tokamak plasmas
  • 15h10 - A. Nicolopoulos (LJLL) - Resonant heating of a tokamak plasma: mathematical and numerical modeling
  • 15h30 - F. Marcotte (IJLRA) - The spherical Taylor-Couette Flow dynamo: a non-convective scenario for astrophysical dynamos


15h50 - Coffee break

16h10 - Review n°3 with F. Amiranoff (LULI), What’s the use of high-power lasers?

16h40 - Session 4: Extreme laboratory astrophysics

Chair: Florian Condamine (LULI)

  • 16h40 - M. Guarguaglini (LULI) - Planetology in laboratory using laser-driven shocks
  • 17h00 - J. Capitaine (LPP/LERMA) - Energetic particle dynamics in colliding laser-produced plasma
  • 17h20 - A. Vanthieghem (IAP) - Stability analysis of a periodic system of relativistic current filaments
  • 17h40 - L. Chantry (LUTH) - Inflow and Outflow meridional self-similar MHD models for plasma pairs around Kerr Black Holes

 

18h00 - Nomination of the best presentation and poster of the conference

End of the day

 

Scientific Committee:

Nicolas Aunai – LPP – Ecole Polytechnique

Nicolas Jidenko – LPGP – Université Paris Saclay

Mickael Grech – LULI – Sorbonne Université – Ecole Polytechnique

 

Abstracts


Tat Loon Chng
Time evolution of atomic nitrogen density in a nanosecond capillary discharge
Tat Loon Chng1, Nikita Lepikhin1, Inna Orel1 and Svetlana Starikovskaia1
Presenter: Tat Loon CHNG

This paper describes measurements of atomic nitrogen (N) density conducted in a nanosecond capillary discharge.  Such a discharge is characterized by its high reduced electric fields (on the order of hundreds of Townsends) and high specific energy deposition per molecule (up to 1 eV per molecule).  The specific goal of this study is to quantify the N production in a pure molecular nitrogen (N2) capillary discharge and more generally, facilitate an improved understanding of the plasma kinetics under conditions of high reduced fields and specific energy deposition.  Two-photon absorption laser induced fluorescence (TALIF) is used to track the time evolution of the N density in the early to late afterglow of the discharge. Absolute densities are obtained via calibration against known concentrations of krypton (Kr), which is an inert gas.  One of the most important findings is the presence of significant levels of N concentrations (corresponding to a peak dissociation fraction of at least 10%) up to even 10 ms after the initiation of the discharge. These long-lived atoms are believed to be a result of the slow atomic recombination rate associated with this reaction.  Ongoing experimental efforts are now focused on measuring the N production at lower specific energy deposition levels for comparison with the current data.


[1] Laboratory of Plasma Physics (CNRS, Ecole Polytechnique, Sorbonne University, University Paris-Sud, Observatoire de Paris, University Paris-Saclay) Palaiseau, 91128, France

 

Basile Wurmser
Photoemission delays in 2D model molecules

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Florian Condamine
Very high-resolution spectroscopic study of Vanadium He-like Rydberg series of laser created plasmas and photo-pumped by the LCLS X-ray Free Electron Laser

F.P. Condamine1,2,3, D. Khaghani4, E. Galtier3, L. Gournay1,2, O. Renner5, F.B. Rosmej1,2, S.H. Glenzer3

1. Sorbonne Université, Paris, France
2. LULI, Ecole Polytechnique, Palaiseau, France
3. SLAC National Accelerator Laboratory, Menlo Park, California, USA
4. Friedrich Schiller Universität, Jena, Germany
5. ELI Beamlines, Prague, Czech Republic

Higher-than-predicted solar opacities reported by Bailey et al. [Nature 517, 56 (2015)] are questioning our present understanding of radiation interaction with atoms in hot and dense plasmas. Study of He-like Rydberg series (1s1nl -> 1s2) in a laser-created plasma can allow researchers to better understand phenomena occurring in these extreme conditions. Rydberg series are well suited for a detailed analysis of line shapes and frequency redistribution of bound-bound and bound-free transitions which are a key for opacity measurements. Especially as their width is highly-sensitive to plasma density due to Stark broadening.


To study the frequency redistribution of these lines with extreme detail, the use of an X-ray Free Electron Laser (XFEL) is of great interest.

We present first results of an experiment conducted at the LCLS facility at the MEC (Matter in Extreme Conditions) end-station located at SLAC National Accelerator Laboratory in California.

We created hot (Tbulk » 700eV) and dense (ne » 1021-22 cm-3) plasmas using the 1.5J, 150ps MEC optical laser on Vanadium targets. These plasmas have then been irradiated by using the LCLS seeded beam allowing us to pump inside a very narrow spectral band (DE » 2eV).

The LCLS seeded beam has been irradiating the plasma at different delays and at different positions inside the plume in order to study line profiles and frequency redistributions all along the plasma lifetime and expansion.

Two high spectral and spatial resolutions X-ray spherical spectrometers (FSSR) were used to record spectral data. A wave front sensor recorded the imaging of the plasma during the shots.

Tsveta Miteva
Interatomic Coulombic decay mediated by ultrafast superexchange energy transfer

Tsveta Miteva1, Sevan Kazandjian1, Premysl Kolorenč2, Petra Votavová2 and Nicolas Sisourat1

1 Sorbonne Université UPMC Univ Paris 06, UMR 7614, Laboratoire de Chimie Physique – Matière et Rayonnement, F-75005 Paris, France

2 Charles University, Faculty of Mathematics and Physics, Institute of Theoretical Physics, V Holešovičkách 2, 180 00 Prague, Czech Republic

Keywords: Interatomic Coulombic decay, decay widths, rare gas clusters, Fano resonances

Inner-valence ionized states of atoms and molecules live shorter if these species are embedded in an environment due to the possibility for ultrafast de-excitation known as interatomic Coulombic decay (ICD) [1]. In this process the initially excited species de-excites by transferring its energy to a neighbor and ionizing it within femtoseconds. The ICD lifetime, or going from the time to the energy domain, the ICD width, depends on the distance between the interacting monomers. At large interatomic separations, the process can be viewed as an exchange of a virtual photon between the monomers and thus, the decay width displays a 1/R6 dependence on the distance [2, 3].

In this work we show that the lifetime of the ICD active states decreases further when a bridge atom is in proximity to the two interacting monomers. This novel mechanism, termed superexchange ICD, is driven by the efficient transfer of excitation energy via virtual states of the bridge atom (Fig. 1). As a showcase system we consider the NeHeNe trimer. The decay widths of the Ne2+(2s-1) 2Σg+ state in the presence of He and in the isolated dimer were computed using the Fano-CI method [4]. We demonstrate that the decay width of the Ne2+(2s-1) 2Σg+ resonance increases 6 times in the presence of a He atom at a distance of 4 Å between the two Ne atoms. Using a simple model, we provide a qualitative explanation of the superexchange ICD and we derive an analytical expression for the dependence of the decay width on the distance between the neon atoms [5].

Figure 1. Schematic representation of the superexchange ICD process in NeHeNe trimer.

References

1. L. S. Cederbaum, J. Zobeley, and F. Tarantelli (1997), Phys. Rev. Lett. 79:4778.
2. R. Santra, J. Zobeley, and L. S. Cederbaum (2001), Phys. Rev. B 64:245104.
3. V. Averbukh, I. B. Müller, and L. S. Cederbaum (2004), Phys. Rev. Lett. 93:263002.
4. T. Miteva, S. Kazandjian, and N. Sisourat (2017), Chem. Phys. 482:208.
5. T. Miteva, S. Kazandjian, P. Kolorenč, P. Votavovà and N. Sisourat (2017), Phys. Rev. Lett. 119:083403.

Morgan Deal
Importance of opacities for the computation of atomic diffusion in stellar models

Atomic diffusion, including the effect of radiative accelerations on individual elements, leads to variations of the chemical composition inside the stars as well as the surface abundances evolution. Indeed the accumulation in specific layers of the elements, which are the main contributors of the local opacity, modifies the internal stellar structure and surface abundances. Monochromatic opacity data are thus crucial in order to compute the effects of atomic diffusion in stellar interiors. Here we show that the variations of the chemical composition induced by atomic diffusion in G and F type stars can lead to an increase of the iron surface abundance and to an increase of the Rosseland mean opacity at the bottom of the surface convective zone. This induces a modification of the size of the surface convective zone, of the radius of the star, of some seismic parameters, and more importantly of [Fe/H].

Mengxue Zhang
Experimental and numerical investigation of the radical chemistry within a plasma/liquid micro-reactor

2PM group, Chimie ParisTech, PSL Research University, CNRS, Institut de Recherche de Chimie Paris

A novel plasma/liquid microreactor has been developed to generate and inject radical species with the aim to perform chemical synthesis reactions in liquid phase in this study. Widely used for the surface modification, plasma is a versatile source of reactive species, such as radicals, atoms, electrons, etc. These reactive species created by the plasma, can as well be injected to the liquid phase, initiating liquid phase radical reactions. The use of micro-structured systems can enhance the gas/liquid interactions with a high surface-area-to-volume ratio. Herein is reported a plasma/liquid microreactor for liquid phase radical reactions. Radicals are generated in the gas phase in a steady flow microreactor and then transported to the liquid phase. A spin-trap molecule in the liquid phase help to identify and quantify the radical species generated in the microreactor, thanks to the electron paramagnetic resonance (EPR) spectroscopy. Hydroxyl radicals and hydrogen atoms have been detected and measured in the liquid phase, indicating the huge potential of the microreactor as a handful tool for chemical synthesis.


Florian Judée
Are all cold plasma jet designs safe for in vivo applications?
Application to cholangiocarcinoma tumors

F. Judée1, J. Vaquero2, L. Fouassier2 and T. Dufour1
1 LPP, UPMC Univ. Paris 06, Sorbonne Universités, CNRS, Ecole Polytech., Univ. Paris-Sud, Observatoire de Paris, Université Paris-Saclay, PSL Research University, 4 Place Jussieu, 75252 Paris, France
2 Sorbonne Universités, UPMC Univ Paris 06, INSERM, Centre de Recherche Saint-Antoine (CRSA), Paris, France
E-mail: judee@lpp.polytechnique.fr

Cold atmospheric plasma jets (CAPJ) have attracted tremendous interest over the last decade for many applications related to Life Sciences. Long time limited to the sterilization of medical equipments, they are today investigated in dentistry, ophthalmology, dermatology but also in cancerology. While few plasma devices like the Kinpen®MED are marketed and homologated for clinical trials, an overwhelming majority of the plasma labs develop their home-made plasma devices with – therefore – very different designs and sometimes unsuspected performances. Today, one can legitimely wonder if any CAPJ configuration is safely operable upon in-vivo experiments. Cholangiocarcinomes (CCA) have been considered as a relevant tumor model to deal with this issue.
CCA is a type of liver cancer, i.e. a heterogeneous group of malignancies that can emerge at every point of the biliary tree. To date, the unique effective therapy, surgical resection, is only possible in 20% of cases with a 5-year survival rate of CCA patients varies among 30-40%. Since innovative treatments are highly expected and since plasma medicine has already been successfully applied to other carcinomas, the current study aims to evaluate the efficacy of CAPJ treatment on CCA comparing two different designs relying on the same materials. The first one, generally called Plasma-Gun (PG), is composed of a glass tube with a grounded electrode wrapping the outer glass tube and an inner cylinder high voltage electrode. The second design,  called Plasma-Pulser (PP), presents a tecnological incrementation that allows CCAs treatment without inducing any burns. Analysis of safely plasma-treated mice skin and bile duct carcinoma heterotopic tumor (EGI-1 cell line) will be the support of a discussion about the effects of the plasma design on the treatment of cholangiocarcinoma. 

Rajkumar Hajra
A comparative study on the solar wind impacts on the comet and the Earth

Interaction of the solar wind with different solar system bodies is an interesting plasma physics problem. In the present paper we will show a comparative study on the impacts of interplanetary corotating interaction regions (CIRs) on the plasma environments of the comet 67P/Churyumov-Gerasimenko (67P) and of the Earth. While the Earth has its intrinsic magnetosphere and ionosphere, 67P being a non-magnetized solar system body possesses an ionosphere (a partially ionized atmosphere) that interacts with the solar wind through the formation of an induced magnetosphere. Specific examples will be shown to indicate the distinguishing responses of the cometary plasma and of the Earth’s ionosphere to the CIR.

François Orain
Control of edge instabilities by magnetic perturbations in tokamak plasmas

Instabilities occurring at the edge of tokamak plasmas, called Edge Localized Modes (ELMs), are a key concern for ITER, as they can induce large heat loads on tokamak materials. It is therefore crucial to control them in a reliable way. A promising method is the application of magnetic perturbations, found to be capable of mitigating or suppressing ELMs in existing tokamaks. However, the necessary conditions to achieve ELM suppression are so far not clearly understood. The non-linear modeling of the ELM control by magnetic perturbations, performed with the MHD code JOREK, is presented, highlighting different regimes depending on the applied magnetic perturbations: unaffected, mitigated or suppressed ELMs.

Anouk Nicolopoulos
Resonant heating of a tokamak plasma: mathematical and numerical modeling

We propose a new mathematical framework for a resonant heating model to derive stable numerical methods.

A standard model for plasma heating is the harmonic in time Maxwell's equations with a cold plasma dielectric tensor, with a small ion-electron friction parameter. For very small values (1e-7 in the ITER tokamak), numerical tests show instabilities which reflect the fact that the limit problem is mathematically ill-posed. Numerical fixes can be used but they involve a delicate tuning between an artificial friction and the discretization step. We propose a new formulation of the resonant equations that is mathematically well-posed and leads to naturally stable numerical methods.

For the Budden problem, we are able to construct an analytic solution to the X-mode that captures the singularity of the problem, and to characterize this solution via an integral relation involving non-singular manufactured quasi-solutions. It means we can control what happens at the resonance by propagating the regularity of the non-resonant zone.

This characterization can then be extended to the case of mode coupling.

A finite element discretization is then carried on. In particular we are able to compute a numerical heating.


Florence Marcotte
The spherical Taylor-Couette Flow dynamo: a non-convective scenario for astrophysical dynamos?

Authors: Florence Marcotte (1,2,*) and Christophe Gissinger (3)

We present a new scenario for astrophysical dynamos relying on differential rotation in a spherical shell (spherical Couette flow) with thin aspect-ratio. When the angular momentum sufficiently decreases outwards, a primary hydrodynamic instability is widely known to develop in the equatorial region, characterized by pairs of counter-rotating, axisymmetric toroidal vortices (Taylor vortices) similar to those observed in cylindrical Couette flow. We show that when the fluid is electrically conducting, this spherical Taylor-Couette flow can amplify and maintain a magnetic field against ohmic dissipation. We characterize the subcritical dynamo generated by this particular flow and study its evolution as the flow successively breaks into wavy and turbulent Taylor vortices for increasing Reynolds number. The role of global rotation on the dynamo threshold and the implications for stellar interiors are finally discussed.

1: Laboratoire de RadioAstronomie (LRA), Département de Physique de l'Ecole Normale Supérieure, Paris
2: Institut de Physique du Globe de Paris
3: Laboratoire de Physique Statistique (LPS), Département de Physique de l'Ecole Normale Supérieure, Paris
*: current affiliation: Institut Jean le Rond d'Alembert, Université Pierre et Marie Curie, Paris


Marco Guarguaglini
Planetology in laboratory using laser-driven shocks

LULI, École Polytechnique/CNRS

The study of planetary interiors is one of the keys for the knowledge of planetary formation, evolution, and structure. This knowledge is also required in the field of research and discovery of extrasolar planets, with particular attention to habitable ones.

Up to now, probing the interior of planets other than our Earth has been unfeasible and we could only collect data about their surface or atmosphere, together with gravitational and magnetic fields, luminosity, etc. These data should be coupled in a self-consistent way with the interior structure and dynamics. These latter can be assessed only if structural and transport properties such as the equation of state, phase diagram, conductivity, are accurately determined for some key materials. Those include iron and silicates for terrestrial planets, hydrogen and helium for gas giants, and water/alcohols/ammonia for the icy giants.

Matter in planetary interiors lies in very extreme conditions of ≈ 1-100 Mbar pressures and ≈ 1000 - 10000 K temperatures. These exotic states, at the interface

between a classic plasma and condensed matter, are referred to as Warm Dense Matter, whose characterisation is challenging from both theoretical and experimental point of view.

Pressures of few Mbar can be reached through static techniques, based on diamond anvil cells. Dynamic methods, that rely on the propagation of a shock wave, are necessary to go to higher pressures. We will focus in particular on the laser-driven shock technique, which employs high-power laser beams (kJ energy delivered in some ns) focused onto a structured target which includes the material under study. Ultrafast optical diagnostics allow to measure the shock velocity, the optical reflectivity of the shock front, and the self-emission of the shocked region. Those data are used to assess the equation of state and electrical conductivity of the sample.

In this review we will briefly describe the methods and challenges of the experimental study of planetary interiors using high-power lasers, with particular attention to the recently conducted experiments at the GEKKO XII (Japan) and LULI 2000 (France) laser facilities in the framework of the POMPEI ANR project.


Julien Guyot
Energetic particle dynamics in colliding laser-produced plasma

J. Guyot1 , A. Ciardi1 , P. Savoini2 , G. Revet3 , J. Fuchs3

1 Sorbonne Université, Observatoire de Paris, Université PSL, CNRS, LERMA, F-75005, Paris, France
2 Ecole Polytechnique, Sorbonne Université, CNRS, LPP, France
3 Ecole Polytechnique, CNRS, LULI, France


The acceleration of charged particles to high-energies is ubiquitous in space.
Several mechanisms are thought to play a role, with classical examples being magnetic reconnection and Fermi acceleration.
We present numerical simulations of experiments aimed at studying the acceleration of particles in colliding plasma flows. The plasma is generated by
irradiating with a ns-laser, two oppositely facing solid targets. The expanding plumes are collimated into jets by an externally imposed magnetic field of 20 T and the collision of the two jets generates a region of strong shocks, turbulence and large scale field reversal. Measurements using a Thomson parabola indicate particles with energies up to ~ 0.1 MeV.
To understand the mechanisms leading to the acceleration of the particles, simulations are performed with the 3D resistive MHD code GORGON coupled with test-particles solver. The dynamics of the plasma and the energization of the particles will be presented.

Arno Vanthieghem
Stability analysis of a periodic system of relativistic current filaments

The nonlinear evolution of current filaments generated by the Weibel-type filamentation instability is a topic of prime interest in space and laboratory plasma physics. In this paper, we investigate the stability of a stationary periodic chain of nonlinear current filaments in counterstreaming pair plasmas. We make use of a relativistic four-fluid model and apply the Floquet theory to compute the two-dimensional unstable eigenmodes of the spatially periodic system. We examine three different cases, characterized by various levels of nonlinearity and asymmetry between the plasma streams: a weakly nonlinear symmetric system, prone to purely transverse merging modes; a strongly nonlinear symmetric system, dominated by coherent drift-kink modes whose transverse periodicity is equal to, or an integer fraction of the unperturbed filaments’; a moderately nonlinear asymmetric system, subject to a mix of kink and bunching-type perturbations. The growth rates and profiles of the numerically computed eigenmodes agree with particle-in-cell simulation results. In addition, we derive an analytic criterion for the transition between dominant filament-merging and drift-kink instabilites in symmetric two-beam systems.

Loïc Chantry
Inflow and Outflow meridional self-similar MHD models for plasm of pairs a round Kerr Black Holes

The jets produced by AGN are extremely energetic natural phenomena and thus constitute a real laboratory of high energy physics. To describe the inner-spine jet of AGN in the context of ideal, stationary and axial-symetric MHD, we build a meridional self-similar model in Kerr metric. The choice of this metric is justified in order to describe the flow near the super-massive central black hole, and in particular to study the effects of its rotation. The model, characterized by 8 parameters, is based on a first order expansion of the governing general relativistic equations in the magnetic flux function around the symmetry axis of the system. Using the regularity conditions at the Alfvén transition surface, we introduced a parameter to take into account the light cylinder effects and the meridional increase of the Alfvén number with the magnetic flux function. This complete treatment for an outflow in a Kerr metric allowed us to present four enthalpy driven solutions with different field geometries and Lorentz factors, wherein the contribution of the Poynting flux is rather small. The jet power of the ultra-relativistic outflow solutions are of the same order as that determined from numerical simulations conducted by several groups.

Furthermore, our model is able to describe both an incoming and outgoing flow at the level of the stagnation radius; at this radius, pairs are created from neutrinos or highly energetic photons coming from the disk. Coupling inflow and outflow models allows us to describe the MHD flow from the horizon of the black hole up to infinity. We can estimate the different contributions of each of those processes: at the black hole level the energetic component coming from the Blandford-Znajek effect or the generalized Penrose mechanism, and the energetic input due to the creation of pairs.

 

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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 

 

PROGRAM:

 

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

 

Abstracts


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.

References

[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: ana-sofia.morillo-candas@lpp.polytechnique.fr


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

Fig.2.

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: shiqiang.zhang@lpp.polytechnique.fr

Abstract:
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
E-mail: bruno.honnorat@lpp.polytechnique.fr, antoine.rousseau@lpp.polytechnique.fr

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

Abstract

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].

Capture decran 2017 05 11 a 15.29.53

References

[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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