The reduction of pollutant emissions in aircraft engines and power plants has become a major issue for gas turbine manufacturers as a result of more stringent environmental regulations and increased environmental concern. An efficient solution to reduce pollutant formation is to maintain a relatively low temperature in the combustor primary zone, by decreasing for instance the mixture equivalence ratio. The issue is that a low flame temperature induces slower chemical reaction rates often resulting in an increase of flame instabilities and extinctions. An emerging solution to enable flame stabilization in leaner regimes, suitable to a wide range of combustion applications, is to generate electrical discharges at the flame basis. Among these various types of discharges, the Nanosecond Repetitively Pulsed discharges have shown to beparticularly efficient. Despite this proven efficiency, the fundamental mechanisms of plasma-assisted combustion are not well understood. Also, the numerical tools needed by engineers to assess the performance of NRP discharge in practical configurations and optimize their design do not exist. The objective of this project is to elaborate and validate against experimental data a modeling route suitable to perform simulations of realistic turbulent combustion systems accounting for plasma-flame interactions. The discharge properties will be first characterized numerically and experimentally in a mixture representative of a combustor, which may contain fuel and recirculating burnt gases. These temporal and spatial distributions of species and temperature within the discharge will serve to calibrate a semi-empirical plasma-assisted combustion model recently developed. This model will be formulated in a LES context and implemented in an unstructured CFD solver. To build the validation database, experiments of plasma-assisted combustion will be conducted on two configurations: - The first one is a bluff body flame on which it has been already shown that the NRP discharge enables the flame stabilization over very lean regimes. The NRP discharge is efficient when located in small gases recirculation zone. We will perform complementary measurements on this configuration to characterize the composition and flow properties within the recirculation zone. - The second configuration is a swirled combustor representative of aeronautical combustion chambers. It is composed of a two-stage swirled injector and a rectangular combustion chamber with optical access ports. We will perform measurements to characterize the effect of the plasma on the flame stabilization process. It will be interesting to show that the plasma impacts significantly the stabilization mechanisms. The LES plasma-assisted combustion model will be applied to both bluff-body flames and swirled combustor configuration. Finally, we will perform the LES of a practical Lean Premixed Turbomeca combustor stabilized by NRP discharges as a project final big challenge.

In an increasingly competitive satellite market, electric satellites are expected to garner a growing share of the market, between 25% and 50% by 2020, as estimated by industry players. Among the different electric propulsion systems, Hall effect Thrusters are developed in France by SNECMA, the industrial partner of the chair. SNECMA has pioneered electric propulsion systems in Europe and has successfully sold plasma propulsion systems based on Hall effect thrusters for orbital propulsion and control of space probes and satellites. A key issue for SNECMA in coming years is to develop low power (300-500W) Hall effect thrusters to address the exploding market of small satellites in low-Earth orbits (i.e. at altitudes from 500 to 2000 km). Hall effect thrusters have been extensively studied since their invention in the 1960s. However, the physics of magnetized plasmas typical of these thrusters is complex; several plasma processes that have direct relevance to the thruster performance and lifetime are still poorly understood. Today, the design and development of Hall effect Thrusters is still semi empirical with long and expensive life tests. The final objective of the POSEIDON Chair is to develop a new experimental/numerical methodology to reduce the number of experimental tests in the development of future Hall effect thrusters. The chair is structured around four scientific axes, plus one axis on the project management and coordination, and one axis on know-how transmission, expertise, training and teaching. In the scientific axes, we propose to develop innovative fundamental and applied research activities, for both experimental and numerical studies, to better understand crucial plasma processes occurring in Hall effect thrusters: electron transport, interaction with walls and erosion, and address the question of alternative propellants. The main goals of this project are to better understand plasmas in the real architectures of Hall effect thrusters, to develop 3D numerical tools for the simulation of such problems and to make them available to the industry, to use these tools to improve the efficiency of existing products and in this manner to provide the foundation for breakthroughs in the designs of new electric thrusters. The chair is hosted by LPP, a joint research laboratory between CNRS, Ecole Polytechnique, Université Pierre et Marie Curie, Université Paris Sud and Observatoire de Paris. LPP contributes through its internationally recognized expertise in plasma physics. The Chair holder Anne Bourdon is a CNRS research director (DR2). In 2014, she joined the LPP laboratory to contribute to the development of numerical simulations. The Chair will inject the needed expertise and energy in a fundamental and applied research domain of strategic interest, both scientifically and economically. As a joint project involving academics and industry, the POSEIDON Chair will reinforce the collaboration between LPP and SNECMA. For LPP, it will allow to anchor a strategic axis of research in a long-term partnership with an industrial leader in the field. For SNECMA, the POSEIDON project will improve its reactivity, expand its market position and confirm its leadership position in the very competitive market of electric propulsion. Regarding the international recognition of the partners, this Chair will participate to the visibility of the French expertise in the field of electric propulsion worldwide. Finally, this chair will allow the training of experts on electric propulsion that could be recruited by research laboratories or the industrial partner in order to sustain its investment in a long-term strategy.

Despite decades of intense research, the production of large amounts of nitrogen atoms remains a major roadblock for many industrial applications such as the enhancement of nitridation processes, the synthesis of novel nanomaterials and large band gap nitrides for high power electronics, or biomedical treatment. It is also important to understand the mechanisms of N production/removal in plasma-assisted combustion and pollutant abatement. This collaborative project seeks to elucidate the pathways of production of atomic species, particularly nitrogen, using nanosecond and microwave plasma discharges with high energy density. The project will focus on the kinetic mechanisms involving electronically excited states of N2. In nitrogen plasmas, many electronic excited states with energies greater than 11.5 eV are produced by electron impact reactions under the action of high electric fields. These excited states can spontaneously predissociate, forming nitrogen atoms in the ground state N(4S) and in the first two excited metastable states, N(2P) and N(2D). This route is the dominant pathway for nitrogen dissociation at low pressures where collisions between neutral species are infrequent. At higher pressure, however, these excited states can also dissociate by collisions with ground state nitrogen molecules. Some authors predict that collisional dissociation prevails over predissociation at pressures above a few atmospheres. Other processes that become important at high pressure (typically above a fraction of an atmosphere) include pooling reactions by which two electronically excited molecules of nitrogen collide and dissociate one of them. Despite this apparent beneficial effect of operating at high pressures, it should be noted that two and three-body recombination of nitrogen atoms also increases with the pressure, thus potentially reducing the overall nitrogen atom production. Because the rates of collisional excitation by electron impact increases exponentially with the reduced electric field E/N, where E is the electric field and N the total gas number density, it is also expected that the density of electronically excited states increases with E/N. Thus higher reduced fields result in higher dissociation of nitrogen atoms and a lower energy cost per atom produced. Typical values reported in the literature indicate that the energy cost is about 340 eV/atom at E/N = 140 Td (1 Td = 10-17 V-cm2), and it decreases to values as low as 40 eV/atom above 300 Td. Few experimental results have been reported in the literature to confirm these trends over a wide range of reduced electric fields and pressures. Thus, the objective of this project is to improve our understanding of these processes. To this end, we will perform experiments with several plasma discharges capable of operating from the non-collisional regime (1-10 Pa) to the highly collisional regime at 10 atm, with reduced electric fields from 100 to 400 Td. Advanced diagnostic techniques, namely femto-, pico-, and nano-second TALIF and quantitative OES will be developed to quantify the density of ground and excited species. In parallel, kinetic and discharge models will be developed to guide and analyze the measurements. The expected outcomes include a detailed understanding of nitrogen production kinetics, and a comparison of the various types of discharges over the wide range of pressures and reduced electric fields investigated that will serve as a reference to guide the needs of the applications envisioned. The consortium assembles a complementary team of experts in plasma discharge characterization, plasma modeling, and advanced optical diagnostics. We will also benefit from international collaborations with leading experts in chemical mechanisms, in particular the Chemistry group of Prof. Capitelli (University of Bari), and N. Popov (Moscow State University) who participates in the LIA of one of the project partners.

Magnetic reconnection is a universal phenomenon enabling large scale transfer of magnetic energy to plasma kinetic energy and affecting its macroscopic transport by changing its magnetic connectivity. Among many systems in the universe, the Earth magnetopause, being close and “easily” targeted by spacecraft missions, is a fantastic laboratory to study the reconnection process in great details, besides being, by itself, an important space weather actor, as reconnection there critically couples the solar wind to our magnetosphere, leading to geomagnetic activity. The magnetopause is a three-dimensional collisionless asymmetric magnetic boundary separating the solar wind from the magnetospheric plasma, and through which the magnetic field is sheared between the interplanetary magnetic field (IMF) and the Earth dipole. Although we know magnetopause reconnection is overall greatly influenced by the IMF orientation, we do not understand how the magnetic shear affects the microphysics resulting in this large scale perspective. Besides the asymmetrical magnetopause configuration distinguishes it from the majority of reconnection models, mostly focused on magnetotail-like, symmetric current sheets, which guide our intuition although, strictly speaking, are quite singular. This three year project proposes to tackle the crucial issue of the impact of mesoscale environmental properties on collisionless magnetic reconnection, focusing on the impact of i) varying the magnetic shear angle in a fixed, asymmetric, reconnecting current sheet ii) the impact of a slowly varying degree of asymmetry of the current sheet on the reconnection process with a fixed magnetic shear and iii) the three-dimensional aspect of the problem. Such a systematic survey will lead to much clearer results than the simulation of a unique and arbitrary shear angle and high degree of asymmetry. We will use state-of-the-art 2D fully and hybrid kinetic simulations, later confronted to 3D kinetic and fluid simulations, and always in a close relationship with multi-mission space observations, at the magnetopause and in the solar wind, making an heavy use of innovative tools developed at the Institute for Research in Astrophysics and Planetology (IRAP), improving them and developing new ones. In october 2014, NASA will launch the major mission Magnetospheric MultiScale (MMS) to study the reconnection microphysics down to electron scales, and will explore the dayside magnetopause during its first phase. Our ambitious objectives are highly relevant to the MMS science priorities and very competitive. They will be reached by the gathering of the complementary strengths of the French space plasma community in theory, numerical modeling and space observations, together with the world leading experts in reconnection physics and its kinetic modeling, in a new and strong international collaboration, on a cross-disciplinary topic that is widely recognized as one of the most important and challenging one in experimental, spatial and astrophysical plasma communities. The project will be mainly performed at IRAP, but will also involve researchers from the Laboratory of Plasma Physics (LPP) and NASA Goddard Space Flight Center (GSFC). If the latter, building the MMS four satellites is obviously deeply engaged in the mission, IRAP and LPP are also strongly involved, as they both contribute to the spacecraft instrumentation. This project is at the heart of the IRAP Geophysical and Space Plasma group’s scientific activities, to which it will bring, as well as to the French astrophysical plasma community as a whole, a highly desirable expertise on numerical modeling of collisionless magnetic reconnection. It will be decomposed in five tasks, among which the coordination one and four scientific tasks based on a very strong theory/observation/simulation synergy and designed to deliver key results on reconnection physics, original databases, codes and innovative observational tools for the community.

CO2 recycling is a major environmental, economical and societal priority. Carbon capture technologies have improved significantly and instead of being a waste, CO2 could become a raw material for a “green” organic chemistry or fuel production. Many techniques are investigated to achieve an efficient conversion of CO2 and a lot of efforts are especially made in the development of new catalysts. However the difficulty to dissociate CO2 which is a strongly endothermic process still remains. Like any other molecular chemical reaction, the reactivity of CO2 in gas phase and on surfaces could be strongly enhanced if the CO2 molecule is vibrationally excited. Low Temperature Plasmas can excite molecules very efficiently with high vibrational levels. For pressures favorable to energy transfer between vibrational levels, typically between 10 to 300 mbar, up to 90% of the energy injected into LTP can be stored into vibrational excitation of molecules. Therefore an efficient coupling of highly vibrationally excited molecular plasmas with a catalyst surface is a promising approach for CO2 conversion or any other molecule conversion process. Plasma/catalysis coupling is usually studied at atmospheric pressure with non homogeneous filamentary plasmas and high collision rate converting vibrational energy into gas heating. On the contrary, the coupling of mid range pressure low temperature plasma (MP-LTP) with catalytic materials is an original approach that can advance the understanding of plasma kinetic and plasma/surface interaction in several respects. First, the vibrational kinetic of molecular plasmas, especially with CO2 and its three vibrational modes, still needs both experimental and modelisation works for an accurate description. Second, the possible role of vibrationally excited molecules on surface mechanisms (adsorption, reactivity, desorption) is still to a large extent unknown. Third, the enhanced reactivity of a population of molecules with a given vibrational distribution needs to be clarified. SYCAMORE aims to address these questions by using a combination of well controlled plasma sources and a set of time resolved is situ diagnostics, both in gas phase and on surfaces to achieve a deep understanding of plasma surface interaction at mid range pressures. Vibrational excitation of molecules is often seen in plasma physic as a loss of energy for sustaining the plasma. The vision behind this project is on the contrary that LTP have the appropriate mean electron energy to build up a large energy reservoir into vibrationally excited molecules that should be used for efficient chemical reactions. The little use made of highly vibrationally excited plasmas for chemical reactions certainly come from the complexity of vibrational kinetic in plasmas. SYCAMORE aims to know if reactions occurring on a surface exposed to plasma can take advantage of vibrationally excited molecules or not. Therefore the first plasma source will not be designed to optimize the vibrational excitation, but to make diagnostics (electric field, gas and vibrational temperatures, radicals and molecule densities) and modelisation easier in order to build an accurate kinetic model of pure CO2 plasmas. When a precise description of this source will be achieved, the influence of model surfaces such as porous SiO2, CaO or MgO will be evidence and quantify with both gas phase and surface in situ diagnostics, before suing these materials in combination with more efficient plasma sources. The results are expected to be generally useful to any CO2 conversion by plasma in pure CO2, or with CH4 and H2 for instance. It would be usefull also for the production of O2 for Mars exploration. The methods developed in SYCAMORE can later be efficiently applied for studying other molecule synthesis by plasma such as NO or NH3 production.