Transformation de l'énergie électrique en PREcurseurs actifs par Plasmas Froids diffus à la Pression Atmosphérique – PREPA

Plasma discharges at atmospheric pressure are rapidly gaining popularity for their ability to produce active species in well-controlled environments and at very low energy cost. Their potential is now well established for a wide array of applications currently studied in the partner laboratories of this consortium. Applications include plasma-assisted combustion for the reduction of pollutant emissions, a topic studied in particular at EM2C, thin film coatings for encapsulation of organic components for portable electronics devices studied at LAPLACE, on-line plasma thin film coatings for photovoltaic cells studied at PROMES, and biomedical treatment and decontamination studied at LAPLACE and EM2C. The diversity of gases and discharge configurations used in these applications has led to numerous independent developments by many research laboratories worldwide. A concerted approach is now needed to bring together the advances of the various groups in order to resolve some of the key common roadblocks encountered for the range of applications investigated. The most pressing issue in the development of new reactors or new processing methods is to maximize and optimize the efficiency of energy deposition into the gas by increasing the discharge volume and the production of the desired active species. The goal of the present project is to follow a synergistic approach for two of the most promising low temperature discharge types: the dielectric barrier discharges (DBD) and the Nanosecond Repetitively Pulsed Discharges (NRPD). Although different in essence, these two types of discharges present many striking similarities, notably their ability to operate in a diffuse mode with comparable levels of power deposition. The central problem is to determine how to maximize the power deposited and how to optimize the energy transfer to create the desired active precursors, while maintaining discharge operation in the diffuse mode. It is of course unpractical to consider the entire spectrum of reactive gases utilized in the wide variety of applications of ultimate interest. However, the concentration of these reactive gases, which are often trace species, is largely determined by the excitation conditions of the main carrier gas, namely its temperature and degree of dissociation, ionization, and internal excitation. Our objective is therefore to focus on three types of carrier gases (nitrogen, air, and argon/ammonia) that are sufficiently representative of the range of applications of interest because they have different properties in terms of electronegativity, internal excitation and Penning processes. The aim of the proposed program is to investigate and understand how to control the energy branching in atmospheric pressure diffuse plasma and to increase the plasma power of diffuse low temperature plasma discharge at atmospheric pressure. From the results we will produce synthetic guidelines for choosing the most appropriate diffuse atmospheric plasma type and configuration according to the application requirements of end users. At the end of the project, each team will implement the most promising discharge type for its own applications. The scientific approach for this project follows three steps: first, we will determine the electric field and the gas temperature as well as the active precursors (positive and negative ions, radicals, metastable, vibrational and rotational excited states, electron energy distribution function, photons) in each mixture. Then, the influence of the parameters on the relative density of these different active precursors will be studied to understand the mechanisms controlling the energy branching and to investigate how to optimize this energy branching. The third step will be dedicated to finding how to increase the diffuse discharge power while maintaining the desired energy branching, in order to maximize the production of the active precursors of interest. To reach the objectives of the proposed work, we propose a dual approach combining experiments (PROMES, EM2C, LAPLACE) and advanced numerical modeling of the phenomena involved (EM2C, LGE, LAPLACE). The consortium brings together a multidisciplinary team of experts in plasma physics and plasma chemistry (LAPLACE, EM2C, LGE, PROMES), electrical engineering (LGE, LAPLACE) and optical diagnostics (EM2C, LAPLACE and on-going collaboration with national and international laboratories).