This research project focuses on the fundamental study of breakdown phenomena in gases at atmospheric pressure in micrometer gap systems. The prediction of gas breakdown in micro-gaps is still a wide topic to explore, since its understanding cannot be explained the classical breakdown theory. This project proposes to investigate the elementary processes involved in the present conditions, in particular the role of electron field emission via tunneling electrons. Several key parameters will be studied such as the electrode geometry, surface materials, gas, pressure, electrical excitation waveform. Advanced experiments will be conducted involving optical laser spectroscopy techniques. The main outcome of this project will support to refine understanding of breakdown in micro-gaps and will unveil substantial fundamental knowledge to explain the deviation of breakdown prediction derived from the scaling Paschen’s law.

The existence of an atmosphere enriched in H and He around the Earth as it formed has often been proposed. One hypothesis suggests that it could have been captured from the gas present in the proto-planetary disk, before its evaporation. Subsequently, a secondary atmosphere would have been degassed or brought in by a late veneer of chondritic/cometary material. Although this model is regularly evoked using giant planets for comparison, there is no geological proof for its existence, except possibly for the neon in the Earth's mantle. While the model has a flaw (mainly relating to chronology, as the gas from the disk is lost in <6 My while the Earth formed over a period of more than 30My), the solar-type neon in the Earth's mantle is an argument for the existence of such a captured atmosphere, which partially dissolved into a magma ocean. A second scenario for a primordial H2/He-rich atmosphere is the degassing of a mantle that contained implanted solar wind. The APATE project aims to study the isotopic composition of neon in the Earth's mantle in order to determine if this composition is the same as that of the nebula or the solar wind material. I will investigate the degassing processes of magmas experimentally and numerically in order to study the isotopic fractionation that occurs during bubble formation and to determine whether the measured neon isotopic composition can provide an accurate composition for the original mantle. The project aims to calculate the amount of neon that can be incorporated into a magma ocean by establishing the atmospheric pressure of the captured atmosphere and by studying the dynamics of the magma ocean. I will also explore the hypothesis involving solar wind irradiation. Using simulations of irradiation, I will identify those conditions under which this model is realistic and its implications for the Earth’s (isotopic/chemical) composition. The origin of light solar volatiles will then be explored by the APATE project.

Many engineering applications foreseen the usage of small particles for groundwater remediation or for sealing damaged geological confinement barriers, however, delivering materials to a contaminated or damaged region is challenging. TRACE-it aims at controlling the flow of colloidal particles in subsurface geological environments using in situ solute concentration gradients. The phenomenon, known as diffusiophoresis, has a tremendous potential to move colloids to regions that are inaccessible by conventional transport. Diffusiophoretic transport in porous media, however, has received very little attention so far, especially in standard transport in porous media models where it remains unconsidered. What is the magnitude and location of solute concentration gradients produced during subsurface processes? How to use these gradients to transport colloids towards target regions? The answers will be found through a combined experimental-modelling approach to: (i) measure coupled hydro-electro-chemical dynamics, (ii) characterize concentration gradients generated in situ in geological porous media, (iii) identify the influence of concentration gradients on particle transport and develop a macroscale model of transport in porous media that includes diffusiophoresis. TRACE-it integrates the usage of microfluidic experiments, observation techniques, and multi-scale computational fluid dynamics to describe the transport mechanisms at the pore-scale before upscaling to the continuum-scale. The experimental-modelling toolset will open new ways for moving colloidal particles by sensing chemical gradients generated naturally or from human activity, leading them to their target such as oil, contaminants, or reacting minerals. During column-scale experiments, controlling colloid transport will be achieved through the characterization of solute concentration gradients and the use of specifically designed particles.