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Introduction to Low-temperature plasmas
"Cold plasmas" refer to all ionized gases where electrons can be heated to tens of thousands of degrees Kelvin, but the surrounding gas, as well as the positive ions, remain at temperatures closer to room temperature (although they can still reach hundreds of degrees). Since electrons are very light, they cannot transfer their "heat" to the heavier particles. This situation, where coexisting particles have different temperatures, is called "non-thermal equilibrium."
Two phenomena arise from this and characterize the specifics of cold plasmas:
- Positive ions can be accelerated towards the walls of reactors or other surfaces, inducing physical sputtering or promoting chemical processes.
- Electrons can transfer enough energy to neutral particles to make them chemically reactive, particularly through molecular dissociation and the excitation of very short-lived or (meta)stable energy states.
These two phenomena, either alone or in combination, or even in synergy, create a wide range of physical-chemical processes in the gas phase and on surfaces exposed to the plasma.
The low-temperature plasma team is dedicated to studying the physical-chemistry of these non-thermal equilibrium environments, covering a spectrum ranging from fundamental studies of atomic and molecular physics to technology transfer. This research involves experimental work based on innovative optical diagnostics and theoretical work, with a significant portion dedicated to cutting-edge numerical simulations. This close theory-experiment interaction is a cornerstone of the team, generating numerous publications among its members and addressing fundamental questions such as the coupling between the electromagnetic field and the plasma, plasma-surface interaction and chemical reactivity, particle transport and acceleration phenomena, and plasma-flow coupling, which are key points for various applications.
In the laboratory, these plasmas are generated by an external electromagnetic energy source inside reactors filled with gas. The control of external parameters such as pressure and gas composition, reactor geometry, and electrical power characteristics (frequency, pulse shape, amplitude) allows the creation of a wide range of systems to study.
