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Accueil > Séminaires & Soutenances > Séminaires, soutenances de thèses et HDR précédents > 2019 > Soutenances de thèses et HDR 2019 > Le mercredi 18 décembre 2019 à 11h
Le mercredi 18 décembre 2019 à 11h
Soutenance de thèse de Julien Guyot - Particle acceleration in colliding laser-produced plasmas
Location : Jussieu, towers 24-34, room 509
Abstract :
Energetic charged particles are ubiquitous in the Universe and are accelerated by galactic and extragalactic sources. Understanding the origin of these "cosmic rays" is crucial in astrophysics and within the framework of high-energy-density laboratory astrophysics we have developed a novel platform on the LULI laser facilities to study particle acceleration in the laboratory. In the experiments, the collision of two laser-produced counter-propagating plasmas generates a distribution of non-thermal particles with energies up to 1 MeV.
The aim of this work is to provide a theoretical framework to understand their origin. Magneto-hydrodynamic simulations with test particles show that the plasma collision leads to the growth of bubble and spike structures driven by the magnetic Rayleigh-Taylor instability and the generation of strong electric fields. We find that particles are accelerated to energies up to a few hundred of keV in less than 20 ns, by repeated interactions with these growing magnetic Rayleigh-Taylor perturbations. The simulations and a stochastic acceleration model recover very well the experimentally measured non-thermal energy spectrum. In conclusion, we have identified in the laboratory a new particle acceleration mechanism that relies on the growth of the magnetic Rayleigh-Taylor instability to stochastically energize particles. This instability is very common in astrophysical plasmas, with examples including supernovae remnants and coronal mass ejections, and we suggest that it may contribute to the energization of particles in these systems.
Dans la même rubrique :
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