Plans d'accès
Webmail
Accueil > A propos du LPP > Communication > Actualités archivées > 2021 > Alexis MARRET defended his PhD "The non-resonant streaming instability : from theory to experiment"
Alexis MARRET defended his PhD "The non-resonant streaming instability : from theory to experiment"
Toutes les versions de cet article : [English] [français]
Alexis MARRET defended his PhD "The non-resonant streaming instability : from theory to experiment" under the supervision of Andrea CIARDI (LERMA) and Roch SMETS (LPP), on November 15, 2021.
Summary
Cosmic rays can power the exponential growth of a seed magnetic field by exciting instabilities that feed on the kinetic energy of the particles collective streaming motion. Of the different streaming instabilities, the non-resonant mode, also called Bell’s mode, has received growing attention as it can amplify the magnetic field well beyond its initial intensity, and generate the necessary turbulence to help confine and accelerate cosmic rays in supernovae remnants and young stellar jets shocks via the first order Fermi mechanism. In general, it can develop in a large variety of environments, ranging from the cold and dense molecular clouds to the hot and diffuse intergalactic medium. This work aims at elucidating the behaviour of the non-resonant cosmic rays streaming instability in such environments, where thermal and collisional effects
can substantially modify its growth and saturation. In the first part of this thesis, we describe the instability within fluid theory by highlighting the basic physical mechanism leading to the exponential amplification of electromagnetic perturbations, and obtain analytical predictions for the growth rate for arbitrary ion elements. Owing to its non-resonant nature, a fluid description is a sufficiently accurate model of the instability only when the background plasma temperature is negligible. To study the instability in hot environments, where finite Larmor radius effects are important, we then resort to linear kinetic theory and extend the existing analytical results to the case of demagnetized ions. We find that the unstable wavelengths are not entirely suppressed, but are instead shifted toward larger scales with a strongly reduced growth rate. The linear theory results are confirmed, and extended to the non-linear evolution in the second part of the thesis, by multi-dimensional hybrid-Particle-In-Cell simulations (kinetic ions and fluid electrons). The simulations highlight an important reduction of the level of magnetic field amplification in the hot regime [Marret et al. MNRAS 2021], indicating that it may be limited in hot astrophysical plasmas such as in superbubbles or the intergalactic medium. In colder and denser environments, such as H II regions and molecular clouds, particle collisions in the background plasma must be taken into account. We investigate numerically their impact by including Monte-Carlo Coulomb and neutral collisions in the simulations. We find that in poorly ionized plasmas, where proton-hydrogen collisions dominate, the instability is rapidly suppressed and our results from kinetic simulations confirm quantitatively existing, multi-fluid linear theory calculations. In contrast, we find that in fully ionized plasmas, Coulomb collisions unexpectedly favour the development of the instability by reducing self-generated pressure anisotropies that would otherwise oppose its growth. Numerical simulations are currently the only means to investigate the non-linear evolution of the instability and to obtain quantitative estimates of the saturated magnetic field intensity. The final part of this thesis is devoted to answer the growing need for an experimental verification of the linear theory and simulations predictions. We describe the requirements on the plasma parameters to generate the instability in an experiment, and propose two possible setups based on existing high-power laser facilities, aiming at observing and characterizing the non-resonant mode for the first time in the laboratory.
Jury
M. Andrea CIARDI - Directeur de thèse
M. Roch SMETS - CoDirecteur de thèse
M. Julien FUCHS - Membre invité
Mme Katia FERRIèRE - Membre du jury
M. Fabien CASSE - Membre du jury
M. Nuno LOUREIRO - Membre du jury
Mme Laurence REZEAU - Membre du jury
M. Emmanuel D’HUMIèRES - Rapporteur du jury
M. Anatoly SPITKOVSKY - Rapporteur du jury
Dans la même rubrique :
- Création d’un groupe climat au LPP
- Audrey Chatain lauréate du prix solennel de thèse 2021 de la Chancellerie de Paris
- Georgy Pokrovskiy a soutenu sa thèse "Dissociation of carbon dioxide in pulsed plasma at high electric fields : role of energy exchange with electronically excited species"
- Olivier Le Contel a soutenu son HDR "Processus cinétiques et fluides dans les plasmas non collisionnels du système solaire"
- Prix de thèse DGA remis à Constance Duchesne pour ses travaux de recherche sur l’application des plasmas froids pour la cicatrisation des plaies cutanées
- Mhedine Alicherif a soutenu sa thèse "Étude de l’interaction des plasmas hors équilibre et des détonations : réduction de la largeur des cellules et longueur de transition"
- La start-up ThrustMe publie un article dans Nature sur les premiers résultats en vol d’un propulseur à iode
- La 12ème édition de l’European Cubesat Symposium se tiendra du 24 au 26 Novembre à l’Ecole polytechnique
- Alexis MARRET a soutenu sa thèse "The non-resonant streaming instability : from theory to experiment"
- Le LPP participe à la Fête de la Science 2021
- Coordination des observations multi-satellites durant la phase de croisière de BepiColombo
- Renaud Ferrand a soutenu sa thèse "Turbulence multi-échelles compressible dans les plasmas astrophysiques : une approche théorique, numérique et observationnelle"
- Turbulence d’ondes gravitationnelles
- Contribution du LPP à un important article de synthèse sur les plasmas de CO2
- Un nouveau modèle de cascade 2D décrivant turbulence plasma et atmosphérique
- Hanen Oueslati a soutenu sa thèse "Modélisation et simulation des plasmas de tokamak : états stationnaires axisymétriques à flot non nul"
- Chenyang Ding a soutenu sa thèse sur "l’Etude expérimentale des paramètres du plasma dans la décharge filamentaire à barrière diélectrique de surface nanoseconde"
- Mesure directe de la section efficace d’absorption à deux photons du xénon et son impact sur les mesures des densités d’oxygène atomique par la méthode TALIF dans les plasmas froids
- Sébastien Galtier publie un nouveau livre « Physique de la turbulence : des tourbillons aux ondes »
- Nadira Frescaline a soutenu son habilitation à diriger des recherches sur « invasion microbienne de la peau : nouvelles modalités de diagnostic et approches de traitement »
