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International audience; We prove a uniqueness result for weak solutions to the Vlasov-Navier-Stokes system in two dimensions, both in the whole space and in the periodic case, under a mild decay condition on the initial distribution function. The main result is achieved by combining methods from optimal transportation (introduced in this context by G. Loeper) with the use of Hardy's maximal function, in order to obtain some fine Wassestein-like estimates for the difference of two solutions of the Vlasov equation.

We study the linearized Vlasov–Poisson system around suitably stable homogeneous equilibria on $${\mathbb {R}}^d\times {\mathbb {R}}^d$$ (for any $$d \ge 1$$ ) and establish dispersive $$L^\infty $$ decay estimates in the physical space.

We study the large time behaviour of small data solutions to the Vlasov–Navier–Stokes system set on Ω × R 3 , for a smooth bounded domain Ω of R 3 , with homogeneous Dirichlet boundary condition for the fluid and absorption boundary condition for the kinetic phase. We prove that the fluid velocity homogenizes to 0 while the distribution function concentrates towards a Dirac mass in velocity centred at 0, with an exponential rate. The proof, which follows the methods introduced in Han-Kwan et al (2020 Arch. Ration. Mech. Anal. 236 1273–323), requires a careful analysis of the boundary effects. We also exhibit examples of classes of initial data leading to a variety of asymptotic behaviours for the kinetic density, from total absorption to no absorption at all.

Vlasov equations can be formally derived from N-body dynamics in the mean-field limit. In some suitable singular limits, they may themselves converge to fluid dynamics equations. Motivated by this heuristic, we introduce natural scalings under which the incompressible Euler equations can be rigorously derived from N-body dynamics with repulsive Coulomb interaction. Our analysis is based on the modulated energy methods of Brenier and Serfaty., Minor typos corrected

This work is concerned with the quasineutral limit of the Vlasov–Poisson system in two and three dimensions. We justify the formal limit for very small but rough perturbations of analytic initial data, generalizing the results of [12] to higher dimension.

International audience; We study the large time behavior of Fujita–Kato type solutions to the Vlasov–Navier–Stokes system set on $\T^3 \times \R^3$. Under the assumption that the initial so-called modulated energy is small enough, we prove that the distribution function converges to a Dirac mass in velocity, with exponential rate. The proof is based on the fine structure of the system and on a bootstrap analysis allowing us to get global bounds on moments.

We revisit the proof of Landau damping near stable homogenous equilibria of Vlasov-Poisson systems with screened interactions in the whole space $\mathbb{R}^d$ (for $d\geq3$) that was first established by Bedrossian, Masmoudi and Mouhot. Our proof follows a Lagrangian approach and relies on precise pointwise in time dispersive estimates in the physical space for the linearized problem that should be of independent interest. This allows to cut down the smoothness of the initial data required in Bedrossian at al. (roughly, we only need Lipschitz regularity). Moreover, the time decay estimates we prove are essentially sharp, being the same as those for free transport, up to a logarithmic correction., Comment: 25 pages, minor typos fixed

International audience; In this paper, we study the Vlasov-Maxwell system in the non-relativistic limit, that is in the regime where the speed of light is a very large parameter. We consider data lying in the vicinity of homogeneous equilibria that are stable in the sense of Penrose (for the Vlasov-Poisson system), and prove Sobolev stability estimates that are valid for times which are polynomial in terms of the speed of light and of the inverse of size of initial perturbations. We build a kind of higher-order Vlasov-Darwin approximation which allows us to reach arbitrarily large powers of the speed of light.

International audience; We study the quasineutral limit of a Vlasov-Poisson system that describes the dynamics of ions in a plasma. We handle data with Sobolev regularity under the sharp assumption that the profile of the initial data in the velocity variable satisfies a Penrose stability condition. As a by-product of our analysis, we obtain a well-posedness theory for the limit equation (which is a Vlasov equation with Dirac distribution as interaction kernel) for such data.

In this paper, we study the controllability of the two-dimensional relativistic Vlasov-Maxwell system in a torus, by means of an interior control. We give two types of results. With the geometric control condition on the control set, we prove the local exact controllability of the system in large time. Our proof in this case is based on the return method, on some results on the control of the Maxwell equations, and on a suitable approximation scheme to solve the non-linear Vlasov-Maxwell system on the torus with an absorption procedure. Without geometric control condition, but assuming that a strip of the torus is contained in the control set and under certain additional conditions on the initial data, we establish a controllability result on the distribution function only, also in large time. Here, we need some additional arguments based on the asymptotics of the Vlasov-Maxwell system with large speed of light and on our previous results concerning the controllability of the Vlasov-Poisson system with an external magnetic field [14].

We prove local exact controllability in arbitrary short time of the two-dimensional incompressible Euler equation with free surface, in the case with surface tension. This proves that one can generate arbitrary small amplitude periodic gravity-capillary water waves by blowing on a localized portion of the free surface of a liquid., Comment: 71 pages

This work is concerned with the broad question of propagation of regularity for smooth solutions to nonlinear Vlasov equations. For a class of equations (that includes Vlasov–Poisson and relativistic Vlasov–Maxwell systems), we prove that higher regularity in space is propagated, locally in time, into higher regularity for the moments in velocity of the solution. This in turn can be translated into some anisotropic Sobolev higher regularity for the solution itself, which can be interpreted as a kind of weak propagation of space regularity. To this end, we adapt the methods introduced by D. Han-Kwan and F. Rousset (Ann. Sci. Ecole Norm. Sup. 49:6 (2016) 1445–1495) in the context of the quasineutral limit of the Vlasov–Poisson system.

We introduce a long wave scaling for the Vlasov-Poisson equation and derive, in the cold ions limit, the Korteweg-De Vries equation (in 1D) and the Zakharov-Kuznetsov equation (in higher dimensions, in the presence of an external magnetic field). The proofs are based on the relative entropy method.

In this work, we study the quasineutral limit of the one-dimensional Vlasov-Poisson equation for ions with massless thermalized electrons. We prove new weak-strong stability estimates in the Wasserstein metric that allow us to extend and improve previously known convergence results. In particular, we show that given a possibly unstable analytic initial profile, the formal limit holds for sequences of measure initial data converging sufficiently fast in the Wasserstein metric to this profile. This is achieved without assuming uniform analytic regularity.

International audience; In this paper, we study the Vlasov-Navier-Stokes system in a 2D pipe with partially absorbing boundary conditions. We show the existence of stationary states for this system near small Poiseuille flows for the fluid phase, for which the kinetic phase is not trivial. We prove the asymptotic stability of these states with respect to appropriately compactly supported perturbations. The analysis relies on geometric control conditions which help to avoid any concentration phenomenon for the kinetic phase.

We consider a strongly magnetized plasma described by a Vlasov-Poisson system with a large external magnetic field. The finite Larmor radius scaling allows to describe its behaviour at very fine scales. We give a new interpretation of the asymptotic equations obtained by Frenod and Sonnendrucker [SIAM J. Math. Anal. 32 (2001) 1227–1247] when the intensity of the magnetic field goes to infinity. We introduce the so-called polarization drift and show that its contribution is not negligible in the limit, contrary to what is usually said. This is due to the non linear coupling between the Vlasov and Poisson equations.

Consider a system of $N$ particles interacting through Newton's second law with Coulomb interaction potential in one spatial dimension or a $\mathcal{C}^2$ smooth potential in any dimension. We prove that in the mean field limit $N \to + \infty$, the $N$ particles system displays instabilities in times of order $\log N$ for some configurations approximately distributed according to unstable homogeneous equilibria., Comment: minor typos corrected; Journal of Statistical Physics, accepted

We study the instability of solutions to the relativistic Vlasov--Maxwell systems in two limiting regimes: the classical limit when the speed of light tends to infinity and the quasineutral limit when the Debye length tends to zero. First, in the classical limit, $\varepsilon \to 0$, with $\varepsilon$ being the inverse of the speed of light, we construct a family of solutions that converge initially polynomially fast to a homogeneous solution $\mu$ of Vlasov--Poisson systems in arbitrarily high Sobolev norms, but become of order one away from $\mu$ in arbitrary negative Sobolev norms within time of order $|\log \varepsilon|$. Second, we deduce the invalidity of the quasineutral limit in $L^2$ in arbitrarily short time.

We study a two-fluid description of high and low temperature components of the electron velocity distribution of an idealized tokamak plasma. We refine previous results on the laminar steady-state solution. On the one hand, we prove global stability outside a parameter set of possible linear instability. On the other hand, for a large set of parameters, we prove the primary instabilities for varying temperature difference stem from the lowest spatial harmonics. We moreover show that any codimension-one bifurcation is a supercritical Andronov-Hopf bifurcation, which yields stable periodic solutions in the form of traveling waves. In the degenerate case, where the instability region in the temperature difference is a point, we prove that the bifurcating periodic orbits form an arc of stable periodic solutions. We provide numerical simulations to illustrate and corroborate our analysis. These also suggest that the stable periodic orbit, which bifurcated from the steady-state, undergoes additional bifurcations., 25 pages

International audience; In this paper, we study the quasineutral limit of the isothermal Euler-Poisson equation for ions, in a domain with boundary. This is a follow-up to our previous work \cite{GVHKR}, devoted to no-penetration as well as subsonic outflow boundary conditions. We focus here on the case of supersonic outflow velocities. The structure of the boundary layers and the stabilization mechanism are different.

This work is devoted to the analysis of the linear Boltzmann equation on the torus, in the presence of a force deriving from a potential. The collision operator is allowed to be degenerate in the following two senses: (1) the associated collision kernel may vanish in a large subset of the phase space; (2) we do not assume that it is bounded below by a Maxwellian at infinity in velocity. We study how the association of transport and collision phenomena can lead to convergence to equilibrium, using concepts and ideas from control theory. We prove two main classes of results. On the one hand, we show that convergence towards an equilibrium is equivalent to an almost everywhere geometric control condition. The equilibria (which are not necessarily Maxwellians with our general assumptions on the collision kernel) are described in terms of the equivalence classes of an appropriate equivalence relation involving transport and collisions. On the other hand, we characterize the exponential convergence to equilibrium in terms of the Lebeau constant, which involves some averages of the collision frequency along the flow of the transport. We also explain how to handle the case of linear Boltzmann equations posed on the phase space associated to a compact Riemannian manifold without boundary.

This work is concerned with the quasineutral limit of the one-dimensional Vlasov-Poisson equation, for initial data close to stationary homogeneous profiles. Our objective is threefold: first, we provide a proof of the fact that the formal limit does not hold for homogeneous profiles that satisfy the Penrose instability criterion. Second, we prove on the other hand that the limit is true for homogeneous profiles that satisfy some monotonicity condition, together with a symmetry condition. We handle the case of well-prepared as well as ill- prepared data. Last, we study a stationary boundary-value problem for the formal limit, the so-called quasineutral Vlasov equation. We show the existence of numerous stationary states, with a lot of freedom in the construction (compared to that of BGK waves for Vlasov-Poisson): this illustrates the degeneracy of the limit equation., 50 pages

We study the quasineutral limit of the isothermal Euler-Poisson system describing a plasma made of ions and massless electrons. The analysis is achieved in a domain of $\R^3$ and thus extends former results by Cordier and Grenier [Comm. Partial Differential Equations, 25 (2000), pp.~1099--1113], who dealt with the same problem in a one-dimensional domain without boundary., Comment: 32 pages

The purpose of this note is to extend the $L^1$ averaging lemma of Golse and Saint-Raymond \cite{GolSR} to the case of a kinetic transport equation with a force field $F(x)\in W^{1,\infty}$. To this end, we will prove a local in time mixing property for the transport equation $\partial_t f + v.\nabla_x f + F.\nabla_v f =0$., Comment: 15 pages, to be published in Kinetic and Related Models

In this paper, we study the quasineutral limit (in other words the limit when the Debye length tends to zero) of Vlasov-Poisson like equations describing the behaviour of ions in a plasma. We consider massless electrons, with a charge density following a Maxwell-Boltzmann law. For cold ions, using the relative entropy method, we derive the classical Isothermal Euler or the (inviscid) Shallow Water systems from fluid mechanics. In a second time, we study the combined quasineutral and strong magnetic field regime for such plasmas., Comment: 37 pages

This paper is concerned with the analysis of a mathematical model arising in plasma physics, more specifically in fusion research. It directly follows \cite{DHK1}, where the tri-dimensional analysis of a Vlasov-Poisson equation with finite Larmor radius scaling was led, corresponding to the case of ions with massless electrons whose density follows a linearized Maxwell-Boltzmann law. We now consider the case of electrons in a background of fixed ions, which was only sketched in \cite{DHK1}. Unfortunately, there is evidence that the formal limit is false in general. Nevertheless, we formally derive a fluid system for particular monokinetic data. We prove the local in time existence of analytic solutions and rigorously study the limit (when the Debye length vanishes) to a new anisotropic fluid system. This is achieved thanks to Cauchy-Kovalevskaya type techniques, as introduced by Caflisch \cite{Caf} and Grenier \cite{Gre1}., Comment: 28 pages

The goal of this paper is to understand from a mathematical point of view the magnetic confinement of plasmas for fusion. Following Fr\'enod and Sonnendr\"ucker \cite{FS2}, we first use two-scale convergence tools to derive a gyrokinetic system for a plasma submitted to a large magnetic field with a slowly spatially varying intensity. We formally derive from this system a simplified bi-temperature fluid system. We then investigate the behaviour of the plasma in such a regime and we prove nonlinear stability or instability depending on which side of the tokamak we are looking at. In our analysis, we will also point out that there exists a temperature gradient threshold beyond which one can expect stability, even in the "bad" side : this corresponds to the so-called H-mode., Comment: 31 pages, accepted for publication in SIAM J. Math. Anal.

Following Frenod and Sonnendrucker (SIAM J. Math. Anal. 32(6) (2001) 1227-1247), we consider the finite Larmor radius regime for a plasma submitted to a large magnetic field and take into account both the quasineutrality and the local thermodynamic equilibrium of the electrons. We then rigorously establish the asymptotic gyrokinetic limit of the rescaled and modified Vlasov-Poisson system in a three-dimensional setting with the help of an averaging lemma.

In this work, we are interested in the controllability of Vlasov–Poisson systems in the presence of an external force field (namely a bounded force field or a magnetic field), by means of a local interior control. We are able to extend the results of Glass (2003) [8], where the only present force was the self-consistent electric field.

In this dissertation, we study the Vlasov-Maxwell system of partial differential equations, describing the evolution of the distribution function of charged particles in a plasma. More precisely, we study the regularity of solutions to this system, and the question of the non-relativstic limit.In the first part, we study a Toy-model, combining the Vlasov equation with a system of transport equations. We use the methods developed to obtain and imrpove the Glassey-Strauss criterion, which gives a sufficient condition under which strong solutions do not develop singularities. The loss of regularity occures when the speed of the particles is close to the characteristic speed of the joined hyperbolic system. The same phenomenon occures for the solutions of the Toy-model, but its structure is easier to handle.In the second part, we focus on the question of the non-relativistic limit. After a rescaling of the equations, the speed of light can be considered as a big parameter. When it tends to infinity, it is called the non-relativistic limit. At first order, the non-relativistic limit of the Vlasov-Maxwell system is the Vlasov-Poisson system. First, an iterative method giving arbitrary high non-relativistic approximations is established. These systems combine the Vlasov-equation with elliptic systems of equations, and are well-posed in some weigthed Sobolev spaces. We also prove a result on the non-relativistic limit to the Vlasov-Poisson system under the weaker assumption of boundedness of the macroscopic density. We study a functional quantifying the Wasserstein distance between weak solutions of both systems.; Cette thèse est consacrée à l'étude du système d'équations aux dérivées partielles de Vlasov-Maxwell qui décrit l'évolution au cours du temps de la fonction de distribution de particules chargées dans un plasma. Nos travaux portent plus particulièrement sur la régularité des solutions de ce système et le problème de la limite non-relativiste.Dans un premier temps, on étudie un modèle jouet combinant une équation de Vlasov et un système d'équations de transport. On utilise les méthodes utilisées pour obtenir et améliorer le critère de Glassey-Strauss qui donne une condition suffisante sous laquelle une solution forte du système de Vlasov-Maxwell ne développe pas de singularités. La perte de régularité se manifeste lorsque la vitesse des particules est proche de la vitesse de résonnance du système hyperbolique adjoint. Le même phénomène se produit pour les solutions de notre système jouet, mais il possède une structure moins complexe.Dans un deuxième temps, on aborde la question de la limite non relativiste. Après adimensionnement, la vitesse de la lumière peut être considérée comme un grand paramètre du système. Lorsque celui ci tend vers l'infini, on parle de limite non-relativiste. Au premier ordrer, la limite non relativiste du système de Vlasov-Maxwell est le système de Vlasov-Poisson. Dans un premier chapitre, on établit une méthode itérative qui permet formellement d'obtenir des systèmes couplant l'équation de Vlasov à un système elliptique et formant une approximation non relativiste d'ordre arbitrairement élevé du système de Vlasov-Maxwell. Ces systèmes sont de plus bien posés dans certains espaces de Sobolev. Dans un second chapitre on démontre un résultat de limite non relativiste vers le système de Vlasov-Poisson sous des conditions ne portant que sur la densité macroscopique de charges. Pour ce faire on étudie une fonctionnelle quantifiant la distance de Wasserstein entre les solutions faibles des deux systèmes.

In this dissertation, we study the Vlasov-Maxwell system of partial differential equations, describing the evolution of the distribution function of charged particles in a plasma. More precisely, we study the regularity of solutions to this system, and the question of the non-relativstic limit.In the first part, we study a Toy-model, combining the Vlasov equation with a system of transport equations. We use the methods developed to obtain and imrpove the Glassey-Strauss criterion, which gives a sufficient condition under which strong solutions do not develop singularities. The loss of regularity occures when the speed of the particles is close to the characteristic speed of the joined hyperbolic system. The same phenomenon occures for the solutions of the Toy-model, but its structure is easier to handle.In the second part, we focus on the question of the non-relativistic limit. After a rescaling of the equations, the speed of light can be considered as a big parameter. When it tends to infinity, it is called the non-relativistic limit. At first order, the non-relativistic limit of the Vlasov-Maxwell system is the Vlasov-Poisson system. First, an iterative method giving arbitrary high non-relativistic approximations is established. These systems combine the Vlasov-equation with elliptic systems of equations, and are well-posed in some weigthed Sobolev spaces. We also prove a result on the non-relativistic limit to the Vlasov-Poisson system under the weaker assumption of boundedness of the macroscopic density. We study a functional quantifying the Wasserstein distance between weak solutions of both systems., Cette thèse est consacrée à l'étude du système d'équations aux dérivées partielles de Vlasov-Maxwell qui décrit l'évolution au cours du temps de la fonction de distribution de particules chargées dans un plasma. Nos travaux portent plus particulièrement sur la régularité des solutions de ce système et le problème de la limite non-relativiste.Dans un premier temps, on étudie un modèle jouet combinant une équation de Vlasov et un système d'équations de transport. On utilise les méthodes utilisées pour obtenir et améliorer le critère de Glassey-Strauss qui donne une condition suffisante sous laquelle une solution forte du système de Vlasov-Maxwell ne développe pas de singularités. La perte de régularité se manifeste lorsque la vitesse des particules est proche de la vitesse de résonnance du système hyperbolique adjoint. Le même phénomène se produit pour les solutions de notre système jouet, mais il possède une structure moins complexe.Dans un deuxième temps, on aborde la question de la limite non relativiste. Après adimensionnement, la vitesse de la lumière peut être considérée comme un grand paramètre du système. Lorsque celui ci tend vers l'infini, on parle de limite non-relativiste. Au premier ordrer, la limite non relativiste du système de Vlasov-Maxwell est le système de Vlasov-Poisson. Dans un premier chapitre, on établit une méthode itérative qui permet formellement d'obtenir des systèmes couplant l'équation de Vlasov à un système elliptique et formant une approximation non relativiste d'ordre arbitrairement élevé du système de Vlasov-Maxwell. Ces systèmes sont de plus bien posés dans certains espaces de Sobolev. Dans un second chapitre on démontre un résultat de limite non relativiste vers le système de Vlasov-Poisson sous des conditions ne portant que sur la densité macroscopique de charges. Pour ce faire on étudie une fonctionnelle quantifiant la distance de Wasserstein entre les solutions faibles des deux systèmes.

Ce mémoire présente les travaux réalisés au cours de ma thèse dans le but d’étudier la contrôlabilité de quelques équations aux dérivées partielles.La première partie de cette thèse est consacrée à l’étude de la contrôlabilité de quelques équations cinétiques dans différents régimes. Dans un régime collisionnel, nous étudions la contrôlabilité de l’équation de Kolmogorov, un modèle de type Fokker-Planck cinétique, posée dans l’espace de phases R d ×R d . Nous obtenons la contrôlabilité à zéro de cette équation grâce à l’utilisation d’une inégalité spectrale associée à l’opérateur Laplacien dans tout l’espace. Dans un régime non-collisionnel, nous étudions la contrôlabilité de deux systèmes de couplage fluide-cinétique, les systèmes de Vlasov-Stokes et de Vlasov-Navier-Stokes, comportant des non-linéarités dues au terme de couplage. Dans ces cas, l’approche repose sur la méthode du retour.Dans la deuxième partie nous étudions la contrôlabilité d’une famille d’équations paraboliques dégénérées 1-D par la méthode de platitude, qui permet la constructions de contrôles explicites.La troisième partie porte sur le problème de la contrôlabilité de l’équation de Schrödinger par la forme du domaine, c’est-à-dire, en utilisant le domaine comme variable de contrôle. Nous obtenons un résultat de ce type dans le cas du disque unité bidimensionnel. Nos méthodes sont basées sur un résultat de contrôle exact local autour d’une certaine trajectoire, obtenu grâce au théorème d’inversion locale.; This memoir presents the results obtained during my PhD, whose goal is the study of the controllability of some PartialDifferential Equations.The first part of this thesis is concerned with the study of the controllability of some kinetic equations undergoing differentregimes. Under a collisional regime, we study the controllability of the Kolmogorov equation, a particular case of kinetic Fokker-Planck equation, in the phase space R d × R d . We obtain the null-controllability of this equation thanks to the use of a spectral inequality associated to the Laplace operator in the whole space. Under a non-collisional regime, we study the controllability of two fluid-kinetic models, the Vlasov-Stokes system and the Vlasov-Navier-Stokes system, which exhibe nonlinearities due to the coupling terms. In those cases, the strategy relies on the Return method.In the second part, we study the controllability of a family of 1-D degenerate parabolic equations by the flatness method,which allows the construction of explicit controls.The third part is focused on the problem of the controllability of the Schrödinger equation via domain deformations, i.e., using the domain as a control. We obtain a result of this kind in the case of the two-dimensional unit disk, for radial data. Our methods are based on a local exact controllability result around a certain trajectory, obtained thanks to the Inverse Mapping theorem.