Dissertations / Theses on the topic 'Vlasov's theory'

This thesis is focused on the structural behaviour of high-rise buildings subjected to transversal loads expressed in terms of shears and torsional moments. As horizontal reinforcement, the resistant skeleton of the construction can be composed by different vertical bracings, such as shear walls, braced frames and thin-walled open section profiles, having constant or variable geometrical properties along the height. In this way, most of the traditional structural schemes can be modelled, from moment resisting frames up to outrigger and tubular systems. In particular, an entire chapter is addressed to the case of thin-walled open section shear walls which are defined by a coupled flexural-torsional behaviour, as described by Vlasov’s theory of the sectorial areas. From the analytical point of view, the three-dimensional formulation proposed by Al. Carpinteri and An. Carpinteri (1985) is considered and extended in order to perform dynamic analyses and encompass innovative structural solutions which can twist and taper from the bottom to the top of the building. Such approach is based on the hypothesis of in-plane infinitely rigid floors which assure the connection between the vertical bracings and, consequently, reduce the number of degrees of freedom being only three for each level. By means of it, relevant design information such as the floor displacements, the external load distribution between the structural components, the internal actions, the free vibrations as well as the mode shapes can be quickly obtained. The clearness and the conciseness of the matrix formulation allow to devise a simple computer program which, starting from basic information as the building geometry, the number and type of vertical stiffening, the material properties and the intensity of the external forces, provides essential results for preliminary designs.

The Vlasov equation of kinetic theory is introduced and the Hamiltonian structure of its moments is presented. Then we focus on the geodesic evolution of the Vlasov moments [1.2]. As a first step, these moment equations generalize the Camassa-Holm equation [3] to its multi-component version [4]. Subsequently, adding electrostatic forces to the geodesic moment equations relates them to the Benney equations [5] and to the equations for beam dynamics in particle accelerators. Next, we develop a kinetic theory for self assembly in nano-particles. The Darcy law [6] is introduced as a general principle for aggregation dynamics in friction dominated systems (at different scales). Then, a kinetic equation is introduced [7,8] for the dissipative motion of isotropic nano-particles. The zeroth-moment dynamics of this equation recovers the classical Darcy law at the macroscopic level [7]. A kinetic-theory description for oriented nano-particles is also presented [9]. At the macroscopic level, the zeroth moments of this kinetic equation recover the magnetization dynamics of the Landau-Lifshitz-Gilbert equation [10]. The moment equations exhibit the spontaneous emergence of singular solutions (clumpons) that finally merge in one singularity. This behaviour represents aggregation and alignment of oriented nano-particles. Finally, the Smoluchowsky description is derived from the dissipative Vlasov equation for anisotropic interactions. Various levels of approximate Smoluchowsky descriptions are proposed as special cases of the general treatment. As a result, the macroscopic momentum emerges as an additional dynamical variable that in general cannot be neglected.

Thesis (Ph.D.)--City University of Hong Kong, 2009.
"Submitted to Department of Mathematics in partial fulfillment of the requirements for the degree of Doctor of Philosophy." Includes bibliographical references (leaves [90]-94)

The Vlasov technique is used to model the electron cooling force. Limitations of the applicability of the method is obtained by considering the perturbations of the electron plasma. Analytical expressions of the electron cooling force, valid beyond the Coulomb logarithm approximation, are derived and compared to numerical calculations using adaptive Monte Carlo integration. The calculated longitudinal cooling force is verified with measurements in CELSIUS. Transverse damping rates of betatron oscillations for a nonlinear cooling force is explored. Experimental data of the transverse monochromatic instability is used to determine the rms angular spread due to solenoid field imperfections in CELSIUS. The result, θrms= 0.16 ± 0.02 mrad, is in agreement with the longitudinal cooling force measurements. This verifies the internal consistency of the model and shows that the transverse and longitudinal cooling force components have different velocity dependences. Simulations of electron cooling with applications to HESR show that the momentum reso- lution ∆p/p smaller than 10−5 is feasible, as needed for the charmonium spectroscopy in the experimental program of PANDA. By deflecting the electron beam angle to make use of the monochromatic instability, a reasonable overlap between the circulating antiproton beam and the internal target can be maintained. The simulations also indicate that the cooling time is considerably shorter than expected.

Kinetic microinstabilities in the solar wind arise when its non-thermal properties become too extreme. This thesis project focused specifically on the four instabilities associated with ion temperature anisotropy: the cyclotron, mirror, and parallel and oblique firehose instabilities. Numerous studies have provided evidence that proton temperature anisotropy in the solar wind is limited by the actions of these instabilities. For this project, a fully revised analysis of data from the Wind spacecraft's Faraday cups and calculations from linear Vlasov theory were used to extend these findings in two respects. First, theoretical thresholds were derived for the \(\alpha\)-particle temperature anisotropy instabilities, which were then found to be consistent with a statistical analysis of Wind \(\alpha\)-particle data. This suggests that \(\alpha\)-particles, which constitute only about 5% of ions in the solar wind, are nevertheless able to drive temperature anisotropy instabilities. Second, a statistical analysis of Wind proton data found that proton temperature was significantly enhanced in plasma unstable due to proton temperature anisotropy. This implies that extreme proton temperature anisotropies in solar wind at 1 AU arise from ongoing anisotropic heating (versus cooling from, e.g., CGL double adiabatic expansion). Together, these results provide further insight into the complex evolution of the solar wind's non-fluid properties.
Astronomy

Vlasov-Maxwell equilibria are characterised by the self-consistent descriptions of the steady-states of collisionless plasmas in particle phase-space, and balanced macroscopic forces. We study the theory of Vlasov-Maxwell equilibria in one spatial dimension, as well as its application to current sheet and flux tube models. The ‘inverse problem' is that of determining a Vlasov-Maxwell equilibrium distribution function self-consistent with a given magnetic field. We develop the theory of inversion using expansions in Hermite polynomial functions of the canonical momenta. Sufficient conditions for the convergence of a Hermite expansion are found, given a pressure tensor. For large classes of DFs, we prove that non-negativity of the distribution function is contingent on the magnetisation of the plasma, and make conjectures for all classes. The inverse problem is considered for nonlinear ‘force-free Harris sheets'. By applying the Hermite method, we construct new models that can describe sub-unity values of the plasma beta (βpl) for the first time. Whilst analytical convergence is proven for all βpl, numerical convergence is attained for βpl = 0.85, and then βpl = 0.05 after a ‘re-gauging' process. We consider the properties that a pressure tensor must satisfy to be consistent with ‘asymmetric Harris sheets', and construct new examples. It is possible to analytically solve the inverse problem in some cases, but others must be tackled numerically. We present new exact Vlasov-Maxwell equilibria for asymmetric current sheets, which can be written as a sum of shifted Maxwellian distributions. This is ideal for implementations in particle-in-cell simulations. We study the correspondence between the microscopic and macroscopic descriptions of equilibrium in cylindrical geometry, and then attempt to find Vlasov-Maxwell equilibria for the nonlinear force-free ‘Gold-Hoyle' model. However, it is necessary to include a background field, which can be arbitrarily weak if desired. The equilibrium can be electrically non-neutral, depending on the bulk flows.

Thesis (Ph.D.)--City University of Hong Kong, 2009.
"Submitted to Department of Mathematics in partial fulfillment of the requirements for the degree of Doctor of Philosophy." Includes bibliographical references (leaves [84]-87)

Cette thèse contient deux parties. Dans la première partie, on démontre deux théorèmes limites de la quantification optimale. Le premier théorème limite est la caractérisation de la convergence sous la distance de Wasserstein d’une suite de mesures de probabilité par la convergence simple des fonctions d’erreur de la quantification. Ces résultats sont établis en Rd et également dans un espace de Hilbert séparable. Le second théorème limite montre la vitesse de convergence des grilles optimales et la performance de quantification pour une suite de mesures de probabilité qui convergent sous la distance de Wasserstein, notamment la mesure empirique. La deuxième partie de cette thèse se concentre sur l’approximation et la simulation de l’équation de McKean-Vlasov. On commence cette partie par prouver, par la méthode de Feyel (voir Bouleau (1988)[Section 7]), l’existence et l’unicité d’une solution forte de l’équation de McKean-Vlasov dXt = b(t, Xt, μt)dt + σ(t, Xt, μt)dBt sous la condition que les fonctions de coefficient b et σ sont lipschitziennes. Ensuite, on établit la vitesse de convergence du schéma d’Euler théorique de l’équation de McKean-Vlasov et également les résultats de l’ordre convexe fonctionnel pour les équations de McKean-Vlasov avec b(t,x,μ) = αx+β, α,β ∈ R. Dans le dernier chapitre, on analyse l’erreur de la méthode de particule, de plusieurs schémas basés sur la quantification et d’un schéma hybride particule- quantification. À la fin, on illustre deux exemples de simulations: l’équation de Burgers (Bossy and Talay (1997)) en dimension 1 et le réseau de neurones de FitzHugh-Nagumo (Baladron et al. (2012)) en dimension 3
This thesis contains two parts. The first part addresses two limit theorems related to optimal quantization. The first limit theorem is the characterization of the convergence in the Wasserstein distance of probability measures by the pointwise convergence of Lp-quantization error functions on Rd and on a separable Hilbert space. The second limit theorem is the convergence rate of the optimal quantizer and the clustering performance for a probability measure sequence (μn)n∈N∗ on Rd converging in the Wasserstein distance, especially when (μn)n∈N∗ are the empirical measures with finite second moment but possibly unbounded support. The second part of this manuscript is devoted to the approximation and the simulation of the McKean-Vlasov equation, including several quantization based schemes and a hybrid particle-quantization scheme. We first give a proof of the existence and uniqueness of a strong solution of the McKean- Vlasov equation dXt = b(t, Xt, μt)dt + σ(t, Xt, μt)dBt under the Lipschitz coefficient condition by using Feyel’s method (see Bouleau (1988)[Section 7]). Then, we establish the convergence rate of the “theoretical” Euler scheme and as an application, we establish functional convex order results for scaled McKean-Vlasov equations with an affine drift. In the last chapter, we prove the convergence rate of the particle method, several quantization based schemes and the hybrid scheme. Finally, we simulate two examples: the Burger’s equation (Bossy and Talay (1997)) in one dimensional setting and the Network of FitzHugh-Nagumo neurons (Baladron et al. (2012)) in dimension 3

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

The subject of the thesis is the derivation of non-local diffusion equations from kinetic models with heavy-tailed equilibrium in velocity. We are particularly interested in confining the kinetic equations and developing methods that allow us, from the confined kinetic models, to derive confined versions of non-local diffusion equations.

The work in this thesis focuses primarily on equilibrium and stability properties of collisionless current sheet models, in particular of the force-free Harris sheet model. A detailed investigation is carried out into the properties of the distribution function found by Harrison and Neukirch (Physical Review Letters 102, 135003, 2009) for the force-free Harris sheet, which is so far the only known nonlinear force-free Vlasov-Maxwell equilibrium. Exact conditions on the parameters of the distribution function are found, which show when it can be single or multi-peaked in two of the velocity space directions. This is important because it may have implications for the stability of the equilibrium. One major aim of this thesis is to find new force-free equilibrium distribution functions. By using a new method which is different from that of Harrison and Neukirch, it is possible to find a complete family of distribution functions for the force-free Harris sheet, which includes the Harrison and Neukirch distribution function (Physical Review Letters 102, 135003, 2009). Each member of this family has a different dependence on the particle energy, although the dependence on the canonical momenta remains the same. Three detailed analytical examples are presented. Other possibilities for finding further collisionless force-free equilibrium distribution functions have been explored, but were unsuccessful. The first linear stability analysis of the Harrison and Neukirch equilibrium distribution function is then carried out, concentrating on macroscopic instabilities, and considering two-dimensional perturbations only. The analysis is based on the technique of integration over unperturbed orbits. Similarly to the Harris sheet case (Nuovo Cimento, 23:115, 1962), this is only possible by using approximations to the exact orbits, which are unknown. Furthermore, the approximations for the Harris sheet case cannot be used for the force-free Harris sheet, and so new techniques have to be developed in order to make analytical progress. Full analytical expressions for the perturbed current density are derived but, for the sake of simplicity, only the long wavelength limit is investigated. The dependence of the stability on various equilibrium parameters is investigated.

Ce travail a porté sur l'étude des instabilités de gradient de température ioniques (ITG) en géométrie cylindrique, le champ magnétique étant supposé constant et dirigé selon l'axe du cylindre. Une fonction de distribution discrète en forme de marche d'escalier est utilisée pour décrire la direction de vitesse parallèle au champ magnétique. L'équation de Vlasov se résume à un système de type multi fluides couplés par l'équation de quasi neutralité. Chaque fluide est décrit par un système fermé d'équations (continuité, Euler et fermeture adiabatique), caractéristiques d'un fluide incompressible, d'où la dénomination de sac d'eau ou "water bag". Le recours à cette description water bag est particulièrement intéressant dans le cas de problèmes à une seule dimension en vitesse. Ainsi, dans le cas des plasmas fortement magnétisés, un modèle water bag peut se combiner avantageusement aux modèles dits girocinétiques. Les paramètres associés a la représentation water bag ont pu être identifiés et reliés aux grandeurs macroscopiques par le biais d'une méthode originale d'équivalence au sens des moments. L'analyse water bag des ITG a permis de valider le modèle et les méthodes choisies. Ce travail a également permis de montrer que le concept de water bag peut sans problème prendre en compte des effets variés comme ceux liés a l'introduction d?un rayon de Larmor fini, tout comme à la description d'un plasma composé de plusieurs espèces d'ions
A drift-kinetic model in cylindrical geometry has been used to study Ion Temperature Gradients (ITG). The cylindrical plasma is considered as a limit case of a stretched torus. The magnetic field is assumed uniform and constant; it is directed along the axis of the column. A discrete distribution function f taking the form of a multi-step like function is used in place of the continuous distribution function along the parallel velocity direction. With respect to the properties of the Heaviside?s distribution, the Vlasov equation is reduced to a system of fluids coupled by the electromagnetic fields. This model is well suited mainly for problems involving a phase space with one velocity component. In the case of magnetized plasmas it gives an alternative way to study turbulence thanks to the gyro-average whose allows reducing the 3D velocity space into a 1D space. Parameters introduced by the water bag formalism have been linked to physical quantities by an original method of moment-sense equivalence. In the linear approximation, the water bag study of the ITG instability allows an interesting comparison with some well-known analytical results. The water-bag concept is not affected by taking into account Finite Larmor Radius effects. It well describes the case of multi-species plasma

Nuclear spinodal instabilities are investigated in non-relativistic and relativistic stochastic mean-field approaches for charge asymmetric and charge symmetric nuclear matter. Quantum statistical effect on the growth of instabilities are calculated in non-relativistic approach. Due to quantal effects, in both symmetric and asymmetric matter, dominant unstable modes shift towards longer wavelengths and modes with wave numbers larger than the Fermi momentum are strongly suppressed. As a result of quantum statistical effects, in particular at lower temperatures, amplitude of density fluctuations grows larger than those calculated in semi-classical approximation. Relativistic calculations in the semi-classical limit are compared with the results of non-relativistic calculations based on Skyrme-type effective interactions under similar conditions. A qualitative difference appears in the unstable response of the system: the system exhibits most unstable behavior at higher baryon densities around $rho_{B}=0.4 rho_{0}$ in the relativistic approach while most unstable behavior occurs at lower baryon densities around $rho_{B}=0.2 rho_{0}$ in the non-relativistic calculations.

2009/2010
In this Thesis we describe the theoretical-computational study performed on the behavior of isolated systems, far from thermodynamic equilibrium. Analyzing models well-known in literature we follow a path bringing to the classification of different behaviors in function of the interaction range of the systems' particles. In the case of systems with long-range interaction we studied the "Quasi-Stationary states" (QSSs) which emerge at short times when the system evolves with Hamiltonian dynamics. Their interest is in the fact that in many physical systems, such as self-gravitating systems, plasmas and systems characterized by wave-particle interaction, QSSs are the only experimentally accessible regime. QSS are defined as stable solutions of the Vlasov equation and, as their duration diverges with the system size, for large systems' size they can be seen as the true equilibria. They do not follow the Boltzmann statistics, and it does not exists a general theory which describes them. Anyway it is possible to give an approximate description using Lynden-Bell theory. One part of the thesis is devoted to shed light on the characteristics of the phase diagram of the "Hamiltonian mean field" model (HMF), during the QSS, calculated with the Lynden-Bell theory. The results of our work allowed to confirm numerically the presence of a phase re-entrance. In the Thesis is present also a detailed description on the system's caloric curves and on the metastability. Still in this context we show an analysis of the equivalence of the statistical ensembles, confirmed in almost the totality of the phase diagram (except for a small region), although the presence of negative specific heat in the microcanonical ensemble, which in Boltzmannian systems implies the non-equivalence of statistical ensembles. This result allowed us to arrive to a surprising conclusion: the presence of negative specific heat in the canonical ensemble. Still in the context of long-range interacting systems we analyze the linear stability of the non-homogeneous QSSs with respect to the Vlasov equation. Since the study of QSS find an application in the Free-electron laser (FEL) and other light sources, which are characterized by wave-particle interaction, we analyze, in the last chapter, the experimental perspectives of our work in this context. The other class of systems we studied are short-range interacting systems. Here the behavior of the components of the system is strongly influenced by the neighbors, and if one takes a system in a disordered state (a zero magnetization state for magnetic systems), which relaxes towards an ordered equilibrium state, one sees that the ordering process first develops locally and then extends to the whole system forming domains of opposed magnetization which grow in size. This process is called "coarsening". Our work in this field consisted in investigating numerically the laws of scale, and in the Thesis we characterize the temporal dependence of the domain sizes for different interaction ranges and we show a comparison between Hamiltonian and Langevin dynamics. This work inserts in the open debate on the equivalence of different dynamics where we found that, at least for times not too large, the two dynamics give different scaling laws.
In questa Tesi è stato fatto uno studio di natura teorico-computazionale sul comportamento dei sistemi isolati lontani dall'equilibrio termodinamico. Analizzando modelli noti in letteratura è stato seguito un percorso che ha portato alla classificazione di differenti comportamenti in funzione del range di interazione delle particelle del sistema. Nel caso di sistemi con interazione a lungo raggio sono stati studiati gli "stati quasi-stazionari" (QSS) che emergono a tempi brevi quando il sistema evolve con dinamica hamiltoniana. Il loro interesse risiede nel fatto che in molti sistemi fisici, come i sistemi auto-gravitanti, plasmi e sistemi caratterizzati da interazione onda-particella, i QSS risultano essere gli unici regimi accessibili sperimentalmente. I QSS sono definiti come soluzioni stabili dell'equazione di Vlasov, e visto che la loro durata diverge con la taglia del sistema, per sistemi di grandi dimensioni possono essere visti come i veri stati di equilibrio. Questi non seguono la statistica di Bolzmann, e non esiste una teoria generale che li descriva. E' tuttavia possibile fare una descrizione approssimata utilizzando la teoria di Lynden-Bell. Una parte della tesi è dedicata alla comprensione delle caratteristiche del diagramma di fase del modello "Hamiltonian mean field" (HMF) durante il QSS, calcolato con la teoria di Lynden-Bell. Il risultato del nostro lavoro ha permesso di confermare numericamente la presenza di fasi rientrati. E' inoltre presente un'analisi dettagliata sulle curve caloriche del sistema e sulla metastabilità. Sempre in questo contesto è stata fatto uno studio sull'equivalenza degli ensemble statistici, confermata nella quasi totalità del diagramma di fase (tranne in una piccola regione), nonostante la presenza di calore specifico negativo nell'insieme microcanonico, che in sistemi Boltzmanniani è sinonimo di non-equivalenza degli ensemble statistici. Questo risultato ci ha permesso di arrivare ad una sorprendente conclusione: la presenza di calore specifico negativo nell'insieme canonico. Sempre nel contesto dei sistemi con interazione a lungo range, è stata analizzata la stabilità lineare rispetto all'equazione di Vlasov degli stati quasi-stazionari non-omogenei. Poiché lo studio dei QSS trova applicazione nel Free-electron laser (FEL) e in altre sorgenti di luce, caratterizzate dall'interazione onda-particella, abbiamo analizzato anche le prospettive sperimentali del nostro lavoro in questo contesto. L'altra classe di sistemi che è stata studiata sono i sistemi con interazione a corto raggio. Qui il comportamento dei componenti del sistema è fortemente influenzato dai vicini, e se si prende un sistema in uno stato disordinato (a magnetizzazione nulla nei sistemi magnetici) che rilassa verso l'equilibrio ordinato, si vede che il processo di ordinamento si sviluppa prima localmente e poi si estende a tutto il sistema formando dei domini di magnetizzazione opposta che crescono in taglia. Questo processo si chiama "coarsening". Il nostro lavoro in questo contesto è consistito in una investigazione numerica delle leggi di scala, e nella tesi è stata caratterizzata la dipendenza temporale della taglia dei domini per differenti range di interazione ed è stato fatto un confronto fra dinamica hamiltoniana e dinamica di Langevin. Questi risultati si inseriscono nel dibattito aperto sull'equivalenza di differenti dinamiche, e si è mostrato che, almeno per tempi non troppo grandi, le due dinamiche portano a leggi di scala differenti.
XXIII Ciclo
1982

This master thesis is devoted to the kinetic description in phase space of strongly magnetized plasmas. It addresses the problem of stability near equilibria for magnetically confined plasmas modeled by the relativistic Vlasov Maxwell system. A small physically pertinent parameter ε, with 0 < ε << 1, related to the inverse of a gyrofrequency, governs the strength of a spatially inhomogeneous applied magnetic field given by the function x→ε−1Be(x). Local C1-solutions do exist. But these solutions may blow up in finite time. This phenomenon can only happen at high velocities [14] and, since ε−1is large, standard results predict that this may occur at a time Tε shrinking to zero when ε goes to 0. It has been proved recently in [7] that, in the case of neutral, cold, and dilute plasmas (like in the Earth’s magnetosphere), smooth solutions corresponding to perturbations of equilibria exist on a uniform time interval [0,T], with 0< T independent of ε. We investigate here the hot situation, which is more suitable for the description of fusion devices. A condition is derived for which perturbed W1,∞-solutions with large initial momentum also exist on a uniform time interval, they remain bounded in the sup norm for well-prepared initial data, and moreover they inherit some kind of stability.
Graduate

Various properties of linear infinite-dimensional Hamiltonian systems are studied. The structural stability of the Vlasov-Poisson equation linearized around a homogeneous stable equilibrium [mathematical symbol] is investigated in a Banach space setting. It is found that when perturbations of [mathematical symbols] are allowed to live in the space [mathematical symbols], every equilibrium is structurally unstable. When perturbations are restricted to area preserving rearrangements of [mathematical symbol], structural stability exists if and only if there is negative signature in the continuous spectrum. This analogizes Krein's theorem for linear finite-dimensional Hamiltonian systems. The techniques used to prove this theorem are applied to other aspects of the linearized Vlasov-Poisson equation, in particular the energy of discrete modes which are embedded within the continuous spectrum. In the second part, an integral transformation that exactly diagonalizes the Caldeira-Leggett model is presented. The resulting form of the Hamiltonian, derived using canonical transformations, is shown to be identical to that of the linearized Vlasov-Poisson equation. The damping mechanism in the Caldeira-Leggett model is identified with the Landau damping of a plasma. The correspondence between the two systems suggests the presence of an echo effect in the Caldeira-Leggett model. Generalizations of the Caldeira-Leggett model with negative energy are studied and interpreted in the context of Krein's theorem.
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