Academic literature on the topic 'Plasmoids'

Within the framework of an Institutional Partnership of the Alexander von Humboldt Foundation, the Budker Institute of Nuclear Physics Novisibirsk (BINP) and Forschungszentrum Dresden-Rossendorf worked together in a joint project devoted to the research at the coupled GDT-SHIP facility of the BINP with the focus on the study of plasma phenomena within the SHIP mirror section. The project began at July 1st, 2005 and ended on August 30th, 2008. It included work packages of significant theoretical, computational and analyzing investigations. The focus of this final report is on the presentation of results achieved whereas the work that was done is described briefly only. Chapter 2 illustrates the GDT-SHIP facility and describes shortly the planned topics of the SHIP plasma research. Chapter 3 explains the main extensions and modifications of the Integrated Transport Code System (ITCS) which were necessary for the calculations of the fast ion and neutral gas particle fields in SHIP, describes briefly the scheme of computations and presents significant results of pre-calculations from which conclusions were drawn regarding the experimental program of SHIP. In chapter 4, the theoretical and computational investigations of self-organizing processes in two-component plasmas of the GDT-SHIP device are explained and the results hitherto achieved are presented. In chapter 5, significant results of several experiments with moderate and with enhanced plasma parameters are presented and compared with computational results obtained with the ITCS. Preparing neutron measurements which are planned for neutron producing experiments with deuterium injection, Monte Carlo neutron transport calculations with the MCNP code were also carried out. The results are presented. Finally, from the results obtained within the joint research project important conclusions are drawn in chapter 6.

Within the framework of an Institutional Partnership of the Alexander von Humboldt Foundation, the Budker Institute of Nuclear Physics Novisibirsk (BINP) and Forschungszentrum Dresden-Rossendorf worked together in a joint project devoted to the research at the coupled GDT-SHIP facility of the BINP with the focus on the study of plasma phenomena within the SHIP mirror section. The project began at July 1st, 2005 and ended on August 30th, 2008. It included work packages of significant theoretical, computational and analyzing investigations. The focus of this final report is on the presentation of results achieved whereas the work that was done is described briefly only. Chapter 2 illustrates the GDT-SHIP facility and describes shortly the planned topics of the SHIP plasma research. Chapter 3 explains the main extensions and modifications of the Integrated Transport Code System (ITCS) which were necessary for the calculations of the fast ion and neutral gas particle fields in SHIP, describes briefly the scheme of computations and presents significant results of pre-calculations from which conclusions were drawn regarding the experimental program of SHIP. In chapter 4, the theoretical and computational investigations of self-organizing processes in two-component plasmas of the GDT-SHIP device are explained and the results hitherto achieved are presented. In chapter 5, significant results of several experiments with moderate and with enhanced plasma parameters are presented and compared with computational results obtained with the ITCS. Preparing neutron measurements which are planned for neutron producing experiments with deuterium injection, Monte Carlo neutron transport calculations with the MCNP code were also carried out. The results are presented. Finally, from the results obtained within the joint research project important conclusions are drawn in chapter 6.

La reconnexion magnétique est une modification de la topologie du champ magnétique, responsable de la libération explosive d'énergie magnétique dans les plasmas astrophysiques, comme dans le cas des orages magnétosphériques et des éjections de masse coronale, ainsi que dans les plasmas de laboratoire, comme dans le cas des crashs en dents de scie dans les tokamaks. Dans les plasmas sans collisions comme, par exemple, la magnétosphère et le vent solaire, l'inertie des électrons devient particulièrement pertinente pour provoquer la reconnexion dans les régions de courant localisé intense, appelées feuilles de courant. Dans ces environnements non collisionnels, la température peut souvent être anisotrope et les effets à l'échelle électronique sur le processus de reconnexion peuvent devenir non négligeables.Dans cette thèse, la stabilité des feuilles de courant bidimensionnelles dans des plasmas sans collisions avec un fort champ guide est analysée sur la base de modèles gyrofluides assumant des ions froids. Ces modèles peuvent prendre en compte une anisotropie de température d'équilibre, et un βe fini. Ce dernier est un paramètre correspondant au rapport entre la pression cinétique électronique d'équilibre et la pression magnétique.Nous dérivons et analysons une relation de dispersion pour le taux de croissance des modes tearing sans collisions tenant compte de l'anisotropie de la température d'équilibre des électrons. Les prédictions analytiques sont testées par des simulations numériques, montrant un très bon accord quantitatif.Dans le cas isotrope, en tenant compte des effets βe finis, nous observons une stabilisation du taux de croissance du mode tearing lorsque les effets du rayon de Larmor fini des électrons deviennent pertinents. Dans la phase non linéaire, des phases de ralentissement et des phases d'accélération sont observées, de manière similaire à ce qui se produit en présence d'effets de rayon de Larmor fini ionique.Nous étudions également les conditions de stabilité marginale des feuilles de courant secondaires, pour le développement de plasmoïdes, dans des plasmas sans collisions. Dans le régime isotrope βe → 0, nous analysons la géométrie qui caractérise le feuillet de courant, et identifions les conditions pour lesquelles elle devient instable à l'instabilité plasmoïde. Notre étude montre que des plasmoïdes peuvent être obtenus, dans ce contexte, à partir de feuille de courants aillant un rapport d'aspect beaucoup plus petit que dans le régime collisionnel. De plus, nous étudions la formation de plasmoïdes en comparant les simulations gyrofluides et gyrocinétiques.Ceci a permis de montrer que l'effet de βe favorise l'instabilité plasmoïde. Enfin, nous étudions l'impact de la fermeture appliquée sur les moments, effectuée lors de la dérivation du modèle gyrofluide, sur la distribution et la conversion de l'énergie lors de la reconnexion<br>Magnetic reconnection is a change of topology of the magnetic field, responsible for explosive release of magnetic energy in astrophysical plasmas, as in the case of magnetospheric substorms and coronal mass ejections, as well as in laboratory plasmas, which is the case of sawtooth crashes in tokamaks. In collisionless plasmas as, for instance, the magnetosphere and the solar wind, electron inertia becomes particularly relevant to drive reconnection at regions of intense localized current, denoted as current sheets. In these non-collisional environments, the temperature can often be anisotropic and effects at the electron scale on the reconnection process can become non-negligible.In this thesis, the stability of two-dimensional current sheets, with respect to reconnecting perturbations, in collisionless plasmas with a strong guide field is analysed on the basis of gyrofluid models assuming cold ions. These models can take into account an equilibrium temperature anisotropy,and a finite βe, a parameter corresponding to the ratio between equilibrium electron kinetic pressure and magnetic pressure.We derive and analyze a dispersion relation for the growth rate of collisionless tearing modes accounting for equilibrium electron temperature anisotropy. The analytical predictions are tested against numerical simulations, showing a very good quantitative agreement.In the isotropic case, accounting for finite βe effects, we observe a stabilization of the tearing growth rate when electron finite Larmor radius effects become relevant. In the nonlinear phase, stall phases and faster than exponential phases are observed, similarly to what occurs in the presence of ion finite Larmor radius effects.We also investigate the marginal stability conditions of secondary current sheets, for the development of plasmoids, in collisionless plasmas. In the isotropic βe → 0 regime, we analyze the geometry that characterizes the reconnecting current sheet, and identify the conditions for which it is plasmoid unstable. Our study shows that plasmoids can be obtained, in this context, from current sheets with an aspect ratio much smaller than in the collisional regime. Furthermore, we investigate the plasmoid formation comparing gyrofluid and gyrokinetic simulations.This made it possible to show that the effect of finite βe, promotes the plasmoid instability. Finally, we study the impact of the closure applied on the moments, performed during the derivation of the gyrofluid model, on the distribution and conversion of energy during reconnection<br>La riconnessione magnetica è un cambiamento nella topologia delcampo magnetico, responsabile del rilascio esplosivo di energia magnetica nei plasmiastrofisici, come nelle tempeste magnetosferiche e nelle espulsioni di massa coronale,nonché nei plasmi di laboratorio, come nel caso delle oscillazioni a dente di sega neitokamak. Nei plasmi non-collisionali come, ad esempio, la magnetosfera e il vento solare,l’inerzia elettronica diventa particolarmente efficace nel causare la riconnessionein regioni di corrente intensa e localizzata, detti strati di corrente. In tali plasmi noncollisionali,la temperatura può essere spesso anisotropa e gli effetti su scala elettronicasul processo di riconnessione possono diventare non trascurabili.In questa tesi, viene analizzata la stabilità di strati di corrente bidimensionali inplasmi non-collisionali con un forte campo guida, sulla base di modelli girofluidi cheassumono ioni freddi. Questi modelli possono tenere conto di un’anisotropia di temperaturadi equilibrio e di un βe finito. Quest’ultimo è un parametro corrispondente alrapporto tra la pressione cinetica elettronica di equilibrio e la pressione magnetica.Deriviamo e analizziamo una relazione di dispersione per il tasso di crescita dei moditearing non-collisionali tenendo conto dell’anisotropia della temperatura di equilibriodegli elettroni. Le previsioni analitiche sono verificate mediante simulazioni numeriche,che mostrano un ottimo accordo quantitativo. Nel caso isotropico, tenendoconto degli effetti di βe finito, si osserva una stabilizzazione del tasso di crescita delmodo tearing quando diventano rilevanti gli effetti del raggio finito di Larmor deglielettroni. Nella fase non lineare si osservano fasi di decelerazione e fasi di accelerazione,simili a quanto avviene in presenza di effetti del raggio di Larmor finito ionico.Studiamo anche le condizioni di stabilità marginale degli strati di corrente secondaria,per lo sviluppo di plasmoidi, in plasmi senza collisioni. Nel regime isotropicocon βe → 0, analizziamo la geometria che caratterizza lo strato di corrente e identifichiamole condizioni in cui esso diventa instabile a causa di un’instabilità che generaplasmoidi. Il nostro studio mostra che i plasmoidi possono essere ottenuti, in questocontesto, da strati di corrente aventi un rapporto d’aspetto molto più piccolo rispettoal regime collisionale. Inoltre, studiamo la formazione di plasmoidi confrontando simulazionigirofluidi e girocinetiche. Ciò ha permesso di dimostrare che l’effetto di βe promuove l’instabilità che genera plasmoidi. Infine, si studia l’impatto della chiusuraapplicata ai momenti, eseguita durante la derivazione del modello girofluido, sulla distribuzionee conversione dell’energia durante la riconnessione

Tailoring surface plasmon (SP) resonances using metallic nanostructures for optical manipulation has been widely investigated in recent years; and there are many puzzles yet to be solved in this relatively new area. This thesis covers the study of the interaction of light with SP-supporting planar/patterned metallo-dielectric multilayer structures. Two separate, but closely related subjects were investigated using such structures, which are: SP-assisted optical transmission and optical metamaterials. The physical mechanisms of the SP-assisted transmission phenomenon were studied using planar/grating and planar/hole-array multilayer structures. Extraordinary light transmission has been demonstrated through experimental work and simulations for both arrangements; and the effects of different structural parameters on the transmission efficiencies of the structures were analyzed systematically. The interplays of the surface plasmon polaritons (SPPs) and localized surface plasmons (LSPs) in the extraordinary optical transmission (EOT) phenomenon were identified. The potential of the planar/hole-array multilayer structures as optical magnetic metamaterials was evaluated using two independent electromagnetic simulation techniques. The ability of such structures to produce strong magnetic resonances from infrared down to visible side of spectrum was revealed. The methods of tuning the magnetic response of the structures were suggested. A novel design of optical metamaterial based on high-order multipolar resonances in a single-layer plasmonic structure was also proposed. Numerical results from two different computation methods indicate that a simultaneously negative permittivity and permeability can be achieved in such a structure.

This thesis investigated factors affecting the sensitivity of nano-optical sensors that could be used for the detection of trace amounts of explosives and environmental pollutants in air. By delivering air to regions of enhanced electric field produced by metallic nanostructures, as well as using structures that localise and guide light at nanoscale levels, detection limits can be reduced.

This thesis details original experimental investigations in to the interaction of light with the mobile electrons at the surface of metallic diffraction gratings. The gratings used in this work to support the resultant trapped surface waves (surface plasmon polaritons), may be divided into two classes: ‘crossed’ bigratings and ‘zigzag’ gratings. Crossed bigratings are composed of two diffraction gratings formed of periodic grooves in a metal surface, which are crossed at an angle relative to one another. While crossed bigratings have been studied previously, this work focuses on symmetries which have received comparatively little attention in the literature. The gratings explored in this work possesses two different underlying Bravais lattices: rectangular and oblique. Control over the surface plasmon polariton (SPP) dispersion on a rectangular bigrating is demonstrated by the deepening of one of the two constituent gratings. The resulting change in the diffraction efficiency of the surface waves leads to large SPP band-gaps in one direction across the grating, leaving the SPP propagation in the orthogonal direction largely unperturbed. This provides a mechanism to design surfaces that support highly anisotropic propagation of SPPs. SPPs on the oblique grating are found to mediate polarisation conversion of the incident light field. Additionally, the SPP band-gaps that form on such a surface are shown to not necessarily occur at the Brillouin Zone boundaries of this lattice, as the BZ boundary for an oblique lattice is not a continuous contour of high-symmetry points. The second class of diffraction grating investigated in this thesis is the new zigzag grating geometry. This grating is formed of sub-wavelength (non-diffracting) grooves that are ‘zigzagged’ along their length to provide a diffractive periodicity for visible frequency radiation. The excitation and propagation of SPPs on such gratings is investigated and found to be highly polarisation selective. The first type of zigzag grating investigated possesses a single mirror plane. SPP excitation to found to be dependant on which diffracted order of SPP is under polarised illumination. The formation of SPP band-gaps is also investigated, finding that the band-gap at the first Brillouin Zone boundary is forbidden by the grating’s symmetry. The final grating considered is a zigzag grating which possesses no mirror symmetry. Using this grating, it is demonstrated that any polarisation of incident light may resonantly drive the same SPP modes. SPP propagation on this grating is found to be forbidden in all directions for a range of frequencies, forming a full SPP band-gap.

Depuis plusieurs années les physiciens de la matière condensée s'intéressent aux propriétés optiques et magnétiques des nanoparticules métalliques. Deux propriétés restent largement étudiées : les résonances plasmon localisées et l'anisotropie magnétique à l'échelle nanométrique. Ces deux effets résultant de propriétés électroniques bien différentes sont habituellement rencontrés dans des nanosystèmes distincts. Depuis les années 2000 des études ont montré qu'il était possible de bénéficier de ces deux caractéristiques dans un seul et même système nanométrique. Dans cette thèse, nous nous intéresserons à la combinaison des propriétés magnétiques et plasmoniques dans des systèmes de taille inférieure à la dizaine de nanomètres: les agrégats bimétalliques de CoAg et de CoAu synthétisés par voie physique sous ultravide encapsulés en matrice (alumine et carbone). Nous nous intéresserons à la structure de ces agrégats bimétalliques de différentes stœchiométries et à l'effet de leur environnement à travers l'étude de leurs propriétés optiques, magnétiques et électroniques (par spectroscopie électronique par perte d'énergie (EELS) sur des particules individuelles). Nous montrerons l'effet de la matrice, carbone ou alumine, sur la structure des agrégats ainsi que sur leurs propriétés magnétiques (moment par agrégat, anisotropie). En optique nous verrons également l'importance de la stœchiométrie entre métal noble et cobalt sur les phénomènes d'amortissement et de décalage de résonance plasmon. Enfin nous montrerons la répartition spatiale des plasmons de surface sur des particules unique par des mesures de STEM-EELS<br>For several years condensed matter physicists have been interested in the optical and magnetic properties of metallic nanoparticles. Two properties remain largely studied: localized plasmon resonances and magnetic anisotropy at the nanoscale. These two effects resulting from very different electronic properties which are usually encountered in separate nanosystems. Since the 2000's, studies have shown that it is possible to benefit from these two characteristics in a single nanometric system. In this thesis, we will focus on the combination of magnetic and plasmonic properties in systems of size less than ten nanometers: bimetallic clusters of CoAg and CoAu synthesized physically under ultrahigh vacuum and embedded in a matrix (alumina and carbon). We will study the structure of these bimetallic clusters of different stoichiometries and the effect of their environment through the investigation of their optical, magnetic and electronic properties (by electron energy loss spectroscopy (EELS) on individual particles ). We will show the effect of the matrix, carbon or alumina, on the structure of the clusters as well as on their magnetic properties (moment by cluster, anisotropy). In optics we will also see the importance of stoichiometry between noble metal and cobalt on the phenomena of the damping and shifting of the plasmon resonance. Finally we will show the spatial distribution of surface plasmons on single particles by STEM-EELS measurements

With the recent emergence of the field of metamaterials, the study of subwavelength propagation of plane waves and the dissipation of their energy either in the form of Joule losses in the case of electomagnetic waves or in the form of viscous dissipation in the case of acoustic waves in different interfaced media assumes great importance. with this motivation, I have worked on problems in two different areas, viz., plasmonics and surface acoustics. the first part (chapters 2 & 3) of the dissertation deals with the emerging field of plasmonics. Researchers have come up with various designs in an efort to fabricate efficient plasmonic waveguides capable of guiding plasmonic signals. However, the inherent dissipation in the form of Joule losses limits efficient usage of surface plasmon signal. a dielectric-metal-¬dielectric planar structure is one of the most practical plasmonic structures that can serve as an efficient waveguide to guide electromagnetic waves along the metal-dielectric boundary. I present here a theoretical study of propagation of surface plasmons along a symmetric dielectric-metal-dielectric structure and show how proper orientation of the optical axis of the anisotropic substrate enhances the propagation length. an equation for propagation length is derived in a wide range of frequencies. I also show how the frequency of coupled surface plasmons can be modulated by changing the thickness of the metal film. I propose a Kronig-Penny model for the plasmonic crystal, which in the long wavelength limit, may serve as a homogeneous dielectric substrate with high anisotropy which do not exist for natural optical crystals. in the second part (chapters 4 & 5) of the dissertation, I discuss an interesting effect of extraordinary absorption of acoustic energy due to resonant excitation of Rayleigh waves in a narrow water channel clad between two metal plates. Starting from the elastic properties of the metal plates, I derive a dispersion equation that gives resonant frequencies, which coincide with those observed in the experiment that was performed by Wave Phenomena Group at Polytechnic University of Valencia, Spain. Two eigenmodes with different polarizations and phase velocities are obtained from the dispersion equation. at certain critical aperture of the channel, an interesting cutoff effect, which is unusual for an acoustic wave, is observed for one of the eigenmodes with symmetric distribution of the pressure field. the theoretical prediction of the coupling and synchronization of Rayleigh waves strongly supports the experimentally measured shift of the resonant frequencies in the transmission spectra with channel aperture. the observed high level of absorption may find applications in designing metamaterial acoustic absorbers.

Plasmonics is a recently emerged technology that enables the compression of electromagnetic waves into miniscule metallic structures, thus enabling the focusing and routing of light on the nanoscale. Plasmonic waveguides can be used to miniaturise the size of integrated chip circuits while increasing the data transmission speed. Plasmonic waveguides are used to route the plasmons around a circuit and are a major focus of this thesis. Also, plasmons are highly sensitive to the surrounding dielectric environment. Using this property we have experimentally realised a refractive index sensor to detect refractive index change in solutions.