Les bosons chargés identiques confinés dans une grande boite dont les parois portent une charge de signe contraire mais de même densité assurant la neutralité du système, constituent un plasma neutre à une composante. On obtient un plasma neutre à deux composantes lorsque les bosons identiques de charge positive et ceux de charge négative de même densité sont contenus dans la même boite. Le plasma non-neutre des bosons s'obtient en confinant l'assemblée des bosons identiques chargés dans un piège des particules chargées de Penning ou de Paul. Nous avons fait l'étude théorique de la dégénérescence quantique du plasma non-neutre des bosons de spin zéro confinés dans un piège de Paul à haute densité et à très basse température. Cette étude a porté d'abord sur un système sans transition de phase dans le piège, et ensuite sur le régime gazeux (de Mathieu) et sur le régime intermédiaire (liquide). Nous avons utilisé la théorie microscopique en considérant le champ scalaire complexe ou champ des mésons chargés pour construire les opérateurs bosons chargés de spin zéro, définir l'espace des états quantiques du système, construire les opérateurs champs de création et d'annihilation des bosons d'impulsion p au point r . Ces derniers nous ont permis de construire l'opérateur Hamiltonien de la seconde quantification du plasma et la matrice densité à une particule. La matrice densité du plasma non neutre de bosons de spin zéro et la prescription de Bogoliubov révèlent l'occupation macroscopique d'un état quantique dans le piège harmonique radiofréquence de Paul. Nous avons déterminé pour ce plasma l'énergie de l'état fondamental, le spectre des excitations élémentaires, l'équation de Hartree-Fock etc. Nos résultats sont comparés dans un tableau aux résultats de l'application de la théorie microscopique aux assemblées des bosons neutres confinés dans un piège magnétique et au gaz électronique.

Multiphase flows are frequently encountered in many important physical and industrial applications. These flows are usually characterized by very complicated structure that involves free moving surfaces inside the fluid domain and discontinuous or even singular material properties of the flow. The application range for the multiphase flow phenomena is extremely wide, ranging from processing industry to environmental problems, from biological applications to food industry and so on. Unfortunately, due to the inherent complexity of these problems, their solution proved to be a considerable challenge. Thus, in the many applications, the predictive capability and physical understanding must rely heavily on numerical models. In this thesis we develop and analyze a finite element based method for the solution of multiphase problems. This thesis consists of four papers. In paper 1 we develop our finite element based method for the elliptic interface problems. The interface jump conditions that are present due to the discontinuity of the coefficients and presence of the singular forces are derived. Using these jump conditions, we enrich the finite element spaces in order to account for the irregularities in the flow. The resulting method was applied to the interface Stokes problem, modeling a thin elastic rubber band immersed in the homogeneous fluid. In order to apply the introduced method, the interface Stokes problem was rewritten as a sequence of three Poisson problems, one for the pressure and two for the velocity components. Paper 2 is an extension of the ideas used in paper 1. Namely, third order Hermitian polynomials are used as basis functions, their modification according to the interface jump conditions is presented and analyzed, both theoretically and numerically. The rigorous error analysis of the introduced method for two-dimensional elliptic problems is presented in paper 3. The results imply that our method is second order accurate in the L2 norm. Finally, paper 4 concerns with the extension of our method to a coupled interface Stokes problem, that contains both singular forces and discontinuities in the material properties. An application to the Rayleigh-Taylor instability problem is presented. / QC 20100806

Broadband extremely low-frequency wave emissions below the ion plasma frequency have been observed by a number of spacecraft and rockets on auroral field lines. The importance of these broadband emissions for transverse ion heating and electron acceleration in the auroral regions is now reasonably well established. However, the exact mechanism(s) for mediating this energy transfer and the wave mode(s) involved are not well known. In this thesis we focus on the identification of broadband waves by different methods. Two wave analysis methods, involving different approximations and assumptions, give consistent results concerning the wave mode identification. We find that much of the broadband emissions can be identified as a mixture of ion acoustic, electrostatic ion cyclotron and, ion Bernstein waves, which all can be described as different parts of the same dispersion surface in the linear theory of waves in homogeneous plasma. A new result is that ion acoustic waves occur on auroral magnetic field lines. These are found in relatively small regions interpreted as acceleration regions without cold (tens of eV) electrons. From interferometry we also determine the phase velocity and k vector for parallel and oblique ion acoustic waves. The retrieved characteristic phase velocity is of the order of the ion acoustic speed and larger than the thermal velocity of the protons. The typical wavelength is around the proton gyro radius and always larger than the Debye length which is consistent with ion acoustic waves. We have observed quasi-static parallel electric fields associated with the ion acoustic waves in regions with large-scale currents. Waves, in particular ion acoustic waves, can create an anomalous resistivity due to wave-particle interaction when electrons are retarded or trapped by the electric wave-field. To maintain the large-scale current, a parallel electric field is set up, which then can accelerate a second electron population to high velocities.

This thesis is dedicated to the theory of solar radar experiments. The Sun exhibits a variety of interesting and complicated physical phenomena, examined mainly through analysis of its radiation. Active solar probing by radar provides an alternative possibility to study the Sun. This concept was tested originally in the 1960's by solar radar experiments at El Campo, Texas, but due to an insufficient level of technology at that time the experimental results were of a poor quality and thus difficult to interpret. Recently, the space weather program has stimulated interest in this topic. New experimental proposals require further development of the theory of solar radar experiments to meet the current knowledge about the Sun and the modern level of technology. Three important elements of solar radar experiments are addressed in this thesis: i) generation of wave turbulence and radiation in the solar corona, ii) propagation of the radar signal to the reflection point, and iii) reflection (scattering) of the incident radar signal from the Sun. It is believed that the radio emission of solar type II and III bursts occurs due to conversion of Langmuir waves, generated by electron beams, into electromagnetic radiation (plasma emission mechanism). The radar signal propagating through the emission source region can get scattered by the Langmuir turbulence and finally deliver the observer insights of the physics of this turbulence. Such process of scattering is considered in this thesis in the weak turbulence limit by means of the wave-kinetic theory. Scattering frequency shifts, scattering cross-sections, efficiency of scattering (the coefficient of absorption due to scattering), optical depths, and the spectra of the scattered signal are estimated. Type II solar radio bursts are known to be associated with the electron beams accelerated by interplanetary shocks. From their dynamic spectra the properties of the shocks and regions in the vicinity of the shock are usually inferred by assuming a plasma emission mechanism. In situ observations of the source region of type II burst, presented in this thesis, suggest that an additional emission mechanism may be present. This mechanism is related to energetic particles crossing the shock front, known in electrodynamics as transition radiation. Plasma density fluctuations are known to scatter radio waves and thus broadening their angular dispersion. In the thesis this process is studied in the solar wind and terrestrial electron and ion foreshocks on the basis of in situ observations of density fluctuations. It is shown that the angular broadening of the radar signal is negligible in this regions. The results of this thesis can be applied for the preparation of future solar radar experiments and interpretation of experimental data.

The Neutral Particle Detector (NPD) is a new type of instrumentation for energetic neutral atom (ENA) diagnostics. This thesis deals with development of the NPD sensor designed as a part of the plasma and neutral particle packages ASPERA-3 and ASPERA-4 on board Mars Express and Venus Express, the European Space Agency (ESA) satellites to Mars and Venus, respectively. It describes how the NPD sensors were designed, developed, tested and calibrated. It also presents the first scientific results obtained with NPD during its operation at Mars. The NPD package consists of two identical detectors, NPD1 and NPD2. Each detector has a 9o x 90o intrinsic field-of-view divided into three sectors. The ENA detection principle is based on the surface interaction technique. NPD detects ENA differential fluxes within the energy range of 100 eV to 10 keV and is capable of resolving hydrogen and oxygen atoms by time-of-flight (TOF) measurements or pulse height analysis. During the calibration process the detailed response of the sensor was defined, including properties such as an angular response function and energy dependent efficiency of each of the sensor sectors for different ENA species. Based on the NPD measurements at Mars the main scientific results reported so far are: - observation of the Martian H-ENA jet / cone and its dynamics, - observations of ENA emissions from the Martian upper atmosphere, - measurements of the hydrogen exosphere density profile at Mars, - observations of the response of the Martian plasma environment to an interplanetary shock, - observations of the H-ENA fluxes in the interplanetary medium.

This thesis is focused on the role of Alfvén waves in the energy transformation and transport in the magnetosphere. Different aspects of Alfvén wave generation, propagation and dissipation are considered. The study involves analysis of experimental data from the Freja, Polar and Cluster spacecraft, as well as theoretical development. An overview of the linear theory of Alfvén waves is presented, including the effects of fnite parallel electron inertia and fnite ion gyroradius, and nonlinear theory is developed for large amplitude Alfvén solitons and structures. The methodology is presented for experimental identification of dispersive Alfvén waves in a frame moving with respect to the plasma, which facilitates the resolution of the space-time ambiguity in such measurements. Dispersive Alfvén waves are identified on field lines from the topside ionosphere up to the magnetopause and it is suggested they play an important role in magnetospheric physics. One of the processes where Alfvén waves are important is the establishment of the field aligned current system, which transports the energy from the reconnection regions at the magnetopause to the ionosphere, where a part of the energy is dissipated. The main mechanism for the dissipation in the top-side ionosphere is related to wave-particle interactions leading to particle energization/heating. An observed signature of such a process is the presence of parallel energetic electron bursts associated with dispersive Alfvén waves. The accelerated electrons (electron beams) are unstable with respect to the generation of high frequency plasma wave modes. Therefore this thesis also demonstrates an indirect coupling between low frequency Alfvén wave and high frequency oscillations.

The space around Earth, confined in the terrestrial magnetosphere, is to some extent shielded from the Sun's solar wind plasma and magnetic field. During certain conditions, however, strong interaction can occur between the solar wind and the magnetosphere, resulting in magnetospheric activity of several forms, among which substorms and storms are the most prominent. A general framework for how these processes work have been outlayed through the history of research, however, there still remain questions to be answered. The most striking example regards the onset of substorms, where both the onset cause and location in the magnetosphere/ionosphere are still debated. These are clearly not easily solved problems, since a substorm is a global process, ideally requiring simultaneous measurements in the magnetotail and ionosphere. Investigated in this work are temporal and spatial scales for substorm and convection processes in the Earth's magnetosphere and ionosphere. This is performed by combining observations from a number of both ground-based and spacecraft-borne instruments. The observations indicate that the magnetotail's cross-section is involved to a larger spatial extent than previously considered in the substorm process. Furthermore, convection changes result in topological changes of the magnetosphere on a fast time scale. The results show that the magnetosphere is, on a global magnetospheric scale, highly dynamic during convection changes and ensuing substorms.

Plasma physics governs the area of interactions between charged particles. As 99% of the visible universe is in a plasma state, it is an important topic in astronomy and space physics, where we already at an altitude of 60 km reach the plasma environment surrounding our planet in the form of the ionosphere. The search for fusion, the source of power for the sun, as well as industrial use have been the main topics for earth bound plasma reasurch. A plasma is composed of charged particles which interact by the electromagnetic force. In the kinetic description, via the Vlasov-Maxwell equations, the system is described in terms of probability distribution functions for each particle species, expressed in terms of particles position and velocity. The particles interact via self-consistent fields as determined by Maxwell's equations. For understanding the complex behaviour of the system, we need numerical solvers. These come in two flavours, Lagrangian methods, dealing with the moving around of synthetic particles, and Eulerian methods, which solve the set of partial differential, Vlasov and Maxwell equations. To perform the computations within reasonable time, we need to distribute our calculations on multiple machines, i.e. parallel programming, with the best possible matching between our computational needs and the need of splitting algorithms to adapt to our processing environment. Paper I studies electron and ion beams within a Lagrangian and fluid model and compare the results with experimental observations. This is continued with studies of a full kinetic system, using an Eulerian solver, for a closer look at electron-ion interactions in relation to ionospheric observations, (Papers II and IV). To improve the performance of the Eulerian solver it was parallelised (Paper III). The thesis is ending with the possibility to observe ultrahigh energy neutrinos from an orbiting satellite by using the Moon's surface as a detector Paper V.

Diagnostic measurements play a vital role in experiments. Without them we would be in the dark with no way of knowing what was happening; of understanding the processes and behaviour occurring; or even of judging the success or failure of our experiments. The development of fusion plasma devices is no different. In this thesis we concentrate on visible spectroscopy based diagnostics: examining the techniques for measurement and analysis; the breadth of plasma parameters that can be extracted from the spectroscopic data; and how the application of these diagnostic techniques gives us a broader picture of the plasma and the events taking place within. Techniques are developed and applied to plasmas in three fusion experiments, EXTRAP T2R, ASDEX Upgrade and JET. The diagnostic techniques exploit different features of the measurements of the emitted photons to obtain various useful plasma parameters. Determination of the ion temperature and rotation velocity of oxygen impurity ions in the EXTRAP T2R plasma is achieved through measurement and analysis of, respectively, the Doppler broadening and the Doppler wavelength shift of visible wavelength atomic spectral lines. The evolution of the temperature and rotation is studied as a function of the discharge parameters, in particular looking at the effect of applying active feedback control schemes to the resistive wall modes and/or pulsed poloidal current drive. Measurements of multiple ionisation stages are used to estimate radial profiles of the toroidal rotation and the ion temperature and correlations between the ion rotations and the rotation velocities of tearing modes are also established. Radial profiles of the emissivity and density (or concentration) of the oxygen ions are obtained by means of measurements of the spectral line intensities on a small array of linesof- sight through the plasma. Changes to the profiles for different plasma schemes and the implications for particle transport are investigated. The derived emissivity profiles are used in the analysis for some of the other spectroscopic diagnostics. Spectral line intensity measurements (in this case of neutral ions) are also the basis for calculations of both the electron temperature and the particle fluxes at the plasma edge. The latter is an indicator of the degree and type of interaction between the plasma and the surrounding surfaces. Particle fluxes of the operating gas hydrogen and of chromium and molybdenum impurities are investigated in EXTRAP T2R for different operating scenarios, in particular changes in the metallic influx with the application of active feedback mode control are examined along with the correspondence between spectroscopic and collector probe results. In the ASDEX Upgrade divertor estimates of the particle flux of the deuterium operating gas are also made through analysis of spectral intensities. Molecular D2 band structure is explored in addition to the Balmer Dα spectral line intensity to acquire both atomic and molecular particle fluxes, investigate the contribution of the dissociating D2 to the Dα line and study the effect of changes in the divertor. Analysis of the D2 molecular band structure (the relative intensities of the rotational lines and vibrational bands) also enables calculation of the upper state rotational and ground state vibrational temperatures. The locations of emitting atomic ions in JET are estimated from Zeeman splitting analysis of the structure of their spectral lines. The measurement and analysis of visible wavelength light is demonstrated to be a sensitive diagnostic tool in the quest for increased knowledge about fusion plasmas and their operating scenarios. / QC 20100810

Understanding of plasma confinement modes is an essential component in development of a fusion reactor. Plasma confinement directly relates to performance of a fusion reactor in terms of energy replacement time requirements on other design parameters. Although a variety of levels of confinement have been achieved under different operating conditions in tokamaks, tokamak confinement is generally identified as being either Low (L-mode--poor confinement) or High (H-mode--good confinement) In operation of a tokamak experiment, the plasma confinement condition generally changes from L-mode to H-mode over a few hundred milliseconds, sometimes quite sharply. Such a difference in transition period seems to be largely due to operating conditions of the plasma. Comparison of experimental data exhibits various distinctions between confinement modes. One noteworthy distinction between confinement modes is development of steep density and temperature gradients of electrons and ions in the plasma edge region of High confinement, H-modes, relative to Low-confinement, L-modes. The fundamental reason for the change for L-mode to H-mode is not understood. Previous studies have suggested i) the development of reduced diffusive transport coefficients that require a steepening of the gradients in a localized region in the edge plasma, the "transport barrier" in H-mode confinement ii) the radial force balance between pressure gradient forces and electromagnetic (radial electric field and VxB) forces require radial particle fluxes to satisfy a pinch-diffusion relation. A recent study suggests that the major difference between L-mode and H-mode are associated with the electromagnetic forces in the "pinch velocity" and the pressure gradient, not in the diffusion coefficients that multiplies the pressure gradient. The research will examine in detail the time evolution of the radial force balance and the particle and energy transport during the L-H transition. For the analysis, DIII-D shot #118897 is selected for transition between L- and H-mode confinements. Plasma conditions in L-mode, near the L-H transition and following the transition are selected for analysis of various parameter profiles. The initial analysis will be based on the four principal equations for plasma: particle balance, momentum balance, force balance and heat conduction. Based on these equations, specific equations have been derived: toroidal and radial momentum balances, diffusion coefficient, pinch velocity and heat conduction relation for calculation of parameters. The analysis of these equations, using the measured data, will establish how various terms in the radial force balance (radial electric field, VXB (electromagnetic) force, and pressure gradient) and the diffusive transport coefficients evolve over the confinement mode transition.