<p>One of the most conspicuous problems in space physics for the last decades has been to theoretically describe how the large parallel electric fields on auroral field lines can be generated. There is strong observational evidence of such electric fields, and stationary theory supports the need for electric fields accelerating electrons to the ionosphere where they generate auroras. However, dynamic models have not been able to reproduce these electric fields. This thesis sheds some light on this incompatibility and shows that the missing ingredient in previous dynamic models is a correct description of the electron temperature. As the electrons accelerate towards the ionosphere, their velocity along the magnetic field line will increase. In the converging magnetic field lines, the mirror force will convert much of the parallel velocity into perpendicular velocity. The result of the acceleration and mirroring will be a velocity distribution with a significantly higher temperature in the auroral acceleration region than above. The enhanced temperature corresponds to strong electron pressure gradients that balance the parallel electric fields. Thus, in regions with electron acceleration along converging magnetic field lines, the electron temperature increase is a fundamental process and must be included in any model that aims to describe the build up of parallel electric fields. The development of such a model has been hampered by the difficulty to describe the temperature variation. This thesis shows that a local equation of state cannot be used, but the electron temperature variations must be descibed as a nonlocal response to the state of the auroral flux tube. The nonlocal response can be accomplished by the particle-fluid model presented in this thesis. This new dynamic model is a combination of a fluid model and a Particle-In-Cell (PIC) model and results in large parallel electric fields consistent with in-situ observations.</p>

La thèse porte sur l'excitation multifréquence dans les décharges capacitives basse pression utilisées pour la gravure en microélectronique. L'intérêt majeur que représente l'utilisation d'une décharge capacitive excitée à deux fréquences provient du fait qu'elle est susceptible d'offrir un contrôle indépendant entre l'énergie des ions et le flux des ions. Dans la première partie j'ai développé un modèle global analytique basé sur (i) un modèle d'une gaine de charge d'espace capacitive, inhomogène, et excitée à deux fréquences, (ii) un modèle de chauffage dans ces gaines (ohmique et stochastique). Les résultats de ce modèle montrent que le chauffage couple dans la gaine de charge d'espace la composante basse fréquence et la composante haute fréquence ce qui a pour conséquence que le flux et l'énergie des ions ne sont pas indépendants. Cette affirmation a été validée par l'obtention des lois d'échelles relatives à l'énergie des ions et au flux des ions. A haute fréquence nous pouvons voir la décharge comme la propagation d'une onde de surface du centre du plasma vers la périphérie à l'interface plasma-gaine de charge d'espace. Lorsque la longueur d'onde dans le plasma λ correspondant à la plus haute fréquence d'excitation est de l'ordre des dimensions des électrodes, alors des effets électromagnétiques apparaissent. Il s'agit de l'effet d'onde stationnaire (λ

<p>The Auroral Large Imaging System (ALIS) was proposed in 1989 by Åke Steen as a joint Scandinavian ground-based nework of automated auroral imaging stations. The primary scientic objective was in the field of auroral physics, but it was soon realised that ALIS could be used in other fields, for example, studies of Polar Stratospheric Clouds (PSC), meteors, as well as other atmospheric phenomena.</p><p>This report describes the design, operation and scientic results from a Swedish prototype of ALIS consisting of six unmanned remote-controlled stations located in a grid of about 50 km in northern Sweden. Each station is equipped with a sensitive high-resolution (1024 x 1024 pixels) unintensified monochromatic CCDimager. A six-position filter-wheel for narrow-band interference filters facilitates absolute spectroscopic measurements of, for example, auroral and airglow emissions. Overlapping fields-of-view resulting from the station baseline of about 50 km combined with the station field-of-view of 50° to 60°, enable triangulation as well as tomographic methods to be employed for obtaining altitude information of the observed phenomena.</p><p>ALIS was probably one of the first instruments to take advantage of unintensi- fied (i.e. no image-intensifier) scientific-grade CCDs as detectors for spectroscopic imaging studies with multiple stations of faint phenomena such as aurora, airglow, etc. This makes absolute calibration a task that is as important as it is dificult.</p><p>Although ALIS was primarily designed for auroral studies, the majority of the scientific results so far have, quite unexpectedly, been obtained from observations of HF pump-enhanced airglow (recently renamed Radio-Induced Aurora). ALIS made the first unambiguous observation of this phenomena at high-latitudes and the first tomography-like inversion of height profiles of the airglow regions. The scientific results so far include tomographic estimates of the auroral electron spectra, coordinated observations with satellite and radar, as well as studies of polar stratospheric clouds. An ALIS imager also participated in a joint project that produced the first ground-based daytime auroral images. Recently ALIS made spectroscopic observations of a Leonid meteor-trail and preliminary analysis indicates the possible detection of water in the Leonid.</p>

<p>This thesis discusses the reasons for space exploration and space science. Space plasma physics is identified as an essential building block to understand the space environment and it is argued that observation and analysis of space plasma waves is an important approach.</p><p>Space plasma waves are the main actors in many important processes. So-called broadband waves are found responsible for much of the ion heating in the auroral region. We investigate the wave properties of broadband waves and show that they can be described as a mixture of electrostatic wave modes. In small regions void of cold electrons the broadband activity is found to be ion acoustic waves and these regions are also identified as acceleration regions. The identification of the wave modes includes reconstructions of the wave distribution function. The reconstruction technique allow us to determine the wave vector spectrum, which cannot be measured directly. The method is applied to other wave events and it is compared in some detail with a similar method.</p><p>Space plasma wave are also sensitive tools for investigations of both the fine-structure and the dynamics of space plasmas. Studies of whistler mode waves observed in the boundary layer on the magnetospheric side of the magnetopause reveal that the plasma is organized in tube-like structures moving with the plasma drift velocity. The perpendicular dimension of these tubes is of the order of the electron inertial length. We present evidence that each tube is linked to a reconnection site and argue that the high density of tube-like structures indicates patchy reconnection.</p>

<p>The concept of energy production through the fusion of two light nuclei has been studied since the 1950’s. One of the major problems that fusion scientists have encountered is the confinement of the hot ionised gas, i.e. the plasma, in which the fusion process takes place. The most common way to contain the plasma is by using at magnetic field configuration, in which the plasma takes a doughnut-like shape. Experimental devices of this kind are referred to as tokamaks. For the fusion process to proceed at an adequate rate, the temperature of the plasma must exceed 100,000,000C. Such a high temperature forces the plasma out of thermodynamical equilibrium which plasma tries to regain by exciting a number of turbulent processes. After successfully quenching the lager scale magnetohydrodynamic turbulence that may instantly disrupt the plasma, a smaller scale turbulence revealed itself. As this smaller scale turbulence behaved contrary to the common theory at the time, it was referred to as anomalous. This kind of turbulence does not directly threaten existents of the plasma, but it allows for a leakage of heat and particles which inhibits the fusion reactions. It is thus essential to understand the origin of anomalous turbulence, the transport it generates and most importantly, how to reduce it. Today it is believed that anomalous transport is due to drift-type waves driven by temperature and density inhomogeneities and the theoretical treatment of these waves is the topic of this thesis.</p><p>The first part of the thesis contains a rigorous analytical two-fluid treatment of drift waves driven solely by density inhomogeneities. Effects of the toroidal magnetic field configuration, the Landau resonance, a peaked diamagnetic frequency and a sheared rotation of the plasma have been taken into account. These effects either stabilise or destabilise the drift waves and to determine the net result on the drift waves requires careful analysis. To this end, dispersion relations have been obtained in various limits to determine when to expect the different effects to be dominant. The main result of this part is that with a large enough rotational shear, the drift waves will be quenched.</p><p>In the second part we focus on temperature effects and thus treat reactive drift waves, specifically ion temperature gradient and trapped electron modes. In fusion plasmas the α-particles, created as a by-product of the fusion process, transfer the better part of their energy to the electrons and hence the electron temperature is expected to exceed the ion temperature. In most experiments until today, the ion temperature is greater than the electron temperature and this have been proven to improve the plasma confinement. To predict the performance of future fusion plasmas, where the fusion process is ongoing, a comprehensive study of hot-electron plasmas and external heating effects have been carried out. Especially the stiffness (heat flux vs. inverse temperature length scale) of the plasma has been examined. This work was performed by simulations done with the JETTO code utilising the Weiland model. The outcome of these simulations shows that the plasma response to strong heating is very stiff and that the plasma energy confinement time seems to vary little in the hot-electron mode.</p>

<p>Polarisation, which was first studied in optics, is a fundamental property of all electromagnetic fields. A convenient way to describe the polarisation of two dimensional electromagnetic fields is given by the Stokes parameters. This thesis deals with different aspects of wave polarisation and electromagnetic field measurements. A generalisation of the Stokes parameters to three dimensions is presented. The theory has been used to develop methods and systems for obtaining the polarisation parameters of electromagnetic waves. The methods can be applied for a wide range of electromagnetic fields, measured both on ground and onboard satellites. The applications include, e.g., direction-finding, polarisation analysis, radar, and several examples in the field of wireless communication. Further applications are given in the analysis of satellite data, where a whistler wave is considered. Whistlers are circularly polarised electromagnetic waves propagating in the magnetosphere along the geomagnetic field. Dispersion in the magnetospheric plasma make the whistler frequencies travel at different speeds and the signal takes the form of a chirp. From instantaneous polarisation analysis of the whistler´s magnetic wave field, the normal to the polarisation plane is obtained and found to precess around the geomagnetic field. A statistic analysis of ionospheric stimulated electromagnetic emissions (SEE) is also presented. SEE is generated by injecting a powerful high frequency radio wave into the ionosphere. It is shown that the SEE features have a statistical behaviour indistinguishable from the amplitude and phase distributions of narrow-band Gaussian noise. The results suggests that SEE cannot be explained by simple coherent processes alone. Finally, an expression for the complex Poynting theorem is derived for the general case of anharmonic fields. It is found that the complex Poynting theorem, for real fields and sources, is not a conservation law of the imaginary part of electromagnetic energy.</p>

<p>The magnetospheric cusps are two funnel-like regions of Earth's magnetosphere where solar wind plasma can have direct access to the ionosphere. The cusps are very dynamic regions where wave-particle interactions continuously take place and redistribute energy among different particle populations. In this thesis, both low and high frequency plasma waves in the cusp have been studied in detail using data from the Cluster spacecraft mission. The waves were studied with respect to frequency, Poynting flux and polarization. Wavelengths have also been estimated using multi-spacecraft techniques. At low frequencies, kinetic Alfvén waves and nonpotential ion cyclotron waves are identified and at high frequencies, electron cyclotron waves, whistler waves, upper-hybrid and RX-waves are observed. A common generation mechanism called the shell-instability is proposed for several of the wave modes present in the cusp, both at low and high frequencies. </p><p>The plasma in the cusp is shown to be strongly inhomogeneous. In an inhomogeneous low-frequency magnetoplasma, kinetic Alfvén waves couple to drift-waves. Such drift-kinetic Alfvén waves have long been believed to nonlinearly self-interact and form coherent structures in the form of drift-kinetic Alfvén vortices. In this thesis the first unambiguous direct measurements confirming the existence of such vortices in a turbulent space plasma are presented. Some of the crucial parameters such as the vortex radius are determined. </p><p>Plasma theory is electrodynamics applied to a large collection of charged particles. In this thesis a new way of looking at the fundamental Maxwell tensor is presented. A covariant spectral density tensor containing information on electromagnetic waves is formed. This tensor is then decomposed into irreducible components by using the spinor formalism for an arbitrary metric. The obtained fundamental tensors are shown to correspond both to well known tensors in Maxwell's theory, as well as several physically interesting new tensors.</p>

Les sources d'atomes, la protection thermique pour la rentrée atmosphérique et la dépollution de l'air par couplage plasma-catalyseur voici quelques exemples d'applications pour lesquelles l'interaction plasma-surface joue un rôle principal. Les mécanismes des réactions hétérogènes dans les plasmas contenant les gaz atmosphériques N2/O2 sont encore peu compris. La précision et la capacité de prédiction des modèles cinétiques sont limitées par la connaissance des conditions de la surface. Dans la première partie de ce travail, nous avons étudié l'adsorption et les réactions chimiques des atomes O et N sur des surfaces de différents oxydes (silice, Pyrex, TiO2) sous exposition plasma. Nous avons utilisé la spectroscopie d'absorption par laser accordable, la spectroscopie d'absorption UV, la fluorescence induite par laser à deux photons (TALIF) et la spectrométrie de masse pour suivre l'interaction entre les espèces en phase gaz et les surfaces. L'analyse chimique de surface a été effectuée par spectrométrie photoélectronique X (XPS). Nous avons montré que des atomes stables Nads et Oads peuvent être chimisorbés sur la surface par plasma dans O2 et N2 à basse pression (~ 1 mbar). Leur densité et la réactivité ont été évaluées par réactions avec des molécules stables (NO, C2H2) et des radicaux (O, N) sur la surface prétraitée. Le rôle des atomes chimisorbés pour la recombinaison hétérogène d'atomes a été étudié en utilisant l'échange isotopique 15N ↔ 14Nads et 18O ↔ 16Oads sous exposition plasma. Dans la deuxième partie de cette thèse, nous avons étudié la relaxation vibrationnelle des molécules de N2 sur des surfaces catalytiques par la technique de titrage infrarouge (IR). Des mélanges contenant 0,05 - 1% de CO2 (CO ou N2O) dans N2 à la pression p = 1,3 mbar ont été excités par une décharge dc pulsée. La cinétique de la relaxation vibrationnelle des traceurs IR dans la post-décharge a été mesurée par un laser à cascade quantique. Grace à un couplage très efficace entre N2 et CO2 (CO ou N2O), l'excitation vibrationnelle de CO2 (CO ou N2O) reflet l'excitation de N2. Un modèle numérique de la cinétique vibrationnelle a été développé afin d'interpréter les mesures de relaxation. La probabilité de perte d'un quanta vibrationnel de N2 sur la surface a été déterminée à partir du meilleur accord entre l'expérience et le modèle.

Etude au voisinage de la résonnance des ondes dans le plasma-fréquence hybride basse en propagation perpendiculaire A B la résonnance hybride Boore fait intervenir un couplage entre l'onde et l'ensemble des espèces ionisées. On établit des approximations aux cas des plasmas ionosphérique et magnétosphérique. Analyse des raies des spectres en fréquence de signaux obtenus lors des expériences ISIS 2 et ELECTRON ECHO 1 (expliquée par l'excitation des modes de Berstein ioniques).

The Auroral Large Imaging System (ALIS) was proposed in 1989 by Åke Steen as a joint Scandinavian ground-based nework of automated auroral imaging stations. The primary scientic objective was in the field of auroral physics, but it was soon realised that ALIS could be used in other fields, for example, studies of Polar Stratospheric Clouds (PSC), meteors, as well as other atmospheric phenomena. This report describes the design, operation and scientic results from a Swedish prototype of ALIS consisting of six unmanned remote-controlled stations located in a grid of about 50 km in northern Sweden. Each station is equipped with a sensitive high-resolution (1024 x 1024 pixels) unintensified monochromatic CCDimager. A six-position filter-wheel for narrow-band interference filters facilitates absolute spectroscopic measurements of, for example, auroral and airglow emissions. Overlapping fields-of-view resulting from the station baseline of about 50 km combined with the station field-of-view of 50° to 60°, enable triangulation as well as tomographic methods to be employed for obtaining altitude information of the observed phenomena. ALIS was probably one of the first instruments to take advantage of unintensi- fied (i.e. no image-intensifier) scientific-grade CCDs as detectors for spectroscopic imaging studies with multiple stations of faint phenomena such as aurora, airglow, etc. This makes absolute calibration a task that is as important as it is dificult. Although ALIS was primarily designed for auroral studies, the majority of the scientific results so far have, quite unexpectedly, been obtained from observations of HF pump-enhanced airglow (recently renamed Radio-Induced Aurora). ALIS made the first unambiguous observation of this phenomena at high-latitudes and the first tomography-like inversion of height profiles of the airglow regions. The scientific results so far include tomographic estimates of the auroral electron spectra, coordinated observations with satellite and radar, as well as studies of polar stratospheric clouds. An ALIS imager also participated in a joint project that produced the first ground-based daytime auroral images. Recently ALIS made spectroscopic observations of a Leonid meteor-trail and preliminary analysis indicates the possible detection of water in the Leonid.