The turbulen flow in an asymmetric diffuser has been en studied by the means of Reynold average Navier-Stokes equations with both differential and explict algebraic expressions to model the Reynolds stress tensor. Modifications to the differential stress model have been derived, using the inverse turbulence timescale to obtain the dissipation of turbuence kinetic energy. The explicit algebraic Reynolds stress model has been used in combination with a two-equation platform to close the system of equations. Modifications made to the transport equation for the inverse turbulence timescale has made it possible to substantially relax the deman on near-wall resolution of this quantity. The rapid growth wth present in the original formulation can be treated as an explicit function of the wall-normal distance. In order to use the new formulation for the transport equation, an equation has as been derived to obtain the shortest distance bettwee a point and the closest wall, regardles of the geometric complexity of the domain. An explicit algebraic expression to model the passive scalar flux vector has been investigated using a comparison with a standard eddy-diffusivity model in the asymmetric diffuser. Results show a substantial improvement of the complexity of the scalar field and scalar flux vector in sepaarated flows. Automated code generation has been used in all the above studies to generate versatile model testing tools for general two-dimensional geometries. Finite element formulations are used for these tools.

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.

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

In this work, we investigate the relation between the diffusion behavior of Ti1-xAlxN at elevated temperatures and the microstructure. Thinfilm samples are synthesized by reactive co-sputtering with two cathodes. One cathode equipped with Ti target is connected to a highpower impulse magnetron sputtering (HiPIMS) power supply, and the other cathode equipped with Al target is operated with a directcurrent power source. The spinodal decomposition of cubic metastable Ti1-xAlxN controlled by thermally activated diffusion is observe fordiffusion behavior. Various HiPIMS pulsing frequencies are used to achieve different microstructure, while altered power applied to Altarget is used to change the Al content in films. In the phase composition analysis achieved by GI-XRD, the right-shift of (111) film peakalong with increasing Al-power is observed. A saturation of the right-shift and h-AlN peaks are also observed at certain Al-power. Thechemical composition determined by ERDA shows trends of reducing Al solubility limit in metastable phase and O contamination upondecreasing the pulsing frequency. More N deficiency is found in samples deposited with higher frequency. In the 500 Hz and 250 Hzsamples deposited into similar composition and thickness, no apparent difference of the microstructure is observed from the SEM crosssectionalimages. From HT-XRD, we observe higher intensity of TiO2 and h-AlN peaks in 500 Hz sample at elevated temperature ascompared with 250 Hz one. From the reduction of O contamination, denser Ti1-xAlxN films are able to be deposited with lower HiPIMSpulsing frequency. In addition, the higher intensity observed in HT-XRD patterns indicates that the 500 Hz sample is more open todiffusion and therefore allows the new formed phases to grow in larger grains.

<p>The turbulen flow in an asymmetric diffuser has been en studied by the means of Reynold average Navier-Stokes equations with both differential and explict algebraic expressions to model the Reynolds stress tensor. Modifications to the differential stress model have been derived, using the inverse turbulence timescale to obtain the dissipation of turbuence kinetic energy. The explicit algebraic Reynolds stress model has been used in combination with a two-equation platform to close the system of equations. Modifications made to the transport equation for the inverse turbulence timescale has made it possible to substantially relax the deman on near-wall resolution of this quantity. The rapid growth wth present in the original formulation can be treated as an explicit function of the wall-normal distance. In order to use the new formulation for the transport equation, an equation has as been derived to obtain the shortest distance bettwee a point and the closest wall, regardles of the geometric complexity of the domain. An explicit algebraic expression to model the passive scalar flux vector has been investigated using a comparison with a standard eddy-diffusivity model in the asymmetric diffuser. Results show a substantial improvement of the complexity of the scalar field and scalar flux vector in sepaarated flows. Automated code generation has been used in all the above studies to generate versatile model testing tools for general two-dimensional geometries. Finite element formulations are used for these tools.</p>

<p>The overall goal of the research presented in this thesis is to extend the physical understanding of the unsteady external aerodynamics associated with highly maneuverable delta-wing aircraft by using and developing novel, more efficient computational fluid dynamics (CFD) tools. More specific, the main purpose is to simulate and better understand the basic fluid phenomena, such as vortex breakdown, that limit the performance of delta-wing aircraft. The problem is approached by going from the most simple aircraft configuration - a pure delta wing - to more complex configurations. As the flow computations of delta wings at high angle of attack have a variety of unusual aspects that make accurate predictions challenging, best practices for the CFD codes used are developed and documented so as to raise their technology readiness level when applied to this class of flows.</p><p>Initially, emphasis is put on subsonic steady-state CFD simulations of stand-alone delta wings to keep the phenomenon of vortex breakdown as clean as possible. For half-span models it is established that the essential characteristics of vortex breakdown are captured by a structured CFD code. The influence of viscosity on vortex breakdown is studied and numerical results for the aerodynamic coefficients, the surface pressure distribution and breakdown locations are compared to experimental data where possible.</p><p>In a second step, structured grid generation issues, numerical aspects of the simulation of this nonlinear type of flow and the interaction of a forebody with a delta wing are explored.</p><p>Then, on an increasing level of complexity, time-accurate numerical studies are performed to resolve the unsteady flow field over half and full-span, stationary delta wings at high angle of attack. Both Euler and Detached Eddy Simulations (DES) are performed to predict the streamwise oscillations of the vortex breakdown location about some mean position, asymmetry in the breakdown location due to the interaction between the left and right vortices, as well as the rotation of the spiral structure downstream of breakdown in a time-accurate manner. The computed flow-field solutions are visualized and analyzed in a virtual-reality environment.</p><p>Ultimately, steady-state and time-dependent simulations of a full-scale fighter-type aircraft configuration in steady flight are performed using the advanced turbulence models and the detached-eddy simulation capability of an edge-based, unstructured flow solver. The computed results are compared to flight-test data.</p><p>The thesis also addresses algorithmic efficiency and presents a novel implicit-explicit algorithm, the Recursive Projection Method (RPM), for computations of both steady and unsteady flows. It is demonstrated that RPM can accelerate such computations by up to 2.5 times.</p>