Effects of a magnetic field on the double-probe technique are studied experimentally by means of symmetric floating computer controlled fast double probes in low and intermediate pressure plasmas. In addition, the effects of the magnetic field on the electron temperature, electron density, and electric field have been investigated. As it is expected, when there is no magnetic field, properties of the discharge plasma are best described by Langmuir theory. Whereas, when there&rsquo / s a magnetic field of sufficient strength Schottky&rsquo / s theory of ambipolar diffusion applies.

This thesis deals with a one and two dimensional numerical modeling of a low-pressure DC glow discharge in argon gas. We develop two-component fluid model which uses the diffusion-drift theory for the gas discharge plasma and consists of continuity equations for electrons and ions, as well as Poisson equation for electric field. Numerical method is based on the control volume technique. Calculations are carried out in MATLAB environment. Computed results are compared with the classic theory of glow discharges and available experimental data.

This thesis is about the designing and constructing a microwave ion source. The ions are generated in a thermal and dense hydrogen plasma by microwave induction. The plasma is generated by using a microwave source with a frequency of 2.45 GHz and a power of 700 W. The generated microwave is pulsing with a frequency of 50 Hz. The designed and constructed microwave system generates hydrogen plasma in a pyrex plasma chamber. Moreover, an ion extraction unit is designed and constructed in order to extract the ions from the generated hydrogen plasma. The ion beam extraction is achieved and ion currents are measured. Th e plasma parameters are determined by a double Langmuir probe and the ion current is measured by a Faraday cup. The designed ion extraction unit is simulated by using the dimensions of the designed and constructed ion extraction unit in order to trace out the trajectories of the extracted ions.

The problem of bluff body flows and the drag associated with them has been the subject of numerous investigations in the literature. In the two-dimensional case, the flow past a circular cylinder has been most widely studied both experimentally and computationally. As a result, a well documented understanding of the gross features of the near-wake around a circular cylinder exists in the literature. In contrast, very little is understood on the general features of three-dimensional bluff body near-wakes, except that the vortex shedding is known to be less intense. Control or management of bluff body flows, both from the point of view of drag reduction as well as suppressing unsteady forces caused by vortex shedding, has been an area of considerable interest in engineering applications. The basic aim in the different control methods involves direct or indirect manipulation (or modification) of the near-wake structure leading to weakening or inhibition of vortex shedding. Many passive and energetic techniques (such as splitter plates, base and trailing edge modifications and base bleed) have been effective in the two-dimensional case in increasing the base pressure, leading to varying amounts of drag reduction; a large body of this work is centered around circular cylinders because of direct relevance in applications. The present work is an attempt to understand some of the major aspects of the near-wake structure of a sphere and to control the same for drag reduction employing a passive technique. Many of the passive control techniques found useful in two-dimensional flows are not appropriate in the context of a sphere. In this thesis, the effects of natural ventilation on the wake and drag of a sphere at low speeds have been studied experimentally in some detail. Natural bleed into the base is created when the stagnation and base regions of a sphere are connected through an internal duct. Although natural ventilation has features broadly similar to the well known base-bleed technique (both involve addition of mass, momentum and energy into the near-wake), there are many significant differences between the two methods; for example, in base bleed, the mass flow injected can be controlled independent of the outer flow, whereas in natural ventilation, it is determined by an interaction between the internal and the external flow around the body. Experiments have been conducted in both wind and water tunnels, which covered a wide range of Reynolds number (ReDj based on the diameter of the sphere) from of 1.7 x 103 to 8.5 x 105 with natural boundary layer transition. The ratio of the frontal vent area to the maximum cross sectional area of the sphere was varied from 1% to 2.25% and the effect of the internal duct geometry, including a convergent and a divergent duct was examined as well. After preliminary force measurements involving different duct geometries and vent areas, it was decided to make detailed measurements with a straight (parallel) duct with a vent area ratio of 2.25%. Extensive flow visualization studies involving dye-flow, hydrogen bubble, surface oil-flow and laser-light-sheet techniques were employed to gain insight into many aspects of the near-wake structure and the flow on the surface of the sphere. Measurements made included model static pressures, drag force using a strain gauge balance and velocity profiles in the near-wake and internal flow through the vent. In addition, wake vortex shedding frequency was measured using a hotwire. In the subcritical range of Reynolds numbers (ReD< 2 x 105), the near-wake of the sphere (without ventilation) was found to be vortex shedding, with laminar separation occurring around a value of0s = 80° (where 0s is the angle between the stagnation point and separation location). In contrast, there was little evidence of vortex shedding in the supercritical range (ReD> 4 x 105), consistent with many earlier observations in the literature; however, flow visualization studies in the near-wake clearly showed the existence of a three-dimensional vortex-like structure exhibiting random rotations about the streamwise axis. In this range of Reynolds numbers, surface flow visualization studies indicated the existence of a laminar separation bubble which was followed by a transitional/turbulent reattachment and an ultimate separation around 0S = 145°. All the above observations are broadly consistent with the results available in the literature. With ventilation at subcritical Reynolds numbers, the pressure distributions on the sphere including in the base region was only weakly altered, resulting in a marginal reduction in the total drag; because of the higher pressure difference between the stagnation and base regions, the mean velocity in the vent-flow was about 0.9 times the free-stream velocity. As may be expected, there was little change in the location of laminar separation on the sphere and the vortex shedding frequency was virtually unaltered due to ventilation. The relatively small effects on pressure distribution and drag suggest weak interaction between the vent-flow and the separated shear layer in the subcritical regime. The time-averaged near-wake flow revealed a stagnation point occurring between the vent-flow and the reverse flow in the near-wake, along with the formation of a torroidal vortex between the stagnation point and the near-wake closure; these features bear some resemblance to those observed with base bleed from a blunt base. With ventilation in the supercritical range of Reynolds numbers (ReD > 4 x 105), significant reduction in the total drag, of as much as 65%, was observed from force measurements. Pressure distributions showed higher pressures in the separated flow zone (consistent with reduced drag) as a result of which the internal mass and the mean velocity of the vent-flow were lower (0.69 times the free-stream velocity) compared to the value in the subcritical flow regime. Flow visualization studies clearly showed that the three-dimensional rotating structure (associated with the wake of the unvented sphere) was significantly modified by ventilation, leading to more symmetric and steady near-wake features. The larger effects on pressure distribution and drag suggest strong interaction between the vent-flow and the separated shear layer, promoted by their close proximity. The comparison of power spectral density of u1 signals in the near-wake showed significant reduction in the amplitude at all frequencies, consistent with observations from flow visualization studies. The time-averaged near-wake flow features a pair of counterrotating ring vortices which are trapped between the outer separated shear layer and the vent-flow shear layer; such a mean flow pattern is qualitatively similar to that behind an axisymmetric base with a central jet with unequal freestream velocities in the jet and outer flow. This study strongly suggests that natural ventilation can provide significant total drag reduction provided the vent-flow is in close proximity of the separated shear layer promoting a strong interaction between them. Drag reduction is associated with more symmetric and relatively steady near-wake features in contrast with the unvented sphere.

PEGASES est un nouveau propulseur conçu et développé au LPP. Un propulseur électrique classique éjecte de la matière positive à grande vitesse depuis un plasma électropositif pour générer la poussée. La nouveauté introduite par PEGASES est le fait que la poussée est générée par l'accélération successive d'ions positifs et d'ions négatifs issus d'un plasma ion-ion continu. Le propulseur PEGASES est composé de trois étages: (i) un étage d'ionisation constitué d'une source radiofréquence (rf) pour le couplage inductif d'un plasma électronégatif à partir d'un gaz contenant des halogènes, (ii) un étage de filtrage magnétique des électrons pour obtenir un plasma ion-ion, et (iii) l'étage d'accélération des ions utilisant des grilles polarisées alternativement pour créer un champ électrique dont le sens varie dans le temps. Durant ma thèse, j'ai travaillé essentiellement sur les premier et troisième étages sur deux prototypes de PEGASES. Un plasma ion-ion a été obtenu dans le premier prototype à partir de SF6 grâce à un filtrage magnétique important. Mais des limitations inhérentes et significatives rendent les performances insuffisantes pour le processus d'accélération voulu. Afin d'obtenir une source d'ions électriquement performante, le second prototype utilise une source inductive plane avec une bobine à noyau de ferrite et une boîte d'accord d'impédance comportant un transformateur à faibles pertes. Le couplage capacitif parasite a été réduit en optimisant la boîte d'accord et les progrès sont évalués grâce à la mesure du spectre du potentiel plasma par sonde capacitive. Le plasma est étudié à l'aide de sondes de Langmuir et d'un analyseur de l'énergie des ions (RFEA) dans les deux prototypes. Le potentiel d'un plasma ion-ion peut être contrôlé par une électrode polarisée en contact avec le plasma. L'accélération des ions issus du plasma ion-ion est étudiée dans le cas continu où la polarisation des grilles est fixée puis en imposant une tension créneau d'amplitude comprise entre 0 et ± 350 V avec une fréquence de 1 kHz. Dans le cas alternatif, les ions positifs et les ions négatifs sont accélérés durant les demi-périodes de polarisation positive et négative respectivement. L'énergie respective des deux populations d'ions peut être contrôlée indépendamment, en continu et en alternatif. Avec ces résultats est démontrée la faisabilité du concept PEGASES et l'étude du propulseur peut passer à l'étape de développement et réalisation.

The possibility and feasibility is investigated of including in the modelling of nuclear cluster reactions a unified treatment of the effects both of the non-orthogonalities between transfer channels, and of the antisymmetrisation required by the Pauli Principle. The deuteron - nucleus interaction, the simplest cluster reaction, is considered in detail within the Coupled Channels framework. The Coupled Channels formalism was chosen because it accurately handles inelastic and transfer couplings of arbitary strengths. The fact that transfer channels are orthogonal to each other only asymptotically is taken into account by reallocating the wave function in the internal region, from the deuteron channels to the transfer channels, taking components from the deuteron channels in ways exactly analogous to the way the antisymmetrisation requirements remove blocked deuteron-core components. Thus a unified treatment of the two effects is facilitated. It is found further that when all possible transfer channels are included, along with all Pauli blockings from the core nucleons, then under certain conditions at low energies, the wave function in the deuteron channel is small and oscillatory in the internal region, leaving the deuteron as a cluster to have largely asymptotic significance. In this limit, the exact non-local potential governing the deuteron channel simplifies considerably in one approximation to be replaceable by just several orthogonality conditions, and these are easily modelled in solving the coupled equations for the radial wave functions. This simplified and unified model has the advantage, since the deuteron's internal wave form is significant only asymptotically, of allowing automatically for arbitary deuteron polarisation by the core (though not vice-versa). Furthermore, the asymptotic matching is not at a fixed radius as in R-matrix theory, but is a continuous process that depends on the binding energies of the actual proton & neutron bound states in the residual nucleus.

The possibility and feasibility is investigated of including in the modelling of nuclear cluster reactions a unified treatment of the effects both of the non-orthogonalities between transfer channels, and of the antisymmetrisation required by the Pauli Principle. The deuteron - nucleus interaction, the simplest cluster reaction, is considered in detail within the Coupled Channels framework. The Coupled Channels formalism was chosen because it accurately handles inelastic and transfer couplings of arbitary strengths. The fact that transfer channels are orthogonal to each other only asymptotically is taken into account by reallocating the wave function in the internal region, from the deuteron channels to the transfer channels, taking components from the deuteron channels in ways exactly analogous to the way the antisymmetrisation requirements remove blocked deuteron-core components. Thus a unified treatment of the two effects is facilitated. It is found further that when all possible transfer channels are included, along with all Pauli blockings from the core nucleons, then under certain conditions at low energies, the wave function in the deuteron channel is small and oscillatory in the internal region, leaving the deuteron as a cluster to have largely asymptotic significance. In this limit, the exact non-local potential governing the deuteron channel simplifies considerably in one approximation to be replaceable by just several orthogonality conditions, and these are easily modelled in solving the coupled equations for the radial wave functions. This simplified and unified model has the advantage, since the deuteron's internal wave form is significant only asymptotically, of allowing automatically for arbitary deuteron polarisation by the core (though not vice-versa). Furthermore, the asymptotic matching is not at a fixed radius as in R-matrix theory, but is a continuous process that depends on the binding energies of the actual proton & neutron bound states in the residual nucleus.

The possibility and feasibility is investigated of including in the modelling of nuclear cluster reactions a unified treatment of the effects both of the non-orthogonalities between transfer channels, and of the antisymmetrisation required by the Pauli Principle. The deuteron - nucleus interaction, the simplest cluster reaction, is considered in detail within the Coupled Channels framework. The Coupled Channels formalism was chosen because it accurately handles inelastic and transfer couplings of arbitary strengths. The fact that transfer channels are orthogonal to each other only asymptotically is taken into account by reallocating the wave function in the internal region, from the deuteron channels to the transfer channels, taking components from the deuteron channels in ways exactly analogous to the way the antisymmetrisation requirements remove blocked deuteron-core components. Thus a unified treatment of the two effects is facilitated. It is found further that when all possible transfer channels are included, along with all Pauli blockings from the core nucleons, then under certain conditions at low energies, the wave function in the deuteron channel is small and oscillatory in the internal region, leaving the deuteron as a cluster to have largely asymptotic significance. In this limit, the exact non-local potential governing the deuteron channel simplifies considerably in one approximation to be replaceable by just several orthogonality conditions, and these are easily modelled in solving the coupled equations for the radial wave functions. This simplified and unified model has the advantage, since the deuteron's internal wave form is significant only asymptotically, of allowing automatically for arbitary deuteron polarisation by the core (though not vice-versa). Furthermore, the asymptotic matching is not at a fixed radius as in R-matrix theory, but is a continuous process that depends on the binding energies of the actual proton & neutron bound states in the residual nucleus.

The possibility and feasibility is investigated of including in the modelling of nuclear cluster reactions a unified treatment of the effects both of the non-orthogonalities between transfer channels, and of the antisymmetrisation required by the Pauli Principle. The deuteron - nucleus interaction, the simplest cluster reaction, is considered in detail within the Coupled Channels framework. The Coupled Channels formalism was chosen because it accurately handles inelastic and transfer couplings of arbitary strengths. The fact that transfer channels are orthogonal to each other only asymptotically is taken into account by reallocating the wave function in the internal region, from the deuteron channels to the transfer channels, taking components from the deuteron channels in ways exactly analogous to the way the antisymmetrisation requirements remove blocked deuteron-core components. Thus a unified treatment of the two effects is facilitated. It is found further that when all possible transfer channels are included, along with all Pauli blockings from the core nucleons, then under certain conditions at low energies, the wave function in the deuteron channel is small and oscillatory in the internal region, leaving the deuteron as a cluster to have largely asymptotic significance. In this limit, the exact non-local potential governing the deuteron channel simplifies considerably in one approximation to be replaceable by just several orthogonality conditions, and these are easily modelled in solving the coupled equations for the radial wave functions. This simplified and unified model has the advantage, since the deuteron's internal wave form is significant only asymptotically, of allowing automatically for arbitary deuteron polarisation by the core (though not vice-versa). Furthermore, the asymptotic matching is not at a fixed radius as in R-matrix theory, but is a continuous process that depends on the binding energies of the actual proton & neutron bound states in the residual nucleus.

The possibility and feasibility is investigated of including in the modelling of nuclear cluster reactions a unified treatment of the effects both of the non-orthogonalities between transfer channels, and of the antisymmetrisation required by the Pauli Principle. The deuteron - nucleus interaction, the simplest cluster reaction, is considered in detail within the Coupled Channels framework. The Coupled Channels formalism was chosen because it accurately handles inelastic and transfer couplings of arbitary strengths. The fact that transfer channels are orthogonal to each other only asymptotically is taken into account by reallocating the wave function in the internal region, from the deuteron channels to the transfer channels, taking components from the deuteron channels in ways exactly analogous to the way the antisymmetrisation requirements remove blocked deuteron-core components. Thus a unified treatment of the two effects is facilitated. It is found further that when all possible transfer channels are included, along with all Pauli blockings from the core nucleons, then under certain conditions at low energies, the wave function in the deuteron channel is small and oscillatory in the internal region, leaving the deuteron as a cluster to have largely asymptotic significance. In this limit, the exact non-local potential governing the deuteron channel simplifies considerably in one approximation to be replaceable by just several orthogonality conditions, and these are easily modelled in solving the coupled equations for the radial wave functions. This simplified and unified model has the advantage, since the deuteron's internal wave form is significant only asymptotically, of allowing automatically for arbitary deuteron polarisation by the core (though not vice-versa). Furthermore, the asymptotic matching is not at a fixed radius as in R-matrix theory, but is a continuous process that depends on the binding energies of the actual proton & neutron bound states in the residual nucleus.