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.

La stabilité des modes magnéto-hydrodynamiques dans les plasmas de tokamaks est modifiée par la présence de particules rapides. Dans un tokamak tel qu'ITER ces particules rapides peuvent être soit les particules alpha créées par les réactions de fusion, soit les ions et électrons accélérés par les dispositifs de chauffage additionnel et de génération de courant. Les modes appelés fishbones électroniques correspondent à la déstabilisation du mode de kink interne due à la résonance avec le lent mouvement de précession toroidale des électrons rapides. Ces modes sont fréquemment observés dans les plasmas des tokamaks actuels en présence de chauffage par onde cyclotronique électronique (ECRH) ou de génération de courant par onde hybride basse (LHCD). La stabilité de ces modes est particulièrement sensible aux détails de la fonction de distribution électronique et du facteur de sécurité, ce qui fait des fishbones électroniques un excellent candidat pour tester la théorie linéaire des instabilités liées aux particules rapides. Dans le tokamak Tore Supra, des fishbones électroniques sont couramment observés lors de décharges où l'utilisation de l'onde hybride basse crée une importante queue de particules rapides dans la fonction de distribution électronique. Bien que ces modes soit clairement liés à la présence de particules rapides, la fréquence observée de ces modes est plus basse que celle prévue par la théorie. En effet, si on estime l'énergie des électrons résonants en faisant correspondre la fréquence du mode avec la fréquence de précession toroidale des électrons faiblement piégés, on obtient une valeur comparable à celle des électrons thermiques. L'objet principal de cette thèse est l'analyse linéaire de la stabilité des fishbones électroniques. La relation de dispersion de ces modes est dérivée et la forme obtenue prend en compte, dans la condition de résonance, la contribution du mouvement parallèle des particules passantes. Cette relation de dispersion est implémentée dans le code MIKE qui est ensuite testé avec succès en utilisant des fonctions de distributions analytiques. En le couplant au code Fokker-Planck relativiste LUKE et à la plate-forme de simulation intégrée CRONOS, MIKE peut estimer la stabilité des fishbones électroniques en utilisant les données reconstruites de l'expérience. En utilisant des fonctions de distributions et des équilibres analytiques dans le code MIKE nous montrons que les électrons faiblement piégés ou faiblement passants peuvent déstabiliser le mode de kink interne en résonant avec lui. Si l'on s'éloigne de la frontière entre électrons passants et piégés, les effets résonants s'affaiblissent. Cependant les électrons passants conservent une influence déstabilisante alors que les électrons piégées tendent à stabiliser le mode. D'autres simulations avec MIKE, utilisant cette fois des distributions complètes similaires à celles obtenues en présence de chauffage de type ECRH, montrent que l'interaction avec les électrons faiblement passants peut entraîner une déstabilisation du mode à une fréquence relativement basse ce qui pourrait permettre d'expliquer les observations sur le tokamak Tore Supra.

Plasma turbulence limits the performance of fusion reactors. Measuring and character- izing the turbulence properties is therefore a crucial issue in order to understand such phenomena. The goal of this thesis is to study the properties of plasma turbulence from ultrafast sweeping reflectometry measurements performed on the Tore Supra Tokamak. Reflectometry is a radar technique that is used to measure the electron density and its fluctuations. In the first part, we compare Langmuir probe and reflectometer data and discuss the possibility to characterize turbulence properties from the reconstructed fluctuating density profiles. Then, we show that the radial variation of the time and spatial scales of the turbulence as well as its radial velocity can be estimated from a cross-correlation analysis applied to the raw reflectometer signals. The modifications of the turbulence properties observed during a parametric scan are interpreted in the light of TEM and ITG turbulence. Finally, we show that the additional heating leads to a significant increase of the radial velocity in the plasma close to the tokamak wall.

L'objectif de la fusion par confinement magnétique, et notamment du tokamak, est de produire de l'énergie à partir des réactions de fusion nucléaire, dans un plasma à faible densité et haute température. Expérimentalement, une amélioration de la performance des tokamaks a été observée en présence de rotation toroïdale. Or, les sources extérieurs de quantité de mouvement seront très limitées dans les futurs tokamaks, et notamment ITER. Une compréhension de la physique de la génération intrinsèque de rotation toroïdale permettrait donc de prédire les profils de rotation dans les expériences futures. Parmi les mécanismes envisagés, on s'intéresse ici à la génération de rotation par la turbulence, qui domine le transport de la chaleur dans les tokamaks. Les plasmas de fusion étant faiblement collisionnels, la modélisation de cette turbulence suppose un modèle cinétique décrivant la fonction de distribution des particules dans l'espace des phases à six dimensions (position et vitesse). Cependant, ce modèle peut être réduit à cinq dimensions pour des fréquences inférieures à la fréquence cyclotronique des particules. Le modèle gyrocinétique qui découle de cette approximation est alors accessible avec les ressources numériques actuelles. Les travaux présentés portent sur l'étude du transport de quantité de mouvement toroïdale dans les plasmas de tokamak, dans le cadre du modèle gyrocinétique. Dans un premier temps, nous montrons que ce modèle réduit permet une description précise du transport de quantité de mouvement en dérivant une équation locale de conservation. Cette équation est vérifiée numériquement à l'aide du code gyrocinétique GYSELA. Ensuite, nous montrons comment la turbulence électrostatique peut briser l'axisymétrie du système, générant ainsi de la rotation toroïdale. Un lien fort entre transport de chaleur et transport de quantité de mouvement est mis en évidence, les deux présentant des avalanches à grande échelle. La dynamique du transport turbulent est analysée en détail et, bien que l'estimation standard gyro-Bohm soit vérifiée en moyenne, des phénomènes non-diffusifs sont observés. L'effet des écoulements de bord du plasma sur la rotation toroïdale dans le coeur est étudié en modifiant les conditions aux bords dans le code GYSELA. Enfin, le champ magnétique d'équilibre, qui n'est pas rigoureusement axisymétrique, peut également participer à la génération de rotation toroïdale, via des mécanismes purement collisionnels. Dans un tokamak, cet effet est suffisamment important pour entrer en compétition avec la rotation générée par la turbulence électrostatique.

The proton polarization in the 3He(d,p)4He reaction induced by unpolarized deuterons has been measured at deuteron lab. energies of 2.0, 2.8, 3.9 and 6.0MeV for 20 angles between 0° and 150° (c.m.). Statistical uncertainties are typically ± 0.01. The measurements were made with a proton polarimeter in which the left-right asymmetry of scattering at 60° (lab.) in 4He is determined. The polarimeter employs "venetian-blind" collimation of the protons by conical vanes and 75 cm2 plastic scintillator detectors. Four detectors are included for use in polarization transfer experiments. For 10.5 MeV protons and a helium pressure of 250 p.s.i. the target thickness is 3 MeV and the efficiency per detector per unpolarized proton incident is 10-4. For each polarimeter detector a triple coincidence with a 15 ns resolving time was required with two scintillator transmission detectors preceding the polarimeter. Spectra of random coincidences were accumulated simultaneously and subtracted. Asymmetries resulting from polarimeter-target misalignment and other geometrical effects are discussed. All results quoted are geometric means of pairs of measurements for 180° rotation of the polarimeter and are also arithmetic means of such measurements to left and right of the 3He target. The absolute analyzing power is estimated by computer simulation of trajectories to be -0.638 ± 0.020 for protons entering at 10.3 MeV. The product of polarization and cross section is fitted to an expansion of first-order associated Legendre polynomials using these results and earlier measurements. Only four terms are required except at 6.0MeV where a fifth is necessary. The energy dependence of these coefficients suggests resonances in 5Li at deuteron energies of 60MeV (odd coefficients) and 7.5 MeV (even coefficients) in agreement with results for the polarized-beam analyzing powers(1). Comparison of the results with vector-polarized-beam (1) and polarized-target(2) analyzing powers shows no evidence for the postulated simple relations(3) based on DWBA cal calculations. Comparison of the results with recent measurements of the neutron polarization in the mirror reaction(4) shows no significant differences. The theory of angular correlations in charged particle reactions is developed and used to calculate outgoing nucleon polarizations. Expressions are given for polarization transfer coefficients. These coefficients are evaluated in terms of the T-matrix elements for the interference of various channels with the dominant S-wave, JΠ = 3+/2 channel in 3He(d,p)4He at the 0.43 MeV resonance. Two experiments to measure combinations of these elements are discussed. (1) Gruebler, W. et al., 1971, Nucl. Phys. Al76, 631 (2) Leemann, Ch., W. Gruebler et al., 1971, in Polarization Phenomena in Nuclear Reactions (University of Wisconsin Press), p. 548 (3) Tanifuji,M. and K. Yazaki, 1968, Prog. Theor. Phys. 40, 1023 (4) Mutchler, G.S., W.B. Broste and J.E. Simmons, 1971, Phys. Rev. C3, 1031

This thesis investigates the properties of an atomic system exhibiting a giant Kerr nonlinearity. The atomic energy level scheme involves four energy levels. A three level A subsystem in the atom exhibits the effect of electromagnetically induced transparency (EIT), reducing the spontaneous emission noise. The fourth level leads to an ac-Stark shift of the ground state, which in turn leads to a giant, noiseless Kerr nonlinearity. Two different environments are explored. First, a system comprising of large number of atoms in an optical cavity is analysed. Detailed aspects of noise reduction in this system are investigated. In particular, strong squeezing in the quadrature in phase with the field driving the cavity mode is found, if the effective coupling of light to the atoms is strong. However, the linewidth of the predicted squeezing is found to be very narrow. This is attributed to a very steep linear susceptibility of the atomic medium. Since the widening of the squeezing window is possible only for weaker effective coupling, in turn reducing the squeezing level, a different environment is proposed. This involves a single four level atom, strongly coupled to the cavity mode. In such a strongly coupled system, the most appropriate approach is found to be that formulated in terms of polaritons – composite excitations of the 'atom-cavity molecule'. Adopting the polariton approach, nonclassical correlations in the field leaving the cavity are investigated. Strong photon antibunching is found and the effect of photon blockade predicted and described. The photon blockade effect can also be found in a system comprised of a two level atom coupled to the cavity mode, if the external driving is tuned to one of the vacuum Rabi resonances. A comparison between the two schemes is performed, and it is found that the four level scheme exhibits much better photon blockade. The reason for this is quantum interference between secondary transitions in the dressed states picture. Destructive interference cancels the transitions that would otherwise introduce a second photon into the system, hence producing a more robust photon blockade. All of these results are valid in the regime where external driving is weak. If the external driving strength is increased, the photon statistics (as measured by the zero-delay second order correlation function) changes from strong antibunching to strong bunching, over a relatively narrow range of driving strengths. The occurrence of this change can again be attributed to quantum interference. It is shown that the interference effect prevents the excitation of the composite system by a second photon, but not excitation by a two-photon transition (following the first excitation). Therefore, the third excitation manifold is excited, which then decays back to the first manifold in a two photon cascade. This two photon cascade is the source of correlated photon pairs causing an increase in the second order correlation function. The dynamics of forward scattering of light is presented, and nonclassical behaviour of the delay dependence of correlation function ('overshoots' and 'undershoots') is discussed. For the analytical treatment of this system, a method based on the polariton approach is devised, which includes the treatment of driving and damping. It is shown that this method is ideally suited to the analysis of strongly coupled systems, where only a few photons contribute to the dynamics.

The proton polarization in the 3He(d,p)4He reaction induced by unpolarized deuterons has been measured at deuteron lab. energies of 2.0, 2.8, 3.9 and 6.0MeV for 20 angles between 0° and 150° (c.m.). Statistical uncertainties are typically ± 0.01. The measurements were made with a proton polarimeter in which the left-right asymmetry of scattering at 60° (lab.) in 4He is determined. The polarimeter employs "venetian-blind" collimation of the protons by conical vanes and 75 cm2 plastic scintillator detectors. Four detectors are included for use in polarization transfer experiments. For 10.5 MeV protons and a helium pressure of 250 p.s.i. the target thickness is 3 MeV and the efficiency per detector per unpolarized proton incident is 10-4. For each polarimeter detector a triple coincidence with a 15 ns resolving time was required with two scintillator transmission detectors preceding the polarimeter. Spectra of random coincidences were accumulated simultaneously and subtracted. Asymmetries resulting from polarimeter-target misalignment and other geometrical effects are discussed. All results quoted are geometric means of pairs of measurements for 180° rotation of the polarimeter and are also arithmetic means of such measurements to left and right of the 3He target. The absolute analyzing power is estimated by computer simulation of trajectories to be -0.638 ± 0.020 for protons entering at 10.3 MeV. The product of polarization and cross section is fitted to an expansion of first-order associated Legendre polynomials using these results and earlier measurements. Only four terms are required except at 6.0MeV where a fifth is necessary. The energy dependence of these coefficients suggests resonances in 5Li at deuteron energies of 60MeV (odd coefficients) and 7.5 MeV (even coefficients) in agreement with results for the polarized-beam analyzing powers(1). Comparison of the results with vector-polarized-beam (1) and polarized-target(2) analyzing powers shows no evidence for the postulated simple relations(3) based on DWBA cal calculations. Comparison of the results with recent measurements of the neutron polarization in the mirror reaction(4) shows no significant differences. The theory of angular correlations in charged particle reactions is developed and used to calculate outgoing nucleon polarizations. Expressions are given for polarization transfer coefficients. These coefficients are evaluated in terms of the T-matrix elements for the interference of various channels with the dominant S-wave, JΠ = 3+/2 channel in 3He(d,p)4He at the 0.43 MeV resonance. Two experiments to measure combinations of these elements are discussed. (1) Gruebler, W. et al., 1971, Nucl. Phys. Al76, 631 (2) Leemann, Ch., W. Gruebler et al., 1971, in Polarization Phenomena in Nuclear Reactions (University of Wisconsin Press), p. 548 (3) Tanifuji,M. and K. Yazaki, 1968, Prog. Theor. Phys. 40, 1023 (4) Mutchler, G.S., W.B. Broste and J.E. Simmons, 1971, Phys. Rev. C3, 1031

This thesis investigates the properties of an atomic system exhibiting a giant Kerr nonlinearity. The atomic energy level scheme involves four energy levels. A three level A subsystem in the atom exhibits the effect of electromagnetically induced transparency (EIT), reducing the spontaneous emission noise. The fourth level leads to an ac-Stark shift of the ground state, which in turn leads to a giant, noiseless Kerr nonlinearity. Two different environments are explored. First, a system comprising of large number of atoms in an optical cavity is analysed. Detailed aspects of noise reduction in this system are investigated. In particular, strong squeezing in the quadrature in phase with the field driving the cavity mode is found, if the effective coupling of light to the atoms is strong. However, the linewidth of the predicted squeezing is found to be very narrow. This is attributed to a very steep linear susceptibility of the atomic medium. Since the widening of the squeezing window is possible only for weaker effective coupling, in turn reducing the squeezing level, a different environment is proposed. This involves a single four level atom, strongly coupled to the cavity mode. In such a strongly coupled system, the most appropriate approach is found to be that formulated in terms of polaritons – composite excitations of the 'atom-cavity molecule'. Adopting the polariton approach, nonclassical correlations in the field leaving the cavity are investigated. Strong photon antibunching is found and the effect of photon blockade predicted and described. The photon blockade effect can also be found in a system comprised of a two level atom coupled to the cavity mode, if the external driving is tuned to one of the vacuum Rabi resonances. A comparison between the two schemes is performed, and it is found that the four level scheme exhibits much better photon blockade. The reason for this is quantum interference between secondary transitions in the dressed states picture. Destructive interference cancels the transitions that would otherwise introduce a second photon into the system, hence producing a more robust photon blockade. All of these results are valid in the regime where external driving is weak. If the external driving strength is increased, the photon statistics (as measured by the zero-delay second order correlation function) changes from strong antibunching to strong bunching, over a relatively narrow range of driving strengths. The occurrence of this change can again be attributed to quantum interference. It is shown that the interference effect prevents the excitation of the composite system by a second photon, but not excitation by a two-photon transition (following the first excitation). Therefore, the third excitation manifold is excited, which then decays back to the first manifold in a two photon cascade. This two photon cascade is the source of correlated photon pairs causing an increase in the second order correlation function. The dynamics of forward scattering of light is presented, and nonclassical behaviour of the delay dependence of correlation function ('overshoots' and 'undershoots') is discussed. For the analytical treatment of this system, a method based on the polariton approach is devised, which includes the treatment of driving and damping. It is shown that this method is ideally suited to the analysis of strongly coupled systems, where only a few photons contribute to the dynamics.

The proton polarization in the 3He(d,p)4He reaction induced by unpolarized deuterons has been measured at deuteron lab. energies of 2.0, 2.8, 3.9 and 6.0MeV for 20 angles between 0° and 150° (c.m.). Statistical uncertainties are typically ± 0.01. The measurements were made with a proton polarimeter in which the left-right asymmetry of scattering at 60° (lab.) in 4He is determined. The polarimeter employs "venetian-blind" collimation of the protons by conical vanes and 75 cm2 plastic scintillator detectors. Four detectors are included for use in polarization transfer experiments. For 10.5 MeV protons and a helium pressure of 250 p.s.i. the target thickness is 3 MeV and the efficiency per detector per unpolarized proton incident is 10-4. For each polarimeter detector a triple coincidence with a 15 ns resolving time was required with two scintillator transmission detectors preceding the polarimeter. Spectra of random coincidences were accumulated simultaneously and subtracted. Asymmetries resulting from polarimeter-target misalignment and other geometrical effects are discussed. All results quoted are geometric means of pairs of measurements for 180° rotation of the polarimeter and are also arithmetic means of such measurements to left and right of the 3He target. The absolute analyzing power is estimated by computer simulation of trajectories to be -0.638 ± 0.020 for protons entering at 10.3 MeV. The product of polarization and cross section is fitted to an expansion of first-order associated Legendre polynomials using these results and earlier measurements. Only four terms are required except at 6.0MeV where a fifth is necessary. The energy dependence of these coefficients suggests resonances in 5Li at deuteron energies of 60MeV (odd coefficients) and 7.5 MeV (even coefficients) in agreement with results for the polarized-beam analyzing powers(1). Comparison of the results with vector-polarized-beam (1) and polarized-target(2) analyzing powers shows no evidence for the postulated simple relations(3) based on DWBA cal calculations. Comparison of the results with recent measurements of the neutron polarization in the mirror reaction(4) shows no significant differences. The theory of angular correlations in charged particle reactions is developed and used to calculate outgoing nucleon polarizations. Expressions are given for polarization transfer coefficients. These coefficients are evaluated in terms of the T-matrix elements for the interference of various channels with the dominant S-wave, JΠ = 3+/2 channel in 3He(d,p)4He at the 0.43 MeV resonance. Two experiments to measure combinations of these elements are discussed. (1) Gruebler, W. et al., 1971, Nucl. Phys. Al76, 631 (2) Leemann, Ch., W. Gruebler et al., 1971, in Polarization Phenomena in Nuclear Reactions (University of Wisconsin Press), p. 548 (3) Tanifuji,M. and K. Yazaki, 1968, Prog. Theor. Phys. 40, 1023 (4) Mutchler, G.S., W.B. Broste and J.E. Simmons, 1971, Phys. Rev. C3, 1031

This thesis investigates the properties of an atomic system exhibiting a giant Kerr nonlinearity. The atomic energy level scheme involves four energy levels. A three level A subsystem in the atom exhibits the effect of electromagnetically induced transparency (EIT), reducing the spontaneous emission noise. The fourth level leads to an ac-Stark shift of the ground state, which in turn leads to a giant, noiseless Kerr nonlinearity. Two different environments are explored. First, a system comprising of large number of atoms in an optical cavity is analysed. Detailed aspects of noise reduction in this system are investigated. In particular, strong squeezing in the quadrature in phase with the field driving the cavity mode is found, if the effective coupling of light to the atoms is strong. However, the linewidth of the predicted squeezing is found to be very narrow. This is attributed to a very steep linear susceptibility of the atomic medium. Since the widening of the squeezing window is possible only for weaker effective coupling, in turn reducing the squeezing level, a different environment is proposed. This involves a single four level atom, strongly coupled to the cavity mode. In such a strongly coupled system, the most appropriate approach is found to be that formulated in terms of polaritons – composite excitations of the 'atom-cavity molecule'. Adopting the polariton approach, nonclassical correlations in the field leaving the cavity are investigated. Strong photon antibunching is found and the effect of photon blockade predicted and described. The photon blockade effect can also be found in a system comprised of a two level atom coupled to the cavity mode, if the external driving is tuned to one of the vacuum Rabi resonances. A comparison between the two schemes is performed, and it is found that the four level scheme exhibits much better photon blockade. The reason for this is quantum interference between secondary transitions in the dressed states picture. Destructive interference cancels the transitions that would otherwise introduce a second photon into the system, hence producing a more robust photon blockade. All of these results are valid in the regime where external driving is weak. If the external driving strength is increased, the photon statistics (as measured by the zero-delay second order correlation function) changes from strong antibunching to strong bunching, over a relatively narrow range of driving strengths. The occurrence of this change can again be attributed to quantum interference. It is shown that the interference effect prevents the excitation of the composite system by a second photon, but not excitation by a two-photon transition (following the first excitation). Therefore, the third excitation manifold is excited, which then decays back to the first manifold in a two photon cascade. This two photon cascade is the source of correlated photon pairs causing an increase in the second order correlation function. The dynamics of forward scattering of light is presented, and nonclassical behaviour of the delay dependence of correlation function ('overshoots' and 'undershoots') is discussed. For the analytical treatment of this system, a method based on the polariton approach is devised, which includes the treatment of driving and damping. It is shown that this method is ideally suited to the analysis of strongly coupled systems, where only a few photons contribute to the dynamics.