This thesis deals with a new solution for medium voltage drives. Load Commutated Inverter (LCI) fed synchronous motor drive is a popular solution for high power drive applications. Though the induction machine is more rugged and cheaper compared to the synchronous machine, LCI fed induction motor drive solution is not available. The basic advantage of a synchronous machine over an induction machine is the fact that the synchronous machine can operate at leading power factor. Due to this property load commutation of SCR switches of the LCI is achievable for synchronous machine. On the contrary an induction machine always draws lagging power factor current; this makes it unsuitable as a drive motor for LCI technology. In this thesis a new LCI fed induction motor drive configuration is developed as an alternative for synchronous motor drives. A new variant of six phase induction motor is proposed in this context. The machine is named as Active Reactive Induction Machine (ARIM). The ARIM contains two sets of three-phase windings with isolated neutral. Both the windings have a common axis. One winding carries the active power and can be wound for higher voltage (say 11kV). The other winding supplies the total reactive power of the machine and can be wound for lower voltage (say 2.2 kV). The rotor is a standard squirrel cage. High power induction machines usually demand lesser magnitude of reactive power compared to the total power rating of the machine ( 20% ). Therefore excitation winding has a smaller fraction of the total machine rating compared to the power winding. A VSI with an LC filter supplies reactive power to the ARIM through the excitation winding and ensures leading power factor at the power winding. This is similar to the excitation control of the LCI fed synchronous machine. The direct VSI connection is possible due to the lower voltage rating for the excitation winding. In this way, the VSI voltage rating does not limit the highest motor voltage that can be handled. An LCI supplies the real power into the ARIM from the power winding. The LCI currents are quasi square wave in shape. Therefore they have rich low order harmonic content. They cause 6th and 12th harmonic torque pulsations in the machine. This is a problem for the LCI fed synchronous machine drive. In the proposed drive, the VSI can compensate these low frequency m.m.f. harmonics inside the machine air gap to remove torque pulsation and rotor harmonic losses. The advantage of the proposed topology is that no transformer is required to drive an 11kV machine. It is always desirable to feed sinusoidal voltage and current to both the power winding and the excitation winding. To address this problem, a second configuration is proposed. A low power three-level VSI is connected in shunt at the power winding with the proposed ARIM drive as discussed above. This VSI compensates the low frequency harmonic currents to achieve sinusoidal motor currents at the motor winding. This VSI acts as a shunt active filter and compensates for the lower order harmonics injected by the LCI. The proposed topologies have LC filters to maintain sinusoidal motor voltages and currents by absorbing the VSI switching frequency components. But the motor terminal voltage oscillates at system resonant frequency due to the presence of LC filters. These resonant components in the terminal voltages are required to be eliminated for smooth terminal voltages and safe load commutation of the thyristors. In this thesis a simple active damping method is proposed to mitigate these issues. The proposed topologies are experimentally verified with an ARIM with 415 V power winding and 220 V excitation winding. The control is carried out on a digital platform having a TMS 320LF 2407A DSP processor and an ALTERA CYCLONE FPGA processor. Results from the prototype experimental drive are presented to show the feasibility and performance of the proposed drive configurations.

The electronic control, instrumentation and communication hardware is becoming more and more compact and faster in operation due to the increased use of large scale integration of semiconductor devices operating at higher speeds. The use of VLSI circuit based systems in various industrial and defence sectors is also increasing continuously. Since the operating threshold voltages and currents of these devices are very small they are very prone to electrical disturbance in their operation by the Electromagnetic Interference (EMI) signals. Their proper functioning is very important particularly in the case of systems used in mission mode, critical defence/industrial platforms. EMI can be generated within the electronic system/equipment itself or may result due to some external electromagnetic source. The high power Ultra Wide Band system is one such kind of external High Power Electromagnetic (HPEM) interference source which may cause malfunctioning/physical damage to the sensitive electronic systems. Hence it is necessary to test the susceptibility of electronics to such high power UWB based intentional EMI or IEMI sources. The sources for generating these transient EM fields may also be used in impulse radars and offensive applications to mal-operate/damage non-friendly electronics. The UWB system consists of a high voltage pulsed power source called pulser along with a high bandwidth (Ultra Wide Band) antenna to radiate the UWB signal. The pulse fed by the pulser to the antenna through a switch is of high voltage type (amplitude of few 10s of kV to about a MV) and has a sub-nanosecond rise time. Most of the UWB systems developed over the world have the switch employing gaseous dielectric switching media used at pressures above the atmospheric level to generate such a fast rise time voltage pulse. Use of gaseous switching media at sub-atmospheric pressures to achieve sub-ns rise time, short duration high voltage pulses required for the high power UWB applications is another possibility. This possibility has not been exploited till date. Hence it was decided to develop a pulser switch with gaseous switching media at sub-atmospheric pressures (up to 50 mbar) and achieve sub-ns rise time voltage pulses of up to 50 kV. The energy delivered out by the UWB system depends upon the pulser output energy per switching shot and the repetitive switching rate of the pulser. To achieve maximum energy output it is required to maximize either the energy per switching shot or the pulse repetition rate (PRR) of the pulser switch. The optimization of the pulser operation to achieve maximum pulser energy output in every switching shot has not been tried so far. In this work it was decided to analyze the circuit so as to achieve maximum pulser output energy per switching shot. Another objective of the study was to systematically characterize the pulser switch using various gases and gas mixtures as the switching media to evaluate the switch performance as a function of gas pressure and switch breakdown voltage. The effect of pulser and antenna performance parameters on the UWB system performance was also decided to be evaluated. Hence the present thesis work deals with the design, development, evaluation and performance optimization of a 50 kV, 25 MW UWB system based on Half Impulse Radiating Antenna (HIRA) fed by a coaxial capacitive pulser. The spark gap type self triggered pulser switch is designed to have a fixed gap spacing and variable gas pressure in order to vary the switch breakdown voltage. The switch is designed for operation with dry air, nitrogen, sulphur hexafluoride (SF6) and a mixture of different gases as the dielectric switching media with pressures of up to 5 bar above the atmospheric level and up to 50 mbar below the atmospheric level. Physical placement of the switch just above the coaxial pulser capacitor terminal offered a low inductance geometry. The rise time estimation of the switch has been carried out as a function of gas pressure and the switch arc inductance. These rise time values have been compared with the measured ones and a good agreement was found between the two. The rise time values indicate that an inverse relationship exists between the gas pressure and the rise time. The rise time was found to decrease at increased pressures. SF6 gas offered the minimum rise time out of all the gases/mixtures studied. The pulse repetition rate (PRR) of the UWB system depends upon the dielectric recovery of the gaseous switch and the charging time of the pulser capacitor. To estimate the PRR a circuit model has been proposed based on these parameters. The model shows an inverse relationship between the switch breakdown voltage (BDV) and the gas pressure with the PRR. The estimated PRR values were found to vary between 800 Hz and 5 kHz in the experimented range of the switch breakdown voltage. The PRR values have also been experimentally measured. There is a good match between the measured and the estimated values up to the switch BDV of 12.5 kV after which the difference is increased to about 20 %. The feed for the reflector of the HIRA antenna consists of a pair of coplanar conical transverse electromagnetic (TEM) feed plates as they have a better antenna aperture blockage performance. The angles of the TEM feed plates have been chosen using stereographic projections of the feed plates into the HIRA reflector. Each TEM feed plate of 200  characteristic impedance has been terminated by matched resistor. An analytical expression has been derived to optimize the pulser output voltage at which the energy output per switching shot of the UWB system is maximum. It was found that when the pulser output voltage i.e. the switch breakdown voltage is 75 % of the dc source voltage the output energy delivered is maximum. It was possible to achieve a maximum output energy of 10 J per switching shot for the designed 25 MW high power UWB system. The HIRA antenna has been analysed for the impedance profile for frequencies up to 3.5 GHz and was found to maintain a reflection performance better than -10 dB over the frequency range. The radiated field analysis of the antenna was carried out using an analytical model and numerically by using a commercially available software. It was found that as per the analytical model, the Figure of Merit (FoM) of the designed UWB system is 1.41 V for a normalized excitation feed pulse of 1 V and the 3 dB spectral content of the radiated field is between 180 MHz-1.8 GHz. The corresponding results using computer simulations of the UWB system indicate a slightly lesser FoM of 1.1. Higher FoM obtained using the analytical model is due to ignoring the antenna aperture blockage and the field diffraction effects over the TEM feed arms as well as from the rim of the reflector of the antenna. The radiated field amplitude and gain of the HIRA antenna were found to be a direct function of the frequency of the radiated signal. Higher gains and narrower beam width for the radiated field were observed with an increase in the frequency. The radiated field spectral waveform in the near field region was observed to have a notch at a particular frequency and its harmonics. The notch frequency was found to be a function of the propagation time difference called clear time. The effect of pulser rise time, antenna feed arm impedance and position on the radiated far field amplitude and wave shape was analysed. It was observed that with decrease in the pulser rise time from 700 ps to 100 ps, the radiated field amplitude increases by about 600 %. A matched termination impedance with position of 30of the TEM feed arms with respect to the vertical symmetry axis of the antenna provides a higher radiated field amplitude and lower post pulse oscillations in the radiated field waveform. The pulser switch was evaluated systematically for various performance parameters such as BDV, rise time, PRR, voltage recovery and jitter characteristics as a function of switch gas pressure, type of gaseous switching media and breakdown voltage at pressures above and below the atmospheric level. The switch BDV was found to be a linear function of pressure of the gas used i.e. dry air, nitrogen, sulphur hexafluoride (SF6) and a mixture of air and SF6. The measured rise times of all the gases were found to be in inverse proportion to the switch gas pressure. SF6 gas offered the best rise time and hence was found to be a good contender for achieving higher radiated field amplitudes and bandwidth. The voltage recovery characteristics of SF6 gas and air were experimentally studied as a function of the recovery time. It is found that both the gases have similar recovery characteristics having a distinct saturation plateau region. It was found that for a given recovery time SF6 recovers to a higher voltage than air and the recovery further improves for SF6 at increased pressures (between 0.5-2 bar). The effect of the number of switching shots on the jitter in the switch rise time was measured by operating the switch continuously at a PRR of 1 kHz and for total number shots up to 10.8 M. It was observed that the jitter increases by an order of magnitude after 10.8 M shots. This indicates that for the present switch design, the switch electrodes require maintenance (buffing, polishing, etc.) after every 3.5 M shots to maintain a reasonably low jitter. SF6 gas was characterized for a fixed source voltage to determine the effect of pressure on rise time in the sub atmospheric regime (up to 50 mbar). It was found that the rise time vs. pressure characteristics follows the Paschen’s curve with a value of pressure at which rise time is the lowest for a given source voltage. With increase in the source voltage the rise time was found to decrease. The HIRA based UWB radiating system was evaluated for radiated fields in the near and far field region for the temporal and spectral characteristics. It was found that for the source voltage of 25 kV, the FoM in the near and far field region are 29.4 kV and 28.9 kV respectively. The fields in the distant far field region have more oscillatory post pulses due to the effect of ground reflections and the low frequency dipole moment mismatch of the antenna. Since SF6 gas offered the best rise time of 193 ps at a voltage of 46 kV than the other gases tried, the radiated field is the highest (5.3 kV/m) with SF6 at a distance of 10 m offering a gain factor of 1.15. Dry air offered a radiated field gain factor of 0.83 which got improved by 33 % by just 30 % addition of SF6 gas into the air. The field amplitudes measured were in good agreement with those computed using the analytical model and the computer simulations and they follow the 1/R rule as a function of the far field distance, R in the bore sight direction. The measured radiation pattern of the UWB system showed a focussed and narrow radiated field beam at higher frequencies with a half field beam width (HFBW) of 8 at 2 GHz. The UWB system was measured to have dominant highest cut off frequency of 1.79 GHz with a band ratio and percentage band width of 9.56 and 162.11 % respectively. This confirmed that the developed system is of sub-hyper band radiator type. The UWB system developed through this work is having a better performance than some of the other systems developed elsewhere in the world, in terms of FoM (53 kV) and the PRR (> 1 kHz). The system can be further improved in terms of consistency (jitter) and intensity by use of a triggered switch and hydrogen gas at 100 bar pressure as the switching medium respectively. The profile of the TEM feed plates of the HIRA antenna may be further improved to have a better antenna aperture fill factor. Such multiple systems in an arrayed manner may be used either for higher power output/better agility of the radiated field beam. This system will be fully exploited for the applications of susceptibility evaluation of electronic circuits, non-friendly applications as well as impulse radars

Digital communication systems which use Orthogonal Frequency Division Multiplexing (OFDM) are now widely used and have many advantages. The main disadvantage is the requirement for highly linear analogue electronics including the high power amplifier (HPA). This requirement cannot be met in all circumstances because of the occurrence of symbols with high peak to average power ratio (PAPR). Such symbols may be non-linearly distorted by limiting. Approaches to solve this problem have been either to reduce the PAPR at the transmitter or to try to mitigate the effect of the non-linearity at the receiver. Soft-limiting, i.e. applying limiting in software prior to the HPA is a simple way to reduce the PAPR. It produces non-linear distortion which will cause an increase in the bit-error-rate (BER) at the receiver. This thesis surveys existing alternatives ways of reducing the effect of non-linearity and proposes some new ones. Two iterative receiver techniques, based on statistical analysis of the nature of the non-linearity, have been implemented and investigated. These are the ‘Bussgang Noise Cancellation’ (BNC) technique and the ‘Decision Aided Reconstruction’ (DAR) techniques. As these techniques are valid for any memory-less nonlinearity, an alternative form of limiting, named as Inverted-Wraparound (IWRAP) has been included in the BNC investigation. A new method is proposed which is capable of correcting the received time-domain samples that are clipped, once they have been identified. This is named the ‘Equation-Method’ and it works by identifying constellation symbols that are likely to be correct at the receiver. If there are a sufficient number of these and they are correctly identified, the FFT may be partitioned to produce a set of equations that may be solved for the clipped time-domain samples. The thesis proposes four enhancements to this new method which improve its effectiveness. It is shown that the best form of this method outperforms conventional techniques especially for severe clipping levels. The performance of these four enhancements is evaluated over channels with additive white Gaussian noise (AWGN) in addition to clipping distortion. A technique based on a ‘margin factor’ is designed to make these methods work more effectively in the presence of AWGN noise. A new combining algorithm referred as ‘HARQ for Clipping’ is presented where soft bit decisions are combined from multiple transmissions. ‘HARQ for Clipping’ has been combined with the best version of the Equation-Method, and the performance of this approach is evaluated in terms of the BER with different levels of AWGN. It has been compared to other approaches from the literature and was found to out-perform the BNC iterative receiver by 3dB at signal to noise ratios around 10dB. Without HARQ, the best version of the Equation-Method performs better than the BNC receiver, at signal-to-nose ratios above about 17dB.

Neste trabalho realizamos o estudo da cinética e formação de agregados em cristais iônicos halogenetos alcalinos dopados com impurezas divalentes, através da técnica de espectroscopia de absorção de dois fótons (ADF). Analisamos a formação dos agregados em cristais envelhecidos a temperaturas fixas (50 e 250&#176C), através de medidas de ADF das transições 4f7 &#8594 4f7 do Eu2+, proibidas por um fóton. A evolução do espectro de ADF em função do tempo, mostrou a existência de três fases distintas de agregação. A primeira fase consiste na formação de dímeros e é observada no espectro de ADF através de três absorções muito próximas às absorções do dipolo isolada. As outras duas fases (II e III) evoluem a partir dos dímeros, dependendo do tratamento térmico a que a amostra é submetida. Estas fases são observadas no espectro de ADF através de absorções relativamente afastadas das absorções do dipolo isolado. Todo sistema experimental foi montado em nosso laboratório, consistindo de um sistema de aquisição de dados controlado por um micro-computador; laser de corante bombeado por um YAG:Nd3+; motores de passos para a varredura do comprimento de onda do laser de corante; sistema de detecção; etc. / In this work we realize the study of the Kinetic and formation of precipitates in ionic crystals doped with divalent impurities by the TPA (two photon absorption) spectroscopy technique. We analyze the formation of the aggregates in crystals annealed at temperatures of 50 and 250&#176C. We measured the TPA of the transition 4f7 &#8594 4f7 of the Eu2+, which is forbidden by one photon. The evolution of the TPA spectra at the time showed us three phases of the precipitates. The dimmers formation was observed in the first phase, by three absorptions bands near the one of the impurity vacancy dipole. The others phases (II and III) involve from the dimmers, depending on the annealing temperature that the samples were submitted. Those phases are observed in the TPA spectra through absorptions which are relatively far from the absorptions due to the isolated (I-V) dipole. All experimental system employed is home made. It consists of a data acquisition system controlled by a micro-computer; a Dye laser pumped by a YAG:Nd3+ laser; step motors to scan the wavelength of the Dye laser; detection system and others devices.

O desenvolvimento da Odontologia Restauradora culminou com a era das restaurações estéticas adesivas e da intervenção minimamente invasiva, para as quais técnicas inovadoras e materiais de última geração vêm sendo constantemente introduzidos. As técnicas conservadoras visam não somente a remoção do substrato dental cariado, mas também o preparo das paredes da cavidade para a realização da restauração adesiva. Este estudo visou avaliar a possibilidade de introdução dos lasers de pulsos ultracurtos na Odontologia Restauradora, com o intuito de suprir os requisitos básicos para a realização de uma restauração conservadora adequada. A intenção foi de manter os benefícios já conhecidos relacionados à remoção seletiva de cárie com os lasers de alta potência, bem como superar as desvantagens relacionadas às fontes lasers atualmente disponíveis para este fim, como aumento excessivo de temperatura e adesão prejudicada da superfície irradiada à resina composta. Para a melhor avaliação da interação entre os lasers de pulsos ultracurtos e o substrato dental, os experimentos foram realizados em três fases. A Fase 1 visou avaliar o efeito de diferentes comprimentos de onda (355 nm, 532 nm, 1045 nm e 1064 nm), durações de pulso (pico e femtossegundos) e protocolos de irradiação (velocidade de escaneamento da superfície, espessura do espécime, método de refrigeração e taxa de repetição de pulso) em esmalte e dentina. Para a Fase 2, os parâmetros de irradiação que apresentaram resultados mais favoráveis na Fase 1 foram analisados para relacionar o aumento de temperatura com a taxa de ablação e a eficiência de ablação para cada parâmetro. A Fase 3 teve como objetivo analisar a interface adesiva e os valores de microtração da dentina irradiada com os parâmetros selecionados e estudados na Fase 2, utilizando sistemas adesivos do tipo condicione e lave e autocondicionante com diferentes protocolos de adesão (Clearfil SE Bond com e sem Primer, Adper Single Bond com e sem condicionamento ácido). Os resultados obtidos na Fase 1 indicam que a dentina e o esmalte irradiados com lasers de femtossegundos de 1045 nm e picossegundos de 1064 nm apresentam superfície rugosa livre de carbonização. Os protocolos de irradiação selecionados mostram que a irradiação deve ser conduzida com maior velocidade de escaneamento da superfície, e não há necessidade de refrigeração durante a irradiação. Todos os parâmetros utilizados promoveram ablação seletiva do substrato dental, e apresentaram maior taxa de ablação para dentina que para esmalte. A Fase 2 permitiu observar que todos os parâmetros de irradiação selecionados não provocaram aumento de temperatura maior que 6,1 ºC para esmalte e 4,6 ºC para dentina, quando o aumento de temperatura foi aferido no lado oposto ao irradiado, em espécimes de 1 mm de espessura e sem refrigeração. Exceção foi observada para a maior potência do laser de picossegundos, para a qual a temperatura aumentou até 12 ºC em esmalte e 15 ºC em dentina. Os valores obtidos no ensaio de microtração variaram de acordo com os parâmetros de irradiação e o sistema adesivo. A adesão à dentina irradiada com lasers de pulsos ultracurtos apresentou valores de resistência adesiva semelhantes ou significantemente maiores que os obtidos nos grupos controle, para todos os parâmetros de irradiação selecionados. Os resultados obtidos neste estudo indicam que os lasers de pulsos ultracurtos apresentaram resultados favoráveis para o preparo cavitário em esmalte e dentina em relação à morfologia produzida na superfície e ao aumento de temperatura provocado durante a irradiação. A resistência adesiva à dentina irradiada foi semelhante, ou mesmo significantemente maior que a obtida nos grupos controle. Portanto, os lasers de pulsos ultracurtos são considerados uma técnica promissora para a realização de intervenção minimamente invasiva com lasers de alta potência. / The development of restorative dentistry has reached the era of esthetic adhesive restorations and minimally invasive approach, for which innovative techniques and advanced materials are constantly introduced. Conservative techniques aim not only to remove carious dental substrate, but also to prepare cavity surfaces for adhesive restoration. The main objective of this study was to evaluate the possibility of introducing ultra-short pulsed lasers in Restorative Dentistry, in attempt to fulfill the basic requirements of adequate conservative restoration, by maintaining the well-known benefits of lasers for caries removal, but also overcoming disadvantages related to current laser sources available for this purpose, such as temperature increase and damaged adhesion to resin composite. In order to better evaluate the interaction between ultra-short pulsed lasers and dental substrates, experimental procedures were divided in three phases. Phase 1 aimed to evaluate the effect of different wavelengths (355 nm, 532 nm, 1,045 nm, and 1,064 nm), pulse durations (pico and femtoseconds) and irradiation protocols (surface scanning speed, sample thickness, cooling method, pulse repetition rate) on enamel and dentin. For Phase 2, laser parameters with most favorable results in Phase 1 were evaluated to relate temperature increase to ablation rate or ablation efficiency. Phase 3 aimed to analyze adhesive interface and microtensile bond strength to dentin irradiated with the selected parameters by using etch-and-rinse and self-etch adhesive systems with different bonding protocols (Clearfil SE Bond with and without Primer, Adper Single Bond with and without acid etching). The results of Phase 1 indicate that dentin and enamel irradiated with 1,045-nm fs-laser and 1,064-nm ps-laser present a rough surface without carbonization. Irradiation should be conducted with higher scanning speed, and no additional cooling during irradiation was necessary. All parameters provided selective tissue ablation, with higher ablations rate for dentin than enamel. Phase 2 indicated that all parameters tested provoked temperature increase of up to 6.1 ºC for enamel and 4.6 ºC for dentin, when temperature increase was measured at the back side of 1-mm thick samples without cooling during irradiation, except for higher power for ps-laser, for which temperature increased up to 12 ºC for enamel and 15 ºC for dentin. Microtensile bond strength values varied according to laser parameters and adhesive systems used. Adhesion to dentin irradiated with ultra-short pulsed lasers resulted in similar or significantly higher bond strength values than control groups, for all laser parameters analyzed. Based on the results of this study, ultra-short pulsed lasers presented favorable results for cavity preparation in dentin and enamel regarding surface morphology and temperature increase. Adhesion to irradiated dentin was either similar or superior to traditional techniques. Thus, ultra-short pulsed lasers are considered a promising technique for the promotion of laser-supported minimally invasive approach.

Pour des applications médicales ou en histoire de l'art, un système compact de production de rayonnement X monochromatique à haut flux par effet Compton nécessite de disposer d’une source laser impulsionnelle de forte puissance moyenne avec des durées de quelques picosecondes. Pour atteindre un haut flux de rayonnement X, le laser devra être injecté dans une cavité Fabry-Perot de haute finesse afin d’atteindre les puissances laser moyennes requises. Par conséquent, le laser devra avoir une bonne qualité de mode et de faibles bruits. Afin d’atteindre ces objectifs, nous avons étudié la réalisation d’oscillateurs à blocage de modes passif délivrant des puissances moyennes de plus de 10 W avec des impulsions d’une durée entre 10 et 20 ps. Au cours de ce travail, deux oscillateurs de haute puissance moyenne ont été conçus et réalisés : l’un à pompage radial avec Nd:YAG comme milieu de gain et l’autre à pompage longitudinal avec comme milieu de gain Nd:YVO4. Le développement du second oscillateur a donné lieu à une étude expérimentale de la réduction de la durée des impulsions qui nous permet d’ajuster la durée entre 46 ps et 12 ps en régime de blocage de modes passif. Les résultats expérimentaux ont été expliqués à l’aide d’une simulation numérique et une solution analytique a été trouvée pour prédire la durée des impulsions. Enfin, une étude des caractéristiques des bruits de l’oscillateur Nd:YVO4 a été réalisée. Ces mesures ont permis de mettre en évidence qu’un oscillateur de forte puissance moyenne a les capacités pour être aussi peu bruyant que des oscillateurs de faible puissance et à faibles bruits. En résumé nous avons développé un oscillateur puissant (20W), à une longueur d’onde de 1064 nm, avec des durées d’impulsions courtes (15 ps), une bonne qualité de faisceau (M2<1,2) et de faibles bruits (gigue temporelle <1,2 ps RMS 100Hz-1MHz non asservi). Par conséquent, notre oscillateur puissant est un excellent candidat pour faire partie de la machine compacte de rayonnement X monochromatique et à haut flux. / For medical or cultural heritage applications, a compact, monochromatic, Compton x-ray source system needs a powerful, few picosecond laser source. To obtain high-x-ray-flux, the laser should be coupled to a high-finesse Fabry-Perot cavity to reach the required laser power. Therefore, the laser should have a good beam quality and low noises. In order to reach theses requirements, we have studied passive mode-locking oscillators delivering more than 10 W average power and between 10 and 20 ps pulse duration.Two high-power oscillators have been designed and implemented: a side-pumped Nd:YAG and an end-pumped Nd:YVO4 oscillator. With the second oscillator, we have studied the experimental reduction of pulse duration. We obtained a decrease from 46 ps to 12 ps in the continuous-wave mode-locked regime. Those experimental results have been explained by a numerical simulation and furthermore, we have developed an analytical solution to predict the pulse duration of such oscillator. Finally, we studied the noise characteristics of the Nd:YVO4 oscillator. Our measurements have shown that a high-power oscillator might be as low-noise as other low-power, low-noise oscillators. In conclusion, we have developed a powerful (20W), 1064nm-wavelength, short-pulses (15ps), good-beam-quality (M2<1.2) and low-noise free-running oscillator (timing jitter <1.2 ps RMS 100Hz-1MHz). Therefore, our high-power oscillator is an excellent candidate to be part of a compact, high-flux, monochromatic x-ray source.

Pas de résumé en français / Malaria is a devastating global health problem that affected 219 million people and caused 660,000 deaths in 2010. Inaccurate estimation of the level of infection may have adverse clinical and therapeutic implications for patients, and for epidemiological endpoint measurements. The level of infection, expressed as the parasite density (PD), is classically defined as the number of asexual parasites relative to a microliter of blood. Microscopy of Giemsa-stained thick blood smears (TBSs) is the gold standard for parasite enumeration. Parasites are counted in a predetermined number of high-power fields (HPFs) or against a fixed number of leukocytes. PD estimation methods usually involve threshold values; either the number of leukocytes counted or the number of HPFs read. Most of these methods assume that (1) the distribution of the thickness of the TBS, and hence the distribution of parasites and leukocytes within the TBS, is homogeneous; and that (2) parasites and leukocytes are evenly distributed in TBSs, and thus can be modeled through a Poisson-distribution. The violation of these assumptions commonly results in overdispersion. Firstly, we studied the statistical properties (mean error, coefficient of variation, false negative rates) of PD estimators of commonly used threshold-based counting techniques and assessed the influence of the thresholds on the cost-effectiveness of these methods. Secondly, we constituted and published the first dataset on parasite and leukocyte counts per HPF. Two sources of overdispersion in data were investigated: latent heterogeneity and spatial dependence. We accounted for unobserved heterogeneity in data by considering more flexible models that allow for overdispersion. Of particular interest were the negative binomial model (NB) and mixture models. The dependent structure in data was modeled with hidden Markov models (HMMs). We found evidence that assumptions (1) and (2) are inconsistent with parasite and leukocyte distributions. The NB-HMM is the closest model to the unknown distribution that generates the data. Finally, we devised a reduced reading procedure of the PD that aims to a better operational optimization and a practical assessing of the heterogeneity in the distribution of parasites and leukocytes in TBSs. A patent application process has been launched and a prototype development of the counter is in process.

L’étude du comportement des composantes des intérieurs planétaires dans des conditions extrêmes de pression (megabar) et température (milliers de Kelvin) est essentielle afin de construire des modèles fiables décrivant l’évolution et la structure des planètes. Dans ce travail, nous avons étudié plusieurs composantes par compression par choc laser sur les installations LULI2000 (France) et GEKKO XII (Japon).Nous avons employé des chocs décroissants pour étudier des conditions de haute-pression / haute-température. Afin d’accéder à des conditions de température modérée, nous avons utilisé des techniques de pre-compression statique (couplage compression par choc — cellules à enclumes de diamant) et dynamique (génération de doubles chocs).Nous avons étudié l’équation d’état des mélanges eau-ethanol-ammoniac et de l’eau et ammoniac purs, d’intérêt pour la description des intérieurs des planètes géantes de glace. L’étude de l’ammoniac a été particulièrement délicate en raison de sa forte réactivité et donc de la complexité du design des cibles ; nous présentons les premières données obtenues par choc laser, dans un domaine de pression jamais exploré. Les données des mélanges confirment des calculs ab initio récents basés sur une approximation de mélange linéaire.Nous avons également mesuré la réflectivité des mélanges liquides et de la silice, une composante-clé des intérieurs des planètes terrestres. Nous avons ensuite estimé la conductivité électrique — un paramètre crucial pour modéliser la génération des champs magnétiques planétaires dans les intérieurs via un mécanisme dynamo — de ces composantes.Eau, ammoniac et mélanges eau-ethanol-ammoniac affichent des réflectivités différentes, ce qui suggère que l’eau pure ne peut pas être considérée comme représentative des mélanges planétaires dans les modèles dynamo.Par ailleurs, nous avons apporté une confirmation expérimentale de calculs ab initio récents selon lesquels la conductivité de la silice n’est pas monotone le long d’une ligne isotherme pour des températures modérées.Nos données supportent des calculs qui prédisent qu’une dynamo peut avoir lieu dans les océans de magma dans des super-Terres ainsi que dans la jeune Terre. / Characterising the behaviour of planetary interiors’ components at extreme conditions (megabar pressures, temperatures of a few thousand Kelvin) is essential to build reliable models describing the evolution and structure of planets. In this thesis, we investigated various components on a wide set of conditions using laser-driven shock compression techniques at the LULI2000 (France) and GEKKO XII (Japan) facilities.Single decaying shocks were employed to study high-pressure / high-temperature states. To reach moderate-temperature conditions, closer to planetary interior profiles, we employed static and dynamic pre-compression techniques coupling Diamond Anvil Cells to shock compression and generating double shocks, respectively.We studied the equation of state of water-ethanol-ammonia mixtures and of pure liquid water and ammonia, of interest for icy giant structure models. Pure ammonia measurements have been particularly challenging due to cell design complexity in reason of its reactivity; we provide the first data obtained with laser shocks, in a pressure domain up to now unexplored. Mixtures data are in agreement with recent ab initio calculations based on the linear mixing approximation.We measured the optical reflectivity of liquid mixtures and silica, a key component of rocky planets’ interiors. From reflectivity data we estimated the electrical conductivity of such components — a crucial parameter for modelling the generation of planetary magnetic fields in the interiors via a dynamo mechanism.Water, ammonia, and water-ethanol-ammonia mixtures exhibit different reflectivity (hence conductivity) behaviours as a function of pressure and temperature. This suggests that pure water should not be used in dynamo models as representative of the icy mixtures.Moreover, we provide the first experimental confirmation of recent ab initio studies showing that the conductivity of silica along isothermal lines is not monotonic at moderate temperatures. Our data provide experimental support for the calculations predicting a dynamo action to occur in super-Earths’ and early Earth’s magma oceans.

This master thesis is based on realization of the previous university project, design of locomotive reconstruction and solving accompanying problems. In this thesis there are described all parts of a converter. The end of thesis involved theory about driver circuits of power transistors IGBT. Nowadays is still more often to think about reconstruction of the old technology rather than design a complete new construction. Investors take this decision from the financial reasons and because to the old technology designer can add only the converter. In this instant we talk about electrical locomotive, there should be kept a supply transformer and a driving unit (DC engine). The aim of this thesis is to design the converter between these two basic parts. The converter must taking the quasi-sinusoidal current which is in the phase with the input voltage, also must be able to control the engine and recuperate energy back to the network. For realization of these conditions, the converter must contain the active rectifier working in the DC-link and from which the step-down DC/DC converter is fed. Converter output is connected to the driving unit. The digital control of the power transistors is provided by processor MOTOROLA DSP56F. The control impulses, switching the power transistors, go through the driver circuits to transistors. All problems are described in the following text.

This work deals with high power pulse converters (tens of kW) using new semiconductor devices of silicon carbide (SiC). Firstly the current state of the issue is analyzed. A research in a specific area of high power buck converters with pulse transformer follows. There was a strong emphasis on minimizing size and weight. The design process was focused also on reliability and robustness. To achieve the defined objectives, it was necessary to use the latest available switching transistors and diodes, and an unusually high switching frequency (100 kHz at a power of about 16 kW). Due to the high switching frequency, we achieved small size of pulse transformers and output chokes. An optimization of high-frequency pulse transformer with demand on minimum volume and weight of core and windings represents a separate theoretical part of the thesis. There have been proposed several analytical solutions of optimization problems, the results of which could overlap with the implementation in practice of switching power supplies. The combination of high switching frequency, fast semiconductors and the high power brings various parasitic effects to the power circuit. In the thesis, these parasitic effects are analyzed. Solutions which minimize or completely remove those effects were theoretically designed and successfully implemented, tested and finalized in experimental part of the work. Detailed description of the implementation of functional sample and series of validation measurements are included in the final part.