This thesis is about theory of switching power supplies and about a specific solution of switching power supply for electron microscope. In the beginning of the thesis are mentioned various solutions of part blocks of switching power supplies, their advanteges and disadvanteges, and their suitability for electron microscopy. In the next part of the thesis are described requirements and design scheme of switching power supply for scanning part of electron microscope. The thesis i also about technical solution and practical testing of the switching power supply and verification of its functions.

<p>The development of a deuterium-deuterium/ tritium-deuterium (D-D/ D-T) pulsed neutron generator based on the principle of the Plasma Immersion Ion Implantation (PI3) technique is presented, in terms of investigating development of a compact system to generate an ultra short burst of mono-energetic neutrons (of order 1010 per second) during a short period of time (&lt / 20&mu / s) at repetition rates up to 1 kHz. The system will facilitate neutron detection techniques, such as neutron back-scattering, neutron radiography and time-of-flight activation analysis.</p> <p><br /> Aspects addressed in developing the system includes (a) characterizing the neutron spectra generated as a function of the target configuration/ design to ensure a sustained intense neutron flux for long periods of time, (b) the system was also characterised as a function of power supply operating conditions such as voltage, current, gas pressure and plasma density.</p>

Ce travail s’inscrit dans le processus de développement d’un dispositif de traitement de composés organiques volatils (COV) par plasma non-thermique. L’application industrielle des dispositifs de dépollution par plasma froid se heurte à deux limitations majeures que sont une consommation énergétique importante et la formation de sous-produits. Deux axes d’amélioration de l’efficacité énergétique du procédé à décharges sur barrière diélectrique sont explorés dans ce travail de thèse : le mode de dépôt d’énergie dans la décharge et le couplage du réacteur plasma avec un dispositif catalytique. Concernant le premier axe, l’étude a montré que dans le cas des réacteurs DBD étudiés, le paramètre gouvernant la réactivité chimique du plasma à pression atmosphérique était la densité d’énergie, qu’il s’agisse de production d’ozone ou d’élimination d’un COV de la phase gazeuse. L’étude chimique des sous-produits de dégradation par décharge a été conduite pour trois molécules cibles : l’éthanol, l’acétone et la méthyléthylcétone. Dans le cas de l’éthanol, un schéma cinétique 0D est proposé, montrant l’importance de la dissociation dans les mécanismes de dégradation du COV. Pour le second axe exploré, le réacteur plasma a été couplé à un catalyseur. Deux formulations de catalyseurs ont été utilisées, avec et sans métaux précieux. Dans les deux cas, l’activation du catalyseur à basse température par couplage avec le réacteur plasma est démontrée. La dernière partie de l’étude présente les résultats obtenus sur un réacteur plasma à échelle pilote visant à estimer l’impact de l’augmentation des capacités de traitement d’un réacteur DBD sur l’efficacité énergétique du procédé. / This work deals with the development of a VOC removal method by non-thermal plasma which has several advantages including flexibility, compactness and limited investment costs. Further development of this technology needs to overcome major drawbacks such as high energy consumption for high flow rate treatment and the presence of by-products. The first part of the study focuses on the method of discharge energy deposition and the search for optimization of the process energy efficiency. Development of experimental and measurement tools, in particular for the determination of the electrical power injected into the discharge were carefully carried out. The effect of voltage waveform, signal frequency and electrode shape were investigated. The results show that no energy efficiency improvement could be brought by variation of these parameters and that only energy density is important in the gas treatment process. The second part of the study was devoted to the study of conversion of three pollutants (acetone, ethanol and methylethylketone). Formation of by-products was analyzed and a kinetic scheme is proposed for ethanol conversion. To decrease the level of by-products at the reactor outlet, the association between cold plasma and catalysis was investigated. Catalysis was found to allow an improvement in the oxidation of the pollutants and of the discharge by-products. The last part of this work focused on results obtained with a large flow rate plasma reactor to confirm extension of laboratory scale results to larger equipment. Results confirmed that the extension of low flow rate experimental results is possible.

<p>The development of a deuterium-deuterium/ tritium-deuterium (D-D/ D-T) pulsed neutron generator based on the principle of the Plasma Immersion Ion Implantation (PI3) technique is presented, in terms of investigating development of a compact system to generate an ultra short burst of mono-energetic neutrons (of order 1010 per second) during a short period of time (&lt / 20&mu / s) at repetition rates up to 1 kHz. The system will facilitate neutron detection techniques, such as neutron back-scattering, neutron radiography and time-of-flight activation analysis.</p> <p><br /> Aspects addressed in developing the system includes (a) characterizing the neutron spectra generated as a function of the target configuration/ design to ensure a sustained intense neutron flux for long periods of time, (b) the system was also characterised as a function of power supply operating conditions such as voltage, current, gas pressure and plasma density.</p>

Magister Scientiae - MSc / The development of a deuterium-deuterium/ tritium-deuterium (D-D/ D-T) pulsed neutron generator based on the principle of the Plasma Immersion Ion Implantation (PI3) technique is presented, in terms of investigating development of a compact system to generate an ultra short burst of mono-energetic neutrons (of order 1010 per second) during a short period of time (< 20μs) at repetition rates up to 1 kHz. The system will facilitate neutron detection techniques, such as neutron back-scattering, neutron radiography and time-of-flight activation analysis. Aspects addressed in developing the system includes (a) characterizing the neutron spectra generated as a function of the target configuration/ design to ensure a sustained intense neutron flux for long periods of time, (b) the system was also characterised as a function of power supply operating conditions such as voltage, current, gas pressure and plasma density. / South Africa