Dissertation (PhD) -- Stellenbosch University, 2001 / ENGLISH ABSTRACT: Millisecond pulse forming networks (PFNs) as applicable to electro-thermal chemical (ETC) loads fall into the <1 MJ energy bracket. The energy requirements of these loads require specialised power sources involving staged energy conversion. For the <1MJ energy bracket, capacitive storage systems are usually employed. However, these systems exhibit low volume energy density and for volume sensitive applications; alternatives need to be considered. Inductive storage supplies form a sub-group of the static supplies that have theoretically superior volume energy density characteristics. This thesis documents the execution of a project concerned with the volumeoptimisation of an inductive storage supply. The system is composed of a three stage energy conversion chain. A prime power source (low power) charges an intermediate storage (IS) which is characterised by its medium power delivery capabilities. Energy is then transferred from the IS to the storage inductor which is characterised by its high power delivery capabilities. When sufficiently charged, the energy is then transferred to the load. Where pulse forming is required, the inductor storage must necessarily be modular. Switching elements to control the energy flow are also required. Work performed at Soreq, Israel, is used as the starting point. A topology variation of the XRAM topology presented by Soreq, original to this thesis, is presented and all its functioning modes are analysed. An existing volume model is analysed and expanded to incorporate heretofore unmodelled yet non-negligible considerations. The volume model generalises the effect of system modularity, subsystem technologies and allows for the incorporation of practical construction issues into the design process. The aim is to develop a 500 kJ, 80 kA, 20 kV system with a volume not exceeding lm3. This volume must include the IS, storage inductor and full switch volume. The optimisation algorithm and system topology developed in this thesis is validated through the construction and testing of a 1.2 kA, 2.5 kV 4 module prototype. A potential full ratings system, composed of contemporary device technologies and exhibiting a volume of just over 0.8m3, is proposed. / AFRIKAANSE OPSOMMING: Millisekonde pulsvormingsnetwerke, soos toegepas op elektrotermies-chemiese laste, val in die <1 MJ energievlak. Die energievereistes van hierdie tipe las vereis gespesialiseerde kragbronne wat die gestoorde energie in verskillende stadiums aan die las beskikbaar stel. Tans word kapasitiewe stelsels gewoonlik vir toepassings wat minder as 1 MJ energie benodig gebruik. ‘n Nadeel van hierdie stelsels is egter hulle relatiewe lae energiedigtheid. Vir toepassings waar lae volume van belang is, moet altematiewe metodes ondersoek word. Pulskragbronne wat van ‘n induktiewe energiestoor gebruik maak vorm ‘n deel van die klas van statiese kragbronne met hoe energiedigtheid. Hierdie tesis handel oor die optimering, in terme van volume, van ‘n induktiewe pulskragbron. Die stelsel bestaan uit drie stadiums, wat die energie van een vorm na ‘n ander omskakel en sodoende die vorm van die puls wat aan die las gelewer word, beheer. A lae-drywing primere kragbron laai ‘n medium-dry wing intermediere energiestoor. Energie word dan van die intermediere energiestoor na ‘n hoe-drywing stoorinduktor oorgedra. Nadat die induktor volgelaai is, word die energie aan die las oorgedra. Indien pulsvorming benodig word, kan van ‘n modulere induktor gebruik gemaak word. Vaste-toestand skakelelemente word gebruik om die energievloei te beheer. Navorsing wat by Soreq, in Israel, uitgevoer is, word as die vertrekpunt vir die studie gebruik. ‘n Verandering aan die XRAM topologie word voorgestel en die werking daarvan word in detail geanaliseer. ‘n Bestaande volume model word ondersoek en uitgebrei om ‘n aantal nie-weglaatbare verskynsels in aanmerking te neem. Die nuwe volume model maak voorsiening vir modulariteit, die effek van substelseltegnologie en ‘n aantal praktiese oorwegings wat in die ontwerp van die stelsel ‘n rol speel. Die finale doel is om ‘n 500 kJ, 80 kA, 20 kV stelsel in ‘n volume van 1 m3 in te pas. Hierdie volume van 1 m3 moet die intermediere energiestoor, die stoorinduktor, asook die skakelaars, bevat. Die optimeringsalgoritme en stelseltopologie wat ontwikkel is, word eksperimenteel deur middel van ‘n 1.2 kA, 2.5 kV, 4 module prototipe geverifieer. Laastens word aangetoon hoe ‘n finale stelsel, gebaseer op huidige skakelaartegnologie, met ‘n totale volume van 0.8 m3 moontlik in die toekoms ontwikkel kan word.

This thesis presents a study of a pulsed distributed arc plasma deposition method that has been developed to produce highly ionized pulsed plasma plumes of metallic species in the presence of a low-pressure inert or reactive gas glow discharge. A pulse-forming network (PFN) is used to form a transient electrical discharge in a hollow electrode which is triggered by two different methods; a pulsed CO2 laser or a pulsed high voltage glow discharge. With the PFN charged to a voltage of 70 - 100 VDC, current pulses with peak currents up to 3 kA and pulse widths as long 3.7 milliseconds have been reached. A detailed treatment of the influence of process parameters, such as the PFN discharge energy and ambient gas pressure and type, on the plasma properties is presented. These experiments also demonstrated a higher on-axis growth rate of carbon in an ambient of nitrogen than in argon. The higher argon mass leads to broader plasma expansion producing broader deposition profiles which results in lower on-axis growth rates. Deposition rates of 3.5 angstrom/pulse for carbon and 2.1 angstrom/pulse for titanium have been achieved. Thickness profiles and the morphology of carbon films and titanium films deposited by this method, which utilize the energetic advantage of ions in film formation allowing reduced substrate temperatures and good adhesion, are presented.

Using isolation and noise immunity techniques, this thesis designs and constructs a low cost measurement system to safely and accurately measure high voltage, high frequency pulses in harsh EM environments. High voltage pulses apply to medical, plasma, and food industries. The difficulty of accurately measuring high voltage pulses continues to pose an issue. Measuring high voltage systems can cause damage to the system, the measurement system, and the user. High voltage and high frequency pulses create a harsh environment of electromagnetic fields that can disrupt the circuitry of the measurement system and harm the user. Implementing isolation from the high voltage system protects the measurement and user. An ideal pulse has sharp rising and falling edges, introduction high frequencies that prove difficult to sense and characterize. The measurement system requires a sufficiently large bandwidth to accurately measure the pulse edges. Commercial off the shelf pulse measurement systems such as oscilloscopes and multimeters cost thousands of dollars. Cheaper but simpler designs fail to provide isolation for safety. The measurement system in this thesis addresses all of these issues, allowing people to measure and characterize high voltage pulses. Technologies used in this measurement network include optocouplers, transimpedance amplifiers, and analog-to-digital converters. The development process describes design, simulations, characterizations, construction, testing, and troubleshooting. Simulations show expected operations of components and characterizations assist in determining performance parameters of the system. Testing involves performing a low voltage test and a high voltage test and identifying limitations of the design. Finally, this thesis suggests future work to improve performance and lower cost of the measurement system.

Made available in DSpace on 2016-06-02T20:15:28Z (GMT). No. of bitstreams: 1 5160.pdf: 6005480 bytes, checksum: 6aae866e51fab054ffc455e4b0479f2f (MD5) Previous issue date: 2013-02-25 / Financiadora de Estudos e Projetos / Considering the search for miniaturization of electronic devices, the development of new methods and techniques for the production and characterization of nanostructured materials is fundamental, beyond understanding of the effect of grain size on the properties of materials in nanoscale. Therefore, it was proposed in this work the obtaining of nanostructured multiferroic materials, in bulk, with high density and microstructural control, with grains ranging from micrometer to nanometer scale. To achieve this goal, was developed a methodology for obtaining the powder of lead iron niobate, Pb(Fe1/2Nb1/2)O3 (PFN) and lead iron tungstate, Pb(Fe2/3W1/3)O3 (PFW), with average particle size around 150 nm, contamination-free, minimal agglomeration and with highly reproductive results using the micro-milling technique. Regarding consolidation materials, conventional sintering requires higher temperatures and long holding times for a satisfactory densification, resulting in a grain growth higher than the desired. Through the fast sintering technique, only high heating rates are not sufficient to ensure a satisfactory densification and also inhibit the growth of grains. The obtain nanostructured dense samples with average grain size of approximately 200 nm was only possible using spark plasma sintering technique (SPS), which allows sintering at temperatures corresponding to the intermediate sintering stage, inhibiting the grain growth. PFN and PFW samples obtained through the SPS technique showed high conductivity at room temperature due the extreme reduction suffers in the system plus the use of high current densities during sintering, being necessary the samples oxidation. Through the dielectric characterization, the decrease in grain size of micrometer to nanometer scale results in lower permittivity values in phase transition temperature, besides a peak broadening. Moreover, the SPS technique added to the oxidation process makes it possible to obtain PFW samples with high dielectric values (in order of 104) at room temperature, a motivation results with regard to the application. / Considerando a busca pela miniaturização dos dispositivos eletrônicos é fundamental o desenvolvimento de novos métodos e técnicas para a produção e caracterização de materiais nanoestruturados, além do entendimento do efeito do tamanho de grão sobre as propriedades dos materiais em escala nanométrica. Dessa forma, propôs-se neste trabalho a obtenção de materiais multiferróicos nanoestruturados, na forma de bulk com alta densidade e controle microestrutural, com grãos variando de escala micrométrica a nanométrica. Para alcançar este objetivo, foi desenvolvida uma metodologia para a obtenção de pós de niobato de ferro e chumbo, Pb(Fe1/2Nb1/2)O3 (PFN) e tungstanato de ferro e chumbo, Pb(Fe2/3W1/3)O3 (PFW), com tamanhos médios de partículas em torno de 150 nm, livre de contaminação, mínima aglomeração e com resultados altamente reprodutivos por meio da técnica de micromoagem. Em relação à consolidação dos materiais, o procedimento convencional requer altas temperaturas e longos tempos de patamar para uma densificação satisfatória, resultando em um crescimento de grão superior ao desejado. Por meio da técnica de sinterização rápida fast sintering , somente altas taxas de aquecimento não são suficientes para garantir uma densificação satisfatória bem como inibir o crescimento de grãos. A obtenção de amostras densas nanoestruturadas com tamanhos médio de grão de aproximadamente 200 nm só foi possível utilizando a técnica spark plasma sintering (SPS), que permite a sinterização a temperaturas correspondentes ao estágio intermediário de sinterização, inibindo o crescimento de grãos. As amostras de PFN e PFW obtidas por meio da técnica de SPS apresentaram alta condutividade à temperatura ambiente devido às condições extremas de redução que a amostra sofre somada ao uso de altas densidades de corrente durante a sinterização, sendo necessária a oxidação das mesmas. Através da caracterização dielétrica, verifica-se que a diminuição nos tamanhos de grãos de escala micrométrica para nanométrica resulta em menores valores de permissividade na temperatura de transição de fase, além de um alargamento dos picos. Contudo, a técnica de sinterização SPS somada ao processo de oxidação torna possível a obtenção de amostras de PFW com altos valores de constate dielétrica (na ordem de 104), a temperatura ambiente, resultado extremamente motivador no que diz respeito à aplicação.

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