High repetition frequency nanosecond pulses have been shown to be effective in generating plasma for reconfigurable RF systems. In the present work, the focus is on simulation of nanosecond pulsed discharges in Argon at 3 Torr and inter-electrode spacing of 2 cm with pulse repetition frequency of 30 kHz. The simulations have been carried out using a hybrid model, HPEM code developed by Prof. Mark J. Kushner at University of Michigan. The simulation results were compared to the experiments. Although a mismatch of results has been found, the simulations seem to capture the underlying physical phenomena. The electron temperature in the afterglow of the pulse seems to decay faster compared to the electron number density in the plasma, which is an essential feature in designing low noise plasma antennas.

O principal objetivo deste trabalho foi apresentar o projeto, o desenvolvimento, a caracterização e a aplicação de um novo dispositivo híbrido gerador de plasma. Este dispositivo consiste em uma tocha de plasma híbrida, a qual é caracterizada pela formação simultânea de dois arcos plasmas, em apenas um dispositivo, que geram um jato de plasma com elevada densidade de energia. Esta tocha é proveniente da união de dois processos geradores de plasma: Plasma Não-Transferido e Propulsor Magnetoplasmadinâmico. A tocha de plasma híbrida desenvolvida no Laboratório de Soldagem & Técnicas Conexas foi submetida aos seguintes testes: testes iniciais de funcionamento para verificar possíveis problemas de projeto e limites de operação da tocha; testes experimentais para caracterização da tocha de plasma híbrida, os quais consistiram em determinar as curvas características de tensão e corrente, o comprimento do jato de plasma, a distribuição de temperatura do jato de plasma expulso para fora da câmara, e a força propulsora resultante do jato de plasma; e testes de aplicação da tocha de plasma híbrida em processos de fabricação, tais como soldagem, corte e endurecimento superficial. Com base nos resultados obtidos para os testes de funcionamento do dispositivo, alguns problemas de isolamento elétrico e térmico foram encontrados e resolvidos. Quanto aos resultados dos testes de caracterização, os parâmetros de funcionamento da tocha de plasma híbrida apresentaram influência significativa sobre as curvas características de tensão e corrente, os comprimentos do jato de plasma, as forças propulsoras resultantes e as distribuições de temperatura. Os resultados obtidos nos testes de aplicação do dispositivo em processos de fabricação foram satisfatórios, isto é, foi possível realizar soldagens, cortes e endurecimento superficial com a tocha de plasma híbrida. Contudo, um novo dispositivo gerador de plasma foi desenvolvido para aplicações em processos de fabricação, porém novos estudos devem ser realizados para encontrar melhores parâmetros e assim conseguir soldagem, corte e endurecimento superficial com excelentes qualidades. / The main objective of this work was to present the project, development, characterization and application to a new hybrid plasma generator device. This device consists of a hybrid plasma torch that is characterized by the simultaneous formation of two plasma arcs in only one device, generating a plasma jet with high energy density. This torch arises from the union of two different plasma processes: Plasma Non-transferred and Magnetoplasmadynamic Thruster. The hybrid plasma torch developed in the Welding & Related Techniques Laboratory was submitted to the following trials: trials of operation to identify possible design problems and operations torch limits; trials to characterization of hybrid plasma torch that determined the characteristics curves of voltage and current, the length, the temperature distribution, and the thruster of the plasma jet; and application trials of hybrid plasma torch in manufacturing process, such as welding, cutting and hardening surface. Based at initial operation trials results with the device, some electrical and thermal insulation problems were found and solved. Concerning the results of the characterization trials, the hybrid plasma torch parameters had a significant influence over the voltage and current curves, the lengths of the plasma jet, the resultant thrusters and the temperature distributions. The results obtained in manufacturing process application trials were satisfactory, i.e. was possible to carry out welding, cutting and hardening surface with the hybrid plasma torch. However, a new plasma generated device was developed for application in manufacturing processes, but further studies should be performed to find the best parameters to acquire excellent qualities of welding, cutting and hardening surface.

<p>Thin films of metals and compounds have a very wide range of applications today. Many of the deposition methods used for the production of such films utilize plasma to support the growth the film, e.g. by the supply of energy and the enhancement of reactivity. This thesis focuses on the physical vapor deposition (PVD) of thin films by high density plasma sources based on hollow cathodes and aims to increase the understanding of the deposition process and its influence on the film properties.</p><p>Titanium nitride films reactively deposited by the low-pressure hybrid plasma (HYP LP) source exhibited excellent properties and was deposited at considerable higher rates than films deposited by conventional methods.</p><p>An original finding in this work is the influence of substrate material on the deposition process and consequently on the properties of the deposited film. In the deposition of TiN films by the HYP LP source it was found that the substrate temperature was higher for Si substrates than for steel substrates due to a more efficient absorption of microwave power in Si than in steel. Further, it was found that ferromagnetic substrates influence the film growth in magnetized plasma systems. An effect of the ferromagnetic substrates is the enhancement of ion bombardment that increases the growth temperature and affects the texture and morphology of the growing films. It was also found that a DC bias can change the TiN film properties considerably and compensate the effect of ferromagnetic substrates.</p><p>High rate depositions of chromium and chromium nitride films by the RF hollow cathode plasma jet (RHCPJ) source were studied. The performance of the reactive diffuse arc process and the CrN film properties indicates that the process can be transferred from small cylindrical cathodes to linear magnetized hollow cathodes which allow deposition on considerable larger areas and this is important for industrial applications.</p>

Thin films of metals and compounds have a very wide range of applications today. Many of the deposition methods used for the production of such films utilize plasma to support the growth the film, e.g. by the supply of energy and the enhancement of reactivity. This thesis focuses on the physical vapor deposition (PVD) of thin films by high density plasma sources based on hollow cathodes and aims to increase the understanding of the deposition process and its influence on the film properties. Titanium nitride films reactively deposited by the low-pressure hybrid plasma (HYP LP) source exhibited excellent properties and was deposited at considerable higher rates than films deposited by conventional methods. An original finding in this work is the influence of substrate material on the deposition process and consequently on the properties of the deposited film. In the deposition of TiN films by the HYP LP source it was found that the substrate temperature was higher for Si substrates than for steel substrates due to a more efficient absorption of microwave power in Si than in steel. Further, it was found that ferromagnetic substrates influence the film growth in magnetized plasma systems. An effect of the ferromagnetic substrates is the enhancement of ion bombardment that increases the growth temperature and affects the texture and morphology of the growing films. It was also found that a DC bias can change the TiN film properties considerably and compensate the effect of ferromagnetic substrates. High rate depositions of chromium and chromium nitride films by the RF hollow cathode plasma jet (RHCPJ) source were studied. The performance of the reactive diffuse arc process and the CrN film properties indicates that the process can be transferred from small cylindrical cathodes to linear magnetized hollow cathodes which allow deposition on considerable larger areas and this is important for industrial applications.

O principal objetivo deste trabalho foi apresentar o projeto, o desenvolvimento, a caracterização e a aplicação de um novo dispositivo híbrido gerador de plasma. Este dispositivo consiste em uma tocha de plasma híbrida, a qual é caracterizada pela formação simultânea de dois arcos plasmas, em apenas um dispositivo, que geram um jato de plasma com elevada densidade de energia. Esta tocha é proveniente da união de dois processos geradores de plasma: Plasma Não-Transferido e Propulsor Magnetoplasmadinâmico. A tocha de plasma híbrida desenvolvida no Laboratório de Soldagem & Técnicas Conexas foi submetida aos seguintes testes: testes iniciais de funcionamento para verificar possíveis problemas de projeto e limites de operação da tocha; testes experimentais para caracterização da tocha de plasma híbrida, os quais consistiram em determinar as curvas características de tensão e corrente, o comprimento do jato de plasma, a distribuição de temperatura do jato de plasma expulso para fora da câmara, e a força propulsora resultante do jato de plasma; e testes de aplicação da tocha de plasma híbrida em processos de fabricação, tais como soldagem, corte e endurecimento superficial. Com base nos resultados obtidos para os testes de funcionamento do dispositivo, alguns problemas de isolamento elétrico e térmico foram encontrados e resolvidos. Quanto aos resultados dos testes de caracterização, os parâmetros de funcionamento da tocha de plasma híbrida apresentaram influência significativa sobre as curvas características de tensão e corrente, os comprimentos do jato de plasma, as forças propulsoras resultantes e as distribuições de temperatura. Os resultados obtidos nos testes de aplicação do dispositivo em processos de fabricação foram satisfatórios, isto é, foi possível realizar soldagens, cortes e endurecimento superficial com a tocha de plasma híbrida. Contudo, um novo dispositivo gerador de plasma foi desenvolvido para aplicações em processos de fabricação, porém novos estudos devem ser realizados para encontrar melhores parâmetros e assim conseguir soldagem, corte e endurecimento superficial com excelentes qualidades. / The main objective of this work was to present the project, development, characterization and application to a new hybrid plasma generator device. This device consists of a hybrid plasma torch that is characterized by the simultaneous formation of two plasma arcs in only one device, generating a plasma jet with high energy density. This torch arises from the union of two different plasma processes: Plasma Non-transferred and Magnetoplasmadynamic Thruster. The hybrid plasma torch developed in the Welding & Related Techniques Laboratory was submitted to the following trials: trials of operation to identify possible design problems and operations torch limits; trials to characterization of hybrid plasma torch that determined the characteristics curves of voltage and current, the length, the temperature distribution, and the thruster of the plasma jet; and application trials of hybrid plasma torch in manufacturing process, such as welding, cutting and hardening surface. Based at initial operation trials results with the device, some electrical and thermal insulation problems were found and solved. Concerning the results of the characterization trials, the hybrid plasma torch parameters had a significant influence over the voltage and current curves, the lengths of the plasma jet, the resultant thrusters and the temperature distributions. The results obtained in manufacturing process application trials were satisfactory, i.e. was possible to carry out welding, cutting and hardening surface with the hybrid plasma torch. However, a new plasma generated device was developed for application in manufacturing processes, but further studies should be performed to find the best parameters to acquire excellent qualities of welding, cutting and hardening surface.

O principal objetivo deste trabalho foi apresentar o projeto, o desenvolvimento, a caracterização e a aplicação de um novo dispositivo híbrido gerador de plasma. Este dispositivo consiste em uma tocha de plasma híbrida, a qual é caracterizada pela formação simultânea de dois arcos plasmas, em apenas um dispositivo, que geram um jato de plasma com elevada densidade de energia. Esta tocha é proveniente da união de dois processos geradores de plasma: Plasma Não-Transferido e Propulsor Magnetoplasmadinâmico. A tocha de plasma híbrida desenvolvida no Laboratório de Soldagem & Técnicas Conexas foi submetida aos seguintes testes: testes iniciais de funcionamento para verificar possíveis problemas de projeto e limites de operação da tocha; testes experimentais para caracterização da tocha de plasma híbrida, os quais consistiram em determinar as curvas características de tensão e corrente, o comprimento do jato de plasma, a distribuição de temperatura do jato de plasma expulso para fora da câmara, e a força propulsora resultante do jato de plasma; e testes de aplicação da tocha de plasma híbrida em processos de fabricação, tais como soldagem, corte e endurecimento superficial. Com base nos resultados obtidos para os testes de funcionamento do dispositivo, alguns problemas de isolamento elétrico e térmico foram encontrados e resolvidos. Quanto aos resultados dos testes de caracterização, os parâmetros de funcionamento da tocha de plasma híbrida apresentaram influência significativa sobre as curvas características de tensão e corrente, os comprimentos do jato de plasma, as forças propulsoras resultantes e as distribuições de temperatura. Os resultados obtidos nos testes de aplicação do dispositivo em processos de fabricação foram satisfatórios, isto é, foi possível realizar soldagens, cortes e endurecimento superficial com a tocha de plasma híbrida. Contudo, um novo dispositivo gerador de plasma foi desenvolvido para aplicações em processos de fabricação, porém novos estudos devem ser realizados para encontrar melhores parâmetros e assim conseguir soldagem, corte e endurecimento superficial com excelentes qualidades. / The main objective of this work was to present the project, development, characterization and application to a new hybrid plasma generator device. This device consists of a hybrid plasma torch that is characterized by the simultaneous formation of two plasma arcs in only one device, generating a plasma jet with high energy density. This torch arises from the union of two different plasma processes: Plasma Non-transferred and Magnetoplasmadynamic Thruster. The hybrid plasma torch developed in the Welding & Related Techniques Laboratory was submitted to the following trials: trials of operation to identify possible design problems and operations torch limits; trials to characterization of hybrid plasma torch that determined the characteristics curves of voltage and current, the length, the temperature distribution, and the thruster of the plasma jet; and application trials of hybrid plasma torch in manufacturing process, such as welding, cutting and hardening surface. Based at initial operation trials results with the device, some electrical and thermal insulation problems were found and solved. Concerning the results of the characterization trials, the hybrid plasma torch parameters had a significant influence over the voltage and current curves, the lengths of the plasma jet, the resultant thrusters and the temperature distributions. The results obtained in manufacturing process application trials were satisfactory, i.e. was possible to carry out welding, cutting and hardening surface with the hybrid plasma torch. However, a new plasma generated device was developed for application in manufacturing processes, but further studies should be performed to find the best parameters to acquire excellent qualities of welding, cutting and hardening surface.

In the present study, the applicability of the hybrid plasma arc welding, in which a keyhole is responsible of deep penetration and a filler wire electrode supplies a high deposition rate, was examined. The microstructural evolutions in grade 2205 duplex stainless steel plates joined by keyhole and melt-in techniques were investigated. The specimens obtained from welded plates having thickness of 8 mm were examined via optical and scanning electron microscopy. Metallographic investigations were supported by X-ray diffraction and energy dispersed spectra analyses by characterizing the phases formed after welding. Impact toughness properties, hardness profiles, and crack propagation behavior of welding zones were quantitatively and qualitatively compared for mechanical characterization. Fracture characteristics were determined via scanning electron microscopy examinations. It was observed that single-pass HPA weldment seemed to be free of secondary austenite precipitation in acicular form, which is inevitable in multi-pass conventional arc welding methods. Besides &delta / -ferrite was successfully kept under 70%, which is presented as a limit to not to deteriorate the mechanical properties of DSS. High linear welding speed and high power density supplied by HPAW presented narrower weld metal and heat affected zone with not only lower hardness but also higher impact toughness energies. Synergic effect of the keyhole formed by a plasma arc and the metal transfer supplied by gas metal arc gave reasonable dilution in the weld metal. Furthermore, fatigue crack growth tests revealed that crack propagation rates in HPAW joints were comparable to GMAW joints.

This thesis presents experimental and modelling research on atmospheric pressure hollow cathodes and hollow electrodes. Experiments with the hybrid hollow electrode activated discharge (H-HEAD), which is a combination of a hollow cathode and a microwave plasma source, is presented. The experiments show that this source is able to produce long plasma columns in air and nitrogen at atmospheric pressure and at very low gas flow rates. Measurements of the vibrational temperature of the nitrogen molecules are also presented in this thesis. The vibrational temperature is an indication of the electron temperature in the plasma, an important characteristic of the plasma. Modelling work on the hollow cathode at atmospheric pressure with fluid equations is also presented. It is shown that the inclusion of fast and secondary electrons, characteristic of the hollow cathode plasmas, increases the sheath width. The sheath width was found to be of the order of 100 μm. By modelling the plasma as highly collisional by using the drift-diffusion approximation, it was shown that the increase in sheath thickness was larger at lower pressures than at higher pressures. Still, the sheath width can be of the order of 100 μm. A pulsed atmospheric plasma in a hollow electrode geometry was also modelled by the drift-diffusion fluid equations, with the addition of the energy equation for electrons. Rate and transport coefficients for the electrons were calculated from the solution to the Boltzmann equation as functions of mean electron energy. The dynamics of the plasma at pulse rise time showed large electron density and mean energy peaks at the cathode ends, but also that these quantities were enhanced at the centre of the discharge, between the cathode plates.

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