Orientador: Aruy Marotta / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-10T20:43:05Z (GMT). No. of bitstreams: 1 Bubliyeuski_DzmitryAlexandrovich_D.pdf: 2691341 bytes, checksum: 7b8e0d82f84d333a723eb14e64832cf3 (MD5) Previous issue date: 2008 / Resumo: Uma nova técnica de diagnóstico, denominada termo-espectroscópica, foi introduzida neste trabalho para estudo da interação do arco elétrico com o catodo frio de cobre numa instalação coaxial magnética, com catodo não-refrigerado, operando em gases plasmagênicos ar e nitrogênio. A técnica foi aplicada ao estudo da velocidade de rotação da mancha do arco e da densidade efetiva de corrente na mancha. Estes parâmetros têm estreita relação com o fenômeno da erosão de eletrodos frios. A nova técnica combina a técnica óptico-espectroscópica e a técnica térmica, e se baseia na teoria térmica da erosão. Por espectroscopia, registra-se a evolução temporal da intensidade da linha de emissão do vapor de cobre. Pelo método térmico, registra-se a evolução da temperatura da superfície do eletrodo. A técnica permite um grande aumento na sensibilidade de detecção do ponto de transição do regime de micro para macroerosão, através da observação do abrupto aumento da intensidade da linha espectral do cobre. Observamos que para o regime de microerosão, a velocidade é sempre maior, e a dispersão da velocidade sempre menor que na macroerosão. Esse fato confirma a existência de uma força de arraste superficial ao movimento do arco, que pode ser proporcionada pela fusão do eletrodo, por jatos catódicos e/ou por óxidos na superfície do eletrodo. A densidade de corrente na mancha apresenta um grande crescimento para valores baixos do campo magnético e certa saturação para altos valores. Para o ar foi observada uma forte influência dos óxidos na mobilidade da mancha, que é significativamente maior do que com nitrogênio. A diferença entre medidas obtidas no ar e nitrogênio é atribuída ao processo de decomposição de óxidos na superfície, que afeta a determinação correta do ponto de transição. O estudo experimental realizado nesta tese permite uma melhor compreensão dos fenômenos que ocorrem em manchas de arcos elétricos de eletrodos frios / Abstract: In the present work a new diagnostic technique, named thermo-spectroscopic one, was introduced for study of the interaction of the electric arc with a cold copper electrode using the coaxial magnetic installation with non-refrigerated cathode operated in air and nitrogen. The technique was applied to the measurement of the arc spot rotation velocity and the effective spot current density. These parameters have a direct relation with the phenomenon of the cold electrode erosion. The new technique combines the optic-spectroscopic method and the thermal method, and is based on the erosion thermophysical theory. Using spectroscopy, the temporal evolution of the intensity of the copper vapor emission line was registered. Via the thermal method, the evolution of the electrode surface temperature was recorded. By the observation of the abrupt increase of the copper spectral line intensity, the new technique permits a significative increase in the sensibility of the detection of the transition from the microerosion process to the macroerosion one. It was observed that the arc velocity for the microerosion regime is always higher and the velocity dispersion is always lesser then the ones for the macroerosion regime. This fact confirms the existence of the surface drag force to the arc movement, which can be provided by the electrode fusion process, by cathode jets and/or by oxides formed on the electrode surface. The arc spot current density presents a high growth for the low values of the magnetic field and certain saturation for the high values ones. For the air, a strong influence of oxides on the spot mobility was observed, that is more significant then the one for the nitrogen. The difference between the measurements for the air and the nitrogen is attributed to the oxide decomposition process on the electrode surface that affects the correct transition point determination. The experimental study, carried out in this thesis, allows a better understanding of the phenomenon taking place in cold electrode arc spots / Doutorado / Física de Plasmas e Descargas Elétricas / Doutor em Ciências

Low-dielectric (k) films are one of the performance drivers for continued scaling of integrated circuit devices. These films are needed in microelectronic device interconnects to lower power consumption and minimize cross talk between metal lines that "interconnect" transistors. Low-k materials currently in production for the 45 and 65 nm node are most often organosilicate glasses (OSG) with dielectric constants near 2.8 and nominal porosities of 8-10%. The next generation of low-k materials will require k values 2.6 and below for the 45 nm device generation and beyond. The continuous decrease in device dimensions in ultra large scale integrated (ULSI) circuits have brought about the replacement of the silicon dioxide interconnect dielectric (ILD), which has a dielectric constant (k) of approximately 4.1, with low dielectric constant materials. Lowering the dielectric constant reduces the propagation delays, RC constant (R = the resistance of the metal lines; C = the line capacitance), and metal cross-talk between wires. In order to reduce the RC constants, a number of low-k materials have been studied for use as intermetal dielectrics. The k values of these dielectric materials can be lowered by replacing oxide films with carbon-based polymer films, incorporating hydrocarbon functional groups into oxide films (SiOCH films), or introducing porogens in the film during processing to create pores. However, additional integration issues such as damage to these materials caused by plasma etch, plasma ash, and wet etch processes are yet to be overcome. This dissertation reports the effects of plasma, temperature and chemical reactions on low-k SiOCH films. Plasma ash processes have been known to cause hydrophobic films to lose their hydrophobic methyl groups, rendering them to be hydrophilic. This allows the films to readily absorb moisture. Supercritical carbon dioxide (SC-CO2) can be used to transport silylating agents, hexamethyldisilazane (HMDS) and diethoxy-dimethlysilane (DEDMS), to functionalize the damaged surfaces of the ash-damaged films. The thermal stability of the low-k films after SC-CO2 treatment is also discussed by performing in-situ heat treatments on the films. UV curing has been shown to reduce the amount of pores while showing only a limited change dielectric constant. This work goes on to describe the effect of UV curing on low-k films after exposing the films to supercritical carbon dioxide (CO2) in combination with tetramethylorthosilicate (TMOS).

Orientador: Munemasa Machida / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica, Gleb Wataghin / Made available in DSpace on 2018-08-14T10:48:49Z (GMT). No. of bitstreams: 1 Nascimento_Fellypedo_M.pdf: 4493365 bytes, checksum: 50c2d66d1ba6fb6004585fe057e964e5 (MD5) Previous issue date: 2009 / Resumo: Neste trabalho, foram feitas medidas simultâneas e três linhas e emissão e hidrogênio no tokamak NOVA-UNICAMP. A partir das medidas e brilho as emissões das linhas Ha , H b e Hg e fazendo uso de coeficientes que constam nas tabelas de Johnson e Hinnov, foi possível determinar temperaturas e densidades eletrônicas no plasma ao longo de descargas o tokamak. Para isto, foi utilizada, e aperfeiçoada, uma técnica desenvolvida num trabalho e doutoramento recente do nosso grupo, a qual faz uso do conceito de unicidade do tempo de confinamento de partículas. Os principais aprimoramentos realizados neste diagnóstico foram: utilização de três espectrômetros para medidas simultâneas das emissões e hidrogênio, instalação e fibras ópticas para coletar a luz emitida pelo plasma, adoção de um sistema de colimação para obter um certo grau e definição espacial nas medidas, uso de um maior número e valores e temperaturas na análise dos dados e desenvolvimento de um novo método (algorítimo) para obter os valores de temperaturas e densidades dos elétrons no plasma. As temperaturas e densidades eletrônicas médias obtidas ficaram em torno e 7,5 eV e 7,0 ·10 12cm-3, respectivamente. Estes valores estão entro do espera o para tais parâmetros na borda do tokamak NOVA-UNICAMP. Isto indica que este diagnóstico pode ser usado para monitorar ensidades e temperaturas e elétrons em plasmas gerados por tokamaks. Além isso, foram efetuados alguns experimentos com detectores multicanal e o gás hidrogênio foi trocado pelo hélio, na tentativa de mostrar a versatilidade do diagnóstico proposto. / Abstract: In this work, we have made simultaneous measurements of three hydrogen emission lines on our tokamak. From the measurements of absolute brightness of the Ha , H b e Hg lines an using data from Johnson an Hinnov table, was possible to determine electronic ensities an temperatures during the tokamak ischarges. For this,we have used, an refined, a technique developed in a recent PhD thesis in our work group. This technique uses the concept of particle confinement time uniqueness. The main upgrades made in this diagnostic were: the use of three spectrometers for simultaneous measurements of the hydrogen emissions, installation of optical fibers to collect the light emitte by the plasma, adoption of a collimation system for having some spatial definition of the measurements, use of a greater range of temperature values uring the data analysis and development of a new method (algorithm) for obtaining the electronic densities and temperatures in the plasma. The average temperature and density obtained was about 7.5 eV and 7.0 ·1012cm-3, respectively. The results obtained are in accordance with the expected values for these parameters at the edge of the NOVA-UNICAMP tokamak plasma. This indicates that this diagnostic can be used to monitor the electronic densities and temperatures in tokamak plasmas. Additionally, we have made experiments with multichannel detectors, and the hydrogen gas was replaced by helium, in an attempt to show the versatility of the proposed diagnostic. / Mestrado / Física / Mestre em Física

The problem with which this investigation is concerned is that of determining the steady-state and dynamic characteristics of the admittance of a metallic probe immersed in a laboratory plasma which has the low electron densities and low electron temperatures characteristic of the ionospheric plasma. The problem is separated into three related topics: the design and production of the laboratory plasma, the measurement of the steady-state properties of dc and very low frequency probe admittance, and the study of transient ion sheath effects on radio frequency probe admittance.

Electron densities and collision frequencies were obtained on a number of gases in a dc discharge at low pressures (0.70-2mm of Hg). These measurements were performed by microwave probing of a filament of the dc discharge placed coaxially in a resonant cavity operating in a TM₀₁₀ mode. The equipment and techniques for making the microwave measurements employing the resonant cavity are described. One of the main features of this investigation is the technique of differentiating the resonance signal of the loaded cavity in order to make accurate measurements of the resonant frequency and half-power point frequencies.

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Halo currents (HCs) in post-disruption plasmas can be large enough to exert significant electromagnetic loads on structures surrounding the plasma. These currents have axisymmetric and non-axisymmetric components, both of which pose threats to the vacuum vessel and other components. However, the non-axisymmetric forces can rotate, amplifying the displacements they cause when the rotation is close to the structures’ resonant frequencies. A new physically motivated scaling law has been developed that describes the rotation frequencies of these HCs and has been validated against measurements on HBT-EP, Alcator C-Mod, and other tokamaks. This scaling law can describe the time-evolution of the asymmetric HC rotation throughout disruptions on HBT-EP as well as the time-averaged rotation on C-Mod. The scaling law can also be modified to include the edge safety factor at the onset of rotation (𝒒_𝑜𝑛𝑠𝑒𝑡), which significantly improves its validity when applied to machines like C-Mod, where 𝒒_𝑜𝑛𝑠𝑒𝑡 changes frequently. The 𝒒_𝑜𝑛𝑠𝑒𝑡 dependence is explained by the relationship between the poloidal structure of the HC asymmetries and the MHD instabilities that drive them, which has been observed experimentally for the first time using a novel set of current sensing limiter tiles installed on HBT-EP. The 1/𝑎² and 𝒒_𝑜𝑛𝑠𝑒𝑡-dependence of the rotation suggest that the HCs predominantly rotate poloidally. This remains consistent with the toroidal rotation observed on HBT-EP and other tokamaks through the “Barber Pole Illusion” and the direction of rotation’s dependence on the direction of 𝐼_𝑝. This scaling law is used to make projections for next generation tokamaks like ITER and SPARC, which predicts that rotation will be resonant on ITER. However, resonant effects can still be avoided if the duration of the disruption is kept short enough to prevent two rotations from being completed.

This thesis reports observations of kink and tearing modes in the High Beta Tokamak - ExtendedPulse (HBT-EP) experiment. When unstable, these modes could limit the operation of tokamaks used for fusion power by terminating the plasma discharge and causing rapid loss of plasma energy. The aim of this work is to characterize the sudden transition after a sawtooth crash of coupled 2/1-3/1 tearing-kink modes into a sustained and disruptive 2/1 tearing mode. The following diagnostic techniques are used. Kink and tearing modes in HBT-EP distort the plasma edge, measured by a large array of Mirnov sensors, and perturb the interior of the plasma, observed routinely with Extreme Ultraviolet (EUV) detector arrays. Two arrays, with different transmission filters, are located with tangential views to estimate the time evolution of the plasma temperature profile. Four EUV arrays, with 16 detectors each, are positioned with different poloidal views for poloidal Extreme Ultraviolet (pEUV) emission tomography. The 2D emissive structures producing the pEUV signals are reconstructed with tomographic inversion using a pixel basis and fixed weighting smoothness regularization. Spatial and temporal correlations across these independent diagnostics are used to measure the evolution and structure of coupled modes using a technique called multidiagostic Singular Value Decomposition (mdSVD). In mdSVD, orthogonal modes are identified within any fixed time window with their unique spatial and temporal characteristics. The technique uncovers: coherent behavior of coupled (𝑚/𝑛) = (2/1) and (3/1) tearing-kink modes and rapid changes in plasma structure associated with sawtooth crashes which trigger disruptive and nondisruptive tearing modes. HBT-EP’s unique radially movable wall is found to significantly influence sawtooth triggering of disruptive tearing modes. The onset of sawtooth-triggered modes depends both on the plasma-wall separation, or wall coupling, and on the value of edge safety factor qₐ. We confirm that the condition for sawtooth triggering of disruptive (𝑚/𝑛) = (2/1) tearing modes does not correspond to the mode’s single-helicity stability condition Δ′₂/₁. We identify a dependency of the sawtooth period 𝝉_𝑠𝑡 on the wall position and qa as a candidate to explain the onset of the saturated tearing mode. This thesis motivates future efforts to model the influence of a nearby resistive wall on sawtooth triggering of tearing modes.

Resonant Magnetic Perturbation (RMP) fields produced by external control coils are considered a viable option for the suppression of Edge Localized Modes (ELMs) in present and future tokamaks. Repeated reversals of the toroidal phase of the I-coil magnetic field in RMP shot 147170 on DIII-D has generated uniquely different edge pedestal profiles, implying different edge transport phenomena. The causes, trends, and implications of RMP toroidal phase reversal on edge transport is analyzed by comparing various parameters at 0 and 60 degree toroidal phases, with an I-coil mode number of n=3. An analysis of diffusive and non-diffusive transport effects of these magnetic perturbations it the plasma edge pedestal for this RMP shot is characterized by interpreting the ion and electron heat diffusivities, angular momentum transport frequencies, ion diffusion coefficients, and pinch velocities for both phases.