A contribuição dos eventos extremos, chamados \\emph{bursts}, relacionados com estruturas coerentes que se propagam na turbulência, parece ser parte da explicação para o transporte anômalo que acontece em plasmas confinados. Porém, ainda não existe um modelo adequado no quadro da teoria neoclássica de transporte, para explicar adequadamente a contribuição destes eventos extremos. Assim, a caracterização do transporte de partículas e energia, devido a esses eventos extremos, e a sua estrutura interna, são questões relevantes no estudo do plasma de fusão. Para isso, medições locais da temperatura dos elétrons são necessárias, pois o transporte de partículas e energia sofre correções devido à temperatura. Por terem boa resolução espacial e serem relativamente fáceis de construir, as sondas eletrostáticas são comumente utilizadas em tokamaks para medir a temperatura local na região da borda de plasmas confinados magneticamente. Os métodos de varredura de tensão e a configuração de sonda tripla estão dentre os métodos mais usados para medir a temperatura local na borda do plasma com sondas eletrostáticas. Neste trabalho, é apresentada uma comparação entre as medições de temperatura usando esses dois métodos no tokamak TCABR. Para esse fim, foram utilizadas descargas de plasma em condições padrão, onde a corrente de plasma e a densidade são mantidas praticamente estáveis e há baixa atividade MHD, isto é, a fase estacionária da descarga, com os parâmetros macroscópicos de equilíbrio aproximadamente constantes. As medições da temperatura pelos dois métodos têm boa correspondência na região da sombra do limitador, mas existem discrepâncias quando as medidas são feitas dentro da coluna de plasma. Verificou-se que esta discrepância se deve ao efeito de expansão da região de transição entre o plasma e a superfície da sonda, conhecida como bainha de plasma. Portanto, foram modificadas as equações do método da sonda tripla a fim de considerar, de maneira adequada, este efeito. Esta modificação conduz a medições de temperatura compatíveis entre os dois métodos. Também se estudou as estruturas coerentes que se propagam na turbulência da borda (bursts), que são detectados como picos no sinal de corrente de saturação iônica. Para esse fim, foi usada a técnica da análise condicional. Os resultados obtidos parecem ser compatíveis com estruturas que apresentam uma inclinação no plano radial-poloidal. Esta inclinação implica que o método comumente usado para medir a velocidade de propagação das estruturas, baseado no atraso entre a detecção do pico entre dois pinos próximos, pode levar a resultados completamente errados. Os resultados para a evolução média da temperatura durante os bursts são incompatíveis entre os dois métodos. De fato, os resultados fornecidos pelo método de sonda tripla aparentam estar fisicamente errados, uma vez que indicam um alto gradiente de temperatura dentro dos bursts. Constatou-se que este problema é devido aos altos gradientes de potencial dentro dos bursts que inviabilizam a hipótese de potencial uniforme na região entre os pinos da sonda tripla. / The contribution of the extreme events related to propagating structures in the turbulence, the so-called bursts, seems to be part of the explanation to anomalous transport in confined plasma. But, up to now, there is not an adequate model in the frame of neoclassical transport theory to properly account the contribution of these extreme events. Therefore, the characterization of the particle and energy transport due to the extreme events and the burst internal structure are an important issue in fusion plasma research. However, local electron temperature measurements are necessary to investigate those topics, because particles and energy transport have temperature corrections. Due to their good spatial resolution and relatively easy construction, electrostatic probes are often used to measure temperature in the plasma edge of tokamak. The triple probe configuration and voltage sweep technique are among the most common techniques used with electrostatic probes to measure local temperature in the plasma edge. We present a comparison between the temperature measurement using these two techniques in the tokamak TCABR. For this purpose, it was used stationary standard plasma discharges (it is, discharges with almost stable plasma current and density and with low MHD activity). For temperature measurement, the two methods have good correlation in the Scrape-Off-Layer region but there are discrepancies between their values inside the plasma column. We found that this discrepancy is due to the sheath expansion effect. Therefore, the triple probe equations were modified to properly consider this effect. The modification leads to compatible average temperature measurements between the two methods. We also studied coherent structures propagating in the edge turbulence (detected as bursts in the saturation current) by using the conditional analysis technique. The results seem to be compatibles with structures tilted in the radial-poloidal plane. This tilt implies that the common method to measure the propagation velocity using the delay time of detection between two probes, could produce wrong values. The results for the average temporal behavior of temperature during the bursts are inconsistent between the two methods. Indeed, the triple probe results seems to be physically wrong, once it indicates a strong temperature gradient inside the bursts. We found that this problem is due to the strong potential gradients inside the burst, breaking the assumption that the pins used in the triple probe configuration are in a homogeneous plasma.

Este trabalho de mestrado tem o intuito de caracterizar plasmas do tipo indutivo (ICP). Para a caracterização do plasma, foram usadas técnicas de espectroscopia e medidas elétricas. Foram analisados plasmas de Argônio, por ser um gás inerte, oxigênio, por ser um pouco eletronegativo, SF6, por ser um gás muito eletronegativo e útil para a corrosão de silício, misturas de oxigênio e SF6 com Ar, CF4 e misturas de CF4 com Ar. Observou-se que obtêm-se plasmas indutivamente acoplados quando se cria uma condição de concentração mínima de elétrons livres no plasma. Isso acontece quando há uma certa potência aplicada no eletrodo e outra potência aplicada na bobina. Quanto menos eletronegativo o gás, menores são estas potências. Nos casos estudados significa que é mais fácil obter acoplamento indutivo com Ar puro, depois com as misturas dos gases. Em nosso reator foi mais difícil conseguir obter plasmas indutivamente acoplados com O2 e SF6 puros, pois não tivemos condições de “hardware" para aplicar as potências altas as suficientes para criar o plasma indutivo. Também estudamos dois materiais como material de eletrodo, estanho e alumínio e observamos que para o SF6 há uma maior concentração de F com eletrodo de Sn enquanto para CF4 a concentração de F e maior com eletrodo de Al. / In this work, inductively coupled plasmas have been studied, using optical emission spectroscopy and electrical measurements. Four gases were analysed : argon, being an inert gas, oxygen because it is slightly electronegative, SF6 because it is very eletronegative and also etches silicon and its compounds and CF4 because it also etches silicon and its compounds and is slightly electronegative. Also the mixtures of oxygen, SF6, important to silicon etching and CF4 with argon were studied. The studies indicated that it is necessary to have a minimum concentration of free electrons in the plasma to obtain an inductively coupled plasma. This depends very strongly on the power levels applied to the cathode and the coil of the reactor, The less electronegative the gas, the lower these power levels. Hence it was easiest to obtain argon inductively coupled plasmas, followed by the argon mixtures and with the pure gases it more difficult to obtain ICP plasmas with the available hardware. Two materials were studied as cathode material: tin and aluminium. When using SF6, the highest F concentration was obtained with the tin electrode, but for CF4 gases, the highest fluorine concentration was obtained with the aluminium electrode.

Desenvolvemos neste trabalho, um formalismo alternativo de \"dois níveis\" sugerido por Cattani, para o cálculo dos alargamentos e deslocamentos de linhas espectrais produzidos por colisões, quando é valida a aproximação de impacto. Este formalismo foi usado para calcular alargamentos e deslocamentos eletrônicos de algumas linhas do átomo de hélio neutro em um plasma, para as quais, foi possível aplicar a teoria de \"dois níveis\". A contribuição das colisões iônicas aos alargamentos e deslocamentos das linhas espectrais foi avaliada, utilizando a aproximação quase estática de Griem, Baranger, Kolb e Oertel. Os resultados dos cálculos foram comparados com os resultados experimentais de Kelleher, Berg e colaboradores, Wulff e Diatta e com as previsões dos formalismos, convergente e de corte. / In this work we develop an alternative formalism of \"two levels\" suggested by Cattani to the calculation of widths and shifts of spectral lines produced by collisions, in the impact approximation. This formalism was used to calculate in a plasma the electronic widths and shifts of neutral helium lines for which is valid the \"two levels\" approach. To take into account the ions contribution to the widths and shifts of the lines, we have . used the quasistatic approximation of Griem, Baranger, Kolb and Oertel. Our theoretical predictions are compared with the experimental results of Kelleher, Berg and collaborators, Wulff and Diatta and also with the predictions of the convergent and cutoff formalisms.

by Lee Kwan-Chuen. / Title also in Chinese. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1989. / Bibliography : leaves 86-88.

Experimental studies of MHD modes, including dynamics and stability, using a biased electrode for rotation control on the High Beta Tokamak –- Extended Pulse (HBT-EP) are presented. When the probe is inserted into the edge of the plasma and a voltage applied, the rotation of long-wavelength kink instabilities is strongly modified. A large poloidal plasma flow results at the edge, measured with a bi-directional Mach probe with changes in edge kink mode rotation at different biases. This poloidal plasma rotation cannot fully account for the large mode rotation frequency on HBT-EP. By including the electron fluid motion, the mode rotation predictions agree with measurements, indicating that the modes travel with the electron fluid. A GPU-based digital feedback system is used to adjust the probe voltage in real time for controlling both the plasma flow and mode rotation. This active mode rotation control is desirable because it allows for MHD stabilization, as well as studies under conditions of varying mode rotation rates. Mode dynamics were studied using various diagnostics to understand how plasma conditions fluctuate during mode activity and to understand the interaction of the bias probe with the plasma during this activity. Phase-dependent mode behavior was observed, especially at slow mode rotation, which might be attributed to an intrinsic error field or a nonlinear interaction between the bias probe and the mode. Applied resonant magnetic perturbations were used to study the dynamic response of a stable plasma with different mode rotations. At slower rotation, the plasma had a greater response to the perturbations and the plasma reached a saturated response with large perturbations, similar to previous results. At large positive biases, the probe current induces a torque that opposes the natural direction of mode rotation. By applying a sufficiently large torque, a transition is induced into a fast rotation state (both mode and plasma rotation). High poloidal shear flows at the edge were measured in this state, similar to conditions in H-mode plasmas on other devices. The bias required to induce the transition is shown to depend on an applied error field. A technique was established using this transition to determine the natural error field on HBT-EP.

Made available in DSpace on 2014-06-11T19:22:21Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-02-06Bitstream added on 2014-06-13T19:07:46Z : No. of bitstreams: 1 rocha_v_me_guara.pdf: 8713768 bytes, checksum: 78a8daf2c93d3384356543e4273f0b6d (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Este trabalho teve por objetivo estudar a propriedade do plasma em pressão atmosférica para esterilização de materiais termossensíveis. Para testar a propriedade do plasma frio de esterilizar materiais termossensíveis, concentramos nossos experimentos no plasma gerado por descarga com barreira dielétrica (DBD). Para realizar nossos experimentos usamos os microrganismos Cândida albicans ATCC18804, Escherichia coli ATCC23922, Bacillus subtilis ATCC19659, e Staphylococcus aureus ATCC 6538. Primeiramente, realizamos descarga DBD sobre uma placa de microtitulação contendo suspensões de microrganismos, mas observamos que, neste caso, a descarga DBD não teve eficácia na esterilização, devido a não penetração das entidades reativas (ozônio, UV), dentro desse volume de microrganismos. Modificamos nosso sistema, colocando um eletrodo adaptado a uma placa de Petri, e aplicamos a descarga DBD sobre os microrganismos em suspensão semeados em Agar. Realizamos exposição de 2, 5, 10, 15 e 20 minutos, com 1,1W de potência, tensão de 40kV pico-a-pico e aproximadamente 1 cm de distância entre o eletrodo superior e o meio de cultura. Observamos o crescimento dos meios de cultura tratados (contagem de UFC) e analisamos a morfologia dos microrganismos tratados em comparação com as amostras sem tratamento, através de microscopia eletrônica de varredura (MEV). Através desses experimentos, pudemos observar que, no caso de superfícies, o plasma é um método de esterilização eficiente e rápido. Isso porque, durante a descarga são formados ozônio, fótons UV, e partículas livres carregadas, que podem contribuir para o efeito esterilizante / The objective of this work was to investigate the application of plasma at atmospheric pressure for sterilization of termosensitive materials. To test the capability of cold plasma to sterilize termosensitive materials, we concentrated our study on the plasma generated by a dielectric barrier discharge (DBD). In our experiments we used the microorganisms Candida albicans ATCC18804, Escherichia coli ATCC23922, Bacillus subtilis ATCC19659, and Staphylococcus aureus ATCC 6538. Firstly, we produce a DBD discharge in a microtitulation plate containing suspensions of the microorganism and no sterilization effect was observed. This is due to the fact that no penetration of the reactivates species (ozone, UV) inside of the volume of microorganisms. We modified our system, putting an adapted electrode on the cover of a Petri plate, and we applied the DBD discharge on microorganisms in suspension sowed in Agar. We used different times of treatment (2, 5, 10, 15 and 20 minutes), with mean power of 1,1W, 40kV pick-to-pick voltage and approximately 1 cm of distance between the superior electrode and the culture media. We evaluate the growth on the treated culture media (counting the colony-forming unit - CFU) and also analyzed the morphology of the treated microorganisms in comparison with the samples without treatment, through scanning electronic microscopy (SEM). Through these experiments, we could observe that, applied on a surfaces, the plasma is an efficient and fast sterilization method. This is because during the discharge are formed ozone, UV photons, and free particles, that can contribute to the effect of sterilization

Orientador: Helmut Karl Bockelmann / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica / Made available in DSpace on 2018-09-26T18:20:22Z (GMT). No. of bitstreams: 1 Kayama_MiltonEiji_D.pdf: 5536651 bytes, checksum: 2a4fabce98ccec64ad3f1c3a6fcdba86 (MD5) Previous issue date: 1987 / Resumo: A reconexão de tinhas magnéticas e a formação da configuração reversa de campo (FRC) foi estudada num theta-pincn sem espelhos magnéticos. O plasma foi diagnosticado por sondas magnética múltiplas, sonda diamagnética compensada (sonda de fluxo excluído), espectroscopia na região do visível e fotografia ultra-rápida. Foi observado um valor da resistividade efetiva no plasma maior que o predito classicamente. O tempo de reconexão das linhas magnéticas foi menor que 0,2 microseg; esta reconexão rápida mostrou boa concordância com modelos teóricos que associam este fenômeno às instabilidades de ruptura (tearing) e de Krusk al- Schwartzschild / Abstract: The reconnection of magnetic field Iines and the formation of field reversed configuration (FRC) were studied on a mirrorless theta-pinch. The applied diagnostics were multiple magnetic probe, compensated diamagnetic probe (excluded flux probe). visible spectroscopy and fast photograph. We observe an high, value on the effective plasma resistivity, greater than the classic Spitzer resistivity value. A fast reconnection was also observed, in a time less than 0.2 microsec; this phenomena is in good agreement with theoretical models which associate it to the resistive tearing mode instability and the Kruskal- Schwartzschild instability / Doutorado / Mestre em Engenharia Elétrica

Nesta tese, investigamos o transporte caótico de partículas por ondas de deriva ressonantes na borda do plasma em tokamaks com fluxo poloidal de deriva do tipo ~E × ~B, um problema crítico para compreender, na fusão, as propriedades de confinamento dos plasmas. Usamos, para tokamaks com grande razão de aspecto, um modelo hamiltoniano não integrável (proposto por Horton) para descrever a contribuição dinâmica não linear ao transporte. Assim, embora o fluxo total, composto pelo fluxo de equilíbrio e por duas ondas de deriva ressonantes, não seja turbulento na descrição euleriana, as trajetórias lagrangianas das partículas são caóticas. Foi estudada a influência do perfil radial do campo elétrico nas barreiras de transporte e nas células convectivas criadas pela interação não linear entre o fluxo de equilíbrio e as ondas ressonantes. Para equilíbrios com fluxo reverso, nossos resultados mostram que o transporte de partículas pode ser reduzido pela alteração do perfil do campo elétrico. Finalmente, nossos resultados são aplicados para propor uma interpretação das experiências recentes em tokamaks que mostram uma redução do transporte quando um eletrodo polarizado é inserido na borda do plasma. Como um exemplo, usamos valores experimentais obtidos no TCABR para os perfis radiais do campo elétrico de equilíbrio e suas flutuações, durante o regime ôhmico padrão e durante o regime de confinamento melhorado. / We investigate the chaotic particle transport by resonant drift waves propagating in tokamaks plasma edges with ~E × ~B poloidal zonal flow, a critical problem for the understanding of the confinement properties of fusion plasmas. We assume, for large aspect ratio tokamaks, a non integrable hamiltonian model (proposed by Horton) to describe the non linear dynamical contribution to the transport. Thus, although the total flow, formed by the equilibrium flow and two dominant resonant drift waves, is not turbulent in the eulerian point of view, the lagrangian particle trajectories are chaotic. We study the influence of the electric field radial profile on the transport barriers and convective cells created by the non linear interaction between the poloidal flow and the resonant waves. For equilibria with reverse shear flows, our results show that the particle transport can be reduced by modifying the electric field profile. Futhermore, our results are applied to propose an interpretation of recent tokamak experiments developed for studying the transport reduction when a biased electrode is inserted into the plasma edge or the Scrape-Off-Layer. As an example, we use the equilibrium and fluctuating electric field radial profiles measured in the TCABR tokamak to calculate the transport during the standard ohmic and improved confinement regimes obtained in this tokamak.

This thesis describes physics research carried out at the Columbia Neutral Torus (CNT) stellarator after its adaptation from a non-neutral plasma experiment to a device relevant to magnetic fusion energy research. Results are presented in the areas of plasma heating and related topics (microwave-assisted plasma start-up, overdense heating, inversion of stellarator images), as well as to stellarator stability and related topics (high β, error fields). This thesis also describes the engineering improvements which enabled the said adaptation of CNT. The first step of that process involved the installation of a low-power, pulsed 2.45 GHz magnetron. In those initial experiments it was found that the simultaneous use of microwave start-up and of an emissive hot cathode resulted in non-linearly increased electron densities, implying a synergy between the two start-up methods. Then, a 10 kW, 2.45 GHz heating system was commissioned including a custom-designed transmission line and launch antenna. Highly overdense plasmas (a factor of 4 above the cutoff density) were obtained with this system, both for O-mode and X-mode polarization. The analysis of Langmuir probe profiles of density and temperature required the accurate mapping of the minor radius in the plasma, which motivated a study of CNT error fields. This resulted in a new numerical method for inferring coil misalignments from flux surface measurements. The improved knowledge of the actual magnetic field geometry of CNT permitted to develop and successfully apply an inversion technique to experimental plasma images. This technique (“onion peeling”) reconstructs radial emissivity profiles, and can be considered a 3D generalization of Abel inversion. Finally, simulations of high-β plasma equilibria in different CNT magnetic configurations indicate that (1) ballooning stability limits should be accessible at volume-averaged β as low as 0.9% and (2) ballooning-stable β values as high as 3.0% should be attainable with heating powers as low as 40-100 kW and 1-3 MW respectively, according to stellarator energy confinement scaling laws.

The first study of magnetohydrodynamic (MHD) equilibria and external kink modes in shaped plasmas on the High Beta Tokamak - Extended Pulse (HBT-EP) is described. A new poloidal field coil and high-current, low-voltage capacitive power supply was designed and installed. The new coil significantly modifies the shape of the plasma cross section and provides a new research tool for the study of kink mode structure and control. When fully energized, the coil creates a magnetic separatrix, which defines the boundary between confined and unconfined plasma. The separatrix is set by a poloidal field null called an “X-point”, which is on the inboard side of the torus, above the midplane. Several arrays of magnetic sensors observe and characterize the plasma equilibrium and the MHD fluctuations from kink modes. Free-boundary plasma equilibria are reconstructed using standard methods that minimize the mean-square error between the numerically reconstructed equilibria and various measurements. Reconstructions of shaped plasma equilibria show the creation of fully diverted plasmas with shaped outer boundaries. The reconstructions are confirmed by direct measurements using arrays of magnetic sensors and a moveable Langmuir probe to measure the outermost closed flux surface. Measurements of individual kink modes are obtained from the magnetic fluctuations using a technique known as biorthogonal decomposition. External kink modes that naturally arise in shaped plasmas are observed and described. The poloidal structure of modes in shaped plasmas are found to be similar to those that arise in circular plasmas, except near the X-point. The magnetic signature of kink modes on the surface of the plasma are calculated using the ideal MHD code DCON. For plasmas with an X-point, DCON shows a short-wavelength, low amplitude structure near the X-point. The code VALEN is used to calculate the perturbed magnetic field measured at the sensors due to the DCON mode at the plasma surface. VALEN includes the effects of sensor/plasma separation and eddy currents induced in conducting structures by rotation of the modes. Good agreement is found between the measured mode structures and the ideal kink mode structures calculated at the sensors by VALEN. A distributed array of forty active control coils was used to perturb the plasma equilibria, and for both shaped and circular equilibria, the structure of the response to the perturbation was found to be the same as the that of the dominant naturally occurring mode in that equilibrium. Finally, the magnitude of the plasma’s response to applied magnetic perturbations was found to be comparable between shaped and unshaped plasmas, even though separation between the sensors and the boundary of the shaped plasmas increases relative to circular plasmas with the same plasma current and radial positions. In addition to demonstrating a new research tool for study of kink modes on HBT-EP, this research demonstrates the importance of accurate electromagnetic calculations, including eddy currents, when comparing measured and predicted mode structure.