Agradecimentos Agradeço aos meus pais, Giacomo e Laura, e meus irmãos, Fábio e Felipe, pelo total apoio recebido. Ao meu orientador, Prof. Dr. Iberê Luiz Caldas, pelo imprescindível papel nesta etapa acadêmica, transmitindo seus conhecimentos, não apenas científicos, que foram de grande valia em minha formação pessoal e profissional. A todos os colegas do grupo Controle de Oscilações do IFUSP, que sempre me ajudaram em nossas inúmeras discussões. A Coordenação de Aperfeiçoamento de Pessoal de

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... vel Superior (CAPES), pela bolsa de estudos de Doutorado. Ao Instituto de Física da Universidade de São Paulo, pelos auxílios financeiros concedidos para participações em congressos. Abstract We develop a symplectic (conservative) bidimensional map to study the evolution of magnetic field lines of a confined plasma in a tokamak. First, we considered two profiles for the plasma current density, studied in the literature: monotonic and non-monotonic, which give rise to different profiles for the poloidal magnetic field and different analytical profiles for the safety factor. In our simulations, we consider the system initially at equilibrium, where we observe, in Poincaré sections, only invariant lines. Then, we add a perturbation (external current), where we observe island chains and chaos in the system. In the second part, we consider a non-monotonic profile, but with a region which the current density becomes negative, which causes a divergence in the safety factor profile. Even considering only the sistem at equilibrium, very small island chains appeared around the shearless curves, and localized chaos. This feature was not observed for the other profiles at equilibrium. We can control the appearance of the regions with island chaind around the shearless curves and chaotic regions, by variation of parameters related to the density current expression. To comprove our results, we aplly the same profile to the other symplectic map. Finally, we consider a safety factor profile in a divertor configuration. We also have a divergence on in the safety factor profile. We observe similar features (island chains around shearless curves and localized chaos) when we consider a non-monotonic safety factor profile with a reversed density current.