García Martínez, Pablo L. (2010) Procesos de relajación y auto-organización en plasmas de fusión. / Relaxation and self-organization processes in fusión plasmas. Tesis Doctoral en Física, Universidad Nacional de Cuyo, Instituto Balseiro.
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Resumen en español
Bajo determinadas condiciones, se observa que un plasma ligeramente turbulento evoluciona hacia un estado preferencial, de equilibrio, con una estructura magnética coherente, de tamaño característico comparable al de todo el sistema. En tales situaciones se dice que el plasma experimenta un proceso de relajación y auto-organización. Este proceso ha sido explicado mediante un principio variacional, conocido como teoría de relajación: el plasma minimiza su energía, manteniendo su helicidad magnética. Este vínculo, la helicidad, cuantifica ciertas propiedades topológicas del campo magnético, que se ven poco afectadas por procesos de reconexión magnética. Se ha observado la posibilidad de formar y sostener configuraciones magnéticas de interés en fusión nuclear, mediante la inyección de helicidad. Estos métodos se basan en la tendencia del plasma a relajarse, y en la dinámica de ese proceso. La teoría de relajación predice el estado final hacia el cual el plasma evoluciona, pero no brinda información sobre cómo se alcanza dicho estado. En esta Tesis estudiamos la dinámica de la relajación en configuraciones magnéticas de interés en fusión nuclear. En particular, estudiamos la evolución no lineal de inestabilidades magnetohidrodinámicas (MHD) en configuraciones representativas de spheromaks en etapa de sostenimiento. Este estudio se lleva a cabo resolviendo, numéricamente, las ecuaciones del modelo MHD, en tres dimensiones espaciales, como problema de valores iniciales y de contorno. Consideramos tres aproximaciones al problema. En primer lugar, estudiamos la evolución de configuraciones magnéticamente aisladas. En segundo lugar, extendemos el análisis incorporando una cierta cantidad de fujo magnético que atraviesa la frontera del dominio. Por último, estudiamos la inyección de helicidad al sistema y observamos la formación espontánea de un spheromak, y su posterior sostenimiento. Analizamos las fluctuaciones, la redistribución de corrientes y flujos magnéticos, el dínamo producido por las fluctuaciones y las estructuras magnéticas que resultan de la evolución de las configuraciones inestables consideradas. Recuperamos las predicciones de la teoría de relajación y muchos aspectos de la dinámica del proceso, observados previamente en experimentos. Mostramos, por primera vez, la posibilidad de formar y sostener un spheromak mediante velocidades tangenciales al contorno del plasma. Este es un mecanismo de inyección de helicidad muy poco explorado en el ámbito de fusión nuclear.
Resumen en inglés
Under the appropriate conditions, a turbulent plasma evolves toward a preferred, equilibrium state, with a coherent magnetic structure of size comparable with the size of the whole system. In such situations, it is said that the plasma undergoes a relaxation and self-organization process. This process has been explained using a variational principle, known as relaxation theory: the plasma minimizes its energy, maintaining its magnetic helicity. This constraint, the helicity, quantifies certain topological properties of the magnetic field, which remain almost unchanged during magnetic reconnection. The possibility of forming and sustaining configurations relevant to fusion research, injecting helicity, has been demonstrated. These methods are based on the tendency of the plasma to relax, and on the dynamics of this process. The relaxation theory predicts the final state toward which the plasma evolves, but it says nothing about how this state is achieved. In this Thesis we study the dynamics of the relaxation in magnetic configurations relevant to fusion research. In particular, we study the no-linear evolution of magnetohydrodynamic (MHD) instabilities in configurations representative of sustained spheromaks. Using numerical methods, we solve the equations of the MHD model, in three spatial dimensions, as an initial and boundary value problem. We consider three different approaches. Firstly, we study the evolution of magnetically isolated configurations. Secondly, we extend the analysis incorporating magnetic ux that intercepts the boundary of the domain. Finally, we study the helicity injection to the system and we observe the spontaneous formation of a spheromak, and its subsequent sustainment. We analyze the fluctuations, the redistribution of currents and magnetic fluxes, the dynamo produced by the fluctuations and the magnetic structures that arise during the evolution of the unstable configurations considered. We reproduce the predictions of the relaxation theory and several aspects of the dynamics of the process, previously observed in experiments. We show, for the first time, the possibility of forming and sustaining a spheromak using tangential ows at the plasma boundary. This helicity injection mechanism has been almost unexplored in fusion research.
| Tipo de objeto: | Tesis (Tesis Doctoral en Física) |
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| Palabras Clave: | Magnetohydrodynamics; Magnetohidrodinámica; Plasma; Magnetic relaxation; Relajación magnética; Self-organization; Auto-organización |
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| Divisiones: | Investigación y aplicaciones no nucleares > Física > Fusión nuclear y física de plasmas |
| Código ID: | 303 |
| Depositado Por: | Marisa G. Velazco Aldao |
| Depositado En: | 31 Ene 2012 11:15 |
| Última Modificación: | 31 Ene 2012 11:15 |
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