Lampugnani, Leandro G. (2019) Inestabilidades magnetohidrodinámicas y relajación en tokamaks esféricos con columnas central de plasma. / Magnetohydrodynamic instabilities and relaxation in spherical tokamaks with a plasma center column. Tesis Doctoral en Física, Universidad Nacional de Cuyo, Instituto Balseiro.
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Resumen en español
Los tokamaks esféricos (STs, por sus siglas en inglés) presentan muchas ventajas para ser utilizados como un reactor de fusión. Una mejora adicional sugiere reemplazar el conductor central por una columna de plasma (PCC). En este caso, se pueden utilizar electrodos para generar una corriente a través del PCC y producir el campo magnético toroidal. Más aun, la inyección de helicidad magnética (HI) por el PCC puede ser usada para formar y sostener la configuración mediante la relajación magnética. Se estudiaron los equilibrios, la estabilidad y la dinámica de los tokamaks esféricos con una columna central de plasma (ST-PCC) y/o un cañón coaxial (ST-PCC-CG/STCG) en reemplazo del conductor central. Inicialmente, se resolvió de manera numérica la ecuación de Grad-Shafranov para calcular los equilibrios MHD ideales con cero y diferentes distribuciones de flujos magnéticos externos. Se han considerado casos con estados relajados, λ (λ = J • B=B"2) uniforme, y no relajados, λ no uniforme. Los resultados mostraron la posibilidad de producir configuraciones magnéticas interesantes, con elevada amplificación de flujo poloidal y factor de seguridad (q) similar al alcanzado en un tokamak. La estabilidad de este equilibrio fue estudiada calculando su contenido de energía magnética y mediante la realización de simulaciones no lineales, MHD resistivas. En las simulaciones dependiente del tiempo, los equilibrios fueron usados como condiciones iniciales y perturbados con los modos correspondientes al \tilt" y al\kink". La información obtenida de los cálculos numéricos y analíticos fue utilizada para producir mapas de estabilidad y así mostrar regiones de operación estable como función de la elongación, los flujos magnéticos externos, la distribución de corriente y el factor de amplicación. Ademas, se ha demostrado la formación y el sostenimiento de conguraciones STPCC con una elevada corriente toroidal y perles de q de relevancia mediante la inyección de helicidad (HI). En el régimen de sostenimiento se observaron elevados niveles de fluctuaciones, producidos por una inestabilidad de kink localizada en el PCC, con incrementos abruptos en la amplitud de los modos no asimétricos. También se estudio el dínamo producido por las fluctuaciones y la amplificación de flujo que este produce. Adicionalmente, se han observado procesos de reconexión magnética y su contribución a la redistribución de la energía. Finalmente, cuando se detuvo la inyección de helicidad las fluctuaciones decayeron, permitiendo la aparición de superficies magnéticas cerradas. De esto surge la posibilidad de utilizar HI para formar ST-PCC junto con una combinación de forzado auxiliar de corriente (haces neutros y/o radiofrecuencias (RF)) con una elevada corriente de \bootstrap" para sostener una configuración libre de fluctuaciones.
Resumen en inglés
Spherical tokamaks (STs) have many advantages from the perspective of a fusion reactor. A further improvement would be to replace the center post by a plasma center column (PCC). In this case, biased electrodes could be used to drive current along the PCC and produce the toroidal magnetic field. Moreover, the magnetic helicity injected (HI) by the PCC can be used to form and sustain the conguration via magnetic relaxation. The equilibrium, stability and dynamics of Spherical Tokamaks with a Plasma Central Column (ST-PCC) and/or a Coaxial Gun (ST-PCC-CG / ST-CG) replacing the standard Central Post were studied. First, the Grad-Shafranov equation was solved numerically to calculate zero ideal MHD equilibria with different external flux distributions. Both relaxed, uniform λ (λ = J • B=B"2), and non relaxed, non uniform λ , cases were considered. The results showed the possibility of producing interesting magnetic congurations, with high poloidal flux amplication and tokamak like safety factor proles (q). The stability of these equilibria was studied by calculating their magnetic energy content and by performing non linear, resistive MHD simulations. In the time dependent simulations, the equilibria were used as initial conditions and perturbations corresponding to the "tilt" and "kink" modes were applied. The information obtained from the analytical and numerical calculations was employed to produce stability maps showing the stable regions of operation as a function of the elongation, the external flux, the current distributions and the amplication factor. The formation and sustainment of ST-PCC congurations with high toroidal current and relevant q proles via helicity injection (HI) was also demonstrated. In the sustainment regime a high level of fluctuations was observed, with abrupt increases in the amplitude of non axsymmetric modes produced by a kink instability localized in the PCC. The dynamo produced by the fluctuations, and the flux amplication it produces, were also studied. In addition, magnetic reconnection processes, and their contribution to the energy redistribution were observed. Finally, when helicity injection was switched off, the fluctuations decayed and nested, closed magnetic surfaces appeared. This opens the possibility of using HI to form the ST-PCC and a combination of auxiliary current drive (neutral beams and/or radio-frequency (RF)) and high bootstrap current to sustain a fluctuation free configuration.
| Tipo de objeto: | Tesis (Tesis Doctoral en Física) |
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| Palabras Clave: | Magnetohydrodynamics; Magnetohidrodinámica; Magnetic confinement; Confinamiento magnético; [Tokamak; Auto organization; Auto organización] |
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| Materias: | Física |
| Divisiones: | Gcia. de área de Investigación y aplicaciones no nucleares > Gcia. de Física > Interacción de la radiación con la materia > Física nuclear y física de plasmas |
| Código ID: | 810 |
| Depositado Por: | Tamara Cárcamo |
| Depositado En: | 01 Mar 2021 07:52 |
| Última Modificación: | 01 Mar 2021 07:52 |
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