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| Home > Publications database > Modeling of Plasma Response to Magnetic Field Perturbations from the Dynamic Ergodic Divertor (DED) and Comparison with Experiment |
| Dissertation / PhD Thesis/Book | PreJuSER-56777 |
2007
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/2631
Report No.: Juel-4251
Abstract: For several decades, physicists try to get under laboratory conditions fusion of deuterium and tritium nuclei, with the aim to provide a practically inexhaustible source of energy. The present work is focused onto tokamaks only, which are torus-shaped devices with the magnetic field produced by external coils and electric current in the plasma. This magnetic field restrains the particle motion to a translation along the field lines, and a gyration in a plane perpendicular to them, with a gyro-radius small compared to the size of the machine. The control of particle and heat transport is a critical issue to obtain the high temperatures and densities required for fusion in future reactors. Collisions between particles lead to transport of both heat and charged particles towards the walls of the tokamak. This transport mechanism is well understood. However, the experimentally observed transport level is much higher than the expected one due to collisions and it is commonly believed that there are additional transport mechanisms. These mechanisms are referred to as anomalous transport and result from microscopic plasma instabilities of different types. Ergodic Divertors (ED) have been introduced in order to provide means to control the transport at the plasma edge. Such devices superpose a small magnetic perturbation from additional coils onto the main magnetic field. Without such perturbations, the magnetic field lines lie on nested toroidal magnetic surfaces. When a perturbation is applied, field lines exhibit small deviations in the direction perpendicular to the unperturbed magnetic surfaces. A sufficiently strong perturbation results in a chaotic behaviour of magnetic field lines, or magnetic field stochastization, allowing transport towards the walls along field lines. In the present work, a model for transport in a stochastic magnetic field [61] is further developed and applied for modelling of plasma behaviour with EDs. This model implies that the transport towards the walls takes place predominantly along the so called ’optimal’ paths. Such paths consist of a succession of segments aligned with the field lines, and segments perpendicular to them. This model provides effective transport coefficients in the [...]
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